Parameters of some reflexes of human jaw elevator muscles

Because of the potential diagnostic value in mandibular joint dysfunction, the similarities and differences in 3 open-close-clench (OCC) cycles, at ad libitum, 1 s and 2 s , were investigated. The response to chin taps with the jaw elevator muscles both relaxed (CTRL) and clenched (CTCL) were also studied from surface electromyographs over the masseter and anterior temporalis muscles of 10 normal adults. In OCC cycles, there were positive correlations between total cycle length and the inactive component and the duration of muscle activity (clench) after inhibition induced by tooth contact. Negative correlations were found between the duration of muscle activity before tooth contact and the clench and inactive components. The inactive and clench components changed most with variations in cycle duration and the latency between tooth contact and resultant inhibition varied little. For chin tap responses, there were no significant differences between masseter and temporalis muscles. The latency between mallet contact and inhibition in CTCL responses was the same as the latency in OCC cycles but shorter than the equivalent sum of latency and activity in the CTRL responses. If a common mechanism exists for the three reflexes, their parameters suggest that OCC and CTCL reflexes are facilitated with respect to CTRL.