Dimensional Changes of Masticatory Muscles Following Camouflage Orthodontic Treatment in Skeletal Class III Patients: A Pilot MRI-Based Clinical Trial

Objectives: To evaluate dimensional changes in masticatory muscles, dentoskeletal relationships, and correlations between muscular and vertical skeletal changes following Class III camouflage treatment. Methods: This clinical trial included ten participants with skeletal Class III malocclusion who met the eligible criteria and provided them non-extraction camouflage treatment using Class III elastics. MR images (T1W) and lateral cephalograms were taken before treatment (T0) and after achieving normal occlusion (T1). Length, width, and cross-sectional area (CSA) of the masseter (MM), temporalis (TM), lateral pterygoid (LPM), and medial pterygoid (MPM) muscles were measured using MicroDicom DICOM viewer software. Dentoskeletal changes were assessed by Dolphin® imaging software. Statistical analyses were conducted using IBM® SPSS® software to analyze differences between T0 and T1, and correlations. Results: Significant changes were observed in jaw-closing muscles, with increased length (MM 1.0±0.4 mm, TM 0.7±0.2 mm, MPM 0.5±0.5 mm), decreased thickness (MM 1.3±0.7 mm, TM 0.2±0.2 mm, MPM 0.8±0.6 mm), and decreased CSA (MM 79.3±70.5 mm2, TM 16.2±14.9 mm2, MPM 16.2±8.8 mm2). Minimal changes were noted in lateral pterygoid muscles. No significant correlations were found between muscular changes and vertical skeletal changes. Conclusions: Masseter, temporalis, and medial pterygoid muscles exhibited significant changes following Class III camouflage treatment using Class III elastics, but no significant correlations were observed between muscular dimensional changes and vertical skeletal changes.