MASSETER MUSCLE-RELAXATION RATE IN VOLUNTEERS WITH A MYOGENOUS CRANIOMANDIBULAR DISORDER

Twelve volunteers were investigated to determine their masseter muscle relaxation rate following voluntary contractions. Four of these volun teers were patients diagnosed as having a myogenous craniomandibular d isorder. Electromyograms were recorded from the left and right massete r muscles and maximum bite force was recorded in the midline between t he incisor teeth. A sustained contraction was maintained at 50% maximu m voluntary bite force for 90s, during which there was a brief relaxat ion every 10s. Recordings were continued for a 3 min recovery period. This sequence was then repeated at 25% of maximum bite force. Median p ower frequencies were calculated from the power spectra for the first and last 3 s of the sustained contractions. Relaxation rates were meas ured for each brief relaxation during the sustained contraction and fo r the relaxation from each brief clench during the recovery period. It was found that maximum bite force values were very similar for volunt eers in both the patient and control groups. Relaxation rates slowed m ore and percentage changes in median frequency were greater in the con trols than in the patients during the sustained contractions. However, relaxation rates returned to initial levels more quickly in the contr ols than in the patients.