Preliminary Considerations for Operative Dentistry










e1
14
Instruments and Equipment for
Tooth Preparation
TERENCE E. DONOVAN, LEE W. BOUSHELL, R. SCOTT EIDSON
a
R
emoval and shaping of tooth structures are essential aspects
of restorative dentistry. Initially, this was a dicult process
accomplished entirely by the use of hand instruments. e
introduction of rotary-powered cutting equipment was a major
advance in dentistry. From the time of the rst hand-powered
dental drill to the present-day air-driven and electric handpiece,
tremendous strides have been made in the mechanical alteration
of tooth structure and in the ease with which teeth may be restored.
Modern high-speed equipment has eliminated the need for many
hand instruments for tooth preparation. Nevertheless, hand instru-
ments remain an essential part of the armamentarium for restorative
dentistry.
Hand Instruments for Cutting
e early hand-operated instruments—with their large, heavy
handles (Fig. 14.1) and inferior (by present standards) metal alloys
in the blades—were cumbersome, awkward to use, and ineective
in many situations. As the commercial manufacture of hand
instruments increased and dentists began to express ideas about
tooth preparation, it became apparent that some scheme for
identifying these instruments was necessary. Among his many
contributions to modern dentistry, Black is credited with the rst
acceptable nomenclature for and classication of hand instruments.
1
His classication system enabled dentists and manufacturers to
communicate more clearly and eectively about instrument design
and function.
Modern hand instruments, when properly used, produce
benecial results for the operator and the patient. Some results
may only be satisfactorily achieved with hand instruments (i.e.,
not with rotary instruments). Preparation form dictates some
circumstances in which hand instruments are to be used, whereas
accessibility dictates others.
Terminology and Classication
Categories
Hand instruments used in the dental operatory may be categorized
as (1) cutting (excavators, chisels, and others) or (2) noncutting
(amalgam condensers, mirrors, explorers, probes).
1
Excavators may
be subdivided further into ordinary hatchets, hoes, angle formers,
and spoons. Chisels are primarily used for cutting enamel and
may be subdivided further into straight chisels, curved chisels,
bin-angle chisels, enamel hatchets, and gingival margin trimmers.
Other cutting instruments may be subdivided as knives, les, scalers,
and carvers.
Design
Most hand instruments, regardless of use, are composed of three
parts: handle, shank, and blade. For many noncutting instruments,
the part corresponding to the blade is termed nib. e end of the
nib, or working surface, is known as face. e blade or nib is the
working end of the instrument and is connected to the handle by
the shank. Some instruments have a blade on both ends of the
handle and are known as double-ended instruments (Fig. 14.2).
e blades are of many designs and sizes, depending on their
functions.
Handles are available in various sizes and shapes. Early
hand instruments had handles of quite large diameter and were
grasped in the palm of the hand. A large, heavy handle is not
always conducive to delicate manipulation. In North America,
most instrument handles are small in diameter (5.5 mm) and
light. ey are commonly eight-sided and knurled to facilitate
control. In Europe, the handles are often larger in diameter and
tapered.
Shanks, which serve to connect the handles to the working
ends of the instruments, are normally smooth, round, and tapered.
ey often have one or more bends to overcome the tendency of
the instrument to twist while in use when force is applied.
Enamel and dentin are dicult substances to cut and require
the generation of substantial forces at the tip of the instrument.
erefore, cutting hand instruments must be balanced and sharp.
Balance allows for the concentration of force onto the blade
without causing rotation of the instrument in the operator’s grasp.
Sharpness concentrates the force onto a small area of the edge,
producing high stress and resultant ability to remove/modify tooth
structure.
Balance is accomplished by designing the angles of the shank
so that the cutting edge of the blade lies within the projected
diameter of the handle and nearly coincides with the projected
long axis of the handle (
Fig. 14.3; see also Fig. 14.2). For optimal
antirotational design, the blade edge must not be positioned away
from the axis by more than 1 to 2 mm. All dental instruments
and equipment need to satisfy this principle of balance.
a
Dr Eidson was an inactive author in this edition.

e2 CHAPTER 14 Instruments and Equipment for Tooth Preparation
Formulas
Cutting instruments have formulas describing the dimensions and
angles of the working end. ese are placed on the handle using
a code of three or four numbers separated by dashes or spaces
(e.g., 10–85–8–14) (Fig. 14.4; see also Fig. 14.3). e rst number
indicates the width of the blade or primary cutting edge in tenths
of a millimeter (0.1 mm) (e.g., 10 = 1 mm). e second number
of a four-number code indicates the primary cutting edge angle,
measured from a line parallel to the long axis of the instrument
handle in clockwise centigrade. e centigrade angle is expressed
as a percent of 360 degrees (e.g., 85 = 85% × 360 degrees = 306
degrees). e instrument is positioned so that this number always
exceeds 50. If the edge is locally perpendicular to the blade, this
number is normally omitted, resulting in a three-number code
(see Fig. 14.4). e third number (second number of a three-number
code) indicates the blade length in millimeters (e.g., 8 = 8 mm).
e fourth number (third number of a three-number code) indicates
the blade angle, relative to the long axis of the handle in clockwise
centigrade (e.g., 14 = 50.4 degrees). e instrument is positioned
such that this number is always 50 or less. e most commonly
used hand instruments, including those specied in this text, are
shown in Figs. 14.5, 14.6, 14.7, 14.8, and 14.9.
In some instances, an additional number on the handle is the
manufacturers identication number (see Fig. 14.4). Identication
numbers are included to assist specic manufacturers in cataloging
and should not be confused with formula numbers.
Bevels
Most hand-cutting instruments have a single bevel on the end of
the blade that forms the primary cutting edge. Two additional bevels
Shank Angles
e functional orientation and length of the blade determine
the number of angles in the shank necessary to balance the
instrument. Black classified instruments on the basis of the
number of shank angles as mon-angle (one), bin-angle (two),
or triple-angle (three).
2
Instruments with small, short blades
may be easily designed in mon-angle form while conning the
cutting edge within the limits required for balance and control.
Instruments with longer blades or more complex orientations may
require two or three angles in the shank to bring the cutting
edge close to the long axis of the handle. Such shanks are termed
contra-angled.
Names
Black classied all of the instruments by name.
2
In addition, for
hand-cutting instruments, he developed a numeric formula to
characterize the dimensions and angles of the working end (see
the next section for details of the formula). Blacks classication
system by instrument name categorized instruments by (1)
function (e.g., scaler, excavator), (2) manner of use (e.g., hand
condenser), (3) design of the working end (e.g., spoon excava-
tor, sickle scaler), or (4) shape of the shank (e.g., mon-angle,
bin-angle, contra-angle).
2
ese names were combined to form
the complete description of the instrument (e.g., bin-angle spoon
excavator).
Fig. 14.1 Designs of some early hand instruments. These instruments
were individually handmade, variable in design, and cumbersome to use.
Because of the nature of the handles, effective sterilization was a problem.
ab
cb
a
Fig. 14.2 Double-ended instrument illustrating three component parts
of hand instruments: blade (A), shank (B), and handle (C). (Modied from
Boyd LRB: Dental instruments: a pocket guide, ed 4, St. Louis, 2012,
Saunders.)
3
4
1
2
Long axis
of instrument
10-85-8-14
Fig. 14.3 Instrument shank and blade design (with primary cutting
edge positioned close to handle axis to aid in limiting unwanted instrument
rotation). The complete instrument formula (four numbers) is expressed
as the blade width (1) in 0.1-mm increments, cutting edge angle (2) in
centigrades, blade length (3) in millimeters, and blade angle (4) in
centigrades.

CHAPTER 14 Instruments and Equipment for Tooth Preparation e3
Fig. 14.4 Examples of instruments with three-number and four-num-
ber instrument formulas.
Secondary cutting edge
Secondary cutting edge
Primary
cutting
edge
Fig. 14.5 Chisel blade design showing primary and secondary cutting
edges.
Inside surface
Inside surface
A
B
C
Fig. 14.6 Examples of hand instruments called excavators. A, Bi-
beveled ordinary hatchet. B, Hoe with distal bevel. C, Angle former with
distal bevel.
A
B
C
Fig. 14.7 Examples of hand instruments called spoon excavators. A,
Bin-angle spoon. B, Triple-angle spoon. C, Spoon.
A
B
C
Fig. 14.8 Examples of hand instruments called chisels. A, Enamel
hatchet. B, Gingival margin trimmer. C, Gingival margin trimmer.
Outside surface
Outside surface
Mesial
A
B
C
Fig. 14.9 Examples of hand instruments called chisels. A, Straight.
B, Wedelstaedt with mesial bevel. C, Bin-angle with mesial bevel.

e4 CHAPTER 14 Instruments and Equipment for Tooth Preparation
Excavators
e four subdivisions of excavators are (1) ordinary hatchets, (2)
hoes, (3) angle formers, and (4) spoons. An ordinary hatchet
excavator has the cutting edge of the blade directed in the same
plane as that of the long axis of the handle and is bi-beveled (see
Fig. 14.6A). ese instruments are used primarily on anterior teeth
for preparing retentive areas and sharpening internal line angles,
particularly in preparation for direct gold restorations.
e hoe excavator has the primary cutting edge of the blade
perpendicular to the axis of the handle (see Fig. 14.6B). is type
of instrument is used for planing tooth preparation walls and for
forming line angles. It is commonly used in Class III and V
preparations so as to ensure removal of any unsupported enamel
prior to restoration with amalgam and composite and is especially
useful in preparations to be restored with direct gold. Some sets
of cutting instruments contain hoes with contra-angled shanks
and long, heavy blades. ese are intended for use on the prepared
enamel walls of posterior teeth.
A special type of excavator is the angle former (see Fig. 14.6C).
It is used primarily for sharpening line angles and creating retentive
features in dentin in preparation for gold restorations. It also may
be used when placing a bevel on enamel margins. e angle former
is mon-angled and has the primary cutting edge at an angle (other
than 90 degrees) to the blade. It may be described as a combination
of a chisel and a gingival margin trimmer and is available in pairs
(right and left).
Spoon excavators (see Fig. 14.7) are used for removing soft
carious tissue and carving amalgam or direct wax patterns. e
shanks may be bin-angled or triple-angled to facilitate access to
various anatomical areas.
Chisels
Chisels are intended primarily for cutting enamel and may be
grouped as (1) straight, slightly curved, or bin-angle; (2) enamel
hatchets; and (3) gingival margin trimmers. e straight chisel has
a straight shank and blade, with the bevel on only one side. Its
primary cutting edge is perpendicular to the axis of the handle. It
is similar in design to a carpenter’s wood chisel (see Fig. 14.9A).
e shank and blade of the chisel also may be slightly curved
(Wedelstaedt design) (see Fig. 14.9B) or may be bin-angled (see
Fig. 14.9C). e force used with chisels is essentially a straight
thrust or a pushing motion. A right or left type is not needed
in a straight chisel because a 180-degree turn of the instrument
allows for its use on either side of the preparation. e bin-angle
and Wedelstaedt chisels have the primary cutting edges in a plane
perpendicular to the axis of the handle and may have either a distal
bevel or a mesial (reverse) bevel. e blade with a distal bevel is
designed to plane a wall that faces the blades inside surface (see Fig.
14.6B and C). e blade with a mesial bevel is designed to plane
a wall that faces the blades outside surface (see Fig. 14.9B and C).
e enamel hatchet is a chisel similar in design to the ordinary
hatchet except that the blade is larger, heavier, and beveled on
only one side (see Fig. 14.8A). It has its cutting edges in a plane
that is parallel with the axis of the handle. It is used for cutting
enamel and comes as right or left types for use on opposite sides
of the preparation.
e gingival margin trimmer is designed to eliminate unsup-
ported enamel on gingival walls of proximal preparations. It is
similar in design to the enamel hatchet except the blade is curved
and the primary cutting edge is at an angle (other than perpen-
dicular) to the axis of the blade (see
Fig. 14.8B and C). It is made
as right and left types. e gingival margin trimmer may be designed
form secondary cutting edges and extend from the primary edge for
the length of the blade (see
Fig. 14.5). Bi-beveled instruments
such as ordinary hatchets have two bevels that form the cutting
edge (see Fig. 14.6A).
Certain single-beveled instruments, such as spoon excavators
(see Fig. 14.7) and gingival margin trimmers (see Fig. 14.8B and
C), are used with a scraping or lateral cutting motion. Enamel
hatchets (see Fig. 14.8A) may be used with a planing, direct cutting
motion and lateral cutting motion. Hatches have the primary
cutting edge aligned parallel with the long axis of the handle.
Single-beveled designs require that the instruments be made
in pairs, with the bevels on opposite sides of the blade. ese
instruments are designated as right beveled or left beveled and
are indicated by appending the letter R or L to the instrument
formula. To determine whether the instrument has a right or
left bevel, the primary cutting edge is held down and pointing
away, and if the bevel appears on the right side of the blade, it
is the right instrument of the pair. is instrument, when used
in a scraping motion, is moved from right to left. e opposite
holds true for the left instrument of the pair. One instrument
is suited for work on one side of the preparation and the other
is suited for the opposite side of the preparation. e primary
cutting edge of the hatchet may be useful for planing the facial
and lingual walls of proximal preparations by using a pushing
motion and the gingival wall by using a lateral motion. In addition,
the secondary cutting edge of the enamel hatchet may be useful
for planing the occlusal and gingival walls of posterior Class V
preparations.
Most instruments are available with blades and shanks on both
ends of the handle. Such instruments are termed double ended. In
many cases, the right instrument of the pair is on one end of the
handle and the left instrument is on the other end. Occasionally
similar blades of dierent widths are placed on a single double-ended
instrument. If one observes the inside of the blade curvature (or
the inside of the angle at the junction of the blade and shank)
and the primary bevel is not visible, the instrument has a distal
bevel (see Fig. 14.6). Conversely, if the primary bevel is seen (from
the same viewpoint), the instrument has a mesial (or “reverse”)
bevel (see Fig. 14.9).
