## 3 Results  
### Study Selection  
At the beginning, according to the electronic and manual search, 4129 articles were found (see Table 2). A total of 4129 published articles were considered from the initial search. After excluding duplicates (3925) and unsuitable studies (150), 52 studies were included. Figure 1 exhibits a flowchart of the search process used in this review that is based on PRISMA guidelines for systematic reviews. General Characteristics of this Study. The decision of analyzing only AHI values in the polysomnographic data was done in order to standardize the articles with the only common outcomes observed in all the 102 children of this meta-analysis. In fact, [PERSON] et al. (2014), [PERSON] et al. (2015), and [PERSON] et al. (2015) have analyzed the outcomes of AHI and LSAT indexes. [PERSON] et al. (2015) have reported outcomes of AHI index and mean oxygen saturation index (MSAT). [PERSON]'s case report ([PERSON] et al., 2015) analyzed AHI, LSAT and respiratory disturbance index (RDI) outcomes. [PERSON] et al. (2017) described cephalospor \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Search Method**} \\
**No. of Abstracts without Overlap** & \\ \hline Wiley Online & 1200 \\ PubMed & 611 \\ Cochrane Controlled Clinical Trials Register & 8 \\ Springer Link & 1435 \\ Science Direct & 855 \\ Reference selected articles & 20 \\ Total & 4129 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Abstracts Retrieved by Electronic, Manual and Reference Searching. Primary outcome. The demographic and AHI values pre and post rapid maxillary expansion, with or without surgery in children \(<18\) years old were summarized in Table 4. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Study** & **No.** & **Age, Year*** & \
\begin{tabular}{c} **BMI,** \\ **kg/m2** \\ \end{tabular} & **F/U** &
\begin{tabular}{c} **Pre-RME** \\ **AHI** \\ \end{tabular} & **Post-RME** & **AHI\%** \\ \hline [PERSON] et al. 2015 & 23 & 8.6 & \(22.7\pm 1.3\) & \(12.3\pm 1.5\) year & \(12.2\pm 2.6\) & \(0.4\pm 1.6\) & \(-97.7\)\% \\ [PERSON] et al. 2015 & 22 & \(8.3\pm 0.9\) & NR & 1 year & \(5.0\pm 1.5\) & \(1.5\pm 0.6\) & \(-70\)\% \\ [PERSON] 2014 & 1 & 11 & 22.4 & 2 year 5 month & \(18.9\) & \(1\) & \(-94.7\)\% \\ [PERSON] et al. 2012 & 15 & \(5.9\pm 1.6\) & NR & \(1.6\pm 0.6\) year & \(4.5\pm 3.8\) & \(3.4\pm 4.3\) & \(-24.4\)\% \\ [PERSON] et al. 2011 & 31 & \(6.5\pm 1.1\) & NR & 3 month & \(7.9\pm 3.2\) & \(3.1\pm 2.3\) & \(-60.7\)\% \\ [PERSON] et al. 2011 & 10 & \(6.6\pm 2.1\) & \(16.7\pm 3.6\) & 2 year 11 month & \(6.3\pm 4.7\) & \(2.3\pm 1.7\) & \(-63.4\)\% \\ TOTAL & 102 & \(6.7\pm 1.3\) & \(19.4\pm 2.5\) & \(\leq\)3 year & \(7.5\pm 3.2\) & \(2.5\pm 2.6\) & \(-66.1\)\% \\ \hline \hline \end{tabular}  
* Age at baseline;
* Mean oxygen saturation (MSAT); AHI = apnea–hypopnea index; BMI = body mass index at baseline; F/U = follow-up; NR = not reported; RME = rapid maxillary expansion.  
\end{table} 
Table 4: Demographic and Polysomnographic Data Before and After Rapid Maximlay Expansion with or without Surgery in Children. Figure 1: Study search flowchart. Apnea-Hypopnea index values. From the pre-RME to the post-RME, the overall AHI decreased by 66.1%. In fact, AHI improved from a M \(\pm\) SD of \(7.5\pm 3.2\)/h to \(2.5\pm 2.6\)/h. Regarding AHI \(<\) 1/h, no success rates were reported in the studies by [PERSON] et al., [PERSON] et al., [PERSON] et al., [PERSON] et al., and [PERSON] et al. [PERSON] et al. as well as the other studies, demonstrated a decrease in the AHI index 24 months after the end of the orthodontic treatment. [PERSON] et al. demonstrated a success rate only after \"Treatment 2\". The 31 children in their study were divided into two groups: group 1 received surgery followed by orthodontics, while group 2 received orthodontics followed by surgery. After \"Treatment 1\", the AHI values in group 1 decreased from \(12.5\pm 0.8\)/h to \(4.9\pm 0.6\)/h. After \"Treatment 2\", the AHI values in group 1 decreased to \(0.9\pm 0.3\).