Evaluation of masseter muscle morphology in different types of malocclusions using cone beam computed tomography

Summary Objectives To evaluate the length and orientation of masseter in different types of malocclusions using Cone Beam Computed Tomography (CBCT). Methods Samples of 180 patients seeking orthodontic treatment at the University of Nevada, Las Vegas School of Dentistry, were included in the study. Pre-treatment multi-slice CBCT scans of these patients were divided into three anteroposterior groups: Class I subjects with ANB angle 0° to 5°; Class II subjects with ANB angle > 5°; and Class III subjects with ANB angle  30°, hypodivergent subjects with mandibular plane angle Results ANOVA found significant differences in muscle length among the three vertical groups for both the left and right muscles. Paired t test showed significantly shorter muscle length for the hypodivergent group (43.3 ± 4.0 mm) compared to the normodivergent group (45.6 ± 4.5 mm, P P P Conclusions These results suggest that certain types of malocclusion may have different masseter lengths and orientations and these differences may have implications for the mechanical advantage in bite force. For example, Class III individuals may have greater bite force than Class II individuals because the muscle fibers are oriented more along the arch of closure.