title: Glutamate-evoked jaw muscle pain as a model of persistent myofascial TMD pain?
abstract: OBJECTIVE
  Compare pain-related measures and psychosocial variables between glutamate-evoked jaw muscle pain in healthy subjects (HS) and patients with persistent myofascial temporomandibular disorder (TMD) pain.
  
  
  METHODS
  Forty-seven female HS and 10 female patients with persistent myofascial TMD pain participated. The HS received an injection of glutamate into the masseter muscle to model persistent myofascial TMD pain. Participants filled out a coping strategies questionnaire (CSQ), the symptom checklist 90 (SCL-90) and McGill pain questionnaire (MPQ). Pain intensity was assessed on an electronic visual analogue scale (VAS). Pain-drawing areas, numerical rating scale (NRS) scores of unpleasantness, pressure pain thresholds (PPTs) and pressure pain tolerance (PPTOL) were measured. Unpaired t-tests and correlation tests were used for analyses.
  
  
  RESULTS
  The groups were significantly different when comparing the CSQ scores of control, decrease, diverting attention, increase of behavioural activities and somatization. The peak VAS pain, NRS of unpleasantness and MPQ scores were not significantly different between groups, but PPT and PPTOL were significantly lower in the TMD patients. Significant positive correlations were found in the TMD patients between peak VAS pain and CSQ catastrophizing score and SCL-90 somatization. The scores of PPTs and PPTOLs, in patients showed positive correlations with CSQ reinterpreting pain sensations scores and PPTs correlated with CSQ praying/hoping scores.
  
  
  CONCLUSIONS
  Glutamate-evoked pain responses in HS and persistent myofascial TMD pain have similar sensory-discriminative and affective-unpleasantness components but differ in psychosocial features. This study suggests that experimental designs based on glutamate injection into muscle can provide an appropriate model for elucidating persistent myofascial pain conditions.
authors.affiliation: Department of Clinical Oral Physiology, School of Dentistry, University of Aarhus, Aarhus C, Denmark. ecastrillon@odont.au.dk
authors.forename: Eduardo E
authors.initials: EE
authors.lastname: Castrillon
authors.forename: Brian E
authors.initials: BE
authors.lastname: Cairns
authors.forename: Malin
authors.initials: M
authors.lastname: Ernberg
authors.forename: Kelun
authors.initials: K
authors.lastname: Wang
authors.forename: Barry
authors.initials: B
authors.lastname: Sessle
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.forename: Peter
authors.initials: P
authors.lastname: Svensson
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004333:Drug Administration Routes; D005157:Facial Pain / Q000139:chemically induced* / Q000503:physiopathology / Q000523:psychology; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular; D007568:Jaw / Q000187:drug effects* / Q000503:physiopathology; D008406:Masseter Muscle / Q000187:drug effects*; D008954:Models, Biological; D017288:Pain Threshold / Q000187:drug effects* / Q000502:physiology; D011312:Pressure; D012970:Sodium Glutamate; D011795:Surveys and Questionnaires; D013705:Temporomandibular Joint Disorders / Q000139:chemically induced* / Q000503:physiopathology / Q000523:psychology; D055815:Young Adult
chemical_list: D012970:Sodium Glutamate