## 4 Discussion
Since the relationship between the IC and the teeth is more clinically important than the morphological change of the IC itself, the level was set using the roots of the maxillary central incisors. However, in a third of the total samples, IC was positioned at a different vertical level from the maxillary central incisors. Therefore, the plane was set based on the skeletal landmarks in these samples. That is, in about one-third of the patients, there was no risk of root-incisive canal contact due to retraction of the maxillary arch unless intrusion of maxillary anterior teeth was planned. CBCTs taken 6 months after completion of the expansion were compared with T0 to provide sufficient time for remodeling of the ICs and ossification of the midpalatal sutures. However, some of the samples had an irregular and ambiguous margin in the anterior and posterior area of the IC due to insufficient ossification of midpalatal sutures. In these cases, an imaginary ellipse was created along the lateral wall of the IC, and the anterior and posterior points were marked. The labiopalatal width of the IC was possibly slightly changed due to the cortical ossification of the IC progress. The mean increase in mediolateral width of the IC was about 2 mm, similar to the interdental distance increase between the maxillary central incisors. This suggests that MARPE did not increase the likelihood of contact between the IC and the roots of the maxillary central incisors by expanding the IC laterally. In patients with maxillary transverse deficiency, most of the central incisors were inclined distally. Therefore, unless the amount of expansion was large, there was little chance that the distance between the roots of the teeth would decrease significantly during orthodontic treatment. According to our findings, the biological anteroposterior distances between the roots of the central incisors in the maxilla and the incisive canal were about 4-5 mm, which is a little smaller than [PERSON]'s study. Although not statistically significant, the distance between the maxillary central incisor and IC showed a tendency to decrease slightly after treatment compared to before MARPE treatment. Taking into account the morphologic aspects of the incisive canal, the central incisor roots, the L1 or L2 apical third's posterior-median aspect of the roots as opposed to the root apex itself is most likely to approximate with the canal after retraction and root movement of the maxilla [22]. However, anterior intrusion occurs in a variety of clinical circumstances, increasing the potential for approximation along the tooth movement. As a result, 3D images may be useful in determining the distance between the incisive canal and the dimensional properties when a substantial maxillary incisor retraction with vertical control is planned. After MARPE, the anteroposterior distance between the maxillary central incisor and the IC decreased only at the L1 level. One of the most apparent changes related to rapid Maximillary expansion is the formation of a diastema between the maxillary central incisors. The incisors are anticipated to separate roughly half the distance the expansion screw has been extended during active suture opening. Following this separation, the crowns of the incisors converge and make proximal contact. The elastic rebound of the transseptal fibers causes the crowns to mesially tip. The persistent pull of the fibers enables the roots to converge toward their original axial inclinations after the crowns make contact. This cycle takes approximately 4 months [38]. Considering that the distance between the crown points of the maxillary incisors did not increase after MARPE means that the maxillary central incisors moved mesiopalatally toward the diastema. As a result, the decrease in the anterior-posterior distance between the maxillary central incisor and the IC was about 0.5 mm, which was statistically significant but not clinically significant.