Force-related changes in the masseter muscle reflex response to tooth-taps in man.

In 14 subjects with no disorder of the masticatory apparatus, excitatory and inhibitory reflex responses in the masseter muscles were derived by standardized mechanical stimulation of the upper central incisor. A series of eight taps was delivered during isometric contraction at 40% of maximum EMG activity, with tapping forces ranging from 0.25-9 N. The mean post-stimulus masseteric EMG complex (PSEC) consisted of up to three inhibitory (I-1, I-2 and I-3) and three excitatory phases. The first inhibitory wave increased in duration with increasing tapping force, and the second and third inhibitory waves occurred at higher thresholds than the first inhibitory wave.