Jaw pain and stiffness levels after repeated maximum voluntary clenching.

Ten normal male volunteers performed six maximum voluntary isometric jaw-closing muscle contractions within an 80-minute experimental period. Each individual contraction was sustained until maximum pain tolerance was reached. Before and one, two, three, and seven days after the experiment, the following measures were made: (1) superficial masseter and anterior temporalis muscle tenderness (pain threshold), (2) jaw movement (opening and lateral excursion), and (3) current pain level for the right and left sides of the jaw. In this study, measures of current jaw pain, muscle pain threshold, maximum active opening, and maximum lateral excursions showed no significant post-experimental changes. These results challenge the idea that sustained isometric clenching in healthy male subjects could be used as a model for chronic or even subacute muscle pain, as has been suggested by previous investigators.