Topical review: new insights into the pathology and diagnosis of disorders of the temporomandibular joint.

The collection of conditions affecting the temporomandibular joint (TMJ) and masticatory muscles, the so-called temporomandibular disorders, can be classified according to the Research Diagnostic Criteria for Temporomandibular Disorders. Of the 3 subgroups--muscle disorders (Group I); disc displacements (Group II); and arthralgia, arthritis, and arthrosis (Group III)--the muscle disorders are most frequently seen in community samples; Group II and Group III diagnoses are less prevalent. This may explain the relative scarcity of studies involving intracapsular TMJ disorders. In this review, new insights into the functional anatomy, imaging, and pathology of disorders of the TMJ are presented. Studies of TMJ dynamics may provide insight into the functional anatomy of the TMJ and thereby into the consequences of Group II and Group III disorders. The clinical use of imaging modalities such as computed tomography and magnetic resonance imaging for the TMJ and related structures remains controversial. Nevertheless, imaging is regularly used in the diagnosis of some Group II and Group III disorders. Magnetic resonance imaging may be of use not only for the visualization of disc displacements but also for the study of bone mineral density of the condyle. Cytokines such as interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) play an important role in TMJ pathology. For example, IL-1beta, which has been associated with TMJ pain, hyperalgesia, and anterior bite opening, is mostly absent in the synovial fluid of healthy joints. Since both IL-1 and TNFalpha are involved in the development of chronic pain and joint destruction, they may be the targets for specific treatments. While the advances reviewed in this paper are significant, multidisciplinary efforts and formation of international research collaborations will be necessary to continue advancement in the understanding of TMJ pathology and diagnosis.