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16614 Radiography of the Temporomandibular JointEDUCATIONAL OBJECTIVESUpon completing this chapter, the student will be able to:1. Dene the key terms listed at the beginning of the chapter.2. Explain why the anatomy of the temporomandibular joint (TMJ) can cause imaging of the area to be dicult, and list the pathologic lesions related to TMJ disorders that can be seen on radiographs.3. State the clinical indication; receptor, patient, and central ray positioning; and the exposure setting for the transcranial TMJ projection.4. Describe the use of the submentovertex, panoramic, conventional tomography, computed tomography (CT), and cone beam computed tomography (CBCT) in TMJ dental imaging.5. Explain the unique role of magnetic resonance imaging (MRI) in dentistry for TMJ evaluation.6. Dene arthrography, and explain its use in TMJ dental imaging.KEY TERMSarthrographytemporomandibular joint (TMJ)transcranial projectioncondyle, the mandibular fossa (glenoid fossa), the neck of the condyle, and the articular eminence. e internal and external pterygoid muscles and the articular disc (meniscus) are not seen with routine radiographic imaging (Figs. 14.1 and 14.2), because they have soft tissue components. Some of the structures associated with TMJ images are radiolu-cent, and some are radiopaque. e articular disc, which is a major source of TMJ disorders, is not seen on conventional radiographic images, because it is brocartilaginous and thus appears radiolucent on radiographic images.e pathologic lesions associated with TMJ disorders that are seen on radiographs include fractures, benign and malignant tumors, arthritic changes, ankylosis, disc displacement, brous adhesions, and congenital absence of structures. Because the condyle is a mobile structure, it is benecial to image it in various positions (e.g., open, rest, and closed).Transcranial Temporomandibular Joint ProjectionIn addition to the panoramic view, the transcranial projec-tion is also used in the dental oce for TMJ radiography.IntroductionPatients with symptoms relating to the temporomandibular joint (TMJ) are not uncommon in dental practice. Patients may be referred for specialized treatment by other dentists or physicians when they are experiencing facial pain issues related to the TMJ. In these cases, they may bring previ-ously exposed radiographs with them or may require new or additional radiographs to be taken. Some TMJ imaging can be done in the dental oce, whereas some may have to be referred to advanced imaging centers for the appropri-ate radiographs. In either case, dental professionals should feel comfortable in dealing with these radiographic images focusing on the TMJ.Anatomy of the Temporomandibular JointBy understanding the hard tissue and soft tissue anatomy of the TMJ, a better understanding of the problems in imaging the TMJ can be appreciated. e joint is bounded laterally by the zygomatic arch and medially by the petrous ridge of the temporal bone. Structures that the dental professional should be able to identify on radiographs are the external meatus of the ear, the mastoid air cells, the mandibular 167CHAPTER 14 Radiography of the Temporomandibular JointExposure SettingsAn average exposure time at 65 kV and 10 mA would be 7 to 15 impulses (Fig. 14.3). Positioning boards (angling boards) are available to use with the transcranial technique. ese boards also incorporate means to hold the patient in a xed position while allowing movement of the receptor to give up to three exposures for each condyle (open, closed, and rest) on an 8 × 10-inch receptor.Submentovertex (Basilar) ProjectionBesides the clinical indications noted in Chapter 13, submental or basilar views can also be used to view the TMJ from the axial plane (Fig. 14.4), allowing visualiza-tion of the medial and lateral aspects of the condyle. e submentovertex projection is also used as a scout lm for tomograms of the TMJ, because the projection will relates the position of the long axis of the condyles with the patient’s midsagittal plane.Panoramic ProjectionA conventional panoramic projection shows both left and right joints in the lateral plane, as well as an overall view of the mandible and maxilla. ese