Instruments having the primary cutting edge perpendicular to
the axis of the handle are generally termed chisels (see Fig. 14.9).
Examples include bin-angle chisels (see Fig. 14.9C), instruments
with a slight blade curvature (Wedelstaedt chisels) (see Fig. 14.9B),
and hoes (see Fig. 14.6B), which are single beveled and not des-
ignated as right or left but as having a mesial bevel or a distal
bevel. e primary cutting edge of chisels may be useful in planing
the occlusal and gingival walls of posterior Class V preparations
by using a pushing and/or pulling motion. e primary cutting
edge of the hoe is particularly useful for planing the occlusal and
gingival walls of Class III preparations. e secondary cutting edge
of the hoe is useful for planing the occlusal and gingival walls of
Class V preparations as well as walls oriented in an axial direction.
Note that hoes may also serve as excavators (see discussion later
in text).
Applications
Cutting instruments are used to cut enamel/dentin and restorative
materials. Excavators are used for removal of carious tissue, rene-
ment of the internal aspects of the preparation, and establishment
of correct anatomical restoration form. Chisels are used primarily
for cutting enamel.

CHAPTER 14 Instruments and Equipment for Tooth Preparation e5
applied through the blade to the area requiring modication. e
instrument should cross over the proximal phalange of the index
nger and should not cross over at the junction area of the thumb
and index nger as in the conventional pen grasp (contrast Fig.
14.11A with B). A balanced instrument design allows the application
of suitable force without the instrument tending to rotate in the
ngers (see Fig. 14.3).
Inverted Pen Grasp
e nger positions of the inverted pen grasp are the same as for
the modied pen grasp. e hand is rotated, however, so that the
palm faces more toward the operator (Fig. 14.12). is grasp is
used mostly for tooth preparations employing the lingual approach
on anterior teeth.
e modied pen and inverted pen grasps are the primary
grasps used in the preparation and direct restoration of teeth.
Palm-and-Thumb Grasp
e palm-and-thumb grasp is similar to that used for holding a
knife while paring an apple. e handle is placed in the palm of
to aord access to mesial or distal gingival walls. When the second
number in the instrument formula (found on the handle) is 90
to 100, the pair is used on the distal gingival preparation wall.
When the number is 75 to 85, the pair is used to remove unsup-
ported enamel on the mesial gingival wall of the preparation. e
90 and 85 pairs are for preparations for direct restorations and are
used to align the gingival wall so that it is perpendicular with the
external surface of the tooth structure (to ensure supported enamel).
Indirect gold restorations require the placement of a distinct bevel
associated with the gingival walls, and gingival margin trimmers
with 100-degree and 75-degree angle pairs are designed specically
for this purpose. Among other uses for these instruments is the
beveling (“blunting” or “rounding”) of the axiopulpal line angle
of two-surface preparations so as to limit areas of stress concentration
in subsequently placed restorations.
Other Cutting Instruments
Other hand-cutting instruments such as the knife, le, and discoid-
cleoid instrument are used for trimming restorative material rather
than for cutting tooth structure. Knives, known as nishing knives,
amalgam knives, or gold knives, are designed with a thin, knifelike
blade that is made in various sizes and shapes (Fig. 14.10A and
B). Knives are used for trimming excess restorative material on
the gingival, facial, or lingual margins of a proximal restoration
or trimming and contouring the surface of a Class V restoration.
Sharp secondary edges on the heel aspect of the blade are useful
in a scrape–pull mode.
Files (see Fig. 14.10C) also may be used to trim excess restorative
material and are particularly useful at gingival margins. e blades
of the le are extremely thin, and the teeth of the instrument on
the cutting surfaces are short and designed to make the le a push/
pull instrument. Files are manufactured in various shapes and
angles to enhance access to various restoration surfaces.
e discoid-cleoid (see Fig. 14.10D and E) instrument is used
principally for carving occlusal anatomy in unset amalgam restora-
tions. e blades are slightly curved and the cutting edges are
either circular or clawlike. e circular edge is known as a discoid,
whereas the clawlike blade is termed cleoid. It also may be used
to trim or burnish inlay–onlay margins. e working ends of this
instrument are usually larger than the discoid end of an excavator.
Hand Instrument Techniques
Four grasps are used with hand instruments: (1) modied pen,
(2) inverted pen, (3) palm-and-thumb, and (4) modied palm-
and-thumb. e conventional pen grasp is not an acceptable
instrument grasp (Fig. 14.11A).
Modied Pen Grasp
e grasp that permits the greatest control of the instrument,
while simultaneously maintaining ergonomic positioning of the
wrist and elbow, is the modied pen grasp (see Fig. 14.11B). As
the name implies, it is similar but not identical to that used in
holding a pen. e pads of the thumb and of the index and middle
ngers contact the instrument, while the tip of the ring nger (or
tips of the ring and little ngers) is placed on a nearby tooth
surface of the same arch as a rest. e palm of the hand generally
is facing away from the operator. e pad of the middle nger is
placed near the topside of the instrument; by this nger working
with the wrist and the forearm, cutting or cleaving pressure is
E
A
C
D
B
Secondary
edges
Primary
edge
Fig. 14.10 Examples of other hand instruments for cutting. A, Finish-
ing knife. B, Alternative nishing knife design emphasizing secondary
cutting edges. C, Dental le. D, Cleoid blade. E, Discoid blade carving
amalgam.

e6 CHAPTER 14 Instruments and Equipment for Tooth Preparation
Modied Palm-and-Thumb Grasp
e modied palm-and-thumb grasp may be used when it is feasible
to rest the thumb on the tooth being prepared or the adjacent
tooth (Fig. 14.14). e handle of the instrument is held by all
four ngers, whose pads press the handle against the distal area
of the palm and the pad and rst joint of the thumb. Grasping
the handle under the rst joints of the ring nger and little nger
provides stabilization and enables optimal control of the instrument.
e modied palm-and-thumb grasp usually is employed in the
area of the maxillary arch and is best adopted when the dentist is
operating from a rear-chair position.
Rests
A proper instrument grasp must include a rm rest to steady the
hand during operating procedures. When the modied pen and
inverted pen grasps are used, rests are established by placing the
ring nger (or both ring and little ngers) on a tooth (or teeth)
of the same arch and as close to the operating site as possible (see
Fig. 14.12). e closer the rest areas are to the operating area, the
Fig. 14.12 Inverted pen grasp. Palm faces more toward operator. The
rest is similar to that shown for modied pen grasp (see Fig. 14.11B).
(Courtesy Dr. Mohammad Atieh.)
Fig. 14.13 Palm-and-thumb grasp. This grasp has limited use, such
as preparing incisal retention in a Class III preparation on a maxillary
incisor. The rest is tip of thumb on tooth in same arch. (Courtesy Dr.
Mohammad Atieh.)
Fig. 14.14 Modied palm-and-thumb grasp. This modication allows
greater ease of instrument movement and greater instrument control
during pull stroke compared with palm-and-thumb grasp. The rest is tip
of thumb on tooth being prepared or adjacent tooth. Note how the instru-
ment is braced against pad and end joint of thumb. (Courtesy Dr. Moham-
mad Atieh.)
A
B
Fig. 14.11 Pen grasps. A, Conventional pen grasp. Side of middle
nger is on writing instrument. B, Modied pen grasp. Correct position of
middle nger is near the “topside” of the instrument for good control and
cutting pressure. The rest is tip (or tips) of ring nger (or ring and little
ngers) on tooth (or teeth) of same arch. (Courtesy Dr. Mohammad Atieh.)
the hand and grasped by all the ngers, while the thumb is free
of the instrument, and the rest is provided by supporting the tip
of the thumb on a nearby tooth of the same arch or on a rm,
stable structure. For suitable control, this grasp requires careful
use during cutting. An example of an appropriate use is holding
a handpiece for cutting incisal retention for a Class III preparation
on a maxillary incisor (
Fig. 14.13).

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e114 Instruments and Equipment for Tooth PreparationTERENCE E. DONOVAN, LEE W. BOUSHELL, R. SCOTT EIDSONaRemoval and shaping of tooth structures are essential aspects of restorative dentistry. Initially, this was a dicult process accomplished entirely by the use of hand instruments. e introduction of rotary-powered cutting equipment was a major advance in dentistry. From the time of the rst hand-powered dental drill to the present-day air-driven and electric handpiece, tremendous strides have been made in the mechanical alteration of tooth structure and in the ease with which teeth may be restored. Modern high-speed equipment has eliminated the need for many hand instruments for tooth preparation. Nevertheless, hand instru-ments remain an essential part of the armamentarium for restorative dentistry.Hand Instruments for Cuttinge early hand-operated instruments—with their large, heavy handles (Fig. 14.1) and inferior (by present standards) metal alloys in the blades—were cumbersome, awkward to use, and ineective in many situations. As the commercial manufacture of hand instruments increased and dentists began to express ideas about tooth preparation, it became apparent that some scheme for identifying these instruments was necessary. Among his many contributions to modern dentistry, Black is credited with the rst acceptable nomenclature for and classication of hand instruments.1 His classication system enabled dentists and manufacturers to communicate more clearly and eectively about instrument design and function.Modern hand instruments, when properly used, produce benecial results for the operator and the patient. Some results may only be satisfactorily achieved with hand instruments (i.e., not with rotary instruments). Preparation form dictates some circumstances in which hand instruments are to be used, whereas accessibility dictates others.Terminology and ClassicationCategoriesHand instruments used in the dental operatory may be categorized as (1) cutting (excavators, chisels, and others) or (2) noncutting (amalgam condensers, mirrors, explorers, probes).1 Excavators may be subdivided further into ordinary hatchets, hoes, angle formers, and spoons. Chisels are primarily used for cutting enamel and may be subdivided further into straight chisels, curved chisels, bin-angle chisels, enamel hatchets, and gingival margin trimmers. Other cutting instruments may be subdivided as knives, les, scalers, and carvers.DesignMost hand instruments, regardless of use, are composed of three parts: handle, shank, and blade. For many noncutting instruments, the part corresponding to the blade is termed nib. e end of the nib, or working surface, is known as face. e blade or nib is the working end of the instrument and is connected to the handle by the shank. Some instruments have a blade on both ends of the handle and are known as double-ended instruments (Fig. 14.2). e blades are of many designs and sizes, depending on their functions.Handles are available in various sizes and shapes. Early hand instruments had handles of quite large diameter and were grasped in the palm of the hand. A large, heavy handle is not always conducive to delicate manipulation. In North America, most instrument handles are small in diameter (5.5 mm) and light. ey are commonly eight-sided and knurled to facilitate control. In Europe, the handles are often larger in diameter and tapered.Shanks, which serve to connect the handles to the working ends of the instruments, are normally smooth, round, and tapered. ey often have one or more bends to overcome the tendency of the instrument to twist while in use when force is applied.Enamel and dentin are dicult substances to cut and require the generation of substantial forces at the tip of the instrument. erefore, cutting hand instruments must be balanced and sharp. Balance allows for the concentration of force onto the blade without causing rotation of the instrument in the operator’s grasp. Sharpness concentrates the force onto a small area of the edge, producing high stress and resultant ability to remove/modify tooth structure.Balance is accomplished by designing the angles of the shank so that the cutting edge of the blade lies within the projected diameter of the handle and nearly coincides with the projected long axis of the handle (Fig. 14.3; see also Fig. 14.2). For optimal antirotational design, the blade edge must not be positioned away from the axis by more than 1 to 2 mm. All dental instruments and equipment need to satisfy this principle of balance.aDr Eidson was an inactive author in this edition. e2 CHAPTER 14 Instruments and Equipment for Tooth Preparation FormulasCutting instruments have formulas describing the dimensions and angles of the working end. ese are placed on the handle using a code of three or four numbers separated by dashes or spaces (e.g., 10–85–8–14) (Fig. 14.4; see also Fig. 14.3). e rst number indicates the width of the blade or primary cutting edge in tenths of a millimeter (0.1 mm) (e.g., 10 = 1 mm). e second number of a four-number code indicates the primary cutting edge angle, measured from a line parallel to the long axis of the instrument handle in clockwise centigrade. e centigrade angle is expressed as a percent of 360 degrees (e.g., 85 = 85% × 360 degrees = 306 degrees). e instrument is positioned so that this number always exceeds 50. If the edge is locally perpendicular to the blade, this number is normally omitted, resulting in a three-number code (see Fig. 14.4). e third number (second number of a three-number code) indicates the blade length in millimeters (e.g., 8 = 8 mm). e fourth number (third number of a three-number code) indicates the blade angle, relative to the long axis of the handle in clockwise centigrade (e.g., 14 = 50.4 degrees). e instrument is positioned such that this number is always 50 or less. e most commonly used hand instruments, including those specied in this text, are shown in Figs. 14.5, 14.6, 14.7, 14.8, and 14.9.In some instances, an additional number on the handle is the manufacturer’s identication number (see Fig. 14.4). Identication numbers are included to assist specic manufacturers in cataloging and should not be confused with formula numbers.BevelsMost hand-cutting instruments have a single bevel on the end of the blade that forms the primary cutting edge. Two additional bevels Shank Anglese functional orientation and length of the blade determine the number of angles in the shank necessary to balance the instrument. Black classified instruments on the basis of the number of shank angles as mon-angle (one), bin-angle (two), or triple-angle (three).2 Instruments with small, short blades may be easily designed in mon-angle form while conning the cutting edge within the limits required for balance and control. Instruments with longer blades or more complex orientations may require two or three angles in the shank to bring the cutting edge close to the long axis of the handle. Such shanks are termed contra-angled.NamesBlack classied all of the instruments by name.2 In addition, for hand-cutting instruments, he developed a numeric formula to characterize the dimensions and angles of the working end (see the next section for details of the formula). Black’s classication system by instrument name categorized instruments by (1) function (e.g., scaler, excavator), (2) manner of use (e.g., hand condenser), (3) design of the working end (e.g., spoon excava-tor, sickle scaler), or (4) shape of the shank (e.g., mon-angle, bin-angle, contra-angle).2 ese names were combined to form the complete description of the instrument (e.g., bin-angle spoon excavator).