Properties of tonic episodes of masseter muscle activity during waking hours and sleep in subjects with and without history of orofacial pain.

PURPOSE: To provide a scientific data related to the tonic activity of masseter muscle in subjects with and without history of orofacial pain during their normal daily life.

METHODS

Thirty-three subjects were divided into two groups, a pain history group (PHG) and a non-pain history group (non-PHG), based on their responses to the Research Diagnostic Criteria for Temporomandibular Disorders questionnaire. After excluding four subjects with incomplete recordings, full-day masseter muscle surface EMGs of 29 subjects (10 men, 19 women; mean age 24.1 years) were analyzed. Tonic episode (TE) was defined as continuous EMG activity with a duration at least 2s with intensities above twice the baseline noise level. TEs were classified into 6 strength categories (<7.5%, 7.5-10%, 10-15%, 15-25%, 25-40% and >40% of the maximum voluntary clenching (MVC)). The mean duration of activity observed in the non-PHG+2 SD was adopted as a cutoff for identifying sustained TE.

RESULTS

During waking hours, the incidence of sustained TEs was significantly higher in the PHG than in the non-PHG (p<0.05). The incidence and total duration of sustained TEs were significantly higher in the PHG than in the non-PHG at intensities of 7.5-10% MVC, 10-15% MVC, and 15-25% MVC (p<0.05). No significant difference was observed during sleep.

CONCLUSIONS

Within the limitations of this study, it would be concluded that sustained TEs may have a correlation with orofacial pain and the intensity range of 7.5-25% MVC would be an important range for future clenching studies.