## 4 Discussion  
Over the years, several appliances have been proposed for the treatment of transverse discrepancy, and among these one of the most commonly used for orthopedic expansion is the Rapid Maximillary Expander (RME) [1; 3; 4; 5; 6; 7]. However, in recent years, Align Technology introduced Invisalign(\(\cong\))First System as an orthodontic approach that can be used to resolve crowding, improving the dental arch form by inducing dento-alveolar changes in growing subjects presenting with early mixed dentition [8; 9]. The purpose of this study was to analyze the dento-alveolar changes obtained on the maxillary arch at the end of treatment with RME and Clear aligners. These two appliances are different from each other; the RME is an orthopedic device which aims to have skeletal effects rather than dental by opening the mid-palatal suture in growing individuals [15; 16], whereas Clear aligners operate by pushing on the clinical dental crown, inducing dento-alveolar modifications [9]. The choice to select patients with the RME anchored on the first maxillary molars was taken to make the two study samples as homogenous as possible even if the second deciduous molars were suitable for anchorage. The results of the present study showed a greater increase in the inter-canine width (+1.5 mm \(\pm\) 0.5 mm) and in the first inter-deciduous molar width (+1.4 mm \(\pm\) 0.4 mm), \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline
**Variables** & \multicolumn{2}{c}{**CAG**} & \multicolumn{2}{c}{**RG**} & & & & & \\ \multicolumn{2}{c}{**(_tr_ = 15; 8 F; 7 M)**} & \multicolumn{2}{c}{**(_tr_ = 17; 9 F; 8 M)**} & & & & & \\ \hline  & **Mean** & **SD** & **Mean** & **SD** & **Diff** & **SD** & **95\% CI** & \(p\) **Value** \\ \hline \multicolumn{2}{l}{**Angular measurements (\({}^{\circ}\))**} & & & & & & & & \\ \hline Right deciduous canine crown & \(-\)7 & 1.3 & 2.4 & 0.6 & \(-\)9.4 & 0,4 & \(-\)10.116 to \(-\)8.684 & *** \\ \hline Left deciduous canine crown & \(-\)6.4 & 0.9 & 2.7 & 0.7 & \(-\)9.1 & 0.3 & \(-\)9.678 to \(-\)8.522 & *** \\ \hline Right first deciduous molar & \(-\)10.6 & 6.3 & 1.1 & 0.5 & \(-\)11.7 & 1.5 & \(-\)14.825 to \(-\)8.575 & *** \\ \hline Left first deciduous molar & \(-\)12.8 & 2.0 & 1.6 & 1.2 & \(-\)14.4 & 0.6 & \(-\)15.574 to \(-\)13.226 & *** \\ \hline Right second deciduous molar & \(-\)6.1 & 2.6 & \(-\)6.8 & 2.4 & 0.7 & 0.9 & \(-\)1.105 to 2.505 & NS \\ \hline Left second deciduous molar & \(-\)6.8 & 2.4 & \(-\)7 & 1.8 & 0.2 & 0.7 & \(-\)1.320 to 1.720 & NS \\ \hline Right first molar crown & \(1.1\) & 0.7 & \(-\)7.2 & 2.7 & 8.3 & 0.7 & 6.832 to 9.768 & *** \\ \hline Left first molar crown & \(2.1\) & 0.5 & \(-\)7.0 & 1.5 & 9.1 & 0.4 & 8.270 to 9.930 & *** \\ \hline \multicolumn{2}{l}{NS: not significant, *** \(p\) \(<\) 0.001; CI: confidence interval; SD: standard deviation.} & & & & & \\ \end{tabular}
\end{table} 
Table 3: Descriptive and statistical comparison of T2-T1 changes for angular measurements between Clear aligners and RME groups. and also at the transpalatal level, in the CAG group when compared with the RG group (Table 2). Conversely, in the posterior region of the upper arch, a greater increase in the first inter-molar distal width was found in the RG group (+1.2 mm \(\pm\) 0.4 mm) when compared with the CAG group. This could be explained by the reverse \"V\" pattern RME expansion related to the anteroposterior increase in skeletal resistance. In fact, in the anterior region, where skeletal resistance is minimal, no dental compensation was observed, while across the molar region, where maximal skeletal resistance occurs, minor sutural and major dental response was realized [16], as overall maxillary expansion is a result of both skeletal and dentoalveolar displacement. On the other hand, Clear aligners push against the palatal tooth surface, inducing lateral dental displacement and an increase in the distance among dental cusps.