Abstract
This study aimed to evaluate the effectiveness of passive stretch training (PST) using electromyographic analysis and the pain visual analogue scale (VAS), and to investigate changes in mouth opening, masseter activity, and pain level before and after PST in patients with myofascial pain and temporomandibular joint disc displacement. The study sample comprised 37 patients with Temporomandibular disorders (TMD) and limited mouth opening (LMO, < 40 mm) and 27 healthy volunteers. Patients were divided into three groups: disc displacement (DD), disc displacement with myofascial pain (DD + M), and myofascial pain (M). At the first visit, all participants were instructed to perform three repetitions of maximum mouth opening (O(max)), each held for 5 s. After a brief rest period, they underwent PST using finger-generated force to support mouth opening, holding each stretch for 5 s and repeating the task 15 times. Three additional O(max) repetitions were then performed. After the first experiment, all patients were instructed to continue PST at home for three months before returning for the second experiment. The masseter muscle activity in the DD + M and M groups exhibited significantly lower electromyographic potentials after PST in both the first and second experiments (p < .05). Furthermore, mouth opening significantly increased and pain VAS scores significantly decreased after three months of home-based PST in the DD + M and M groups (p < .05). These electromyographic findings confirm the short- and long-term effectiveness of PST in TMD patients with myofascial pain and limited mouth opening. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-026-39696-w.