• Fig. 14.1 Designs of some early hand instruments. These instruments were individually handmade, variable in design, and cumbersome to use. Because of the nature of the handles, effective sterilization was a problem. abcba• Fig. 14.2 Double-ended instrument illustrating three component parts of hand instruments: blade (A), shank (B), and handle (C). (Modied from Boyd LRB: Dental instruments: a pocket guide, ed 4, St. Louis, 2012, Saunders.)3412Long axisof instrument10-85-8-14• Fig. 14.3 Instrument shank and blade design (with primary cutting edge positioned close to handle axis to aid in limiting unwanted instrument rotation). The complete instrument formula (four numbers) is expressed as the blade width (1) in 0.1-mm increments, cutting edge angle (2) in centigrades, blade length (3) in millimeters, and blade angle (4) in centigrades. CHAPTER 14 Instruments and Equipment for Tooth Preparation e3 • Fig. 14.4 Examples of instruments with three-number and four-num-ber instrument formulas. Secondary cutting edgeSecondary cutting edgePrimarycuttingedge• Fig. 14.5 Chisel blade design showing primary and secondary cutting edges. Inside surfaceInside surfaceABC• Fig. 14.6 Examples of hand instruments called excavators. A, Bi-beveled ordinary hatchet. B, Hoe with distal bevel. C, Angle former with distal bevel. ABC• Fig. 14.7 Examples of hand instruments called spoon excavators. A, Bin-angle spoon. B, Triple-angle spoon. C, Spoon. ABC• Fig. 14.8 Examples of hand instruments called chisels. A, Enamel hatchet. B, Gingival margin trimmer. C, Gingival margin trimmer. Outside surfaceOutside surfaceMesialABC• Fig. 14.9 Examples of hand instruments called chisels. A, Straight. B, Wedelstaedt with mesial bevel. C, Bin-angle with mesial bevel. e4 CHAPTER 14 Instruments and Equipment for Tooth Preparation Excavatorse four subdivisions of excavators are (1) ordinary hatchets, (2) hoes, (3) angle formers, and (4) spoons. An ordinary hatchet excavator has the cutting edge of the blade directed in the same plane as that of the long axis of the handle and is bi-beveled (see Fig. 14.6A). ese instruments are used primarily on anterior teeth for preparing retentive areas and sharpening internal line angles, particularly in preparation for direct gold restorations.e hoe excavator has the primary cutting edge of the blade perpendicular to the axis of the handle (see Fig. 14.6B). is type of instrument is used for planing tooth preparation walls and for forming line angles. It is commonly used in Class III and V preparations so as to ensure removal of any unsupported enamel prior to restoration with amalgam and composite and is especially useful in preparations to be restored with direct gold. Some sets of cutting instruments contain hoes with contra-angled shanks and long, heavy blades. ese are intended for use on the prepared enamel walls of posterior teeth.A special type of excavator is the angle former (see Fig. 14.6C). It is used primarily for sharpening line angles and creating retentive features in dentin in preparation for gold restorations. It also may be used when placing a bevel on enamel margins. e angle former is mon-angled and has the primary cutting edge at an angle (other than 90 degrees) to the blade. It may be described as a combination of a chisel and a gingival margin trimmer and is available in pairs (right and left).Spoon excavators (see Fig. 14.7) are used for removing soft carious tissue and carving amalgam or direct wax patterns. e shanks may be bin-angled or triple-angled to facilitate access to various anatomical areas.ChiselsChisels are intended primarily for cutting enamel and may be grouped as (1) straight, slightly curved, or bin-angle; (2) enamel hatchets; and (3) gingival margin trimmers. e straight chisel has a straight shank and blade, with the bevel on only one side. Its primary cutting edge is perpendicular to the axis of the handle. It is similar in design to a carpenter’s wood chisel (see Fig. 14.9A). e shank and blade of the chisel also may be slightly curved (Wedelstaedt design) (see Fig. 14.9B) or may be bin-angled (see Fig. 14.9C). e force used with chisels is essentially a straight thrust or a pushing motion. A right or left type is not needed in a straight chisel because a 180-degree turn of the instrument allows for its use on either side of the preparation. e bin-angle and Wedelstaedt chisels have the primary cutting edges in a plane perpendicular to the axis of the handle and may have either a distal bevel or a mesial (reverse) bevel. e blade with a distal bevel is designed to plane a wall that faces the blade’s inside surface (see Fig. 14.6B and C). e blade with a mesial bevel is designed to plane a wall that faces the blade’s outside surface (see Fig. 14.9B and C).e enamel hatchet is a chisel similar in design to the ordinary hatchet except that the blade is larger, heavier, and beveled on only one side (see Fig. 14.8A). It has its cutting edges in a plane that is parallel with the axis of the handle. It is used for cutting enamel and comes as right or left types for use on opposite sides of the preparation.e gingival margin trimmer is designed to eliminate unsup-ported enamel on gingival walls of proximal preparations. It is similar in design to the enamel hatchet except the blade is curved and the primary cutting edge is at an angle (other than perpen-dicular) to the axis of the blade (see Fig. 14.8B and C). It is made as right and left types. e gingival margin trimmer may be designed form secondary cutting edges and extend from the primary edge for the length of the blade (see Fig. 14.5). Bi-beveled instruments such as ordinary hatchets have two bevels that form the cutting edge (see Fig. 14.6A).Certain single-beveled instruments, such as spoon excavators (see Fig. 14.7) and gingival margin trimmers (see Fig. 14.8B and C), are used with a scraping or lateral cutting motion. Enamel hatchets (see Fig. 14.8A) may be used with a planing, direct cutting motion and lateral cutting motion. Hatches have the primary cutting edge aligned parallel with the long axis of the handle. Single-beveled designs require that the instruments be made in pairs, with the bevels on opposite sides of the blade. ese instruments are designated as right beveled or left beveled and are indicated by appending the letter R or L to the instrument formula. To determine whether the instrument has a right or left bevel, the primary cutting edge is held down and pointing away, and if the bevel appears on the right side of the blade, it is the right instrument of the pair. is instrument, when used in a scraping motion, is moved from right to left. e opposite holds true for the left instrument of the pair. One instrument is suited for work on one side of the preparation and the other is suited for the opposite side of the preparation. e primary cutting edge of the hatchet may be useful for planing the facial and lingual walls of proximal preparations by using a pushing motion and the gingival wall by using a lateral motion. In addition, the secondary cutting edge of the enamel hatchet may be useful for planing the occlusal and gingival walls of posterior Class V preparations.Most instruments are available with blades and shanks on both ends of the handle. Such instruments are termed double ended. In many cases, the right instrument of the pair is on one end of the handle and the left instrument is on the other end. Occasionally similar blades of dierent widths are placed on a single double-ended instrument. If one observes the inside of the blade curvature (or the inside of the angle at the junction of the blade and shank) and the primary bevel is not visible, the instrument has a distal bevel (see Fig. 14.6). Conversely, if the primary bevel is seen (from the same viewpoint), the instrument has a mesial (or “reverse”) bevel (see Fig. 14.9).Instruments having the primary cutting edge perpendicular to the axis of the handle are generally termed chisels (see Fig. 14.9). Examples include bin-angle chisels (see Fig. 14.9C), instruments with a slight blade curvature (Wedelstaedt chisels) (see Fig. 14.9B), and hoes (see Fig. 14.6B), which are single beveled and not des-ignated as right or left but as having a mesial bevel or a distal bevel. e primary cutting edge of chisels may be useful in planing the occlusal and gingival walls of posterior Class V preparations by using a pushing and/or pulling motion. e primary cutting edge of the hoe is particularly useful for planing the occlusal and gingival walls of Class III preparations. e secondary cutting edge of the hoe is useful for planing the occlusal and gingival walls of Class V preparations as well as walls oriented in an axial direction. Note that hoes may also serve as excavators (see discussion later in text).ApplicationsCutting instruments are used to cut enamel/dentin and restorative materials. Excavators are used for removal of carious tissue, rene-ment of the internal aspects of the preparation, and establishment of correct anatomical restoration form. Chisels are used primarily for cutting enamel. CHAPTER 14 Instruments and Equipment for Tooth Preparation e5 applied through the blade to the area requiring modication. e instrument should cross over the proximal phalange of the index nger and should not cross over at the junction area of the thumb and index nger as in the conventional pen grasp (contrast Fig. 14.11A with B). A balanced instrument design allows the application of suitable force without the instrument tending to rotate in the ngers (see Fig. 14.3).Inverted Pen Graspe nger positions of the inverted pen grasp are the same as for the modied pen grasp. e hand is rotated, however, so that the palm faces more toward the operator (Fig. 14.12). is grasp is used mostly for tooth preparations employing the lingual approach on anterior teeth.e modied pen and inverted pen grasps are the primary grasps used in the preparation and direct restoration of teeth.Palm-and-Thumb Graspe palm-and-thumb grasp is similar to that used for holding a knife while paring an apple. e handle is placed in the palm of to aord access to mesial or distal gingival walls. When the second number in the instrument formula (found on the handle) is 90 to 100, the pair is used on the distal gingival preparation wall. When the number is 75 to 85, the pair is used to remove unsup-ported enamel on the mesial gingival wall of the preparation. e 90 and 85 pairs are for preparations for direct restorations and are used to align the gingival wall so that it is perpendicular with the external surface of the tooth structure (to ensure supported enamel). Indirect gold restorations require the placement of a distinct bevel associated with the gingival walls, and gingival margin trimmers with 100-degree and 75-degree angle pairs are designed specically for this purpose. Among other uses for these instruments is the beveling (“blunting” or “rounding”) of the axiopulpal line angle of two-surface preparations so as to limit areas of stress concentration in subsequently placed restorations.Other Cutting InstrumentsOther hand-cutting instruments such as the knife, le, and discoid-cleoid instrument are used for trimming restorative material rather than for cutting tooth structure. Knives, known as nishing knives, amalgam knives, or gold knives, are designed with a thin, knifelike blade that is made in various sizes and shapes (Fig. 14.10A and B). Knives are used for trimming excess restorative material on the gingival, facial, or lingual margins of a proximal restoration or trimming and contouring the surface of a Class V restoration. Sharp secondary edges on the heel aspect of the blade are useful in a scrape–pull mode.Files (see Fig. 14.10C) also may be used to trim excess restorative material and are particularly useful at gingival margins. e blades of the le are extremely thin, and the teeth of the instrument on the cutting surfaces are short and designed to make the le a push/pull instrument. Files are manufactured in various shapes and angles to enhance access to various restoration surfaces.e discoid-cleoid (see Fig. 14.10D and E) instrument is used principally for carving occlusal anatomy in unset amalgam restora-tions. e blades are slightly curved and the cutting edges are either circular or clawlike. e circular edge is known as a discoid, whereas the clawlike blade is termed cleoid. It also may be used to trim or burnish inlay–onlay margins. e working ends of this instrument are usually larger than the discoid end of an excavator.Hand Instrument TechniquesFour grasps are used with hand instruments: (1) modied pen, (2) inverted pen, (3) palm-and-thumb, and (4) modied palm-and-thumb. e conventional pen grasp is not an acceptable instrument grasp (Fig. 14.11A).Modied Pen Graspe grasp that permits the greatest control of the instrument, while simultaneously maintaining ergonomic positioning of the wrist and elbow, is the modied pen grasp (see Fig. 14.11B). As the name implies, it is similar but not identical to that used in holding a pen. e pads of the thumb and of the index and middle ngers contact the instrument, while the tip of the ring nger (or tips of the ring and little ngers) is placed on a nearby tooth surface of the same arch as a rest. e palm of the hand generally is facing away from the operator. e pad of the middle nger is placed near the topside of the instrument; by this nger working with the wrist and the forearm, cutting or cleaving pressure is EACDBSecondaryedgesPrimaryedge• Fig. 14.10 Examples of other hand instruments for cutting. A, Finish-ing knife. B, Alternative nishing knife design emphasizing secondary cutting edges. C, Dental le. D, Cleoid blade. E, Discoid blade carving amalgam. e6 CHAPTER 14 Instruments and Equipment for Tooth Preparation Modied Palm-and-Thumb Graspe modied palm-and-thumb grasp may be used when it is feasible to rest the thumb on the tooth being prepared or the adjacent tooth (Fig. 14.14). e handle of the instrument is held by all four ngers, whose pads press the handle against the distal area of the palm and the pad and rst joint of the thumb. Grasping the handle under the rst joints of the ring nger and little nger provides stabilization and enables optimal control of the instrument. e modied palm-and-thumb grasp usually is employed in the area of the maxillary arch and is best adopted when the dentist is operating from a rear-chair position.RestsA proper instrument grasp must include a rm rest to steady the hand during operating procedures. When the modied pen and inverted pen grasps are used, rests are established by placing the ring nger (or both ring and little ngers) on a tooth (or teeth) of the same arch and as close to the operating site as possible (see Fig. 14.12). e closer the rest areas are to the operating area, the • Fig. 14.12 Inverted pen grasp. Palm faces more toward operator. The rest is similar to that shown for modied pen grasp (see Fig. 14.11B). (Courtesy Dr. Mohammad Atieh.)• Fig. 14.13 Palm-and-thumb grasp. This grasp has limited use, such as preparing incisal retention in a Class III preparation on a maxillary incisor. The rest is tip of thumb on tooth in same arch. (Courtesy Dr. Mohammad Atieh.)