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April 13, 2008

By Joanne Éthier, DMD, MBA, Tara Maghsoodi, DDS, and Marcel Noujeim, DDS, MS

The main functions of the temporomandibular joint (TMJ) are mastication and speech. The TMJ is one of a variety of synovial joints and is similar to the knee articulation. These can be qualified as ginglymoarthrodial joints, a term that comes from the Latin ginglymus, meaning a hinge joint which permits motion only backward and forward in one plane, and arthrodia, which means that it permits a gliding motion of the surfaces.

The common features of all synovial joints are a disk, bone, fibrous capsule, fluid, synovial membrane, and various ligaments to strengthen the articulation and prevent excess movement. However, what makes the TMJ unique and differentiates it from all the other synovial joints are its articular surfaces which are covered by fibrocartilage instead of hyaline cartilage like in the knee. Its movement is guided by the shape of the bones, the muscles, the ligaments, and the occlusion of the teeth.(1) Although the TMJ is composed of two joints that are both joined by only one bone, the mandible, they cannot move independently of one another and therefore, it is considered as only one component. The movements are by masticatory muscles working together in a synchronized manner and are controlled in part through the sensory innervation of the joint. According to Hilton's law, the muscles acting on a joint have the same nerve supply as the joint.(2)

Temporomandibular disorder (TMD)

According to Dr. Edward Wright, temporomandibular disorder (TMD) is a collective term used for a number of clinical problems that involve the masticatory muscle, TMJ, and/or its multiple related structures. It has plagued humanity throughout history and treatment has been reported even during the time of the ancient Egyptians. TMD is an extremely common disorder that is most often reported in females between the ages of 20 and 40. Approximately 33% of the population has at least one TMD symptom and 3.6% to 7% of the population has TMD with sufficient severity to cause patients to seek treatment. It is plausible that more women than men present for treatment of TMJ diseases and although difficult to explain, the higher prevalence of degenerative lesions in women is supported by the literature.(3)

Patients with radiographically normal joints may have pain, just as those with clear signs of bone abnormalities may be pain-free.(4) These TMJ disorders can vary from static and dynamic displacements to multiple forms of disk deformations.(5) It might be due to an internal derangement which consists of a pathological process that can progress from a luxation of the disk with reduction (a popping or clicking sound that is usually nonpainful) to a disk perforation (a painful grinding sound that cannot be diagnosed only from a clinical evaluation). The close association between permanent disk displacement (i.e., without reduction) and bone changes is well documented and has been statistically validated in many studies.(5,6)

Different modalities for TMJ disorder evaluation

All imaging techniques are not equally effective for each of the many conditions that affect the TMJ.(4) Traditionally, MRI, arthrography, and sometimes ultrasound have been used to obtain a precise diagnosis of soft-tissue pathologies and were permitting the assessment of internal derangements of the TMJ articulation.

Magnetic resonance imaging (MRI) has been proven to demonstrate disk position and morphologic condition better than CT. It is an expensive examination because of the cost of the equipment, facilities, staffing, and replacement cryogens for the magnet. The osseous structures are not as well visualized as on some other modalities.(4) According to Milano et al.,(5) identification of the position and structure of the disk is the most common reason for requesting MRI of the TMJ. Although it can provide information on the position and morphology of the disk, the quantity of synovial fluid, posterior attachment, and the retrodiskal tissues, it is not very sensitive for demonstrating disk perforations and adhesions, which are better investigated with arthrography. According to Milano et al.,(5) anterior and posterior displacement are the most common and the rarest respectively, and the MRI can feature each type of displacement except posterior displacement.

TMJ arthroscopy was introduced in the United States by Sanders in the 1980s.(7) It is mostly used for visualization of disk perforations, adhesions, and capsular tears. Disk attachments can also be seen by flow of contrast medium into one space. Murakami and Segami(8) determined the effectiveness of diagnostic arthroscopy in indicating the presence of intracapsular adhesions. However, the diagnostic value of arthroscopy is much less reliable in determining perforations. K. Kurita et al.,(9) reported that two-thirds of the perforations identified at fresh cadaveric dissection were not visualized arthroscopically.

In panoramic imaging, because of the superimposition of some bone structures, only marked changes of the bone such as obvious erosions, sclerosis, and osteophytes of the condyle can be seen. In addition, to the superimposition, a distortion effect not seen in conventional tomography may affect the quality of the image.

For pathological conditions and trauma in the maxillofacial region, CT has been traditionally used. There are several conditions with TMD that can be detected using CT such as osteophytes formation, erosion, fractures, ankylosis, developmental abnormalities, as well as positioning of the condyle in the glenoid fossa. The advantage of tomography over panoramic radiography is the capability to give multiple thin slices through the region of interest. This overcomes the distortion or superimposition of the bony structures encountered in panoramic radiographs and permits all mineralized structures of the joint to be assessed. However, just like in panoramic imaging, no visualization of the disk position and soft tissues is possible.(4)

While based on the same principle as the conventional tomography, which is to visualize bone structures, in computed tomography (CT), thin sections of the regions of interest can be made in several planes and viewed under varying conditions that emphasize, depending on the window, either hard or soft tissue as well as eliminate the blurring of the structures positioned outside the image layer of conventional tomography. CT also can provide three-dimensional reconstructed images from the original data. CT is suitable for the diagnosis of bony abnormalities including fractures, dislocations, arthritides, ankylosis, and neoplasia.(4) However, the high radiation dosage in CT should not allow the practitioner to choose it as the main imaging modality.

