Part One: Fundamentals










Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
3
Introduction
A
The objective of this textbook is to offer the
reader a concise summary of the fundamentals
and principles of dental radiology. In addition,
brief synopses are included of the more com-
mon osseous pathologic lesions and dental
anomalies. This book is intended to be a handy
resource for the student, the dental auxiliary
and the practicing clinician.
What is dental radiology?
Dental radiology is both an art and a science.
Anart is a skill acquired by experience, study or
observation and a science is a technique that is
tested through scientific method. Scientific
principles of physics, chemistry, mathematics
and biology are integral to dental radiology.
Capturing and viewing a digital dental image
requires sophisticated technology, while the
operator’s proper physical positioning of the
intraoral receptor requires a skill that is based
upon scientific principles. The art of dental
radiology involves the interpretation of black
and white images that often resemble ink blots.
Deriving a differential diagnosis involves the
application of the clinician’s knowledge, cogni-
tive skills and accumulated experience. The
term “radiograph” originally applied to an x‐ray
image made visible on a processed piece of
x‐ray film. A photograph is similar to a radio-
graph except it is taken with a light‐sensitive
camera and printed on photographic paper.
Today the term “radiograph” is used to
describe an image whether it was acquired
with x‐ray film or with a digital receptor. It is
more accurate to use the term “x‐ray image”
when viewing it on a monitor and “digital
radiograph” when a hardcopy is viewed. In
the future, “radiograph” should be updated to
a more appropriate term.
What are x rays?
X rays are a form of energy belonging to the
electromagnetic (EM) spectrum. Some of the
members of the EM family include radio waves,
microwave radiation, infrared radiation, visible
light, ultraviolet radiation, x‐ray radiation and
gamma radiation. These examples are differ-
entiated by their wavelength and frequency.
Awavelength is defined as the distance between
two identical points on consecutive waves
(e.g. distance from one crest to the next crest)
(Fig.A1). Longer wavelengths have lower fre-
quencies and are considered to be less damaging
to living tissues. Conversely, shorter wavelengths

4 Fundamentals of Oral and Maxillofacial Radiology
have higher frequencies and are considered
to be more damaging to living tissues. One
end of the EM spectrum includes the long
wavelengths used for radio signal communica-
tions while at the short wavelength end of the
spectrum is gamma radiation. The EM spectrum
covers wavelengths, ranging from nanometers
to kilometers in length (Fig.A2). Dental x rays
are 0.1 to 0.001 nanometers (nm) in length. For
comparison purposes, dental x rays may be the
size of a single atom while some radio waves
are equivalent to the height of a tall building.
As with all types of EM radiation, x rays are
pure energy. They do not have any mass and
because they have very short wavelengths, xrays
can easily penetrate and potentially damage
living tissues. All forms of EM radiation must
not be confused with particulate radiation
, such
as alpha
and beta radiation . Particulate
radiation is not discussed in this textbook.
The EM spectrum is divided into the non‐
ionizing forms and the ionizing
forms of radi-
ation. The boundary between non‐ionizing and
ionizing radiation is not sharply delineated.
Ionizing radiation is considered to begin with
the shorter wavelength ultraviolet rays and
the increasingly shorter wavelengths which
include x rays and gamma rays. The longer
wavelengths of ultraviolet rays and beyond
which include microwaves, radio waves, etc. are
all considered to be non‐ionizing forms of radi-
ation. The difference is that ionizing radiation is
powerful enough to knock an electron
out of
its atomic orbit, while non‐ionizing radiation is
Short wavelength
High frequency
A
B
Long wavelength
Crest Crest
Trough
Low frequency
Fig.A1 Diagrams showing wave pattern of electromagnetic
radiation. A. High frequency equals short wavelength.
B.Low frequency equals long wavelength.
Radio Microwave Infrared Visible Ultraviolet X ray Gamma Ray
10
4
10
2
10
–2
Wavelength in centimeters
10
–5
10
–6
10
–8
10
–10
10
–12
1
About the size of...
Buildings Humans Bumble Bee Pinhead Protozoans Molecules Atoms Atomic Nuclei
Fig.A2 Electromagnetic (EM) spectrum.

A Introduction 5
not powerful enough to remove an electron.
The removal of an electron from an atom is
referred to as “ionization.” Exposure to ionizing
radiation is recognized as being more hazardous
to living tissue than non‐ionizing radiation.
Note:X ray” is actually a noun composed
of two separate words and it should only be
hyphenated when it is used as an adjective,
e.g. x‐ray tube. In addition, each individual
unit of electromagnetic radiation is referred to
as a photon
. Consequently, the correct term
for x ray is x‐ray photon. In published litera-
ture, x‐ray photons are often incorrectly
referred to as “x‐rays.
In lay terms, x‐ray images reveal the different
parts of our bodies or other matter in varying
shades of black and white. Why? This is because
skin, bone, teeth, fat and air absorb different
quantities of radiation. Within the human body,
the calcium in bones and teeth absorbs the most
x rays. Tooth enamel is the most mineralized
substance in the human body (over 90%
mineralized). Consequently, mineralized struc-
tures such as teeth and bones appear as varying
shades of white (i.e. radiopaque
) on dental
images. Fat and other soft tissues absorb less
radiation, and consequently they will look
darker (i.e. radiolucent
) in comparison to
bone. Air absorbs the least amount of x rays, so
airways and sinuses typically look black in
comparison to mineralized substances. The
denser or thicker the material, the more x‐ray
photons are absorbed by it. This results in a
more radiopaque appearance on an x‐ray image.
The thinner or less dense an object is, the fewer
the number of x‐ray photons absorbed or
blocked by it. Thus more x‐ray photons are able
to penetrate through the object to expose the
image recording receptor. This results in a more
radiolucent appearance.
What’s thebig deal about x‐ray images?
Just as the early pioneers in radiology were
astonished to see the previously unknown in
their first x‐ray images, modern day clinicians
may be astonished to see osseous and dental
pathology, anatomic variations, effects of
trauma, etc. on their x‐ray images. Consequently,
the benefits of x‐ray images are immense. The
combination of both clinical and x‐ray images
provides vital information to the dentist for
preparing comprehensive dental treatment
plans. The end result is a continual improve-
ment in oral healthcare today.

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
6
History
B
Discovery ofx rays
On November 8, 1895, Wilhelm Konrad Röntgen
(alternately spelled Wilhelm Conrad Roentgen),
a professor of physics and the director of
the Physical Institute of the Julius Maximilian
University at Würzburg in Germany, while
working in his laboratory discovered what we
commonly call “x rays” (Fig.B1). On that day
in his darkened laboratory, he noticed light
emanating on a table located across the room,
far from the experiment that he was conducting.
Professor Röntgen was researching the effects
of electrical discharge using a Crookes–Hittorf
tube
. The glowing object was a fluorescent
screen used in another experiment. This per-
plexed him because electrons emanating from
his electric discharge tube were known to only
travel short distances in air. His fluorescing
screen was too far away for these electrons to
produce the fluorescence. In addition, his lab
was completely darkened and the Crookes–
Hittorf tube was completely covered with black
cardboard to prevent light leakage. Light leak-
age otherwise could have caused the screen to
fluoresce. It was obvious to Professor Röntgen
that he was dealing with an unknown invisible
phenomenon. Professor Röntgen called this
new phenomenon “x rays.” “X” because that is
the universal symbol for the unknown and
“ray” because it traveled in a straight line. He
was a modest gentleman and did not wish to
call these new rays “Röntgen rays” after himself
which is standard protocol for new discoveries.
Following his discovery of x rays, he was deter-
mined to learn what were the properties and
characteristics of these mysterious invisible
rays. He secretly tested this phenomenon for
weeks and did not divulge any information
about his new discovery to anyone. At first he
experimented by placing objects in the path of
the x rays between the tube and the fluorescent
screen. Ultimately, he decided to place his own
hand in front of the x‐ray beam and he was
amazed at what he saw on the fluorescent
screen. He observed shadows of his skin and
underlying bones. For the first recorded image,
he asked his wife, Bertha, to place her hand on
a photographic plate while he operated the
experimental apparatus. Professor Röntgen
was able to produce an x‐ray image of her bones
and soft tissue. This x‐ray image, which includes
the wedding ring on her finger, is recognized
as the first x‐ray image of the human body
(Fig.B2).
On December 28, 1895, Professor Röntgen
delivered his first of three manuscripts on
xrays to the president of the Physical Medical

B History 7
Society of Würzburg. The first manuscript was
entitled “On a New Kind of Rays, A Preliminary
Communication.” The unedited manuscript
went to press immediately and was published
in the Annals of the Society. Immediately after-
wards, announcements were published in
newspapers and in scientific journals around
the world. In the United States, the announce-
ment of Professor Röntgen’s discovery was on
January 7, 1896 in the New York Herald news-
paper. The English translations of the original
paper were printed in Nature, a London publi-
cation, on January 23, 1896 and in Science, a
New York publication, on February 14, 1896.
Professor Röntgen did not seek nor enjoy public
acclaim and as a result he would make only a
single presentation on the topic of x rays. This
presentation was given to the Physical Medical
Society of Würzburg on January 23, 1896.
The prevalence of Ruhmkorff coils
and
Crookes–Hittorf tubes in nearly every physics
laboratory at the time permitted x‐ray research
to be conducted globally without much delay.
These two ingredients were the primary
components necessary for producing x rays.
Consequently, prior to Professor Röntgen’s dis-
covery anyone who was studying high voltage
electricity was unknowingly generating x rays.
But no one prior to Professor Röntgen recog-
nized this phenomenon, nor understood the
value of it even if they did suspect something
unusual. Sir William Crookes, whose collabora-
tion produced the Crookes–Hittorf tubes, had
outright complained to the manufacturer that
unopened boxes of photographic plates were
arriving at his lab already exposed. Sir Crookes
Fig.B1 Wilhelm Konrad Röntgen: credited with being the
first person to discover x rays.
Fig. B2 First x‐ray image of the human body: Bertha
Röntgen’s hand.

8 Fundamentals of Oral and Maxillofacial Radiology
surmised the problem was simply due to the
manufacturer’s poor quality control. It was not
until after Professor Röntgen’s discovery was
announced that Sir Crookes and other scientists
finally understood that x rays were the cause of
some of their photographic plate problems.
Professor Röntgen was awarded the first
Nobel Prize for Physics in 1901 for his discovery
of x rays even though some tried to discredit his
claim to the discovery. Sadly, Professor Röntgen
became reclusive and very bitter in his later years
as a result of this controversy concerning the
discovery of x rays. He even stipulated in his will
that all of his correspondences written regarding
the discovery of x rays be destroyed at his death.
He died on February 10, 1923. Unbeknownst to
Professor Röntgen, his recognition of x rays is
considered by many today to be the greatest
scientific discovery of all time. X rays have truly
revolutionized modern healthcare practices.
Who took theworld’s first “dental”
radiograph?
Poor records make it difficult to say conclu-
sively who took the first dental radiograph.
However, Professor Walter König in Frankfurt,
Germany, Dr. Otto Walkoff, a dentist in
Brunschweig, Germany and Dr. Frank Harrison,
a dentist in Sheffield, England have all been
reported to have taken dental radiographs
within a month of Röntgen ’s reported discov-
ery. Dr. Walkoff on January 14, 1896 used a glass
photographic plate. The glass plate was
wrapped in black paper to block out light and it
was covered with rubber dam to keep out saliva.
He inserted this glass plate into his own mouth
and subjected himself to a 25 min exposure to
radiation (Fig.B3). If not the first dental radio-
graph, it certainly was one of the earliest dental
radiographs. Most people claim that Dr. C.
Edmund Kells, Jr. took the first dental radiograph
of a living person in the United States. Itshould be
emphasized that this was on a living person
because it had been reported earlier in a Dental
Cosmos publication that Dr. Wm. J. Morton, a
physician, presented his research work before
the New York Odontological Society and it
included four dental x‐ray radiographs. But his
dental radiographs were taken on dried labo-
ratory skulls and not on a living person.
According to Dr. Kells, “Just when I took my
first dental radiograph, I cannot say, because I
have no record of it, but in the transactions of
the Southern Dental Association, there is
reported my x‐ray clinic given in Asheville in
July 1896, and I remember full well that I had
had the apparatus several months before giving
this clinic and had developed a method of tak-
ing dental radiographs. Thus I must have begun
work in April or May 1896.” Regardless of who
was first to expose a dental radiograph, the
value of dental radiography was recognized
almost immediately after Professor Röntgen’s
discovery of x rays.
Dr. C. E. Kells, Jr., aNew Orleans dentist
andtheearly days ofdental radiography
Shortly after the announcement of Professor
Röntgen’s discovery, Professor Brown Ayres
of Tulane University in New Orleans gave a
Fig.B3 First dental radiograph (unconfirmed). In January
1896, Dr. Otto Walkoff, a German dentist, covered a small
glass photographic plate and wrapped it in a rubber
sheath. He then positioned it in his mouth and subse-
quently exposed himself to 25 min of radiation.

B History 9
public demonstration of x rays using a crude
apparatus set‐up. Since the general public
marveled at the thought of being able to stand
next to a piece of equipment and shortly
thereafter see a photograph of the inside of
the body, he devoted a portion of his demon-
stration to expose a volunteer’s hand. Although
it required a lengthy 20 min exposure, the crowd
was patient, including one curious soul,
Dr. C. Edmund Kells, Jr. (Fig.B4). It immedi-
ately occurred to him that x rays would be an
invaluable tool for observing inside the jaws
and teeth. Dr. Kells met Professor Ayres and
they discussed the idea of taking pictures of
teeth. Professor Ayres became instrumental in
assisting Kells to acquire the necessary equip-
ment for building an x‐ray laboratory to conduct
his own research.
It was a crude and difficult procedure for
taking x rays in the early days. For example,
one of the original problems encountered was
the variability in output of the x‐ray tube. The
few molecules of air that were inside the tube
were vital for producing x rays. To do so, some
of these air molecules would have to be bom-
barded into the walls of the tube, which would
convert their energy into x rays. The air mole-
cules received that energy when a very high
voltage was supplied to the tube. In doing this,
however, these molecules of air would gradu-
ally adhere to the inner walls of the tube and
without any free air molecules present floating
inside the tube, x rays could not be produced.
To reverse this situation, the x‐ray tube would
have to be heated by means of an alcohol lamp.
The heat would drive the air molecules off
the walls, allowing x rays to be produced
once again. The constantly changing condi-
tions within the tube meant that the apparatus
had to be reset for each and every patient.
Otherwise, there was no way of determining
how long a photographic plate would need to
be exposed to get a good image.
To complicate matters further, meters were
not available in the early days to measure
exactly how much radiation was being pro-
duced by the x‐ray apparatus. The accepted
method of choice was for a clinician, such as
Dr. Kells, to pick up a fluoroscope and place
one hand in front of it. The radiation output
would be adjusted until the bones of the hand
were visible in the fluoroscope. An equally
hazardous technique would be for the operator
to place a hand in front of the beam and adjust
the radiation output until the skin began to turn
red. This is referred to as the erythema dose
.
The patient would then be positioned in front
of the x‐ray beam and the exposure taken. The
absence of any immediate accompanying sen-
sation by the patient frequently led to radiation
overexposure. Furthermore, the clinician was
in close proximity to the patient during the
entire exposure and was completely unshielded.
Dr. Kells immediately could foresee several
problems with incorporating x rays into a dental
practice. His primary concern was the expo-
sure time. If it took 20 min for a hand to be
exposed, it theoretically might require hours
to expose a tooth because a tooth is a much
denser object. How could a patient hold a
Fig. B4 Dr. C. Edmund Kells, Jr.: New Orleans dentist,
inventor and author.

10 Fundamentals of Oral and Maxillofacial Radiology
dental x‐ray film motionless for that length of
time? Dr. Kells’ early trials showed that it
would require up to 15 min to expose a molar
tooth, which was much better than he antici-
pated, but it still was a monumental problem
to overcome. If dental x rays were to be rou-
tinely taken by the dental practitioner, technical
improvements to reduce time exposures were
crucial. Within three years of Professor Röntgens
discovery rapid improvements in the design
of the x‐ray tube dramatically reduced that
15min exposure down to 1–2 min. Then there
was a major alteration in the tube design on
May 12, 1913. This was the patent application
date for the Coolidge tube and this ushered in
the “golden age of radiology.” W. O. Coolidge,
the director of research at the General Electric
Company, found that using a coil of tungsten
in a low vacuum tube could generate signifi-
cantly more x rays than the old gas style tubes
could ever produce. As a result, in the 1920s
x‐ray exposures were dramatically reduced to
4–10 s in duration.
There were also electrical dangers. An unin-
sulated and unprotected wire carried a high
voltage current to the discharge tube which
led to injuries to both patients and clinicians.
In 1917, Henry Fuller Waite, Jr. patented the
design for an x‐ray unit that eliminated the
exposed high voltage wire. General Electric
introduced the Victor CDX shockproof dental
x‐ray unit about a year later.
All x‐ray demonstrations on human
patients initially used large glass plates for
recording the images. It was not until 1919 that
the first machine‐wrapped dental x‐ray film
packet became commercially available. It was
called regular film and was manufactured by
the Eastman Kodak Company. Now that x‐ray
film was small enough to place inside a
patient’s mouth, how were patients supposed
to hold it in place and keep it steady? To over-
come both these problems, Dr. Kells produced
his own rubber film holder with a pocket in it
for holding the film. The side of the film holder
was made of an aluminum plate and the
wrapped film was placed in the pocket. With
the patient’s mouth closed, the film holder
was held in place by the opposing teeth. He
selected one of his dental assistants to be his
subject. This person is regarded as being the
first living person in the United States to have
experienced a dental x‐ray exposure. She sat in
a dental chair with the film holder in place
with her face placed up against the side of a
thin board. In this manner, she was able to
hold perfectly still for the required time.
Unbeknownst to Dr. Kells at the time, using
the thin board acted as an x‐ray filter that
helped to prevent his assistant from receiving
a radiation burn to her face from the prolonged
exposure. Filters eventually would become a
standard feature in all modern x‐ray units.
Just as there were extravagant claims made
for using x rays for the eradication of facial
blemishes such as birth‐marks and moles,
removal of unwanted hair and curing cancer,
early advocates met with considerable oppo-
sition to the diagnostic use of x rays and it
often came from within the profession. Not
only did they oppose the use of x rays, they
openly condemned it. Dr. John S. Marshall in
June of 1897 told the members of the Section
on Stomatology of the American Medical
Association that he had intended to use the
rays in his practice, but had been deterred by
the danger. Tragically, many early pioneers
eventually developed fatal cancers from expo-
sure to tremendous amounts of accumulated
radiation received in monitoring and operat-
ing the x‐ray apparatus. Dr. Kells himself
developed cancer that was attributed to radia-
tion exposure. Even so, he stated in the last
article he wrote “Do I murmur at the rough
deal the fates have dealt me? No, I can’t do
that. When I think of the thousands of suffer-
ing patients who are benefited every day by
the use of x rays, I cannot complain. That a
few suffer for the benefits of the millions is a
law of nature.” Sadly, after years of suffering
and failed medical treatments, he committed
suicide in his dental office in 1928.

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
11
Generation ofX Rays
C
X rays occur in nature (e.g. solar x rays) but
dental x rays are strictly a man‐made entity.
Dental x‐ray equipment is manufactured by
multiple companies, each offering varying
styles, sizes, features and prices for their own
particular units. The physical dental x‐ray unit
primarily consists of two components. There is
a control panel with a circuit board to control
the kilovoltage (kV)
, milliamperage (mA)
and time. In addition, there is a tubehead that
physically houses the x‐ray tube, filter, colli-
mator and transformers
(Fig.C1). The tube-
head and control panel may be physically
separate (e.g. wall‐mounted x‐ray unit) or they
may be combined (e.g. hand‐held x‐ray unit).
Individual mA and kV controls are features that
vary from one unit to another. Higher quality
x‐ray units tend to have independent controls
to modify the kV, mA and exposure time while
basic intraoral units may have fixed or a very
limited number of mA and kV settings that an
operator may alter. All intraoral x‐ray units
allow the operator to modify the exposure time.
Extraoral x‐ray units (eg. panoramic) generate x
rays in a similar way to intraoral x‐ray units but
are physically very different.
The heart of an x‐ray unit is the x‐ray tube
(Fig.C2). An x‐ray tube primarily consists of a
cathode
and an anode . The operator’s
simple act of powering on a dental x‐ray unit
(i.e. on–off switch) sends a low voltage current
to the cathode which results in the production
of a cloud of electrons at the cathode. The x‐ray
unit is in a stand‐by mode at this time.
When it is time to expose the intraoral x‐ray
image, the operator must press an exposure
button. Pressing the exposure button will
convert standard wall outlet electricity to a
high voltage current via a step‐up transformer
and send it directly to the x‐ray tube. A step‐up
transformer is the actual device that boosts the
voltage high enough for x‐ray production. The
effect of this high voltage is that it accelerates
the electrons from the cathode across the tube
to the anode. The anode is composed of a cop-
per stem and a smaller target area composed of
tungsten. The tungsten target area is referred to
as a focal spot. The purpose of the copper stem
is to assist dissipating the heat generated when
electrons strike the focal spot, thereby extend-
ing the useful life of the x‐ray tube. Once these
energized electrons accelerate across the tube
and strike the focal spot, only about 1% of the
resulting kinetic energy
is converted into x
rays, while the remaining 99% of the energy is
converted into heat. Oil fills the tubehead to
act as an electrical insulator and helps to dis-
sipate the heat generated from x‐ray production.

12 Fundamentals of Oral and Maxillofacial Radiology
A step‐up transformer may generate voltages
upwards of 120 kV. Modern day intraoral x‐ray
units typically operate in the 60–70 kV range;
extraoral dental x‐ray units generally require
voltages up to 120 kV. There is also a step‐down
transformer located within the confines of the
tubehead. The step‐down transformer reduces
the voltage from a standard household elec-
trical outlet to approximately 8–10 V. This low
voltage is then sent to the filament of the cath-
ode, which produces an electron cloud
that
will be used to produce our dental x‐rays.
Reducing the voltage to the cathode filament
also extends the useful life of the x‐ray unit.
The cathode filament and anode focal spot
typically are both made of tungsten. Obviously
a 1% production rate for an x‐ray unit is a very
inefficient use of electricity, but it generates
adequate amounts of x radiation for our dental
needs. With normal office usage, dental x‐ray
units will last many years.
Note: At the end of the working day, both
intraoral and extraoral x‐ray units should be
powered off. Keeping an x‐ray unit powered
on indefinitely results in a continuous flow of
current to the x‐ray tube, thereby shortening
the useful life of that tube. Unlike intraoral
and panoramic x‐ray units, when a cone beam
computed tomographic unit is powered down
overnight it will typically need upwards of
30 min for the flat panel receptor to properly
warm‐up again prior to taking the first patient
exposure.
Fig.C1 Dental x‐ray tubehead.
Fig.C2 X‐ray tube.

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
13
Exposure Controls
D
FigureD1 shows an x‐ray control panel displaying
variable exposure parameters.
Voltage (V)
Voltage controls the penetrability of the x‐ray
beam and the degree of contrast
in the image.
One kilovolt (kV) is equivalent to 1000 V. When
exposing intraoral images, selecting a higher
kilovoltage increases the number of shades of
gray between black and white in the image.
This is referred to as a lower contrast image. This
is particularly useful for diagnosing periodon-
tal issues where varying bone level heights
are a concern. Higher kilovoltage also is useful
for imaging maxillary posterior teeth where the
patient’s alveolar ridge and soft tissue thickness
are typically greater. Additionally, increasing
the penetrability of the x‐ray beam through
superimposing osseous structures, such as the
zygoma, will improve the diagnostic quality
of the image. Meanwhile a lower kilovoltage
exposure setting reduces the number of shades
of gray in the intraoral image. This is referred to
as a higher contrast image. This is particularly
useful for detecting caries. This benefits the
clinician who wishes to only differentiate between
healthy tooth structure and decayed tooth
structure. On both intraoral and extraoral dental
images, tooth decay will appear radiolucent.
Amperage (A)
Amperage primarily controls the quantity of
xrays generated. Dental units use milliamperes
(mA). One milliampere is one‐thousandth of
an ampere
. Amperage controls the number
of electrons in the cloud that will ultimately
travel across the x‐ray tube, hit the anode and
produce x‐ray photons. A basic dental x‐ray
unit typically has a single milliamperage set-
ting, while a higher quality x‐ray unit will have
multiple millamperage settings. Intraoral x‐ray
units generally produce 4–15 mA. Selecting a
higher milliamperage will increase the number
of x rays generated and result in an overall
denser (i.e. darker) x‐ray image. If an initial
x‐ray image appears too dark, reducing the
milliamperage for a follow‐up exposure will
lighten the overall density of the new image.

14 Fundamentals of Oral and Maxillofacial Radiology
Exposure timer
All intraoral dental x‐ray units must include an
exposure timer to control the duration of radia-
tion production. Modern digital timers are
capable of expressing time in thousandths of
a second. Some manufacturers’ timers use
“number of impulses” not “fractions of a second”
as exposure increments. However, impulses can
easily be converted into seconds. Impulses are
associated with the electrical frequency (i.e.
number of hertz). To convert impulses into
seconds, simply divide the number of impulses
by the number of hertz (Hz)
. In North America,
standard household electric current is 60 Hz
(cycles per second), while in Europe it is 50 Hz.
Selecting a 30 impulse time would translate into
an exposure of 0.5 s (30 impulses divided by 60)
in the United States. The function of altering the
exposure time permits adapting to different
patient types (e.g. physical size, gagging reflex,
etc.) to achieve optimal image quality. Increasing
the exposure time will result in the generation of
more x rays and consequently produce an over-
all denser (i.e. darker) x‐ray image. Conversely, a
shorter time of exposure will result in a less
dense (i.e. lighter) x‐ray image. In general, image
contrast is not affected by exposure time.
Fig.D1 X‐ray control panel display-
ing variable kilovoltage (kV), milli-
amperage (mA) and time settings.

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
15
Radiation Dosimetry
E
The terminology used to differentiate radiation
doses includes: (i) absorbed dose; (ii) equivalent
dose; and (iii) effective dose. The international
system of units (abbreviated SI from the French
derivation Le Système Internationale d’Unités)
is the modern form of the metric system and
is the world’s most widely used system of
radiation measurement, used in both everyday
commerce and science (see Appendix 6).
Exposure
Exposure refers to the radiation output of an
x‐ray machine. It is a measure of the ionization
in air produced by x rays or gamma rays.
Roentgen (R)
is the traditional unit of measure.
The SI term that is the equivalent of a roentgen
is coulombs per kilogram. One roentgen is equiva-
lent to 2.58 × 10
–4
C/kg.
Absorbed dose
Radiation absorbed dose (rad) quantifies the energy
from x radiation that is absorbed by a given
mass of tissue. This is the numeric difference
between how much x radiation enters and how
much x radiation exits a mass of tissue. The SI
unit for absorbed dose is called a gray (Gy). The
conversion rate is 1 Gy equals 100 rad.
Equivalent dose
Clinical dentistry is typically limited to using
one type of radiation, “x rays.” However, the
general public is continually exposed to a
variety of types of radiation during a lifetime,
whether it is medical or environmental in
origin. Equivalent dose is a measure specifically
used to compare the biologic effects of different
types of radiation on living tissues. The biologic
effects due to different types of radiation are
significant. The SI unit for equivalent dose is
sievert (Sv)
. The original unit for equivalent
dose was referred to as a rem, which is an acronym
for radiation equivalent man (rem)
. Similar to
converting rad units to gray units, the conversion
is 1 Sv equals 100 rem.
Note: In clinical dentistry, the terms rads, rems,
grays and sieverts are often used interchangeably
when discussing patient exposures. However,
when a researcher wishes to conduct a scien-
tific study, using the precise nomenclature is
critical.

16 Fundamentals of Oral and Maxillofacial Radiology
Effective dose
Different cell types may react differently to an
identical dose of x‐radiation exposure (e.g.
muscle cell versus erythrocyte cell). Effective
dose
takes into account the differences in
cellular response from radiation. It is also
useful for comparing risks from different
imaging procedures (e.g. dental imaging ver-
sus medical imaging) because it factors into
account the absorbed dose to all body organs,
the relative harm from radiation and the
sensitivities of each organ to radiation. As a
result, effective dose is a good indicator of
thepossible long‐term radiation risks to the
individual.

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
17
Radiation Biology
F
Shortly after the discovery of x radiation, adverse
effects of radiation exposure were being
observed. The cellular effects would begin with
erythema, followed by dermatitis, ulceration
and ultimately the growth of tumors. All of
which are associated with increasing amounts
of radiation exposure. Pioneers in the dental
field were ignorant of the hazards of radiation
and some clinicians required amputations of
fingers as a result of excessive radiation expo-
sure from holding the image receptors in their
patients’ mouths.
The time lag between an individual’s expo-
sure to radiation and the observed effect of the
radiation is called the latent period. The latent
period may be a very brief period as in the time it
takes for a sunburn to become visible. Sunburn is
caused by an excessive skin exposure to ultraviolet
radiation in a relatively short period of time. The
reddening of the skin typically appears several
hours after exposure to the sun. This is consid-
ered to be a short latent period. At the opposite
end, we do not have a defined maximum length
of time for an effect to be observed. A latent
period may require decades or generations before
an effect is ultimately observed. Why? Because
x‐radiation damage to an individual’s germ cells
(i.e. sperm and ova), will not be observed in
the exposed individual. Rather, the radiation
effects will be observed in the affected indi-
vidual’s future offspring. Because of this,
the offspring of the survivors of the 1945
Hiroshima and Nagasaki atomic bombings
continue to be followed today for possible
long‐term genetic effects.
Currently, we do not know the long‐term
effects from low doses of radiation. One reason
for why the effects of low‐dose radiation expo-
sure are still unknown is because individuals
cannot be ethically studied in a controlled envi-
ronment where a researcher can completely
monitor and control a person’s day to day life-
style. Lifestyle factors include diet, vocation,
home environment and chronic habits such as
smoking, etc. All of these lifestyle choices can
deleteriously affect an individual’s long‐term
health and cloud the effects of radiation alone.
Consequently, with uncertainty as to the effects
of low‐dose radiation, all precautions to reduce
unnecessary exposure to both the patient and
the operator should be followed (see Section G).
Biologic effects of radiation are classified as
either a direct or an indirect effect. If an incoming
x‐ray photon modifies a biologic molecule, it is
called a direct effect (e.g. break in a chromosomal
chain). However, when the biologic effect is the
result of a subsequent intermediary change to a
molecule, the effect is termed an indirect effect.

