13 Extraoral Techniques










158
13
Extraoral Techniques
EDUCATIONAL OBJECTIVES
Upon completing this chapter, the student will be able to:
1. Dene the key terms listed at the beginning of the chapter.
2. List and explain the two main categories of the indications
for use of extraoral projections in dental radiography.
3. Know the equipment that is needed for extraoral
projections, in addition to the function of each of them
listed. Also, discuss the lm-screen combination used in
extraoral techniques.
4. Describe the lm sensitivity of extraoral lm, the handling
of these lms in the darkroom, and the processing
requirements for these lms.
5. Discuss extraoral radiographic technique, including:
• Listanddescribethesixstepstobetakenwhen
exposing an extraoral projection for dental radiographic
purposes.
• Statetheindicationsforuse;thereceptor,patient,and
centralraypositioning;andtheexposuresettingsfor
each of the extraoral projections mentioned in this
chapter.
Newer imaging techniques—such as tomography, com-
puted tomography, and magnetic resonance imaging—also
are used by dentists to make complicated diagnoses and
treatment plans. ey are discussed in Chapter 16.
Indications
ere are two main categories of indications for the use of
extraoral projections. e rst is when patients cannot
or will not open their mouths to allow the receptor to be
placed intraorally. Handicapped patients may be unable to
open their mouths for receptor placement, and uncoopera-
tive patients may simply refuse (see Chapter 18). Patients
with trismus or temporomandibular joint (TMJ) ankylosis
cannot open their mouths. ese indications are very similar
to those listed for panoramic radiography.
e second indication is when the area being radio-
graphed is larger than or cannot be seen on intraoral projec-
tions. Many areas of the mandible and maxilla cannot be
seen on intraoral images. e scope of dental treatment,
as mentioned previously, is not limited to the teeth and
alveolar bone; it may be necessary to radiograph areas,
such as the angle and ramus of the mandible, to visualize
Introduction
e scope of dental radiology is constantly expanding; it
is not limited to panoramic radiography and the intraoral
periapical, bitewing, and occlusal lms that have been previ-
ously described. ere is an ever-increasing use of the term
maxillofacial radiology, which is that specialty of dentistry
concerned with performance and interpretation of diagnos-
tic imaging used for examining the craniofacial, dental, and
adjacent structures. ere are many accessory techniques,
intraoral and extraoral, using dierent imaging systems and
lm-screen combinations, dierent projections, and digital
systems. Operators responsible for the maxillofacial area
must be able to expose the area of interest in any way
possible to obtain a diagnostic image. e extraoral tech-
niques that are described in this chapter can be performed
with conventional or digital radiography. As is the case
with intraoral radiographs, dental professionals should be
knowledgeable and skilled in these accessory techniques.
However, some states have statutes that prohibit or limit
some dental professionals from performing certain extraoral
techniques. Information about these restrictions is readily
available from the appropriate agencies in individual states.