• Fig. 14.14 Modied palm-and-thumb grasp. This modication allows greater ease of instrument movement and greater instrument control during pull stroke compared with palm-and-thumb grasp. The rest is tip of thumb on tooth being prepared or adjacent tooth. Note how the instru-ment is braced against pad and end joint of thumb. (Courtesy Dr. Moham-mad Atieh.)AB• Fig. 14.11 Pen grasps. A, Conventional pen grasp. Side of middle nger is on writing instrument. B, Modied pen grasp. Correct position of middle nger is near the “topside” of the instrument for good control and cutting pressure. The rest is tip (or tips) of ring nger (or ring and little ngers) on tooth (or teeth) of same arch. (Courtesy Dr. Mohammad Atieh.)the hand and grasped by all the ngers, while the thumb is free of the instrument, and the rest is provided by supporting the tip of the thumb on a nearby tooth of the same arch or on a rm, stable structure. For suitable control, this grasp requires careful use during cutting. An example of an appropriate use is holding a handpiece for cutting incisal retention for a Class III preparation on a maxillary incisor (Fig. 14.13). CHAPTER 14 Instruments and Equipment for Tooth Preparation e7 advantage of electric handpieces is that they oer a single motor with multiple attachments that may be used for dierent cutting applications. Attachments include straight type for 0.0925-inch-diameter instruments and contra-angle type for 0.0925- and 0.0626-inch-diameter instruments (see subsequent section under Shank design). e torque and concentricity of the air-driven turbines degrade in a relatively short period, requiring replacement. More vibration and bur chatter are associated with air-driven handpieces. Some disadvantages of electric handpieces are the initial setup expense and weight and balance issues for some clinicians.Rotary Speed Ranges for Diferent Cutting Applicationse rotational speed of an instrument is reported in rotations per minute (rpm). ree speed ranges are generally recognized: low or slow speeds (<12,000 rpm), medium or intermediate speeds (12,000–200,000 rpm), and high or ultrahigh speeds (>200,000 rpm). e terms low speed, medium speed, and high speed are used preferentially in this textbook. Most useful instruments are rotated at either low speed or high speed. Electric handpiece motors operate up to 40,000 rpm. is speed is signicantly less than the 400,000 rpm generated by air-driven handpieces. However, the electric handpiece motor has attachments with multipliers that increase rotation in ratios of 5 to 1 or 4 to 1, which enable rotational speeds eectively in the same range as air-driven handpieces. e dierence in the amount of cutting power is substantial in electric handpieces. Air-driven handpieces produce up to 20 watts of cutting power, whereas electric handpieces are able to produce up to 60 watts of cutting power. e extra cutting power in electric handpieces allows the constant torque necessary to cut various restorative materials and tooth structure regardless of the load. Unlike in the air-driven handpiece, the rotary instrument in the electric handpiece does not slow or stop (i.e., stall) as the load is increased.A crucial factor is the surface speed of the instrument—that is, the velocity at which the edges of the cutting instrument pass across the surface being cut. is speed is proportional to the rotational speed and the diameter of the instrument, with large instruments having higher surface speeds at any given rate of rotation. Although intact tooth structure may be removed by an instrument rotating at low speeds, it is a traumatic experience for the patient and the dentist. Low-speed cutting is ineective, is time consuming, and requires a relatively heavy force application; this results in heat production at the operating site and produces vibrations of low frequency and high amplitude. Heat and vibration are the main sources of patient discomfort.3 At low speeds, burs have a tendency to roll out of the tooth preparation and may damage the cavosurface margin or tooth surface. In addition, slow speed operation of carbide burs reduces bur life as their brittle blades are easily broken at low rpm.Many of these disadvantages of low-speed operation do not apply when the objective is some procedure other than cutting tooth structure. e low-speed range is used for cleaning teeth, caries excavation, and nishing and polishing procedures. At low speeds, tactile sensation is better, and generally overheating of cut surfaces is less likely. e availability of a low-speed option provides a valuable adjunct for many dental procedures.At high rpm, the surface speed needed for ecient cutting may be attained with smaller and more versatile cutting instruments. is speed is used for tooth preparation and removing old restora-tions. Other high rpm advantages include (1) diamond and carbide cutting instruments remove tooth structure faster and with less pressure, vibration, and heat generation; (2) the types of rotary cutting instruments needed is reduced because smaller sizes are more reliable they are. When the palm-and-thumb grasps are used, rests are created by placing the tip of the thumb on the tooth being operated on, on an adjacent tooth, or on a convenient area of the same arch (see Figs. 14.13 and 14.14). In some instances, it is impossible to establish a rest on tooth structure, and soft tissue must be used. Neither soft tissue rests nor distant hard tissue rests aord reliable control, and they reduce the force or power that may be used safely. Occasionally, it is impossible to establish normal nger rests with the hand holding the instrument. Under these circumstances, instrument control may be gained using the forenger of the opposite hand on the shank of the instrument or using an indirect rest (i.e., the operating hand rests on the opposite hand, which rests on a stable oral structure).GuardsGuards are hand instruments or other items (e.g., cotton rolls, dry angles, interproximal wedges) used to protect soft tissue from contact with sharp cutting or abrasive instruments (see Fig. 14.10E, and Online Chapter 15).Contemporary Powered Cutting EquipmentRotary-Powered Cutting EquipmentPowered rotary cutting instruments, known as dental handpieces, are the most commonly used instruments in contemporary dentistry. Dentistry, as practiced today, would not be possible without the use of powered cutting instruments. Current dental handpieces are now highly ecient and sophisticated instruments that have evolved from their beginnings in the early 1950s. Changes in ergonomic design, weight, and balance have made handpieces more comfortable to use for longer periods. Improved design helps to minimize operator arm and shoulder fatigue. Incorporation of durable beroptics has greatly improved operator visibility. Develop-ment of light emitting diode (LED) technology has improved the quality, intensity, and longevity of handpiece light sources. Modern handpieces are able to withstand the sterilization requirements of dental practice. New bearing materials and cartridges have been developed to enhance their service longevity and to contribute to noise level reduction. Handpiece chuck mechanisms have evolved such that pushbuttons, instead of chuck latches or chuck tools, are used to release and change rotary instruments.Two technologies are used today for dental handpieces, and each has unique characteristics and benets. e air-driven handpiece was, for many years, the mainstay for cutting teeth in dentistry. e electric motor–driven handpiece is now becoming increasingly popular for use in all cutting applications in dentistry. e technolo-gies for both air-driven and electric systems continue to evolve, and both systems remain very popular for everyday use in operative dentistry procedures.Air-driven and electric systems have both advantages and dis-advantages. Air-driven systems are less costly on initial startup and are less expensive with regard to replacing turbines compared with electric handpieces. Air-driven handpieces weigh less than electric handpieces, and this quality may be the most signicant adjustment for clinicians who make the change from air-driven handpieces to electric handpieces. e size of the head of the air-driven handpiece is usually smaller. e advantages of electric handpieces are that they (1) are quieter than air-driven handpieces, (2) cut with high torque (i.e., with very little stalling), and (3) oer absolute control over rotary instrument revolutions per minute (rpm). Another e8 CHAPTER 14 Instruments and Equipment for Tooth Preparation determine the cutting progress within the tooth preparation. Additionally the abrasive dust interfered with visibility of the cutting site and tended to mechanically etch the surface of the dental mirror. Preventing the patient or oce personnel from inhaling abrasive dust posed an additional diculty.Contemporary air abrasion equipment is helpful for stain removal, debriding pits and ssures before sealing, and microme-chanical roughening of surfaces to be bonded (enamel, cast-metal alloys, or porcelain) (Fig. 14.15).7 This approach works well when organic material is being removed and when only a limited amount of enamel or dentin is involved. Although promoted for caries excavation, air abrasion is not able to produce well-dened preparation wall and margin details that are possible with con-ventional rotary cutting techniques. Generally, the nest stream of abrading particles still generates an eective cutting width that is far greater than the width of luted cement margins or the errors tolerable in most caries excavations. Air abrasion does allow the roughening of surfaces to be bonded, luted, or repaired and this may be accomplished intraorally or extraorally. Roughen-ing by air abrasion by itself is not a substitute for acid-etching techniques. Roughening improves bonding. Acid etching alone or after roughening, however, always produces a better bond than air abrasion alone.8Air abrasion techniques rely on the transfer of kinetic energy from a stream of powder particles on the surface of tooth structure or a restoration to produce a fractured surface layer, resulting in roughness for bonding or disruption for cutting. e energy transfer event is aected by many things, including powder ow rate, particle size, pressure, angulation, surface composition, and clearance angle variables (Fig. 14.16). e most common error made by operators of air abrasion units is holding the tip at the wrong distance from the surface for the desired action. Greater distances signicantly reduce the energy of the stream.9 Short distances may produce unwanted cutting actions, such as when only surface stain removal is being attempted. e potential for unwanted cutting is a signicant problem when employing an air-polishing device (e.g., Prophy Jet) to clean the surfaces of dentin and enamel.10-13 When used properly however, units designed for air polishing tooth surfaces may be quite eective and ecient (Fig. 14.17).more universal in application; (3) the operator has better control and greater ease of operation; (4) instruments last longer; (5) patients are generally less apprehensive because annoying vibrations and operating time are decreased; and (6) increased operation eciency results in the opportunity to treat several teeth in the same arch at the same appointment.Variable control of rpm makes the handpiece more versatile. is feature allows the operator to easily obtain the optimal speed for the size and type of rotating instrument at any stage of a specic operation. Air-driven handpiece rpm may be controlled, but precise control is more dicult since the operator’s pressure on the foot-operated rheostat controls the speed of the handpiece. All electric handpieces have an electronic control module that, in concert with an adjustable rheostat, allow precise control of maximum rpm for specic procedural situations.For infection control, all dental handpieces are now sterilized. Continual sterilization will produce degradation in clinical per-formance (longevity, power, turbine speed, beroptic transmission, eccentricity, noise, chuck performance, water spray pattern).4 Most handpieces require lubrication after sterilization, and excess oil may be present during the startup operation and increase risk of contamination of the preparation. Several companies oer automated equipment to precisely clean and lubricate the handpiece after each use. It is recommended to run the handpiece for a few seconds before initiating dental procedures in which the deposition of oil spray onto tooth structure might interfere with processes such as dental adhesion.Laser EquipmentLasers are devices that produce beams of coherent and very-high-intensity light. Numerous current and potential uses of lasers in dentistry have been identied that involve the treatment of soft tissues and the modication of hard tooth structures.5,6 e word laser is an acronym for “light amplication by stimu-lated emission of radiation.” A crystal or gas is excited to emit photons of a characteristic wavelength that are amplied and ltered to make a coherent light beam. e eects of the laser depend on the power of the beam and the extent to which the beam is absorbed.Current laser units are relatively expensive compared with air-driven and electric motor cutting instruments. ese units are used primarily for either soft tissue applications and have few applications for hard tissue surface modication. ey may be used for tooth preparations; however, generation of a dened margin or tooth preparation surface is not possible. Lasers are an inecient means by which to remove large amounts of enamel or dentin and have the potential to generate unwanted amounts of heat. ey are not able to remove existing amalgam or ceramic dental restorations. No single laser type is suitable for all potential laser applications. Lasers may never replace the high-speed dental handpiece. Currently, available laser instruments have proven to be relatively inecient and impractical for tooth preparation and have not achieved widespread popularity.Other EquipmentAlternative methods of cutting enamel and dentin have been assessed periodically. In the mid-1950s, air-abrasive cutting was tested, but several clinical problems precluded general acceptance. Most importantly, no tactile sense was associated with air-abrasive cutting of tooth structure. is made it dicult for the operator to • Fig. 14.15 Example of contemporary air abrasion unit for removal of supercial enamel defects or stains, debriding pits and ssures for sealant application, or roughening surfaces to be bonded or luted. (Courtesy Danville Materials, Inc., San Ramon, CA.) CHAPTER 14 Instruments and Equipment for Tooth Preparation e9 parts: (1) shank, (2) neck, and (3) head (Fig. 14.18). Each has its own function, inuencing its design and the materials used for its construction. e term shank has dierent meanings as applied to rotary instruments and to hand instruments.Shank Designe shank is the part that ts into the handpiece, accepts the rotary motion from the handpiece, and provides a bearing surface to control the alignment and concentricity of the instrument. e shank design and dimensions vary with the handpiece for which it is intended. e American Dental Association (ADA) Specication No. 23 for dental excavating burs includes ve classes of instrument shanks.14 ree of these (Fig. 14.19)—the straight handpiece shank, the right angle latch handpiece shank, and the friction-grip handpiece shank—are commonly encountered. e shank portion of the straight handpiece instrument is a simple cylinder that is held in the handpiece by a metal chuck. Straight handpiece instruments are now rarely used for preparing teeth but are used for oral surgery extraction procedures. ey are com-monly used however for external nishing and polishing indirect restorations.e more complicated shape of the right angle latch-type shank reects the dierent mechanisms by which these instruments are held in the handpiece. eir shorter overall length substantially improves access to posterior regions of the mouth compared with straight handpiece instruments. Handpieces that use right angle latch-type burs normally have a metal bur tube within which the instruments t as closely as possible, while still permitting easy interchange. e posterior portion of the shank is attened on one side so that the end of the instrument ts into a D-shaped socket at the bottom of the bur tube. Engagement in this area is required for bur rotation to occur. Latch-type instruments are not retained in the handpiece by a chuck, but by a retaining latch that slides into the groove found at the shank end of the instrument. is type of instrument is used predominantly at low-speed and medium-speed ranges for caries excavation and nishing procedures. At these speeds, the small amount of potential wobble inherent in the clearance between the rotary instrument and the handpiece bur tube is controlled by the lateral pressure exerted during cutting procedures. At higher speeds, the latch-type shank/bur tube design is inadequate to provide required alignment and concentricity for Rotary Cutting Instrumentse individual instruments intended for use with dental handpieces are manufactured in hundreds of sizes, shapes, and types. is variation is in part a result of the need for specialized designs for particular clinical applications or to t particular handpieces, but much of the variation also results from individual preferences on the part of dentists. Since the introduction of high-speed techniques in clinical practice, a rapid evolution of technique and an accom-panying proliferation of new instrument designs have occurred. Nevertheless, the number of instruments essential for use with any one type of handpiece is comparatively small, especially in the case of high-speed handpieces.Common Design CharacteristicsDespite the great variation among rotary cutting instruments, they share certain design features. Each instrument consists of three Connectionto device• AIR PRESSURE (20-55 psi)• WATER FLOW RATE• POWDER FLOW RATE• PARTICLE SIZE (25-250 m)• PARTICLE TYPE and HARDNESS• TIP DIAMETER• TIP GEOMETRY (e.g., round)• ANGLE OF ATTACK (60-90 to surface)• MOTION (e.g., 12 mm/s scanning pattern)• DURATION (e.g., 2-20 seconds)• SUBSTRATE  Enamel, dentin, cementum, amalgam, composite, casting alloy, or ceramic• DISTANCE  3-5 mm• Fig. 14.16 Schematic representation of range of variables associated with any type of air abrasion equipment. The cleaning or cutting action is a function of kinetic energy imparted to the actual surface, which is affected by variables concerning the particle size, air pressure, angulation with surface, type of substrate, and method of clearance. (Courtesy B. Kunselman [Master’s thesis, 1999], School of Dentistry, University of North Carolina, Chapel Hill, NC.)