# Factors Associated with the Proximity of the Incisive Canal to the Maximally Central Incisor
## 4 Discussion
Multivariate analysis demonstrated a negative correlation between the mandibular plane and MCI apex and the distance to the CI. Considering the vertical skeletal pattern, a shorter face, smaller mandibular angle, and greater muscle strength characterize brachyfacial individuals compared with dolichofacial individuals with longer faces [39]. Several studies have demonstrated that brachyfacial individuals have a greater alveolar bone thickness in the anterior maxillary region [18; 47; 48; 49; 50; 51; 52]. This result is consistent with the distance between the upper central incisor root, and the IC tends to be shorter in dolichofacial than in brachyfacial individuals. The proximity of the MCI and IC is not affected by the sagittal skeletal pattern [39]; in the present study, the position of the maxilla relative to the mandible, as indicated by the ANB angle, did not affect the proximity of the MCI apex and the IC. Meanwhile, the position of the maxilla relative to the cranium, such as at the SNA landmark, or the anteroposterior size of the maxilla demonstrated an association with the distance to the CI. Thus, the greater the maxillary deficiency an individual exhibits, the more likely it is to cause proximity between the MCI and IC. Statistically significant sex-related differences have been reported in the anatomical characteristics of the IC, such as length and diameter [53; 54], and males have a greater MCI-IC distance than females [42; 55]. However, other studies showed that the MCI-IC distance is not significantly affected by sex [39]; the results of the current study were also consistent with this observation. Age has also been shown to significantly influence the IC length. The IC and MCI are proximate to each other in younger individuals [42]. However, one study revealed that the MCI-IC distance has no association with age [56]. In the present study, age did not substantially affect the MCI-IC distance. The influence of age and sex was limited; however, it is important to consider that differences in occlusion and skeletal class can affect anterior tooth recession in orthodontic treatment [39]. Caution should be exercised in cases where maximum anterior retraction is needed to improve soft tissue [57]. In this study, the more labially inclined the maxillary anterior teeth were, the greater the negative correlation with the distance between the root and IC. Because the anatomical morphology of the IC is related to the dental axis inclination of the maxillary anterior teeth and the MCI apex region is more proximal to the IC than other regions [27], we suggest that more attention should be paid to cases warranting lingual inclination of the anterior teeth. Orthodontic treatment in the maxillary central incisor region should always be preceded by careful radiographic analysis owing to the anatomic approximation between the IC and the roots of these teeth. In particular, a thorough and careful analysis of the IC and MCI and positional relationship using CBCT imaging should precede the treatment goals to obtain the best prognosis for orthodontic treatment of the maxillary anterior region. Based on the CBCT-based findings of the present study, the vertical skeletal pattern, especially in the dolichofacial type and the inclination of the MCI, has been associated with the relationship between the MCI-IC distance. Therefore, it provides some insight into clinical practice; especially in the case of camouflage treatment of occlusion in Class II patients of dolichofacial type, special care and precautions should be taken to avoid intrusion into the IC. A 3D evaluation during orthodontic diagnosis and observation of the incisal roots during treatment are useful in preventing possible complications, especially in patients requiring maximum retraction. Concurrently, changes in the position and inclination of the maxillary incisors result in morphological changes in the maxillary alveolar region [58; 59].