Masticatory muscle activity in children and adults with different facial types.

The purpose of this study was to examine the relationship between the duration of masticatory muscle activity during daytime and vertical craniofacial morphology in children and adults. Thirty children (12 boys and 18 girls) and 30 adults (20 men and 10 women) with normal anteroposterior skeletal relations, acceptable occlusions, and without any temporomandibular joint disorders, were selected as subjects. Activities of the masseter, temporal, and digastric muscles were recorded for 3 hours during daytime, excluding the periods for meals, sleep, and hard-exercise, using a portable electromyogram recording system. A lateral cephalogram was taken of each subject at the intercuspal position to divide the subjects into 3 different facial types, ie, low, average, and high angle groups. Masseter, temporal, and digastric muscle activities mainly consisted of low-amplitude bursts during daytime. Children exhibited longer duration of temporal muscle activity, whereas the masseter muscle presented longer duration of activity in adults. The activities of masseter and digastric muscles were significantly related with the vertical facial type in both children and adults, although temporal muscle activity presented no significant relationship with the craniofacial morphology. The duration of masticatory muscle activity during daytime showed a significant difference between children and adults, indicating a close association with vertical craniofacial morphology in children and adults.