[Effects of occlusal position on masticatory muscle activity].

The effects of different occlusal position on the masticatory muscle function were investigated on 5 subjects. Two types of maxillary stabilization splints were fabricated in order to change the occlusal position. One type of the splints was to increase the occlusal height and the other was to shift the occlusal position laterally. The EMG activities of the masseter (M) and the anterior and posterior temporal muscles (AT, PT) were measured in various occlusal positions at 50% of maximal voluntary activity of the M and AT. The results were as follows: 1. When the occlusal height was increased. 1) The activity of the PT decreased in most subjects. 2) Asymmetry index (AI) of each tested muscle did not always indicate a similar value. 2. When the occlusal position was shifted laterally, 1) The activities of the ipsilateral AT and PT were higher than those of the contralateral side. 2) The AI of the AT and the PT changed gradually when the occlusal height was large while they changed greatly near the intercuspal position (IP) when the occlusal height was smaller. Therefore, the symmetry of the temporal muscle activity was thought to be influenced sensitively by the lateral shift of jaw position near the IP.