Masseter inhibitory periods and sensations evoked by electrical tooth pulp stimulation in patients with oral-facial pain and mandibular dysfunction.
The masseter inhibitory period (silent period) and sensations evoked by tooth-pulp stimulation were examined in 12 healthy subjects and 12 patients with oral-facial pain and mandibular dysfunction (MPD). Trains of 30 pulses were applied to an upper incisor and the threshold intensities for detecting sensation, for detecting pain sensation and for the masseter inhibitory period were determined. Masseter activity was monitored during tooth stimulation by electromyographic recordings from surface electrodes. Electrical tooth stimulation elicited three different configurations of masseter inhibitory periods in both groups: single, double and merged. MPD patients exhibited a greater proportion of single inhibitory periods. The combined average total durations of the three types of configurations were less in MPD. The findings are consistent with the hypothesis that there is an increase in excitability of the central masseter motorneuron pool in MPD, resulting in a reduction in the effective duration of the masseter inhibitory period. The higher incidence of single inhibitory periods in MPD patients also could result from this increased central excitatory state. There was no difference between masseter inhibitory periods evoked in either painful or non-painful muscles, and no particular configuration associated with pain sensation. The findings do not support the hypothesis that nociceptive input contributes to the increase in duration of the silent period in MPD. Although there were no significant differences between masseter inhibitory period threshold, detection thresholds or pain threshold for both groups, MPD patients had detection thresholds higher than their masseter inhibitory thresholds. These effects may be related to differential central neural influences on sensory-discriminative and reflex pathways in the trigeminal system.
D000293:Adolescent; D000328:Adult; D003782:Dental Pulp / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D005152:Facial Muscles / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D008410:Masticatory Muscles / Q000503:physiopathology*; D009209:Myofascial Pain Syndromes / Q000503:physiopathology; D009433:Neural Inhibition; D010146:Pain / Q000503:physiopathology; D012677:Sensation / Q000502:physiology; D013706:Temporomandibular Joint Dysfunction Syndrome / Q000503:physiopathology*