## 4 Discussion  
Despite the high success rate of MARPE, its failure can be a great burden on patients and clinicians. Therefore, alternative treatment options, such as dental expansion or surgically assisted RPE, should be considered before the start of the treatment. Our aim was to investigate the potential predictors of MARPE success that could be helpful for clinicians in predicting the prognosis of patients with maxillary transverse deficiencies, and thus help in the process of treatment planning. We found that younger patients, females, and those with a forward position of the maxilla showed a greater chance of MARPE success. The mean age of patients in the S group was 25.1 \(\pm\) 8.1 years as opposed to 27.7 \(\pm\) 10.8 years in patients in the F group. Although the mean age was significantly greater in the F group, we were still able to expand the maxilla in some middle-aged patients. Out of the five patients aged over 40 years, three patients were successfully treated, and the oldest patient in the S group was 52 years old. All subjects were older than 18 years and had a CVMI of 6; thus, they were considered as skeletally mature, but there was an increased tendency of failure in older patients. However, [PERSON] reported that MPSD is the major source of resistance to maxillary expansion [21], rather than age. Our patients showed a weak positive correlation between age and MPSD, but it lacked statistical significance. There may be additional factors associated with older age, other than the sutural bone density, such as the increased interlocking pattern of the suture interdigitation that restricts maxillary expansion in older patients [13; 22]. MPSD was associated with the amount of skeletal expansion, rather than the success itself. The zygomatic buttress area is one of the major areas of resistance to maxillary skeletal expansion, and significant lateral displacements in the zygomatic and maxillary bones are observed following MARPE [23]. However, the ZMSD was not associated with the success or amount of maxillary expansion. The association of MPSD with maxillary expansion following MARPE was similar to that of a previous study by [PERSON] [15], conducted on growing patients. They reported greater maxillary expansion in patients with lower MPSD. In contrast, [PERSON] et al. conducted their study on adult patients and showed that the rate of ossified tissues in the midpalatal suture was low in all patients aged 18-63 years and that suture ossification did not restrict RPE in adults [24]. Patients with maxillary retrusion showed a lower chance of MARPE success, which is not a favorable result because patients with maxillary hypoplasia often show concurrent maxillary transverse deficiency and require maxillary skeletal expansion. Patients in the F group had a mean SNA of 78.2 \(\pm\) 4.5 degrees, which is lower than normal. Clinicians should be aware that in patients with severe maxillary retrusion, there is a higher chance of \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **MPSD\_T1** & **ZMSD\_T1** & **SN-MP** & **ANB** & **A-Nperp** & **Age** \\ \hline Nasal\_change & \(-\)0.322 & \(-\)0.192 & 0.382 * & 0.006 & \(-\)0.011 & \(-\)0.161 \\ Zygo\_change & \(-\)0.371 * & \(-\)0.192 & \(-\)0.002 & \(-\)0.139 & 0.004 & \(-\)0.211 \\ Palatal\_change & \(-\)0.027 & \(-\)0.038 & 0.350 * & \(-\)0.085 & \(-\)0.217 & 0.002 \\ \hline \hline \end{tabular} Nasal\_change: amount of expansion as a result of miniscrew-assisted rapid palatal expansion (MARPE) in the nasal cavity, Zygo\_change: amount of expansion as a result of MARPE in the zygomatomaxillary suture. Palatal\_change: amount of expansion as a result of MARPE in the maxillary width at the level of the uppermost area of the palate. MPSD\_T1: midpalatal-sutture density before micromiplamt-assisted rapid palatal expansion at pretreatment. ZMSD\_T1: zygomatomaxillary-sutture density at pretreatment. SN-MP\_T1: sella–nasion line to mandibular-plane angle at pretreatment. * Statistically significant.  
\end{table}