Differential roles of periodontal mechanoreceptors of working-side posterior teeth in triggering nonworking-side temporalis activities.

The purpose of this study was to examine how the periodontal sensory inputs of working-side maxillary posterior, teeth affect nonworking-side anterior temporalis activities at the starting jaw position of the slow-closing phase in mastication. Six subjects with normal occlusion were asked to bite an incisal block to maintain the initial jaw position of the slow-closing phase and to generate jaw-closing muscle activities. Bipolar needle electrodes were inserted into the nonworking-side anterior temporalis to record spike discharges from a single motor unit. To stimulate the periodontal mechanoreceptors, mechanical stimulations were applied to the working-side maxillary first molar, first and second premolar in bucco-palatal, palato-buccal, and apical directions. Meanwhile, we examined changes in the discharge frequency of the motor unit activities of the nonworking-side anterior temporalis. We found that the palato-buccal stimulation to the working-side maxillary first molar and the apical stimulation to each working-side maxillary posterior tooth significantly increased the nonworking-side anterior temporalis activities; however, palato-buccal and bucco-palatal stimulations applied to the first and second premolar didn't. Thus, differential responses of the nonworking-side anterior temporalis are found by the working-side maxillary first molar and premolar stimulations. These findings may be due to some differences in function between molar and premolar.