KEY TERMS
anteroposterior projection
cassette
cephalometric radiography
cephalostat
extraoral lms
extraoral projections
grid
lateral oblique projection
lateral skull projection
maxillofacial radiology
posteroanterior projection
submentovertex projection
Waters view

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15813 Extraoral TechniquesEDUCATIONAL OBJECTIVESUpon completing this chapter, the student will be able to:1. Dene the key terms listed at the beginning of the chapter.2. List and explain the two main categories of the indications for use of extraoral projections in dental radiography.3. Know the equipment that is needed for extraoral projections, in addition to the function of each of them listed. Also, discuss the lm-screen combination used in extraoral techniques.4. Describe the lm sensitivity of extraoral lm, the handling of these lms in the darkroom, and the processing requirements for these lms.5. Discuss extraoral radiographic technique, including:• Listanddescribethesixstepstobetakenwhen exposing an extraoral projection for dental radiographic purposes.• Statetheindicationsforuse;thereceptor,patient,andcentralraypositioning;andtheexposuresettingsforeach of the extraoral projections mentioned in this chapter.Newer imaging techniques—such as tomography, com-puted tomography, and magnetic resonance imaging—also are used by dentists to make complicated diagnoses and treatment plans. ey are discussed in Chapter 16.Indicationsere are two main categories of indications for the use of extraoral projections. e rst is when patients cannot or will not open their mouths to allow the receptor to be placed intraorally. Handicapped patients may be unable to open their mouths for receptor placement, and uncoopera-tive patients may simply refuse (see Chapter 18). Patients with trismus or temporomandibular joint (TMJ) ankylosis cannot open their mouths. ese indications are very similar to those listed for panoramic radiography.e second indication is when the area being radio-graphed is larger than or cannot be seen on intraoral projec-tions. Many areas of the mandible and maxilla cannot be seen on intraoral images. e scope of dental treatment, as mentioned previously, is not limited to the teeth and alveolar bone; it may be necessary to radiograph areas, such as the angle and ramus of the mandible, to visualize Introductione scope of dental radiology is constantly expanding; it is not limited to panoramic radiography and the intraoral periapical, bitewing, and occlusal lms that have been previ-ously described. ere is an ever-increasing use of the term maxillofacial radiology, which is that specialty of dentistry concerned with performance and interpretation of diagnos-tic imaging used for examining the craniofacial, dental, and adjacent structures. ere are many accessory techniques, intraoral and extraoral, using dierent imaging systems and lm-screen combinations, dierent projections, and digital systems. Operators responsible for the maxillofacial area must be able to expose the area of interest in any way possible to obtain a diagnostic image. e extraoral tech-niques that are described in this chapter can be performed with conventional or digital radiography. As is the case with intraoral radiographs, dental professionals should be knowledgeable and skilled in these accessory techniques. However, some states have statutes that prohibit or limit some dental professionals from performing certain extraoral techniques. Information about these restrictions is readily available from the appropriate agencies in individual states.KEY TERMSanteroposterior projectioncassettecephalometric radiographycephalostatextraoral lmsextraoral projectionsgridlateral oblique projectionlateral skull projectionmaxillofacial radiologyposteroanterior projectionsubmentovertex projectionWaters’ view 159CHAPTER 13 Extraoral Techniquesthe processed lm, or it will not be possible to orient the nished radiograph. Lead strips are available to imprint the patient’s name and the date on the lm as well. e cassettes have a front side that is usually composed of plastic and a back side that is made of metal to reduce scatter radia-tion. e front side of the cassette is the side that should face the patient and the source of radiation during an exposure.Film-Screen Combinatione imaging system used in conventional, lm-based extraoral radiography is a lm-screen system (see Chapter 4). To reduce radiation exposure to the patient, the lm is used in combination with intensifying screens. Previously in dentistry, to obtain better detail, some extraoral projections were taken with lm alone in the so-called nonscreen tech-nique. Today, with improved lm quality and concern