Electromyographic evaluation of masticatory, neck, and trunk muscle activity in patients with posterior crossbites.

This study investigated the pattern of masticatory, neck, and trunk muscle activity in patients with posterior crossbites and associated mandibular displacement. The test group consisted of 75 patients [45 males mean age 19.5 years, SD 5.6 years, and 30 females mean age 20.4 (SD 3.2) years]. Of this group, 25 patients presented a left posterior crossbite, 25 a right posterior crossbite, and the remaining 25 patients a bilateral posterior crossbite. A control group of 25 subjects (19 males and 6 females aged 22.5 ± 5.8 years) without any crossbite were included. Surface electromyographic (sEMG) activity was recorded bilaterally, in the mandibular rest position and during maximum voluntary clenching (MVC), at the following sites: anterior and posterior temporal, masseter, sternocleidomastoid (SCM), upper and lower trapezius, and cervical muscles. In the mandibular rest position, patients with unilateral crossbites showed a significant difference (P < 0.05) in sEMG activity of the anterior temporal muscle, with the greatest activity being detected on the side to which the mandible displaced. Control subjects demonstrated significantly lower (P < 0.05) sEMG activity but only in the SCM muscle when compared with patients with bilateral posterior crossbites; no such differences were detected in relation to unilateral crossbites. During MVC, control subjects showed significantly lower (P < 0.01) sEMG activity in both the SCM and the posterior cervical muscles compared with patients demonstrating both unilateral and bilateral crossbites. The findings of the present study indicate that the presence of a crossbite can affect electromyography activity of masticatory, neck, and trunk muscles.