Aims: To investigate whether static jaw clenching can activate endogenous pain modulation and to compare the magnitude between healthy individuals and patients with temporomandibular disorder (TMD) myalgia.
Methods: Thirty-three healthy volunteers (17 women and 16 men) and 20 women with TMD myalgia participated. Exercise-induced hypoalgesia (EIH) was examined by recording pressure pain thresholds (PPTs) in the masseter (MA) and brachioradialis (BR) muscles during tooth clenching until exhaustion. Pain and fatigue were assessed before and after clenching, and pain amplification was examined by applying a painful mechanical pressure at the MA for 2 minutes while assessing pain every 30 seconds. Analyses of data included repeated measures analysis of variance.
Results: In the contracting MA, PPTs increased over time in all three groups (P < .001), while PPTs in the relaxed BR increased only in the men (P = .045). Pain intensity and fatigue in the MA increased after contraction in all groups (P < .003) and was higher in the women with TMD than in the healthy women (P < .001). Only the women with TMD showed pain amplification (P < .001).
Conclusion: Tooth clenching until exhaustion could activate EIH locally; ie, the magnitude of EIH in the MA was similar in women with TMD myalgia and pain-free women, indicating no deficient EIH in women with TMD. However, only women with TMD showed pain amplification during application of continuous painful pressure.