Electromyographic data from TMD patients with myofascial pain and from matched control subjects: evidence for statistical, not clinical, significance.

This study tested the hypotheses that electromyographic (EMG) activity at rest would be significantly greater for temporomandibular disorder (TMD) patients with myofascial pain than for nonpain control subjects, and that a cutoff score based on EMG values could be established to accurately separate the two groups. Fifty-four TMD patients diagnosed with myofascial pain and 54 nonpain control subjects who were matched for age and gender were examined. Both groups participated in an EMG scanning procedure in which the left and right frontalis, temporalis, and masseter muscles were examined. Results showed that the TMD group had significantly higher EMG activity at rest for three of the six sites examined. The application of a cutoff value that produced the smallest classification error nonetheless resulted in misclassification of about one third of the TMD and nonpain individuals. These data provide little support for the use of resting EMG data obtained via a scanning procedure in accurately distinguishing facial pain patients from nonpain control subjects.