## 2 Materials and Methods
### CBCT Landmarks, Reference Planes and Measurements  
CBCT multiplanar reconstruction images were reoriented using nasion, right porion and right and left orbitale and were examined using OnDemand 3D software (Cybermed, Seoul, South Korea). Landmarks around the IC and maxillary central incisors were traced on the T0 and T1 CBCT images of each subject. The Frankfort-horizontal (FH) plane served as a horizontal reference plane for the axial plane. It was found that the sagittal plane was parallel to the plane that passed across the anterior and posterior nasal spines and that it was perpendicular to the axial plane. The landmarks and measurements used in this study are described in Figure 3A and Table 1[22]. When the position of the root apex of the left and right central incisors was vertically different, L3 was set based on the apex located further below. In ten of the samples, the root apex was located lower than the oral opening of the IC. Therefore, the IC level through the root of the maxillary incisor was not available for these samples. Therefore, in this case, we used another method using ANS and IC nasal bifurcation to measure the IC dimension (Figure 3B, bottom) [29]. The anteroposterior \begin{table}
\begin{tabular}{l l} \hline \hline
**Measurement** & **Definition** \\ \hline \#11 Rm-\#21 Rm & Mediolateral distance between \#11 Rm and \#21 Rm (mm) \\ \hline \#11 Rm-Cat & Anteriorposterior distance between \#11 Rm and anterior margin of IC (mm) \\ \hline \#21 Rm-Cat & Anteriorposterior distance between \#21 Rm and anterior margin of IC (mm) \\ \hline IC LP width & Labiopalatal width of IC (mm) \\ \hline IC ML width & Mediolateral width of IC (mm) \\ \hline \#11R-\#21 Rt & Mediolateral distance between root apices of \#11 and \#21 (mm) \\ \hline \#11 Cr-\#21 Cr & Mediolateral distance between crown tips of \#11 and \#21 (mm) \\ \hline IC volume & Volume of IC from oral opening to nasal bifurcation (px, cm\({}^{3}\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Measurements used in this study (summary of abbreviations). Figure 2: MSE treatment protocol. distances between the IC and the maxillary central incis were not measured. The IC ML width, IC LP width, and the distance between the crown tip of the maxillary central incisors and the distance between the apex of the maxillary central incisors were measured regardless of the vertical level setting. In the previous study by [PERSON] [22], three indices for measuring the anterior-posterior distance between the maxillary central incisor and the IC were established: Rm-Cat, the distance from Rm to the tangent line through the most anterior point of the incisive canal; Rm-Canal, the distance from Rm to the anterior border of the incisive Canal; and IC Lt (or Rt)-Root, the distance from Cl to the posterior border of the maxillary central incisor root. As a result of the measurement, these three values did not show a significant difference according to the vertical level. Therefore, in our study, Rm-Cat was set as a representative value for measuring the anteroposterior distance between the maxillary central incisor and the IC in consideration of the convenience and accuracy of measurement. The IC was segmented using semi-automatic 3D segmentation and image analysis software (Medilabel, Ingradient, Seoul, Korea), and 3D volumetric models of the IC were generated from these segmentations (Figure 4). The volume of the IC was automatically calculated in pixels and cubic centimeters. Figure 3: Assessment of incisive canal (IC) and central incisor relationship. Landmarks and linear measurements. (**A**).