Functions of condylar translation in human mandibular movement

Mandibular movement in many mammals is controlled by a pure hinge joint. Since condylar translation is a structurally complex adaptation and a common source of human clinical dysfunction, there have been many attempts to evaluate the biologic significance of human condylar translation. The three hypotheses concerning condylar translation considered in this study are (1) that it results in a center of rotation of the mandible in the area of the mandibular foramen, minimizing displacement of the inferior alveolar neurovascular bundle during mandibular movement, (2) that it reduces the amount of stretch in the masseter muscle during opening, allowing the muscle to function within an efficient portion of the muscle fiber length-tension curve, and (3) that it prevents compromise of the airway and other cervical structures by the tongue and mandible during opening. Ten subjects with cephalometric radiographs taken both in centric relation and with the mandible wide open are evaluated. The movement of the mandibular foramen, the stretch of the masseter muscle, and the proximity of the tongue and mandible to the airway are compared during actual opening and when mandibular opening is modeled as a pure hinge movement. The results indicate that condylar translation performs all three functions. However, a review of other data leads to the conclusion that airway preservation in human beings may be a more critical problem and a more essential function of condylar translation than either reducing movement of the mandibular foramen or reducing stretch of the masseter muscle.