The relationship between dental occlusion, muscle activity and associated jaw movement in man

Abstract

Experiments were carried out on adult subjects before and after occlusal adjustment, and during atypical mastication, to study the relationship between occlusion of the teeth, muscle activity and associated jaw movements. A computer-based system was used to record and analyze the electromyographic activity in the right and left anterior temporal, posterior temporal and masseter muscles, as well as the displacement, in 3 planes, of an incisor point on the mandible. Clinical examination of the occlusion was performed by means of a standard procedure, which permitted numerical values to be assigned to variables commonly observed in clinical practice. Unilateral gum-chewing tasks were carried out by each subject. Five subjects were tested both before and two weeks after occlusal adjustment. Two subjects acted as controls. The series also included one subject with a history of bruxism and another who undertook specific chewing tasks. The results indicated a tendency for occlusal adjustment to be associated with an increase in the lateral excursions of the mandible during jaw closure and, in some cases, with a closer approximation of peak muscle activity to the intercuspal position of the teeth. Specific occlusal features showed no clear association with either muscle activity or jaw displacement, although all subjects developed maximum muscle effort very close to, or at, the intercuspal position. Jaw-closing speed during natural chewing appeared to decrease abruptly before maximum bolus resistance was met by the teeth, suggesting the existence of a neuromuscular control mechanism which operates before closing forces become very large.