## 3 Results  
Posterior crossbite was clinically corrected in all the subjects with an improvement of the transversal maxillary dimension. The ICC values for the intra- and interobserver agreement were always larger than 0.88. The mean error was less than 0.3 mm. The method error was considered negligible. Descriptive statistics and statistical results of maxillary and mandibular measurements at T0 and T1 in the test and control group are shown in Tables 2-5. Figure 4: Test Group—Leaf: Mandibular arch before (**a**), after the expansion (**b**) and the superimposition of the two digital casts (**c**). Figure 5: Control Group—RME: Mandibular arch before (**a**), after the expansion (**b**) and the superimposition of the two digital casts (**c**). Figure 6: Control Group—RME: Maximillary arch before (**a**), after the expansion (**b**) and the superimposition of the two digital casts (**c**) with the digital landmarks traced by means of 3 Shape Ortho Analyzer software. Statistically significant differences were found in all of the intragroup comparisons of the test group (\(p<0.05\)). SME--test group: all the interdental widths of the maxilla (Table 2) increased significantly: first permanent molars +2.51 mm (SD 1.58 mm), second primary molar +5.06 mm (SD 0.98 mm), first primary molar +5.41 mm (SD 1.81 mm), primary canine +5.22 mm (SD 1.91 mm). As shown in Table 3, even the mandibular interdental width of the test group increased significantly: intercolor width increased by 1.24 mm (SD 1.09 mm), first primary intercolor 1.63 mm (SD 1.57 mm), second primary intercolor by 0.93 mm (SD 1.08 mm), intercanine width 1.03 mm (SD 1.25 mm). RME--control group: all the interdental widths increased significantly in both arches and are shown in Tables 4 and 5. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Interdental** & & & & & & & & & \\
**Mandibular** & **T0 Mean** & **SD** & **CI 95\%** & **T1 Mean** & **SD** & **CI 95\%** & **Increase** & **SD** & **CI 95\%** & **Significance** \\ \hline
16–26 width & 43.36 & 2.34 & 42.4–44.4 & 47.17 & 2.1 & 46.3–48.1 & 3.81 & 1.43 & 3.2–4.44 & \(<\)0.001 \\
55–65 width & 39.93 & 2.01 & 35.4–41.6 & 43.12 & 1.78 & 42.3–43.9 & 3.2 & 1.1 & 2.74–3.68 & \(<\)0.001 \\
54–64 width & 34.52 & 1.99 & 33.6–35.4 & 37.82 & 1.63 & 37.1–38.5 & 3.3 & 1.22 & 2.77–3.83 & \(<\)0.001 \\
53–63 width & 31.51 & 2.61 & 30.4–32.6 & 35.15 & 2.45 & 34.2–36.3 & 3.63 & 1.51 & 2.99–4.29 & \(<\)0.001 \\ \hline \multicolumn{10}{c}{SD = standard deviation CI = confidence interval; \(p\) value \(<\) 0.05 were considered to indicate statistical significance.} \\ \end{tabular}
\end{table} 
Table 4: Paired \(t\)-test comparing the mean interdental maxillary width (mm) increase after RME treatment—Control Group (n°21). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Interdental** & & & & & & & & & \\
**Mandibular** & **T0 Mean** & **SD** & **CI 95\%** & **T1 Mean** & **SD** & **CI 95\%** & **Increase** & **SD** & **CI 95\%** & **Significance** \\ \hline
16–26 width & 44 & 2.17 & 43.46–44.54 & 46.51 & 2.46 & 45.97–47.05 & 2.51 & 1.58 & 2.14–2.88 & \(<\)0.001 \\
55–65 width & 38.85 & 2.13 & 38.36–39.33 & 43.91 & 2.13 & 43.43–44.40 & 5.06 & 0.98 & 4.84–5.28 & \(<\)0.001 \\
54–64 width & 33.52 & 1.84 & 33.00–34.04 & 38.93 & 2.44 & 38.41–39.46 & 5.41 & 1.8 & 5–5.84 & \(<\)0.001 \\
53–63 width & 30.52 & 2.23 & 29.95–31.10 & 35.75 & 2.73 & 35.17–36.33 & 5.22 & 1.91 & 4.77–5.41 & \(<\)0.001 \\ \hline \multicolumn{10}{c}{SD = standard deviation CI = confidence interval; \(p\) value \(<\) 0.05 were considered to indicate statistical significance.} \\ \end{tabular}
\end{table} 
Table 2: Paired \(t\)-test comparing the mean interdental maxillary width (mm) increase after SME treatment—Test Group (n°69).