18 Fundamentals of Oral and Maxillofacial Radiology
Water being the predominate molecule of a
living human, it is frequently affected by ioniz-
ing radiation. An incoming x‐ray photon may
hydrolyze (i.e. split) a water molecule. This first
action is a direct effect of radiation. However,
following the hydrolysis of water, there may be
a recombination of the byproducts, hydroperoxyl
and hydrogen, which can produce a molecule
of an organic hydrogen peroxide. This would
be an indirect effect of radiation. This organic
hydrogen peroxide molecule can lead to cell
death or a future mutation of the cell. Overall,
direct effects of radiation account for approxi-
mately 33% of all biologic damage, while the
remaining 67% of biologic damage is the result
of indirect effects. Tissue sensitivity to radiation
varies depending upon the tissue type (see
Effective dose in Section E).
What happens tothedental x‐ray
photons that are directed at apatient?
X rays can pass through unchanged
The relative vastness of space in the atom
separating electrons and the infinitesimally
small size of each x‐ray photon permits a small
percentage of x‐ray photons to pass directly
through the atom without any interaction,
possibly up to 10% of the total dose. In practice,
the patient is typically positioned between
the x‐ray tubehead and the operator. Since we
know that 100% of the x‐ray beam is not
absorbed by the patient, it is imperative that the
operator not stand directly in‐line with the
beam of x‐radiation (see Section G).
X rays can undergo acoherent scatter
Coherent scatter (aka Thompson scatter) occurs
rarely when a low energy incoming x‐ray photon
collides with an outer shell electron of an atom.
The photon does not have enough energy to eject
that electron from its orbit. The net result is: (i) no
net change to the atom; (ii) the incoming x‐ray
photon loses some of its energy upon impact
with the electron; and (iii) the x‐ray photon is
redirected (i.e. scattered). This x‐ray photon will
continue interacting with other atoms until all of
its energy is dissipated. These redirected x‐ray
photons are called scattered x rays. Even though
the scatter dose is low, this author recommends
that the operator should place a protective apron
on every patient and that the operator should
stand behind a protective barrier during an x‐ray
exposure. These are simple methods to reduce
the effects of scatter radiation for both the patient
and the operator. Further reducing radiation
exposure to both the patient and the operator
when feasible is still the best principle.
X rays can produce aphotoelectric effect
Photoelectric effect accounts for upwards of 25% of
x‐ray interactions. The incoming x‐ray photon col-
lides and is absorbed entirely by an inner shell elec-
tron. This incoming photon imparts enough energy
to the electron so that together they are ejected from
its orbit. This ejected electron is now called a
photoelectron (i.e. photon + electron = photoelectron).
This photoelectron travels short distances before
giving up all of its energy during additional colli-
sions. Within the same atom, another electron from
a higher orbit may drop into the void created by the
photoelectron. In so doing, it generates an addi-
tional low energy x‐ray photon, referred to as a
characteristic or secondary x ray. Secondary x‐ray
photons do not benefit the patient or the clinician.
They are generally absorbed by the patient’s soft
tissues but they also can produce image fog
.
Secondary x rays pose no external threat to the
operator.
X rays can produce aCompton scatter
Compton scatter accounts for the majority of
interactions with dental x‐ray photons. In this
scenario, an incoming x‐ray photon has sufficient

F Radiation Biology 19
energy to knock out an outer shell electron. The
result is a redirection of the incoming x‐ray
photon after it collides with an electron and the
formation of an ion pair. An ion pair consists of
a negatively‐charged ejected electron and the
resultant positively‐charged atom. The term
ionizing radiation is applied to this phenome-
non. X rays are classified as a form of ionizing
radiation. Both the ejected electron and the
weakened scattered x‐ray photon can continue
to interact with other atoms. This can result in
additional ionizations and with each ensuing
impact the x‐ray photon will continue to be
weakened while other atoms attempting to
reach a state of maximum stability will seek
out the recoil electron.
Determinants ofbiologic damage
fromx‐radiation exposure
Exposure dose
Any amount of ionizing radiation will produce
some biologic damage. Regardless of how
minute the radiation exposure dose may be,
there will always be some long‐term residual
damage to the radiated area. Minimal residual
damage may not be visible initially. However,
after repeated exposures to ionizing radiation,
termed chronic exposure, a biologic effect will
ultimately present itself. This classification of
cellular response is referred to as a deterministic
effect
. The total amount of radiation expo-
sure required to elicit a cellular effect is called
the threshold dose
. Below the threshold level
of exposure, no effect will be observed. A sim-
ple example of a threshold radiation dose effect
is sunburn. Acute biologic effects from increas-
ing doses of ionizing begin with erythema, fol-
lowed by dermatitis, ulceration, tanning and
ultimately the loss of glandular function.
Erythema occurs after exposure to approxi-
mately 250 cGy of radiation that is delivered in
a relatively short span (e.g. two weeks). Incom-
parison, a dental bitewing exposure is minimal
at approximately 0.08 μGy. A second type of
biologic effect of ionizing radiation is called a
stochastic effect
. In this classification, either
the effect occurs or it does not occur–it is an all
or nothing response. Cancer is an example of a
stochastic effect. Individuals do not develop a
mild case of cancer or a severe case of cancer.
They are all cancers.
In dentistry, exposure dose is affected by
variable factors that include the distance of the
x‐ray source from the face, kilovoltage, milli-
amperage and exposure time. All these factors
combined will determine the total radiation
dose to the patient.
Note: It is extremely important for all of us to
remember that although the biologic effects
resulting from high doses of radiation expo-
sure are known, the long‐term effects from
low doses of ionizing radiation are still
unknown. This is why we need to refrain
from exposing individuals to any unnecessary
imaging procedures whenever possible or, at
the very least, utilize a projection that requires
a minimum of radiation exposure. In addi-
tion, the operator should take all precautions
to minimize their own exposure to radiation
while performing imaging procedures.
Dose rate
The time interval between repeated exposures
to ionizing radiation influences the extent of
biologic damage. A rapid rate of recurring radi-
ation exposure with minimal time between
each exposure will result in more biologic dam-
age than if an equal cumulative radiation dose
(i.e. total dose) was administered over a longer
time frame. Incremental doses of radiation are
preferable because it permits the body time to
repair some of the biologic damage before the
next dose is administered. Multiple smaller
doses of radiation administered over an
extended time interval allows greater cellular
repair. Conversely, a high dose of radiation

20 Fundamentals of Oral and Maxillofacial Radiology
administered in a single session diminishes a
body’s ability to recuperate and repair the non‐
cancerous cells. A skin tan is a threshold effect
that occurs from gradual cumulative doses of
ultraviolet radiation versus a sunburn effect
that results from a single concentrated dose of
ultraviolet radiation. But to be clear, the ultra-
violet “tan” effect is still biologic damage to the
individual’s skin, but just not as severe as a
sunburn effect. We also know that individuals
with years of repeated ultraviolet skin damage
have a greater incidence of basal cell or squa-
mous cell carcinomas.
Area ofexposure
The volume of tissue exposed to radiation plays
a significant role in the overall well‐being of the
patient. Patients receiving localized oral cancer
radiotherapy, possibly up to 70 Gy, may encoun-
ter severe biologic effects in the irradiated field
that often will culminate in the loss of glandular
function and osteoradionecrosis
. However,
total exposure to a much lower dose of 3–5 Gy
administered over the entire body would very
likely result in death of the individual. Whole
body radiation affects all of the body’s biologic
systems simultaneously and, as a result, the
body’s attempt to repair cellular damage is
overwhelmed. Consequently, death of an indi-
vidual will occur from far less whole body
radiation exposure compared with administering
a mega dose of radiation that is concentrated to
a localized area.
Current guidelines from the National Council
on Radiation Protection and Measurements
(NCRP) stipulate that rectangular collimation
shall be used for periapical and bitewing
imaging and should be used for occlusal imag-
ing when possible. Rectangular collimation
shall also be used with hand‐held devices
whenever possible and x‐ray equipment for
cephalometric imaging shall provide for asym-
metric collimation of the beam to the area of
clinical interest. All of these NCRP guidelines
are made to reduce the area of radiation
exposure to the patient.
Age
All living beings are susceptible to the effects
of x radiation. However, younger and older
individuals are most susceptible. High meta-
bolic rates in younger individuals and the
poor recuperative healing powers in older
individuals result in greater risks from radia-
tion exposure. This does not eliminate the
intermediate age group from experiencing ill
effects from ionizing radiation, it only means
that this age group is less susceptible to the
effects. Precautions to reduce exposure to
ionizing radiation apply to all age groups.
NCRP recommendations for pediatric patients
include: (i) select x rays for individual needs;
(ii) use the fastest image receptor possible;
(iii) collimate the beam to the area of interest;
(iv) always use a thyroid collar unless it inter-
feres with imaging the needed anatomy; and
(v) use cone beam computed tomography
(CBCT) only when necessary.
Cell type
The Law of Bergonie and Tribondeau of 1906
states that the most radiation‐sensitive cells
types are undifferentiated, divide quickly and
are highly active metabolically. Amongst the
most sensitive cell types are erythrocytes and
stem cells. Among the least sensitive cell types
are neural and muscle cells. Two exceptions to
the law are oocytes and lymphocytes. These
two varieties are very specialized cell types and
they are very sensitive to radiation. It is not
clear as to why these two cell types are particu-
larly sensitive to radiation.
Pioneers in dental radiology were ignorant of
the dangers of x radiation and many suffered
the consequences of excessive exposure. Dental

F Radiation Biology 21
exposure doses today are considered to be very
low in comparison. However, as stated earlier,
any amount of exposure to ionizing radiation
produces some cellular damage. Although a
carcinoma is statistically unlikely to result from
dental x rays, theoretically it could result from
the minute amount of radiation exposure used
to produce a single dental image. Consequently,
exposing patients to any amount of x radiation
should be limited and imaging should only be
ordered when it is vital for diagnosing the
patient’s oral health.

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
22
Radiation Protection
G
Very soon after x rays were discovered, it became
apparent that x rays were harmful. As early as
1897, there were cases of skin damage. In 1901,
a pioneer in dentistry, William H. Rollins, DDS,
MD, observed that x rays could cause tissue
burns and attempted to warn dentists and
physicians of the dangers of x rays. Little heed
was taken of Dr. Rollins warnings but, shortly
after, the dental profession began to take meas-
ures to reduce the damaging effects of radiation.
However, many pioneers in dentistry, whether
through ignorance or neglect, suffered the loss
of one or more fingers because they repeatedly
held the x‐ray film used to record the dental
image in the patient’s mouth. X‐ray film was
the standard for recording dental images at the
time.
Utilization of radiation in a dental office
requires regulations to protect the patient, the
operator and any employees or bystanders
located within the working environment. ALARA
is an acronym for “as low as reasonably
achievable.” If the exposure dose to a patient
can be easily reduced, then it should be. The
ALARA principle is recognized by the American
Dental Association (ADA) and is expected to
be followed by dental practitioners. Because of
concerns today about the overutilization of
ionizing radiation procedures in medicine,
ALARA is morphing into ALADA. ALADA
is an acronym for “as low as diagnostically
acceptable.” Reducing the exposure dose to a
patient to a minimum, yet still being able to
diagnose the images, is beginning to be prac-
ticed in the medical community and should be
adopted in dentistry as well.
Quality assurance (QA) refers to optimized
dental images produced with minimum radia-
tion exposure. Minimum exposure to radiation
applies not only to the patient, but also the dental
operator and any bystanders in proximity to the
dental x‐ray equipment. The ADA and NCRP set
guidelines that every dental healthcare setting
adopts regarding maintaining x‐ray equipment,
image receptors, protective aprons, etc.
1. RADIATION PROTECTION: PATIENT
Protecting the patient entails both reducing the
exposure dose from the primary x‐ray beam
that is directed at the patient’s head and the
subsequent scatter radiation that may affect
other regions of the body.

G Radiation Protection 23
Protective apron
Protective covering to shield a patient from
scatter radiation
comes in many forms. The
method of choice to date has been the protec-
tive apron (Fig. G1). The US Environmental
Protection Agency (EPA) has designated lead as
a hazardous material. Although the term lead
apron is commonly used to describe the standard
apron that is draped on a patient prior to x‐ray
exposure, many companies today manufacture
lead‐equivalent aprons (i.e. lead‐free). Regarding
intraoral procedures, assuming that one adheres
to the guidelines outlined by the NCRP and
ADA, there is no need to use a protective apron
on adult patients due to the minute amount of
scatter radiation outside of the field of interest.
These guidelines require the use of rectangular
collimation with either a digital receptor or
f‐speed film. The NCRP guidelines also state that
pediatric patients are not simply small adult
patients and operators should take extra care to
reduce children’s exposure to radiation. The
thyroid gland in children sits higher in the neck
and will therefore be automatically exposed to
more radiation than in an adult. As a result, the
NCRP recommends that protective aprons with
thyroid collars
should always be used on
pediatric patients unless it interferes with imag-
ing the needed anatomy. For extraoral imaging
procedures such as panoramic projections,
a double‐sided protective apron without a
thyroid collar should be used (Fig.G2). In this
situation a thyroid collar would obscure ana-
tomic structures that are relevant to the patient’s
oral examination.
Note: Do not fold the protective apron when
not in use. It is best to either hang the apron
upright or leave it lying flat and unfolded.
AB
Fig.G1 A. Child protective apron with thyroid collar for intraoral imaging. B. Adult protective apron with thyroid collar
for intraoral imaging.

24 Fundamentals of Oral and Maxillofacial Radiology
Repeated folding of the apron will lead to
cracking of the inner lining and it will become
less effective at blocking x rays. The NCRP
also recommends a visual examination of pro-
tective aprons monthly for damage.
Collimation
The radiation produced within the x‐ray tube-
head exits as a divergent beam. The US govern-
ment requires manufacturers of intraoral x‐ray
equipment to limit the size of the x‐ray beam to
be no more than 2.75 inches (7 cm) in diameter.
The open‐ended plastic attachment on the
x‐ray tubehead is referred to as a PID
.
A PID has historically been referred to as a
cone. The open end of the PID is aligned closely
to the patient’s face prior to taking an exposure.
A PID may be interchangeable on some intraoral
tubeheads. Limiting the size of the beam
reduces unnecessary exposure to the areas out-
side of the desired field. A means to further
reduce the conventional round beam size is to
use a rectangular‐shaped beam that more
closely matches the size of the imaging recep-
tor (FigsG3, G4, G5 and G6). The NCRP guide-
lines state that rectangular collimation of the
beam shall be used routinely for periapical
and bitewing images and should be used for
occlusal images when possible. In addition,
rectangular collimation shall be used with
hand‐held devices when possible. If a rectan-
gular PID is not already attached to the x‐ray
tubehead, a rectangular‐shaped beam can still
be accomplished by any one of the following
solutions: (i) detaching the existing round PID
and replacing it with a rectangular PID; (ii) a
secondary rectangular collimator can be
attached to the open end of the round PID; and
(iii) a rectangular collimator can be attached
Fig. G2 Double‐sided (i.e. front and back) protective
apron without thyroid collar for extraoral imaging.
Fig. G3 Rinn® universal collimator which converts a
round PID to a rectangular collimated PID to restrict the
size of the x‐ray beam to approximate the size of the
image receptor.

G Radiation Protection 25
directly to the receptor holder. For cephalomet-
ric images, the x‐ray unit shall provide for
appropriate collimation of the beam to the area
of clinical interest. This will prevent unneces-
sary exposure to hard and soft tissues outside
the area of interest.
Filtration
X‐ray tubes simultaneously generate x rays of
varying energies. The purpose of x‐ray filtra-
tion is to absorb the weaker, low energy x rays
that may not be powerful enough to penetrate
AB
Fig.G4 A. Rectangular collimation with XCP‐ORA® positioning system. B. Rectangular collimation with a Snap‐A‐Ra
DS (without an alignment ring).
AB
Fig.G5 XDR‐ALARA® rectangular collimators.

26 Fundamentals of Oral and Maxillofacial Radiology
through a patient’s soft tissue. Filtering out
these low energy x‐ray photons reduces the
total absorbed dose to the patient and will not
compromise the final diagnosis. X‐ray filters
typically made of aluminum are inherently
built into conventional dental x‐ray units
(Fig.G7). In the United States, manufacture of
x‐ray equipment is regulated by the Food and
Drug Administration (FDA) and consequently
x‐ray filtration should not be a concern for
clinicians.
Digital versus analog
The world’s first digital dental intraoral system
was introduced in 1987 by the French company
Trophie Radiologie; it was called RadioVisio-
Graphy. Today, many different manufacturers
produce dental digital receptors. Digital recep-
tors have significantly reduced the total dose
of radiation required to produce diagnostic
images that are comparable to the prior stand-
ard image receptor, dental x‐ray film. Looking
back to the earliest intraoral x‐ray images
back in 1896, exposure times were upwards of
25 min in length. Today’s dental exposure time
is typically only a fraction of a second in length,
thereby dramatically reducing a patient’s over-
all exposure to radiation compared with the
historical doses that many patients received
during the early days of dental radiology. The
recent transition from x‐ray film to a digital
receptor is not as dramatic a dose reduction as
that of the cumulative advances that occurred
with film over the decades, but it has definitely
contributed to further dose reduction to the
patient.
Exposure settings
Radiation exposure dose to a patient is directly
controlled by the operator’s selection of
kilovolt peak (kVp), milliamperage (mA) and
exposure time. However, optimum settings are
subjective; one size does not fit all here. Each
dentist has their own image quality prefer-
ences. In addition, an x‐ray unit’s radiation
output will vary according to the age of the
unit, manufacturer’s specs, etc. In this regard,
government inspectors will periodically inspect
each dental office’s x‐ray equipment to ensure
that their equipment is operating according
to the manufacturer’s guidelines. Improper
functioning x‐ray equipment may result in
unnecessary additional radiation exposure to
the patient.
Operator technique
An operator’s technique is critical in producing
diagnostic images with minimal distortion,
missed apices, etc. Undiagnostic images will
Fig.G6 Round PID collimation.
Fig.G7 Aluminum filter integrated into the body of the
x‐ray tubehead.

G Radiation Protection 27
require re‐exposure of the patient. Intraoral
instrumentation for holding the receptor and
aligning the PID do not guarantee acquisition
of diagnostic images, they simply aid the patient
and the operator in the attempt to acquire a good
diagnostic image. Similarly, the operator’s proper
exposure setting selection and patient position-
ing in an extraoral unit will reduce the number
of unnecessary retakes.
2. RADIATION PROTECTION: OFFICE
PERSONNEL
The NCRP requires that the construction and
design of a dental office must include safety
features to protect all personnel working with
or near x‐ray equipment. In addition, the owner
of a dental practice must protect the front‐end
personnel such as receptionists and those indi-
viduals working in adjacent offices to reduce
their exposure to dental x radiation.
The NCRP x‐ray protection guidelines for
dental offices are as follows:
The dentist (or, in some facilities, the designated radia-
tion safety officer) shall establish a radiation protection
program. The dentist shall seek guidance of a qualified
expert.
The qualified expert should provide guidance for the
dentist or facility engineer in the layout and shielding
design of new or renovated dental facilities and when
equipment is installed that will significantly increase
the air kerma
[kinetic energy released per unit
mass] incident in walls, floors and ceilings.
New dental facilities shall be designed such that no
individual member of the public will receive an effective
dose in excess of 1 mSv annually.
The qualified expert should perform a pre‐installation
radiation shielding design and plan review to determine
the proper location and composition of barriers used to
ensure radiation protection in new or extensively
remodeled facilities and when equipment is installed
that will significantly increase the air kerma incident in
walls, floors and ceilings.
Shielding design for new offices for planned fixed x‐ray
equipment installations shall provide protective bar-
riers for the operator. The barriers shall be constructed
so operators can maintain visual contact and communi-
cation with patients throughout the procedures.
The exposure switch should be mounted behind the pro-
tective barrier such that the operator must remain
behind the barrier during the exposure (Fig.G8).
Adequacy of shielding shall be determined by the quali-
fied expert whenever workload increases by a factor of
two or more from initial design criteria.
In the absence of a barrier in an existing facility, the
operator shall remain at least two meters, but prefer-
ably three meters from the x‐ray tubehead during
exposure. If the two meter distance cannot be main-
tained, then a barrier shall be provided. This recom-
mendation does not apply to hand‐held units with
integral shielding.
The qualified expert should perform a post‐installa-
tion radiation protection survey to assure that radia-
tion exposure levels in nearby public and controlled
areas are ALARA and below the level limits estab-
lished by the state and other local agencies with
jurisdiction.
The qualified expert should assess each facility individ-
ually and document the recommended shielding in a
written report.
The qualified expert should consider the cumulative radi-
ation exposures resulting from representative workloads
Fig.G8 Operator standing behind a protective barrier (the
lower portion is a lead shield and the upper portion is
made of leaded glass) during radiation exposure of a
patient.

28 Fundamentals of Oral and Maxillofacial Radiology
in each modality when designing radiation shielding for
rooms in which there are multiple x‐ray machines.
A qualified expert shall evaluate x‐ray equipment to
ensure that it is in compliance with applicable laws and
regulations.
All new dental x‐ray installations shall have [a] radia-
tion protection survey and equipment performance
evaluation carried out by or under the direction of a
qualified expert.
For new or relocated equipment, the facilities shall pro-
vide personal dosimeters for at least one year in order to
determine and document the doses to personnel.
Equipment performance evaluations shall be per-
formed at regular intervals thereafter, preferably at inter-
vals not to exceed four years for facilities only with
intraoral, panoramic or cephalometric units. Facilities
with CBCT units shall be evaluated every one to two
years.
Source: National Council on Radiation Protection
andMeasurement (2017)
Practitioners must comply if they want to
eliminate or at least reduce their risk of potential
liability.
Additional methods to protect an operator
from occupational exposure to radiation
include the following:
1. If assistance is required for a child or a
handicapped patient to stabilize the recep-
tor instrument, non‐occupationally exposed
persons (preferably a member of the
patient’s family) should be asked to assist
so that the operator can stand outside the
operatory. Offering the volunteer a protec-
tive apron may reduce any apprehension
the individual might have about being
exposed alongside the patient. The ration-
ale for substituting a surrogate is because
this individual will be exposed to a mini-
mum of radiation exposure possibly this
one occasion, while the operator may be
required to repeat this procedure on numer-
ous different patients and thereby receive
far greater cumulative levels of radiation
exposure.
2. When a protective barrier is unavailable,
the operator should stand at least 2 m from
the x‐ray tubehead and between 90° and
135° from the direction of the primary x‐ray
beam. Standing distance measured from
the x‐ray source incorporates the inverse
square law
which allows for additional
dissipation of the x rays. This standing
position also utilizes the patient’s body as a
barrier for absorbing some of the scattered
x rays (Fig.G9).
90°
135°
90°
90°
135°
135°
135°
90°
Low x-ray
scatter
area
Low x-ray
scatter
area
Low x-ray
scatter
area
Low x-ray
scatter
area
Fig.G9 Illustration demonstrating the safest position for
the operator to stand when there is no protective barrier
and the operator is within 2 m of the patient.

G Radiation Protection 29
The monitoring of radiation exposure to
personnel in a dental office is typically accom-
plished through the use of an individual
radiation dosimetry badge
(Fig. G10). The
NCRP guidelines (2017) state that “Provision
of personal dosimeters for external exposure
measurement should be considered for
workers who are likely to receive an annual
effective dose in excess of 1 mSv. Personal
dosimeters shall be provided for declared
pregnant occupationally‐exposed personnel”
(see Section P).
How much occupational radiation
exposure is permitted?
Both the NCRP and the International Com-
mission on Radiological Protection (ICRP) have
published guidelines for occupational and non‐
occupational dose limits. The NCRP and ICRP
state that occupational workers should not be
exposed to more than 50 millisieverts (mSv) per
year, referred to as maximum permissible dose
(MPD)
. The calculated value of an individuals
total lifetime occupational effective dose shall
be limited to 10 mSv multiplied by the age of
that individual. For example, a total lifetime
occupational exposure for a 25‐year‐old worker
is 25 × 10 = 250 mSv. In reality, if a proper safety
protocol is adhered to in a dental office, occupa-
tional doses should fall well below the MPD.
However, if the operator’s exposure level
exceeds the permitted annual level, the opera-
tor would be temporarily prohibited from
working around x‐ray equipment until the
accumulated dose fell below the level permit-
ted based on the 50 mSv/year calculation.
Note: There is no MPD for patients because the
radiation exposure that healthcare profession-
als deliver is deemed to be beneficial for the
patient in either a diagnostic or a therapeutic
capacity. Obviously, keeping the patient expo-
sure dose to a minimum should be a primary
objective.
Fig.G10 Radiation dosimeter badge (clip‐on style).

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
30
Patient Selection Criteria
H
The dentist must weigh the benefits of taking dental
radiographs against the risk of exposing a patient to x rays,
the effects of which accumulate from multiple sources over
time. The dentist, knowing the patient’s health history and
vulnerability to oral disease, is in the best position to
make this judgment in the interest of each patient. For this
reason, the guidelines are intended to serve as a resource for
the practitioner and are not intended as standards of care,
requirements or regulations.
Source: American Dental Association Council on
Scientific Affairs (2006)
The ADA guidelines quoted above differen-
tiate between symptomatic and asymptomatic
patients. For symptomatic patients, a radio-
graphic examination should be limited to
images required for diagnosis and planned
treatment of current disease. In a radiographic
examination of asymptomatic patients such
as new patients or returning patients, the prac-
titioner should adhere to published selection
criteria. The operative word in the ADA state-
ment is “guidelines.” All healthcare providers
must use their good judgment when prescribing
x‐ray images as they are not limited to or pro-
hibited from requesting any x‐ray image if it
may benefit the patient’s care (see Appendix 1).
The ADA guidelines for prescribing images
vary amongst different demographic groups,
although this is not to say that a particular health
concern can only occur in a specific group.
Historically there are patterns that warrant
modifying imaging protocol to accommodate
these variations. As mentioned earlier, the
dental practitioner has the authority to request
whatever x‐ray images are deemed necessary
for a thorough diagnosis of the patient. Pre‐
existing dental x‐ray images taken at other
dental offices should also be obtained whenever
possible before prescribing new x‐ray proce-
dures. A chronological sequence of dental
images can be very useful for documenting
both developmental and pathological changes
to the oral cavity. All patients are entitled to
copies of dental images and may request them
from their current or former dentist(s). Addi-
tional fees may be incurred by the patient for
producing copies of x‐ray images. It is at the
discretion of each dental practitioner to decide
whether to charge or waive any fees for this
service. All dental practitioners should keep
permanent records of all x‐ray images for all
current and former patients. Why? This is
because a dentist may be called upon to pro-
duce x‐ray images to assist in the postmortem
forensic identification of an individual or pos-
sibly the dentist may be at the center of a legal
dispute arising from a disgruntled patient who
has filed a lawsuit. Pre‐ and post‐treatment

H Patient Selection Criteria 31
x‐ray images can be vital in the dentist’s legal
defense for disproving false claims about per-
forming unnecessary or poor quality dental
treatment.
What about pregnant patients? To be safe, it is
always best to avoid exposing the mother to any
x‐ray images during the entire term of her
pregnancy. The risks to the developing fetus are
known to be minimal but the dentist does not
want to be indicted afterwards by the mother as
being the cause of a child’s unforeseen birth
defect. However, treating the mother’s dental
problem is also essential to the health of the
developing baby. If the mother is experiencing
undue stress or has an untreated dental infec-
tion, more harm could result to the baby than
by exposing a few intraoral x‐ray images and
properly treating the oral problem. The author
recommends that the dentist expose the mini-
mum number of x‐ray images necessary to treat
the current problem and to take all precautions
to reduce the radiation exposure to the patient.
Additional protection for the fetus is made pos-
sible by placing a full‐length protective apron
on the patient. This will absorb 99.9% of the stray
x rays that might reach the mother’s abdominal
region. Of course, elective treatment should be
postponed until after birth of the child.

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/hubar/radiology
32
Film versus Digital
Imaging
I
Film
X rays were first discovered in 1895. At that
time emulsion‐coated glass plates were used
torecord both photographic and x‐ray images.
The first commercial roll of photographic film
was introduced in 1899 by the Eastman Kodak
Company. However, the transition to using
flexible film rather than glass plates to record
x‐ray images did not occur until the 1910s. Once
flexible x‐ray film was introduced, it was
repeatedly improved over the years until its use
began to decline with the introduction of digital
imaging beginning in the 1980s. The last sig-
nificant advancement in x‐ray film was back in
the year 2000 when Kodak introduced “Insight”
intraoral film. From the earliest days of x rays,
when a 20 min exposure to radiation may have
been required to produce an x‐ray image, the
last incarnation of intraoral film reduced the
patient exposure time to seconds.
Two categories of dental x‐ray film are non‐
screen and screen film. Intraoral x‐ray film is a
non‐screen film type, also referred to as a direct
exposure film. It is composed of a flexible piece
of transparent cellulose acetate which acts as
the base to support an emulsion that is coated
on both the front and the back sides. This
emulsion consists of silver halide crystals sus-
pended in a thin layer of gelatin. To protect
the soft gelatin from incurring damage from
mishandling, it is manufactured with a protec-
tive coating applied over it. X‐ray film is not
only sensitive to x rays but also to white light
sources. Consequently, intraoral x‐ray film is
individually prepackaged in a sealed, lightproof
packet. This protective packet prevents the film
from being exposed to white light and it also
prevents the patient’s saliva from contaminat-
ing the film’s emulsion. Within each intraoral
film packet there is also a thin sheet of lead foil
located behind the film and a piece of black
paper. The lead foil serves two functions:
1. It provides additional protection to the
patient by absorbing some of the incoming
and scattered x rays. Some x rays can rico-
chet off the teeth and bones behind the film
packet and could expose the film from the
backside. These scattered x rays would con-
tribute to degrading the quality of the final
image. This effect is referred to as film fog.
The lead foil blocks these back‐scattered
xrays and thereby reduces film fog.

