THE USE OF SPIRAL COMPUTED-TOMOGRAPHY IN THE LOCALIZATION OF IMPACTEDMAXILLARY CANINES

Purpose: To compare spiral CT with conventional radiography in plannin g the orthodontic treatment of impacted permanent maxillary canines. M ethods: Nineteen patients with 29 malpositioned permanent maxillary ca nines (15 palatal and 12 buccal impactions, one ectopic and one transp osition) were examined with conventional panoramic and lateral cephalo metric radiography and with spiral CT (at 1 mm slice thickness, and 1: 1 or 2.1 pitch) using multiplanar (MPR) and 3D reconstruction. Results : Conventional radiography failed to depict root resorption especially on the buccal surfaces of the incisor teeth. CT located impacted teet h better. Contact between impacted maxillary canines and incisor roots was demonstrated in 26 cases and root resorption in eight. MPR proved to be superior for the orientation of impacted teeth, and, in two cas es, confirmed the presence of minimal root lesions for which axial ima ges had proved inconclusive. The 3D reconstructions were useful in tar geting the MPR. Conclusions: CT facilitates the treatment of impacted canine especially when the teeth are very oblique to the arch. Root re sorption is better demonstrated especially on the palatal and buccal s urfaces of the adjacent incisors. Spiral CT reduces examination time a nd risk of accidental movement, thus optimizing MPR quality. Examinati on at 2:1 pitch enables a significant reduction in radiation exposure without loss of image quality.