for radiation safety, all extraoral lms should be taken using intensifying screens. e screen lm used is more sensitive to the light emitted by the intensifying screens than it is to radiation. However, the lm used must be sensitive to the type of light emitted by the particular screen (e.g., blue light or green light).As mentioned in Chapter 4, extraoral lm is available in 5 × 7-inch or 8 × 10-inch sizes. For panoramic radiography impactions or the skull for orthodontic cephalometric radiography analysis. Extraoral radiographs can be used to image the TMJ, maxillary sinus, or lesions that grow so large that they cannot be captured completely on periapical or bitewing projections. rough a combination of extra-oral radiographs, it is also possible to locate objects in the buccolingual dimension, which is necessary for implant evaluation and with occlusal radiography (see Chapter 10).NOTEIn summary, extraoral projections can be used:• Whenthepatientcannotorwillnotacceptintraoralreceptors• Toviewareasthatrequirealargeeldsize,asinevaluatingtheangleofthemandible,theramus,theskull,themaxillarysinus,orthetemporomandibularjoint(TMJ)• Forevaluatinggrowthanddevelopment• Toobserveandradiographicallyexamineimpactedteethandtheirsurroundingarea• Toexaminelargelesionsandconditionsthatcannotbeviewedonintraoralradiographs• ToexaminetraumaticconditionsofthejawsBA• Figure 13.1 A, Front view of 8 × 10-inch cassette with markingletters. B,Rigid-typelmcassettewithintensifyingscreen.(FromBirdDL, Robinson DS: Modern Dental Assisting, ed 12, St Louis, 2018,Elsevier.)Equipmente radiographic equipment needed to perform standard extraoral projections is minimal, because extraoral radio-graphs can be taken with a standard intraoral dental x-ray unit and dental chair. Conventional extraoral techniques require a regular dental x-ray unit, 8 × 10-inch or 5 × 7-inch cassettes intensifying screens, and cassette holders or angling boards. When using lm as the receptor, the darkroom must have the capacity to process the larger lm size. e use of grids, although optional, results in better image denition, because they are placed between the patient and the x-ray lm to reduce the scattered radiation and thus improve image contrast.X-Ray UnitFor extraoral radiographs, the x-ray machine must be posi-tioned in the operatory so that a target-receptor distance (or focal-lm distance [FFD]) of 36 inches can be achieved. is distance is necessary to get a suciently large divergent beam size at the patient’s face so that the complete area of interest can be radiographed and seen on the image.CassettesWhen lms are used, they are contained in a carrier called a cassette. Cassettes can be rigid or exible and are available in varying sizes corresponding to the size of the lm used (Fig. 13.1). A cassette must be light-tight but allow the passage of x-rays to aect the lm and intensifying screen contained in the cassette.Cassettes must be marked with lead letters on the front side of the cassette to identify the left or the right side of 160 CHAPTER 13 Extraoral Techniquesradiotransparent and radio-absorptive strips that is placed in front of the cassette. e grid absorbs all radiation, leaving the object that is not at right angles to the lm. In doing so, it decreases the eect of scatter on the diagnostic image. Grids are not used in intraoral radiography, because the secondary radiation does not greatly degrade the image as a result of the small eld size. e panoramic units, with their narrow exposure eld size, also do not need grids. Medical x-ray units use grids routinely. Extraoral radiographs taken with a medical x-ray machine have better-quality density and contrast than similar lms taken with a dental x-ray unit because of the use of a grid.Film Sensitivity and ProcessingExtraoral screen lms used with conventional extraoral radi-ography are more sensitive to light than are intraoral lms. erefore, what would be acceptable safelight conditions in the darkroom for processing intraoral lms might fog the extraoral lms. e lms used in panoramic radiography are also especially sensitive to excessive safelighting and may not be merely fogged but ruined. Safelighting always should be checked by the coin test before processing extraoral lms. It is also advised not to expose extraoral lms to cell phone lighting while processing them in the darkroom. Conse-quently, it is advised to turn cell phones o before entering the darkroom or not to bring them in the darkroom at all.Extraoral lms are processed in the same manner as intraoral lms, either manually or by automatic proces-sors that can accommodate large-size lm. For manual processing, the time-temperature method is used with the same