Causes and Potential Solutions of Molar Buccal Inclination in Maxillary Skeletal Expander: A Retrospective CBCT Analysis.

Objective: This study aimed to investigate the causes of molar buccal inclination following maxillary skeletal expander (MSE) treatment and explore potential solutions by analyzing MSE appliance design and patient-specific factors to mitigate this inclination. Materials and Methods: Cone-beam computed tomography (CBCT) data from 120 patients with maxillary transverse deficiency (MTD) were analyzed using Materialise's Interactive Medical Image Control System (MIMICS) software. The buccal inclination of the zygomaticomaxillary complex (ZMC), alveolar bone, and molars was measured using angular analysis to identify the contributing factors to molar buccal inclination. Results: Significant changes were observed in the frontozygomatic angle (FZA), frontoalveolar angle (FAA), frontodental angle (FDA), ZMC angle (ZMCA), maxillary first molar angle (MFMA), and maxillary second molar angle (MSMA) (p ≤ 0.001, p < 0.05). ΔFZA was less than ΔFDA (p=0.019, p < 0.05), while no significant difference was found between ΔZMCA and ΔMSMA (p=0.390, p > 0.05). However, a significant difference was noted between ΔZMCA and ΔMFMA (p ≤ 0.001, p < 0.05). The ratio of ΔZMCA/ΔMFMA was higher in the age ≤18 group (0.712 ± 0.044) compared to the age >18 group (0.511 ± 0.048) (p ≤ 0.001, p < 0.05). Conclusions: During MSE expansion, the buccal inclination of the molars will still occur, primarily due to the buccal expansion force transmitted to the molars by the bracket and the band. Additionally, this inclination is partly influenced by the left and right ZMC rotating buccally in the coronal plane.