Correlation between facial patterns and function of the masticatory muscles in girls and women.

The relationship between maxillo-facial patterns and function of the masticatory muscles was evaluated using electromyography, in 16 women with functional normal occlusion and 16 girls with chronological normal occlusion half of them had the dolico facial pattern and the others had the brachyo facial pattern by Ricketts analysis. For the electromyography, loads of 1, 2, 3, 4, and 5 kg were applied to the mandible, and muscular activity waves were obtained from the masseter muscle and the anterior belly of the temporal muscle during isometric contraction by surface electrode induction. The median frequency value (MFV) in a frequency curve obtained by high-speed Fourier transform of the electromyographic waves was set to the evaluation index. The MFV at each applied load was higher in the adult brachyo facial pattern group than in the adult dolico facial pattern group in both the masseter and temporal muscles, whereas the differences in the MFV were slight in the child group at a 5% significance level. The child group showed approximately half the incidence of significant correlation coefficients in comparison with the adult group and a large standard deviation without marked differences in the facial patterns due to their individual differences in growth with a 5% significant level. The adult brachyo facial pattern group showed a high regression coefficient of the MFV in the masseter muscle according to the increase in the amount of the applied load. Although differences in the cooperative contraction patterns similar to those in the adult group were observed in both the child dolico and brachyo facial pattern groups, no marked significant differences were observed in the child group, who had large individual differences due to their immature growth.