title: Prolonged Jaw Opening Promotes Nociception and Enhanced Cytokine Expression.
abstract: OBJECTIVE
  To test the hypothesis that prolonged jaw opening, as can occur during routine dental procedures, increases nociceptive sensitivity of the masseter muscle and increases cytokine expression.
  
  
  METHODS
  Sprague-Dawley rats were used to investigate behavioral and cellular changes in response to prolonged jaw opening. A surgical retractor was placed around the maxillary and mandibular incisors, and the jaw was held at near maximal opening for 20 minutes. Head-withdrawal responses to mechanical stimuli applied to the facial skin overlying the left and right masseter muscles were determined following jaw opening. Cytokine levels in the upper cervical spinal cord containing the caudal part of the spinal trigeminal nucleus were evaluated using protein antibody microarrays (n = 3). Statistical analysis was performed using a nonparametric Mann-Whitney U test.
  
  
  RESULTS
  Prolonged jaw opening significantly increased nocifensive head withdrawal to mechanical stimuli at 2 hours, and days 3 and 7 postinduction (P < .05). The increase in nociceptive response resolved after 14 days. Sustained jaw opening also stimulated differential cytokine expression in the trigeminal ganglion and upper cervical spinal cord that persisted 14 days postprocedure (P < .05).
  
  
  CONCLUSIONS
  These findings provide evidence that near maximal jaw opening can lead to activation and prolonged sensitization of trigeminal neurons that results in nociceptive behavior evoked by stimulation of the masseter muscle, a physiologic event often associated with temporomandibular disorders (TMD). Results from this study may provide a plausible explanation for why some patients develop TMD after routine dental procedures that involve prolonged jaw opening.
authors.forename: Jordan L
authors.initials: JL
authors.lastname: Hawkins
authors.forename: Paul L
authors.initials: PL
authors.lastname: Durham
mesh_terms: D000818:Animals; D054360:Chemokine CXCL1 / Q000032:analysis; D020934:Ciliary Neurotrophic Factor / Q000032:analysis; D016207:Cytokines / Q000032:analysis*; D019416:Head Movements / Q000502:physiology; D007378:Interleukins / Q000032:analysis; D008297:Male; D008334:Mandible / Q000503:physiopathology; D008406:Masseter Muscle / Q000294:innervation / Q000503:physiopathology*; D059225:Nociception / Q000502:physiology*; D009619:Nociceptors / Q000737:chemistry / Q000502:physiology; D010812:Physical Stimulation; D016059:Range of Motion, Articular / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000737:chemistry / Q000503:physiopathology; D013704:Temporomandibular Joint / Q000503:physiopathology*; D013997:Time Factors; D014110:Touch / Q000502:physiology; D012668:Trigeminal Ganglion / Q000737:chemistry / Q000503:physiopathology; D014279:Trigeminal Nucleus, Spinal / Q000737:chemistry / Q000503:physiopathology; D014409:Tumor Necrosis Factor-alpha / Q000032:analysis
chemical_list: D054360:Chemokine CXCL1; D020934:Ciliary Neurotrophic Factor; C513297:Cxcl1 protein, rat; D016207:Cytokines; D007378:Interleukins; D014409:Tumor Necrosis Factor-alpha
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