I Film versus Digital Imaging 33
2. Embossed upon each piece of lead foil is a
geometric pattern that each manufacturer
selects (e.g. honeycomb). If the operator
erred and placed the film packet reversed
in the patient’s mouth and exposed it, the
foil’s embossed pattern would now be vis-
ible on the final image and this would alert
the dentist that the image must be reversed
to properly orientate the patient’s dentition.
Failure to do so could lead to performing
unnecessary dental treatment on healthy
teeth and leaving untreated diseased teeth.
Extraoral x‐ray film is classified as a screen
film. As the term extraoral infers, these films are
positioned outside of the patient’s mouth
during an x‐ray exposure. This category of film
is always sandwiched between two intensify-
ing screens within a light‐tight film cassette. An
intensifying screen’s composition includes
layers of phosphor crystals. When a phosphor
crystal in the screen is hit by an x‐ray photon, it
fluoresces. This fluorescent light diverges and
simultaneously exposes multiple halide crys-
tals in the film. As a result, intensifying screens
help to reduce the total amount of radiation
exposure to the patient but they also produce an
image with poorer image resolution
compared
with a non‐screen film image. Consequently,
non‐screen intraoral films are better for diag-
nosing small lesions like caries where finer
detail is required. Intensifying screens are not
used with intraoral films.
Whether an operator uses a screen or a non‐
screen film, the exposed x‐ray film needs to be
chemically processed before a dental image will
be visible to our eyes. The hidden image on an
unprocessed x‐ray film is referred to as a latent
image. Processing can either be performed man-
ually by the operator or with a film processor
,
where the film is automatically drawn through
the solutions. Either way, the film must be pro-
cessed in a dark environment to avoid extrane-
ous exposure to white light. Chemical
processing of a dental film consists of first sub-
merging each film into a developing solution
for a specified time, then the films are submersed
in a fixer solution for a set length of time and
finally each film is washed in water. The func-
tion of the developer solution is to precipitate
the silver atoms within the emulsion, the fixer
serves to remove the unaffected crystals and
water removes all traces of the chemical solu-
tions. The precipitated silver appears black on
the image. A film accidentally exposed to white
light will turn totally black during processing.
Proponents of x‐ray film generally claim that
dental images acquired on x‐ray film are still
superior to digital receptor images.
Digital imaging
In 1987, the first digital image receptor was
introduced for intraoral imaging. Since that
time, digital imaging has gradually become the
new standard for acquiring and viewing of
dental images.
Direct digital imaging refers to directly capturing
a latent image onto an appropriate receptor.
Currently, there are two different technologies
of intraoral digital systems. One system incor-
porates solid state electronics that use either
CCD
(charge coupled device) or CMOS
(complementary metal oxide semiconductor)
technology (Fig.I1). Both the CMOS and CCD
receptors typically are wired directly to a
Fig.I1 Direct digital receptor. (Source: Courtesy of Adam
Chen, XDR Radiology.)

34 Fundamentals of Oral and Maxillofacial Radiology
computer. However, some manufacturers have
introduced a modified direct system that uses
a Wi‐Fi signal to transmit the data from the
receptor directly to the computer rather than via
a physical wire. in either wired or Wi‐Fi signal
transmission, both receptor designs directly
send the image to a computer. The alternative
digital receptor technology uses photostimulable
phosphor plates (PSP plates) (Fig.I2). A phosphor
coating is deposited onto a thin, flexible piece
of polyester acetate. The x‐ray image is cap-
tured and stored as a latent image in the phos-
phor coating. Each manufacturer of PSP plates
produces a specific scanner to digitize the
acquired latent images.
Indirect digital imaging refers to the conver-
sion of the latent analog image captured on a
PSP plate into a digital image. Once the PSP
plate has been scanned, the image can be erased
by exposing the PSP plate to a room‐intensity
white light. A PSP plate can be erased and
re‐exposed multiple times. Operator care should
be taken not to scratch or bend the PSP plate so
as to prolong its functional life. The flexibility
and thinness of the PSP plate makes it much
more patient friendly. Unlike the limited selec-
tion of solid‐state digital receptor sizes, PSP
plates come in several different sizes. PSP plate
image quality is comparable to solid‐state
digital images but the added time and steps
involved to visualize the digital image make it
unappealing to many practitioners at this time.
On the flip side, the cost for each intraoral PSP
plate is minimal. Typical cost ranges between
twenty‐five and thirty‐five dollars per intraoral
PSP plate compared to thousands of dollars for
a single solid‐state receptor.
Dental equipment manufacturers may offer
three sizes (0, 1 and 2) of solid‐state intraoral digi-
tal receptors. Digital receptor sizes closely match
intraoral film sizes. Numerically, the higher the
receptor number, the larger is the physical area
that is captured in the image. Ofthe three differ-
ent choices, size 2 acquires the largest area while
AB
Fig.I2 A. PSP plate scanner. B. PSP plates and pouches: sizes 0, 1 and 2.

I Film versus Digital Imaging 35
0 acquires the smallest area. Most operators use
size 2 for all posterior periapical views and also
for bitewing images, while size 1 is used for ante-
rior periapical views. Size 0 is ideal for children
whose smaller mouths accommodate it much
better. This will be discussed further in Section L
on intraoral techniques. Solid‐state intraoral
receptors are currently not made larger than a
size 2. Limited demand for larger intraoral
images such as occlusal views and the high price
to manufacture larger size solid‐state receptors
are the obvious reasons why they are not avail-
able today. PSP plates, because of their modest
prices, are available in larger sizes.
Advantages ofdigital x‐ray imaging
Digital imaging has always been marketed as
being a significant time saver in comparison to
using dental x‐ray film. This is somewhat true.
It is accurate that a solid‐state digital receptor
can process an image in mere seconds, but PSP
plates require added time because the operator
must scan each PSP plate individually. In
addition, each plate must “blanked” to reuse
it and then repackaged. Consequently, opera-
tional time savings are not as pronounced as
may be expected using PSP systems.
Manufacturers also cite dose reduction to
the patient as a significant benefit when using
digital imaging systems compared with dental
x‐ray film. Historically, the first dental expo-
sures were upwards of 25 min in length. Today,
intraoral images using digital receptors typically
utilize exposure times in mere thousandths of a
second. To be fair, however, the latest intraoral
dental x‐ray film has reduced exposure times to
a second in length, being only slightly more
than a digital exposure setting. Manufacturers’
claims of upwards of a 75% reduction in expo-
sure time compared with using film in reality
often translates into a mere fraction of a second
reduction per exposure.
Unlike dental x‐ray film, where “what you
see is what you get,” digital x‐ray images, like
digital photographs, can be easily altered to
enhance them. Imaging software typically per-
mits modifying image brightness
, contrast
and image resolution . As a consequence, a
subdiagnostic digital image may be improved
just enough that it may negate the need for a
retake which would expose the patient to addi-
tional radiation. This applies to both solid‐state
and PSP plate receptors. In addition, combining
an x‐ray image with a clinical photograph on a
screen offers the dental professional a powerful
tool to educate patients. Viewing both images
together allows the dentist to demonstrate
the patient’s specific dental problems and the
proposed treatment options. Digital imaging
technology facilitates transmission of dental
images to fellow colleagues for consultation
purposes or for the submission of images to den-
tal insurance companies for pre‐authorization
of proposed treatment plans.
Patients may request copies of their x‐ray
images for a variety of reasons, such as they are
relocating to another city and will be treated by a
new dentist. Previously, with only x‐ray film
available, it was much more cumbersome to
duplicate radiographs, especially since dentists
have always been advised to keep the original
radiographs and only supply copies to the
patient and insurance companies. In the event a
dentist is called to a court of law, original x‐ray
images are critical for the dentist’s defense. It is
important to mention that patients are legally
entitled to copies, in any format, of all their x‐ray
images. The simple reason is that a patient
should not have to be exposed to additional
radiation simply because a dentist opted not to
release the existing radiographs to the patient.
However, it is up to the discretion of every dentist
to decide whether or not to charge a duplication
fee for providing this service to the patient.
Disadvantages ofdigital imaging
An obvious disadvantage of a solid‐state intraoral
receptor is its physical bulk. These receptors are

You're Reading a Preview

Become a DentistryKey membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here

Was this article helpful?

Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology3IntroductionAThe objective of this textbook is to offer the reader a concise summary of the fundamentals and principles of dental radiology. In addition, brief synopses are included of the more com-mon osseous pathologic lesions and dental anomalies. This book is intended to be a handy resource for the student, the dental auxiliary and the practicing clinician.What is dental radiology?Dental radiology is both an art and a science. Anart is a skill acquired by experience, study or observation and a science is a technique that is tested through scientific method. Scientific principles of physics, chemistry, mathematics and biology are integral to dental radiology. Capturing and viewing a digital dental image requires sophisticated technology, while the operator’s proper physical positioning of the intraoral receptor requires a skill that is based upon scientific principles. The art of dental radiology involves the interpretation of black and white images that often resemble ink blots. Deriving a differential diagnosis involves the application of the clinician’s knowledge, cogni-tive skills and accumulated experience. The term “radiograph” originally applied to an x‐ray image made visible on a processed piece of x‐ray film. A photograph is similar to a radio-graph except it is taken with a light‐sensitive camera and printed on photographic paper. Today the term “radiograph” is used to describe an image whether it was acquired with x‐ray film or with a digital receptor. It is more accurate to use the term “x‐ray image” when viewing it on a monitor and “digital radiograph” when a hardcopy is viewed. In the future, “radiograph” should be updated to a more appropriate term.What are x rays?X rays are a form of energy belonging to the electromagnetic (EM) spectrum. Some of the members of the EM family include radio waves, microwave radiation, infrared radiation, visible light, ultraviolet radiation, x‐ray radiation and gamma radiation. These examples are differ-entiated by their wavelength and frequency. Awavelength is defined as the distance between two identical points on consecutive waves (e.g. distance from one crest to the next crest) (Fig.A1). Longer wavelengths have lower fre-quencies and are considered to be less damaging to living tissues. Conversely, shorter wavelengths 4 Fundamentals of Oral and Maxillofacial Radiologyhave higher frequencies and are considered to be more damaging to living tissues. One end of the EM spectrum includes the long wavelengths used for radio signal communica-tions while at the short wavelength end of the spectrum is gamma radiation. The EM spectrum covers wavelengths, ranging from nanometers to kilometers in length (Fig.A2). Dental x rays are 0.1 to 0.001 nanometers (nm) in length. For comparison purposes, dental x rays may be the size of a single atom while some radio waves are equivalent to the height of a tall building. As with all types of EM radiation, x rays are pure energy. They do not have any mass and because they have very short wavelengths, xrays can easily penetrate and potentially damage living tissues. All forms of EM radiation must not be confused with particulate radiation , such as alpha and beta radiation . Particulate radiation is not discussed in this textbook.The EM spectrum is divided into the non‐ionizing forms and the ionizing forms of radi-ation. The boundary between non‐ionizing and ionizing radiation is not sharply delineated. Ionizing radiation is considered to begin with the shorter wavelength ultraviolet rays and the increasingly shorter wavelengths which include x rays and gamma rays. The longer wavelengths of ultraviolet rays and beyond which include microwaves, radio waves, etc. are all considered to be non‐ionizing forms of radi-ation. The difference is that ionizing radiation is powerful enough to knock an electron out of its atomic orbit, while non‐ionizing radiation is Short wavelengthHigh frequencyABLong wavelengthCrest CrestTroughLow frequencyFig.A1 Diagrams showing wave pattern of electromagnetic radiation. A. High frequency equals short wavelength. B.Low frequency equals long wavelength.Radio Microwave Infrared Visible Ultraviolet X ray Gamma Ray10410210–2Wavelength in centimeters10–510–610–810–1010–121About the size of...Buildings Humans Bumble Bee Pinhead Protozoans Molecules Atoms Atomic NucleiFig.A2 Electromagnetic (EM) spectrum. A Introduction 5not powerful enough to remove an electron. The removal of an electron from an atom is referred to as “ionization.” Exposure to ionizing radiation is recognized as being more hazardous to living tissue than non‐ionizing radiation.Note: “X ray” is actually a noun composed of two separate words and it should only be hyphenated when it is used as an adjective, e.g. x‐ray tube. In addition, each individual unit of electromagnetic radiation is referred to as a photon . Consequently, the correct term for x ray is x‐ray photon. In published litera-ture, x‐ray photons are often incorrectly referred to as “x‐rays.”In lay terms, x‐ray images reveal the different parts of our bodies or other matter in varying shades of black and white. Why? This is because skin, bone, teeth, fat and air absorb different quantities of radiation. Within the human body, the calcium in bones and teeth absorbs the most x rays. Tooth enamel is the most mineralized substance in the human body (over 90% mineralized). Consequently, mineralized struc-tures such as teeth and bones appear as varying shades of white (i.e. radiopaque ) on dental images. Fat and other soft tissues absorb less radiation, and consequently they will look darker (i.e. radiolucent ) in comparison to bone. Air absorbs the least amount of x rays, so airways and sinuses typically look black in comparison to mineralized substances. The denser or thicker the material, the more x‐ray photons are absorbed by it. This results in a more radiopaque appearance on an x‐ray image. The thinner or less dense an object is, the fewer the number of x‐ray photons absorbed or blocked by it. Thus more x‐ray photons are able to penetrate through the object to expose the image recording receptor. This results in a more radiolucent appearance.What’s thebig deal about x‐ray images?Just as the early pioneers in radiology were astonished to see the previously unknown in their first x‐ray images, modern day clinicians may be astonished to see osseous and dental pathology, anatomic variations, effects of trauma, etc. on their x‐ray images. Consequently, the benefits of x‐ray images are immense. The combination of both clinical and x‐ray images provides vital information to the dentist for preparing comprehensive dental treatment plans. The end result is a continual improve-ment in oral healthcare today. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology6HistoryBDiscovery ofx raysOn November 8, 1895, Wilhelm Konrad Röntgen (alternately spelled Wilhelm Conrad Roentgen), a professor of physics and the director of the Physical Institute of the Julius Maximilian University at Würzburg in Germany, while working in his laboratory discovered what we commonly call “x rays” (Fig.B1). On that day in his darkened laboratory, he noticed light emanating on a table located across the room, far from the experiment that he was conducting. Professor Röntgen was researching the effects of electrical discharge using a Crookes–Hittorf tube . The glowing object was a fluorescent screen used in another experiment. This per-plexed him because electrons emanating from his electric discharge tube were known to only travel short distances in air. His fluorescing screen was too far away for these electrons to produce the fluorescence. In addition, his lab was completely darkened and the Crookes–Hittorf tube was completely covered with black cardboard to prevent light leakage. Light leak-age otherwise could have caused the screen to fluoresce. It was obvious to Professor Röntgen that he was dealing with an unknown invisible phenomenon. Professor Röntgen called this new phenomenon “x rays.” “X” because that is the universal symbol for the unknown and “ray” because it traveled in a straight line. He was a modest gentleman and did not wish to call these new rays “Röntgen rays” after himself which is standard protocol for new discoveries. Following his discovery of x rays, he was deter-mined to learn what were the properties and characteristics of these mysterious invisible rays. He secretly tested this phenomenon for weeks and did not divulge any information about his new discovery to anyone. At first he experimented by placing objects in the path of the x rays between the tube and the fluorescent screen. Ultimately, he decided to place his own hand in front of the x‐ray beam and he was amazed at what he saw on the fluorescent screen. He observed shadows of his skin and underlying bones. For the first recorded image, he asked his wife, Bertha, to place her hand on a photographic plate while he operated the experimental apparatus. Professor Röntgen was able to produce an x‐ray image of her bones and soft tissue. This x‐ray image, which includes the wedding ring on her finger, is recognized as the first x‐ray image of the human body (Fig.B2).On December 28, 1895, Professor Röntgen delivered his first of three manuscripts on xrays to the president of the Physical Medical B History 7Society of Würzburg. The first manuscript was entitled “On a New Kind of Rays, A Preliminary Communication.” The unedited manuscript went to press immediately and was published in the Annals of the Society. Immediately after-wards, announcements were published in newspapers and in scientific journals around the world. In the United States, the announce-ment of Professor Röntgen’s discovery was on January 7, 1896 in the New York Herald news-paper. The English translations of the original paper were printed in Nature, a London publi-cation, on January 23, 1896 and in Science, a New York publication, on February 14, 1896. Professor Röntgen did not seek nor enjoy public acclaim and as a result he would make only a single presentation on the topic of x rays. This presentation was given to the Physical Medical Society of Würzburg on January 23, 1896.The prevalence of Ruhmkorff coils and Crookes–Hittorf tubes in nearly every physics laboratory at the time permitted x‐ray research to be conducted globally without much delay. These two ingredients were the primary components necessary for producing x rays. Consequently, prior to Professor Röntgen’s dis-covery anyone who was studying high voltage electricity was unknowingly generating x rays. But no one prior to Professor Röntgen recog-nized this phenomenon, nor understood the value of it even if they did suspect something unusual. Sir William Crookes, whose collabora-tion produced the Crookes–Hittorf tubes, had outright complained to the manufacturer that unopened boxes of photographic plates were arriving at his lab already exposed. Sir Crookes Fig.B1 Wilhelm Konrad Röntgen: credited with being the first person to discover x rays.Fig. B2 First x‐ray image of the human body: Bertha Röntgen’s hand. 8 Fundamentals of Oral and Maxillofacial Radiologysurmised the problem was simply due to the manufacturer’s poor quality control. It was not until after Professor Röntgen’s discovery was announced that Sir Crookes and other scientists finally understood that x rays were the cause of some of their photographic plate problems.Professor Röntgen was awarded the first Nobel Prize for Physics in 1901 for his discovery of x rays even though some tried to discredit his claim to the discovery. Sadly, Professor Röntgen became reclusive and very bitter in his later years as a result of this controversy concerning the discovery of x rays. He even stipulated in his will that all of his correspondences written regarding the discovery of x rays be destroyed at his death. He died on February 10, 1923. Unbeknownst to Professor Röntgen, his recognition of x rays is considered by many today to be the greatest scientific discovery of all time. X rays have truly revolutionized modern healthcare practices.Who took theworld’s first “dental” radiograph?Poor records make it difficult to say conclu-sively who took the first dental radiograph. However, Professor Walter König in Frankfurt, Germany, Dr. Otto Walkoff, a dentist in Brunschweig, Germany and Dr. Frank Harrison, a dentist in Sheffield, England have all been reported to have taken dental radiographs within a month of Röntgen ’s reported discov-ery. Dr. Walkoff on January 14, 1896 used a glass photographic plate. The glass plate was wrapped in black paper to block out light and it was covered with rubber dam to keep out saliva. He inserted this glass plate into his own mouth and subjected himself to a 25 min exposure to radiation (Fig.B3). If not the first dental radio-graph, it certainly was one of the earliest dental radiographs. Most people claim that Dr. C. Edmund Kells, Jr. took the first dental radiograph of a living person in the United States. Itshould be emphasized that this was on a living person because it had been reported earlier in a Dental Cosmos publication that Dr. Wm. J. Morton, a physician, presented his research work before the New York Odontological Society and it included four dental x‐ray radiographs. But his dental radiographs were taken on dried labo-ratory skulls and not on a living person. According to Dr. Kells, “Just when I took my first dental radiograph, I cannot say, because I have no record of it, but in the transactions of the Southern Dental Association, there is reported my x‐ray clinic given in Asheville in July 1896, and I remember full well that I had had the apparatus several months before giving this clinic and had developed a method of tak-ing dental radiographs. Thus I must have begun work in April or May 1896.” Regardless of who was first to expose a dental radiograph, the value of dental radiography was recognized almost immediately after Professor Röntgen’s discovery of x rays.Dr. C. E. Kells, Jr., aNew Orleans dentist andtheearly days ofdental radiographyShortly after the announcement of Professor Röntgen’s discovery, Professor Brown Ayres of Tulane University in New Orleans gave a Fig.B3 First dental radiograph (unconfirmed). In January 1896, Dr. Otto Walkoff, a German dentist, covered a small glass photographic plate and wrapped it in a rubber sheath. He then positioned it in his mouth and subse-quently exposed himself to 25 min of radiation. B History 9public demonstration of x rays using a crude apparatus set‐up. Since the general public marveled at the thought of being able to stand next to a piece of equipment and shortly thereafter see a photograph of the inside of the body, he devoted a portion of his demon-stration to expose a volunteer’s hand. Although it required a lengthy 20 min exposure, the crowd was patient, including one curious soul, Dr. C. Edmund Kells, Jr. (Fig.B4). It immedi-ately occurred to him that x rays would be an invaluable tool for observing inside the jaws and teeth. Dr. Kells met Professor Ayres and they discussed the idea of taking pictures of teeth. Professor Ayres became instrumental in assisting Kells to acquire the necessary equip-ment for building an x‐ray laboratory to conduct his own research.It was a crude and difficult procedure for taking x rays in the early days. For example, one of the original problems encountered was the variability in output of the x‐ray tube. The few molecules of air that were inside the tube were vital for producing x rays. To do so, some of these air molecules would have to be bom-barded into the walls of the tube, which would convert their energy into x rays. The air mole-cules received that energy when a very high voltage was supplied to the tube. In doing this, however, these molecules of air would gradu-ally adhere to the inner walls of the tube and without any free air molecules present floating inside the tube, x rays could not be produced. To reverse this situation, the x‐ray tube would have to be heated by means of an alcohol lamp. The heat would drive the air molecules off the walls, allowing x rays to be produced once again. The constantly changing condi-tions within the tube meant that the apparatus had to be reset for each and every patient. Otherwise, there was no way of determining how long a photographic plate would need to be exposed to get a good image.To complicate matters further, meters were not available in the early days to measure exactly how much radiation was being pro-duced by the x‐ray apparatus. The accepted method of choice was for a clinician, such as Dr. Kells, to pick up a fluoroscope and place one hand in front of it. The radiation output would be adjusted until the bones of the hand were visible in the fluoroscope. An equally hazardous technique would be for the operator to place a hand in front of the beam and adjust the radiation output until the skin began to turn red. This is referred to as the erythema dose . The patient would then be positioned in front of the x‐ray beam and the exposure taken. The absence of any immediate accompanying sen-sation by the patient frequently led to radiation overexposure. Furthermore, the clinician was in close proximity to the patient during the entire exposure and was completely unshielded.Dr. Kells immediately could foresee several problems with incorporating x rays into a dental practice. His primary concern was the expo-sure time. If it took 20 min for a hand to be exposed, it theoretically might require hours to expose a tooth because a tooth is a much denser object. How could a patient hold a Fig. B4 Dr. C. Edmund Kells, Jr.: New Orleans dentist, inventor and author. 10 Fundamentals of Oral and Maxillofacial Radiologydental x‐ray film motionless for that length of time? Dr. Kells’ early trials showed that it would require up to 15 min to expose a molar tooth, which was much better than he antici-pated, but it still was a monumental problem to overcome. If dental x rays were to be rou-tinely taken by the dental practitioner, technical improvements to reduce time exposures were crucial. Within three years of Professor Röntgen’s discovery rapid improvements in the design of the x‐ray tube dramatically reduced that 15min exposure down to 1–2 min. Then there was a major alteration in the tube design on May 12, 1913. This was the patent application date for the Coolidge tube and this ushered in the “golden age of radiology.” W. O. Coolidge, the director of research at the General Electric Company, found that using a coil of tungsten in a low vacuum tube could generate signifi-cantly more x rays than the old gas style tubes could ever produce. As a result, in the 1920s x‐ray exposures were dramatically reduced to 4–10 s in duration.There were also electrical dangers. An unin-sulated and unprotected wire carried a high voltage current to the discharge tube which led to injuries to both patients and clinicians. In 1917, Henry Fuller Waite, Jr. patented the design for an x‐ray unit that eliminated the exposed high voltage wire. General Electric introduced the Victor CDX shockproof dental x‐ray unit about a year later.All x‐ray demonstrations on human patients initially used large glass plates for recording the images. It was not until 1919 that the first machine‐wrapped dental x‐ray film packet became commercially available. It was called regular film and was manufactured by the Eastman Kodak Company. Now that x‐ray film was small enough to place inside a patient’s mouth, how were patients supposed to hold it in place and keep it steady? To over-come both these problems, Dr. Kells produced his own rubber film holder with a pocket in it for holding the film. The side of the film holder was made of an aluminum plate and the wrapped film was placed in the pocket. With the patient’s mouth closed, the film holder was held in place by the opposing teeth. He selected one of his dental assistants to be his subject. This person is regarded as being the first living person in the United States to have experienced a dental x‐ray exposure. She sat in a dental chair with the film holder in place with her face placed up against the side of a thin board. In this manner, she was able to hold perfectly still for the required time. Unbeknownst to Dr. Kells at the time, using the thin board acted as an x‐ray filter that helped to prevent his assistant from receiving a radiation burn to her face from the prolonged exposure. Filters eventually would become a standard feature in all modern x‐ray units.Just as there were extravagant claims made for using x rays for the eradication of facial blemishes such as birth‐marks and moles, removal of unwanted hair and curing cancer, early advocates met with considerable oppo-sition to the diagnostic use of x rays and it often came from within the profession. Not only did they oppose the use of x rays, they openly condemned it. Dr. John S. Marshall in June of 1897 told the members of the Section on Stomatology of the American Medical Association that he had intended to use the rays in his practice, but had been deterred by the danger. Tragically, many early pioneers eventually developed fatal cancers from expo-sure to tremendous amounts of accumulated radiation received in monitoring and operat-ing the x‐ray apparatus. Dr. Kells himself developed cancer that was attributed to radia-tion exposure. Even so, he stated in the last article he wrote “Do I murmur at the rough deal the fates have dealt me? No, I can’t do that. When I think of the thousands of suffer-ing patients who are benefited every day by the use of x rays, I cannot complain. That a few suffer for the benefits of the millions is a law of nature.” Sadly, after years of suffering and failed medical treatments, he committed suicide in his dental office in 1928. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology11Generation ofX RaysCX rays occur in nature (e.g. solar x rays) but dental x rays are strictly a man‐made entity. Dental x‐ray equipment is manufactured by multiple companies, each offering varying styles, sizes, features and prices for their own particular units. The physical dental x‐ray unit primarily consists of two components. There is a control panel with a circuit board to control the kilovoltage (kV) , milliamperage (mA) and time. In addition, there is a tubehead that physically houses the x‐ray tube, filter, colli-mator and transformers (Fig.C1). The tube-head and control panel may be physically separate (e.g. wall‐mounted x‐ray unit) or they may be combined (e.g. hand‐held x‐ray unit). Individual mA and kV controls are features that vary from one unit to another. Higher quality x‐ray units tend to have independent controls to modify the kV, mA and exposure time while basic intraoral units may have fixed or a very limited number of mA and kV settings that an operator may alter. All intraoral x‐ray units allow the operator to modify the exposure time. Extraoral x‐ray units (eg. panoramic) generate x rays in a similar way to intraoral x‐ray units but are physically very different.The heart of an x‐ray unit is the x‐ray tube (Fig.C2). An x‐ray tube primarily consists of a cathode and an anode . The operator’s simple act of powering on a dental x‐ray unit (i.e. on–off switch) sends a low voltage current to the cathode which results in the production of a cloud of electrons at the cathode. The x‐ray unit is in a stand‐by mode at this time.When it is time to expose the intraoral x‐ray image, the operator must press an exposure button. Pressing the exposure button will convert standard wall outlet electricity to a high voltage current via a step‐up transformer and send it directly to the x‐ray tube. A step‐up transformer is the actual device that boosts the voltage high enough for x‐ray production. The effect of this high voltage is that it accelerates the electrons from the cathode across the tube to the anode. The anode is composed of a cop-per stem and a smaller target area composed of tungsten. The tungsten target area is referred to as a focal spot. The purpose of the copper stem is to assist dissipating the heat generated when electrons strike the focal spot, thereby extend-ing the useful life of the x‐ray tube. Once these energized electrons accelerate across the tube and strike the focal spot, only about 1% of the resulting kinetic energy is converted into x rays, while the remaining 99% of the energy is converted into heat. Oil fills the tubehead to act as an electrical insulator and helps to dis-sipate the heat generated from x‐ray production. 12 Fundamentals of Oral and Maxillofacial RadiologyA step‐up transformer may generate voltages upwards of 120 kV. Modern day intraoral x‐ray units typically operate in the 60–70 kV range; extraoral dental x‐ray units generally require voltages up to 120 kV. There is also a step‐down transformer located within the confines of the tubehead. The step‐down transformer reduces the voltage from a standard household elec-trical outlet to approximately 8–10 V. This low voltage is then sent to the filament of the cath-ode, which produces an electron cloud that will be used to produce our dental x‐rays. Reducing the voltage to the cathode filament also extends the useful life of the x‐ray unit. The cathode filament and anode focal spot typically are both made of tungsten. Obviously a 1% production rate for an x‐ray unit is a very inefficient use of electricity, but it generates adequate amounts of x radiation for our dental needs. With normal office usage, dental x‐ray units will last many years.Note: At the end of the working day, both intraoral and extraoral x‐ray units should be powered off. Keeping an x‐ray unit powered on indefinitely results in a continuous flow of current to the x‐ray tube, thereby shortening the useful life of that tube. Unlike intraoral and panoramic x‐ray units, when a cone beam computed tomographic unit is powered down overnight it will typically need upwards of 30 min for the flat panel receptor to properly warm‐up again prior to taking the first patient exposure.Fig.C1 Dental x‐ray tubehead.Fig.C2 X‐ray tube. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology13Exposure ControlsDFigureD1 shows an x‐ray control panel displaying variable exposure parameters.Voltage (V)Voltage controls the penetrability of the x‐ray beam and the degree of contrast in the image. One kilovolt (kV) is equivalent to 1000 V. When exposing intraoral images, selecting a higher kilovoltage increases the number of shades of gray between black and white in the image. This is referred to as a lower contrast image. This is particularly useful for diagnosing periodon-tal issues where varying bone level heights are a concern. Higher kilovoltage also is useful for imaging maxillary posterior teeth where the patient’s alveolar ridge and soft tissue thickness are typically greater. Additionally, increasing the penetrability of the x‐ray beam through superimposing osseous structures, such as the zygoma, will improve the diagnostic quality of the image. Meanwhile a lower kilovoltage exposure setting reduces the number of shades of gray in the intraoral image. This is referred to as a higher contrast image. This is particularly useful for detecting caries. This benefits the clinician who wishes to only differentiate between healthy tooth structure and decayed tooth structure. On both intraoral and extraoral dental images, tooth decay will appear radiolucent.Amperage (A)Amperage primarily controls the quantity of xrays generated. Dental units use milliamperes (mA). One milliampere is one‐thousandth of an ampere . Amperage controls the number of electrons in the cloud that will ultimately travel across the x‐ray tube, hit the anode and produce x‐ray photons. A basic dental x‐ray unit typically has a single milliamperage set-ting, while a higher quality x‐ray unit will have multiple millamperage settings. Intraoral x‐ray units generally produce 4–15 mA. Selecting a higher milliamperage will increase the number of x rays generated and result in an overall denser (i.e. darker) x‐ray image. If an initial x‐ray image appears too dark, reducing the milliamperage for a follow‐up exposure will lighten the overall density of the new image. 14 Fundamentals of Oral and Maxillofacial RadiologyExposure timerAll intraoral dental x‐ray units must include an exposure timer to control the duration of radia-tion production. Modern digital timers are capable of expressing time in thousandths of a second. Some manufacturers’ timers use “number of impulses” not “fractions of a second” as exposure increments. However, impulses can easily be converted into seconds. Impulses are associated with the electrical frequency (i.e. number of hertz). To convert impulses into seconds, simply divide the number of impulses by the number of hertz (Hz) . In North America, standard household electric current is 60 Hz (cycles per second), while in Europe it is 50 Hz. Selecting a 30 impulse time would translate into an exposure of 0.5 s (30 impulses divided by 60) in the United States. The function of altering the exposure time permits adapting to different patient types (e.g. physical size, gagging reflex, etc.) to achieve optimal image quality. Increasing the exposure time will result in the generation of more x rays and consequently produce an over-all denser (i.e. darker) x‐ray image. Conversely, a shorter time of exposure will result in a less dense (i.e. lighter) x‐ray image. In general, image contrast is not affected by exposure time.Fig.D1 X‐ray control panel display-ing variable kilovoltage (kV), milli-amperage (mA) and time settings. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology15Radiation DosimetryEThe terminology used to differentiate radiation doses includes: (i) absorbed dose; (ii) equivalent dose; and (iii) effective dose. The international system of units (abbreviated SI from the French derivation Le Système Internationale d’Unités) is the modern form of the metric system and is the world’s most widely used system of radiation measurement, used in both everyday commerce and science (see Appendix 6).ExposureExposure refers to the radiation output of an x‐ray machine. It is a measure of the ionization in air produced by x rays or gamma rays. Roentgen (R) is the traditional unit of measure. The SI term that is the equivalent of a roentgen is coulombs per kilogram. One roentgen is equiva-lent to 2.58 × 10–4 C/kg.Absorbed doseRadiation absorbed dose (rad) quantifies the energy from x radiation that is absorbed by a given mass of tissue. This is the numeric difference between how much x radiation enters and how much x radiation exits a mass of tissue. The SI unit for absorbed dose is called a gray (Gy). The conversion rate is 1 Gy equals 100 rad.Equivalent doseClinical dentistry is typically limited to using one type of radiation, “x rays.” However, the general public is continually exposed to a variety of types of radiation during a lifetime, whether it is medical or environmental in origin. Equivalent dose is a measure specifically used to compare the biologic effects of different types of radiation on living tissues. The biologic effects due to different types of radiation are significant. The SI unit for equivalent dose is sievert (Sv) . The original unit for equivalent dose was referred to as a rem, which is an acronym for radiation equivalent man (rem) . Similar to converting rad units to gray units, the conversion is 1 Sv equals 100 rem.Note: In clinical dentistry, the terms rads, rems, grays and sieverts are often used interchangeably when discussing patient exposures. However, when a researcher wishes to conduct a scien-tific study, using the precise nomenclature is critical. 16 Fundamentals of Oral and Maxillofacial RadiologyEffective doseDifferent cell types may react differently to an identical dose of x‐radiation exposure (e.g. muscle cell versus erythrocyte cell). Effective dose takes into account the differences in cellular response from radiation. It is also useful for comparing risks from different imaging procedures (e.g. dental imaging ver-sus medical imaging) because it factors into account the absorbed dose to all body organs, the relative harm from radiation and the sensitivities of each organ to radiation. As a result, effective dose is a good indicator of thepossible long‐term radiation risks to the individual. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology17Radiation BiologyFShortly after the discovery of x radiation, adverse effects of radiation exposure were being observed. The cellular effects would begin with erythema, followed by dermatitis, ulceration and ultimately the growth of tumors. All of which are associated with increasing amounts of radiation exposure. Pioneers in the dental field were ignorant of the hazards of radiation and some clinicians required amputations of fingers as a result of excessive radiation expo-sure from holding the image receptors in their patients’ mouths.The time lag between an individual’s expo-sure to radiation and the observed effect of the radiation is called the latent period. The latent period may be a very brief period as in the time it takes for a sunburn to become visible. Sunburn is caused by an excessive skin exposure to ultraviolet radiation in a relatively short period of time. The reddening of the skin typically appears several hours after exposure to the sun. This is consid-ered to be a short latent period. At the opposite end, we do not have a defined maximum length of time for an effect to be observed. A latent period may require decades or generations before an effect is ultimately observed. Why? Because x‐radiation damage to an individual’s germ cells (i.e. sperm and ova), will not be observed in the exposed individual. Rather, the radiation effects will be observed in the affected indi-vidual’s future offspring. Because of this, the offspring of the survivors of the 1945 Hiroshima and Nagasaki atomic bombings continue to be followed today for possible long‐term genetic effects.Currently, we do not know the long‐term effects from low doses of radiation. One reason for why the effects of low‐dose radiation expo-sure are still unknown is because individuals cannot be ethically studied in a controlled envi-ronment where a researcher can completely monitor and control a person’s day to day life-style. Lifestyle factors include diet, vocation, home environment and chronic habits such as smoking, etc. All of these lifestyle choices can deleteriously affect an individual’s long‐term health and cloud the effects of radiation alone. Consequently, with uncertainty as to the effects of low‐dose radiation, all precautions to reduce unnecessary exposure to both the patient and the operator should be followed (see Section G).Biologic effects of radiation are classified as either a direct or an indirect effect. If an incoming x‐ray photon modifies a biologic molecule, it is called a direct effect (e.g. break in a chromosomal chain). However, when the biologic effect is the result of a subsequent intermediary change to a molecule, the effect is termed an indirect effect. 18 Fundamentals of Oral and Maxillofacial RadiologyWater being the predominate molecule of a living human, it is frequently affected by ioniz-ing radiation. An incoming x‐ray photon may hydrolyze (i.e. split) a water molecule. This first action is a direct effect of radiation. However, following the hydrolysis of water, there may be a recombination of the byproducts, hydroperoxyl and hydrogen, which can produce a molecule of an organic hydrogen peroxide. This would be an indirect effect of radiation. This organic hydrogen peroxide molecule can lead to cell death or a future mutation of the cell. Overall, direct effects of radiation account for approxi-mately 33% of all biologic damage, while the remaining 67% of biologic damage is the result of indirect effects. Tissue sensitivity to radiation varies depending upon the tissue type (see Effective dose in Section E).What happens tothedental x‐ray photons that are directed at apatient?X rays can pass through unchangedThe relative vastness of space in the atom separating electrons and the infinitesimally small size of each x‐ray photon permits a small percentage of x‐ray photons to pass directly through the atom without any interaction, possibly up to 10% of the total dose. In practice, the patient is typically positioned between the x‐ray tubehead and the operator. Since we know that 100% of the x‐ray beam is not absorbed by the patient, it is imperative that the operator not stand directly in‐line with the beam of x‐radiation (see Section G).X rays can undergo acoherent scatterCoherent scatter (aka Thompson scatter) occurs rarely when a low energy incoming x‐ray photon collides with an outer shell electron of an atom. The photon does not have enough energy to eject that electron from its orbit. The net result is: (i) no net change to the atom; (ii) the incoming x‐ray photon loses some of its energy upon impact with the electron; and (iii) the x‐ray photon is redirected (i.e. scattered). This x‐ray photon will continue interacting with other atoms until all of its energy is dissipated. These redirected x‐ray photons are called scattered x rays. Even though the scatter dose is low, this author recommends that the operator should place a protective apron on every patient and that the operator should stand behind a protective barrier during an x‐ray exposure. These are simple methods to reduce the effects of scatter radiation for both the patient and the operator. Further reducing radiation exposure to both the patient and the operator when feasible is still the best principle.X rays can produce aphotoelectric effectPhotoelectric effect accounts for upwards of 25% of x‐ray interactions. The incoming x‐ray photon col-lides and is absorbed entirely by an inner shell elec-tron. This incoming photon imparts enough energy to the electron so that together they are ejected from its orbit. This ejected electron is now called a photoelectron (i.e. photon + electron = photoelectron). This photoelectron travels short distances before giving up all of its energy during additional colli-sions. Within the same atom, another electron from a higher orbit may drop into the void created by the photoelectron. In so doing, it generates an addi-tional low energy x‐ray photon, referred to as a characteristic or secondary x ray. Secondary x‐ray photons do not benefit the patient or the clinician. They are generally absorbed by the patient’s soft tissues but they also can produce image fog . Secondary x rays pose no external threat to the operator.X rays can produce aCompton scatterCompton scatter accounts for the majority of interactions with dental x‐ray photons. In this scenario, an incoming x‐ray photon has sufficient F Radiation Biology 19energy to knock out an outer shell electron. The result is a redirection of the incoming x‐ray photon after it collides with an electron and the formation of an ion pair. An ion pair consists of a negatively‐charged ejected electron and the resultant positively‐charged atom. The term ionizing radiation is applied to this phenome-non. X rays are classified as a form of ionizing radiation. Both the ejected electron and the weakened scattered x‐ray photon can continue to interact with other atoms. This can result in additional ionizations and with each ensuing impact the x‐ray photon will continue to be weakened while other atoms attempting to reach a state of maximum stability will seek out the recoil electron.Determinants ofbiologic damage fromx‐radiation exposureExposure doseAny amount of ionizing radiation will produce some biologic damage. Regardless of how minute the radiation exposure dose may be, there will always be some long‐term residual damage to the radiated area. Minimal residual damage may not be visible initially. However, after repeated exposures to ionizing radiation, termed chronic exposure, a biologic effect will ultimately present itself. This classification of cellular response is referred to as a deterministic effect . The total amount of radiation expo-sure required to elicit a cellular effect is called the threshold dose . Below the threshold level of exposure, no effect will be observed. A sim-ple example of a threshold radiation dose effect is sunburn. Acute biologic effects from increas-ing doses of ionizing begin with erythema, fol-lowed by dermatitis, ulceration, tanning and ultimately the loss of glandular function. Erythema occurs after exposure to approxi-mately 250 cGy of radiation that is delivered in a relatively short span (e.g. two weeks). Incom-parison, a dental bitewing exposure is minimal at approximately 0.08 μGy. A second type of biologic effect of ionizing radiation is called a stochastic effect . In this classification, either the effect occurs or it does not occur–it is an all or nothing response. Cancer is an example of a stochastic effect. Individuals do not develop a mild case of cancer or a severe case of cancer. They are all cancers.In dentistry, exposure dose is affected by variable factors that include the distance of the x‐ray source from the face, kilovoltage, milli-amperage and exposure time. All these factors combined will determine the total radiation dose to the patient.Note: It is extremely important for all of us to remember that although the biologic effects resulting from high doses of radiation expo-sure are known, the long‐term effects from low doses of ionizing radiation are still unknown. This is why we need to refrain from exposing individuals to any unnecessary imaging procedures whenever possible or, at the very least, utilize a projection that requires a minimum of radiation exposure. In addi-tion, the operator should take all precautions to minimize their own exposure to radiation while performing imaging procedures.Dose rateThe time interval between repeated exposures to ionizing radiation influences the extent of biologic damage. A rapid rate of recurring radi-ation exposure with minimal time between each exposure will result in more biologic dam-age than if an equal cumulative radiation dose (i.e. total dose) was administered over a longer time frame. Incremental doses of radiation are preferable because it permits the body time to repair some of the biologic damage before the next dose is administered. Multiple smaller doses of radiation administered over an extended time interval allows greater cellular repair. Conversely, a high dose of radiation 20 Fundamentals of Oral and Maxillofacial Radiologyadministered in a single session diminishes a body’s ability to recuperate and repair the non‐cancerous cells. A skin tan is a threshold effect that occurs from gradual cumulative doses of ultraviolet radiation versus a sunburn effect that results from a single concentrated dose of ultraviolet radiation. But to be clear, the ultra-violet “tan” effect is still biologic damage to the individual’s skin, but just not as severe as a sunburn effect. We also know that individuals with years of repeated ultraviolet skin damage have a greater incidence of basal cell or squa-mous cell carcinomas.Area ofexposureThe volume of tissue exposed to radiation plays a significant role in the overall well‐being of the patient. Patients receiving localized oral cancer radiotherapy, possibly up to 70 Gy, may encoun-ter severe biologic effects in the irradiated field that often will culminate in the loss of glandular function and osteoradionecrosis . However, total exposure to a much lower dose of 3–5 Gy administered over the entire body would very likely result in death of the individual. Whole body radiation affects all of the body’s biologic systems simultaneously and, as a result, the body’s attempt to repair cellular damage is overwhelmed. Consequently, death of an indi-vidual will occur from far less whole body radiation exposure compared with administering a mega dose of radiation that is concentrated to a localized area.Current guidelines from the National Council on Radiation Protection and Measurements (NCRP) stipulate that rectangular collimation shall be used for periapical and bitewing imaging and should be used for occlusal imag-ing when possible. Rectangular collimation shall also be used with hand‐held devices whenever possible and x‐ray equipment for cephalometric imaging shall provide for asym-metric collimation of the beam to the area of clinical interest. All of these NCRP guidelines are made to reduce the area of radiation exposure to the patient.AgeAll living beings are susceptible to the effects of x radiation. However, younger and older individuals are most susceptible. High meta-bolic rates in younger individuals and the poor recuperative healing powers in older individuals result in greater risks from radia-tion exposure. This does not eliminate the intermediate age group from experiencing ill effects from ionizing radiation, it only means that this age group is less susceptible to the effects. Precautions to reduce exposure to ionizing radiation apply to all age groups. NCRP recommendations for pediatric patients include: (i) select x rays for individual needs; (ii) use the fastest image receptor possible; (iii) collimate the beam to the area of interest; (iv) always use a thyroid collar unless it inter-feres with imaging the needed anatomy; and (v) use cone beam computed tomography (CBCT) only when necessary.Cell typeThe Law of Bergonie and Tribondeau of 1906 states that the most radiation‐sensitive cells types are undifferentiated, divide quickly and are highly active metabolically. Amongst the most sensitive cell types are erythrocytes and stem cells. Among the least sensitive cell types are neural and muscle cells. Two exceptions to the law are oocytes and lymphocytes. These two varieties are very specialized cell types and they are very sensitive to radiation. It is not clear as to why these two cell types are particu-larly sensitive to radiation.Pioneers in dental radiology were ignorant of the dangers of x radiation and many suffered the consequences of excessive exposure. Dental F Radiation Biology 21exposure doses today are considered to be very low in comparison. However, as stated earlier, any amount of exposure to ionizing radiation produces some cellular damage. Although a carcinoma is statistically unlikely to result from dental x rays, theoretically it could result from the minute amount of radiation exposure used to produce a single dental image. Consequently, exposing patients to any amount of x radiation should be limited and imaging should only be ordered when it is vital for diagnosing the patient’s oral health. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology22Radiation ProtectionGVery soon after x rays were discovered, it became apparent that x rays were harmful. As early as 1897, there were cases of skin damage. In 1901, a pioneer in dentistry, William H. Rollins, DDS, MD, observed that x rays could cause tissue burns and attempted to warn dentists and physicians of the dangers of x rays. Little heed was taken of Dr. Rollins warnings but, shortly after, the dental profession began to take meas-ures to reduce the damaging effects of radiation. However, many pioneers in dentistry, whether through ignorance or neglect, suffered the loss of one or more fingers because they repeatedly held the x‐ray film used to record the dental image in the patient’s mouth. X‐ray film was the standard for recording dental images at the time.Utilization of radiation in a dental office requires regulations to protect the patient, the operator and any employees or bystanders located within the working environment. ALARA is an acronym for “as low as reasonably achievable.” If the exposure dose to a patient can be easily reduced, then it should be. The ALARA principle is recognized by the American Dental Association (ADA) and is expected to be followed by dental practitioners. Because of concerns today about the overutilization of ionizing radiation procedures in medicine, ALARA is morphing into ALADA. ALADA is an acronym for “as low as diagnostically acceptable.” Reducing the exposure dose to a patient to a minimum, yet still being able to diagnose the images, is beginning to be prac-ticed in the medical community and should be adopted in dentistry as well.Quality assurance (QA) refers to optimized dental images produced with minimum radia-tion exposure. Minimum exposure to radiation applies not only to the patient, but also the dental operator and any bystanders in proximity to the dental x‐ray equipment. The ADA and NCRP set guidelines that every dental healthcare setting adopts regarding maintaining x‐ray equipment, image receptors, protective aprons, etc.1. RADIATION PROTECTION: PATIENTProtecting the patient entails both reducing the exposure dose from the primary x‐ray beam that is directed at the patient’s head and the subsequent scatter radiation that may affect other regions of the body. G Radiation Protection 23Protective apronProtective covering to shield a patient from scatter radiation comes in many forms. The method of choice to date has been the protec-tive apron (Fig. G1). The US Environmental Protection Agency (EPA) has designated lead as a hazardous material. Although the term lead apron is commonly used to describe the standard apron that is draped on a patient prior to x‐ray exposure, many companies today manufacture lead‐equivalent aprons (i.e. lead‐free). Regarding intraoral procedures, assuming that one adheres to the guidelines outlined by the NCRP and ADA, there is no need to use a protective apron on adult patients due to the minute amount of scatter radiation outside of the field of interest. These guidelines require the use of rectangular collimation with either a digital receptor or f‐speed film. The NCRP guidelines also state that pediatric patients are not simply small adult patients and operators should take extra care to reduce children’s exposure to radiation. The thyroid gland in children sits higher in the neck and will therefore be automatically exposed to more radiation than in an adult. As a result, the NCRP recommends that protective aprons with thyroid collars should always be used on pediatric patients unless it interferes with imag-ing the needed anatomy. For extraoral imaging procedures such as panoramic projections, a double‐sided protective apron without a thyroid collar should be used (Fig.G2). In this situation a thyroid collar would obscure ana-tomic structures that are relevant to the patient’s oral examination.Note: Do not fold the protective apron when not in use. It is best to either hang the apron upright or leave it lying flat and unfolded. ABFig.G1 A. Child protective apron with thyroid collar for intraoral imaging. B. Adult protective apron with thyroid collar for intraoral imaging. 24 Fundamentals of Oral and Maxillofacial RadiologyRepeated folding of the apron will lead to cracking of the inner lining and it will become less effective at blocking x rays. The NCRP also recommends a visual examination of pro-tective aprons monthly for damage.CollimationThe radiation produced within the x‐ray tube-head exits as a divergent beam. The US govern-ment requires manufacturers of intraoral x‐ray equipment to limit the size of the x‐ray beam to be no more than 2.75 inches (7 cm) in diameter. The open‐ended plastic attachment on the x‐ray tubehead is referred to as a PID . A PID has historically been referred to as a cone. The open end of the PID is aligned closely to the patient’s face prior to taking an exposure. A PID may be interchangeable on some intraoral tubeheads. Limiting the size of the beam reduces unnecessary exposure to the areas out-side of the desired field. A means to further reduce the conventional round beam size is to use a rectangular‐shaped beam that more closely matches the size of the imaging recep-tor (FigsG3, G4, G5 and G6). The NCRP guide-lines state that rectangular collimation of the beam shall be used routinely for periapical and bitewing images and should be used for occlusal images when possible. In addition, rectangular collimation shall be used with hand‐held devices when possible. If a rectan-gular PID is not already attached to the x‐ray tubehead, a rectangular‐shaped beam can still be accomplished by any one of the following solutions: (i) detaching the existing round PID and replacing it with a rectangular PID; (ii) a secondary rectangular collimator can be attached to the open end of the round PID; and (iii) a rectangular collimator can be attached Fig. G2 Double‐sided (i.e. front and back) protective apron without thyroid collar for extraoral imaging.Fig. G3 Rinn® universal collimator which converts a round PID to a rectangular collimated PID to restrict the size of the x‐ray beam to approximate the size of the image receptor. G Radiation Protection 25directly to the receptor holder. For cephalomet-ric images, the x‐ray unit shall provide for appropriate collimation of the beam to the area of clinical interest. This will prevent unneces-sary exposure to hard and soft tissues outside the area of interest.FiltrationX‐ray tubes simultaneously generate x rays of varying energies. The purpose of x‐ray filtra-tion is to absorb the weaker, low energy x rays that may not be powerful enough to penetrate ABFig.G4 A. Rectangular collimation with XCP‐ORA® positioning system. B. Rectangular collimation with a Snap‐A‐Ray® DS (without an alignment ring).ABFig.G5 XDR‐ALARA® rectangular collimators. 26 Fundamentals of Oral and Maxillofacial Radiologythrough a patient’s soft tissue. Filtering out these low energy x‐ray photons reduces the total absorbed dose to the patient and will not compromise the final diagnosis. X‐ray filters typically made of aluminum are inherently built into conventional dental x‐ray units (Fig.G7). In the United States, manufacture of x‐ray equipment is regulated by the Food and Drug Administration (FDA) and consequently x‐ray filtration should not be a concern for clinicians.Digital versus analogThe world’s first digital dental intraoral system was introduced in 1987 by the French company Trophie Radiologie; it was called RadioVisio-Graphy. Today, many different manufacturers produce dental digital receptors. Digital recep-tors have significantly reduced the total dose of radiation required to produce diagnostic images that are comparable to the prior stand-ard image receptor, dental x‐ray film. Looking back to the earliest intraoral x‐ray images back in 1896, exposure times were upwards of 25 min in length. Today’s dental exposure time is typically only a fraction of a second in length, thereby dramatically reducing a patient’s over-all exposure to radiation compared with the historical doses that many patients received during the early days of dental radiology. The recent transition from x‐ray film to a digital receptor is not as dramatic a dose reduction as that of the cumulative advances that occurred with film over the decades, but it has definitely contributed to further dose reduction to the patient.Exposure settingsRadiation exposure dose to a patient is directly controlled by the operator’s selection of kilovolt peak (kVp), milliamperage (mA) and exposure time. However, optimum settings are subjective; one size does not fit all here. Each dentist has their own image quality prefer-ences. In addition, an x‐ray unit’s radiation output will vary according to the age of the unit, manufacturer’s specs, etc. In this regard, government inspectors will periodically inspect each dental office’s x‐ray equipment to ensure that their equipment is operating according to the manufacturer’s guidelines. Improper functioning x‐ray equipment may result in unnecessary additional radiation exposure to the patient.Operator techniqueAn operator’s technique is critical in producing diagnostic images with minimal distortion, missed apices, etc. Undiagnostic images will Fig.G6 Round PID collimation.Fig.G7 Aluminum filter integrated into the body of the x‐ray tubehead. G Radiation Protection 27require re‐exposure of the patient. Intraoral instrumentation for holding the receptor and aligning the PID do not guarantee acquisition of diagnostic images, they simply aid the patient and the operator in the attempt to acquire a good diagnostic image. Similarly, the operator’s proper exposure setting selection and patient position-ing in an extraoral unit will reduce the number of unnecessary retakes.2. RADIATION PROTECTION: OFFICE PERSONNELThe NCRP requires that the construction and design of a dental office must include safety features to protect all personnel working with or near x‐ray equipment. In addition, the owner of a dental practice must protect the front‐end personnel such as receptionists and those indi-viduals working in adjacent offices to reduce their exposure to dental x radiation.The NCRP x‐ray protection guidelines for dental offices are as follows:• The dentist (or, in some facilities, the designated radia-tion safety officer) shall establish a radiation protection program. The dentist shall seek guidance of a qualified expert.• The qualified expert should provide guidance for the dentist or facility engineer in the layout and shielding design of new or renovated dental facilities and when equipment is installed that will significantly increase the air kerma [kinetic energy released per unit mass] incident in walls, floors and ceilings.• New dental facilities shall be designed such that no individual member of the public will receive an effective dose in excess of 1 mSv annually.• The qualified expert should perform a pre‐installation radiation shielding design and plan review to determine the proper location and composition of barriers used to ensure radiation protection in new or extensively remodeled facilities and when equipment is installed that will significantly increase the air kerma incident in walls, floors and ceilings.• Shielding design for new offices for planned fixed x‐ray equipment installations shall provide protective bar-riers for the operator. The barriers shall be constructed so operators can maintain visual contact and communi-cation with patients throughout the procedures.• The exposure switch should be mounted behind the pro-tective barrier such that the operator must remain behind the barrier during the exposure (Fig.G8).• Adequacy of shielding shall be determined by the quali-fied expert whenever workload increases by a factor of two or more from initial design criteria.• In the absence of a barrier in an existing facility, the operator shall remain at least two meters, but prefer-ably three meters from the x‐ray tubehead during exposure. If the two meter distance cannot be main-tained, then a barrier shall be provided. This recom-mendation does not apply to hand‐held units with integral shielding.• The qualified expert should perform a post‐installa-tion radiation protection survey to assure that radia-tion exposure levels in nearby public and controlled areas are ALARA and below the level limits estab-lished by the state and other local agencies with jurisdiction.• The qualified expert should assess each facility individ-ually and document the recommended shielding in a written report.• The qualified expert should consider the cumulative radi-ation exposures resulting from representative workloads Fig.G8 Operator standing behind a protective barrier (the lower portion is a lead shield and the upper portion is made of leaded glass) during radiation exposure of a patient. 28 Fundamentals of Oral and Maxillofacial Radiologyin each modality when designing radiation shielding for rooms in which there are multiple x‐ray machines.• A qualified expert shall evaluate x‐ray equipment to ensure that it is in compliance with applicable laws and regulations.• All new dental x‐ray installations shall have [a] radia-tion protection survey and equipment performance evaluation carried out by or under the direction of a qualified expert.• For new or relocated equipment, the facilities shall pro-vide personal dosimeters for at least one year in order to determine and document the doses to personnel.• Equipment performance evaluations shall be per-formed at regular intervals thereafter, preferably at inter-vals not to exceed four years for facilities only with intraoral, panoramic or cephalometric units. Facilities with CBCT units shall be evaluated every one to two years.Source: National Council on Radiation Protection andMeasurement (2017)Practitioners must comply if they want to eliminate or at least reduce their risk of potential liability.Additional methods to protect an operator from occupational exposure to radiation include the following:1. If assistance is required for a child or a handicapped patient to stabilize the recep-tor instrument, non‐occupationally exposed persons (preferably a member of the patient’s family) should be asked to assist so that the operator can stand outside the operatory. Offering the volunteer a protec-tive apron may reduce any apprehension the individual might have about being exposed alongside the patient. The ration-ale for substituting a surrogate is because this individual will be exposed to a mini-mum of radiation exposure possibly this one occasion, while the operator may be required to repeat this procedure on numer-ous different patients and thereby receive far greater cumulative levels of radiation exposure.2. When a protective barrier is unavailable, the operator should stand at least 2 m from the x‐ray tubehead and between 90° and 135° from the direction of the primary x‐ray beam. Standing distance measured from the x‐ray source incorporates the inverse square law which allows for additional dissipation of the x rays. This standing position also utilizes the patient’s body as a barrier for absorbing some of the scattered x rays (Fig.G9).90°135°90°90°135°135°135°90°Low x-rayscatterareaLow x-rayscatterareaLow x-rayscatterareaLow x-rayscatterareaFig.G9 Illustration demonstrating the safest position for the operator to stand when there is no protective barrier and the operator is within 2 m of the patient. G Radiation Protection 29The monitoring of radiation exposure to personnel in a dental office is typically accom-plished through the use of an individual radiation dosimetry badge (Fig. G10). The NCRP guidelines (2017) state that “Provision of personal dosimeters for external exposure measurement should be considered for workers who are likely to receive an annual effective dose in excess of 1 mSv. Personal dosimeters shall be provided for declared pregnant occupationally‐exposed personnel” (see Section P).How much occupational radiation exposure is permitted?Both the NCRP and the International Com-mission on Radiological Protection (ICRP) have published guidelines for occupational and non‐occupational dose limits. The NCRP and ICRP state that occupational workers should not be exposed to more than 50 millisieverts (mSv) per year, referred to as maximum permissible dose (MPD) . The calculated value of an individual’s total lifetime occupational effective dose shall be limited to 10 mSv multiplied by the age of that individual. For example, a total lifetime occupational exposure for a 25‐year‐old worker is 25 × 10 = 250 mSv. In reality, if a proper safety protocol is adhered to in a dental office, occupa-tional doses should fall well below the MPD. However, if the operator’s exposure level exceeds the permitted annual level, the opera-tor would be temporarily prohibited from working around x‐ray equipment until the accumulated dose fell below the level permit-ted based on the 50 mSv/year calculation.Note: There is no MPD for patients because the radiation exposure that healthcare profession-als deliver is deemed to be beneficial for the patient in either a diagnostic or a therapeutic capacity. Obviously, keeping the patient expo-sure dose to a minimum should be a primary objective.Fig.G10 Radiation dosimeter badge (clip‐on style). Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology30Patient Selection CriteriaHThe dentist must weigh the benefits of taking dental radiographs against the risk of exposing a patient to x rays, the effects of which accumulate from multiple sources over time. The dentist, knowing the patient’s health history and vulnerability to oral disease, is in the best position to make this judgment in the interest of each patient. For this reason, the guidelines are intended to serve as a resource for the practitioner and are not intended as standards of care, requirements or regulations.Source: American Dental Association Council on Scientific Affairs (2006)The ADA guidelines quoted above differen-tiate between symptomatic and asymptomatic patients. For symptomatic patients, a radio-graphic examination should be limited to images required for diagnosis and planned treatment of current disease. In a radiographic examination of asymptomatic patients such as new patients or returning patients, the prac-titioner should adhere to published selection criteria. The operative word in the ADA state-ment is “guidelines.” All healthcare providers must use their good judgment when prescribing x‐ray images as they are not limited to or pro-hibited from requesting any x‐ray image if it may benefit the patient’s care (see Appendix 1).The ADA guidelines for prescribing images vary amongst different demographic groups, although this is not to say that a particular health concern can only occur in a specific group. Historically there are patterns that warrant modifying imaging protocol to accommodate these variations. As mentioned earlier, the dental practitioner has the authority to request whatever x‐ray images are deemed necessary for a thorough diagnosis of the patient. Pre‐existing dental x‐ray images taken at other dental offices should also be obtained whenever possible before prescribing new x‐ray proce-dures. A chronological sequence of dental images can be very useful for documenting both developmental and pathological changes to the oral cavity. All patients are entitled to copies of dental images and may request them from their current or former dentist(s). Addi-tional fees may be incurred by the patient for producing copies of x‐ray images. It is at the discretion of each dental practitioner to decide whether to charge or waive any fees for this service. All dental practitioners should keep permanent records of all x‐ray images for all current and former patients. Why? This is because a dentist may be called upon to pro-duce x‐ray images to assist in the postmortem forensic identification of an individual or pos-sibly the dentist may be at the center of a legal dispute arising from a disgruntled patient who has filed a lawsuit. Pre‐ and post‐treatment H Patient Selection Criteria 31x‐ray images can be vital in the dentist’s legal defense for disproving false claims about per-forming unnecessary or poor quality dental treatment.What about pregnant patients? To be safe, it is always best to avoid exposing the mother to any x‐ray images during the entire term of her pregnancy. The risks to the developing fetus are known to be minimal but the dentist does not want to be indicted afterwards by the mother as being the cause of a child’s unforeseen birth defect. However, treating the mother’s dental problem is also essential to the health of the developing baby. If the mother is experiencing undue stress or has an untreated dental infec-tion, more harm could result to the baby than by exposing a few intraoral x‐ray images and properly treating the oral problem. The author recommends that the dentist expose the mini-mum number of x‐ray images necessary to treat the current problem and to take all precautions to reduce the radiation exposure to the patient. Additional protection for the fetus is made pos-sible by placing a full‐length protective apron on the patient. This will absorb 99.9% of the stray x rays that might reach the mother’s abdominal region. Of course, elective treatment should be postponed until after birth of the child. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology32Film versus Digital ImagingIFilmX rays were first discovered in 1895. At that time emulsion‐coated glass plates were used torecord both photographic and x‐ray images. The first commercial roll of photographic film was introduced in 1899 by the Eastman Kodak Company. However, the transition to using flexible film rather than glass plates to record x‐ray images did not occur until the 1910s. Once flexible x‐ray film was introduced, it was repeatedly improved over the years until its use began to decline with the introduction of digital imaging beginning in the 1980s. The last sig-nificant advancement in x‐ray film was back in the year 2000 when Kodak introduced “Insight” intraoral film. From the earliest days of x rays, when a 20 min exposure to radiation may have been required to produce an x‐ray image, the last incarnation of intraoral film reduced the patient exposure time to seconds.Two categories of dental x‐ray film are non‐screen and screen film. Intraoral x‐ray film is a non‐screen film type, also referred to as a direct exposure film. It is composed of a flexible piece of transparent cellulose acetate which acts as the base to support an emulsion that is coated on both the front and the back sides. This emulsion consists of silver halide crystals sus-pended in a thin layer of gelatin. To protect the soft gelatin from incurring damage from mishandling, it is manufactured with a protec-tive coating applied over it. X‐ray film is not only sensitive to x rays but also to white light sources. Consequently, intraoral x‐ray film is individually prepackaged in a sealed, lightproof packet. This protective packet prevents the film from being exposed to white light and it also prevents the patient’s saliva from contaminat-ing the film’s emulsion. Within each intraoral film packet there is also a thin sheet of lead foil located behind the film and a piece of black paper. The lead foil serves two functions:1. It provides additional protection to the patient by absorbing some of the incoming and scattered x rays. Some x rays can rico-chet off the teeth and bones behind the film packet and could expose the film from the backside. These scattered x rays would con-tribute to degrading the quality of the final image. This effect is referred to as film fog. The lead foil blocks these back‐scattered xrays and thereby reduces film fog. I Film versus Digital Imaging 332. Embossed upon each piece of lead foil is a geometric pattern that each manufacturer selects (e.g. honeycomb). If the operator erred and placed the film packet reversed in the patient’s mouth and exposed it, the foil’s embossed pattern would now be vis-ible on the final image and this would alert the dentist that the image must be reversed to properly orientate the patient’s dentition. Failure to do so could lead to performing unnecessary dental treatment on healthy teeth and leaving untreated diseased teeth.Extraoral x‐ray film is classified as a screen film. As the term extraoral infers, these films are positioned outside of the patient’s mouth during an x‐ray exposure. This category of film is always sandwiched between two intensify-ing screens within a light‐tight film cassette. An intensifying screen’s composition includes layers of phosphor crystals. When a phosphor crystal in the screen is hit by an x‐ray photon, it fluoresces. This fluorescent light diverges and simultaneously exposes multiple halide crys-tals in the film. As a result, intensifying screens help to reduce the total amount of radiation exposure to the patient but they also produce an image with poorer image resolution compared with a non‐screen film image. Consequently, non‐screen intraoral films are better for diag-nosing small lesions like caries where finer detail is required. Intensifying screens are not used with intraoral films.Whether an operator uses a screen or a non‐screen film, the exposed x‐ray film needs to be chemically processed before a dental image will be visible to our eyes. The hidden image on an unprocessed x‐ray film is referred to as a latent image. Processing can either be performed man-ually by the operator or with a film processor , where the film is automatically drawn through the solutions. Either way, the film must be pro-cessed in a dark environment to avoid extrane-ous exposure to white light. Chemical processing of a dental film consists of first sub-merging each film into a developing solution for a specified time, then the films are submersed in a fixer solution for a set length of time and finally each film is washed in water. The func-tion of the developer solution is to precipitate the silver atoms within the emulsion, the fixer serves to remove the unaffected crystals and water removes all traces of the chemical solu-tions. The precipitated silver appears black on the image. A film accidentally exposed to white light will turn totally black during processing. Proponents of x‐ray film generally claim that dental images acquired on x‐ray film are still superior to digital receptor images.Digital imagingIn 1987, the first digital image receptor was introduced for intraoral imaging. Since that time, digital imaging has gradually become the new standard for acquiring and viewing of dental images.Direct digital imaging refers to directly capturing a latent image onto an appropriate receptor. Currently, there are two different technologies of intraoral digital systems. One system incor-porates solid state electronics that use either CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) technology (Fig.I1). Both the CMOS and CCD receptors typically are wired directly to a Fig.I1 Direct digital receptor. (Source: Courtesy of Adam Chen, XDR Radiology.) 34 Fundamentals of Oral and Maxillofacial Radiologycomputer. However, some manufacturers have introduced a modified direct system that uses a Wi‐Fi signal to transmit the data from the receptor directly to the computer rather than via a physical wire. in either wired or Wi‐Fi signal transmission, both receptor designs directly send the image to a computer. The alternative digital receptor technology uses photostimulable phosphor plates (PSP plates) (Fig.I2). A phosphor coating is deposited onto a thin, flexible piece of polyester acetate. The x‐ray image is cap-tured and stored as a latent image in the phos-phor coating. Each manufacturer of PSP plates produces a specific scanner to digitize the acquired latent images.Indirect digital imaging refers to the conver-sion of the latent analog image captured on a PSP plate into a digital image. Once the PSP plate has been scanned, the image can be erased by exposing the PSP plate to a room‐intensity white light. A PSP plate can be erased and re‐exposed multiple times. Operator care should be taken not to scratch or bend the PSP plate so as to prolong its functional life. The flexibility and thinness of the PSP plate makes it much more patient friendly. Unlike the limited selec-tion of solid‐state digital receptor sizes, PSP plates come in several different sizes. PSP plate image quality is comparable to solid‐state digital images but the added time and steps involved to visualize the digital image make it unappealing to many practitioners at this time. On the flip side, the cost for each intraoral PSP plate is minimal. Typical cost ranges between twenty‐five and thirty‐five dollars per intraoral PSP plate compared to thousands of dollars for a single solid‐state receptor.Dental equipment manufacturers may offer three sizes (0, 1 and 2) of solid‐state intraoral digi-tal receptors. Digital receptor sizes closely match intraoral film sizes. Numerically, the higher the receptor number, the larger is the physical area that is captured in the image. Ofthe three differ-ent choices, size 2 acquires the largest area while ABFig.I2 A. PSP plate scanner. B. PSP plates and pouches: sizes 0, 1 and 2. I Film versus Digital Imaging 350 acquires the smallest area. Most operators use size 2 for all posterior periapical views and also for bitewing images, while size 1 is used for ante-rior periapical views. Size 0 is ideal for children whose smaller mouths accommodate it much better. This will be discussed further in Section L on intraoral techniques. Solid‐state intraoral receptors are currently not made larger than a size 2. Limited demand for larger intraoral images such as occlusal views and the high price to manufacture larger size solid‐state receptors are the obvious reasons why they are not avail-able today. PSP plates, because of their modest prices, are available in larger sizes.Advantages ofdigital x‐ray imagingDigital imaging has always been marketed as being a significant time saver in comparison to using dental x‐ray film. This is somewhat true. It is accurate that a solid‐state digital receptor can process an image in mere seconds, but PSP plates require added time because the operator must scan each PSP plate individually. In addition, each plate must “blanked” to reuse it and then repackaged. Consequently, opera-tional time savings are not as pronounced as may be expected using PSP systems.Manufacturers also cite dose reduction to the patient as a significant benefit when using digital imaging systems compared with dental x‐ray film. Historically, the first dental expo-sures were upwards of 25 min in length. Today, intraoral images using digital receptors typically utilize exposure times in mere thousandths of a second. To be fair, however, the latest intraoral dental x‐ray film has reduced exposure times to a second in length, being only slightly more than a digital exposure setting. Manufacturers’ claims of upwards of a 75% reduction in expo-sure time compared with using film in reality often translates into a mere fraction of a second reduction per exposure.Unlike dental x‐ray film, where “what you see is what you get,” digital x‐ray images, like digital photographs, can be easily altered to enhance them. Imaging software typically per-mits modifying image brightness , contrast and image resolution . As a consequence, a subdiagnostic digital image may be improved just enough that it may negate the need for a retake which would expose the patient to addi-tional radiation. This applies to both solid‐state and PSP plate receptors. In addition, combining an x‐ray image with a clinical photograph on a screen offers the dental professional a powerful tool to educate patients. Viewing both images together allows the dentist to demonstrate the patient’s specific dental problems and the proposed treatment options. Digital imaging technology facilitates transmission of dental images to fellow colleagues for consultation purposes or for the submission of images to den-tal insurance companies for pre‐authorization of proposed treatment plans.Patients may request copies of their x‐ray images for a variety of reasons, such as they are relocating to another city and will be treated by a new dentist. Previously, with only x‐ray film available, it was much more cumbersome to duplicate radiographs, especially since dentists have always been advised to keep the original radiographs and only supply copies to the patient and insurance companies. In the event a dentist is called to a court of law, original x‐ray images are critical for the dentist’s defense. It is important to mention that patients are legally entitled to copies, in any format, of all their x‐ray images. The simple reason is that a patient should not have to be exposed to additional radiation simply because a dentist opted not to release the existing radiographs to the patient. However, it is up to the discretion of every dentist to decide whether or not to charge a duplication fee for providing this service to the patient.Disadvantages ofdigital imagingAn obvious disadvantage of a solid‐state intraoral receptor is its physical bulk. These receptors are 36 Fundamentals of Oral and Maxillofacial Radiologytypically several millimeters thick and are constructed with a rigid metal housing. Consequently, solid‐state receptors may not be well tolerated by some patients and the opera-tor may at times be unable to expose any intraoral images. However, most patients do cooperate and merely complain about the discomfort when solid‐state receptors are used. In contrast, PSP plates, being very thin and flexible, often are better tolerated by patients. For this reason, PSP plates are generally con-sidered more suitable for children whose reduced tolerance levels and smaller oral cavities further complicate positioning any type of intraoral receptor.For proper infection control, plastic protective barriers are used to cover all varieties of intraoral image receptors. A solid‐state receptor typically is inserted into a disposable protective sleeve, while a PSP plate typically is sealed in a single use plastic envelope. The edges and seams of the plastic barrier cover frequently irritate patients’ soft tissues and as a conse-quence may initiate a pharyngeal spasm (i.e. gag reflex). The discomfort from the barrier cover is often described by patients as either “scratching” or “tickling” (see Fig. O2).Dentists often ignore the importance of the monitor. The resolution of the monitor has a profound effect on the diagnostic quality of digital images, particularly when the images are enlarged. Viewing x‐ray images on a lower resolution monitor in a brightly lit environment will significantly diminish the observer’s ability to detect pathology. Consequently, a dentist should invest in a higher quality viewing moni-tor and locate it in a room with subdued lighting to improve diagnostic performance.There is a high financial cost of using digital imaging. Each solid‐state receptor is priced in the thousands of dollars and they are particu-larly vulnerable to mishandling. Compounding the initial cost outlay for the receptor(s), there may be a substantial annual cost for an insur-ance warranty for unforeseen damages unless one wishes to fully assume the repair costs, which could also be in the thousands of dollars. In contrast, PSP plates themselves are very inexpensive. However, the PSP plates have a very limited lifespan, partly as a consequence of being prone to scratches, bends, etc. Even properly handled PSP plates will still need to be replaced regularly. More significant however is the initial cost of the PSP plate scanner. In the end, PSP plate and solid‐state receptor systems are comparable in overall cost.Imaging softwareToday, x‐ray manufacturers universally utilize the DICOM standard. DICOM is an abbrevia-tion for Digital Imaging and Communication in Medicine. DICOM allows for exchanging files between different manufacturers’ hardware and, more importantly, DICOM files enhance secu-rity. Attached to every image is the patient’s identification which cannot be separated from the image. Consequently, digital images allow for easy transfer of patient x‐ray records from one office to another or submission of digital images to insurance companies for work author-ization and reimbursement.Image enhancementAs with digital photographs, less than perfect digital x‐ray images may be software enhanced to make them more diagnostically useful. Imaging software typically allows modification of contrast, brightness and resolution. The den-sity of an x‐ray film or a digital image always refers to its degree of darkness. If the captured image is too dark (i.e. overexposed) or too light (i.e. underexposed), modifying the image may be valuable in salvaging it. Filtration tools can alter the sharpness of an image. Filtering images is a personal preference. Some observ-ers prefer sharper images to better delineate, for example, dental caries or bone levels, others may not. Other common enhancement tools include colorization and contrast reversal. The I Film versus Digital Imaging 37colorization feature converts the different shades of gray in an image to individual distinctive colors which may be useful for patient educa-tion. Reversing the contrast turns a positive image into a negative image. In this manner what appears black on the untouched image becomes white and vice versa. Neither this function, nor colorization, upgrades the diag-nostic information on an image. They merely alter the visual perception of the image for the observer. Personal preference dictates their usefulness.Image measurementImaging software programs incorporate a meas-urement tool. This can be used for determining tooth length, thicknesses, tooth spacing, etc. However, be aware that the software cannot account for technique (i.e. angulation) errors in the positioning of the receptor in the oral cavity. Consequently, elongation and foreshortening of the image will not be corrected by the soft-ware and as a result the measurements derived are not completely accurate.In summary, software enhancement features are very useful. Different observers may have different visual preferences and therefore wish to alter the viewing ability of the image to suit their particular needs. This is not possible with x‐ray film without exposing additional images. However, software alone may not be enough to eliminate retakes and, as a result of DICOM standards, image enhancements made to the original image are not permanent. This is criti-cal in legal proceedings. Should a dentist be involved in a dispute with a patient and the matter went to court, the original unaltered digital images could be critical in determining the outcome of the case. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology38What do Dental X‐ray Images Reveal?JUpon the discovery of x rays, it immediately occurred to those in the dental field that they would be an invaluable tool for observing inside the jaws and teeth. Modern x‐ray equipment allows the operator to expose various types of dental images in the hope of improving a patient’s overall oral health. Two‐ and three‐dimensional intraoral and extraoral images are routinely used in treatment planning procedures involving endodontics, implants, oral pathology, oral surgery, ortho-dontics, pediatric dentistry, periodontics and prosthodontics.X‐ray images are beneficial for the detec-tion of:1. Alterations to the dentition2. Periodontal disease3. Growth and development4. Alterations to the periapical tissues5. Osseous pathology6. Temporomandibular joint disorder7. Implantassessment (pre‐ and post‐ placement)8. Identification of a foreign bodyAlterations tothedentitionCariesRadiologically, enamel and dentin are differen-tiated based upon their individual mineral content (i.e. hydroxyapatite ). Enamel is over 90% mineralized by weight while dentin is approximately 65% mineralized. Deminerali-zation of enamel and dentin is referred to as dental caries. It results from acid production by Streptococcus bacteria that are directly attached to one or more surfaces of a tooth. Deminerali-zation of the tooth structure allows greater numbers of x‐ray photons to penetrate through to the image receptor. Thus dental caries typi-cally appear radiolucent on dental images. However, current digital receptors are not sensitive enough to detect less than 40% demin-eralization. This means that the percentage of demineralization has to exceed this threshold level before an individual is able to visualize and differentiate caries from normal tooth struc-ture on a dental image. As a result, clinical caries will always be greater than the radiographic J What do Dental X‐ray Images Reveal? 