• Fig. 14.17 Example of air abrasion equipment used for tooth cleaning showing the Prophy tip and handle attached by a exible cord to the control unit with the reservoir of powder and source of water (left). (Cour-tesy DENTSPLY International, York, PA.)Shank Neck Head• Fig. 14.18 Normal designation of three parts of rotary cutting instruments. 1.2500.5200.5000.06280.09250.0925ABC• Fig. 14.19 Characteristics and typical dimensions (in inches) of three common instrument shank designs for straight handpiece (A), right angle latch-type handpiece (B), and friction-grip contra-angle type handpiece (C). e10 CHAPTER 14 Instruments and Equipment for Tooth Preparation Early burs were made of steel. Steel burs perform well, cutting human dentin at low speeds, but dull rapidly at higher speeds or when cutting enamel. When burs are dulled, the reduced eective-ness in cutting creates increased heat and vibration.Carbide burs, which were introduced in 1947, have largely replaced steel burs for tooth preparation. Steel burs now are used mainly for nishing procedures. Carbide burs perform better than steel burs at all speeds, and their superiority is greatest at high speeds. All carbide burs have heads of cemented carbide in which microscopic carbide particles, usually tungsten carbide, are held together in a matrix of cobalt or nickel. Carbide is much harder than steel and less prone to dull during cutting.In most burs, the carbide head is attached to a steel neck (and shank) by welding or brazing. e substitution of steel for carbide in the portions of the bur where greater wear resistance is not required has certain advantages: It permits the manufacturer more freedom of design in attaining the characteristics desired in the instrument and allows economy in the cost of materials of construction.Although most carbide burs have the joint located in the posterior part of the head, others are sold that have the joint located within the shank and have carbide necks and heads. Carbide is stier and stronger than steel, but it is also more brittle. A carbide neck subjected to a sudden blow or shock will fracture, whereas a steel neck will bend. A bur that is even slightly bent produces increased vibration and overcutting as a result of increased runout (see upcoming description of runout). Although steel necks reduce the risk of fracture during use, they may cause severe problems if bent. Either type may be satisfactory, and other design factors are varied to take maximal advantage of the properties of the material used.Bur Classication SystemsTo facilitate the description, selection, and manufacture of burs, it is highly desirable to have some agreed-on shorthand designation, which represents all variables of a particular head design by some simple code. In the United States, dental burs traditionally have been described in terms of an arbitrary numerical code for head size and shape (e.g., 2 = 1-mm-diameter round bur; 57 = 1-mm-diameter straight ssure bur; 34 = 0.8-mm-diameter inverted cone bur).16 Despite the complexity of the system, it is still in common use. Other countries similarly developed and used arbitrary systems. Newer classification systems such as those developed by the International Dental Federation (Federation Dentaire Internationale) and International Standards Organization (ISO) tend to use separate designations for shape (usually a shape name) and size (usually a number giving the head diameter in tenths of a millimeter) (e.g., round 010; straight ssure plain 010; inverted cone 008).17,18Shapese term bur shape refers to the contour or silhouette of the head. e basic head shapes are round, inverted cone, pear, straight ssure, and tapered ssure (Fig. 14.20). A round bur is spherical. is shape customarily has been used for initial entry into the tooth, extension of the preparation, preparation of retention features, and caries removal.An inverted cone bur has a rapidly tapered cone with the apex of the cone directed toward the bur shank. Head length is approxi-mately the same as the head diameter. is shape is particularly suitable for providing undercuts in tooth preparations.A pear-shaped bur has a slightly tapered cone with the small end of the cone directed toward the bur shank. e end of the head either is continuously curved (see Fig. 14.20) or is at with the rotary instrument head; as a result, an improved shank/clutch design is required for these speeds.e friction grip shank design was developed for use with high-speed handpieces. is design is smaller in overall length than the latch-type instruments, providing a further improvement in access to the posterior regions of the mouth. e shank is a simple cylinder manufactured to close dimensional tolerances. As the name implies, friction-grip instruments originally were designed to be held in the handpiece by friction between the shank and a plastic or metal chuck. Newer handpiece designs have metal chucks that close to make a positive contact with the bur shank. Careful dimensional control of the shanks of high-speed instruments is important because even minor variations in shank diameter can cause substantial variation in instrument performance and problems with insertion, retention, and removal.Neck DesignAs shown in Fig. 14.18, the neck is the intermediate portion of an instrument that connects the head to the shank. Except in the case of the larger, more massive instruments, the neck normally tapers from the shank diameter to a smaller size immediately adjacent to the head. e main function of the neck is to transmit rotational and translational forces to the head. At the same time, it is desir-able for the operator to have the greatest possible visibility of the cutting blades (or diamond particles) on the head and the greatest manipulative freedom. For this reason, the neck dimensions represent a compromise between the need for a large cross section to provide strength and a small cross section to improve access and visibility.Head Designe head is the working part of the instrument, the cutting edges or points that perform the desired shaping of tooth structure. e shape of the head and the material used to construct it are closely related to its intended application and technique of use. e heads of instruments show greater variation in design and construction than either of the other main components of the rotary cutting instrument. For this reason, the characteristics of the head form the basis on which rotary instruments are usually classied.Many characteristics of the heads of rotary instruments could be used for classication. Most important among these is the division into bladed instruments and abrasive instruments. Material of construction, head size, and head shape are additional charac-teristics that are useful for further subdivision. Bladed and abrasive instruments exhibit substantially dierent clinical performance, even when operated under nearly identical conditions. is appears to result from dierences in the mechanism of cutting that are inherent to their design. e two main divisions that will be utilized for this discussion are dental burs and diamond abrasive instruments.Dental Burse term bur is applied to all rotary cutting instruments that have bladed cutting heads. is includes instruments intended for nish-ing metal restorations, surgical removal of bone, and tooth preparation.Historical Development of Dental Burse earliest burs were handmade. ey were not only expensive but also variable in dimension and performance. e shapes, dimensions, and nomenclature of modern burs are directly related to those of the rst machine-made burs introduced in 1891.15 CHAPTER 14 Instruments and Equipment for Tooth Preparation e11 of this design with slightly curved tip angles are available. A tapered ssure bur has a slightly tapered cone with the small end of the cone directed away from the bur shank. is shape is used for tooth preparations for indirect restorations, for which freedom from undercuts is essential for successful withdrawal of patterns and nal seating of the restorations. Tapered ssure burs may also be designed with a at end with the tip corners slightly rounded.Among these basic shapes, variations are possible. Fissure and inverted cone burs may have half-round or domed ends. Taper and cone angles may vary. e ratio of head length to diameter may be varied. In addition to shape, other features may be varied, such as the number of blades, spiral versus axial patterns for blades, and continuous versus crosscut blade edges (see Figs. 14.21 and 14.22).SizesIn the United States, the number designating bur size also tradition-ally has served as a code for head design. is numbering system for burs was originated by the S.S. White Dental Manufacturing Company in 1891 for their rst machine-made burs. It was extensive rounded corners where the sides and at end intersect (Fig. 14.21A; 245). e No. 245 is an elongated pear bur (length three times the width) and is advocated for tooth preparations for amalgam.A straight ssure bur is an elongated cylinder. Some dentists advocate this shape for amalgam tooth preparation. Modied burs Round InvertedconePear-shapedStraightfissureTaperedfissure• Fig. 14.20 Basic bur head shapes. (From Finkbeiner BL, Johnson CS: Mosby’s comprehensive dental assisting, St. Louis, 1995, Mosby.)xyz 0.425 mm 0.525 mm 0.525 mm1/21/4 24331/2 169L 245 271• Fig. 14.21 Burs used in recommended procedures. Bur sizes 14, 12, 2, 4, 3312, and 169L are standard carbide burs available from various sources. The 245 and 271 burs are nonstandard carbide burs that do not conform to the current American Dental Association (ADA) standard numbering system. They are designed to combine rounded corners with at ends and are available from several manufactur-ers. The diamond instruments shown are wheel (x), ame (y), and tapered cylinder (z). Various twist drills are illustrated. Particular drills often are provided as specied by manufacturers of pin-retention systems. e12 CHAPTER 14 Instruments and Equipment for Tooth Preparation were added later when smaller instruments were included in the system. All original bur designs had continuous blade edges. Later, when crosscut burs were found to be more eective for cutting dentin at low speeds, crosscut versions of many bur sizes were introduced. is modication was indicated by adding 500 to the number of the equivalent noncrosscut size (e.g., a No. 57 with crosscut was designated No. 557). Similarly, a 900 prex was used to indicate a head design intended for end cutting only (e.g., except for dierences in blade design, a No. 957, No. 557, and No. 57 bur all had the same head dimensions). ese changes occurred gradually over time without disrupting the system. e sizes in common use in 1955 are shown in Table 14.2. e system changed rapidly thereafter, but where the numbers are still used, the designs and dimensions remain the same.Modications in Bur DesignAs available handpiece speeds increased after 1950, particularly after the high-speed turbine handpieces were introduced, a new wave of modication of bur sizes and shapes occurred. Numerous other categories arose as new variations in blade number or design were created. Some of the numbers assigned to the burs were selected arbitrarily. With the introduction of new bur sizes and elimination of older sizes, much of the logic in the system has no longer been maintained, and many dentists and manufacturers no longer recognize the original signicance of the numbers used for burs. e number of standard sizes that have continued in use has been reduced. is has been most obvious in the decreased popular-ity of large-diameter burs. e cutting eectiveness of carbide burs is greatly increased at high speeds.19 is is particularly true of the small-diameter sizes, which did not have sucient peripheral speed for ecient cutting when used at lower rates of rotation. As the eectiveness of small burs has increased, they have replaced larger burs in many procedures. ree other major trends in bur design are discernible: (1) reduced use of crosscuts, (2) extended heads on ssure burs, and (3) rounding of sharp tip angles.Crosscuts are needed on ssure burs to obtain adequate cutting eectiveness at low speeds, but they are not needed at high speeds. and logical, so other domestic manufacturers found it convenient to adopt it for their burs as well. As a result, for more than 60 years, a general uniformity existed for bur numbers in the United States. Table 14.1 shows the correlation of bur head sizes with dimensions and shapes. e table includes not only many bur sizes that are still in common use but also others that have become obsolete.e original numbering system grouped burs by 9 shapes and 11 sizes. e 12 and 14 designations (both very small round burs) AByxvwz• Fig. 14.22 Design features of bur heads (illustrated using No. 701 bur crosscut). A, Lateral view—neck diameter (v), head length (w), taper angle (x), and spiral angle (y). B, End view—head diameter (z). Original Bur Head Sizes (1891–1954)TABLE 14.1Head ShapesHEAD DIAMETERS IN INCHES (mma)0.020 0.025 0.032 0.039 0.047 0.055 0.063 0.072 0.081 0.090 0.099 0.109 0.119(0.5) (0.6) (0.8) (1.0) (1.2) (1.4) (1.6) (1.8) (2.1) (2.3) (2.5) (2.8) (3.0)Round14121 2 3 4 5 6 7 8 9 10 11Wheel —111212 13 14 15 16 17 18 19 20 21 22Cone —221223 24 25 26 27 28 29 30 31 32 33Inverted cone —331234 35 36 37 38 39 40 41 42 43 44Bud —441245 46 47 48 49 50 51 — — — —Straight ssure (at end)5514551256 57 58 59 60 61 62 — — — —Straight ssure (pointed end)661267 68 69 70 71 72 73 — — — —Pear771278 79 80 81 82 83 84 85 86 87 88Oval881289 90 91 92 93 94 95 — — — —aMillimeter values rounded to the nearest 0.1 mm.Courtesy H.M. Moylan, S.S. White Dental Manufacturing Company, Lakewood, NJ. CHAPTER 14 Instruments and Equipment for Tooth Preparation e13 are illustrated in Fig. 14.21. e selection includes standard head designs and modied designs of the types just discussed. Included in Table 14.3 are the signicant head dimensions of these standard and modied burs.A problem related to the dimensions and designations of rotary dental instruments worldwide arose because each country developed its own system of classication. Dentists in the United States often were not aware of the problem because they predominantly used domestic products, and all U.S. manufacturers used the same system. e rapid rate at which new bur designs were introduced during the transition to high-speed techniques threatened to cause a complete breakdown in the numbering system. As various manufacturers simultaneously developed and marketed new burs of similar design, the risk of similar burs being given dierent numbers or dierent burs being given the same number increased. Combined with the growing use of foreign products in the United States, this situation has led to more interest in the establishment of international standards for dimensions, nomenclature, and other characteristics.Progress toward the development of an international numbering system for basic bur shapes and sizes under the auspices of the ISO has been slow. For other design features, the trend instead seems to be toward the use of individual manufacturer’s code numbers. roughout the remaining text, the traditional U.S. numbers are used, where possible. e few exceptions are shown in Fig. 14.21 and Table 14.3.Additional Features in Head DesignNumerous factors other than head size and shape are involved in determining the clinical eectiveness of a bur design.21,22 Fig. 14.22 shows a lateral view and a cross-sectional view of a No. 701 crosscut tapered ssure bur in which several of these factors are illustrated. e lateral view (see Fig. 14.22A) shows neck diameter, head diameter, head