xation and washing time as with intraoral lms. e only dierence is that special sizes of lm hangers are used (Fig. 13.4). Operators should take special care when processing the large lms, because they are easier to scratch when more than one lm is processed at a time.ProjectionsAs in intraoral radiography, certain factors must be known for every extraoral projection exposed, including (1) the extraoral lm is available in 5 × 12-inch and 6 × 12-inch sizes.Holding DevicesConventional extraoral cassette holders can be wall mounted or used on a tabletop if applicable. Holding devices have the advantage of standardizing techniques for comparison of lms and preventing patient and lm movement (Fig. 13.2).Gridse use of grids for extraoral radiography is not common in dental practice and is mostly conned to cephalometric and TMJ radiographs. e function of the grid is to decrease the amount of scatter radiation originating in the object (Fig. 13.3). is scatter degrades the image by decreas-ing the contrast. e grid is a thin plate composed of • Figure 13.2 Cassetteinawall-mounted,lm-holdingdevice.FilmGridScatterradiationPrimary radiation• Figure 13.3 Grid. Note absorption of scatter radiation by radio-resistantstripsofgrid.• Figure 13.4 Piece of 8 × 10-inch lm mounted on an extraoralprocessinglmhanger. 161CHAPTER 13 Extraoral TechniquesReceptor/Patient/Central Ray PositionAn 8 × 10-inch or a 5 × 7-inch receptor may be used for this projection. e receptor is supported by the patient’s shoulder or a holding device on the side of the mandible to be radiographed. e receptor is in contact with the cheekbone and mandible of the patient. e patient’s head is inclined about 15 degrees away from the x-ray tube. e central ray is directed from under the opposite side of the mandible at right angles to the receptor.Exposure Settingse target-receptor distance (or FFD) is 14 inches. An average exposure time at 65 kV and 10 mA would be 5 to 10 impulses (Fig. 13.5).Lateral Skull Projectione lateral skull projection is used to survey the whole skull in the sagittal plane. e right and left sides of the clinical indication for use of the projection; (2) the relation-ship of the receptor to the patient; (3) the relationship of the central ray of the x-ray beam to the patient and the receptor; (4) the target-receptor distance (or FFD); (5) the point of entry of the x-ray beam; and (6) the exposure settings, including the exposure time, the kilovoltage and milliamperage unless it is preset, as it usually is in the newer dental x-ray units.Lateral Oblique Projection of the Mandiblee lateral oblique projection of the mandible is used for surveying one side of the mandible entirely from the distal of the canine to the angle of the ramus, the ramus, condyle, and coronoid process. is projection is ideal for visualizing impactions, fractures, and large areas of pathologic condi-tions that would not be seen on periapical projections. It is not diagnostic anterior to the canine, because of the super-imposition caused by the anterior curve of the mandible. Before the advent of panoramic radiography, it was the most commonly used extraoral technique for mandibular pathologic conditions and impactions.Clinical IndicationTo view mandibular third molar impactions, fractures, and pathologic conditions.PROCEDURE 13.1 EXTRAORAL RADIOGRAPHIC TECHNIQUE1. Properinfectioncontrolproceduresshouldbeperformedforextraoralradiography,includingcoveringordisinfectingtheearrods,chinpositioner,headrest,biteblock,oredentulous positioner.2. Explaintheproceduretothepatient,placethedouble-sidedleadapron(withoutathyroidcollar)properlyonthepatient(belowtheleveloftheclavicles),andremoveallmetallicobjectsintheheadandneckregiontobeexposed.3. Loadtheextraoralcassetteinthedarkroomunderthepropersafelightproceduresforthelmbeingusedifusingscreenlm.Ifyouareusingadigitalsystem,followthemanufacturer’srecommendationsclosely.4. Settheexposuresettings(kilovoltage,milliamperage,andexposuretime)forthedesiredvaluesaccordingtothemanufacturer’srecommendations.5. Placethereceptorintheholdingdevice.6. Positionthepatient’sheadaccordingtotheprojection,alignthex-raybeam,andpresstheexposurebutton. HELPFUL HINTRememberthatextraorallmismoresensitivetolightthanintraorallm.Besuretodoublecheckthatacceptablesafelightconditionsarebeingusedbeforebeginningtoprocessthelm,anddonotexposetheextraorallmtocellphonelight.FilmSagittalplaneCentral rayA• Figure 13.5 Lateralobliqueprojection.Thecentralrayisdirectedat the receptor from beneath the opposite side of the mandible. A,Drawing.B,Radiograph. 