## 3 Results  
No statistically significant difference was obtained when comparing the intra-operator reliability of the two sets of analogic and digital measurements for all the operators (\(p\geq 0.05\)) (Table 1)  
The inter-operator reliability, investigated using ICC, was almost perfect (Table 2), with ICC values of 0.996 and 0.997, respectively, for the analogic measurements on maxillary and mandibular arches, and 0.998 and 0.978, respectively, for the digital measurements on the maxillary and mandibular arches.  
The mean difference between the analogic and digital LII measurements was 0.43 mm for the maxillary jaw and 0.24 mm for the mandibular jaw, showing that the greatest difference was retrieved in the upper arch, with an overestimation of digital measurements in both arches.  
Additionally, when comparing the measurements taken from the digital and plaster casts with a paired \(t\)-test (Table 3), statistically significant differences were obtained for both the lower (\(p\leq 0.05\)) and upper (\(p\leq 0.01\)) arches.  
When comparing the differences between the analogic and digital measurements for the 5 ABO groups of crowding for both the upper and lower arch, no statistically significant correlation, using one-way ANOVA, was obtained (\(p\geq 0.05\)) (Table 4).  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{8}{c}{**Mean (SD)**} \\ \hline  & \multicolumn{3}{c}{**Operator 1**} & \multicolumn{3}{c}{**Operator 2**} \\ \cline{2-13}  & \multicolumn{3}{c}{**Plaster**} & \multicolumn{3}{c}{**Digital**} & \multicolumn{3}{c}{**Plaster**} & \multicolumn{3}{c}{**Digital**} \\ \hline Little’s Index & Measurement & Measurement & \(p\) & Measurement & Measurement & \(p\) & Measurement & Measurement & \(p\) & Measurement & Measurement & \(p\) \\  & 1 & 2 & value & 1 & 2 & value & 1 & 2 & value & 1 & 2 & value \\ Maxillary arch & 10.65 (6.11) & 10.78 (6.23) & NS & 11.08 (5.89) & 11.13 (5.97) & NS & 10.59 (5.99) & 10.91 (6.28) & NS & 11.26 (5.69) & 11.30 (8.01) & NS \\ Mandibular arch & 10.36 (2.21) & 10.46 (3.16) & NS & 10.60 (3.16) & 10.52 (3.15) & NS & 10.48 (3.18) & 10.51 (3.19) & NS & 10.29 (3.00) & 10.49 (3.13) & NS \\ \hline \hline \end{tabular}
\end{table}
Table 1: Intra-operator reliability for Operator 1 and 2. Units are represented in millimeters. The \(p\) value obtained from paired \(t\)-tests. NS = non-significant (\(p>0.05\)).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Mean (SD)**} & \multicolumn{3}{c}{**Digital**} \\ \hline
**Little’s Index** & **Researcher 1** & **Researcher 2** & **ICC** & **Researcher 1** & **Researcher 2** & **ICC** \\ \hline
**Maxillary arch** & 10.65 (6.11) & 10.59 (5.99) & 0.996 & 11.08 (5.89) & 11.26 (5.69) & 0.998 \\ \hline
**Mandibular arch** & 10.36 (3.21) & 10.48 (3.18) & 0.997 & 10.60 (3.16) & 10.29 (3.00) & 0.978 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Inter-operator reliability for the plaster and digital measurements. Units are represented in millimeters. ICC = intraclass correlation coefficient.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{3}{c}{**Mean (SD)**} \\ \hline  & **Plaster** & \multicolumn{3}{c}{**Digital**} \\ \hline
**Little’s Index** & **Researcher 1** & **Researcher 2** & **ICC** & **Researcher 1** & **Researcher 2** & **ICC** \\ \hline
**Maxillary arch** & 10.65 (6.11) & 10.59 (5.99) & 0.996 & 11.08 (5.89) & 11.26 (5.69) & 0.998 \\ \hline
**Mandibular arch** & 10.36 (3.21) & 10.48 (3.18) & 0.997 & 10.60 (3.16) & 10.29 (3.00) & 0.978 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Differences in Little’s Irregularity Index measurements between the plaster and digital models. Units are represented in millimeters. The \(p\) values are based on paired \(t\)-tests. * \(p\leq 0.05\); **\(p\leq 0.01\)**.