Maxillo-mandibular changes after maxillary skeletal expansion according to skeletal subtype: a retrospective cohort study

Objective We aimed to evaluate three-dimensional (3D) maxillary displacement and secondary mandibular changes following miniscrew-assisted rapid palatal expansion (MARPE) according to pretreatment skeletal subtypes, based on the identification of variables affecting site-specific maxillary displacement. Materials and Methods Sixty-three patients (mean age, 21.4 ± 4.3 years) treated with MARPE were categorized by sagittal (Class I, II, III) and vertical (hyperdivergent, nonhypodivergent) subtypes. Pre and postexpansion CBCT scans were used to quantify forward and downward maxillary displacement at the anterior and posterior nasal spine (ANS and PNS), and mandibular positional changes were assessed. Multiple regression analysis was performed to identify craniofacial variables affecting differential ANS and PNS displacement. Finally, maxillo-mandibular changes were compared between Class II hyperdivergent (CII-H) and Class III nonhyperdivergent (CIII-NH) patients. Results After adjustment for age, gender, and the amount of midpalatal suture split, downward displacement at the ANS and PNS was significantly influenced by pretreatment sagittal, vertical, and transverse skeletal subtypes, whereas forward displacement showed no differences among subtypes. The Class III subtype exhibited less downward ANS displacement than Class I and Class II. The hyperdivergent subtype showed greater downward displacement at both ANS and PNS than the nonhyperdivergent subtype. Regarding the mandible, the hyperdivergent subtype showed a greater increase in vertical divergency, while sagittal subtypes showed no significant differences. CII-H patients showed greater 3D maxillary displacement and subsequent mandibular rotation than CIII-NH patients. Conclusions MARPE-induced 3D maxillo-mandibular changes were dependent on pretreatment skeletal subtypes. These findings highlight the importance of subtype-based strategic vertical control to optimize postexpansion orthodontic outcomes.