Risk factors for apical root resorption of maxillary anterior teeth in adult orthodontic patients.

The purpose of this study was to identify risk factors for apical root resorption in adult orthodontic patients. Standardized periapical radiographs of maxillary anterior teeth and cephalograms made before and after treatment and treatment charts of 343 adults, representing groups of consecutively treated patients from four orthodontic practices, were examined. Apical root resorption was calculated by subtracting posttreatment tooth length measurements from the corresponding pretreatment measurements. Root width was measured from the mesial to the distal outline of the roots 4 mm from the apex. Root form was scored subjectively as normal, pointed, eroded, blunt, bent, and bottle shaped. Root movement was calculated from measurements of superimposed tracings of pretreatment and posttreatment cephalograms. Proximity of the central incisor roots to the palatal cortical bone was scored subjectively as present or absent. Severity of initial malocclusion and treatment variables were collected from the charts. Multiple linear regression analyses revealed that amount of root movement, long roots, narrow roots, abnormal root shape, and use of Class II elastics were significant risk factors. However, the statistical model had a low explained variance, strongly suggesting a weak prediction power. No association was found between type of initial malocclusion, treatment time, use of rectangular arch wires, proximity of the root to the palate or treatment with maxillary osteotomy, and root resorption. Endodontic treatment was a preventive factor.