Jaw muscle soreness after tooth-clenching depends on force level.

The effects of prolonged tooth-clenching on masticatory muscle pain have not been fully elucidated. We hypothesized that late-onset soreness may develop depending on the clenching force. Ten pain-free females were asked to endure sustained clenching tasks up to exhaustion in randomized sequences of 7.5%, 10%, 15%, 25%, and 40% of maximum clenching force. Perceived pain, fatigue, and pressure-pain thresholds of masseter and temporalis muscles were assessed before, immediately after, and one day after the tasks. Endurance times differed markedly among participants and force levels, ranging from 1.2 to 245.1 min. Masseter pressure-pain threshold decreased immediately after (-13.7%; p = 0.050) and one day after (-22.0%; p = 0.006) the 7.5% task. Temporalis pressure threshold decreased one day after the 7.5 % task (-14.6%; p = 0.003). It was concluded that prolonged low-level tooth-clenching in healthy young women induces a delayed soreness in the jaw elevator muscles.