Changes in EMG activity during clenching in chronic pain patients with unilateral temporomandibular disorders

J Electromyogr Kinesiol. 2009 Dec;19(6):e543-9. doi: 10.1016/j.jelekin.2008.10.002. Epub 2008 Nov 28.


The study assessed the differences in electromyographic (EMG) activity recorded during clenching in women with chronic unilateral temporomandibular disorders (TMDs) as compared to control subjects. Seventy-five full dentate, normo-occlusion, right-handed, similarly aged female subjects were recruited. Twenty five subjects presented with right side TMD, 25 presented with left side TMD and 25 pain-free control subjects participated. Using integrated surface EMG over a 1 s contraction, the anterior temporalis and masseter muscles were evaluated bilaterally while subjects performed maximum voluntary clenching. Lower EMG activation was observed in patients with TMD as compared to control subjects (temporalis: 195.74+/-18.57 vs. 275.74+/-22.11, P=0.011; masseters: 151.09+/-17.37 vs. 283.29+/-31.87, P<0.001). An asymmetry index (SAI) was calculated to determine ratios of right to left sided activation. Patients with right-sided TMD demonstrated preferential use of their left-sided muscles (SAI -5.35+/-4.02) whereas patients with left-sided TMD demonstrated preferential use of their right-sided muscles (SAI 6.95+/-2.82), (P=0.016). This unilateral reduction in temporalis and masseter activity could be considered as a specific protective functional adaptation of the neuromuscular system due to nociceptive input. The asymmetry index (SAI) may be a useful measure in discriminating patients with right vs. left-sided TMD.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Arthralgia / etiology
  • Arthralgia / physiopathology*
  • Bruxism / complications
  • Bruxism / physiopathology*
  • Chronic Disease
  • Electromyography / methods
  • Female
  • Humans
  • Masticatory Muscles / physiopathology*
  • Muscle Contraction*
  • Temporomandibular Joint Disorders / complications
  • Temporomandibular Joint Disorders / physiopathology*
  • Young Adult