Correlations between orofacial muscle activity and craniofacial morphology in a sample of control and anterior open-bite subjects.

In order to investigate the correlations between genioglossus, masseter, and orbicularis oris muscle activity and craniofacial morphology, an electromyographic and cephalometric analysis was undertaken on a series of twenty-four human subjects. The activity from the muscles was recorded during voluntary opening movements of the mandible monitored by an electronic transducer. A computer-based method was devised to calculate the threshold incisor-separation position corresponding to a 20 percent increase in base line muscle activity for each of the muscles. In addition, twenty-seven anatmoic points were digitized from lateral head films, and a computer-based cephalometric analysis was completed for each subject. A number of significant correlations were found between the threshold muscle values and the thirty-one linear and angular morphologic variables. Low threshold values for the genioglossus muscle were correlated with negative overbites, undererupted maxillary and mandibular incisors, and low total face heights. Low threshold values for the masseter muscle were also associated with low overbite measurements. In contrast, orbicularis oris muscle thresholds did not appear to be correlated with any of the craniofacial variables measured. This interdependence of tongue and jaw muscle activity and facial morphology suggests a contribution of the musculature to the development and/or maintenance of the dentition.