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Effects of Experimental Tooth Clenching on Pain and Intramuscular Release of 5-HT and Glutamate in Patients With Myofascial TMD

Dawson, Andreas DDS, PhD*†; Ghafouri, Bijar PhD‡§∥¶; Gerdle, Björn MD, PhD‡§; List, Thomas DDS, PhD*†#; Svensson, Peter DDS, PhD†**††; Ernberg, Malin DDS, PhD†‡‡

doi: 10.1097/AJP.0000000000000154
Original Articles

Objectives: It has been suggested that tooth clenching may be associated with local metabolic changes, and is a risk factor for myofascial temporomandibular disorders (M-TMD). This study investigated the effects of experimental tooth clenching on the levels of 5-HT, glutamate, pyruvate, and lactate, as well as on blood flow and pain intensity, in the masseter muscles of M-TMD patients.

Methods: Fifteen patients with M-TMD and 15 pain-free controls participated. Intramuscular microdialysis was performed to collect 5-HT, glutamate, pyruvate, and lactate and to assess blood flow. Two hours after the insertion of a microdialysis catheter, participants performed a 20-minute repetitive tooth clenching task (50% of maximal voluntary contraction). Pain intensity was measured throughout.

Results: A significant effect of group (P<0.01), but not of time, was observed on 5-HT levels and blood flow. No significant effects of time or group occurred on glutamate, pyruvate, or lactate levels. Time and group had significant main effects on pain intensity (P<0.05 and <0.001). No significant correlations were identified between: (1) 5-HT, glutamate, and pain intensity; or between (2) pyruvate, lactate, and blood flow.

Discussion: This experimental tooth clenching model increased jaw muscle pain levels in M-TMD patients and evoked low levels of jaw muscle pain in controls. M-TMD patients had significantly higher levels of 5-HT than controls and significantly lower blood flow. These 2 factors may facilitate the release of other algesic substances that may cause pain.

*Department of Orofacial Pain and Jaw Function, Faculty of Odontology, Malmö University, Malmö, Sweden

Departments of Pain and Rehabilitation Center

§Medical and Health Sciences

Occupational and Environmental Medicine, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University

Centre of Occupational and Environmental Medicine, Östergötland County Council, Linköping, Sweden

#Department of Rehabilitation Medicine, Skåne University Hospital, Lund, Sweden

‡‡Section of Orofacial Pain and Jaw Function, Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden

**Department of Dentistry, Section of Clinical Oral Physiology, Aarhus University, Aarhus, Denmark

††Center for Functionally Integrative Neuroscience (CFIN), MindLab, Aarhus University Hospital, Aarhus, Denmark

Scandinavian Center for Orofacial Neurosciences (SCON)

A.D. conducted the experimental sessions and the salivary cortisol analyses, did all statistical analyses, and drafted the manuscript. B.G. analyzed the microdialysates and calculated RR, tissue concentrations of algesic substances, and nutritive blood flow. B.G. provided expertise on the microdialysis technique. T.L. and P.S. participated in designing the study and drafting the manuscript. M.E. conceived the study and was involved in the statistical analysis and drafting of the manuscript. All coauthors discussed the results, commented on the manuscript, and approved the final version of the manuscript.

The authors declare no conflict of interest. The Faculty of Odontology at Malmö University, Malmö, Sweden, the Swedish Dental Society, the Swedish Rheumatism Association, Karolinska Institutet, Huddinge, Sweden, and the Swedish Research Counsil funded this study.

Reprints: Andreas Dawson, DDS, PhD, Department of Orofacial Pain and Jaw Function, Faculty of Odontology, Malmö University, SE -205 06 Malmö, Sweden (e-mail:

Received December 10, 2013

Received in revised form October 13, 2014

Accepted August 26, 2014

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