Incisor root resorption associated with palatally displaced maxillary canines: Analysis and prediction using discriminant function analysis

Introduction: Incisor root resorption associated with palatally displaced canine (PDC-IRR) is an important phenomenon that might alter the orthodontic treatment plan. The aims of this study were to investigate the prevalence and characteristics of PDC-IRRs, to compare PDC-IRR and PDC-No-IRR groups, to identify predictors for PDC-IRR, and to produce a valid PDC-IRR prediction model using discriminant function analysis. Methods: Cone-beam computed tomography images for 107 palatally displaced canines (PDCs) and 51 fully erupted nondisplaced canines (NDC) were analyzed for the presence of incisor root resorption (IRR). The PDCs were divided into 2 groups: PDC-IRR (52 canines) and PDC-No-IRR (55 canines). The 3 groups were compared, and the following variables were measured: canine follicle size, contact with adjacent incisors, associated dental abnormalities, sector analysis, canine vertical relation to adjacent root, lateral incisor angulation and inclination, canine angulation and distance to reference planes (dental midline, midpalatal suture, occlusal plane, pterygoid vertical plane, and lateral incisor), and space available for canine in the dental arch. Discriminant functional analysis was used to produce a discriminant function equation to predict PDC-IRR. Results: Root resorption affected 74% of lateral incisors adjacent to PDCs and 25.5% of lateral incisors adjacent to NDCs. IRR was located lingually in 41% of PDCs and in the mid and apical thirds in 89%. In the PDC-IRR group, 94.2% of canines were in contact with adjacent roots compared with 23.6% in the PDC-No-IRR group (P <0.001). Canine follicle size was >2 mm in 42% of PDC subjects. Overall mean value of follicle width in PDC canines was 1.79 +/- 1.06 mm. Peg-shaped lateral incisors were recorded in 19% of PDC subjects compared with 4% in NDCs (P = 0.012). The stepwise analysis using cone-beam computed tomography records produced a discriminant function based on 3 variables. The analysis correctly predicted the outcome in 83% of subjects. The variables contributing to the prediction equation were canine contact with adjacent incisors, size of canine dental follicle, and the presence of peg-shaped lateral incisor. Conclusions: Canines in contact with adjacent incisor roots was the only risk factor detected for PDC-IRR. Very good predictive discrimination (83%) emerged for PDC-IRR subjects. Predictors of PDC-IRR were canine contact with adjacent incisor, size of canine dental follicle, and presence of peg-shaped lateral incisor.