Internal derangement and the accessory ligaments around the temporomandibular joint.

A model that describes the mechanics of jaw opening and the associated movements of the disc in a healthy human temporomandibular joint is used to explain the abnormal movements associated with internal derangement of the joint. A change in the constraints on jaw opening imposed by the accessory ligaments around the jaw can account for, among other things, clicks on opening and closing, disc displacement and replacement, and the conditions of open and closed lock.