39appearance of caries. This fact is critical to the clinician who is restoring a tooth with a deep carious lesion. Bitewing dental images are par-ticularly beneficial for detecting interproximal caries. Caries limited to the occlusal surface are often more difficult to diagnose radiologically because of the sheer bulk of enamel surround-ing the caries which can obscure the occlusal demineralization (see Section V).Location ofteethDental images are very useful for localizing the positions of both erupted and unerupted teeth, visualizing tooth to tooth relationships and tooth to anatomic structures relationships. This information is essential for orthodontic and oral surgical treatment planning procedures. Teeth that are not in their proper sequential position are referred to as ectopic, transposi-tioned or translocated teeth.Number ofteethUnerupted teeth or the presence of supernumerary teeth can be easily observed on x‐ray images. Clinically, a missing tooth might simply be due to the young developmental age of the patient or possibly the result of being impacted . Both situations can be diagnosed with x‐ray images. Supernumerary teeth may be single or multiple in number, unilateral or bilateral and in one or both jaws.Shape ofteethAbnormal tooth shape is typically developmen-tal in origin. It may be the result of a congeni-tal anomaly, associated with childhood facial trauma, or due to a localized oral infection. Congenital disorders include amelogenesis imperfecta, dentinogenesis imperfecta, dentinal dysplasia, taurodontism, dens in dente, fusion and germination (see Section W).Integrity ofthedentitionPhysical changes to the integrity of a tooth can frequently be visualized on dental images. Examples include enamel or dentin deminerali-zation, crown or root fractures and root resorp-tion. All of these conditions appear as varying degrees of radiolucency on an otherwise nor-mal image of a tooth. Alternatively, conditions can arise where calcification can occur inter-nally within the pulp chamber or externally on the crown or root surface such as the deposition of calculus. Those affected areas will appear more radiopaque on a dental image. Poorer resolution of extraoral images compared with intraoral images may limit the visualization of some of these dental conditions.Periodontal diseaseDental images are extremely beneficial for assessing the supporting bone surrounding the teeth, for evaluating widening of the perio-dontal ligament space and for visualizing the presence of calculus which predisposes an individual to bone loss, furcation involvement, etc. Bone loss surrounding the teeth can be measured by comparing the existing height of the alveolar ridge to the cervical area of the erupted teeth. The height of the alveolar bone surrounding a tooth normally is approximately 1.5 mm from the cemento‐enamel junction. Interproximal bone loss is possible either paral-lel to or angled to the cemento‐enamel junction and is commonly referred to as either horizontal or vertical bone loss .Growth anddevelopmentSkeletal changes to the orofacial complex primarily occur from birth through late ado-lescence. X‐ray images are vital for assessing growth development to consider the need for orthodontic treatment or orofacial surgery. 40 Fundamentals of Oral and Maxillofacial RadiologyConventional extraoral projections such as panoramic, cephalographic images can be used to monitor a patient’s growth and progress of their treatment. In addition, advanced imaging such as CBCT can prove to be invaluable diag-nostic tools in many cases.Alterations toperiapical tissuesRadiologic changes associated with the periapi-cal tissues include widening of the periodontal ligament space, loss of the lamina dura and the presence of a radiopacity or radiolucency at the apex of a tooth. Infection, trauma or a metabolic disease may be the cause(s) for these osseous changes.Osseous pathologyFactors contributing to osseous changes to the mandible and maxilla include congenital and metabolic diseases, trauma, infection and neo-plasms. Number, location, density, shape, size, borders and changes to surrounding structures such as root resorption and tooth displacement are all necessary to determine a differential diag-nosis. However, the final determination of a diagnosis often relies on a biopsy. Density can be altered to become more radiolucent or more radiopaque or to be a combination of both (i.e. mixed). Typically, an aberrant radiolucency within the jaws is indicative of a destructive pro-cess, a radiopacity is indicative of a calcifying process and a mixed radiolucent–radiopaque lesion can be either.Temporomandibular joint disorderConventional extraoral projections such as a panoramic image have limited benefit when it comes to diagnosing osseous changes in the temporomandibular joint. CBCT imaging of the temporomandibular joint has become the standard of care for observing articular bony defects, flattening, osteophyte formation and sclerotic changes of the condyle. Imaging of the articular disk is not visible on x‐ray images, however it can be identified with magnetic reso-nance imaging (MRI) .Implantassessment (pre‐ andpost‐placement)X‐ray images are invaluable both in pre‐surgical planning and postoperative evaluation of implant placement. In particular, cross‐sectional CBCT images assist pre‐surgical treatment planning for assessing bone height, bone width and visu-alization of anatomic variations and anatomic structures such as the mandibular canal. Today many clinicians incorporate implant planning software in conjunction with CBCT imagery for determining the correct size and path of implant placement. Postoperative imaging frequently is also useful in assessing failing implants and to assist in determining causation of chronic postoperative pain.Identification ofaforeign bodyA foreign body is any extraneous object that is introduced into the body. As a result, the size, shape and image density of a foreign body is variable. Generally, it will appear radiopaque on an x‐ray image. The density of the radiopacity will vary depending upon its consistency (e.g. metal, plastic, glass). Localization of a foreign body can sometimes be easily accomplished with the SLOB rule using intraoral images. Foreign bodies include broken dental instru-ments, bullet fragments, tooth fragments and sialoliths. Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.Companion website: www.wiley.com/go/hubar/radiology41Intraoral Imaging TechniquesKTwo fundamental intraoral techniques can be used independently or combined for position-ing an image receptor: the paralleling and the bisecting angle techniques. In general, regardless of which technique the operator decides to utilize, the operator should first be familiar with basic oral anatomy. Basic knowledge of the number of roots for each tooth and the root con-figuration of multirooted teeth are essential to capture the entire apical region. Secondly, with only the crowns of erupted teeth visible to the operator, a mental visualization of the long axes of teeth is useful for accurate receptor place-ment. The long axis of a tooth is an imaginary line that extends lengthwise through the center of the tooth. The long axis will vary from tooth to tooth. A maxillary central incisor’s root is inclined so that the long axis points toward the bregma of the skull, whereas the long axes of maxillary molars generally point toward a mid‐sagittal line at the top of the skull.The ADA requires that every patient must first be clinically examined by a dentist before any x‐ray images are exposed. Patient selection cri-teria must be used to determine the number and type of images to be exposed. The old practice of routinely exposing a full mouth series on all patients does not apply today (see Appendix 1).Conventional intraoral exams may incorpo-rate a combination of periapical, bitewing and, occasionally, occlusal images. A full mouth series of images is designed to show every tooth in both the mandible and the maxilla. Generally speaking, a full mouth series may contain upwards of 21 individual images (Fig. K1). The final tally of images exposed will also vary depending upon the size of the receptors used. An operator may find it preferable to use a larger receptor and capture several teeth on a single image rather than exposing two images using a smaller receptor, thereby reducing the total number of images required. However, the advantage of capturing additional teeth on a single image often may be negated by the pro-duction of less diagnostic images. Separation of interproximal contacts along a curved dental arch requires continually varying the horizontal angulation. If the resultant image has overlapped contacts, it can partially or entirely obscure dental caries, fractures, etc. (see Section L).A periapical image is defined as a projection that captures the entire length of one or more teeth, extending from the incisal or occlusal edge to the apex of each root and the surround-ing tissues. Two millimeters of bone visible beyond the apex of a tooth is desirable for the observer to confidently rule out disorders such http://dentalebooks.com 42 Fundamentals of Oral and Maxillofacial Radiologyas apical pathology. The term periapical image can also apply to edentulous regions of the mouth. Imaging edentulous areas where teeth previously were located is just as important as imaging dentulous regions. In fact, imaging edentulous regions may reveal unexpected pathology, supernumerary teeth, retained root tips, etc. An exception to this requirement would be if a current panoramic image already exists. In this situation, only undiagnostic or suspicious areas should be supplemented with higher reso-lution periapical images.A bitewing image simultaneously shows the coronal portions of both the maxillary and the mandibular teeth. Ideally it will also showthe height of the surrounding alveolar bone. However, if there has been significant bone loss, the crestal bone height may be absent from the image. The unique advantages of bitew-ing images include: (i) the visualization of open proximal contacts; and (ii) a more accu-rate representation of crestal bone height. In addition to revealing interproximal decay, open proximal contacts will reveal overfilled or underfilled restorations, recurrent decay, calculus deposits, etc.An occlusal image reveals a bucco‐lingual perspective that is not visible on either a peri-apical or a bitewing image. It is useful for observing expansion of cortical plates, isolat-ing a foreign body, visualizing displacement of fractures, etc. It is also a particularly useful technique when patients have limited mouth opening and are unable to permit the place-ment of instrumentation for periapical images. The image receptor is placed between the occlusal surfaces of opposing arches and the patient is instructed to gently bite together to support the receptor in position. The PID is then aligned using either the paralleling or bisecting angle technique.1. PARALLELING TECHNIQUEThe principles of the paralleling technique (aka long cone technique) requires that: (i) the long axis of the tooth and the image receptor are positioned parallel to one another; and (ii)the incoming x‐ray beam must be directed perpen-dicular to both of them (FigsK2 and K3). Ifthe operator follows these two principles, itwill result in minimal image distortion. To prop-erly maintain the receptor’s intraoral position, the use of a receptor holding instrument is standard protocol. Manufacturers fabricate Fig.K1 Sample full mouth series of intraoral images.http://dentalebooks.com K Intraoral Imaging Techniques 43different styles of instrumentation for hold-ing film, PSP plates and solid‐state receptors. All of these devices are designed to stabilize the attached receptor. It is highly unlikely that a patient can maintain the receptor in its proper position using fingers alone for the entire length of the procedure. To achieve maximum stability, the operator should insert the instru-ment together with a receptor intraorally and then ask the patient to gently close their upper and lower teeth together for the duration of the image acquisition. A patient in this closed‐mouth position is less likely to move com-pared with an open‐mouth patient trying to maintain a constant position without using aninstrument. Finally, to produce a beam of xrays that emanates from the end of a PID with minimal spatial divergence, a long x‐ray source to receptor distance is required. The longer the distance from the source to the receptor, the greater will be the parallelism of the x‐ray beam. X‐ray parallelism produces less object magnification. However, there are practical limitations to the distance selected. Alonger source to receptor distance requires a longer exposure time. It may also become physically difficult for the operator to align a longer PID in a space‐constrained operatory. Typically, positioning the x‐ray source 30 cm from the receptor is preferred.Tooth longaxisReceptorBite-blockFig.K2 Diagram showing the principles of the paralleling technique for all intraoral views. The image receptor is placed parallel to the long axis of the tooth and the x‐ray beam is directed at a right angle to the receptor. A long x‐ray source to image receptor distance of 30 cm is preferred.AIncisorsCuspidBicuspidsMolarsMolarBicuspidCuspidIncisorBFig. K3 A. Occlusal perspective showing the individual positions of the image receptor on the palatal side of the maxillary teeth for each periapical view. B. Occlusal per-spective showing the individual positions of the image receptor on the lingual side of the mandibular teeth for each periapical view.http://dentalebooks.com 44 Fundamentals of Oral and Maxillofacial RadiologyABCReceptorFig.K4 A. Maxillary central incisors periapical view. B.Maxillary central and lateral incisors periapical view. C.Illustration demonstrating central incisors positioning of the receptor intraorally.http://dentalebooks.com K Intraoral Imaging Techniques 45Maxillary incisors paralleling projection (Fig.K4)Area of interest: Both the central and the lateral incisors.Receptor size: No. 1 (preferable for ease of placement) or no. 2.Position: The long dimension of the receptor is positioned vertically. The receptor should be rotated parallel to the labial surfaces of the central incisor and lateral incisor and set as far back palatally as possible. The posterior aspect of the oral cavity allows the receptor to be posi-tioned higher in the palate to capture the apical regions of the teeth. An additional midline view of the two central incisors may be warranted to better visualize the interproximal surfaces of the two central incisors. If so, the receptor should be aligned parallel to the labial surfaces of the central incisors and set back as far poste-riorly as possible.Maxillary cuspid paralleling projection (Fig.K5)Area of interest: Cuspid.Receptor size: No. 2. The cuspid is generally the longest tooth in the mouth and as a result the smaller receptor may be too short to capture the entire length of the tooth.Position: Regardless of which size receptor is used, the long dimension of the receptor must be attached vertically. Similar to the inci-sor view, the receptor must be positioned fur-ther palatally away from the cuspid. However, the horizontal angulation of the x‐ray beam should be directed through the contact area between the cuspid and first bicuspid to mini-mize overlapping of these two teeth. Curvature of the maxillary arch will undoubtedly result in partial superimposition of the first bicuspid onto the distal surface of the cuspid. However, the distal contact of the cuspid ideally will be open and visible on one or both of the bicuspid bitewing view or the bicuspid periapical view.ABReceptorFig.K5 A. Maxillary cuspid periapical view. B. Illustration demonstrating positioning of the receptor intraorally.http://dentalebooks.com 46 Fundamentals of Oral and Maxillofacial RadiologyMaxillary bicuspid paralleling projection (Fig.K6)Area of interest: First and second bicuspids.Receptor size: No. 2.Position: For this projection, the long dimen-sion of the receptor must be attached horizontally. Intraorally, the receptor should be aligned par-allel to both the buccal surfaces and the long axes of the teeth. To achieve this, the operator will need to position the receptor towards the midline of the palate. This is the deepest area of the palatal vault and consequently will increase the likelihood of capturing the apices of the teeth on the image with minimal distortion of the teeth.Maxillary molar paralleling projection (Fig.K7)Area of interest: First, second and third molars.Receptor size: No. 2.Position: Similar to the bicuspid projec-tion, the long dimension of the receptor must be positioned horizontally. Intraorally, the receptor should be aligned parallel to both the buccal surfaces and the long axes of the teeth. To achieve this, the operator will need to position the receptor towards the midline of the palate. This is the deepest area of the pala-tal vault and consequently will increase the ABReceptorFig.K7 A. Maxillary molar periapical view. B. Illustration demonstrating positioning of the receptor intraorally.ABReceptorFig.K6 A. Maxillary bicuspid periapical view. B. Illustration demonstrating positioning of the receptor intraorally.http://dentalebooks.com K Intraoral Imaging Techniques 47likelihood of capturing the apices of the teeth on the image with minimal distortion of the teeth. The anterior aspect of the receptor should be positioned at approximately the middle of the second bicuspid tooth to ensure visualization of the mesial contact area of the first molar, and the posterior extent of the receptor ideally should extend to the maxil-lary tuberosity region. The receptor may not be large enough to capture the entire region desired in a single view. If a full mouth series of images is being taken, then the operator may decide that the bicuspid view already captured the first molar on it. Consequently, the operator can then position the receptor as  far posteriorly as possible to capture the tuberosity region with only the second and third molars. To avoid unnecessary retakes, position the receptor initially in the bicuspid region and ask the patient to move the recep-tor as far posteriorly in their mouth as they can tolerate. After doing so, if the tuberosity region is still not captured on the image, the operator should resort to acquiring an extraoral image. A panoramic image would be the image of choice to see this region.Mandibular incisor paralleling projection (Fig.K8)Area of interest: Incisors.Receptor size: No. 1 (preferable for ease of placement) or no. 2.Position: The long dimension of the recep-tor is attached vertically. The instrument should be rotated so that the receptor is positioned parallel to the labial surfaces of the incisors and set beneath the patient’s tongue. However, patient discomfort may prohibit proper seat-ing of the receptor resulting in images with missed apices. In this region, as a result of short root lengths compared with the length of the receptor, positioning the receptor upon the dorsal surface of the tongue is permissible. Additionally, the receptor should be positioned lingually back away from the labial surfaces of the teeth, which often alleviates patient dis-comfort and allows the individual to fully bite down on the instrument and thus capture the apices on the image.ABReceptorFig.K8 A. Mandibular incisor view. B. Illustration demon-strating positioning of the receptor intraorally.http://dentalebooks.com 48 Fundamentals of Oral and Maxillofacial RadiologyMandibular cuspid paralleling projection (Fig.K9)Area of interest: Cuspid.Receptor size: No. 2. The cuspid is generally the longest tooth in the mouth and as a result the smaller receptor may be too short to capture the entire length of the tooth. A larger receptor may be more appropriate to use in this situation.Position: The long dimension of the recep-tor must be attached vertically. The receptor must be positioned lingually away from the cuspid. Similar to the mandibular incisors view, patient discomfort may prohibit proper seating of the receptor resulting in images with missed apices. Placement of the receptor on the dorsal surface of the tongue may help alleviate patient discomfort. It also allows the individual to fully bite down and thus cap-ture the apex on the image. The horizontal angulation of the x‐ray beam should be aimed through the contact area between the cuspid and first bicuspid tominimize overlapping of these two teeth. Constriction and curvature of the mandibular arch will undoubtedly result in some superimposition of the first bicuspid onto the distal surface of the cuspid. However, the distal contact of the cuspid ideally will be open and be visible on one or both of the bicuspid bitewing view or the bicuspid peria-pical view.Mandibular bicuspid paralleling projection (Fig.K10)Area of interest: First and second bicuspids.Receptor size: No. 2.Position: Unlike the anterior region of the mouth, the long dimension of the receptor must be attached horizontally. The receptor should be aligned parallel to both the buccal surfaces and the long axes of the teeth. It should not be placed onto the dorsal surface of the tongue because the patient’s tongue may prevent the receptor from extending inferior enough to capture the periapical regions of the teeth. Consequently, the receptor must be posi-tioned between the patient’s tongue and next to the alveolar ridge, which may be quite uncomfortable for the patient. The mandibular bicuspid region tends to be the most tissue‐sensitive region of the oral cavity. Patient discomfort and the cumbersome size of a solid‐state receptor often prevent the operator from BAReceptorFig.K9 A. Mandibular cuspid view. B. Illustration demon-strating positioning of the receptor intraorally.http://dentalebooks.com K Intraoral Imaging Techniques 49extending the receptor far enough anteriorly. This can result in cutting off the mesial portion of the first bicuspid from the image. Using a thinner and more flexible PSP plate will permit gentle bending of the receptor away from the sensitive mucosa. This should allow the opera-tor to place a PSP plate more anteriorly and thereby capture the mesial surface of the first bicuspid on the image. However, care must be taken by the operator not to bend any PSP plate excessively as it may become permanently bent and reduce the PSP plate’s usefulness for acquiring future images.Mandibular molar paralleling projection (Fig.K11)Area of interest: First, second and third molars.Receptor size: No. 2.Position: Similar to the bicuspid projec-tion, the long dimension of the receptor must be positioned horizontally. Similar to the mandibular bicuspid view, the receptor should be aligned parallel to both the buccal surfaces and long axes of the teeth and should not be placed onto the dorsal surface of the tongue. Conse quently, the receptor must be positioned between the patient’s tongue and next to the alveolar ridge. It may not be quite as uncomfortable for a patient as it is for the bicuspid view as the receptor is positioned further from the very sensitive anterior mucosa. The anterior aspect of the receptor should be positioned at approxi-mately the middle of the second bicuspid tooth to ensure visualization of the mesial contact area of the first molar, and the poste-rior extent of the receptor ideally extends to the retromolar region. Similar to the maxil-lary molar view, the receptor may not be large enough to capture this entire region in a sin-gle view. If a full mouth series of images is being exposed, then the operator may see that the bicuspid view has already captured the first molar on it. Consequently, the operator can then position the receptor further posteri-orly to capture the retromolar region. Once again, to avoid unnecessary retakes, the oper-ator should position the receptor initially in the bicuspid region and ask the patient, “Would you please move the receptor as far back in your mouth as you can?” Most patients will oblige and position the receptor even beyond your expectations. However, after requesting the patient to assist in the placement of the receptor, if the operator still determines that the region is not captured on the image, an extraoral projection such as a panoramic view should be prescribed to visu-alize the missing region.ABReceptorFig. K10 A. Mandibular bicuspid view. B. Illustration demonstrating positioning of the receptor intraorally.http://dentalebooks.com 50 Fundamentals of Oral and Maxillofacial Radiology2. BISECTING ANGLE TECHNIQUEThe bisecting angle technique is based on the rule of isometry, which makes this technique more complicated and difficult to perform with-out distortion of the x‐ray image. The mathemat-ical rule of isometry simply states that two triangles are equal when they share a common side. When applied to intraoral imaging, the long axis of a tooth and the plane of the receptor form two sides of a triangle. The operator must then visually bisect the angle of the two sides of the triangle and aim the x‐ray beam perpendicu-lar to this imaginary line (Fig.K12). The imagi-nary line is referred to as a bisector. Referring back to the principle of isometry, the bisector becomes the common side of two triangles.Advantages of the bisecting angle tech-nique include: (i) flexibility to position the receptor wherever the patient permits; (ii) no requirement for an instrument, although one may be used; and (iii) the use of either a short or a long PID.Patients who have a hypersensitive gag reflex or a shallow palate, and young children whose mandibles are still growing, are not suitable for the paralleling technique; they can benefit from using the bisecting angle technqiue. Although exposure times are very short with both the bisecting and paralleling techniques, a short PID also permits using an even shorter exposure time, which can be critical for a patient with a hypersensitive gag response. Finally, operatory space limitations can complicate positioning a ABCReceptorFig.K11 A. Mandibular molar view. Image receptor positioned from distal of the second bicuspid posteriorly. B. Image receptor positioned as far posteriorly as a patient will physically tolerate to capture the retromolar region. The missing first molar will likely be visible on the bicuspid view. C. Illustration demonstrating positioning of the receptor intraorally.http://dentalebooks.com K Intraoral Imaging Techniques 51long PID, which is mandatory for the paralleling technique. A short PID makes it easier for the operator to align it in a confined space.Disadvantages of the bisecting angle technique include: (i) image distortion; (ii) the apices of the maxillary molars are obscured by the zygomatic arch; (iii) there is less detail of the root portion of the tooth compared with the coronal section; and (iv) a lack of standardization of PID alignment angles between patients. Incorrect vertical angula-tion (i.e. over‐ or underangulation) of the PID will distort the size of the image.Overangulation of the x‐ray beam will foreshorten the image, while underangulation of the x‐ray beam will elongate the image. In some situations thelength of a tooth may be longer than the receptor’s length and it cannot be fully imaged accurately. In this scenario, overangulation can beadvantageous by intentionally making the tooth appear shorter so that it can be seen entirely in a single image. If rectangular colli-mation is being used, the operator may easily misalign the PID with the receptor and produce a cone‐cut image. Of course, a cone‐cut image may still occur with round collimation.Maxillary incisor bisecting angle projectionArea of interest: Central and lateral incisors.Receptor size: No. 1 (preferable for ease of placement) or no. 2.Position: The receptor must be rotated so that its long dimension of the receptor is orientated vertically. The receptor should be centered behind the central and lateral incisors. The poste-rior edge of the receptor should be positioned as far palatally as possible while the anterior edge of the receptor should preferably extend 2 mm outward beyond the incisal edges. The mid‐pala-tal and posterior aspect of the oral cavity allows the receptor to be positioned higher in the palate to capture the apical regions of the teeth. If an instrument is not used to hold the receptor in place, the patient’s thumb may be used as the receptor holder. The back of the thumb should press the receptor up against thelingual side of the incisors. If a flexible PSP plate is used, gentle pressure of the thumb should be used to reduce bending of the receptor that would cause distor-tion of the image. The operator must then deter-mine the correct vertical angulation of the PID by first visualizing the plane of the receptor and the long axes of the incisors. The angle that these two lines form must be visually bisected. The central ray of the PID should then be aimed perpendicu-lar to this imaginary line with the lower edge of the PID extending beyond the edge of the recep-tor. An additional midline view of the two cen-tral incisors may be warranted on occasion to better visualize the mesial contacts of the two central incisors. If so, the receptor should be cen-trally aligned behind the lingual surfaces of the two central incisors.Maxillary cuspid bisecting angle projectionArea of interest: Cuspid.Receptor size: No. 2. The cuspid is generally the longest tooth in the mouth and as a result the smaller receptor may be too short to capture the Long axisBisector90°90°ImageReceptorCentralrayFig.K12 Diagram showing the principles of the bisect-ing angle technique for all intraoral views. The x‐ray beam is directed at right angles to a bisector determined by the position of the image receptor and long axis of the tooth.http://dentalebooks.com 52 Fundamentals of Oral and Maxillofacial Radiologyentire length of the tooth. A larger receptor may be more appropriate to use in this situation.Position: The receptor must be rotated so that its long dimension is orientated vertically. Similar to the incisor view, the receptor should be centered behind the cuspid and positioned across the mid‐palatal line and as far posteriorly along the palate as possible. The horizontal angulation of the x‐ray beam should be aimed through the contact area between the cuspid and first bicuspid to minimize overlapping of these two teeth. Curvature of the maxillary arch will undoubtedly result in partial superimposition of the first bicuspid onto the distal of the cuspid. However, the distal contact of the cuspid ideally will be open and visible on one or both of the bicuspid bitewing image or the bicuspid periapical image. The operator must then calculate the correct positive vertical angulation of the PID by first visualizing the plane of the recep-tor and the long axis of the cuspid. The angle that these two lines form must be bisected. The central ray of the PID should then be aimed perpendicu-lar to this imaginary bisecting line with the lower edge of the PID extending beyond the edge of the receptor. At times an approximation of the cor-rect vertical angle can alternatively be done sim-ply using facial landmarks. The cuspid bisector closely corresponds to an imaginary line drawn from the tip of the cuspid to the pupil of the eye on the opposite side of the body. Using this technique, all that remains is ensuring that the entire recep-tor is fully exposed by the PID.Maxillary bicuspid bisecting angle projectionArea of interest: First and second bicuspids.Receptor size: No. 2.Position: The receptor must be rotated so that the long dimension of the receptor is orientated horizontally. The operator should position the receptor towards the midline of the palate, which is the deepest area of the palatal vault, and bring the anterior edge of the receptor up to the distal of the cuspid. This will assist capturing the apical region with minimal distortion of the teeth and include the interproximal region of the first bicus-pid and distal of the cuspid. Ifan instrument is not used to hold the receptor in place, one of the patient’s fingers may be used to press the receptor up against the lingual side of the bicuspids. Generally, having the patient use the hand oppo-site to the side being exposed reduces the likeli-hood of that hand blocking the x‐ray beam. If the operator uses a PSP plate, a gentle finger pressure should be used to reduce bending of the receptor that would cause distortion of the image. The hori-zontal angulation of the x‐ray beam should be aimed through the contact area between the bicus-pids and cuspid to minimize overlapping of these teeth. To determine the correct positive vertical angulation of the PID, the operator must visualize the plane of the receptor and the long axis of the bicuspids and then bisect these two lines. The cen-tral ray of the PID should then be aimed perpen-dicular to this imaginary bisecting line with the lower edge of the PID extending beyond the edge of the receptor. Once again approximation of the correct vertical angle can alternatively be done with facial landmarks. The bicuspid bisector closely corresponds to an imaginary line drawn from the buccal cusp of the bicuspid to the midpoint between the patient’s eyes directly superficial to the skeletal landmark referred to as nasion . Using this technique, all that remains for the oper-ator is to ensure that the entire receptor is fully exposed by the PID.Maxillary molar bisecting angle projectionArea of interest: First, second and third molars.Receptor size: No. 2.Position: Similar to the bicuspid view, the receptor must be rotated so that the long dimension of the receptor is orientated horizon-tally in the patient’s mouth. The operator should position the top of the receptor towards the midline of the palate and bring the anterior edge of the receptor up to the distal of the http://dentalebooks.com K Intraoral Imaging Techniques 53 second bicuspid. The receptor may not be long enough to capture the entire molar region desired in a single view. If a full mouth series of images is being performed, the operator may determine that the bicuspid view has already captured the first molar. Consequently, the operator can then position the receptor further posteriorly to capture the tuberosity region along with the second and third molars. To cap-ture the tuberosity region, it is recommended that the operator position the receptor initially in the bicuspid area and then request the patient to move the receptor with their own hand as far posteriorly as they can tolerate. This will avoid unnecessary retakes as the operator will know that the patient has already placed the receptor as far posteriorly as possible. If the tuberosity region is still not visible, the operator should resort to exposing an extraoral image, such as a panoramic image, if available. If an instrument is not used to hold the receptor in place, the patient’s finger may be used to press the recep-tor up against the lingual side of the molars. Ifthe operator uses a PSP plate, a gentle finger pressure should be used to reduce bending of the receptor that would cause distortion of the image. Generally, having the patient use the hand opposite to the side being exposed reduces the likelihood of that hand blocking the x‐ray beam. The horizontal angulation of the x‐ray beam should be aimed through the contact area between the molars to minimize overlapping of these teeth. To determine the correct positive vertical angulation of the PID, the operator must visualize the plane of the receptor and the long axis of the multirooted molars and then bisect these two lines. The central ray of the PID should then be aimed perpendicular to this imaginary bisecting line with the lower edge of the PID extending beyond the edge of the recep-tor. The vertical angle of the maxillary molars tends to be slightly greater than the premolars angulation. The following suggestion should not to be used as an absolute angle but prese-lecting a 30–40° positive vertical angle of the PID in relation to the occlusal plane often works.Mandibular incisor bisecting angle projectionArea of interest: Incisors.Receptor size: No. 1 (preferable for ease of placement) or no. 2.Position: The long dimension of the receptor should be positioned vertically and parallel to the labial surfaces of the incisors. Note that in the anterior region of the mouth, the receptor can be placed on the dorsal surface of the tongue. This often will allow the operator to fully seat the receptor in the patient’s mouth and still capture the apical region. Furthermore, placing the receptor further posteriorly away from the lin-gual surfaces of the teeth also reduces receptor discomfort and typically allows the patient to fully bite together. The horizontal angulation of the x‐ray beam should be aimed through the contact area between the incisors to minimize overlapping of these teeth. The operator must then determine the correct negative vertical angulation of the PID by first visualizing the plane of the receptor and the long axes of the incisors. The angle that these two lines form must be visually bisected. The central ray of the PID should then be aimed perpendicular to this imaginary line with the lower edge of the PID extending beyond the edge of the recep-tor. Because the mandibular incisors are typi-cally quite narrow, the operator may be able to capture all four incisors in one image. However, if a portion of the left or right lateral incisor is cut off this view, the operator should next image the cuspid. The lateral incisor often is visible on the cuspid view. In so doing, it will eliminate the need for an additional lateral incisor exposure.Mandibular cuspid bisecting angle projectionArea of interest: Cuspid and lateral incisor.Receptor size: No. 2.Position: The long dimension of the receptor should be positioned vertically and parallel to http://dentalebooks.com 54 Fundamentals of Oral and Maxillofacial Radiologythe labial surface of the cuspid. Placing the receptor further away from the lingual surfaces of the teeth will reduce discomfort. The hori-zontal angulation of the x‐ray beam should be aimed toward the contact area between the cuspid and first bicuspid to minimize overlap-ping of these two teeth. Constriction and curva-ture of the mandibular arch will undoubtedly result in some superimposition of the first bicuspid onto the distal surface of the cuspid. However, the distal contact of the cuspid should be visible either on the bicuspid bitewing or periapical images. The correct negative vertical angulation of the PID can be determined by first visualizing the plane of the receptor and the long axis of the cuspid. The angle that these two lines form must be visually bisected. The central ray of the PID should then be aimed perpendicular to this imaginary line with the lower edge of the PID extending beyond the edge of the receptor.Note: The mucosa in this area of the oral cavity tends to be particularly sensitive and the patient may not tolerate fully seating the receptor.Mandibular bicuspid bisecting angle projectionArea of interest: First and second bicuspids.Receptor size: No. 2.Position: For this projection, the long dimen-sion of the receptor must be positioned horizon-tally. Intraorally, the receptor should be aligned parallel to both the buccal surfaces and the long axes of the teeth. Because the long dimension of the receptor is positioned horizontally to capture the posterior teeth, it cannot be placed onto the dorsal surface of the tongue. In this scenario, the tongue would prevent the shorter height of the receptor to be seated far enough inferiorly to capture the entire apical region. Consequently, the instrument must be positioned between the patient’s tongue and next to the alveolar ridge, which may be quite uncomfortable for the patient and often will result in missing the mesial portion of the first bicuspid. Using a PSP plate permits gentle bending of the receptor away from the sensitive mucosa, thus allowing it to be placed more anteriorly to hopefully cap-ture the mesial of the first bicuspid. Care must be taken not to overbend a PSP plate as it may become permanently bent and likely compro-mise future imaging. The horizontal angulation of the x‐ray beam should be aimed toward the contact area between the first and second bicus-pids to minimize overlapping of these two teeth. The correct negative vertical angulation of the PID can be determined by first visualizing theplane of the receptor and the long axes of the bicuspids. The angle that these two lines form must be visually bisected. The central ray of the PID should then be aimed perpendicular to this imaginary line with the lower edge of the PID extending beyond the edge of the receptor. The long axes of the bicuspids are normally almost vertical, thus very little angulation ofthe PID will be required, possibly up to 15° of negative vertical angulation. However, the length of the bicuspids often matches or exceeds the length of the receptor when positioned horizontally. Consequently, the operator may need to com-promise and intentionally overangulate the PID vertically to project the image of the apical region onto the receptor. This will distort the image and likely cut off a portion of the crown(s), but will at least capture the periapical region. The missing coronal region(s) should be visible on a bicuspid bitewing image.Mandibular molar bisecting angle projectionArea of interest: First, second and third molars.Receptor size: No. 2.Position: Similar to the bicuspid view, the receptor must be rotated so the long dimension of the receptor is orientated horizontally and should be positioned between the patient’s tongue and the alveolar ridge. It may not be quite http://dentalebooks.com K Intraoral Imaging Techniques 55as uncomfortable for a patient as the bicuspid view as the receptor is positioned further from the very sensitive anterior mucosa. The anterior aspect of the receptor should be positioned at the middle of the second bicuspid tooth to ensure visualization of the mesial contact area of the first molar. Similar to the maxillary molar view, the receptor may not be long enough to capture the retromolar region. In a full mouth series of images, the bicuspid view typically captures the first molar. Consequently, the operator can posi-tion the receptor further posteriorly to capture the retromolar region. Once again, to avoid unnecessary retakes, the operator should posi-tion the receptor initially in the bicuspid region and then request the patient to move the receptor as far back as they can tolerate with their own hand. After doing so, if the retromolar region is still not captured on the image, the operator should expose an extraoral image, such as a pan-oramic image, ifavailable. The horizontal angu-lation of the x‐ray beam should be aimed toward the contact area between the first and second molars to minimize overlapping of these two teeth. The correct negative vertical angulation of the PID can be determined by first visualizing the plane of the receptor and the long axes of the molars. The angle that these two lines form must be visually bisected. The central ray of the PID should then be aimed perpendicular to this imaginary line with the lower edge of the PID extending beyond the edge of the receptor. The long axes of the molars, like the bicuspids, are typically almost vertical, thus very little angula-tion of the PID will be required, possibly 10–15° of negative vertical angulation. Similar to the bicuspids, the length of the molars often will match or exceed the length of the receptor when positioned horizontally. Consequently, the opera-tor may need to compromise and intentionally overangulate the PID vertically to project the image of the periapical regions onto the receptor. This will distort the image and likely cut off a por-tion of the crown(s), but will at least capture the periapical regions. The missing coronal region(s) should be visible on a molar bitewing image.3. BITEWING TECHNIQUEThe objectives of a bitewing projection are ide-ally to visualize open interproximal contacts and the crest of the alveolar bone of both arches. A conventional full mouth series of x‐ray images often includes a set of four bitew-ings. Bitewing instruments are available. Many operators prefer to only use a disposa-ble tab for the patient to bite down upon to hold the receptor in place, without having any additional alignment device (i.e. ring) attached. An experienced operator may use a freehand technique that allows the operator more flexibility in orientating the PID both horizontally and vertically. An operator