THE ROLE OF GINGIVAL MECHANORECEPTORS IN THE REFLEX CONTROL OF HUMAN JAW-CLOSING MUSCLES

Electromyographic (EMG) experiments were undertaken to investigate the jaw reflexes evoked by activation of gingival receptors in 12 humans. EMG recordings were made from an active masseter muscle whilst ramp-p lateau mechanical stimuli were applied to the gingiva. Stimuli with a constant rate of rise (0.2 N/msec) and a variable plateau force (up to 2 N), evoked a complex set of short-and long-latency inhibitory and e xcitatory responses. These occurred as a sequence of inhibition-excita tion-inhibition-excitation although not all of these elements were see n on every occasion. The median thresholds of these four responses ran ged from 0.5 to 1 N but overall there were no significant differences between them (p > 0.05, Friedman's ANOVA). In other experiments, the s ame reflexes were recorded in response to application to the gingiva o f 1 N ramp-plateau stimuli (5 msec rise time) and 1 N tap stimuli appl ied to the adjacent tooth. The application of a local anaesthetic agen t to the stimulated gingiva produced reductions in the mean magnitude of almost ail the responses but these were significant (p < 0.05; ANOV A) only for the long-latency inhibitions evoked by ramping the gingiva and the long-latency excitations evoked by either stimulus. It is con cluded that mechanoreceptors in the gingiva can mediate long-latency i nhibitory and excitatory jaw reflexes, and that these receptors may al so contribute to long-latency reflexes evoked by tapping teeth. The sc arcity of effects of gingival anaesthesia on the short-latency reflexe s may be due to such responses being mediated by receptors deeper in t he periodontium. (C) 1998 Elsevier Science Ltd. All rights reserved.