Relation between electrical stimulus intensity, masseteric exteroceptive reflex and sensory perception

PURPOSE: The purpose of this study was to characterize the relation between stimulus intensity, masseteric exteroceptive suppression (ES), and sensory perception as a possible quantitative or qualitative tool in the diagnosis of the masticatory system for prosthodontic treatment. METHODS: From 12 males and 12 females (22-41 years), surface EMG was recorded from the left masseter muscle. Visual feedback allowed the subjects to maintain a constant clenching level of 30% maximal voluntary contraction. Thirteen fixed stimulus intensities from 5 to 35 mA in 2.5 mA increments were applied at random. A computer program calculated the duration of ES, based on the 50% level of the mean pre-stimulus EMG. The stimulation intensity at which early (ES1) or late (ES2) exteroceptive suppressions appeared first and at which subjects answered as being painful were defined as the reflex threshold (RT1 or RT2) and pain threshold (PT), respectively. The relation between sensory perception and ES was evaluated using stimulus-response (S-R) curve analysis. RESULTS: Significant differences were found between PT and RT1, and between RT1 and RT2 (P