Effect of spastic cerebral palsy on jaw-closing muscles during clenching.

The motor effort of jaw-closing muscles during maximal voluntary clenching (MVC) was compared between individuals with spastic cerebral palsy (CP) and nondisabled control subjects (CG). Bilateral electromyographic (EMG) activity of the anterior temporalis (AT) and masseter (MS) muscles was obtained during MVC in 22 subjects with CP and 29 nondisabled subjects. The oral functional status of the group with CP was evaluated using the Orofacial Motor Function Assessment Scale. The group with CP presented lower bilateral EMG activity during MVC compared to the control group for both AT and MS muscles. Comparisons of AT and MS EMG activity showed no difference in muscular effort. Subgroups with CP who were only slightly and very slightly orally impaired had a higher bilateral AT EMG activity compared to individuals with CP who were severely and moderately compromised. A statistically significant positive correlation was found between the oral motor function and EMG activity of the group with CP in all the muscles evaluated. Individuals with CP had motor weakness in the jaw-closing muscles, a condition that may compromise their masticatory function.