Objective: This study examined whether any of clinical findings taken from questionnaires and examinations of jaw and oral structures were related to the actual bruxism levels as measured by EMG. Methods: 76 dental students (40 females and 36 males, 24.1 ± 2.1 years of age) agreed to participate in this study. They were asked to fill out questionnaires related to bruxism behavior and TMD symptoms, and go through a clinical examination of their jaw and oral structures. Subsequently, 6 questionnaire based and 6 examination based findings were collected. Further, they recorded their nocturnal EMG activity from the right masseter muscle by means of a portable EMG device for 6 consecutive nights at home. All EMG elevations above 20% and 50% of each subject's maximum voluntary contraction (MVC) level were quantified and the duration and number of bruxism events per hour of sleep were calculated as bruxism level. Multiple stepwise regression analyses were conducted to assess the clinical findings as predictor variables and the bruxism level as outcome variables (p<0.05) in male and female respectively. Results: Multiple regression analyses revealed that the muscle tenderness score was negatively correlated to bruxism level of 20% MVC in male (adjusted R²=0.122, p=0.021)and joint sound score was positively related to bruxism level of both thresholds in female (adjusted R²=0.196, p=0.002). Conclusion: These associations suggest that nocturnal bruxism would not exactly aggravate muscle tenderness in male, and long and frequent bruxism behavior could be a possible causal factor of temporomandibular joint noises, that is, anterior disc displacement in female.

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