with little experience initially should use a bitewing instrument with an alignment device attached. Regardless of the technique used, it is recom-mended that the operator align the patient’s occlusal plane parallel to the floor, particularly if the operator is performing it freehand. This will allow easier determination of the correct horizontal and vertical position of the PID. To avoid overlapping the coronal contacts, the horizontal angulation must be aimed between the contact points of the adjacent teeth (Fig. K13). Tooth rotation or crowding will complicate visualizing multiple open contacts on a single bitewing image. Consequently, the operator may be required totake multiple ReceptorFig.K13 Illustration of the proper horizontal angulation to separate (i.e. open) adjacent surface contacts.http://dentalebooks.com 56 Fundamentals of Oral and Maxillofacial Radiologybitewings, each one using a slightly different horizontal angulation to eliminate overlapping of specific contacts. Overlapped contacts can obscure caries, fractures, etc. Why are periapi-cal images not adequate for viewing bone lev-els? The vertical angulation typically used, regardless of whether paralleling or bisecting angle techniques were used, are greater. Vertical angulation for bitewings is minimal (i.e. 0–8° positive vertical). Consequently, the relationship of bone level to tooth position is maintained on a bitewing image. An exception can be the mandibular molar periapical image which may require almost no vertical angula-tion of the x‐ray beam.Bicuspid bitewing (Fig.K14)Areas of interest: A bicuspid bitewing positioned to include the distal of the cuspid anteriorly.Receptor size: No. 2 for adult dentition, nos. 1 or 0 for children.Position: For this projection, the long dimension of the receptor must be attached horizontally and should be aligned parallel to the buccal surfaces of the teeth. Similar to the periapical technique, the receptor must be positioned between the patient’s tongue and next to the alveolar ridge. Using a PSP plate permits bending of the plate allowing it to be placed more anteriorly to capture the mesial of the cuspid.Molar bitewing (Fig.K15)Position: Similar to the bicuspid projection, the long dimension of the receptor must be posi-tioned horizontally and should be aligned parallel to the buccal surfaces of the teeth and positioned between the patient’s tongue and the alveolar ridge. It may not be quite as uncom-fortable for a patient as the bicuspid view as the receptor is positioned further from the very sensitive anterior mucosa. The anterior aspect of the receptor should be positioned to include the distal of the second bicuspid tooth to ensure visualization of the mesial contact area of the first molar. Unlike a periapical view, the poste-rior extent of the receptor does not need to extend all the way to the retromolar region because bitewings focus on interproximal con-tacts of adjacent teeth.Anterior bitewing projection (Fig.K16)Position: Bitewings in the anterior region are difficult to perform, particularly with solid‐state receptors as a result of the receptor’s bulk and rigidity. However, using a thinner, flexible Fig.K15 Molar bitewing view.Fig. K14 Bicuspid bitewing view, which ideally shows both the maxillary and mandibular bicuspids with open contacts and the height of the alveolar crestal bone.http://dentalebooks.com K Intraoral Imaging Techniques 57PSP plate allows the operator to more easily position the receptor in the anterior region to acquire a bitewing of the incisors. Generally, the same principles that were used for aligning the bicuspid and molar regions also apply here. However in the anterior region, the coronal portions of the maxillary and mandibular inci-sors are in different planes. Consequently, the receptor cannot be aligned perfectly parallel to the crowns of both the maxillary and mandibu-lar incisors simultaneously. This will result in some distortion of the bitewing image. Imaging the maxillary and mandibular teeth indepen-dently can eliminate this problem.4. DISTAL OBLIQUE TECHNIQUEThe distal oblique technique is primarily a standard molar projection using the bisecting angle technique but with a definite modification to the horizontal angulation of the PID and the receptor position (Fig.K17). This technique may compromise the overall quality of the image but it can provide additional information that may otherwise be unattainable. For exam-ple, if the operator encounters a patient with a hypersensitive gag reflex, it may be impossible to position the receptor far enough posteriorly to image the entire tooth or region of interest.For the maxillary third molar region, the operator should begin by positioning the receptor in the typical premolar region where the patient is less likely to gag. If the instru-ment has a ring for aligning the PID, the operator should remove it prior to insertion into the patient’s mouth as it may interfere with the modified PID position. Upon inser-tion, the operator should gently turn the distal end of the receptor away from the teeth of interest so that it is now angled across the midline toward the opposite side, while the anterior end of the receptor is left unchanged. There is not a universal horizontal angulation to use. Aiming the PID from the distal direc-tion toward the receptor at approximately a 45° horizontal angle should be adequate. Unfortunately it may require a trial and error approach. This will project the image of the teeth and the maxillary tuberosity region ante-riorly onto the receptor. It will also likely result in the coronal portions of the teeth being over-lapped. Overlapped crowns should not be a major concern if there is a molar bitewing image to view. In this projection, the roots and apices that were not captured using standard procedures should now be visible.The distal oblique technique for the man-dibular third molar region is slightly different to that of the maxillary molar projection. Ifthe instrument has a ring for the aligning the PID, the operator should remove it prior to insertion into the patient’s mouth. For the mandible, because of physical constraints of the tongue, the receptor must be positioned between the tongue and the alveolar ridge and aligned parallel to the latter, as in the Fig.K16 Anterior bitewing view.http://dentalebooks.com 58 Fundamentals of Oral and Maxillofacial Radiology paralleling and bisecting angle techniques. The operator must then slide the receptor as far posteriorly as the patient will permit. Similar to the maxillary molar distal oblique method, the horizontal angulation of the PID will be aimed obliquely and from the distal end of the region of interest. Aiming the PID at approximately a 45° horizontal angle toward the receptor should work. The oblique angulation will project the image more anteri-orly onto the receptor. Similar to the maxillary projection, the coronal portions of adjacent teeth will likely be overlapped, but the individual roots and their apices should be visible on theimage.5. OCCLUSAL IMAGING TECHNIQUEThe term occlusal technique refers to the physi-cal position of the intraoral receptor only. Theintraoral receptor is aligned horizontally between the occlusal surfaces of the maxillary and mandibular teeth. For this reason, it is also called the “sandwich technique” because it mimics placing a sandwich in one’s mouth. This technique can be performed with any size receptor. When film was the standard receptor, an occlusal‐size film was marketed; its phys-ical size resembled a playing card. Today, PSP plates can be purchased comparable in size to an occlusal film for a reasonable price. Unfortunately, the limited need for occlusal images in private practice makes it impractical for manufacturers to produce a comparably sized solid‐state receptor from a cost perspec-tive. However, a no. 2 solid‐state receptor can still be used to expose an occlusal image. The size of the receptor does not differentiate the principles of the occlusal technique, it merely controls the amount of real estate visible on an image. When utilizing the occlusal technique, a larger receptor is preferable as it will obvi-ously image a larger area compared with a smaller receptor.An occlusal image gives the practitioner a bucco‐lingual perspective of the region that is not visible on a standard periapical or pano-ramic view. This is particularly beneficial in localizing impactions and sialoliths. In addi-tion, an occlusal projection may permit imag-ing when periapical or bitewing images are impossible to acquire, such as in a case of tris-mus . If the patient is not able to open wide enough to allow positioning a receptor attached to an instrument, then the operator ReceptorPIDFig.K17 Diagram demonstrating the distal oblique technique. PID, posi-tion indicating device.http://dentalebooks.com K Intraoral Imaging Techniques 59can request the patient to use their own hand to slide the receptor in place. Since this tech-nique requires minimal mouth opening, it avoids the operator unnecessarily traumatiz-ing the patient further. Occlusal images will offer additional diagnostic information, espe-cially if extraoral imaging equipment is una-vailable. It is recommended that the operator select a posterior periapical setting initially and then adjust the exposure settings either up or down if a retake is necessary.Maxillary occlusal projectionThe maxillary occlusal image requires the same bisecting angle technique that is used for periapical images (Figs K18 and K19). Regardless of the size of the receptor selected for this procedure, the operator must slide the receptor over the area of interest. If this is the posterior right region, the receptor should beslid as far posteriorly as possible and offset to the right side. If the area of interest is the anterior region, then the receptor should be aligned more anteriorly. In this situation, if a no. 2 receptor is used, it may be preferable to position the long dimension of the receptor sideways from right to left. The operator must decide which orientation of the receptor is best for each particular situation. Using the bisect-ing angle principles, the PID should be aimed at a right angle to the bisector of the angle formed by the receptor and the long axes of the teeth. Generally, the vertical angle of the PID will be approximately 65° positive from the occlusal plane. For edentulous patients the operator may use the buccal or lingual plates of the edentulous ridge in lieu of roots to determine a bisector. Attempting to align the PID at a right angle to the receptor is usually not recommended because of superimposition of the cranium over the area of interest and the need for a much higher exposure to penetrate the additional skeletal structures to acquire a diagnostic image.Central ray65°Central ray55°90°Central rayFig.K18 Illustrations demonstrating the principles of the occlusal techniquehttp://dentalebooks.com 60 Fundamentals of Oral and Maxillofacial RadiologyMandibular occlusal projectionUnlike the maxilla, where superimposition of the cranium interferes with performing a right angle projection, the anatomy of the mandibular region permits using either a bisecting angle or a right angle projection (Figs K18 and K20). Aright angle projection is easily accomplished by placing the receptor in the region of interest and then directing the PID at 90° to the receptor from beneath the mandible. This perpendicular angulation is more easily attained when the patient tips their head backwards, thereby allowing the tubehead to lie lower down along the patient’s chest.A bisecting angle view also requires place-ment of the receptor in the region of interest and the PID aimed at a right angle to the bisector of the angle formed by the receptor and the long axes of the teeth. Generally, the vertical angle of the PID will be approximately 55° negative from the occlusal plane. For eden-tulous patients the operator may use the buccal or lingual plates of the edentulous ridge in lieu of roots to determine the bisector.Fig.K19 Occlusal view of the maxillary anterior teeth.Fig.K20 Occlusal view of the mandibular molar region (B, buccal aspect; L, lingual aspect).http://dentalebooks.com 61Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/hubar/radiologyIntraoral Technique ErrorsLRegardless of whether the paralleling or bisecting angle technique is used, several fac-tors must be incorporated to acquire good diagnostic images. This includes: (i) patient and receptor positioning; (ii) proper vertical and horizontal angulation of the PID; and (iii) correct selection of the exposure settings (i.e. mA, kVp and exposure time).The following technical errors are discussed in this section:1. Cone‐cut2. Apex missing3. Elongation4. Foreshortening5. Overlapped contacts6. Missing contact7. Overexposure and underexposure8. Motion artifact9. Foreign objectCone‐cutA cone‐cut refers to an unexposed area of vary-ing size on the periphery of an intraoral image (Fig. L1). For whatever reason, it is a result of the x‐ray beam not being properly aligned with the receptor. The part of the receptor extending outside the beam of radia-tion will not be exposed. Historically, the PID has been called a “cone.” The unexposed area appears blank as if it was “cut,” hence the combined term “cone‐cut.” Even though PID has generally replaced the term cone, the term cone‐cut has remained and it has not been updated to a “PID‐cut.” To confirm that the blank area is a cone‐cut, the outline of the blank area must either be a curved line from using a round PID or a straight line resulting from using a rectangular PID.There are different causes for cone‐cut images. Many teaching institutions commonly use intraoral RINN XCP™ for intraoral imag-ing. This instrument kit may include three dif-ferent set‐ups; each set‐up is used for a specific purpose (i.e. anterior periapical, posterior peri-apical and bitewing projections). If the operator uses the wrong aiming ring or assembles the instruments incorrectly, it will result in a cone‐cut. When using a rectangular PID, it must be very accurately aligned with the surface of the receptor as the rectangular beam size closely matches the receptor size. Occasionally the PID may drift away from the instrument after the operator properly aligns it with the receptor. Over time the weight of the tubehead can loosen the bracket arm, allowing it to drift http://dentalebooks.com 62 Fundamentals of Oral and Maxillofacial Radiologyslightly. In this scenario, the operator may align the PID correctly and walk out of the operatory without observing the drift of the PID. The patient is exposed and the result is a cone‐cut image.Note: If the operator attempts the occlusal technique using a large PSP plate, an unex-posed area will frequently appear on the image. This should not be considered an operator error as it is directly the result of the receptor size being larger than the x‐ray beam size.Apex missingIf an apex of a tooth is absent from an image, the receptor is not positioned far enough api-cally to image the entire tooth (Fig.L2). Using the paralleling technique, the operator can reposition the receptor further away from the lingual surfaces of the teeth. In the mandible, the patient’s tongue may force the receptor up against the alveolar ridge. Pressing the receptor up against the tongue may permit the operator to push the receptor away from the ridge and thereby permit the receptor to be seated more apically. In the maxilla, the midline of the palatal vault is typically the deepest aspect andallows a greater opportunity to capture the apex on the image. However, a shallow palate and a palatal torus are definite contraindica-tions for the paralleling technique. Either obsta-cle can prevent the receptor from being positioned far enough apically to capture an apex, leaving the operator with no option but to intentionally foreshorten the image with verti-cal overangulation. The bisecting angle tech-nique can be used more effectively in this scenario. The operator should slide the receptor along the palate, leaving a minimum of recep-tor surface extending beyond the occlusal edge. Still failing to capture the apex will require the operator to use extraoral imaging techniques, such as a panoramic view to visualize the apical region.An unavoidable cause of a missing apex occurs when a tooth is clinically longer than the length of the receptor. In the anterior region, substituting a no. 1 receptor with a no. 2 recep-tor will provide additional height for acquiring the apices. The maxillary cuspid generally is the longest tooth in the arch and, as a result, it often poses logistical problems in attempts to image it entirely. To accommodate the anatomy in the posterior regions of the maxilla and man-dible, the long dimension of a no. 2 receptor must be positioned horizontally. Substituting a no. 2 receptor with a smaller no. 1 receptor and Fig.L1 Cone‐cut (highlighted).Fig. L2 Missing apices can be due to the receptor not being positioned properly, vertical underangulation or long root length.http://dentalebooks.com L Intraoral Technique Errors 63orientating it vertically generally will not work. Failure to capture the apical region may require the operator to intentionally vertically overan-gulate the PID or to resort to extraoral imaging techniques.ElongationUnderangulation of the PID will elongate the length of the tooth, which may project the apex of the tooth off the receptor (Fig.L3). To correct this, the operator must now increase the vertical angulation of the PID, taking care not to over-compensate and overangulate the PID. Elongation is a common bisecting angle tech-nique error. Even for an experienced operator performing the bisecting angle technique often is a trial and error effort. If the operator is using a PSP plate, care must be taken not to use too much pressure to hold it in position intraorally. This type of receptor is very flexible and pres-sure can cause it to bend, which will elongate the image. Elongation caused by underangula-tion of the PID while using a paralleling instru-ment is physically difficult to do.ForeshorteningForeshortening will make a tooth appear shorter than it should be (Fig.L4). When is foreshorten-ing problematic? Accurate measurement of tooth length is critical for performing, for example, endodontic procedures. Excessive vertical angulation of the PID with either the paralleling or bisecting angle technique will foreshorten the image (see Fig. V1). If the recep-tor is positioned intraorally and the operator observes that the PID is in a steep vertical posi-tion, the PID likely needs to be repositioned. If it is not recognized and subsequently a retake is required, the operator should reposition the receptor further away from the teeth. This posi-tioning adjustment will reduce the vertical angulation and result in a more accurate repre-sentation of the teeth. The operator must also understand that a steep vertical angulation will result in a greater attenuation of the x‐ray beam because the x rays are traveling through more Fig.L3 Elongation of the image as a result of inadequate vertical angulation.Fig.L4 Foreshortening of the image as a result of exces-sive vertical angulation.http://dentalebooks.com 64 Fundamentals of Oral and Maxillofacial Radiology tissue. Consequently, a foreshortened image may also appear somewhat underexposed. Correcting the vertical angulation alone may be all that is required to increase the density of the new image. The point being, the operator must not automatically increase the exposure settings without first taking attenuation into consideration.Overlapped contactsIncorrect horizontal angulation of the PID causes overlapping of the interproximal sur-faces of adjacent teeth (Fig. L5). It should be noted that it may occur either from overangling the PID either from the mesial or from the distal direction toward the region being imaged. The objective is to aim the x‐ray beam directly between the teeth. Factors such as tooth rota-tion and tooth crowding may make it impossi-ble to achieve or at the very least it would require multiple images to accommodate all of these irregularities. Immediately after the expo-sure isprocessed, the operator should examine the x‐ray image to determine what horizontal angulation was used. The key is to check for both the open and the overlapped contacts. Why is it that some of the proximal contacts are open while others are overlapped? Each open contact indicates that the x‐ray beam passed between those two teeth. However, the shape and orientation of those teeth showing over-lapped contacts must be different and therefore require a different horizontal angulation to open them. For example, if a bicuspid bitewing image shows separation only between the cus-pid and first bicuspid, and all of the other teeth distal to them are overlapped, the PID needs to be aimed more from the distal direction. Inessence this means that the PID must be hori-zontally swung around more to the side of the patient. Doing so should open up the contacts between the two bicuspids, but will likely now overlap the previously open contact between the cuspid and first bicuspid area. Beware that overcompensation of the horizontal angulation from the distal direction will also produce undesired overlapping. Separation of contacts is critical for the diagnosis of interproximal caries and the assessment of mesial and distal margins of restorations on bitewing images.Missing contactsIn general, if the receptor position is too far ante-rior or too far posterior intraorally it can easily cut off proximal contacts surfaces (Fig. L6). Fig.L5 Overlapped contacts caused by incorrect horizon-tal angulation (see Fig. K13).Fig. L6 Absent surface: missing mesial surface of the mandibular first bicuspid as a result of the receptor not being positioned far enough anteriorly. Note that proper horizontal angulation produced open contacts.http://dentalebooks.com L Intraoral Technique Errors 65Avery common problematic area is the man-dibular cuspid and first bicuspid region. The anterior curvature of the dental arch can make this area almost impossible to properly image, especially when using bulky solid‐state recep-tors. Compounding this problem, all solid‐state sensors contain a dead space of up to a few millimeters inside the anterior edge of the receptor. The outer casing of the receptor may appear to be far enough anterior but the solid‐state circuits contained within it will not capture the extreme anterior edge. Dead space is not a concern on PSP plates.Overexposure andunderexposureIn general, excessive x‐ray production will result in an overexposed image and, con-versely, inadequate x‐ray production will produce an underexposed image(Fig.L7). It is important to understand that standardized exposure settings are not universal for multi-ple reasons. Factors to consider in determin-ing the proper exposure settings are the physical size of the patient, whether you are imaging the anterior region versus the poste-rior region or the maxillary teeth versus the mandibular teeth, the type of receptor being used, and the distance and angulation ofthe PID toward the receptor. Some intraoral x‐ray units only allow the operator to modify the exposure time. Consequently, increasing or decreasing the exposure time may be the operator’s only option. Finally, one should also be aware that the total radiation output from the x‐ray tube will gradually diminish with usage.ABFig.L7 A. Dark image: overexposure as a result of excessive radiation exposure. B. Light image: underexposure.http://dentalebooks.com 66 Fundamentals of Oral and Maxillofacial RadiologyMotion artifactIdeally, the patient, tubehead and receptor all remain motionless during the exposure. Movement of any of these in any combination will reduce the sharpness of the image(Fig.L8). There is a difference between movements of the receptor alone versus movement of the patient’s head. For example, the patient may use the tongue to reposition the receptor during the exposure and yet keep their head steady. Atother times, the patient and receptor will move in tandem if the patient turns their head. Movement of the receptor or the patient’s headduring the exposure will likely produce noticeable blurriness of the image, while motion effects produced by a drifting x‐ray tubehead alone will be more subtle. The tubehead wouldhave to move significantly during the exposure to cause noticeable image unsharpness. However a more significant conse-quence could be a cone‐cut image.Foreign objectPatients should be instructed to remove den-tures and eyeglasses prior to intraoral imag-ing. Unlike extraoral imaging, jewelry worn around the neck or in the ears may remain in place for intraoral imaging as they will be out-side the field of view. However, the metal framework of partial dentures and eyeglass frames may be projected over the apices of the teeth, which may necessitate retaking the image (Fig. L9). Plastic protective eyewear typically does not pose a problem and may be left on the patient during intraoral imaging. Overangulation of the PID may project the metal arm of the intraoral receptor holder over the incisal edges of teeth (Fig. L10). Fingers should also be kept out of view (Fig.L11).Fig.L8 Blurred image due to patient movement.Fig.L9 Eyeglass frame (highlighted).http://dentalebooks.com L Intraoral Technique Errors 67Fig.L10 Receptor holder (highlighted).Fig.L11 Fingertip (highlighted).http://dentalebooks.com 68Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/hubar/radiologyExtraoral Imaging TechniquesMExtraoral images are acquired when the image receptor is positioned outside of the patient’s mouth. Extraoral images are particularly beneficial for patients requiring orthodontic treatment, dental implants and oral surgical procedures. Typical extraoral x‐ray images include panoramic, cephalometric and CBCT projections.1. PANORAMIC IMAGINGAccording to the Oxford English dictionary a “panorama” is defined as an unbroken view of the whole region surrounding an observer. In dentistry, a panoramic x‐ray image is a single, unobstructed image of the entire mandible and maxilla (Fig. M1). At the outset, the author wishes to acknowledge that a discussion of the physics of the complicated imaging equipment involved is beyond the scope of this book.Panoramic x‐ray units have become ubiqui-tous in dental offices. The first commercially available panoramic unit was introduced in the 1950s. The latest evolution of panoramic x‐ray units has substituted a digital image receptor in lieu of a film receptor. Basic physical differences amongst panoramic units include whether the patient is seated or standing during the procedure, bite‐block design, exposure con-trols, availability of a cephalometric attach-ment, etc. Today, more sophisticated panoramic units also have limited cone‐beam technology capability directly built into them.The primary component of any panoramic x‐ray unit is a horizontal rotating arm that houses at one end the x‐ray tube, and at the other end an image receptor. The generated x rays are immediately collimated into a narrow, vertical beam. The x‐ray beam is usually only a few millimeters wide and has enough vertical height to expose both the mandibular and max-illary arches. During the exposure, the horizon-tal assembly rotates completely around the patient’s head. Of significance is the fact that the patient is only exposed to a narrow beam of radiation at any one moment. This explains why a patient typically receives less radiation from a larger panoramic image compared with a full mouth series of intraoral images. Also, unlike intraoral images where an entire image will be blurred by patient motion during the exposure, only a limited area of a panoramic image will be blurred if there is a momentary period of patient movement. Patient motion only affects the area of the panoramic image http://dentalebooks.com M Extraoral Imaging Techniques 69exposed during that period of time. Once the patient becomes still again, the remaining area of the image will not be affected.Positioning thepatientAccurate patient positioning is critical to acquire a diagnostic panoramic image (Fig.M2). Most modern panoramic units are designed with the patient in a standing posi-tion for the x‐ray exposure. The patient must be guided by the operator into the gantry of the unit. Generally, there will be a bite‐block of some fashion that the operator should instruct the patient to bite onto using their maxillary and mandibular incisors. An alter-native chin rest often is provided by the man-ufacturer for properly positioning fully edentulous patients.Head positioning utilizes three anatomic planes – the sagittal, transverse and coronal planes–and controls the side to side, anterior–posterior and inferior–superior positions of the mandible and maxilla. The patient’s jaws are guided into a focal trough . A focal trough is also called the “zone of sharpness.” Positioning the patient within the focal trough will result in optimum diagnostic quality of the image; fail-ure to do so will result in varying degrees of image distortion. The focal trough is generally horseshoe‐shaped (i.e. U shape), with the open end located in the posterior region. For every model of panoramic unit, the focal trough may vary in size and shape. Panoramic units typi-cally use laser lines that are projected onto the facial soft tissues to assist the operator in posi-tioning the patient’s head. Be cognizant that the actual outline of the focal trough is invisible to the operator as it is not marked on the exterior of the x‐ray unit.The Frankfort horizontal plane is used to determine the proper inferior‐superior position of the patient’s head. It is formed by an imagi-nary line that extends between the external auditory meatus and the inferior margin (floor) of the orbit. This plane is often considered the normal carrying position for the head when a person is facing forward and standing upright. If a patient’s chin is tipped too far down in the panoramic unit, it will collapse the image size of the dental arch, while tipping the chin too far Fig.M1 Panoramic image.http://dentalebooks.com 70 Fundamentals of Oral and Maxillofacial Radiologyupwards may result in the posterior aspect of the ramus and condyle being cut off the image.The mid‐sagittal plane is used to center the patient’s head laterally in the x‐ray unit. It is intended to eliminate the head being off‐center or turned to one side. The operator typically relies on soft tissue landmarks using the midline of the nose and the midpoint between the eyes for positioning the patient. However, the soft tissue midline and the skeletal midline may not coincide with one another. In this scenario, using the soft tissue midline would result in distortion of the image. Whenever a patient’s skeletal midline is positioned off‐center, there will be magnification on one side of the denti-tion and the opposite side will be simultane-ously demagnified. Prior to the exposure, the operator should also confirm the mid‐sagittal positioning by viewing the patient’s head from the back as the mid‐sagittal line may be cen-tered correctly on their face but the posterior aspect of their head may be off‐center and may need to be repositioned by the operator.The mandibular cuspid is typically used as the guide to properly position the patient antero‐posteriorly in a panoramic unit. A patient posi-tioned too far anteriorly will result in demagnification of the anterior teeth on the image. Conversely, if the patient is positioned too far posteriorly, it will magnify the image size of the anterior dentition. Positioning completely edentulous patients is slightly more challeng-ing although the same protocol applies. Manufacturers typically have modified bite‐blocks or chin cups for positioning edentulous patients. However, if a modified bite‐block is not available, the operator can still use a standard bite‐block. In this situation, the operator should ask the patient to gently close their lips around the tip of the bite‐block. Use of the Frankfort hor-izontal position and the mid‐ sagittal plane is the same. However, for antero‐posterior positioning, ABFig.M2 A. Panoramic x‐ray unit. B. Patient properly aligned in a panoramic x‐ray unit.http://dentalebooks.com M Extraoral Imaging Techniques 71the operator can use the corner of the lips as a virtual cuspid. For all patients, partial dentures should be removed prior to placing the patient in the panoramic unit.Exposure settingsAll panoramic units allow the operator to adjust the milliamperage and kilovoltage settings. Unlike intraoral x‐ray units, the panoramic exposure time is always fixed and averages approximately 20 s. Panoramic exposure time is in fact the time it takes for the tubehead and receptor to rotate around the patient’s head andmay vary slightly from one manufacturer’s x‐ray unit to another. Whether the operator manually selects exposure settings or permits the x‐ray unit to automatically determine the exposure, familiarity with the functioning of the panoramic unit will ultimately remove a lot of the guesswork and produce the best images.Advantages anddisadvantagesAdvantages1. Image content2. Image context3. Patient comfort4. Efficiency5. Bitewing mode6. Dose reduction7. Cost effectiveness8. Standing position versus seated style pano-ramic unitImage contentA single panoramic image includes the entire oral region, often including additional struc-tures outside the field of view of conventional intraoral images. These may include the temporomandibular joint, maxillary sinuses, nasal cavity, hyoid bone, etc.Image contextA famous phrase of psychologist Kurt Koffka, “The whole is other than the sum of the parts” is often incorrectly translated as “The whole is greater than the sum of its parts.” One can relate this to x‐ray images by defining a panoramic image as the “whole” and intraoral images as the “parts.” A panoramic image relates the phys-ical relationships of anatomic structures to one another much better than adisjointed full mouth series of intraoral images. In essence a pano-ramic image is a gestalt of the oral region.Patient comfortUnless a patient is extremely claustrophobic, a panoramic projection is a very comfortable pro-cedure to have performed. Patients generally are required to stand upright, rest their chin on a platform and bite onto the tip of a plastic rod. This may also be the only viable option for imaging the dentition of a patient with a hypersensitive gag reflex.EfficiencyIn comparison to the cumulative time it takes to expose a full mouth series of intraoral images, the time to acquire a panoramic image is very brief, at approximately 20 s. For the majority of patients a 20 s exposure time is inconsequential. However, the exposure time can be problematic for patients suffering from any type of tremor who may be unable to hold steady for that long. In this case, intraoral images may actually be preferable where the exposures can be intermit-tent, very brief and ideally timed to counter patient movement.Bitewing modeMore sophisticated panoramic x‐ray units include software functionality for acquiring bitewings. It should be noted that intraoral bite-wings are still the gold standard. The physics of http://dentalebooks.com 72 Fundamentals of Oral and Maxillofacial Radiologyextraoral imaging techniques results in uneven magnification and reduction in the resolution of the image compared with intraoral images. However, in uncooperative patients, such as those with severe gagging reflexes, the bitew-ing mode on a panoramic unit may be an invaluable resource.Dose reductionMany factors determine the actual exposure dose to a patient and therefore make it difficult to compare one procedure directly with another. Exposure dose from a panoramic image is con-sidered to be less than the cumulative exposure dose from a comparable full mouth series of intraoral x‐ray images.Cost effectivenessA commonly used phrase is “time is money.” In this case, an operator can perform the entire panoramic imaging procedure in as little as a few minutes with virtually no discomfort to the patient. Compare this to the much longer time required for an operator to generate a full set of intraoral x‐ray images.Standing position versus seated style panoramic unitA standing position design of a panoramic x‐ray unit offers three primary advantages over a seated version. (i) Seated patients often tend to hunch their back which produces a spi-nal shadow that can obscure a portion of the image. From personal experience, a standing position encourages patients to extend their necks straighter than when they are seated. The result will be a reduction in unwanted spi-nal shadows. (ii) The gantry can be lowered allowing physically handicapped patients in wheelchairs to remain in them for the entire procedure (Fig. M3). A wheelchair‐bound patient simply needs to be wheeled into the panoramic unit and the gantry can then be lowered around them. A sit‐down panoramic unit requires physically transferring the patient from a wheelchair into the fixed pano-ramic chair. (iii) The footprint of a standing panoramic unit is smaller than a seated model, thus taking up less prime real estate space in a dental clinic.Disadvantages1. Diagnostic quality of a panoramic image is inferior to intraoral images2. Distortion3. Increased exposure to radiosensitive tissues4. Misinterpretation5. Equipment cost6. Anatomic limitationsFig.M3 Wheelchair positioned in a panoramic unit.http://dentalebooks.com M Extraoral Imaging Techniques 73Diagnostic quality ofapanoramic image is inferior tointraoral imagesThere are continued improvements occurring in panoramic digital technology. However, there are inherent principles of physics of extraoral imaging that are not encountered with intraoral imaging. As a result, the quality of a panoramic image remains inferior to intraoral images, although it is an excellent screening tool for assessing gross structures.DistortionRegardless of manufacturer, image magnifica-tion is unavoidable. Magnification will vary from one manufacturer’s unit to another; ranging from 15% to 30%. In addition, errant patient positioning will produce uneven magnification within a panoramic image. Theimaging software’s measurement function cannot accurately account for the uneven mag-nification on panoramic images. Consequently, a numeric measure should only be considered as an estimate.Increased exposure toradiosensitive tissuesProtective aprons with attached thyroid collars cannot be worn by patients during panoramic imaging. The protective collar will partially block the x‐ray beam, resulting in a portion of the mandible being completely obscured on the panoramic image. As a result, sensitive regions of the neck cannot be protected from radiation exposure. Fortunately, the primary x‐ray beam is highly collimated and a minimal amount of radiation reaches the thyroid region. In addition, minor amounts of internal scatter-ing (i.e. x rays that bounce off the teeth and bones) may expose the thyroid gland. This is totally unavoidable.Note: A double‐sided protective apron that covers both the patient’s front and back is recommended. During the exposure, the beam of radiation is directed from behind the patient. Therefore, a standard single‐sided apron that covers only the front of the patient serves little benefit for panoramic imaging. Reversing it to cover the patient’s back may be awkward as it may not remain in place.MisinterpretationPanoramic imaging also produces artifacts that can be misinterpreted, commonly referred to as “ghost images.” A ghost image is a faint image of a radiodense object from one side of the patient that is superimposed onto the opposite side. A common example is ear-rings that are not removed prior to exposure. A faint radiopaque image of the right earring will be projected onto the left side and vice versa. Normal anatomic structures also pro-duce ghost images. Regardless of the type of imagebeing interpreted, the practitioner may misdiagnose normal from abnormal.Equipment costThe monetary cost of a panoramic x‐ray unit is typically in the tens of thousands of dollars. Many different manufacturers market pano-ramic units with multiple features and varying costs. The practitioner should be an informed buyer as a panoramic x‐ray unit should not need to be replaced for many years.Anatomic limitationsA patient with scoliosis may not have ade-quate shoulder clearance for the panoramic unit to rotate unimpeded. A dry run without radiation should be attempted first to avoid unnecessarily exposing a patient to radiation. Alternatively, a full mouth series of intraoral images is recommended.http://dentalebooks.com 74 Fundamentals of Oral and Maxillofacial RadiologyTechnique errorsThe following technical errors are discussed in this section:1. Head is rotated or off‐center2. Head is positioned too far anterior (i.e. forward)3. Head is positioned too far posterior (i.e. back)4. Chin is tilted too far down5. Chin is tilted up too high6. Chin rest7. Tongue position8. Movement9. Foreign objects10. Protective (lead) apronHead is rotated or off‐center (Fig.M4)Effect: If the dentition is positioned off‐center, one side of the image will be magnified and the opposite side will be demagnified. The clinician should always compare the size of the teeth as well as the osseous structures bilaterally. Observing uniform differences in size from one side to the other should give the clinician pause to consider that it may simply be the result of an error in patient positioning.Solution: The operator should confirm that the mid‐sagittal line is centered properly on the patient’s face and that the back of the head is not positioned off‐center. A patient can appear to be properly centered from the front but the back of the patient’s head may be turned to one side.Note: A clinical examination of the patient may reveal that the patient has a skeleto‐ dental deformity that will produce an asym-metric image.Head is positioned too far anterior (i.e.forward) (Fig.M5)Effect: If the dentition is positioned too far for-ward, the anterior teeth will be distorted, appearing constricted (i.e. narrowed) and the cervical vertebrae may be partially superim-posed bilaterally over the rami and condyles.Solution: Ensuring that the patient’s ante-rior teeth are biting properly onto the bite‐block along with confirmation that the cuspid indica-tor is aligned properly should eliminate this problem. Patients should be guided by the operator into this position. Anteroposterior positioning errors may be inevitable if the patient has a class II or class III occlusion .Head is positioned too far posterior (i.e.back) (Fig.M6)Effect: If the dentition is horizontally posi-tioned too far back, the anterior teeth will be distorted, appearing magnified (i.e. widened) and the rami and condyles may be partially or wholly absent.Solution: Similar to when the patient’s head is too far forward, the operator must ensure that the patient’s anterior teeth are biting prop-erly onto the bite‐block and that the cuspid is properly aligned. Checking both of these align-ments should eliminate this error. Patients should be guided by the operator into this position. Once again, positioning errors may beinevitable if the patient has a class II or III occlusion.Chin is tilted too far down (Fig.M7)Effect: If the dentition is tipped down too far, the occlusal plane will appear very steep. The steep-ness is dependent upon the amount of downward http://dentalebooks.com M Extraoral Imaging Techniques 75APatient’s right sidePatient’s right sideBCFig.M4 A, B. Head positioned off‐center. In both images the patient’s right side is enlarged (i.e. distorted) compared to the left side. C. Illustration showing that dentition is off‐centered.http://dentalebooks.com 76 Fundamentals of Oral and Maxillofacial Radiologytipping of the patient’s head. The apices of the mandibular anterior teeth will invariably be out of focus as they will likely be positioned