The purpose of this study was to compare skeletal and dentoalveolar shape and size differences in patients with maxillary impacted canines versus unaffected patients using landmarked CBCT images and geometric morphometrics.104 cone-beam computed tomography scans from patients presenting with palatal or buccal impacted maxillary canines and 40 control patients with no impacted dentition were landmarked. 146 landmarks were plotted in Stratovan Checkpoint. Cone-beam computed tomography images including the nasal cavity, palate, sinus, alveolar crest, maxillary lateral walls, and dentition were landmarked by five examiners. No patient had undergone any type of orthodontic treatment in the past. Landmarked CBCT images were evaluated for shape and symmetry using geometric morphometric analysis by performing Procrustes superimposition, principal component analysis, and canonical variates analysis. Shape differences were further investigated by using linear regression analyses. Size differences were then investigated by looking at centroid size based on ratios between dentition and the entire landmarked maxilla. To analyze shape differences, we utilized a principal components analysis and found impaction location of the canine contributed to the primary and secondary principal component of the variance in the shape. Removing the variance of tooth location, a principal component analysis was conduct on the asymmetric component. We found patients with maxillary canine impactions had a constriction of the arch on the side of the impaction as well as lowering of the sinus floor on the side of the maxillary canine impaction compared to the control. The shape differences found were not statistically significant and we found no difference in shape between palatal versus buccal impactions. Looking at size with differences of the dentition, the centroid size of the maxillary canine, central incisor and first molar were statistically different between the impacted and nonimpacted groups with a reduction in centroid size of the canine in the impacted versus nonimpacted groups. There were no statistically significant size differences between the impacted maxillary canine groups however there was a reduction in size in the palatal size versus the buccal side. The centroid sizes of the maxilla without teeth, arch width, and palate size in the impacted versus the nonimpacted group were all statistically different from the control group with the impacted group being smaller while there was no difference between the palatal versus buccal groups. When looking at the size of the maxilla between males versus females, it was found that males consistently had large centroid sizes in their overall maxilla compared to females. We isolating for gender, there was no statistically significant difference in maxilla size between maxillary impaction palatal or buccal impactions. Patients with impacted maxillary canines have both shape and size differences in the overall maxillary structure as well as the maxillary canine compared to patients without impacted maxillary canines. Amongst the dentition there was a general size reduction between the impacted versus nonimpacted tooth sizes. The impacted canines and first incisors and first molars on the side of the impaction had a statistically significant reduction in size compared to the nonimpacted canine patients. We also found a reduction in overall maxillary size in patients with impacted canines. There was also no statistically significant difference in centroid size of teeth or maxillary structures between palatal and buccal groups. These findings reflect that perhaps the etiology of canine impaction location is in line with the genetic theory rather than a lack of guidance from an undersized lateral incisor.

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