title: Can experimentally evoked pain in the jaw muscles or temporomandibular joint affect anterior bite force in humans?
abstract: OBJECTIVE
  To test the hypothesis that experimental pain in the masseter muscle or temporomandibular joint (TMJ) will decrease the anterior maximum voluntary bite force (MVBF) and jaw muscle activity in relation to the perceived effort.
  
  
  METHODS
  Sixteen volunteers participated in two experimental sessions. Participants were injected with 0.2 mL of monosodium glutamate (1.0 M) into either the masseter muscle or TMJ. The MVBF and corresponding electromyographic (EMG) activity of the masseter, anterior temporalis, and digastric muscles were recorded 10 times at an interval of 2 minutes before and after injection. Pain was measured using a visual analog scale and McGill Pain Questionnaire. In addition, participants were asked how they perceived the interference of pain on their biting performance. The data analysis included a two-way analysis of variance model and t test.
  
  
  RESULTS
  There was no significant difference in peak pain intensity (P = .066) and duration of pain (P = .608) between painful muscle and TMJ injections, but TMJ injection produced a significantly larger area under the curve (P = .005) and a significantly higher pain rating index (P = .030). Pain in the muscle (P = .421) and TMJ (P = .057) did not significantly change the MVBF from baseline levels. The EMG activity also did not differ significantly from baseline levels during muscle pain. However, there was a significant increase (P = .028) in the EMG activity of the anterior temporalis and a significant decrease (P = .010) in the EMG activity of the anterior digastric muscle compared to baseline during TMJ pain. Subject-based reports also revealed that in the majority of cases (62.5%), pain did not interfere with the MVBF task.
  
  
  CONCLUSIONS
  Experimental pain from either masseter muscle or TMJ did not affect the MVBF, in accordance with the subject-based reports. Jaw muscle activity, except for EMG activity of the anterior temporalis and anterior digastric muscles during TMJ pain, also remained unaffected by pain. The findings suggest that it is not pain in itself but rather how pain is perceived that may lead to adaptation of motor function, supporting an integrated pain adaptation model.
authors: Abhishek
authors: A
authors: Kumar
authors: Eduardo
authors: E
authors: Castrillon
authors: Peter
authors: P
authors: Svensson
mesh_terms: D000293:Adolescent; D000328:Adult; D001732:Bite Force; D004576:Electromyography / Q000379:methods; D005157:Facial Pain / Q000139:chemically induced / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007270:Injections, Intra-Articular; D007273:Injections, Intramuscular; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D063806:Myalgia / Q000139:chemically induced / Q000503:physiopathology*; D009334:Neck Muscles / Q000503:physiopathology; D010147:Pain Measurement / Q000379:methods; D058748:Pain Perception / Q000502:physiology; D012970:Sodium Glutamate / Q000008:administration & dosage / Q000009:adverse effects; D013703:Temporal Muscle / Q000503:physiopathology; D013705:Temporomandibular Joint Disorders / Q000139:chemically induced / Q000503:physiopathology*; D064232:Visual Analog Scale; D055815:Young Adult
chemical_list: D012970:Sodium Glutamate