effect of lengthy root canal therapy sessions on temporomandibular joint and masticatory muscles

background and aims. trauma is one of the major factors associated with temporomandibular joint disorders (tmd). these disorders result from macro-trauma or micro-trauma. macro-trauma might be iatrogenic; for example, from intubation procedures, third molar extraction procedures, and lengthy dental appointments. the aim of this study was to evaluate the effect of lengthy root canal therapy (more than 2 hours) on tmj and its supporting structures. materials and methods. eighty patients whose root canal therapy session lasted more than 2 hours were examined for the status of tmj and masticatory muscles. after one week the second part of the examination was carried out for tmj problems and pain and tenderness levels of masticatory muscles. data was analyzed using wilcoxon statistical test. results. women showed more pain compared to men. there was a significant increase in pain in the external acoustic meatus examination one week after root canal therapy. patients who were treated for their posterior teeth suffered more pain than those who were treated for the anteriors and premolars. other aspects of the examination were not affected significantly by lengthy root canal therapy. conclusion. lengthy dental treatments can harm tmj and masticatory muscles and wide opening of the mouth during such appointments can worsen the situation. therefore, it is wise to break the appointment into shorter intervals and let the patients rest during treatment to close their mouth to prevent iatrogenic damage to tmj.