Abstract
The present study investigated whether visual sensory inputs influence masticatory muscle activities during tooth tapping movements. The masseter and temporal muscle activities of 25 healthy subjects were analyzed by monitoring electromyograms (EMGs) recorded with a pair of surface electrodes. Jaw movement was also analyzed by monitoring the motion of an LED reference point fixed on the lower incisor with a photo sensor. Mounted glasses with prismatic lenses were used for changing the scenery before the subjects' eyes. The subjects lay in the supine position with their head supported by a pillow. They were asked to perform repetitive tooth tapping movements when putting on or taking off the glasses. A decrease in the ratio between the temporal EMG and the masseter EMG (T-M ratio) was found in almost all the subjects when putting on the glasses. Simultaneously, anterior shift of the tapping point occurred when putting on the glasses. However, when wearing the glasses, a decrease in T-M ratio and anterior shift of the tapping point did not occur when the subjects maintained their head posture with their neck muscles. These results suggest that visual sensory inputs control masticatory muscle activities during tooth tapping movements, and that neck muscle proprioceptors play a role in this regulating system.
