Morphological relationship analysis of impacted maxillary canines and the adjacent teeth on 3-dimensional reconstructed CT images

Abstract

It is now well-established that morphological anomalies of the maxillary lateral incisors are closely associated with maxillary canine impaction. However, most of these studies were conducted to examine the crown of the teeth erupting into the oral cavity based on the diagnostic casts. So far, not many studies have been conducted to examine the relationship between the root of the maxillary lateral incisor and the impacted maxillary canine. Active studies have been conducted using 3-dimensional reconstructed CT images in the field of maxillary canine impaction. So, we were able to observe the incisor root and the impacted canine crown using the 3D reconstructed CT images, in which we cannot see on the diagnostic cast. The aim of this study was to examine whether there is a relationship between maxillary canine impaction and the morphological characteristics of the maxillary dentition, especially the root of the lateral incisor by using the 3D reconstructed CT images. In this study, we selected only cases with unilateral maxillary canine impaction to compare the morphological characteristics of the dentition on the impaction side and the normal eruption side. The sample size was decided to be 40 by the pilot study. To minimize the bias depending on the sex and the location of the maxillary canine impaction, we selected equal numbers (20) of males and females, and equal cases (20) of buccal impaction and palatal impaction. Under the above conditions, the mean age was 13.5 ± 2.3 years. The multislice spiral computed tomography (MSCT) images of these 40 subjects were converted into 3D reconstructed images using the OnDemand 3D program (Cybermed Co., Seoul, Korea). We acquired the 3D tooth images by eliminating the adjacent anatomical structures. Then we measured the morphological characteristics of the individual teeth images. As we expected, there were no statistically significant differences in the morphological characteristics of the maxillary central incisor between the two groups. The length and volume of the maxillary lateral incisors roots were significantly smaller on the impaction side as compared with the normal eruption side (P=0.001 and 0.006, respectively). The width and volume of the canines crown was significantly greater on the impaction side as compared with the normal eruption side (P=0.020 and P<0.0001, respectively). These results might help to prove the hypothesis that the smaller-sized lateral incisor roots and greater-sized canine crowns are the influential etiologic factors in maxillary canine impaction.