[Effect of lingual surface inclination of maxillary canine on jaw muscle activity].

The effect of lingual surface inclination of the maxillary canine on the jaw muscle activity was investigated on five subjects. Several different metal maxillary canine risers were fabricated to change the lingual inclination. The EMG activity of the masseter and posterior temporal muscle was recorded bilaterally by means of bipolar surface electrodes simultaneously with the LED mandibular tracking device. On each subject the lateral gliding movements were carried out while maintaining the occlusal contact on the canine riser. The recorded muscle activity and mandibular gliding movements were analyzed quantitatively. During the lateral gliding, the working-side posterior temporal muscle was more active than the other three muscles. Steeper canine risers caused a reduction of the muscle activity when compared with the more flat guidance. In the gliding movement from maximum intercuspation, the temporal muscle showed more activity than the masseter muscle. However the relative relationships between the individual muscles as well as the working-side muscle and nonworking-side muscle remained unchanged with all canine risers. In the gliding movement into maximum intercuspation, the difference of the canine riser showed no consistent change in the muscle activity. In each subject, it was found that the canine riser with a moderate inclination was more comfortable to move the mandible, but no relationship between the EMG activity and his or her feeling was revealed.