Effects of 5 days of repeated submaximal clenching on masticatory muscle pain and tenderness: an experimental study.

The hypothesis of this short-term study was that repeated episodes of clenching at submaximal bite force levels can induce a progressive increase in pain and tenderness in masticatory muscles. On each day for 5 consecutive days, 10 women clenched on a bite force transducer for 15 minutes at 25% of their maximal bite force. The development of pain, tenderness, and unpleasantness in the masticatory muscles was evaluated with use of 10-cm visual analog scales (VAS) and the McGill Pain Questionnaire (MPQ). Pain detection thresholds (PDT) and pain tolerance thresholds (PTT) to percutaneous pressure stimuli were measured in the masseter and anterior temporalis muscles. Maximal voluntary bite force to brief clenches were assessed. The results showed moderate levels of pain (mean +/- SE; 5.3 +/- 1.0), tenderness (5.2 +/- 1.0), unpleasantness (5.8 +/- 0.8), and MPQ scores (16.4 +/- 4.9) immediately after the submaximal clenching task on the first day. The following days, the clenching tasks did not increase these scores; in contrast, there were significant decreases on day 5 in both pain intensity (-49.8% +/- 14.6%), tenderness (-46.1% +/- 14.2%), unpleasantness (-50.4% +/- 8.5%), and MPQ scores (-45.8% +/- 13.3%) (P < .05) when compared to day 1. The clenching procedure failed to induce a progressive increase in pain and tenderness in the masticatory muscles during 5 days. None of the evaluated parameters from this study suggested the start of a vicious cycle.