## 4 Discussion
Class II or III skeletal malocclusions, open and deep bites, which are managed after the end of growth, usually require either treatment with orthodontic camouflage or decompensation of the defect before orthognathic surgery. In both cases, an extensive range of orthodontic movement may be necessary, depending on the severity of the defect. Skeletal anchorage has contributed to the possibilities and scope of this movement, which does not change the fact that movement should still take place within the bone envelope. Knowledge of the anatomy of the incisive canal, which may interfere with retraction, torque, intrusion, and lingual movement of the upper incisors, e.g., during decompensation of class III malocclusion, is essential for the proper planning of orthodontic treatment. It reduces the risk of root resorption. The anatomy of the incisal canal combined with the knowledge of the different widths of the maxillary alveolar bone may be crucial in preventing root resorption. [PERSON] (1965) showed that patients with mandibular posterior rotation are characterised by a narrower maxillary alveolar process than those with anterior rotation. On the other hand, [PERSON], [PERSON], and [PERSON] (2010); [PERSON] and [PERSON] (2011); [PERSON] _et al._ (2011) described a greater thickness of the alveolar process in the anterior part of the maxilla in brachycephalic patients. Furthermore, changes in the width of the maxillary alveolar ridge before and after retraction may be correlated with the magnitude of this movement. This suggests that greater diagnostic and therapeutic attention should be paid to patients with an initially narrow alveolar ridge ([PERSON] _et al._, 2012). [PERSON] _et al._ (2013) reported that the tipping of the incisor causes more bone resorption than axial movement. It is puzzling, however, that in some patients there is a strong root resorption as a result of contact of the root with the cortical bone, while in others, despite the bone separation, the entire roots are preserved. The applied orthodontic force may play a role, but further research is needed to confirm this hypothesis. The structure of the incisive canal and the anterior part of the maxillary alveolar process are important for root torque. [PERSON], [PERSON], and [PERSON] _et al._ (2013) demonstrated root resorption that extended from the apex and along the palatal surface of the root. It developed as a result of excessive root torque. It could have been related to contact with both the cortical bone of the palatal and canal. The last published study on the anatomy of the incisive canal determined the distance of the roots of the upper incisors from the canal depending on the growth pattern. There were gender differences, especially in the hypodivergent group. The authors also noted that this information may be useful in clinical practice ([PERSON] _et al._, 2012). Figures 4-11 show CBCT and X-ray images of a patient with resorption of the left upper central incisor root due to contact of the mesial and posterior part of the root with the cortical bone of the incisive canal after retraction and lingual movement of the upper incisors. Probably, earlier knowledge of such a risk could allow for the use of greater angulation of the incisors and bypassing of the cortical bone of the canal and, thus, prevent resorption. After analysing the images, it can be assumed that the height at which the root contacts the canal may determine the extent of resorption. The lower the height, the greater the root shortening. Further research is needed to confirm this hypothesis. Figure 4: Root resorption of upper incisor after contact with incisal canal CBCT—sagittal plane. Figure 5: Root resorption of upper incisor after contact with incisal canal CBCT—coronal plane. Figure 6: Contact of upper incisor’s root with incisal canal CBCT. Figure 7: Contact of upper incisor’s root with incisal canal CBCT.