Temporomandibular joint

the articulation between the head of the mandible and mandibular fossa and the articular tubercle of the temporal bone. The major soft tissue structure of the TMJ is a biconcave fibrocartilaginous articular disc (meniscus) that separates the joint into two synovial joints, one superior, between the temporal bone and the disc, and the other inferior, between the disc and the condylar head. As the jaw opens and closes, the disc and condyle move in a complex coordinated fashion. Also, see temporomandibular joint.

2. Pathology

Disorders of the temporomandibular joint may be extracapsular or intracapsular (Table 1).

Temporomandibular joint (TMJ), Table 1. Classification of temporomandibular joint disorders.

Extracapsular disorders are often classified as a myofascial pain-dysfunction syndrome. Some combination of neck and masticatory muscle pain, headache, joint noise, tinnitus, malocclusion, deviation of the mandible, loss of motion, and stress or anxiety are typical. However, results of radiography, arthrography and sectional imaging are normal. Intracapsular disorders may also exhibit similar combinations of symptoms, although imaging workup often discloses a structural or functional abnormality.

Fractures of the mandible may result from a direct force applied to the face. Because the mandible is a ringlike structure, when one fracture is discovered, another mandibular fracture should be sought. Among the complications of these fractures are loss of teeth, malunion or nonunion, displacement with deformity, infection, dental malocclusion and temporomandibular joint internal derangement.

Internal derangement, which represents an abnormal relationship of the disc relative to the condyle, fossa and articular eminence, is the most frequent disorder of the temporomandibular joint. Displacement of the disc results in irregular or limited joint movements, characterized clinically as clicking or locking.

Although conventional radiography produces good results, improved images are obtainable with specialized projections and more advanced techniques. Using the Townes projection, a frontal or coronal image of the condylar head and mandibular fossa of the temporal bone is obtained that reveals detailed features of the medial and lateral poles of the condylar head, the posterosuperior cortical surface and the condylar neck. The submentovertical (base) projection also images the medial and lateral condylar poles and profiles the anterior and posterior cortical surfaces. The panoramic radiographic projection images both temporomandibular joints simultaneously and provides an excellent survey of the mandible and dentition.

CT scanning is also useful diagnostically, especially in the detection of internal derangement of the disc, although MR imaging has surpassed CT as the noninvasive imaging method used in most institutions. Documenting the position of the disc and the status of the bone structures of the temporomandibular joint can be done well with T1-weighted spin-echo MR images alone; however, identification of fluid or masses within the joint or surrounding muscles requires use of some type of T2 weighting. For evaluation of routine internal derangements of the TMJ, two sets of sagittal T1-weighted images, one with the mouth closed and the other with the mouth completely open, constitute a standard protocol.

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