views can be used for screening Clinical Indicatione clinical indication of the transcranial TMJ projection is to examine the articular eminence and the superior plane of the condyle, in addition to evaluating the condyle’s mobility when the patient’s mouth is opened. It can also be used to compare the joint spaces on the patient’s right and left sides.Receptor/Patient/Central Ray PositionA 5 × 7-inch receptor can be used if there is to be only one exposure. Usually, radiographs are taken of both the left and right condyles in both the open and closed posi-tion. Because the diagnostic area is relatively small, the four views can be placed on an 8 × 10-inch receptor when applicable. e patient’s head is positioned parallel to the receptor with the side to be imaged closest to the receptor. e receptor can be supported on the patient’s shoulder or on a positioning device in either the upright (vertical) or horizontal position. e point of entry for the central ray of the x-ray beam is on the opposite side of the head from the condyle being radiographed, approximately 212 inches above and 12 inch in front of the external auditory meatus. e x-ray beam is directed at a vertical angulation of 20 to 25 degrees. e open surface of the position-indicating device approximates the skin.Squamous part oftemporal boneMandibular fossaArticular tubercleHead of condyleNeck of condylePetrotympanicfissureExternal acousticmeatusMastoid air cellsTympanic part oftemporal bone• Figure 14.1 Sagittal view of the temporomandibular joint (TMJ). Neck of condyleHead of condyleMandibular fossaFloor ofsella turcicaClivusStyloid processOdontoidprocess• Figure 14.2 Coronal view of the temporomandibular joint (TMJ). 168 CHAPTER 14 Radiography of the Temporomandibular JointSagittalplaneCentral ray25°BA• Figure 14.3 A, Transcranial temporomandibular joint projection. B, Drawing. C, Radiograph. (A, From Okeson JP: Management of Temporomandibular Disorders and Occlusion, ed 7, St Louis, 2014, Mosby.)• Figure 14.4 Submentovertex projection. Radiograph with arrows pointing to condyles. open and closed positions. e glenoid fossa (mandibular fossa) and the condyle will be seen, but the articular disc will not (Fig. 14.6).Conventional TomographyBefore the wide use of computed tomography (CT) scan-ning, conventional tomography was one of the better ways to examine the condyle radiographically. Dedicated dental tomographic units are available (Fig. 14.7) that produce tomographic images of the TMJ (Fig. 14.8). e images are better than panoramic projections, and in some ways equivalent to a CT scan for TMJ evaluation. Again, however, • Figure 14.5 Conventional panoramic view of the temporoman-dibular joint (TMJ). • Figure 14.6 Modied panoramic view of the temporomandibular joint (TMJ). or as a scout lm to detect any other existing condition that might be the cause of TMJ pathologic processes (Fig. 14.5). If the panoramic image shows a pathologic process, a more advanced projection can be used to formulate the diagnosis. Some panoramic units have specic programs for the TMJ that also allow the dental professional to take views in the 169CHAPTER 14 Radiography of the Temporomandibular JointMagnetic Resonance ImagingMagnetic resonance imaging (MRI) is a very eective means for viewing soft tissue and thus for viewing the articular disc of the TMJ. Because the disc is an important factor in the TMJ pathologic processes, the use of an MRI should be considered. If one remembers the basic anatomy of the TMJ, the images are not dicult to read. What is radio-lucent on a CT scan or radiograph will be opaque on an MRI, indicating high soft tissue density or a strong signal. What is radiopaque on a CT scan will appear lucent on a magnetic resonance image, indicating low soft tissue density or a weak signal (Fig. 14.12).ArthrographyOne of the means of radiographing soft tissue is to outline it with a radiographic opaque contrast medium (see Chapter 18). In the case of the articular disc, a contrast medium is injected into both the upper and lower joint space, thus outlining the disc (Fig. 14.13). Arthrography is an invasive procedure that may have complications if the contrast medium is not placed in the correct space. After considering the options, MRI is the system of choice when imaging the disc and other soft tissues of the TMJ.the articular disc is not seen, but the fossa, neck, and head of the condyle are seen.Computed TomographyAs will be discussed in Chapter 16, CT and cone beam com-puted tomography (CBCT) imaging techniques facilitate viewing of an area in three planes and are excellent means for examining the bones of the TMJ. However, these scans do not include diagnostic images of the articular disc (Figs. 14.9 to 14.11).