Measurement plane of the cross-sectional area of the masseter muscle in patients with skeletal Class III malocclusion: An artificial intelligence model

Introduction: This study aimed to determine a measurement plane that could represent the maximum crosssectional area (MCSA) of masseter muscle using an artificial intelligence model for patients with skeletal Class III malocclusion. Methods: The study included 197 patients, divided into subgroups according to sex, mandibular symmetry, and mandibular plane angle. The volume, MCSA, and the cross-sectional area (CSA) at different levels were calculated automatically. The vertical distance between MCSA and mandibular foramen, along with the ratio of the masseter CSA at different levels to the MCSA (R), were also calculated. Results: The MCSA and volume showed a strong correlation in the total sample and each subgroup (P <0.001). The correlation between the CSA at each level and MCSA was statistically significant (P <0.001). The peak of the r and the correlation coefficient between the CSA at different levels and MCSA were mostly present 5-10 mm above the mandibular foramen for the total sample and the subgroups. The mean of R-A5 to R-A10 was > 0.93, whereas the corresponding correlation coefficient was > 0.96, both for the entire sample and for the subgroups. Conclusions: MCSA could be used as an indicator for masseter muscle size. For patients with skeletal Class III malocclusion, the CSA 5-10 mm above the mandibular foramen, parallel to the Frankfort plane, could be used to estimate the masseter muscle MCSA.