Association Between Masseteric Hypertrophy and ANB Angle in Skeletal Class II Orthodontic Patients

Objectives: To determine the degree of association between masseteric hypertrophy and ANB (nasion point A, nasion point B angle) angle in skeletal class II orthodontic patients, by measuring the muscular silent period (SP) and the Steiner cephalometric analysis.
Methods: 30 patients between 18 and 50 years of age were recruited, without prior orthodontic treatment, with class II skeletal classification. Surface electromyography was performed to obtain the masseteric SP measures. Steiner cephalometric analyses were performed to obtain the ANB angle magnitudes. A regression analysis was performed, including the estimation of Pearson correlation coefficient, as well as the coefficient of determination, using the ANB angle as the independent variable, and SP as the dependent variable.
Results: The median age was 27 years and 26 years for the 19 women and 11 men in the sample, respectively. The ANB angle ranged from 4° to 8°, with a mean of 6.01°. The SP ranged from 10ms to 85ms, with a mean of 33.05ms. The linear regression was statistically significant (p=4X10^-7). The Pearson correlation coefficient was 0.823, with a coefficient of determination of 0.677.
Conclusions: In patients with class II skeletal classification, it is important to understand the relationship between the ANB angle and the degree of masseteric hypertrophy, in order to optimize the individual treatment plans. This analysis shows that there is a direct relationship between the magnitude of ANB degree and the SP values for individuals with class II skeletal classification.