Introduced in the United States in 2001, another modality is becoming more popular within the dental community — the Cone Beam Computed Tomography (CBCT). It not only allows a shorter scanning time, but, depending on the machine, uses six to 10 times less radiation to the patients than the medical CT and, moreover, at a lower cost. With this modality, as in CT, all bony structures are well perceived, and this is often enough to render a diagnosis on TMJ structures. The condyle can be assessed for diverse bony changes such as shape (concavity or exostosis) and advanced bone lesions such as osteoarthrosis. The CBCT offers a better rendering of diagnosis due to the possibility of generating new slices at the angles needed to the long axis of the condylar head. To disclose the amount of the osseous changes and evaluate the possibility of neoplasia, hard tissue imaging of the joint should be done in preferably three planes; therefore, CBCT is the modality of choice and will provide better visualization of the osseous components.(4) The CBCT seems to be as accurate for assessment of the articular space and could become the new standard for TMJ examination. Although CBCT does not permit a dynamic visualization of the joint like arthrography, it is less invasive and involves no pain or discomfort and, therefore, it might eventually become the second step after clinical evaluation for TMJ assessment of all kinds.

In their article, Meng JH et al.(10) concluded that: CBCT, which reproduced multiple images including axial, coronal, and sagittal planes of the joint, provides a complete radiographic investigation of the bony components of the TMJ and is one of the best choices of imaging diagnosis of TMJ osteoarthritis.

The most appropriate imaging procedures provide the most information and will influence patient care. The decision should be supported by the history and clinical findings, diagnosis, cost of the examination, amount of radiation exposure, and prior examinations.(4)

It is essential, however, to mention that radiographic changes are not always testimony of TMD and in many cases, even though severe radiographic changes are noted, the patient might not be symptomatic, and in this circumstance, no radiographic evaluation should be done.(4) The presence of a sign and/or symptom for more than six months should be one of the selection criteria for requesting such a modality, and in all cases, both joints should be imaged for comparison. In suspicion of soft tissue or disk displacement, an adjunct MRI may be required to make a definitive diagnosis.

It is important to mention that from a legal standpoint, since very few general practitioners have been trained to interpret the results of radiological tests relating to TMJ disorders, a CBCT acquisition should always be accompanied with a report from a board certified oral and maxillofacial radiologist.

Joanne Éthier, DMD, MBA, is a fellow in forensic odontology and is a second-year resident in oral and maxillofacial radiology at the University of Texas Health and Science Center in San Antonio.

Tara Maghsoodi, DDS, is a second-year resident in oral and maxillofacial radiology at the University of Texas Health and Science Center in San Antonio.

Marcel Noujeim, DDS, MS, is the assistant program director of oral and maxillofacial radiology at the University of Texas Health and Science Center in San Antonio.

Table 1

As seen in table 1. The Oral and Maxillofacial Radiology Department of the University of Texas Health and Science Center at San Antonio have seen 196 patients that were referred for TMJ consultations. On these 196 patients, less that 5% had to go for further MRI imaging. Therefore, a lot of TMJ problems have been identified or ruled out with CBCT imaging and due to its low cost and low dosage in comparison with medical CT, there was no hesitation to use that modality instead of the medical CT.

Table 2

References

1. X. Alomar, MD, J. Medrano, MD, J. Cabratosa, MD, J.A. Clavero, MD, M. Lorente, MD, I. Serra, MD, J.M. Monill, MD, and A. Salvador, MD, Anatomy of the Temporomandibular Joint,
Semin Ultrasound CT MRI 28:170-183 © 2007 Elsevier Inc.

2. Nanci, A, Ten Cate's Oral Histology: Development, Structure, and Function Elsevier, 2003.

3. Wright, Edward F. Wright. Blackwell Publishing, 03/31/2005, Manual of Temporomandibular Disorders.

4. Sharon L. Brooks, John W. Brand, S. Julian Gibbs, Lars Hollender, Alan G. Lurie, Karl-Ake Omnell, Per-Lennart Westesson, and Stuart C. White, Ann Arbor, Mich., Oklahoma City, Okla., Nashville, Tenn., Seattle, Wash., Farmington, Conn., Rochester, N.Y., and Los Angeles, Calif. Imaging of the temporomandibular joint. A position paper of the American Academy of Oral and Maxillofacial Radiology (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997; 83:609-18).

5. Milano V, Desiate A, Bellino R and Garofalo T. Magnetic resonance imaging of temporomandibular disorders: classification, prevalence and interpretation of disk displacement and deformation.

6. De Leeuw R, Boering G, Van der Kuijl B. Hard and soft-tissue imaging of the temporomandibular joint 30 years after diagnosis of osteoarthrosis and internal derangement. J Oral Maxillofac Surg 1996; 54:1270 ± 1280.

7. Indresano A.T. DMD and Mobati D.D. DDS, MD. History of Temporomandibular Joint Surgery. Oral and Maxillofacial Surgery, Arthur A. Dugoni School of Dentistry, University of the Pacific, 2155 Webster Street 522J, San Francisco, CA 94115, USA.

8. K. Murakami and N. Segami, Intra-articular adhesions of the temporomandibular joint: arthroscopic views and clinical perspectives. In: G. Clark, B. Sanders and C. Bertolami, Editors, Advances in diagnostic and surgical arthroscopy of the temporomandibular joint, WB Saunders, Philadelphia 1993; 15-21.

9. K. Kurita, S.L. Bronstein and P.L. Westesson et al., Arthroscopic diagnosis of perforation and adhesions of the temporomandibular joint: correlation with post mortem morphology. Oral Surg Oral Med Oral Pathol 1989; 68:130?134.

10. JHong Meng et al. Diagnostic evaluation of the temporomandibular joint osteoarthritis using cone beam computed tomography compared with conventional radiographic technology. Beijing Da Xue Xue Bao. 2007 Feb 18; 39(1):26-9 17304321.

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