Quantitative evaluation of the tonic vibration reflex (TVR) in the masseter muscle

This study evaluated the efficacy of the tonic vibration reflex (TVR) elicited by high-frequency vibration in evaluating masticatory muscle excitability.

The experiment was performed on 16 male adult volunteers, 20 to 45 years of age, without spontaneous pain or tenderness in the masticatory muscles. The subjects were seated in a chair in a fixed head position with the mouth kept open with a bite block. TVR was elicited by vibratory stimulation applied to the mandible (approximately 15 m/s2, 160 Hz). An electromyogram (EMG) was recorded bilaterally from the masseter muscles and analyzed quantitatively using an arbitrary index (TVR index) calculated from the response. Bite force was measured during clenching using a pressure-sensitive foil.

Wide variations in the TVR index (maximum, 22.7%; minimum, 0.9%, average, 7.7%) were observed among individuals. The mean index for five subjects with a clenching habit was significantly higher than that for 11 subjects without a history of clenching. Tolperisone HCl (100 mg taken orally), a gamma-drive depressant, was found to reduce the response for 2 hours. There was a negative correlation (r = -.504, P < .05) between bite force and TVR index when the values on both sides were compared.

The TVR may be of use in evaluating masseter muscle excitability.