Reflex response of temporal muscle induced by mechanical stimulation to periodontal ligament--in the lateral jaw movement during mastication

Abstract

In order to investigate the role of periodontal sensation in the regulation of human masticatory movement, particularly during lateral jaw movement from the working side to the intercuspal position, the responses of 8 motor units of contralateral temporal muscle (CTM) from 6 subjects to mechanical stimulation of the maxillary canine on the working side were analysed. The results were as follows: 1. The tonic response of the CTM to tonic mechanical stimulation of the maxillary canine on the working side was observed. The CTM responded much more clearly than the ipsilateral temporal muscle did. 2. After the periodontal sensation was blocked by 2% xylocaine, the CTM gradually showed less response. Therefore, it was proven that the periodontal sensation induced this CTM response. 3. When the load exceeded approximately 200 gf, the response of the motor unit (RMU) in the CTM to the loads reached its maximum response level. The tendency observed was that the more the background activity increased, the more the RMU to the loads decreased. 4. In normal occlusion, D1 stimulation had more effect on the RMU to the direction of mechanical stimulation than that of D2 stimulation. 5. When the maxillary canine in the cross-bite position was stimulated, the RMU to the direction of mechanical stimulation showed an opposite response pattern to that of normal occlusion. It suggested that malocclusion was one of the factors which influenced the RMU pattern of the CTM.