Dental stability and maximal masticatory muscle activity.

The electromyographical (EMG) activity of masticatory muscles during full clenching in the retruded contact position (RCP) and intercuspal position (IP) with and without a posterior stabilizing splint was studied. The linear envelope EMG signal from three bilateral muscles was recorded (masseter, anterior temporal and posterior temporal). Thirty-seven subjects were evaluated. Clenching in the RCP without the splint and with the presence of an unstable occlusal contact inhibited the masseter muscle activity and reduced anterior temporal and posterior temporal muscle activity. The masticatory muscle activity returned to normal when clenching in the RCP with a splint that permitted stability in the dentition. EMG activity was the same in the IP with and without the splint. The results indicate that the determinant of maximal masseter isometric muscle contraction is the amount of stability in the dentition rather than the jaw position. If the dentition takes the major role of stabilizing the mandible, i.e., there is good intercuspation, the masseter muscle can exert maximal isometric contraction. If the stability is not provided by the dentition, i.e., there is a premature contact, the jaw muscles must contribute to the stabilization and reduce the magnitude of the maximal contraction to avoid damage to the structures involved in the compensatory stabilization.