## 4 Discussion  
MARPE approaches are recommended to correct maxillary transverse discrepancies in adult patients, increasing the skeletal effect while minimizing the unwanted dentoulveolar side effects associated with traditional RPE expansion [9]. It was found that even in growing patients, RPE expansion produces the increased buccal flaring of the anchoring teeth regardless of the rate of activation [8] or the type of expander used [3; 4; 10; 36; 37; 38; 39]. Other adverse dentoulveolar effects include fenestration, debiscence, and gingival recession [5], which are more common and critical in non-growing patients. In addition, expansion was found to relapse even in growing patients due to the relapse of dental tipping after the expansion phase [6; 8]. The bone-borne nature of MARPE approaches is aimed at mitigating these adverse effects. The MSE appliance is designed to achieve skeletal expansion by direct bony anchorage with four mini-implants placed next to the midpalatal suture and in between the zygomatic buttress bones with bicortical engagement [20]. The mini-implants allow force to be directly applied against the midpalatal suture with bands on the upper maxillary molars only for stability. The bicortical engagement of the mini-implant also allows the expansion to be more superiorly and posteriorly applied in the maxillary complex [20]. [PERSON] et al. [32] showed that the expansion achieved by the MSE appliance was significant and consisted of almost pure skeletal expansion with negligible and insignificant alveolar bone bending and slight dental tipping. Our results showed that skeletal expansion accounted for 87.50% (2.59\({}^{\circ}\)) on the right side and 88.56% (2.71\({}^{\circ}\)) on the left side. These values were comparable to those previously reported by [PERSON] et al. (96.58% R and 95.44% L) [32]. Furthermore, only the change in FZA was statistically significant, indicating that the observed expansion was mostly skeletal, with the midfacial structures rotating around the fulcrum points located near the frontozygomatic suture [21]. To date, studies on the long-term stability of MSE expansion are limited. A previous study on MARPE expansion found stable outcomes one year after expansion according to linear measurements [31], although the specific appliance used was different and did not have bicortical engagement. Furthermore, the results were linearly measured without taking into account the rotational nature of expansion. The T2 timepoint in our study reflects a mean  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**T1–T0**} & \multicolumn{4}{c}{**T2–T1**} \\ \hline  & \begin{tabular}{c} **Skeletal** \\ **Expansion** \\ \end{tabular}  & \begin{tabular}{c} **Alveolar Bone** \\ **Bending** \\ \end{tabular}  & \begin{tabular}{c} **Dental** \\ **Tipping** \\ \end{tabular}  & \begin{tabular}{c} **Skeletal** \\ **Expansion** \\ \end{tabular}  & \begin{tabular}{c} **Alveolar Bone** \\ **Bending** \\ \end{tabular}  & \ \begin{tabular}{c} **Dental** \\ **Tipping** \\ \end{tabular}  \\ \hline  & \begin{tabular}{c} **Aa** \\ \end{tabular}  & \(\mathbf{\Delta b}-\mathbf{\Delta a}\) & \(\mathbf{\Delta c}-\mathbf{\Delta b}\) & \(\mathbf{\Delta a}\) & \(\mathbf{\Delta b}-\mathbf{\Delta a}\) & \(\mathbf{\Delta c}-\mathbf{\Delta b}\) \\ \hline Right & Mean (\({}^{\circ}\)) & 2.59 & 0.21 & 0.16 & \(-0.29\) & \(-  
time of 19.5 \(\pm\) 7.3 months post-expansion. According to our results, there was a significant skeletal rotational expansion of 2.31\({}^{\circ}\) on the right and 2.34\({}^{\circ}\) on the left from T0 to T2, with a statistically significant relapse of 11.20% (0.29\({}^{\circ}\)) and 13.28% (0.36\({}^{\circ}\)) on the right and left, respectively, between T1 and T2. However, this relatively minimal amount of relapse is a promising clinical result, especially compared to the amount of relapse noted using alternative methods such as surgically assisted rapid palatal expansion (SARPE).