length, taper angle, blade spiral angle, and crosscut size and spacing as they apply to this bur size. Of these features, head length and taper angle are primarily descriptive and may be varied within limits consistent with the intended use of the bur. is bur originally was designed for use at low speeds in preparing teeth for cast restorations. e taper angle is intended to approximate Because crosscut burs used at high speeds tend to produce unduly rough surfaces, many of the crosscut sizes originally developed for low-speed use have been replaced by noncrosscut instruments of the same dimension for high-speed use.20 In many instances, the noncrosscut equivalents were available; a No. 57 bur might be used at high speed, whereas a No. 557 bur was preferred for low-speed use. Noncrosscut versions of the 700 series burs have become popular, but their introduction precipitated a crisis in the bur numbering system because no number traditionally had been assigned to burs of this type.Carbide ssure burs have been introduced with head lengths extended two to three times those of the normal tapered ssure burs of similar diameter. Such a design would never have been practical using a brittle material such as carbide if the bur were to be used at low speed. e applied force required to make a bur cut at speeds of 5000 to 6000 rpm would normally be sucient to fracture such an attenuated head. e extremely light applied pressures needed for cutting at high speed permit many modica-tions of burs, however, that would have been impractical at low speed.e third major trend in bur design has been toward rounding of the sharp tip corners. Early contributions to this trend were made by Markley and Sockwell.8 Sharp angles produced in tooth preparations by conventional burs result in areas of high stress concentration with increased potential for tooth fracture. Bur heads with rounded corners allow better distribution of occlusal stress in restored teeth, help retain the strength of the tooth by preserving vital dentin, and facilitate the adaptation of restorative materials. Carbide burs and diamond instruments with this design last longer because no sharp corners prone to chipping and wear are present. Burs with rounded transitions facilitate tooth preparation with desired features of at preparation oors and rounded internal line angles.Many of these new and modied bur designs simplify the techniques and reduce the effort needed for optimal results. Although the development of new bur sizes and shapes has greatly increased the number of dierent types in current use, the number actually required for clinical eectiveness has been reduced. Most instruments recommended in this text for the preparation of teeth Standard Bur Head Sizes—Carbide and Steel (1955–Present)TABLE 14.2Head ShapesHEAD DIAMETERS IN INCHES (mma)0.020 0.025 0.032 0.040 0.048 0.056 0.064 0.073 0.082 0.091 0.100 0.110 0.120 0.130(0.5) (0.6) (0.8) (1.0) (1.2) (1.4) (1.6) (1.9) (2.1) (2.3) (2.5) (2.8) (3.0) (3.3)Round14121 2 3 4 5 6 7 8 9 10 11 —Wheel —111212 — 14 — 16 — — — — — — —Inverted cone —331234 35 36 37 38 39 40 — — — — —Plain ssure —551256 57 58 59 60 61 62 — — — — —Round crosscut — — — 502 503 504 505 506 — — — — — —Straight ssure crosscut — — 556 557 558 559 560 561 562 563 — — — —Tapered ssure crosscut — — — 700 701 — 702 — 703 — — — — —End cutting ssure — — — 957 958 959 — — — — — — — —Note: Nonstandard burs are not shown in this table.aMillimeter values rounded to the nearest 0.1 mm. e14 CHAPTER 14 Instruments and Equipment for Tooth Preparation and usually only one blade cuts eectively.23 Under these circum-stances, although the high cutting rate of crosscut burs is maintained, the ridges are not removed and a much rougher cut surface results.20A cross-sectional view of the No. 701 bur is shown in Fig. 14.22B. is cross section is made at the point of largest head diameter and is drawn as seen from the shank end. e bur has six blades uniformly spaced with depressed areas between them. ese depressed areas are properly known as utes. e number of blades on a bur is always even because even numbers are easier to produce in the manufacturing process, and instruments with odd numbers of blades cut no better than those with even numbers. e number of blades on an excavating (cutting) bur may vary from 6 to 8 to 10. Burs intended mainly for nishing procedures usually have 12 to 40 blades. e greater the number of blades, the smoother is the cutting action at low speeds. Most burs are made with at least six blades because they may need to be used in this speed range. In the high-speed range, no more than one blade seems to cut eectively at any one time, and the remaining blades are, in eect, spares. e tendency for the bur to cut on a single blade is often a result of factors other than the bur itself. Nevertheless, it is important that the bur head be as symmetrical as possible. Two terms are in common use to measure this char-acteristic of bur heads: concentricity and runout.Concentricity is a direct measurement of the symmetry of the bur head itself. It measures how closely a single circle can be passed through the edges of all of the blades. Concentricity is an indication of whether one blade is longer or shorter than the others. It is a static measurement not directly related to function. Runout is a dynamic test measuring the accuracy with which all blade edges pass through a single point when the instrument is rotated. It measures not only the concentricity of the head but also the accuracy with which the center of rotation passes through the center of the head. Even a perfectly concentric head exhibits substantial runout if the head is not centered precisely on the the desired occlusal divergence of the lateral walls of the preparations, and the head length must be long enough to reach the full depth of the normal preparation. ese factors do not otherwise aect the performance of the bur.Neck diameter is important functionally because a neck that is too small results in a weak instrument unable to resist lateral forces. Too large a neck diameter may interfere with visibility and use of the part of the bur head next to the neck and may restrict access for coolants. As the head of a bur increases in length or diameter, the moment arm exerted by lateral forces increases, and the neck needs to be larger.Compared with these factors, two other design variables, the spiral angle and crosscutting, have considerably greater inuence on bur performance. ere is a tendency toward reduced spiral angles on burs intended exclusively for high-speed operation in which a large spiral angle (which would produce a smoother preparation) is not needed. e smaller spiral angle produces more ecient cutting.As noted previously, crosscut bur designs have notches in the blade edges to increase cutting eectiveness at low and medium speeds. A minimum amount of perpendicular force is required to make a blade grasp the surface and initiate cutting as it passes across the surface. e harder the surface, the duller the blade; and the greater its length, the more is the force required to initiate cutting. By reducing the total length of bur blade that is actively cutting at any one time, the crosscuts eectively increase the cutting pressure resulting from rotation of the bur and the perpendicular pressure holding the blade edge against the tooth.As each crosscut blade cuts, it leaves small ridges of tooth structure standing behind the notches. Because the notches in two succeeding blades do not line up with each other, the ridges left by one blade are removed by the following one at low or medium speed. At the high speed attained with air-driven handpieces however, the contact of the bur with the tooth is not continuous, Names and Key Dimensions of Recommended BursTABLE 14.3Manufacturer’s Size NumberADA Size NumberISO Size NumberHead Diameter (mm)Head Length (mm)Taper Angle (degrees) Shape1414005 0.50 0.40 — Round1212006 0.60 0.48 — Round2 2 010 1.00 0.80 — Round4 4 014 1.40 1.10 — Round33123312006 0.60 0.45 12 Inverted cone169 169 009 0.90 4.30 6 Tapered ssure169La169L 009 0.90 5.60 4 Elongated tapered ssure329 329 007 0.70 0.85 8 Pear, normal length330 330 008 0.80 1.00 8 Pear, normal length245b,c330L 008 0.80 3.00 4 Pear, elongated271b171 012 1.20 4.00 6 Tapered ssure272b172 016 1.60 5.00 6 Tapered ssureADA, American Dental Association; ISO, International Standard Organization.aSimilar to the No. 169 bur except for greater head length.bThese burs differ from the equivalent ADA size by being at ended with rounded corners. The manufacturer’s number has been changed to indicate this difference.cSimilar to the No. 330 bur except for greater head length. CHAPTER 14 Instruments and Equipment for Tooth Preparation e15 Carbide burs normally have blades with slight negative rake angles and edge angles of approximately 90 degrees. eir clearance faces either are curved or have two surfaces to provide a low clearance angle near the edge and a greater clearance space ahead of the following blade.Diamond Abrasive Instrumentse second major category of rotary dental cutting instruments involves abrasive cutting rather than blade cutting. Abrasive instru-ments are based on small, angular particles of a hard substance held in a matrix of softer material. Cutting occurs at numerous points where individual hard particles protrude from the matrix rather than along a continuous blade edge. is design causes denite dierences in the mechanisms by which the two types of instruments cut and in the applications for which they are best suited.Abrasive instruments are generally grouped as diamond or other instruments. Diamond instruments have had great clinical impact because of their long life and great eectiveness in cutting enamel and dentin. Diamond instruments for dental use were introduced in the United States in 1942 at a time before carbide burs were available and when interest in increased rotational speeds was beginning to expose the limitations of steel burs. e earliest diamond instruments were substitutes for previously used abrasive points of other types used for grinding and nishing.24 e vastly superior performance in these applications led to their immediate acceptance. e shortage of burs, as a result of wartime demands of the 1940s, forced the use of diamond instruments. Increased usage revealed their durability in cutting enamel and promoted the development of operative techniques employing them.TerminologyDiamond instruments consist of three parts: (1) a metal blank, (2) the powdered diamond abrasive, and (3) a metallic bonding material that holds the diamond powder onto the blank (Fig. 14.24). e blank in many ways resembles a bur without blades. It has the same essential parts: head, neck, and shank.e shank dimensions, similar to those for bur shanks, depend on the intended handpiece. e neck is normally a tapered section of reduced diameter that connects the shank to the head, but for large disk-shaped or wheel-shaped instruments, it may be the same diameter as the shank. e head of the blank is undersized compared with the desired nal dimensions of the instrument, but its size and shape determine the size and shape of the nished instrument. Dimensions of the head make allowance for a fairly uniform thickness of diamonds and bonding material on all sides. Some abrasive instruments are designed as a mandrel with a detachable head, which is much more practical for abrasive disks that have very short lifetimes.e diamonds employed are industrial diamonds, either natural or synthetic, that have been crushed to powder, then carefully graded for size and quality. e shape of the individual particle is important because of its eect on the cutting eciency and durability of the instrument, but the careful control of particle size is probably of greater importance. e diamonds generally are attached to the blank by electroplating a layer of metal on the blank while holding the diamonds in place against it. Although the electroplating holds the diamonds in place, it also tends to cover much of the diamond surfaces. Various proprietary techniques allow greater diamond exposure and resultant increased cutting eectiveness.long axis of the bur, the bur neck is bent, the bur is not held straight in the handpiece chuck, or the chuck is eccentric relative to the handpiece bearings. e runout can never be less than the concentricity, and it is usually substantially greater. Runout is the more signicant term clinically because it is the primary cause of vibration during cutting and is the factor that determines the minimum diameter of the hole that may be prepared by a given bur. Burs normally cut holes measurably larger than the head diameter because of runout defects.Bur Blade Designe actual cutting action of a bur (or a diamond abrasive) occurs in a very small region at the edge of the blade (or at the point of a diamond chip). In the high-speed range, this eective portion of the individual blade is limited to no more than a few thousandths of a centimeter adjacent to the blade edge. Fig. 14.23 is an enlarged schematic view of this portion of a bur blade. Several terms used in the discussion of blade design are illustrated.Each blade has two sides—the rake face (toward the direction of cutting) and the clearance face—and three important angles—the rake angle, the edge angle, and the clearance angle. e optimal angles depend on such factors as the mechanical properties of the blade material, the mechanical properties of the material being cut, the rotational speed and diameter of the bur, and the lateral force applied by the operator through the handpiece to the bur.e rake angle is the most important design characteristic of a bur blade. For cutting hard, brittle materials, a negative rake angle minimizes fractures of the cutting edge, increasing the bur life. A rake angle is said to be negative when the rake face is ahead of the radius (from cutting edge to axis of bur), as illustrated in Fig. 14.23. Increasing the edge angle reinforces the cutting edge and reduces the likelihood for the edge of the blade to fracture. Carbide bur blades have higher hardness and are more wear resistant, but they are more brittle than steel blades and require greater edge angles to minimize fractures. e three angles cannot be varied independently of each other. An increase in the clearance angle causes a decrease in the edge angle. e clearance angle eliminates rubbing friction of the clearance face, provides a stop to prevent the bur edge from digging into the tooth structure excessively, and reduces the radius of the blade back of the cutting edge to provide adequate ute space or clearance space for the cutting debris that accumulates ahead of the following blade.To axis of burEdge angleClearanceangleClearance faceRakefaceRakeangleDirection of rotation• Fig. 14.23 Bur blade design. Schematic cross section viewed from shank end of head to show rake angle, edge angle, and clearance angle. e16 CHAPTER 14 Instruments and Equipment for Tooth Preparation Head Shapes and SizesDiamond instruments are available in a wide variety of shapes and in sizes that correspond to all except the smallest-diameter burs. e greatest dierence lies in the diversity of other shapes and sizes in which diamond instruments are produced. Even with many subdivisions, the size range within each group is large compared with that found among the burs. More than 200 shapes and sizes of diamonds are currently marketed.Because of their design with an abrasive layer over an underlying blank, the smallest diamond instruments cannot be as small in diameter as the smallest burs, but a wide range of sizes is available ClassicationDiamond instruments currently are marketed in a myriad of head shapes and sizes (Table 14.4) and in all of the standard shank designs. Most of the diamond shapes parallel those for burs (Fig. 14.25). is great diversity arose in part as a result of the relative simplicity of the manufacturing process. Because it is possible to make diamond instruments in almost any shape for which a blank can be manufactured, they are produced in many highly specialized shapes on which it would be impractical to place cutting blades. is has been a major factor in establishing clinical uses for these unique shapes, which are not in direct competition with burs.ABC• Fig. 14.24 Diamond instrument construction. A, Overall view. B, Detail of abrasive layer. C, Detail of particle bonding. Standard Categories of Shapes and Sizes for