Masticatory muscle activity in children and adults with different facial types

The purpose of this study was to examine the relationship between the durat ion 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 re lations, acceptable occlusions, and without any temporomandibular joint dis orders, were selected as subjects. Activities of the masseter, temporal, an d digastric muscles were recorded for 3 hours during daytime, excluding the periods for meals, sleep, and hard-exercise, using a portable electromyogr am 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 th e masseter muscle presented longer duration of activity in adults. The acti vities of masseter and digastric muscles were significantly related with th e vertical facial type in both children and adults, although temporal muscl e activity presented no significant relationship with the craniofacial morp hology. The duration of masticatory muscle activity during daytime showed a significant difference between children and adults, indicating a close ass ociation with vertical craniofacial morphology in children and adults.