Electromyographic evaluation of patients with temporomandibular disorders and limited mouth opening Part I: Masseteric activity during maximum opening

This study aimed to identify the differences in masseteric activity during maximum mouth opening among healthy volunteers, patients with limited mouth opening (LMO) and myofascial pain, and patients with LMO and disc displacement. Thirty-seven patients with temporomandibular disorders and LMO (< 37 mm) and 27 healthy volunteers participated in this study. Patients were categorized into three groups based on magnetic resonance imaging (MRI) findings and clinical symptoms: disc displacement (DD), disc displacement with myofascial pain (DD + M), and myofascial pain (M). After a five-minute relaxation period, the participants were instructed to perform maximum opening (O _max ) and maintain the O _max position for five seconds, and this was repeated three times. Subsequently, the participants were asked to perform maximum voluntary clenching for five seconds, which was repeated twice. At rest, no significant masseter potential differences were observed among the DD, DD + M, M, and healthy groups (p > .05). However, during O _max , the DD + M and M groups exhibited significantly higher masseteric potential than the healthy and DD groups (p < .001). Furthermore, the masseteric potential during O _max correlated with the pain level. Overall, there are distinct differences in masseteric activity levels between patients with LMO and with or without myofascial pain or disc displacement.