Analysis Of Factors Related To Root Resorption Of Maxillary Impacted Canines And Adjacent Lateral Incisors

Objective:The location of maxillary impacted canines was obtained by two-d imensional surface tomography,lateral cephalometry and orthogonal cephalometry,the influence of the impacted position of canines on root resorption of adjacent later al incisors was analyzed.Methods:Twenty cases of unilateral maxillary canine impaction were selected from the orthodontic Department of the Second Affiliated Hospital of Dalian Medical University from 2010 to 2017 strictly.The patients ranged in age from 11 to 15 years,with an average age of 13.25 years.All subjects acquired image data by the same device before and after orthodontic treatment.Measured by the same person three times,one week apart each time,take the average of the three measurements.1.The vertical distance from the apex of impacted maxillary canines to the median sagittal reference line is recorded as D1.The straight line connecting the central point of the cockscomb and the anterior nasal ridge is used as the median sagittal reference line.2.The vertical distance from the apex of maxillary impacted canines to the anatomical occlusal plane is recorded as D2.3.The posterior-upper corner of the long axis of maxillary impacted canines intersects with the anatomical occlusal plane is recorded as Z.4.Measure the root length of maxillary lateral incisors on curved tomography before and after treatment.The degree of root resorption was evaluated according to the improved grading standardre-established by Jiang Ruoping and others according to Sharpe grading method.The adjacent incisors of 20 unilateral impacted canines were divided into mild root resorption group(n=9)and severe root resorption group(n=11).According to the classification criteria of root resorption,the degree of root resorption in mild root resorption group was0 or 1 degree,and that in severe root resorption group was 2 or 3 degrees.Root length of maxillary lateral incisors:the connection line between the midpoint of incisor margin and apical point of maxillary lateral incisors and the distal and distal cementum boundary of maxillary lateral incisors.The distance between the intersection point of the two lines and the apical point is recorded as root length.The vertical distance(D1)from the cusp to the median sagittal reference line,the vertical distance(D2)from the cusp to the anatomical plane of the maxillary impacted canine,and the difference of the posterior-upper angle(Z)between the long axis of the maxillary impacted canine and the anatomical plane were studied by independent sample t-test.The correlation between the location of impacted maxillary canines and the root resorption of adjacent lateral incisors was studied by binary logistic regression analysis.Results:1.The vertical distance from the cusp to the median sagittal reference line of maxillary impacted canines in the severe root resorption group was smaller than that in the mild root resorption group,and the posterior-upper angle of the long axis intersecting with the anatomical plane was smaller(P < 0.05).2.There was no significant difference in the vertical distance between the apex of impacted maxillary canines and the anatomical plane between the mild root resorption group and the severe root resorption group(P > 0.05).3.The vertical distance from maxillary impacted canine to median sagittal reference line was negatively correlated with root resorption of adjacent lateral incisors(P < 0.05).The possibility of severe root resorption was reduced by 37.1% for each additional unit ofvertical distance from impacted maxillary canines to the median sagittal reference line.4.There was a negative correlation between the degree of root resorption of the adjacent lateral incisors and the posterior-upper corner of the maxillary impacted canine whose long axis intersected with the anatomical occlusal plane(P < 0.05).The possibility of severe root resorption was reduced by 17.9% for each unit in the posterior-upper corner of maxillary impacted canine whose long axis intersected with the anatomical occlusal plane.Conclusion:1.The farther the maxillary impacted canines are from the median sagittal reference line,the less the root resorption of the adjacent lateral incisors is.2.There was no significant correlation between the vertical distance from maxillary impacted canines to anatomical occlusal plane and root resorption of maxillary lateral incisors.3.The larger the posterior-upper angle of maxillary impacted canines intersected with the anatomical occlusal plane,the smaller the inclination of impacted canines and the smaller the root resorption of adjacent lateral incisors.