A RADIOGRAPHIC STUDY OF POSTERIOR APICAL ROOT RESORPTION IN ORTHODONTIC PATIENTS

The purpose of this study was to determine the extent of apical root r esorption, after fixed appliance therapy, in the posterior part of the dentition, and to evaluate if predisposing factors can be pointed out retrospectively. Tooth length in the posterior part of the dentition was measured on pretreatment and posttreatment orthopantomograms of 15 3 patients who were treated with standard edgewise appliances. Pretrea tment and posttreatment tooth lengths were determined, and an attempt was made to explain the differences by sex, age, stage of root formati on at onset of orthodontic treatment, extraction versus nonextraction therapy and treatment duration. Patients were divided into two groups according to their root formation. Group A consisted of patients with incompleted root formation at onset of orthodontic treatment except fo r the first molars. Group B consisted of patients where root formation was completed with the exception of second and third molars. Posttrea tment tooth lengths of groups A and B were compared with pretreatment tooth lengths of group B with a paired t test, and correlations with t he variables were calculated with multiple regression analysis only in group B. Posttreatment group A showed no significant differences with the mean root lengths of pretreatment group B. Differences between th e mean pretreatment and posttreatment root lengths in group B were sig nificant. Posterior teeth showed root shortening during active orthodo ntic treatment, independent of sex, age, extraction versus nonextracti on therapy, and duration of active treatment. Teeth with incompleted r oot formation at onset of orthodontic treatment showed root lengthenin g during active treatment, yet did not reach thier ''normal'' tooth le ngth.