The effects of masseter muscle morphology on three-dimensional occlusion and temporomandibular joint in adult patients with skeletal class II malocclusion: a CBCT study.

INTRODUCTION: This retrospective study aimed to compare the masseter muscle morphology, static and dynamic occlusion, and temporomandibular joint (TMJ) characteristics among adult patients with skeletal Class II malocclusion exhibiting different vertical patterns. Additionally, the correlations among these three factors were examined. METHODS: A total of 87 adult participants (mean +/- standard deviation age = 25.98 +/- 4.58 years) were included in the study and categorized into four groups: skeletal Class I, skeletal Class II high-angle, average-angle, and low-angle. Cone beam computed tomography (CBCT) images were obtained before and after treatment, enabling the evaluation of masseter morphology, occlusion, and TMJ variables. These were assessed using One-Way ANOVA. Pearson correlation analysis was used to identify relationships between masseter morphology, occlusion, and TMJ variables. RESULTS: Significant intergroup differences were observed in masseter morphology indexes (T(MM), CSA(MM)) (P < 0.05), occlusal indexes (A(U6), A(L6), T(U6), T(L6), AOP-FH, POP-FH, U1L1-FH, COS, COW, U6-U6, LAD, SAD, CSA(Co), and H(Fo)) (P < 0.05), and TMJ indexes (AJS, SJS, PJS, MJS, CJS, and LJS) (P < 0.05). Furthermore, masseter morphology (T(MM), CSA(MM)) demonstrated significant negative correlations with H(U7), H(L7), A(U6), A(L6), T(U6), POP-FH, COW, and PJS (P < 0.05). Conversely, significant positive correlations were identified with T(L6), COS, U6-U6, LAD, CSA(Co), LAA, H(Fo), AEI, AJS, SJS, MJS, CJS, and LJS (P < 0.05). CONCLUSIONS: The masseter muscle's morphology measured by CBCT significantly influences occlusion and TMJ characteristics in skeletal Class II adults, affecting occlusal planes, curves, condylar position, and articular fossa morphology. These findings highlight masticatory muscles' role in stomatognathic dysfunction etiology. Future orthodontic planning and TMJ evaluation should incorporate CBCT-based muscle assessments to support more comprehensive treatment strategies.