Experimental grinding in healthy subjects: a model for postexercise jaw muscle soreness?

AIMS: Pain in some bruxers has been suggested to represent a state of postexercise muscle soreness. This study examined the effect of voluntary, controlled grinding movements on the development of pain and soreness in the masticatory system. METHODS: Twelve healthy men (21 to 42 years old) without signs or symptoms of temporomandibular disorders (TMD) participated. Nine trials of 5 minutes of repeated grinding from the intercuspal position to the right canine-canine position (0.5 Hz) were performed on the first day. During the lateral excursions, the electromyographic (EMG) activity of the right masseter muscle was kept above 50% of maximal voluntary occlusal force (MVOF) with the use of visual feedback. The subjects rated pain intensity, unpleasantness, and soreness on 100-mm visual analogue scales (VAS); other pain measures, including the McGill Pain Questionnaire, were also used. Before and after the exercise trials, the MVOF was determined, and pain detection thresholds (PDT) to pressure stimuli were measured at 9 different sites on the masseter muscles. The subjects returned to the laboratory the 3 following days, where VAS, PDT, and MVOF were measured. RESULTS: Immediately following the last grinding trial, there was a significant increase in VAS and MPQ scores of pain intensity, unpleasantness, and soreness, as compared to baseline values (analysis of variance, P 0.001). There was still a significant effect from grinding on the VAS score of muscle soreness on the following days, with a peak the first day after the exercise (Tukey test, P 0.023). Pain was frequently (in 7 of 12 subjects) reported in or around the temporomandibular joint. There was a significant effect from grinding on PDT at both masseter muscles (analysis of variance, P 0.043), with significantly lower PDT the first day after the grinding exercise (Tukey test, P 0.046). There were no effects from grinding on MVOF. CONCLUSION: These findings suggest that significant but low levels of postexercise muscle soreness can be elicited by standardized grinding movements in the masticatory system of healthy subjects.