Am J Orthod Dentofacial Orthop 2017;151:357-62
The aim of this study was to investigate the relationships between an apical curvature or a hook and the crown/root ratio in subjects with and without palatally impacted maxillary canines. Methods: An experimental group of 44 patients (17 boys, 27 girls; mean age, 13.6 years) with 59 palatally impacted maxillary canines was selected from the records of patients referred to a radiology practice for cone-beam imaging. If a patient had bilateral palatally impacted canines, 1 canine was randomly selected for analysis. The palatally impacted canine group was matched for age and sex with 49 normal subjects (25 boys, 24 girls; mean age, 13.2 years) with 98 canines. Cone-beam DICOM files were imported into In Vivo imaging software (version 5.3; Anatomage, San Jose, Calif) for analysis. The angulations and linear variables of the maxillary canines were measured by using the software measurement tools. Chi-square and independent t tests were used to test for differences between the groups. Results: The presence of a hook at the apical third and other root curvature were significantly different between the 2 groups (P\0.001 and P\0.05, respectively). Of the 44 palatally impacted canines, 16 (36.4%) had an apical hook and only 1 canine in the control group had an apical hook (1.0%). The mean root length of the palatally impacted canines was 2.66 mm shorter (P \0.001), and the mean crown/root ratio was significantly greater for the palatally impacted canines compared with the nonimpacted group (P\0.001). Conclusions: Palatally impacted canines have a greater tendency to develop apical hooks and are less likely to develop other root curvatures than are nonimpacted canines. Also, they have shorter roots resulting in larger crown/root ratios compared with the control group.