162 CHAPTER 13 Extraoral TechniquesIf the lateral skull projection is to be used for cepha-lometric measurement, then a head-positioning device (cephalostat) must be used (Fig. 13.7). e cephalostat ensures that the patient’s head is accurately aligned with the sagittal plane and allows reproducibility of the patient’s position so that images taken during and after treatment are valid for comparison. As is shown in Fig. 13.7, there are digital radiographic units available that are used to take both panoramic and cephalometric radiographs particularly for orthodontic use.Posteroanterior Projectione posteroanterior projection is the companion projec-tion to the lateral skull, used to survey the skull in the anteroposterior plane (coronal, frontal), and it provides a means of localizing changes in a mediolateral direction. erefore, the left and right sides of the facial structures are not superimposed on each other, as in the lateral skull projection.Clinical IndicationIn dentistry, this projection is used to detect fractures and their displacements, tumors, and large areas of disease. It is not eective for studying the maxillary sinus because of the superimposition of other cranial structures on the sinuses. Although the anteroposterior projection shows the same area, the posteroanterior is preferred in dental radiography, because the structures that are of greatest interest are closer to the receptor in a posteroanterior than an anteroposterior projection and hence show less enlargement.Receptor/Patient/Central Ray PositionAn 8 × 10-inch receptor is used. e receptor can be held in position by the patient, but some type of receptor-holding device is preferable. e patient is positioned with the nose and forehead touching the receptor. e central ray skull are superimposed on each other, with the side nearer the tube magnied slightly more than the side nearer the receptor.Clinical IndicationDetection of pathologic conditions of the skull and cephalometrics. is projection is used in dentistry to detect fractures and systemic pathologic conditions that are also manifested in the jaws, such as Paget disease. It is the radiographic projection used by orthodontists to obtain lateral cephalometric radiographs.Receptor/Patient/Central Ray PositionAn 8 × 10-inch receptor is used. e receptor is held in position by the patient, supported on the patient’s shoulder or by some supportive device. e receptor is positioned parallel to the sagittal plane of the patient’s skull. e central ray is directed at the external auditory meatus at a target-receptor (or FFD) of 36 inches. e vertical angula-tion is zero degrees.Exposure SettingsAn average exposure time for an adult at 65 kVp and 10 mA would be 8 to 15 impulses (Fig. 13.6).Central rayAX-ray beam• Figure 13.6 Lateralskullprojection.Thecentralrayisdirectedatthe external auditory meatus ata minimum target-receptor distanceof36inches.A,Drawing.B,Radiograph.• Figure 13.7 Orthoceph OC100 D direct digital cephalometricimagingunit.Notethecephalostat(headholder).Theunitcanalsobeusedforpanoramicdigital imaging.(Courtesy GEHealthcare,DentalImaging,Milwaukee,WI.) 163CHAPTER 13 Extraoral TechniquesClinical IndicationTo evaluate maxillary sinus pathologic conditions and facial fractures of the middle third of the face.Receptor/Patient/Central Ray PositionIt diers from the posteroanterior projection positioning in that the patient’s mouth is kept open while the nose and chin are touching the cassette. e central ray is again directed at the external occipital protuberance, and a target-receptor distance (or FFD) of 36 inches is used.Exposure SettingsAn average exposure time at 65 kV and 10 mA would be 15 to 20 impulses (Fig. 13.9).Submentovertex Projectione submentovertex projection is used to detect fractures of the zygomatic arch and visualize the sphenoid and is directed at a zero-degree vertical angulation, aimed at the external occipital protuberance (the prominent bump near the base of the skull). e target-receptor distance (or FFD) is 36 inches.Exposure SettingsAn average exposure time at 65 kV and 10 mA would be 8 to 15 impulses (Fig. 13.8).Posteroanterior (Waters’) View of the Sinusese Waters’ view is a variation of the posteroanterior projec-tion that enlarges the middle third of the face and is useful in the diagnosis of maxillary sinus and other pathologic conditions occurring in the middle third of the face.Central rayAX-ray beam• Figure 13.8 Posteroanteriorprojection.Thecentralrayisdirectedat the occipital protuberanceat aminimum target-receptordistanceof36inches.A,Drawing.B,Radiograph.CentralrayFilmA• Figure 13.9 Posteroanterior projection of the sinuses (Waters’view). The central ray is directed perpendicular to the receptor atthe occipital protuberanceusing a 36-inch target-receptor distance. A,Drawing.B,Radiograph. 