Predicting and preventing root resorption: Part II. Treatment factors.

The main objective of this study was to determine which treatment factors are most clearly identified with external apical root resorption that is detectable on periapical radiographs at the end of orthodontic treatment. The records of 868 patients who completed fixed, edgewise treatment from experienced clinicians in private practice were examined. The horizontal and vertical displacement of the root apex of the maxillary central incisor was measured on cephalometric radiographs. Patients who underwent first premolar extraction therapy had more resorption than those patients who had no extractions or had only maxillary first premolars removed. Duration of treatment and the horizontal (but not vertical) displacement of the incisor apices were significantly associated with root resorption. No differences were found for slot size, archwire type, use of elastics, and types of expansion. However, there was considerable variation among the 6 offices that were surveyed; 1 office averaged nearly a full millimeter more of resorption per anterior tooth than the office with the least amount of root resorption. We conclude that the clinician should exercise caution with those patients in whom extraction therapy is planned for overjet correction that requires above average treatment time. Finally, each clinician should be aware that the root resorption seen in one practice may be different from the root resorption found in another practice.