• Figure 14.7 The Gendex GXDP 700 Series is a 3-in-1 system that provides digital panoramic, cephalometric, and 3D radiography. (Courtesy KaVo Kerr, Orange, CA.)• Figure 14.8 Tomographic view of the temporomandibular joint (TMJ). • Figure 14.9 Computed tomography (CT) axial view of the temporo-mandibular joint (TMJ). • Figure 14.10 Computed tomography (CT) coronal view of the temporomandibular joint (TMJ). 170 CHAPTER 14 Radiography of the Temporomandibular Joint• Figure 14.11 Computed tomography (CT) sagittal view of the temporomandibular joint (TMJ). • Figure 14.12 Magnetic resonance image (MRI) of the temporo-mandibular joint (TMJ) showing the articular disc. • Figure 14.13 A, Contrast medium is injected into the joint space. B and C, Arthrogram images of the temporomandibular joint (TMJ). Chapter Summary• Patients withTMJ issues are quite common in dentalpractice and may require appropriate radiographs to aid in the diagnosis and treatment of these issues.• Variousdentalradiographictechniquescanprovidetheimages necessary for the clinical management of these patients.• echoice ofthe imaging techniqueis determinedbythe origin of the signs and symptoms that the patient presents with.• When the etiology of the patient’s TMJ problems arerelated to the bony components of the area, x-ray images are recommended. ese projections include the transcranial projection, submentovertex projection, panoramic projection, conventional tomography, CT and CBCT imaging.• Whentheetiologyofthepatient’sTMJissueisrelatedto the soft tissue structures of the TMJ area, it is recom-mended that the patient have an MRI taken, because this technique is more conducive to demonstrating the soft tissue components, especially the articular disc of the TMJ. 171CHAPTER 14 Radiography of the Temporomandibular Jointompson 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.BibliographyIannucci JM, Howerton LJ: Dental radiography: Principles and tech-niques, ed 5, St Louis, MO, 2016, Elsevier Saunders.Langland OE, Langlais RP: Principles of dental imaging, Baltimore, MD, 1997, Williams & Wilkins.Chapter Review QuestionsFill-in-the-Blank/Multiple Choice:1. _________________________ is a very valuable means of viewing the articular disc of the TMJ. a. Tomography b. CT scanning c. CBCT scanning d. MRI e. Submentovertex projection2. e TMJ is bounded laterally by the __________and medially by the____________. a. Clivus, styloid process b. Odontoid process, head of the condyle c. Zygomatic arch, petrous ridge of the temporal bone d. Articular fossa, neck of the condyle e. External auditory meatus, mastoid air cells3. Angling or positioning boards are used to hold the patient still and allow movement of the receptor while exposing the ______________________ projection. a. Submentovertex b. Tomographic c. Transcranial TMJ d. Panoramic e. Basilar4. Some _______________units have specic programs allowing the TMJ to be viewed radiographically in an open and closed position on the right and left sides of the patient. a. Panoramic b. CT c. Conventional dental radiographic d. Transcranial e. CBCT5. e _________________ projection can be used to visualize the medial and lateral aspects of the mandibular condyle. a. Panoramic b. Transcranial c. MRI d. CT e. Submentovertex6. An excellent means of examining the bones of the TMJ in three planes is produced by exposing a _________________ on the patient. a. Submentovertex projection b. Periapical projection c. Panoramic projection d. CT image e. Transcranial projection7. ______________________ is a means of radiographing the soft tissues associated with the TMJ with the use of an opaque contrast medium. a. Arthrography b. Conventional tomography c. CBCT scanning d. Panoramic radiography e. Cephalometric radiography