Physiological reactions to stress in subjects with and without myofascial pain dysfunction symptoms

Myofascial pain dysfunction syndrome and temporomandibular joint (TMJ) dysfunction syndrome have been suggested as resulting from masticatory muscle hyperactivity. Furthermore, this hyperactivity has been viewed as a response-specific reaction to stress. The present study was designed to assess the effects of laboratory-induced stress (i.e., startle stimulus, buzzer series, serial sevens tasks, and pain threshold/tolerance tests) on physiological responses (i.e. bilateral masseter EMG, skin conductance level, and heart rate) of ten patients (TMJ pain) with a history of facial pain and TMJ sounds. The two control groups, one with TMJ sounds only (TMJ sound) and the other with no history of these symptoms (non-TMJ), were matched for sex and age. The results indicated that the TMJ pain group did not exhibit different masseter EMG levels when comparing symptomatic versus asymptomatic sides. Few significant differences were noted in the masseter EMG recordings of the TMJ pain and non-TMJ group, while no difference occurred between the EMG levels of the TMJ pain and TMJ sound group. Little support was found for the assertion that TMJ pain subjects show greater EMG reactivity and less adaptation than do non-TMJ subjects. Finally, no differences were found among groups in relation to the latency to ischaemic pain onset or tolerance. The discussion focuses on reasons for the findings of the present study being discrepant from previously reported research.