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

Aims: To investigate the association between experimental tooth clenching and the release of β-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 β-endorphin. Neither pain intensity nor PPT correlated significantly with β-endorphin levels. Conclusion: This experimental tooth-clenching task was not associated with significant alterations in β-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 β-endorphinergic system in the etiology of M-TMD.

beta-endorphin; bruxism; masseter muscle; temporomandibular joint disorders

1. Millan MJ. Descending control of pain. Prog Neurobiol 2002; 66:355–474.

2. Bender T, Nagy G, Barna I, Tefner I, Kadas E, Geher P. The effect of physical therapy on beta-endorphin levels. Eur J Appl Physiol 2007;100:371–382.

3. Herz A. Bidirectional effects of opioids in motivational processes and the involvement of D1 dopamine receptors. NIDA Res Monogr 1988;90:17–26.

4. Boecker H, Sprenger T, Spilker ME, et al. The runner's high: Opioidergic mechanisms in the human brain. Cereb Cortex 2008;8:2523–2531.

5. Pilcher WH, Joseph SA, McDonald JV. Immunocytochemical localization of proopiomelanocortin neurons in human brain areas subserving stimulation analgesia. J Neurosurg 1988; 68:621–629.

6. Guillemin R, Vargo T, Rossier J, et al. beta-Endorphin and adrenocorticotropin are selected concomitantly by the pituitary gland. Science 1977;197:1367–1369.

7. Hargreaves KM, Flores CM, Dionne RA, Mueller GP. The role of pituitary beta-endorphin in mediating corticotropin-releasing factor-induced antinociception. Am J Physiol 1990; 258:E235–E242.

8. Machelska H, Schopohl JK, Mousa SA, Labuz D, Schafer M, Stein C. Different mechanisms of intrinsic pain inhibition in early and late inflammation. J Neuroimmunol 2003;141:30–39.

9. King CD, Wong F, Currie T, Mauderli AP, Fillingim RB, Riley JL 3rd. Deficiency in endogenous modulation of prolonged heat pain in patients with irritable bowel syndrome and temporo-mandibular disorder. Pain 2009;143:172–178.

10. Lannersten L, Kosek E. Dysfunction of endogenous pain inhibition during exercise with painful muscles in patients with shoulder myalgia and fibromyalgia. Pain 2010;151:77–86.

11. Van Oosterwijck J, Nijs J, Meeus M, Van Loo M, Paul L. Lack of endogenous pain inhibition during exercise in people with chronic whiplash associated disorders: an experimental study. J Pain 2012;13:242–254.

12. Lobbezoo F, Ahlberg J, Glaros AG, et al. Bruxism defined and graded: An international consensus. J Oral Rehabil 2013; 40:2–4.

13. Kato T, Thie NM, Huynh N, Miyawaki S, Lavigne GJ. Topical review: Sleep bruxism and the role of peripheral sensory influences. J Orofac Pain 2003;17:191–213.

14. Lavigne GJ, Manzini C, Kato T. Sleep bruxism. In: Roth T, Kryger MH, Dement WC (eds). Principles and Practice of Sleep Medicine, ed 4. Philadelphia: Elsevier Saunders, 2005: 946–959.

15. Lavigne GJ, Montplaisir JY. Restless legs syndrome and sleep bruxism: Prevalence and association among Canadians. Sleep 1994;17:739–743.

16. Manfredini D, Lobbezoo F. Relationship between bruxism and temporomandibular disorders: A systematic review of literature from 1998 to 2008. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109:e26–e50.

17. Pergamalian A, Rudy TE, Zaki HS, Greco CM. The association between wear facets, bruxism, and severity of facial pain in patients with temporomandibular disorders. J Prosthet Dent 2003;90:194–200.

18. Raphael KG, Marbach JJ, Klausner JJ, Teaford MF, Fischoff DK. Is bruxism severity a predictor of oral splint efficacy in patients with myofascial face pain? J Oral Rehabil 2003;30:17–29.

19. Svensson P, Jadidi F, Arima T, Baad-Hansen L, Sessle BJ. Relationships between craniofacial pain and bruxism. J Oral Rehabil 2008;35:524–547.

20. Lobbezoo F, Naeije M. Bruxism is mainly regulated centrally, not peripherally. J Oral Rehabil 2001;28:1085–1091.

21. Dawson A, Ghafouri B, Gerdle B, List T, Svensson P, Ernberg M. Pain and intramuscular release of algesic substances in the masseter muscle after experimental tooth-clenching exercises in healthy subjects. J Orofac Pain 2013;27:350–360.

22. Dawson A, Ghafouri B, Gerdle B, List T, Svensson P, Ernberg M. Effects of experimental tooth clenching on pain and intramuscular release of 5-HT and glutamate in patients with myofascial TMD. 2014 (Submitted).

23. Dworkin SF, LeResche L. Research diagnostic criteria for temporomandibular disorders: Review, criteria, examinations and specifications, critique. J Craniomandib Disord 1992;6: 301–355.

24. Hedenberg-Magnusson B, Brodda Jansen G, Ernberg M, Kopp S. Effects of isometric contraction on intramuscular level of neuropeptide Y and local pain perception. Acta Odontol Scand 2006;64:360–367.

25. List T, Helkimo M, Falk G. Reliability and validity of a pressure threshold meter in recording tenderness in the masseter muscle and the anterior temporalis muscle. Cranio 1989; 7:223–229.

26. Esel E, Sofuoglu S, Aslan SS, Kula M, Yabanoglu I, Turan MT. Plasma levels of beta-endorphin, adrenocorticotropic hormone and cortisol during early and late alcohol withdrawal. Alcohol Alcohol 2001;36:572–576.

27. Bragdon EE, Light KC, Costello NL, et al. Group differences in pain modulation: Pain-free women compared to painfree men and to women with TMD. Pain 2002;96:227–237.

28. Feldreich A, Ernberg M, Lund B, Rosen A. Increased beta-endorphin levels and generalized decreased pain thresholds in patients with limited jaw opening and movement-evoked pain from the temporomandibular joint. J Oral Maxillofac Surg 2012; 70:547–556.

29. Graven-Nielsen T, Mense S. The peripheral apparatus of muscle pain: Evidence from animal and human studies. Clin J Pain 2001;17:2–10.

30. Rahkila P, Hakala E, Alen M, Salminen K, Laatikainen T. Beta-endorphin and corticotropin release is dependent on a threshold intensity of running exercise in male endurance athletes. Life Sci 1988;43:551–558.

31. Glaros AG. Awareness of physiological responding under stress and nonstress conditions in temporomandibular disorder. Biofeedback Self Regul 1996;21:261–272.

32. Lyons MF, Rouse ME, Baxendale RH. Fatigue and EMG changes in the masseter and temporalis muscles during sustained contractions. J Oral Rehabil 1993;20:321–331.

33. Kraemer WJ, Patton JF, Knuttgen HG, et al. Hypothalamic-pituitary-adrenal responses to short-duration high-intensity cycle exercise. J Appl Physiol 1989;66:161–166.

34. Farrell PA, Kjaer M, Bach FW, Galbo H. Beta-endorphin and adrenocorticotropin response to supramaximal treadmill exercise in trained and untrained males. Acta Physiol Scand 1987;130:619–625.