Effects of Posterior Tooth Occlusion on the Reflex Response of the Human Masseter Muscle

The purpose of this study was to evaluate whether the reflex response of the human masseter muscle was inhibited by posterior tooth occlusion. The reflex response of the masseter muscle was elicited by the following three kinds of stimulation a) tapping of the upper right centralincisor; b) electrical stimulation of the upper right incisor's labialgingiva; and c) tapping of the menton. These stimulations were delivered while the subjects were clenching their tooth under two different biting conditions, i. e., incisor edge-to-edge and posterior tooth biting position. Masseteric electromyograms were recorded using bipolar surface electrodes. The amplitude and the latency of the reflex responses were measured. The results were as follows: 1. The reflex responses in the masseter muscle induced by three kinds of stimulation were clearly inhibited by posterior tooth occlusion. 2. The reflex response elicited by tapping on the menton was not inhibited after local anesthesia of the gingiva around the posterior tooth in the occlusal position. These results suggest that inhibition of the human masseter muscle activity induced by posterior tooth occlusion may be elicited by afferent impulses from the mechanoreceptors in the periodontal ligament in the area of the posterior tooth.