Effect of Experimental Tooth Clenching on the Release of beta-Endorphin

Aims: To investigate the association between experimental tooth clenching and the release of beta-endorphin in patients with myofascial temporomandibular disorders (M-TMD) and healthy subjects. Methods: Fifteen M-TMD patients and 15 healthy subjects were included and assigned an experimental tooth-clenching task. Venous blood was collected and pain intensity was noted on a visual analog scale. The masseter pressure pain threshold (PPT) was assessed 2 hours before the clenching task and immediately after. A mixed-model analysis of variance was used for statistical analyses. Results: Significant main effects for time and group were observed for pain intensity and PPT, with significantly lower mean values of pain intensity (P < .001) and PPT (P < .01) after the clenching task compared with baseline. M-TMD patients had significantly higher pain intensity (P < .001) and significantly lower PPT (P < .05) than healthy subjects. No significant time or group effects were observed for the level of beta-endorphin. Neither pain intensity nor PPT correlated significantly with beta-endorphin levels. Conclusion: This experimental tooth-clenching task was not associated with significant alterations in beta-endorphin levels over time, but with mechanical hyperalgesia and low to moderate levels of pain in healthy subjects and M-TMD patients, respectively. More research is required to understand the role of the beta-endorphinergic system in the etiology of M-TMD.