Upon completing this chapter, the student will be able to:
1. Dene 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
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:
exposing an extraoral projection for dental radiographic
each of the extraoral projections mentioned in this
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.
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
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 dierent imaging systems and
lm-screen combinations, dierent 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.
lateral oblique projection
lateral skull projection
Was this article helpful?
15813 Extraoral TechniquesEDUCATIONAL OBJECTIVESUpon completing this chapter, the student will be able to:1. Dene 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:• Listanddescribethesixstepstobetakenwhen exposing an extraoral projection for dental radiographic purposes.• Statetheindicationsforuse;thereceptor,patient,andcentralraypositioning;andtheexposuresettingsforeach 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.Indicationsere 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 Introductione 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 dierent imaging systems and lm-screen combinations, dierent 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 Combinatione 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:• Whenthepatientcannotorwillnotacceptintraoralreceptors• Toviewareasthatrequirealargeeldsize,asinevaluatingtheangleofthemandible,theramus,theskull,themaxillarysinus,orthetemporomandibularjoint(TMJ)• Forevaluatinggrowthanddevelopment• Toobserveandradiographicallyexamineimpactedteethandtheirsurroundingarea• Toexaminelargelesionsandconditionsthatcannotbeviewedonintraoralradiographs• ToexaminetraumaticconditionsofthejawsBA• Figure 13.1 A, Front view of 8 × 10-inch cassette with markingletters. B,Rigid-typelmcassettewithintensifyingscreen.(FromBirdDL, Robinson DS: Modern Dental Assisting, ed 12, St Louis, 2018,Elsevier.)Equipmente 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 denition, 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 suciently 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 aect 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 eect 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 dierence 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).Gridse use of grids for extraoral radiography is not common in dental practice and is mostly conned 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 Cassetteinawall-mounted,lm-holdingdevice.FilmGridScatterradiationPrimary radiation• Figure 13.3 Grid. Note absorption of scatter radiation by radio-resistantstripsofgrid.• Figure 13.4 Piece of 8 × 10-inch lm mounted on an extraoralprocessinglmhanger. 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 Settingse 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 Projectione 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 Mandiblee 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. Properinfectioncontrolproceduresshouldbeperformedforextraoralradiography,includingcoveringordisinfectingtheearrods,chinpositioner,headrest,biteblock,oredentulous positioner.2. Explaintheproceduretothepatient,placethedouble-sidedleadapron(withoutathyroidcollar)properlyonthepatient(belowtheleveloftheclavicles),andremoveallmetallicobjectsintheheadandneckregiontobeexposed.3. Loadtheextraoralcassetteinthedarkroomunderthepropersafelightproceduresforthelmbeingusedifusingscreenlm.Ifyouareusingadigitalsystem,followthemanufacturer’srecommendationsclosely.4. Settheexposuresettings(kilovoltage,milliamperage,andexposuretime)forthedesiredvaluesaccordingtothemanufacturer’srecommendations.5. Placethereceptorintheholdingdevice.6. Positionthepatient’sheadaccordingtotheprojection,alignthex-raybeam,andpresstheexposurebutton. HELPFUL HINTRememberthatextraorallmismoresensitivetolightthanintraorallm.Besuretodoublecheckthatacceptablesafelightconditionsarebeingusedbeforebeginningtoprocessthelm,anddonotexposetheextraorallmtocellphonelight.FilmSagittalplaneCentral rayA• Figure 13.5 Lateralobliqueprojection.Thecentralrayisdirectedat 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 Projectione 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 eective 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 magnied 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 Lateralskullprojection.Thecentralrayisdirectedatthe external auditory meatus ata minimum target-receptor distanceof36inches.A,Drawing.B,Radiograph.• Figure 13.7 Orthoceph OC100 D direct digital cephalometricimagingunit.Notethecephalostat(headholder).Theunitcanalsobeusedforpanoramicdigital imaging.(Courtesy GEHealthcare,DentalImaging,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 diers 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 Projectione 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 Sinusese 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 Posteroanteriorprojection.Thecentralrayisdirectedat the occipital protuberanceat aminimum target-receptordistanceof36inches.A,Drawing.B,Radiograph.CentralrayFilmA• Figure 13.9 Posteroanterior projection of the sinuses (Waters’view). The central ray is directed perpendicular to the receptor atthe occipital protuberanceusing 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 frombeneaththechin(menton)at90degreestothereceptorpositionatthevertexoftheskull.B,Radiographshowingdepressedfractureofzygomaticarch.C,Radiographwitharrowspointingtothecondyles.Chapter Summary• Extraoralradiographyisperformedwiththereceptorandsource of x-radiation outside of the patient’s oral cavity.• Someofthegeneralindicationsofusefortheextraoralprojections 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.• Equipmentthatisneededforextraoralprojectionsmayinclude 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 Positione 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. Submentovertexprojection2. Lateralskullprojection3. Lateralobliqueprojectionofthemandible4. Posteroanterior projection5. Waters’viewa. Surveyonesideofthemandibleb. Maxillarysinuspathologyc. Fractures,tumors,orlargeareasofdiseased. Orthodonticcephalometricse. PositionofthecondylesMultiple Choice1. Grids can be used in extraoral imaging to: a. Position the patient correctly b. Hold the receptor in place c. Prevent harmful eects 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