## 4 Discussion  
This study aimed to confirm the efficacy of a new Slow Maximly Expander--The Leaf Expander--in a large sample of growing patients and to compare the results obtained with those of patients treated with a RME. The first main clinical effect achieved is that the maxillary crossbite was corrected in all the patients. We obtained also significant statistical results for the lower dental measurements. Recently in a study by [PERSON] et al. (2014), it was observed that there are no differences when comparing mono or bilateral crossbites; thus, we considered as a unique group all the patients presenting mono or bilateral crossbites. Few studies have been reported about SME effects both on the maxillary and the mandibular arches ([PERSON] et al., 2018; [PERSON] et al., 2019; [PERSON] et al., 2020). In 2018, [PERSON] et al. (2027) evaluated transversal interdental increase in a group of 30 patients treated with a banded Haas-Type appliance activated one quarter-turn every two days. The mean intercanine width increased 4.65 mm with values comparable with those reported also by [PERSON] et al. (2017, 2018). These results were greater than those reported for other patients in mixed dentition treated with SME and RME such as Hyrax appliance, expansion plates, or [PERSON] helix ([PERSON] et al., 2018; [PERSON] et al., 2019). However, our values are even higher than those with an increase in the intercanine width of more than 5 mm in accordance with the preliminary results published on the Leaf Expander appliance ([PERSON] et al., 2019). [PERSON] et al. published a review in 2016 reporting the dental effects of different slow maxillary expansion appliances. From these data, it has been confirmed with moderate evidence the efficacy of the Quad Helix for the increase of the maxillary intermolar and intercanine width ([PERSON] et al., 2019; [PERSON] et al., 2019). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Interdental** \\ **Maxillary Width** \\ \end{tabular} } & \multicolumn{2}{c}{**Leaf Group**} & \multicolumn{2}{c}{**RPE Group**} & \multirow{2}{*}{**CI 95\%**} & \multirow{2}{*}{**Significance**} \\ \cline{2-2} \cline{5-8}  & **Mean** & & & & **Mean** & & **SD** \\ \hline
16–26 width & 2.51 & 1.58 & 2.14–2.88 & 3.8 & 1.4 & 3.22–4.4 & \textless{}0.001 \\
55–65 width & 5.06 & 0.98 & 4.84–5.28 & 3.2 & 1.1 & 2.61–3.85 & \textless{}0.001 \\
54–64 width & 5.41 & 1.8 & 4.98–5.84 & 3.3 & 1.2 & 2.82–3.86 & \textless{}0.001 \\
53–63 width & 5.22 & 1.91 & 4.78–5.66 & 3.6 & 1.5 & 2.98–4.28 & \textless{}0.001 \\ \hline \hline \end{tabular} SD = standard deviation CI = confidence interval; NS = not significant \(p\) value \textless{} 0.05 were considered to indicate statistical significance.  
\end{table} 
Table 6: T test for independent samples comparing the net (\(\Delta\text{T}1-\text{T}0\)) interdental width (mm) increase after Leaf (n\({}^{\circ}\)69) or RPE treatment (n\({}^{\circ}\)21)—maximillary arch. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Interdental** \\ **Mandibular Width** \\ \end{tabular} } & \multicolumn{2}{c}{**Leaf Group**} & \multirow{2}{*}{**CI 95\%**} & \multirow{2}{*}{**RPE Group**} & \multirow{2}{*}{**CI 95\%**} & \multirow{2}{*}{**Significance**} \\ \cline{2-2} \cline{5-8}  & **Mean** & & & & **Mean** & & **SD** \\ \hline
36–46 width & 1.24 & 1.09 & 0.992–1.49 & 2.02 & 1.43 & 1.41–2.63 & 0.009 \\
75–85 width & 1.63 & 1.57 & 1.25–1.95 & 1.75 & 1.38 & 1.16–2.34 & NS–0.753 \\
74–84 width & 0.93 & 1.08 & 0.692–1.18 & 1.39 & 1.18 & 0.885–1.9 & NS–0.098 \\
73–83 width & 1.03 & 1.25 & 0.717–1.28 & 0.95 & 1.10 & 0.482–1.42 & NS–0.792 \\ \hline \hline \end{tabular} SD = standard deviation CI = confidence interval; NS = not significant \(p\) value \textless{} 0.05 were considered to indicate statistical significance.  
\end{table}