# Factors Associated with the Proximity of the Incisive Canal to the Maximally Central Incisor
## 4 Discussion  
It is important to evaluate and consider the distance between the apex of the MCI and IC to prevent root resorption that may occur when the MCI is in contact with the IC [29; 39]. As root contact between the MCI and IC is related to the anatomical morphology around the IC [7; 41], the morphological aspects of the MCI and its proximity to the IC have been evaluated using CBCT in many studies [27; 42]. The present study investigated \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**MCI-IC Distance** & **Age (y)** & **SNA** & **ANB** & **U1 to FH** & **U1 to NP** &
\begin{tabular}{c} **Mandibular Plane** \\ \end{tabular} & **A’-Ptm’** \\ \hline correlation coefficient & 1 & 0.03 & 0.16 & \(-\)0.04 & \(-\)0.24 & \(-\)0.04 & \(-\)0.19 & 0.23 \\ \(p\) & 0.70 & 0.04 & 0.66 & 0.00 & 0.63 & 0.02 & 0.00 \\ \hline \hline \end{tabular}  
* MCI: maxillary central incisors.  
\end{table} 
Table 4: Pearson correlation analysis of the relationship between the MCI-CI distance and age and cephalometric variables. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameters** & **Mean** & **Sex** & **Site** \\ \hline MCI-IC (mm) & 3.36 \(\pm\) 1.33 & Male & 3.37 \(\pm\) 1.30 & right & 3.43 \(\pm\) 1.38 \\  & Female & 3.35 \(\pm\) 1.34 & left & 3.28 \(\pm\) 1.37 \\ \(p\) & & & \(p\) = 0.92 & \(<\)0.05 \\ \hline \hline \end{tabular}  
* MCI: maxillary central incisor.  
\end{table} 
Table 3: Distance measurement between the central incisor and incisal canal. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Model** & **B** & **Sth. Error** & **Beta** & **t** & **Sig.** \\ \hline (constant) & 6.857 & 2.182 & & 3.143 & 0.002 \\ A’-Ptm’ & 0.066 & 0.026 & 0.208 & 2.508 & 0.013 \\ U1 to FH & \(-\)0.049 & 0.014 & \(-\)0.298 & \(-\)3.550 & \(<\)0.001 \\ mandibular plane & \(-\)0.034 & 0.016 & \(-\)0.188 & \(-\)2.171 & 0.032 \\ \hline \hline \end{tabular}  
* MCI: maxillary central incisors.  
\end{table} 
Table 5: Results of the multiple regression analysis using the MCI-CI distance as the objective variable. the associations between the sagittal and vertical skeletal patterns for the IC, dental axis inclination for the MCI, and patient age and sex. The FOV and voxel size affect the accuracy of 3D images obtained from a CBCT system [43]; a larger FOV corresponds to a larger voxel size and lower image resolution. The CBCT images used in this study had a FOV of 230 \(\times\) 170 mm and a voxel size of 0.3 mm. Since the CBCT used in this study was implemented for orthodontic treatment, the maximum FOV was set to cover the entire maxillofacial region. [PERSON] et al. [44] concluded that, when using CBCT to reconstruct and evaluate 3D tooth models for linear, volumetric, and geometric measurements, increasing the voxel resolution from 0.30 to 0.15 mm did not improve accuracy. Furthermore, [PERSON] et al. [45] concluded that a voxel size of 0.3 mm was the best protocol with the highest probability ratio values when evaluating external root resorption with the CBCT system for voxel sizes of 0.2, 0.3, and 0.4 mm. Therefore, CBCT images taken with sufficiently accurate voxel size settings were obtained for this study. Based on the study results, the distance between the apex of the MCI and the IC was approximately 3.3 mm. The distance between the MCI apex and the IC is reportedly more proximal on the right side than on the left side [46]. In contrast, the present study found a significant proximity to the IC on the left side of the MCI compared with the right side. The limit of upper anterior retraction in orthodontic treatment has long been set at 7 mm [10; 11], while measurements of the distance between the MCI and IC using CBCT suggest that it may be less than the conventional guideline [20; 41], which is consistent with the findings of the present study. When the position of the IC exceeds 4 mm before and after treatment, the risk of root invasion into the IC and root resorption increases [31]; our study's results were consistent with this finding.