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. 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. Significant intergroup differences were observed in masseter morphology indexes (TMM, CSAMM) (P < 0.05), occlusal indexes (AU6, AL6, TU6, TL6, AOP-FH, POP-FH, U1L1-FH, COS, COW, U6-U6, LAD, SAD, CSACo, and HFo) (P < 0.05), and TMJ indexes (AJS, SJS, PJS, MJS, CJS, and LJS) (P < 0.05). Furthermore, masseter morphology (TMM, CSAMM) demonstrated significant negative correlations with HU7, HL7, AU6, AL6, TU6, POP-FH, COW, and PJS (P < 0.05). Conversely, significant positive correlations were identified with TL6, COS, U6-U6, LAD, CSACo, LAA, HFo, AEI, AJS, SJS, MJS, CJS, and LJS (P < 0.05). 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.

The physiological homeostasis of the masticatory complex in short-faced patients is too robust to be disintegrated and reconstructed due to the powerful masseter muscle. This study innovatively introduced the botulinum toxin-A (BTX-A) into the field of dental occlusal treatment, providing a novel and minimally invasive therapy perspective for the two major clinical problems in these patients (low treatment efficiency and high rates of complications). In total, 10 adult patients with skeletal low angle seeking occlusal treatment (age: 27.0 ± 6.1 years; 4 males and 6 females) were administered 30–50 U of BTX-A in each masseter muscle and evaluated before and 3 months after injection based on cone-beam computed tomography (CBCT). We found a significant reduction in the thickness of the masseter muscle (MMT) (p < 0.0001). With regards to occlusion, we found a significant increase in the height of the maxillary second molar (U7-PP) (p < 0.05) with significantly flattened occlusal curves (the curve of Spee [COS] (p < 0.01), and the curve of Wilson [COW] (p < 0.05)). Furthermore, the variations in the temporomandibular joint exhibited a significant reduction in the anterior joint space (AJS) (p < 0.05) and superior joint space (SJS) (p < 0.05). In addition, the correlation analysis of the masticatory complex provided the basis for the following multiple regression equation: MMT = 10.08 − 0.11 COW + 2.73 AJS. The findings from our pilot study indicate that BTX-A, as a new adjuvant treatment attempt of occlusal therapy for short-faced patients, can provide a more favorable muscular environment for subsequent occlusal therapy through the adjustment of the biting force and may contribute to the reconstruction of healthier homeostasis of the masticatory complex. However, further research is required to establish the reliability and validity of these findings.