Diamond Cutting InstrumentsTABLE 14.4Head Shapes Prole VariationsRound —Football PointedBarrel —Cylinder Flat-, bevel-, round-, or safe-endInverted cone —Taper Flat-, round-, or safe-endFlame —Curettage —Pear —Needle “Christmas tree”Interproximal Occlusal anatomyDonut —Wheel —Round Football Barrel Flat-endcylinderBeveled-endcylinderInvertedconeFlat-endtaperRound-endtaperFlame Needle Interproximal Pear Donut Wheel• Fig. 14.25 Characteristic shapes and designs for a range of diamond cutting instruments. CHAPTER 14 Instruments and Equipment for Tooth Preparation e17 termed points and stones. Hard and rigid molded instrument heads use rigid polymer or ceramic materials for their matrix and com-monly are used for grinding and shaping procedures. Other molded instrument heads use exible matrix materials, such as rubber, to hold the abrasive particles. ese are used predominantly for nish-ing and polishing procedures. Molded unmounted disks or wheelstones are attached by a screw to a mandrel of suitable size for a given handpiece that has a threaded hole in the end. is design permits the instruments to be changed easily and enable extended use of the mandrel.e coated abrasive instruments are mostly disks that have a thin layer of abrasive cemented to a exible backing. is construc-tion allows the instrument to conform to the surface contour of a tooth or restoration. Most exible disks are designed for reversible attachment to a mandrel. Coated abrasive instruments may be used in the nishing and smoothing procedures of certain enamel walls (and margins) of tooth preparations for indirect restorations but are most often used in nishing procedures for restorations.e abrasives are softer and are less wear resistant than diamond powder; as a result, they tend to lose their sharp edges and cutting eciency with use and are then discarded. In contrast, molded instruments are intended to partially regenerate through the gradual loss of their worn outer layers but may require that the operator reshape them to improve their concentricity or usefulness in nishing various anatomic areas. Reshaping is accomplished by applying a truing or shaping stone against the rotating instrument.Materialse matrix materials usually are phenolic resins or rubber. Some molded points may be sintered, but most are resin bonded. A rubber matrix is used primarily to obtain a exible head on instru-ments to be used for polishing. A harder, nonexible rubber matrix is often used for molded silicon carbide (SiC) disks. e matrix of coated instruments is usually one of the phenolic resins.Synthetic or natural abrasives may be used, including silicon carbide, aluminum oxide, garnet, quartz, pumice, and cuttlebone. e hardness of the abrasive has a major eect on the cutting eciency. e Mohs hardness values for important dental abrasives are shown in Table 14.5. SiC usually is used in molded rounds, tree or bud shapes, wheels, and cylinders of various sizes. ese points are normally gray-green, available in various textures, usually fast cutting (except on enamel), and produce a moderately smooth surface. Molded unmounted disks are black or a dark color, have a soft matrix, wear more rapidly than stones, and produce a moderately rough surface texture. ese disks are termed carbo-rundum disks or separating disks. Aluminum oxide is used for the same instrument designs as those for silicon carbide disks. Points are usually white, rigid, ne textured, and less porous and produce a smoother surface than SiC.Garnet (reddish) and quartz (white) are used for coated disks that are available in a series of particle sizes and range from coarse to medium-ne for use in initial nishing. ese abrasives are hard enough to cut tooth structure and all restorative materials, with the exception of some ceramics. Pumice is a powdered abrasive produced by crushing foamed volcanic glass into thin glass akes. e akes cut eectively, but they break down rapidly. Pumice is used with rubber disks and wheels, usually for initial polishing procedures. Cuttlebone is derived from the cuttlesh, a relative of squid and octopus. It is becoming scarce and gradually is being replaced by synthetic substitutes. It is a soft white abrasive, used only in coated disks for nal nishing and polishing. It is soft for each shape. No one manufacturer produces all sizes, but each usually oers an assortment of instruments that includes popular shapes and sizes. Because of the lack of uniform nomenclature for diamond instruments, it is often necessary to select them by inspection to obtain the desired shape and size. It is essential to indicate the manufacturer when attempting to describe diamond instruments by catalog number.Diamond Particle Factorse clinical performance of diamond abrasive instruments depends on the size, spacing, uniformity, exposure, and bonding of the diamond particles. Increased pressure causes the particles to dig into the surface more deeply, leaving deeper scratches and removing more tooth structure.Diamond particle size is commonly categorized as coarse (125–150 µm), medium (88–125 µm), ne (60–74 µm), and very ne (38–44 µm) for diamond preparation instruments.24 ese ranges correspond to standard sieve sizes for separating particles. When using large particle sizes, the number of abrasive particles that can be placed on a given area of the head is decreased. For any given force that the operator applies, the pressure on each particle tip is greater. e resulting pressure also is increased if diamond particles are more widely spaced so that fewer are in contact with the surface at any one time. e nal clinical per-formance of diamond instruments is strongly aected by the technique used to take advantage of the design factors for each instrument.Diamond finishing instruments use even finer diamonds (10–38 µm) to produce relatively smooth surfaces for nal nishing with diamond polishing pastes. Surface nishes of less than 1 µm are considered clinically smooth (see section Composite Resins in Chapter 13) and may be routinely attained by using a series of progressively ner polishing steps.Proper diamond instrument speed and pressure are the major factors in determining service life.25 Properly used diamond instru-ments last almost indenitely. A primary cause of failure of diamond instruments is loss of the diamonds from critical areas. is loss results from the use of excess pressure in an attempt to increase the cutting rate at inadequate speeds.26Other Abrasive InstrumentsIn addition to diamond instruments, many other types of abrasive instruments are used in dentistry. At one time they were extensively used for tooth preparation, but their use is now primarily restricted to shaping, nishing, and polishing restorations in the clinic and in the laboratory.ClassicationIn these instruments, as in the diamond instruments, the cutting surfaces of the head are composed of abrasive particles held in a continuous matrix of softer material. ey may be divided into two distinct groups—molded instruments and coated instruments. Each uses various abrasives and matrix materials.Molded abrasive instruments have heads that are manufactured by molding or pressing a uniform mixture of abrasive and matrix around the roughened end of the shank or cementing a premolded head to the shank. In contrast to diamond instruments, molded instruments have a much softer matrix and therefore wear during use. e abrasive is distributed throughout the matrix so that new particles are exposed by the wear. ese instruments are made in a full range of shapes and sizes. e mounted heads are often e18 CHAPTER 14 Instruments and Equipment for Tooth Preparation Bladed Cuttinge following discussion focuses on rotary bladed instruments but also is applicable to bladed hand instruments. Tooth structure, similar to other materials, undergoes brittle and ductile fracture. Brittle fracture is associated with crack production usually by tensile forces. Ductile fracture involves plastic deformation of material usually proceeding by shear forces. Extensive plastic deformation also may produce local work hardening and encourage brittle fracture. Low-speed cutting tends to proceed by plastic deformation before tooth structure fracture. High-speed cutting, especially of enamel, proceeds by brittle fracture.e rate of stress application (or strain rate) aects the resultant properties of materials. In general, the faster the rate of loading, the greater are the strength, hardness, modulus of elasticity, and brittleness of a material. A cutting instrument with a large diameter and high rotational speed produces a high surface speed and a high stress (or strain) rate.Many factors interact to determine which cutting mechanism is active in a particular situation. e mechanical properties of tooth structure, the design of the cutting edge or point, the linear speed of the instrument’s surface, the contact force applied, and the power output characteristics of the handpiece inuence the cutting process in various ways.19,29For the blade to initiate the cutting action, it must be sharp, must have a higher hardness and modulus of elasticity than the material being cut, and must be pressed against the surface with sucient force. e high hardness and modulus of elas-ticity are essential to concentrate the applied force on a small enough area to exceed the shear strength of the material being cut. As shown in Fig. 14.26, sheared segments accumulate in a distorted layer that slides up along the rake face of the blade until it breaks or until the blade disengages from the surface as it rotates. These chips accumulate in the clearance space between blades until washed out or thrown out by centrifugal force.Mechanical distortion of tooth structure ahead of the blade produces heat. Frictional heat is produced by the rubbing action of the cut debris against the rake face of the blade and the blade tip against the cut surface of the tooth immediately behind the edge. is can produce extreme temperature increases in the tooth and the bur in the absence of adequate cooling. e transfer of heat is not instantaneous, and the reduced temperature increase observed in teeth cut at very high speeds may be caused, in part, by the removal of the heated surface layer of the tooth structure by a following blade before the heat can be conducted into the tooth.enough that it reduces the risk of unintentional damage to tooth structure during the nal stages of nishing.Cutting MechanismsFor cutting, it is necessary to apply sucient pressure to make the cutting edge of a blade or abrasive particle dig into the surface. Local fracture occurs more easily if the strain rate is high (high rotary instrument surface speed) because the surface that is being cut responds in a brittle fashion. e process by which rotary instruments cut tooth structure is complex and not fully understood. e following discussion addresses cutting evaluations, cutting instrument design, proposed cutting mechanisms, and clinical recommendations for cutting.Evaluation of CuttingCutting may be measured in terms of eectiveness and eciency. Certain factors inuence one but not the other.27 Cutting eective-ness is the rate of tooth structure removal (millimeters per min [mm/min] or milligrams per second [mg/s]). Eectiveness does not consider potential side eects such as heat or noise. Cutting eciency is the percentage of energy actually producing the cutting. Cutting eciency is reduced when energy is wasted as heat or noise. It is possible to increase eectiveness while decreasing eciency. A dull bur may be made to cut faster than a sharp bur by applying a greater pressure, but experience indicates that this results in a great increase in heat production and reduced eciency.28It is generally agreed that increased rotational speed results in increased eectiveness and eciency. Adverse eects associated with increased speeds are heat, vibration, and noise. Heat has been identied as a primary cause of pulpal injury. Air-water sprays do not prevent the production of heat, but do serve to remove it before it causes a damaging increase in temperature within the tooth.Hardness Values of Restorative Materials, Tooth Structure, and AbrasivesTABLE 14.5Knoop HardnessBrinell HardnessMohs HardnessDentin 68 48 3–4Enamel 343 300 5Dental composite 41–80 60–80 5–7Dental amalgam 110 — 4–5Gold alloy (type III) — 110 —Feldspathic porcelain 460 — 6–7Pumice — — 6Cuttlebone — — 7Garnet — — 6.5–7Quartz 800 600 7Aluminum oxide 1500 1200 9Silicon carbide 2500 — 9.5Diamond >7000 >5000 10Blademotion• Fig. 14.26 Schematic representation of bur blade (end view) cutting a ductile material by shearing mechanism. Energy is required to deform the material removed and produce new surface. CHAPTER 14 Instruments and Equipment for Tooth Preparation e19 or diamond instrument. Carbide burs are better for end cutting, produce lower heat, and have more blade edges per diameter for cutting. ey are used eectively for punch cuts to enter tooth structure, intracoronal tooth preparation, amalgam removal, small preparations, and secondary retention features. Diamond instru-ments have higher hardness, and coarse diamonds have high cutting eectiveness. Diamonds are more eective than burs for intracoronal and extracoronal tooth preparations, beveling enamel margins on tooth preparations, and enameloplasty.Hazards With Cutting InstrumentsAlmost everything done in a dental oce involves some risk to the patient, the dentist, or the dental assistant. For the patient, pulpal dangers arise from tooth preparation and restoration pro-cedures. Soft tissue dangers are also present. Everyone is potentially susceptible to eye, ear, and inhalation dangers. Careful adherence to normal precautions can, however, eliminate or minimize most risks associated with the use of cutting instruments.Pulpal Precautionse use of cutting instruments may harm the pulp by exposure to mechanical vibration, heat generation, desiccation and loss of dentinal tubule uid, or transection of odontoblastic processes. As the thickness of remaining dentin decreases, the pulpal insult (and response) from heat or desiccation increases. Slight to moderate injury produces a localized, protective pulpal response in the region of the cut tubules. In severe injury, destruction extends beyond the cut tubules, often resulting in pulpal abscess and death of the pulp. ese pulpal sequelae (recovery or necrosis) take 2 weeks to 6 months or longer to become apparent, depending on the extent and degree of the trauma. Although a young pulp is more prone to injury, it also recovers more eectively compared with an older pulp, in which the recuperative powers are slower and less eective.Enamel and dentin are good thermal insulators and protect the pulp if the quantity of heat is not too great and the remaining thickness of tissue is adequate. e longer the time of cutting and the higher the local temperature produced, the greater is the threat of thermal trauma. e remaining tissue is eective in protecting the pulp in proportion to the square of its thickness. Steel burs produce more heat than carbide burs because of inecient cutting. Burs and diamond instruments that are dull or plugged with debris do not cut eciently, resulting in heat production. When used without coolants, diamond instruments generate more damaging heat compared with carbide burs.e most common instrument coolants are air and air-water sprays. Air alone as a coolant is not eective in preventing pulpal damage because it needlessly desiccates dentin and damages odontoblasts. Air has a much lower heat capacity than water and is much less ecient in absorbing unwanted heat. An air coolant alone should be used only when visibility is a problem, such as during the nishing procedures of tooth preparations. At such times, air coolant combined with lower rotational speed, light, and intermittent instrument application should be used to enhance vision and minimize trauma. Air-water spray is universally used to cool, moisten, and clear the operating site during normal cutting procedures. In addition, the spray lubricates, cleans, and cools the cutting instrument, increasing its eciency and service life. A well-designed and properly directed air-water spray also helps keep the gingival crevice open for better visualization when gingival extension is necessary. e use of a water spray and its removal Abrasive Cuttinge following discussion is pertinent to all abrasive cutting situ-ations, but diamond instruments are used as the primary example.12 