Reproducibility of mandibular motion and muscle activity levels using a commercial computer recording system

A commercial computer recording system (BioPak) was tested for its accuracy and reproducibility in recording mandibular motion and muscle activity levels (EMG). Accuracy of measurements of mandibular motion was tested using sliding calipers. Accuracy of muscle activity levels was checked with a sine-wave calibration signal of known amplitude and frequency. Reproducibility of motion and of EMG was made using five control subjects each tested on 3 separate days. Computer measurements of motion were found to require correction for nonlinearity at openings beyond 45 mm. Most maximum voluntary excursions were found to be more reproducible than motions during mastication. However, lateral deviation during opening was strongly affected by magnet orientation and varied greatly between trials. Electromyographic recordings were distorted by improper treatment of high-frequency components of the signal and also varied greatly between trials. This study suggests that the BioPak system may indicate changes in some measures of mandibular motion and EMG levels in patients for whom no changes have occurred.