outside of the focal trough. Also, extreme downward tip-ping of the head may result in the condyles being projected off the superior aspect of the image.Solution: Accurate head alignment using the Frankfort horizontal plane will eliminate this error. In so doing the operator should observe a small 5–7° downward tilt of the head.Chin is tilted uptoo high (Fig.M8)Effect: If the dentition is tipped up too high, the occlusal plane will appear very flat. The degree of flatness is dependent on the amount of upward tipping of the patient’s head. The result is that the roots of the maxillary anterior teeth will invaria-bly be out of focus as they will be positioned out-side of the focal trough. Also, insufficient head tipping may result in the condyles being projected posteriorly off the posterior aspect of the image.ABFig.M5 A. Head positioned too far anteriorly. Note the spinal vertebrae encroaching from both sides and demagnification of the mandibular incisors. B. Illustration showing that dentition is too far forward.http://dentalebooks.com ABFig.M6 A. Head positioned too far posteriorly. Note that the posterior aspect of the ramus is missing and magnification (i.e. widening) of the anterior maxillary and mandibular incisors. B. Illustration showing that dentition is too far back.Fig.M7 Chin tilted down too far. Note the steep incline (V‐shape) of the lower border of the mandible.http://dentalebooks.com 78 Fundamentals of Oral and Maxillofacial RadiologySolution: As in the case above, accurate head alignment using the Frankfort horizontal plane is vital to prevent this error. Similarly, if the patient is in the proper position, the opera-tor should observe a small 5–7° downward tilt of the head.Chin rest (Fig.M9)Effect: If the mandible is not seated onto the chin rest, the superior region encompassing the nasal fossa and maxillary sinuses will likely be partially cut off the top of the image while the region inferior to the submandibu-lar region will be imaged. The region encom-passing the dentition itself should not be affected.Solution: Most panoramic units allow adjustment of the vertical height of the bite‐block. The operator generally can slide the bite‐block down to lower the patient’s chin onto the chin rest.Fig.M8 Chin tilted up too high. Note the flat contour of the lower border of the mandible and the reverse curve of Spee .Fig.M9 Patient not positioned on chin rest. The yellow line indicates the gap beneath the chin and the chin rest.http://dentalebooks.com M Extraoral Imaging Techniques 79Tongue position (Fig.M10)Effect: The tongue acts as a natural radiation filter and normally rests in the floor of the mouth. If the patient’s tongue is allowed to remain at rest dur-ing a panoramic exposure, then a crescent‐shaped radiolucent band will be produced that extends completely across the maxillary arch. This radio-lucent band is the palatoglossal air space . However, if a patient presses their tongue up against the palate, the tongue will absorb some of the excess radiation in the maxillary region and improve the overall diagnostic quality.Solution: The routine act of swallowing requires pressing one’s tongue upward against the palate. For panoramic imaging, the opera-tor should ask the patient to first swallow and then try to keep their tongue up against the roof of their mouth during the entire exposure.Movement (Fig.M11)Effect: A typical motion artifact will make the image appear wavy and disjointed. The opera-tor should be aware that the source of radiation in a panoramic x‐ray unit is collimated into a narrow vertical beam. The width of the x‐ray beam is similar to the narrow light source that moves across a photocopier. Consequently only a small slice of the patient is actually exposed at any given time. If a patient moves momentarily, only the area exposed during that time of movement will be blurred (i.e. motion artifact), leaving the remainder of the image unaffected. Movement often occurs when one side of the panoramic unit contacts the patient’s shoulder as it rotates around the patient. Reflexively the patient will move and lower their shoulder to permit the x‐ray unit to pass by. Two physical contraindications that may cause motion artifacts are: (i) a short neck; and (ii) body tremor.Solution: When the operator suspects that there may not be adequate shoulder clearance for the x‐ray unit to rotate around the patient because of a short neck, the operator should first do a test run without radiation. Panoramic machines typically have a test mode where there is no radiation output, yet the unit will still rotate normally. Performing a dry run avoids unnecessarily exposing a Fig.M10 Crescent‐shaped radiolucent shadow produced by the palatoglossal air space (highlighted).http://dentalebooks.com 80 Fundamentals of Oral and Maxillofacial Radiologypatient to radiation. If the unit does rotate completely around unimpeded, then the operator should turn the radiation back on and repeat the procedure. For patients with a serious tremor, individual intraoral images are recommended as the exposure time for acquiring each image is very brief. Patient movement due to other reasons may not be predictable or avoidable.Foreign objects (FigsM12 andM13)Effect: Any foreign material can cast a radio-paque shadow on an image. The density of the resultant radiopacity is dependent upon the object’s actual density and thickness. Forpanoramic imaging, the general rule is that metallic accessory items from the neckline upwards (e.g. necklaces, earrings, eyeglasses, Fig.M12 Metallic necklace (highlighted).Fig.M11 Movement: the irregular contours of the patient’s left side indicate patient movement during the exposure.http://dentalebooks.com M Extraoral Imaging Techniques 81partial dentures) should be removed prior to the x‐ray procedure. However, the operator must also be accepting of patients who may refuse or cannot easily remove various types of jewelry such as tongue bars, nose rings, etc. Any fixed dental restorations (e.g. crowns, fill-ings, permanent retainers) obviously cannot be removed. Partial dentures generally have metal clasps which will definitely obscure areas on an image. Therefore partial dentures should be removed prior to taking a panoramic image. Any metal object will produce a ghost image . A ghost image will be located slightly higher and on the opposite side to the object itself. The radiopacity of the ghost image is magnified and blurred compared with the causative object cre-ating the ghost image(FigsM14 and M15).Solution: As a routine, the operator at the outset should ask the patient to remove any jewelry worn from the neck up, including Fig.M13 Partial denture (highlighted).Fig.M14 Ghost images of right and left earrings (highlighted).http://dentalebooks.com 82 Fundamentals of Oral and Maxillofacial Radiology eyewear and any removable dental prostheses. Hearing aids should remain in place until all of the instructions are given to the patient and then the patient should remove their hearing aid(s) for the actual procedure.Note: An exception to this rule is a complete acrylic denture. Generally these will not be visible on an image and may be left in the patient’s mouth to assist the operator when positioning the patient in the x‐ray unit.ABFig.M15 Ghost images of right and left rami (highlighted in B).http://dentalebooks.com M Extraoral Imaging Techniques 83Protective (lead) apron (Fig.M16)Effect: The source of radiation in a panoramic unit is always directed from below the mandi-ble. Consequently, if the protective apron has a thyroid collar attached, it will definitely be in the path of the x‐ray beam. A dense, irregular‐shaped radiopacity will appear in the midline–premolar area of the mandible.Solution: If the apron has an attached thyroid collar, it must be removed or folded flat so as not to block the incoming path of the x‐ray beam.ABFig.M16 Shadow of a thyroid collar worn during the procedure (highlighted in B).http://dentalebooks.com 84 Fundamentals of Oral and Maxillofacial RadiologyAnatomic landmarksFigureM17 shows the following landmarks:1. Maxillary sinus2. Nasal fossa3. Orbit4. Pterygomaxillary fissure5. External auditory meatus6. Mandibular canal7. Mental foramen8. Articular eminence9. Zygoma (highlighted: yellow)10. Condyle11. Coronoid process12. Ramus13. Hard palate14. Hyoid bone15. Cervical vertebrae16. Maxillary tuberosity (highlighted: orange)17. Glenoid fossa1710812141511765431213916Fig.M17 Panoramic anatomy. See text for explanation of numbers 1 to 17.http://dentalebooks.com M Extraoral Imaging Techniques 852. LATERAL CEPHALOGRAPH IMAGINGA lateral cephalograph (aka lateral cephalogram or ceph) is a sagittal projection of the skull that includes both the hard and soft tissues (Fig.M18). The ability to visualize the soft tis-sue profile is essential when facial aesthetics are a concern, such as in orthodontic and oral surgical procedures. A cephalograph x‐ray unit incorporates a head‐holding device called a cephalostat (Fig.M19). Patient posi-tioning requires gently inserting bilateral ear rods into the external auditory meatuses, a nasal rod positioned at the nasion and align-ment of the Frankfort horizontal plane paral-lel to the floor (Fig. M20). In so doing, the patient’s head is locked in place and affords the operator the ability to record the head position coordinates. In addition, it ensures proper alignment of thex‐ray source with the Fig. M18 Cephalograph image. (Source: Courtesy of Dr.Richard Ballard.)ABFig. M19 A. Combined panoramic–cephalometric x‐ray unit. B. Cephalostat attachment.Fig.M20 Patient positioned in cephalostat.http://dentalebooks.com 86 Fundamentals of Oral and Maxillofacial Radiologyimaging receptor. Thepositioning coordinates can be used to reproduce the original head alignment for follow‐up imaging (e.g. moni-tor changes in growth and development). Typically, a cephalostat is an optional add‐on arm attachment for most panoramic x‐ray units, making it a combined panoramic–cephalometric unit. The combined x‐ray unit shares the same x‐ray source. The arm length is standardized at 152 cm and it is measured from the mid‐sagittal plane of the patient’s head to the x‐ray source.In comparison, a conventional lateral skull projection does not require a soft tissue fil-ter nor does it require a cephalostat. At a minimum, a lateral skull projection requires a standard intraoral tubehead for the x‐ray source and an appropriate‐sized image receptor. The resultant image is a view of the osseous structures only (i.e. it lacks the soft tissue pro-file) and it is virtually impossible to accurately duplicate head position for follow‐up images.3. CONE BEAM COMPUTED TOMOGRAPHYIntroductionCone beam computed tomography (CBCT) tech-nology was first developed for medicine in the 1980s. CBCT was introduced into the dental field in the late 1990s and has revolutionized dentistry ever since. Today, CBCT scanners are interna-tionally manufactured in multiple configurations by numerous different companies (Fig.M21).CBCT is a perfect example of how dental radiographic terminology is often self‐ explanatory. A CBCT x‐ray unit generates a beam of x rays in the shape of a cone. Hundreds of indi-vidual x‐ray images are rapidly exposed during the patient’s scan. A computer algorithm com-bines the data to produce multiplanar tomographic images. The literal description isthe techno-logical term “cone beam computed tomography.”Depending upon the manufacturer’s model, the patient may be in a seated, standing or supine position during the scan in any given CBCT x‐ray unit. Most dental practices opt for a standing or seated version because the unit will occupy less floor space. In fact, a CBCT x‐ray unit often physically resembles a conventional panoramic x‐ray unit. However, unlike a pano-ramic unit where the field of view (FOV) is fixed for a given projection, CBCT x‐ray units generally allow the operator to modify the width of the FOV. A flat panel receptor is typically used to capture the images. Maximum image size is dependent upon the size of the receptor. The vertical dimension (i.e. collimation height) is often the operator’s primary consideration, while the horizontal dimension is usually sec-ondary. For example, a large FOV cone beam x‐ray unit may image up to 23 cm vertically, while a small FOV may only image5 cm in a vertical dimension. In practice, a small FOV scan is ideal for endodontic procedures, single arch implants and most extraction cases. A large FOV scan is more practical for complex dual arch implant cases, complex oral surgery and orthodontic treatments. In general, a smaller volume of Fig.M21 Patient positioned in a CBCT x‐ray unit.http://dentalebooks.com M Extraoral Imaging Techniques 87 tissue imaged results in less overall radiation exposure dose to the patient and it also reduces the amount of scatter radiation . Regardless of the size of the FOV, any radiation that deflects off metallic dental restorations, teeth and bones will diminish the overall image quality.After following the manufacturer’s patient positioning guidelines, it is usual for the opera-tor to expose a preview or scout image prior to performing the actual scan. The purpose of the scout image is to confirm that the patient is positioned properly in the CBCT unit prior to performing the scan and for the operator to minimize the FOV to the region of interest. Unlike a panoramic unit, a CBCT gantry rotates a full 360° circle around the patient’s head. Atypical CBCT scan will expose between 100 and 600 individual lateral images sequentially as it rotates around the patient’s head (Fig.M22). The scan acquisition time often is less than 10 s. Image data are characteristically captured using a flat panel receptor . The preselected resolution for the scan will determine the total number of images exposed. A higher resolution scan will expose a greater number of individual images allowing for thinner slice thicknesses compared with a lower resolution scan. From a technical standpoint, the only differences between a high resolution scan and a low resolution scan will be a slightly longer scan time and a longer reconstruction time because of the additional data collected. Regardless of resolution, complete reconstruction of the data is typically done within a few minutes. The cli-nician can selectively view the images in axial , sagittal and coronal planes (Fig.M23).How much radiation does apatient receive fromaCBCT scan?The radiation exposure dose of a CBCT scan is significantly higher than in conventional intraoral and extraoral dental imaging techniques and, as a result, a CBCT scan should not be used rou-tinely on all patients. The National Council on Radiation Protection and Measurements (NCRP) has published CBCT guidelines and the American Academy of Oral and Maxillofacial Radiology has published position papers on CBCT for some of the dental specialties. Exposure doses from CBCT scans will vary significantly depending upon the volume size, image resolution, manu-facturer specs, etc. According to the NCRP, the effective dose for a large FOV scan can be hun-dreds of microsieverts. For comparison, the effec-tive dose of a typical digital panoramic image is approximately 15 μS v.What is thelegal responsibility ofaclinician who orders aCBCT scan?If the ordering clinician does not obtain an inter-pretive report from a radiologist, the clinician is responsible for diagnosing all pathology within the entire scan. It is extremely important to empha-size that this includes noting pathology located outside the area of interest. There are instances where CBCT scans needlessly use a maximum FOV for treatment planning a single mandibular implant. The clinician is still responsible for X-ray sourceReceptorFig.M22 Illustration of a CBCT tubehead rotating around the patient and exposing anywhere from 100 to several hundred individual images.http://dentalebooks.com 88 Fundamentals of Oral and Maxillofacial Radiology identifying pathology located anywhere within the scan. Missed lesions could lead to legal conse-quences. This is a particular concern for clinicians who operate their own CBCT units and who may not seek outside services for an interpretive report.Who should operate aCBCT x‐ray unit?Cone beam computed tomography imaging should only be performed by properly trained radiology personnel.ABCFig.M23 Cone beam computed tomography views. A. Panoramic. B. Coronal. C. Axial.http://dentalebooks.com M Extraoral Imaging Techniques 89Should aCBCT unit bepowered off at theend ofthework day?At the end of the day, similar to intraoral x‐ray units, it is advisable to power down a CBCT x‐ray unit to prolong the life of the x‐ray tube contained within it. Unlike intraoral x‐ray units, if the CBCT x‐ray unit is turned off for an extended period of time, a warm‐up period of approximately 30 min for the flat panel receptor is recommended prior to taking the first expo-sure. If the operator does not allow the unit adequate time to warm up to its proper operat-ing temperature, then it may result in poorer quality images at the outset.Anatomic landmarksFiguresM24 to M27 show the following land- marks.Axial view: condylar level (Fig.M24)1. Condylar head2. Mastoid air cells3. Cervical vertebra4. Nasopharyngeal airway5. Maxillary sinus6. Nasal septum7. Nasal concha8. Lateral pterygoid plate9. Medial pterygoid plate10. Coronoid process11. Soft tissue of the noseAxial view: maxillary level (Fig.M25)1. Styloid process2. Mastoid air cells3. Ramus of the mandible4. Cervical vertebra5. Nasopharyngeal airway6. Palatal torus7. Maxillary archFig.M24 Axial view: condylar level. See text for explana-tion of numbers 1 to 11.Fig.M25 Axial view: maxillary level. See text for explana-tion of numbers 1 to 7.http://dentalebooks.com 90 Fundamentals of Oral and Maxillofacial RadiologyAxial view: mandibular level (Fig.M26)1. Mandibular arch2. Mandibular anterior teeth (i.e. roots of cuspids, lateral and central incisors)3. Mandibular posterior teeth (i.e. roots of first and second molars)4. Nasopharyngeal airway5. Cervical vertebraeCoronal view: molar region (Fig.M27)1. Body of the mandible2. Mental foramen3. Mandibular second premolar4. Palatoglossal airway space5. Maxilla (palatine process)6. Maxillary sinus7. Nasal septum8. Nasal concha9. TongueApplicationsCone beam computed tomography imaging should only be performed when conventional two‐dimensional imaging is unable to adequately assess a patient’s oral health orthe outcome of a treatment. Regardless of thetypeof dental image projection prescribed (i.e. conventional or CBCT), the clinician must review the patient’s history and perform a clinical examination first. The ben-efits to the patient should outweigh the potential risks of exposure to x rays and the minimum exposure necessary to achieve adequate image quality should beused.The following applications will be discussed here:1. Dental implants2. Osseous pathology3. Temporomandibular joint4. Impactions5. Orthodontics6. EndodonticsFig.M27 Coronal view: molar region. See text for expla-nation of numbers 1 to 9.Fig.M26 Axial view: mandibular level. See text for expla-nation of numbers 1 to 5.http://dentalebooks.com M Extraoral Imaging Techniques 91Dental implantsImplants have become ubiquitous for tooth replacement today (Fig. M28). CBCT scans offer the practitioner invaluable pre‐ and post‐surgical information. Some of the benefits include accurate localization of the inferior alve-olar canal, cross‐sectional visualization of the contours of the alveolar ridge and the ability to accurately measure the height and width of the alveolus. Additionally, fabrication of a surgical guide and use of pre‐surgical treatment plan-ning software provides the clinician invaluable information for assessing proper site selection and implant placement.Osseous pathologyThree‐dimensional views of osseous pathol-ogy can greatly assist treatment planning, particularly when oral surgery may be involved(Fig.M29). For example, bucco‐lingual expansion of the mandibular ramus may be assessed from a CBCT scan which would be impossible to accurately view on a conven-tional two‐dimensional panoramic image. Localization of anomalies such as a sialolith and a Stafne bone cyst can be diagnosed easily on sagittal and axial views.Temporomandibular jointTemporomandibular joint dysfunction (TMD) may be related to osseous changes ongoing in the temporomandibular joint. CBCT imaging of the temporomandibular joint is excellent for revealing degenerative and neoplastic changes in the region (FigsM30 and M31).A(a)BFig.M28 (a) Post‐implant placement of implants no. 10 (highlighted in B) and no. 12; both appear well‐positioned. http://dentalebooks.com (c)AB(b)Fig.M28 (Continued) (b) Cross‐sectional image revealing that implant no. 10 has clearly perforated through the labial cortical plate. The surgical error was not visible on the panoramic view. (c) Properly positioned implant within the con-fines of the cortical plates. B, buccal side; L, lingual side.http://dentalebooks.com M Extraoral Imaging Techniques 93ImpactionThree‐dimensional CBCT images revealing tooth to tooth and tooth to anatomic structures relationships can be invaluable. Clinicians performing a routine dental extraction may not benefit from a CBCT scan. However, a CBCT image could be beneficial for localizing impacted teeth. Extractions of impacted man-dibular third molars often are complicated by their proximity to the inferior alveolar canal. Relying on a conventional two‐dimensional panoramic image or intraoral periapical image may inadequately relate the impacted tooth to the canal. Cross‐sectional views will more accurately relate the positions of the two objects to one another (Fig.M32). In addition, the clinician will obtain supplemental infor-mation as to whether a buccal or lingual approach would be best to access the tooth.ABCFig.M29 Osteosarcoma with classic sunburst appearance of the anterior aspect of the mandible. A. Lateral view. B.Three‐dimensional rendering of the afflicted area. C. Cross-sectional view.Fig.M30 Osteochondroma. (Source: Courtesy of Dr. G. Klasser.)http://dentalebooks.com 94 Fundamentals of Oral and Maxillofacial RadiologyOrthodonticsCone beam computed tomography imaging can supplement cephalographic and pano-ramic images for treatment planning (Fig.M33), but it should not be standard protocol for all patients. A CBCT scan is particularly useful when it may be impossible for a clinician to visualize the positional relationships of unerupted teeth using two‐dimensional con-ventional images. Multiplanar images from CBCT scans will supply the clinician much more detailed relational information critical to the treatment.EndodonticsCone beam computed tomography imaging is useful for locating accessory canals, fractures and localization of apical pathology. For exam-ple, a periapical image may reveal a radiolucent lesion that appears to envelope multiple roots. However, a cross‐sectional image may reveal Fig.M32 Impaction. Coronal slices reveal the relationship of crown no. 17 with the unilocular radiolucency and the mandibular canal (highlighted)Fig.M31 Coronal view of metastatic carcinoma affecting the right condyle versus an unaffected condyle on the image labeled “left.”http://dentalebooks.com M Extraoral Imaging Techniques 95that the radiolucency is actually attached to only a single root which will then alter the treat-ment. CBCT x‐ray units designed to image a single quadrant with a small FOV (e.g. 5 cm) is ideally suited for endodontic procedures (Fig. M34). It reduces overall scatter radiation and exposes the patient to significantly less radiation compared with other scans.Fig.M33 Cephalograph reconstruction (CBCT).Fig.M34 Small field of view resulting in reduced patient exposure and fewer artifacts.http://dentalebooks.com Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/hubar/radiology96Quality AssuranceN”Quality assurance” (QA) is defined in the Merriam‐Webster dictionary as a program for the systematic monitoring and evaluation of the various aspects of a service or a facility to ensure that standards of quality are being met. Radiologic quality assurance in a dental prac-tice refers to the proper functioning of all x‐ray equipment to acquire optimum diagnostic images with minimal radiation exposure to the patient, dental office personnel and the general public. Radiation safety within a dental office is the responsibility of the dentist.All x‐ray machines must be periodically inspected for QA either by a state radiation safety inspector or by a private dental service company. There are simple and relatively inexpensive testing procedures that are used to identify problems with all forms of dental x‐ray equipment. These tests and the subse-quent corrections must be performed to avoid subjecting a patient to unnecessary radiation exposure. QA also helps to improve the diag-nostic quality of the resultant x‐ray images. Inspectors will measure the consistency and quantity of radiation output from each x‐ray unit, analyze the collimation and alignment of the beam of radiation and test the accuracy and reproducibility of the exposure timer. All x‐ray equipment sold in the United States must meet minimum beam filtration standards and therefore is unlikely to need correction. For extraoral units such as panoramic x‐ray units, measurements of the slit beam will also be necessary.http://dentalebooks.com Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/hubar/radiology97Infection ControlOUniversal infection control guidelines must be followed by all dental personnel to protect cross‐contamination between patients and between patients and dental healthcare workers. After the recognition of AIDS in the 1980s, infection control procedures became prioritized. Some of the other more common transmissible infections include hepatitis, tuberculosis and herpes. These guidelines are necessary to protect all individ-uals from exposure to disease spread by blood and bodily fluids. Both the American Dental Association (ADA) and the Centers for Disease Control and Prevention (CDC) recommend universal precautions for everyone as many patients may fail to report their illnesses to the dentist or may not even be aware that they are infected at the time of their appointment. The placement of receptors intraorally by an operator and then the handling of the tubehead and con-trol panel results in numerous avenues for cross‐contamination to occur in a dental operatory while performing routine imaging procedures.Excerpt from“CDC Guidelines forInfection Control inDental Health‐Care Settings”When taking radiographs, the potential to cross‐contaminate equipment and environmental surfaces with blood or saliva is high if aseptic technique is not practiced. Gloves should be worn when taking radiographs and handling contaminated film packets. Other PPE (e.g. mask, protec-tive eyewear, and gowns) should be used if spattering of blood or other body fluids is likely. Heat‐tolerant versions of intraoral radiograph accessories are available and these semi‐critical items (e.g. film holding and positioning devices) should be heat sterilized before patient use.Protective barriers should be used, or any surfaces that become contaminated should be cleaned and disinfected with an EPA registered hospital disinfectant of low‐ (HIV and HBV claim) to intermediate‐level (tuberculocidal claim) activity. Radiography equipment (e.g. radiograph tubehead and control panel) should be protected with surface barriers that are changed after each patient. If barri-ers are not used, equipment that has come into contact with DHCP’s gloved hands should be cleaned and then disinfected after each patient use.Digital radiography receptors and other high‐technology instruments (e.g. intraoral camera, electronic periodontal probe, occlusal analyzers, and lasers) come into contact with mucous membranes and are considered semi‐critical devices. They should be cleaned and ideally heat‐sterilized for high level disinfection between patients. However, these items vary by manufacturer or type of device in their ability to be sterilized or high‐level disinfected. Semi‐critical items that cannot be reprocessed by heat sterilization or high‐level disinfection should, at a minimum, be barrier protected by using an FDA cleared barrier to reduce gross contamination during use. Use of a barrier does not always protect from contamination. One study determined that a brand of commercially available plastic barriers used to protect dental digital radiography receptors failed at a substantial rate (44%). This rate dropped to 6% when latex finger cots were used in conjunction with the plastic http://dentalebooks.com 98 Fundamentals of Oral and Maxillofacial Radiologybarrier. To minimize the potential for device‐associated infections, after removing the barrier, the device should be cleaned and disinfected with an EPA registered hospital disinfectant (intermediate‐level) after each patient. Manufacturers should be consulted regarding appropriate barrier and disinfection/sterilization procedures for digital radiography receptors, other high technology intraoral devices and computer components.Source: Kohn et al. (2003)All dental personnel directly involved with patient care must wear protective clothing (Fig.O1). Disposable or non‐disposable gowns must be long‐sleeved, at least three‐quarter in length, and have a closed collar. In addition, disposable protective gloves should always be worn by the operator during receptor and tubehead placement to minimize risks to the operator and patient. It is recommended that gloves not be put on until after the patient is seated in the operatory. After seating the patient, it is recommended that the operator first wash their hands and then glove up in full view of the patient. Gloving up in front of the patient assures the patient that the opera-tor’s gloves are fresh, not having been worn whilst treating a prior patient. Similarly, all x‐ray instrumentation should be unpackaged in open view of the patient to reassure the patient that everything is sterile. For intraoral and extraoral imaging procedures, aerosols are not generated but exposure to bodily fluids is still unavoidable. Consequently, operators may also wish to wear protective eyewear and a mask or face shield. Image receptors must be covered with disposable plastic non‐permeable wraps (Fig.O2).General instructions forcleaning anddisinfecting asolid‐state receptor (courtesy ofSirona™)Unless the manufacturer states differently, the cable should remain attached to the receptor. Similarly, for wireless receptors, the battery pack should be removed from the receptor and cleaned separately, following the same steps as the receptor. Exercise care when cleaning around the battery contacts to avoid damaging them.Fig.O1 Operator in full infection control compliance: wearing a long sleeve gown, disposable gloves, face mask and protective eyewear. The patient is wearing a protective apron with thyroid collar.http://dentalebooks.com O Infection Control 99Before using a receptor the first time and before every new patient, the following protocol is recommended:1. Remove and discard all protective hygienic barriers and/or sheaths from the receptor prior to removing disposable gloves.2. Place the receptor on a tray covered by a dis-posable liner, or in a receptacle that can be thoroughly disinfected.3. Remove and discard gloves.4. Wash hands and put on a new pair of dis-posable gloves.5. Disconnect the receptor from the remote module.6. If the receptor or cable are visibly soiled (e.g. blood or saliva contamination), each should be cleaned with a soapy cloth or paper towel, and then dried with a clean lint‐free cloth or paper towel.7. Thoroughly wipe the receptor and cable (ifapplicable) with a disinfecting product. Do not expose the contacts of the receptor/remote module connection to liquid.8. Repeat step 7. When the receptor has been wiped two times, continue with the following steps.9. Remove potential chemical build‐up from the receptor by wiping it with a sterile lap sponge saturated with de‐ionized water.10. Use a sterile dry lap sponge to dry the receptor or cable, as needed.11. Place the receptor in a clean environment, ready for next use.12. Reconnect the receptor.13. Remove and card gloves.Fig.O2 Intraoral receptor holder attached to a direct dental receptor inside a protective infection control barrier cover.http://dentalebooks.com Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/hubar/radiology100Occupational Radiation Exposure MonitoringPWho should bemonitored?Occupational Safety and Health Administration (OSHA) regulations state that anyone who is occupationally exposed to x rays and could potentially receive more than 25% of the quar-terly occupational dose limit, are required to wear a dosimeter (29 CFR 1910.1096(d)(2)(i)). The NCRP (1998) recommends that all person-nel who are likely to receive an effective dose greater than 1 mSv per year be monitored. If an operator follows normal radiation safety pre-cautions (i.e. avoid being in the primary beam, standing at least 2 m from the source or behind a barrier, etc.) the number of dental workers who exceed this dose will be very few.How is radiation exposure monitored?A personal dosimetry badge is worn by dental personnel for recording cumulative x‐radiation dose in the workplace (see Fig. G10). After a specified period of time, the badge must be returned to the monitoring service provider for reading. The time interval can vary (e.g. 1 week, 1 month, 3 months, etc.). Three months is a practical time interval for many dental offices (exception: see question about pregnant worker). A written report for each dosimeter will be issued by the monitoring provider.Who monitors dental radiation exposure?A number of different companies offer moni-toring services for dental office personnel. A nominal fee is charged for each radiation dosimetry badge.Why should office personnel bemonitored?All ionizing radiation is harmful.What happens if my radiation exposure report exceeds themaximum exposure dose permitted?If a radiation badge records a dose in excess of that recommended by either the OSHA or the NCRP, the individual involved must be http://dentalebooks.com P Occupational Radiation Exposure Monitoring 101informed about the dose and an investigation will need to be undertaken to determine the cause. The individual may be temporarily pro-hibited from working around x‐ray equipment. The dosimetry results are taken very seriously by OSHA, so fellow co‐workers should not play pranks by removing another employee’s badge and intentionally exposing it to radiation.How is apregnant employee monitored forradiation exposure?In addition to the standard radiation badge, a supplemental fetal radiation badge should be worn for monitoring radiation dose to the fetus over the term of the pregnancy. A preg-nant employee should be monitored on a monthly basis for the term of the pregnancy.I work at thefront desk away fromthedental x‐ray unit. Why should Ibemonitored?All personnel should be monitored for a mini-mum of 1 year to ensure that the readings do not exceed the minimum set by the OSHA and NCRP. This includes front desk receptionists, business managers and laboratory technicians within the dental office.How long do Ineed tobemonitored?For new or relocated x‐ray equipment, the pro-prietor shall provide personal radiation badges for at least 1 year to assess and document doses to all personnel. However, if the work environ-ment changes regarding x‐ray exposure for that employee, then monitoring should be reinsti-tuted for another period of time until the radia-tion exposure levels are reported to be negligible. New operators of hand‐held x‐ray units should be monitored for 1 year. If the dosimetry badge reports repeatedly show negligible exposure, the proprietor may decide to discontinue moni-toring after 1 year (see question about pregnant worker).How long should theoffice keep radiation exposure records?Records should be kept permanently. This pro-tects the dental proprietor from possible future litigation. A former employee years later may develop an illness that he or she may attempt to link back to employment in the dental office as the root cause. A dosimetry report would be a beneficial piece of evidence to help exonerate the dentist in this situation.When should radiation badges not beworn?A radiation badge is not to be worn when the wearer is subjected to diagnostic exposures as a patient and it should not be worn outside the dental office. Whenever a radiation badge is not worn, it should be stored in a radiation‐safe area. Tampering with or use of radiation badges for any purposes other than those intended cannot be condoned.http://dentalebooks.com Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/hubar/radiology102Hand‐held X‐ray SystemsQPortable x‐ray units for commercial use have been manufactured for many decades. The Fexitron 845 was a portable x‐ray generator manufactured by the Field Emission Corpo-ration (McMinnville, OR) in the 1960s. This unit was bulky, heavy and unsuitable for intraoral imaging. Today many companies manufacture hand‐held intraoral x‐ray units. They are small, lightweight and often resemble a cordless power drill (Fig. Q1). Contrary to a traditional wall‐mounted x‐ray unit where the operator can be protected by distance and physical barriers, a well‐designed hand‐held system must incorpo-rate additional shielding to minimize the dose to the hands and body of the operator.Dental radiographic examinations: recommendations forpatient selection andlimiting radiation exposureHand‐held, battery‐powered x‐ray systems are available for intra‐oral radiographic imaging. The hand‐held exposure device is activated by a trigger on the handle of the device. However, dosimetry studies indicate that these hand‐held devices present no greater radiation risk than standard dental radiographic units to the patient or the operator. No additional radiation protection precautions are needed when the device is used according to the manufacturer’s instructions. These include: 1. holding the device at mid‐torso height, 2. orienting the shielding ring properly with respect to the operator, and 3. keeping the cone as close to the patient’s face as practical. If the hand‐held device is operated without the ring shield in place, it is recommended that the operator wear a lead apron.All operators of hand‐held units should be instructed on their proper storage. Due to the portable nature of these devices, they should be secured properly when not in use to prevent accidental damage, theft, or operation by an unauthorized user. Hand‐held units should be stored in locked cabinets, locked storage rooms, or locked work areas when not under the direct supervision of an indi-vidual authorized to use them. Units with user‐removable batteries should be stored with the batteries removed. Records listing the names of approved individuals who are granted access and use privileges should be prepared and kept current.Source: American Dental Association (2012)CommentaryThere are several scenarios in which the use of a hand‐held x‐ray unit is advantageous. Examples include treating patients in confined spaces such as a mobile dental clinic, patients under sedation who are unresponsive and for operators conducting forensic work at disaster sites. For all of these situations, it would either be impractical or impossible to use a fixed dental x‐ray unit.http://dentalebooks.com Q Hand‐held X‐ray Systems 103The NCRP and the ADA both condone the use of hand‐held x‐ray units. However it is the opinion of this author that because of unknown risks associated with repeated low doses of radiation to the operator, dental offices should continue to use fixed x‐ray units. Fixed dental x‐ray units result in lower radiation exposure to the operator by using remote activation (i.e. operator standing outside the operatory during the exposure). A fixed unit also offers greater flexibility in selecting exposure settings which can produce a better diagnostic image. Whenever it is possible, the operator should use a fixed dental x‐ray unit.Fig.Q1 NOMAD Pro™ hand‐held (portable) x‐ray unit.http://dentalebooks.com Part Two Interpretationhttp://dentalebooks.com Fundamentals of Oral and Maxillofacial Radiology, First Edition. J. Sean Hubar. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc. Companion website: www.wiley.com/go/hubar/radiology107Localization ofObjects (SLOB Rule)RStandard intraoral periapical and bitewing images only offer two‐dimensional anterior–posterior and superior–inferior perspectives. Localization of foreign objects and impacted teeth, differentiating a buccal versus lingual canal in a single root during endodontic procedures, etc. all require a bucco‐lingual per-spective. An occlusal image taken in conjunc-tion with routine periapical and bitewing images can possibly offer the practitioner such a bucco‐lingual perspective. Superimposition of anatomic structures and distortion of the image are both inherent problems with the occlusal technique that often obfuscate the image.In lieu of using CBCT imaging, an alterna-tive intraoral technique for object localization is the tube‐shift method. It goes by different terms, including Clark’s rule, the buccal object rule andthe SLOB rule. “SLOB” is an acronym for same–lingual, opposite–buccal. C. A. Clark first described this technique back in 1909, thus the eponym “Clark’s rule.” This should not be confused with the unrelated medical term, Clark’s rule, which is a formula to calculate medicine dosage for children.The principle of the tube‐shift technique simply requires exposing two different angulated intraoral x‐ray images of one area. The first image acts as a reference image. The horizontal or vertical angulation of the PID is then modified prior to taking a second image of the same area (FigsR1 and R2). Comparison of the two images for positional changes of the object of interest will determine if it is located more towards the buccal or lingual aspect. For example, if the PID is horizontally shifted mesi-ally in comparison to the first image and the object in question appears to move distally (i.e. in the opposite direction to the PID), the object of interest is positioned on the buccal side. If the object of interest moves in the same direction as the PID, then the object is positioned towards the lingual side. Conversely, if the PID is hori-zontally shifted distally in comparison to the first image and the object moves mesially, the object of interest is positioned on the buccal.The same principle applies in a vertical shift mode. For example, if the PID is shifted superi-orly in comparison to the reference image and the object in question appears to move inferi-orly (i.e. in the opposite direction to the PID), the object of interest is positioned on the buccal side. If the object of interest moves in the same direction as the PID, then the object is posi-tioned more towards the lingual side. Conversely, if the PID is shifted inferiorly in http://dentalebooks.com 108 Fundamentals of Oral and Maxillofacial RadiologyFig.R1 (a) Illustration of the SLOB rule: horizontal angulation shift of the PID. A. Central ray directed perpendicular to the receptor superimposes both objects ( B). B. Central ray directed from posterior position projects B anteriorly (i.e. opposite direction). C. Central ray directed from the anterior position projects B posteriorly (i.e. opposite direction). Conclusion: B is on the buccal and is on the lingual. (b)A.Central lateral view (nos 7 and 8). B.Horizontal shift of the PID (nos 8 and9) resulted in a shift of the mesiodens to the patient’s left. C. Further horizontal shift of the PID (nos 9 and 10) resulted in a further shift of the mesiodens in the same direction. Conclusion: the mesiodens is on the lingual aspect.A(a)BCCentral rayBBBuccalBuccalBuccalX-ray imageBBCentral rayCentral rayBBObject on lingual sideObject on buccal sideABC(b)http://dentalebooks.com

Related Articles

Leave A Comment?