Anatomy and histology of the human temporomandibular joint.

1. The anatomy and histology of the human temporomandibular joint indicates that the meniscus is firmly attached to the mandibular condyle and that during translatory movements the meniscus and condyle move concomitantly. The lateral pterygoid muscle, both inferior and superior heads insert into the meniscus and the pterygoid fovea of the condyle. 2. The structure of the gracilis and pars posterior indicate that these are the parts of the meniscus that are exposed to friction during jaw movement. It is suggested that during hinge movement the sagittal crest of the condyle moves from underneath the pars posterior to underneath the pars gracilis. 3. The restraining ligament for the articulation appears to be the lateral ligament. Its function is to keep the articular surfaces relatively close together during movement and to restrain lateral and posterior movements of the condyle. Its intimate association with the deep fibres of the masseter muscle appears to be important. 4. The fact that the meniscus is thicker medially than laterally would indicate that its major function is to smooth out the incongruities between the joint surfaces. 5. The sphenomandibular ligament as well as being a 'guy' ligament is intimately associated with the postero-superior medial capsular meniscal complex. The medial capsular complex would seem to contribute to the major part of the anterior ligament to the malleus. 6. Remodelling of the articular surfaces occur throughout life by progressive and regressive remodelling. However, if the remodelling processes increase, either the medio-lateral or antero-posterior dimensions of the joint an osteoarthritic condition prevails. 7. Excessive progressive remodelling appears to be due to abnormal positions of the condyle in the maximal intercuspal position. It can be caused by orthodontic procedures or by experimental displacement of the condyle. 8. The transitional zone appears to be important in the aetiology of osteoarthritis since when this zone comes under pressure proliferation of cartilage cells occur which may be transformed into bone, resulting in the hooked condyle.