A study of three-dimensional relationship between the maxillary central incisor roots and the incisive canal in skeletal Class II malocclusion in adults

Objective Using CBCT to analyze the relationship between the maxillary central incisor roots and the incisive canals of the skeletal class Ⅱ adult patients before orthodontic treatment. Methods In our study, 66 skeletal class Ⅱ adult patients were divided into low angle group (23.23±2.79 year, n=21), average angle group (23.30±3.30 year, n=23) and high angle group (22.05±2.67 year, n=22). CBCT was used to measure the vertical distance between the lowest points of incisive canal labial and palatal wall (D1), the vertical distance between the apex of the maxillary central incisor and the lowest point of the incisive canal labial wall (D2). In LRap Plane and LM plane, the distance between the maxillary central incisor roots (Rap-Rap, Rm-Rm, Rp-Rp), incisive canal width (IC1, 2-IC1, 2) and the distance from the maxillary central incisor root to the incisive canal and to the maxillary palatal wall (Rap-canal, Rm-canal, Rp-palate) were measured. Results D1 of the low angle group (5.60±1.91)mm was the least, followed by that of the average angle group (7.11±2.03)mm, and D1 of the high angle group (7.70±1.86)mm was the largest. The D1 difference between low angle group and the average group, and D1 difference between low angle group and high angle group were statistically significant (P<0.05). D2 of the high angle group (9.06±1.76)mm was the least, followed by that of the low angle group (9.85±2.46)mm, and D2 of the average angle group (10.07±1.25)mm was the largest. The D2 difference between the high angle group and the average angle group was statistically significant (P<0.05). Rap-Canal of the high angle group (4.05±1.66)mm was less than that in the average angle group (6.44±2.24)mm and the differences were statistically significant (P<0.05). Rm-Canal of the high angle group (3.01±0.83)mm were less than that in the average angle group (3.63±0.74)mm, and the differences were statistically significant (P<0.05). In the low angle group, or in the average angle group, or in the high angle group, Rm-Canal was less than Rap-Canal but more than Rp-Palate, and the difference between each two of the distances was statistically significant (P<0.05). Conclusions The maxillary central incisor root was closer to the incisive canal in high angle adult patients, and the cervical segment of the incisor root was closer to the incisive canal compared to the apical segment. Key words: incisive canal; CBCT; envelope of discrepancy; apical root resorption