Ultrasonographic Evaluation of the Masseter Muscle in Skeletal Malocclusions (Class I, II, and III).

Background: There is limited research on the sonographic view of people with skeletal malocclusions. Therefore, this study aimed to evaluate the sonographic findings of the masseter muscle in patients with skeletal malocclusions.

Methods: In this descriptive study, 48 patients aged 15-20 years with skeletal class I, II, and III malocclusions (n = 16) who were referred to Mashhad Dental School for treatment were selected. The masseter muscle was evaluated by ultrasound, including transverse and longitudinal scans on both sides of the face in resting and contraction states. The age, gender, muscle thickness, muscle pattern (Malocclusion were classified based on A-point, nasion, B-point (ANB): 0< ANB <4 as class I, ANB > 4 as class II, ANB < 0 as class III), side of chewing, and body mass index (BMI) parameters were measured for each patient. Paired t-tests compared masseter muscle states; ANOVA assessed differences among malocclusion groups.

Results: The most commonly observed pattern in the masseter muscle of patients with class III skeletal malocclusions was type II, and in people with class II malocclusions was type I. There was a positive and significant correlation between the thickness of masseter muscle and BMI in each group separately (P < 0.001). However, the masseter muscle pattern did not show a significant correlation with BMI, gender, and age. A significant difference was observed between the thickness of the masseter muscle in the resting and contracted states in each group (P < 0.001).

Conclusion: This study showed that skeletal malocclusions can affect the pattern and internal structure of the masseter muscle in the anterior-posterior dimension of the face. Ultrasound can be a suitable diagnostic tool for these patients.