Methods: Thirteen individuals participated in five daily 20-minute EMG biofeedback training sessions performed on the left and right temporalis and masseter muscles. Subjects were randomly assigned to one of two groups. Those assigned to the Increase training group were instructed to maintain EMG activity above a threshold of 10 ìV. Those assigned to the Decrease training group were instructed to maintain EMG activity below a threshold of 2 ìV during training. All participants were screened prior to and after training by a blinded examiner. Only individuals without evidence of TMD, as defined by the Research Diagnostic Criteria, were allowed to participate.
Results: After training, two individuals from the Increase group were diagnosed as having myofascial pain and/or arthralgia and no individuals from the Decrease group were diagnosed as having TMD at the end of training. Self-reported pain immediately post-session was significantly higher for the Increase group (p < .05), and non-significantly higher 24 hours after training (p < .10). Temporalis and masseter EMG activity were correlated 0.44 and 0.39, respectively, with self-reported pain.
Discussion: Parafunctional tooth contact conducted in an experimental environment increases pain and can lead to a diagnosis of TMD. The force of contact as measured by EMG activity is moderately correlated with pain reports.
Conclusions: Parafunctional tooth contact produces pain and may be a mechanism by which TMD pain develops in patients.
Supported by a grant from the National Institutes of Health, DE13563 to the first author.