Changes in EMG activity during clenching in chronic pain patients with unilateral temporomandibular disorders
From: J Electromyogr Kinesiol. 2008 Nov 26; [Epub ahead of print]
The study assessed the differences in electromyographic (EMG) activity recorded during clenching in women with chronic unilateral temporomandibular joint disorders 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 temporomandibular joint disorder, 25 presented with left side temporomandibular joint disorder 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 temporomandibular joint disorders as compared to control subjects (temporalis: 195.74+/-18.57 vs. 275.74+/-22.11; masseters: 151.09+/-17.37 vs. 283.29+/-31.87. An asymmetry index was calculated to determine ratios of right to left sided activation. Patients with right sided temporomandibular joint disorders demonstrated preferential use of their left sided muscles (asymmetry index -5.35+/-4.02) whereas patients with left sided temporomandibular joint disorder demonstrated preferential use of their right sided muscles (asymmetry index 6.95+/-2.82). 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 may be a useful measure in discriminating patients with right vs. left sided temporomandibular joint disorders.