e cutting action of diamond abrasive instruments is similar in many ways to that of bladed instruments, but key dierences result from the properties, size, and distribution of the abrasive. e very high hardness of diamonds provides superior resistance to wear. A diamond instrument that is not abused has little or no tendency to dull with use. Individual diamond particles have very sharp edges, are randomly oriented on the surface, and tend to have large negative rake angles.When diamond instruments are used to cut ductile materials, some material is removed as debris, but much material ows laterally around the cutting point and is left as a ridge of deformed material on the surface (Fig. 14.27). Repeated deformation work hardens the distorted material until irregular portions become brittle, break o, and are removed. is type of cutting is less ecient than that by a blade; burs are generally preferred for cutting ductile materials such as dentin.Diamonds cut brittle materials by a dierent mechanism. Most cutting results from tensile fractures that produce a series of subsurface cracks (Fig. 14.28). Diamonds are most ecient when used to cut brittle materials and are superior to burs for the removal of dental enamel. Diamond abrasives are commonly used for milling in computer-assisted design/computer-assisted machining (CAD/CAM) or copy-milling applications (see Chapter 12).Cutting RecommendationsOverall, the requirements for eective and ecient cutting include using a contra-angle handpiece, air-water spray for cooling, high operating speed (>200,000 rpm), light pressure, and a carbide bur AB• Fig. 14.27 Schematic representation of an abrasive particle cutting ductile material. A, Lateral view. B, Cross-sectional view. Material is dis-placed laterally by passage of an abrasive particle, work hardened, and subsequently removed by other particles. AB• Fig. 14.28 Schematic representation of abrasive particle cutting brittle material. A, Lateral view. B, Cross-sectional view. Subsurface cracks caused by the passage of abrasive particles intersect, undermining small pieces of material, which are removed easily by following abrasive particles. e20 CHAPTER 14 Instruments and Equipment for Tooth Preparation an accident does occur and soft tissue is damaged, the operator should remain calm and control any hemorrhage with a pressure pack. e patient should be told what has happened, and medical assistance should be obtained, if needed.Eye Precautionse operator, the assistant, and the patient should wear glasses with side shields to prevent eye damage from airborne particles during operative procedures using rotary instrumentation. When high speeds are used, particles of old restorations, tooth structure, bacteria, and other debris are discharged at high speeds from the patient’s mouth. Suciently strong HVE applied by the dental assistant near the operating site helps limit this problem. Protective glasses are always indicated when rotary instrumentation is being used. e dentist, being in the direct path of such particles, is more likely to receive injury than the assistant or the patient. If an eye is injured, it should be covered by a clean gauze pad until medical attention is obtained.In addition to routine airborne debris, airborne particles may be produced occasionally by matrix failure of molded abrasive cutting instruments. Hard matrix wheels may crack or shatter into relatively large pieces. Soft abrasive wheels or points may increase in temperature during use, causing the rubber matrix to debond explosively from the abrasive into ne particles.Precautions must be taken to prevent eye injury from unusual light sources such as visible light–curing units and laser equipment. Dental personnel and patients should be protected from high-intensity visible light with the use of colored plastic shields (attached to the beroptic tip). Laser light can be inadvertently reected from many surfaces in the dental operatory; the operatory should be closed, and everyone should wear protective goggles (see earlier section Laser Equipment).Ear PrecautionsVarious sounds are known to aect people in dierent ways. Soft music or random sounds such as rainfall usually have a relaxing or sedative eect. Loud noises are generally annoying and may contribute to mental and physical distress. A noisy environment decreases the ability to concentrate, increases risk of accidents, and reduces overall eciency. Extremely loud noises such as explosions by eective high-volume evacuation (HVE) are especially important when old amalgam restorations are removed. HVE helps in rapid, ecient removal of released mercury vapor and aids in increased operator visibility.During normal cutting procedures, a layer of debris, described as a smear layer, is created that covers the cut surfaces of the enamel and dentin. e smear layer on dentin is moderately protective because it occludes the dentinal tubules and inhibits the outward ow of tubular uid and the inward penetration of microleakage contaminants. e smear layer is still porous, however. When air alone is applied to dentin, local desiccation may produce uid ow and aect the physiologic status of the odontoblastic processes in the underlying dentin. Air is applied only to the extent of removing excess moisture, leaving a glistening surface.Soft Tissue Precautionse lips, tongue, and cheeks of the patient are the most frequent areas of soft tissue injury. e handpiece should never be operated unless good access to and visualization of the cutting site are available. A rubber dam is helpful in isolating the operating site. When the dam is not used, the dental assistant may retract the soft tissue on one side with a mouth mirror, cotton roll, or evacuator tip. e dentist usually is able to manage the other side with a mirror or cotton roll, or both. If the dentist must work alone, the patient may help by holding a retraction-type saliva ejector evacuator tip after it is positioned in the mouth.e rotating instrument in a handpiece does not stop imme-diately when the foot control is released. e operator must wait for the instrument to stop or be extremely careful when removing the handpiece from the mouth so as not to contact and lacerate soft tissues. e large disk is one of the most dangerous instruments used in the mouth. Such disks are seldom indicated intraorally. ey should be used with light, intermittent application and with extreme caution.With high-speed and low-speed air-driven handpieces, sluggish handpiece performance will alert the dental practitioner to main-tenance issues such as a dull bur or worn or clogged gears or bearings. A poorly maintained electric handpiece does not provide a similar warning that maintenance is needed. Instead, if an electric handpiece is worn out, damaged, or clogged, the electric motor sends increased power to the handpiece head or attachment in order to maintain handpiece performance. is increased power can rapidly generate heat at the head of the handpiece attachment. Because the heat buildup is so rapid and is eciently conducted through the metal handpiece, a burn occurring in the patient may be the rst indication of handpiece problems. Patients have been severely burned when electric handpieces have overheated during dental procedures (Fig. 14.29). Some patients have suered third-degree burns that required reconstructive surgery. Burns may not be apparent to the operator or the patient until after the tissue damage has occurred because the anesthetized patient is not able to feel the tissue burning and the handpiece housing insulates the operator from the heated attachment. Adhering to strict maintenance guidelines recommended by the manufacturers is critical to prevent overheating in electric handpieces. e clinician must be aware that improperly maintained, damaged, or worn-out devices have the potential to overheat without warning.e dentist and assistant must always be aware of the patient’s response during the cutting procedures. A sudden reex movement caused by patient gagging, swallowing, or coughing has the potential to result in serious injury from a rotating cutting instrument. If • Fig. 14.29 This patient suffered a burn from the overheated bearing of an electric handpiece. Because the patient was anesthetized, he was unaware of the burn as it occurred from the overheated handpiece. CHAPTER 14 Instruments and Equipment for Tooth Preparation e21 eect of excessive noise levels depends on exposure times. Normal use of a dental handpiece is one of intermittent application that generally is less than 30 minutes per day and represents little risk of developing hearing loss over time. Earplugs may be used to reduce the level of exposure, but these have several obvious drawbacks. Room soundproong helps limit sound reection and may be accomplished with absorbing materials used on ceilings, walls, and oors. Antinoise devices also may be used to cancel unwanted sounds.Inhalation PrecautionsAerosols and vapors are created by cutting tooth structure and restorative materials and are a health hazard to all present. Aerosols are ne dispersions in air of water, tooth debris, microorganisms, and/or restorative materials. Cutting amalgam or composite resin produces submicron particles and vapor. e particles that may be inadvertently inhaled have the potential to produce alveolar irritation and tissue reactions. Vapor from cutting amalgam is predominantly mercury and should be captured and removed, as much as possible, by HVE near the tooth being operated on. e vapors generated during cutting or polishing by thermal decomposi-tion of polymeric restorative materials (sealants, acrylic resin, composites) are predominantly resin monomers. e resin monomers may be captured and eciently removed by careful HVE during the cutting or polishing procedures.A rubber dam protects the patient against oral inhalation of aerosols or vapors, but nasal inhalation of vapor and ner aerosol may still occur. Disposable masks worn by dental oce personnel lter out bacteria and all but the nest particulate matter. Masks do not, however, lter out mercury or resin monomer vapors. e biologic eects of mercury hazards and appropriate oce hygiene measures are discussed in Chapter 13.or continuous exposure to high noise levels can cause permanent damage to the hearing mechanism.An objectionable high-pitched whine is produced by some air-driven handpieces at high speeds. Aside from the annoying aspect of this noise, hearing loss could result from continued exposure. Potential damage to hearing from noise depends on (1) the intensity or loudness (decibels [db]), (2) frequency (cycles per second [cps]) of the noise, (3) duration (time) of the noise, and (4) susceptibility of the individual. Older age, existing ear damage, disease, and medications are other factors that can accelerate hearing loss.Normal ears require that the intensity of sound reach a certain minimal level before the ear can detect it. is is known as auditory threshold and may vary with the frequency and exposure to other sounds. When subjected to a loud noise of short duration, a protec-tive mechanism of the ear causes it to lose some sensitivity temporar-ily. is is described as temporary threshold shift. If sucient time is allowed between exposures, complete recovery occurs. Extended or continuous exposure is much more likely to result in a permanent threshold shift with persistent hearing loss. e loss may be caused by all frequencies, but often high-frequency sounds aect hearing more severely. A certain amount of unnoticed noise (ambient noise level) is present even in a quiet room (20–40 db). An ordinary conversation averages 50 to 70 db in a frequency range of 500 to 2500 cps.Air-driven handpieces with ball bearings, free running at 30-lb air pressure, may have noise levels of 70 to 94 db at high frequencies. Noise levels greater than 75 db in frequency ranges of 1000 to 8000 cps may cause hearing damage. Noise levels vary among handpieces produced by the same manufacturer. Handpiece wear and eccentric rotating instruments may cause increased noise. Protective measures are recommended when the noise level reaches 85 db with frequency ranges of 300 to 4800 cps. Protection is mandatory in areas where the level transiently reaches 95 db. e SummaryModern dental equipment allows ecient removal and shaping of tooth structures and restorative materials. Hand instruments and rotary-powered cutting burs and abrasive instruments remain essential components of the dental armamentarium. A wide variety of strategic shapes and sizes of instruments are available for use in patient care. Proper understanding and use of hand instruments, handpieces, burs, and abrasives enable optimal accomplishment of dental procedures with minimal risk to the patient and dental team.References1. Black GV: e technical procedures in lling teeth, 1899, Henry O. Shepard.2. Black GV: Operative dentistry, ed 8, Woodstock, IL, 1947, Medico-Dental.3. Peyton FA: Temperature rise in teeth developed by rotating instruments. J Am Dent Assoc 50:629–630, 1955.4. Leonard DL, Charlton DG: Performance of high-speed dental handpieces. J Am Dent Assoc 130:1301–1311, 1999.5. Myers TD: Lasers in dentistry. J Am Dent Assoc 122:46–50, 1991.6. Zakariasen KL, MacDonald R, Boran T: Spotlight on lasers—a look at potential benets. J Am Dent Assoc 122:58–62, 1991.7. Berry EA, III, Eakle WS, Summitt JB: Air abrasion: an old technology reborn. Compend Contin Educ Dent 20:751–759, 1999.8. Sockwell CL: Dental handpieces and rotary cutting instruments. Dent Clin North Am 15:219–244, 1971.9. Kunselman B: Eect of air-polishing shield on the abrasion of PMMA and dentin [thesis], Chapel Hill, NC, 1999, University of North Carolina.10. Atkinson DR, Cobb CM, Killoy WJ: e eect of an air-powder abrasive system on in vitro root surfaces. J Periodontol 55:13–18, 1984.11. Boyde A: Airpolishing eects on enamel, dentin and cement. Br Dent J 156:287–291, 1984.12. Galloway SE, Pashley DH: Rate of removal of root structure by use of the Prophy-Jet device. J Periodontol 58:464–469, 1987.13. Peterson LG, Hellden L, Jongebloed W, et al: e eect of a jet abrasive instrument (Prophy Jet) on root surfaces. Swed Dent J 9: 193–199, 1985.14. American Dental Association: Council on Dental Research adopts standards for shapes and dimensions of excavating burs and diamond instruments. J Am Dent Assoc 67:943, 1963.15. SS White Dental Manufacturing Company: A century of service to dentistry, Philadelphia, 1944, SS White Dental Manufacturing.16. American National Standards Institute: American Dental Association Specication No. 23 for dental excavating burs. J Am Dent Assoc 104:887, 1982.17. International Standards Organization: Standard ISO 2157: Head and neck dimensions of designated shapes of burs, Geneva, 1972, International Standards Organization. e22 CHAPTER 14 Instruments and Equipment for Tooth Preparation 25. Eames WB, Reder BS, Smith GA: Cutting eciency of diamond stones: eect of technique variables. Oper Dent 2:156–164, 1977.26. Hartley JL, Hudson DC, Richardson WP, et al: Cutting characteristics of dental burs as shown by high speed photomicrography. U S Armed Forces Med J 8:209, 1957.27. Koblitz FF, Tateosian LH, Roemer FD, et al: An overview of cutting and wear related phenomena in dentistry. In Pearlman S, editor: e cutting edge (DHEW Publication No. [NIH] 76-670), Washington, D.C., 1976, US Government Printing Oce.28. Westland IN: e energy requirement of the dental cutting process. J Oral Rehabil 7:51, 1980.29. Lindhe J: Orthogonal cutting of dentine. Odontol Revy (Malma) 15(Suppl 8):11–100, 1964.18. Morrant GA: Burs and rotary instruments: Introduction of a new standard numbering system. Br Dent J 147:97–98, 1979.19. Eames WB, Nale JL: A comparison of cutting eciency of air-driven ssure burs. J Am Dent Assoc 86:412–415, 1973.20. Cantwell KR, Rotella M, Funkenbusch PD, et al: Surface characteristics of tooth structure after cutting with rotary instruments. Dent Progr 1:42–46, 1960.21. Henry EE, Peyton FA: e relationship between design and cutting eciency of dental burs. J Dent Res 33:281–292, 1954.22. Henry EE: Inuences of design factors on performance of the inverted cone bur. J Dent Res 35:704–713, 1956.23. Hartley JL, Hudson DC: Modern rotating instruments: burs and diamond points. Dent Clin North Am 737–745, 1958.24. Grajower R, Zeitchick A, Rajstein J: e grinding eciency of diamond burs. J Prosthet Dent 42:422–428, 1979.

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