164 CHAPTER 13 Extraoral TechniquesCentralrayA• Figure 13.10 Submentovertex projection. A, Drawing shows that the central ray is directed frombeneaththechin(menton)at90degreestothereceptorpositionatthevertexoftheskull.B,Radiographshowingdepressedfractureofzygomaticarch.C,Radiographwitharrowspointingtothecondyles.Chapter Summary• Extraoralradiographyisperformedwiththereceptorandsource of x-radiation outside of the patient’s oral cavity.• Someofthegeneralindicationsofusefortheextraoralprojections discussed in this chapter are when patients cannot or will not open their mouths to accept intraoral receptors, to obtain a larger eld size, to evaluate growth and development in children, to view impacted teeth, and to examine large lesions and traumatic conditions in the head and neck region.• Equipmentthatisneededforextraoralprojectionsmayinclude the conventional dental x-ray unit, lm-screen systems, digital sensors, holding devices, grids, and a panoramic-cephalometric combination digital unit.• When taking extraoral radiographs, the dental profes-sional must follow the extraoral infection control procedures, explain the procedure to the patient, cover the patient with a lead apron, load the extraoral cassette if using screen lm, follow the manufacturer’s directions for digital extraoral procedures, set the desired exposure settings, have the patient remove metallic objects from the head/neck region, position the patient correctly, and then press the exposure button.• is chapter discussed various extraoral imaging tech-niques. Ultimately, the choice of which projection is required depends on what information is needed for the diagnosis and treatment of the individual patient.ethmoid sinuses, as well as the lateral wall of the maxillary sinus. It is also used in tomography as a scout image to determine the positions of the condyles.Clinical IndicationTo locate the position of the condyles, evaluate fractures of the zygomatic arch, and to view the sphenoid, ethmoid, and lateral border of the maxillary sinuses.Receptor/Patient/Central Ray Positione cassette is positioned on the vertex of the patient’s skull, and the central ray is directed from underneath the patient’s chin (menton) perpendicular to the cassette.Exposure SettingsAn average exposure time at 65 kV and 10 mA would be 8 to 10 impulses (Fig. 13.10). 165CHAPTER 13 Extraoral TechniquesLangland OE, Langlais RP: Principles of dental imaging, Baltimore, MD, 1997, Williams & Wilkins.ompson EM, Johnson ON: Essentials of dental radiography for dental assistants and hygienists, ed 9, Upper Saddle River, NJ, 2012, Pearson Education, Inc.White SC, Pharoah MJ: Oral radiology: Principles and interpretation, ed 7, St Louis, MO, 2013, Mosby.BibliographyBrooks SL, Brand JW, Gibbs SJ, et al: Imaging of the temporoman-dibular joint: a position paper of the American Academy of Oral and Maxillofacial Radiology, Oral Surg Oral Med Oral Pathol Oral Radiol Endod 83:609–618, 1997.Iannucci JM, Howerton LJ: Dental radiography: Principles and tech-niques, ed 5, St Louis, MO, 2016, Elsevier Saunders.Chapter Review QuestionsMatchingMatch the extraoral projection in Column A with the indication for use listed in Column B.Column A Column B1. Submentovertexprojection2. Lateralskullprojection3. Lateralobliqueprojectionofthemandible4. Posteroanterior projection5. Waters’viewa. Surveyonesideofthemandibleb. Maxillarysinuspathologyc. Fractures,tumors,orlargeareasofdiseased. Orthodonticcephalometricse. PositionofthecondylesMultiple Choice1. Grids can be used in extraoral imaging to: a. Position the patient correctly b. Hold the receptor in place c. Prevent harmful eects of lead in the double-sided apron d. Absorb scatter radiation e. Manage the digital sensor2. Intensifying screens are used in extraoral lm-screen systems to: a. Decrease radiation exposure to the patient b. Reduce the radiation exposure time c. Secure the cassette d. Both a and b only e. Both b and c only3. e projection that formerly was used primarily for third molar impactions prior to panoramic radiographs is the: a. Lateral skull projection b. Lateral oblique projection of the mandible c. Waters’ view d. Submentovertex projection e. Posteroanterior projection4. e projection primarily used for evaluation of the temporomandibular joint (TMJ) is the: a. Waters’ view b. Posteroanterior projection c. Lateral oblique projection of the mandible d. Lateral skull projection e. Submentovertex projection5. e Waters’ view of the maxillary sinus projection enlarges the: a. Lower third of the face b. Middle third of the face c. Upper third of the face d. 3/4 of the head and neck region e. 2/3 of the head and neck region

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