title: The role of gingival mechanoreceptors in the reflex control of human jaw-closing muscles.
abstract: 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-plateau 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 excitatory responses. These occurred as a sequence of inhibition-excitation-inhibition-excitation, although not all of these elements were seen on every occasion. The median thresholds of these four responses ranged 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 same reflexes were recorded in response to application to the gingiva of 1 N ramp-plateau stimuli (5 msec rise time) and 1 N tap stimuli applied to the adjacent tooth. The application of a local anaesthetic agent to the stimulated gingiva produced reductions in the mean magnitude of almost all the responses but these were significant (p < 0.05; ANOVA) only for the long-latency inhibitions evoked by ramping the gingiva and the long-latency excitations evoked by either stimulus. It is concluded that mechanoreceptors in the gingiva can mediate long-latency inhibitory and excitatory jaw reflexes, and that these receptors may also contribute to long-latency reflexes evoked by tapping teeth. The scarcity of effects of gingival anaesthesia on the short-latency reflexes may be due to such responses being mediated by receptors deeper in the periodontium.
authors.affiliation: Craniofacial Biology Research Unit, King's College London, Strand, England, U.K.
authors.forename: C
authors.initials: C
authors.lastname: Louca
authors.forename: S D
authors.initials: SD
authors.lastname: Vidgeon
authors.forename: S W
authors.initials: SW
authors.lastname: Cadden
authors.forename: R W
authors.initials: RW
authors.lastname: Linden
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000779:Anesthetics, Local / Q000494:pharmacology; D004056:Differential Threshold / Q000502:physiology; D004576:Electromyography; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D005881:Gingiva / Q000187:drug effects / Q000294:innervation*; D006801:Humans; D008406:Masseter Muscle / Q000502:physiology*; D008465:Mechanoreceptors / Q000187:drug effects / Q000502:physiology*; D010474:Percussion; D010519:Periodontium / Q000294:innervation; D010812:Physical Stimulation; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013314:Stress, Mechanical; D014070:Tooth / Q000294:innervation
chemical_list: D000779:Anesthetics, Local