title: Effects of experimental tooth clenching on pain and intramuscular release of 5-HT and glutamate in patients with myofascial TMD.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: *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).
authors.forename: Andreas
authors.initials: A
authors.lastname: Dawson
authors.forename: Bijar
authors.initials: B
authors.lastname: Ghafouri
authors.forename: Björn
authors.initials: B
authors.lastname: Gerdle
authors.forename: Thomas
authors.initials: T
authors.lastname: List
authors.forename: Peter
authors.initials: P
authors.lastname: Svensson
authors.forename: Malin
authors.initials: M
authors.lastname: Ernberg
mesh_terms: D000328:Adult; D001732:Bite Force; D016022:Case-Control Studies; D004958:Estradiol / Q000097:blood; D005157:Facial Pain / Q000503:physiopathology*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D008406:Masseter Muscle / Q000098:blood supply / Q000378:metabolism*; D009043:Motor Activity / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D010147:Pain Measurement; D058748:Pain Perception / Q000502:physiology*; D019289:Pyruvic Acid / Q000378:metabolism; D012039:Regional Blood Flow; D012463:Saliva / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D013705:Temporomandibular Joint Disorders / Q000503:physiopathology*
chemical_list: D012701:Serotonin; D019344:Lactic Acid; D018698:Glutamic Acid; D004958:Estradiol; D019289:Pyruvic Acid; D006854:Hydrocortisone