Facial morphology and activity of temporal and lip muscles during swallowing and chewing.

The correlations between facial and bite morphology and the activity in the temporal muscle and in the musculature of the lip during swallowing and chewing were studied in 50 girls, aged 9-13 years. The activity was recorded electromyographically by determining the maximal mean voltage amplitude and morphologically by analysis of profile roentgenograms and dental casts. The activity in the lower lip during the swallowing was not correlated with any of the variables of the facial morphology with the exception of the width of the upper dental arch. On the other hand, the activity of the upper lip during swallowing, as in the anterior and posterior portions of the temporal muscle, was correlated with a number of variables used for measuring facial form. The activity was low in girls with a facial shape with anterior inclination of the maxilla and mandible, small face height, and pronounced prognathism. The activity in the upper lip during chewing varied, as in the lower lip, independently of facial form, while the activity of the temporal muscle during chewing showed the same relation to facial form as during swallowing. The number of chewing cycles required for trituration of the test media (apples and peanuts) was negatively correlated with the number of teeth and with age. This was interpreted as adaptation in such a way that the number of cycles decreased with development of the dentition.