Morphological Analysis Of The Relationship Between Maxillary Incisors And The Incisive Canal By Cone-beam Computed Tomography In Patients With Different Facial Profiles

Objective: The cone-beam computed tomography(CBCT)was used to evaluate the morphology and position of the incisor canal(IC)and the relationship between the IC and the maxillary middle incisor(U1)tooth roots,and to further compare the differences between different facial profiles to clarify their clinical significance,so as to provide reference for clinical diagnosis and treatment and avoid the risks.Methods: One hundred adult orthodontic patients who attended the Second Hospital of Hebei Medical University from 2017 to 2019 were selected,and their CBCT images before orthodontic treatment were measured,and the relationship between IC morphology and position,IC and U1 position was evaluated.Linear measurements of incisor width(ICW),inter-root distance at U1(U1-U1),and anteroposterior distance between IC and U1 tooth roots(U1-IC)were performed at the level of the lowest point of the buccal lateral opening of the IC(L1),the intermediate level between L1 and L3(L2),and the U1 root tip level(L3),respectively.The angle of the IC to the palatal plane(PP)(IC-PP),the angle of the alveolar protrusion(AP)to PP(AP-PP),the height of the IC relative to the enamel bone boundary(CEJ)(ICH),and the length of the IC(ICL)were measured in the median sagittal section of the CBCT.Vertical and sagittal facial patterns and U1-related angles were measured on CBCT reconstructed cranial lateral slices,and the vertical and sagittal facial patterns were classified according to classification criteria,respectively.To analyze the differences in the positional relationships between different osteoid ICs and U1 tooth roots,correlations between cephalometric measurements and CBCT 3D measurements were assessed using Pearson correlation analysis and multiple regression analysis.To analyze the differences in position relationships between IC and U1 tooth roots of different facial patterns,correlations between cephalometric values and CBCT 3D measurements were assessed using Pearson correlation analysis and multiple regression analysis.Results: 1.U1-IC is about 2-5 mm;2.The percentage of subjects with ICW greater than U1-U1 at L1 and L2 levels is 97% and 80%,respectively;3.There is a significant positive correlation between AP-PP,IC-PP and the angle between the long axis of the upper middle incisor and PP(U1-PP);4.The difference between left and right U1-IC is statistically significant among different vertical facial patterns,and U1-IC is significantly greater in low-angle patients than in average-angle and high-angle patients;5.ICH is positively correlated with U1-U1,and ICH is significantly greater in high-angle patients than in low-angle patients;6.U1-IC is negatively correlated with vertical facial pattern-related angle(MP-FH or SN-MP).However,U1-IC did not correlate significantly with the sagittal facial pattern-related angle(ANB)measure.Conclusions: There are large individual differences between the incisal canals,and conventional cephalogram do not accurately predict the proximity of the incisal canal to the incisal root.Therefore,it is recommended that CBCT be performed at the time of planning a large number of retraction of the anterior teeth to accurately assess the position relationship between the incisor canal and the maxillary middle incisor.