Effect of orthodontic forces on root resorption in molars submitted to experimental periodontitis

The present experimental study addresses the issue of the development and size of root resorption areas in molars of rats submitted to orthodontic forces of 51 or 75 g and the induction of periodontal disease by placing a cotton ligature around the cervix of the first upper molars for 48 hours. Immediately on removal of the ligature or 48 hs later we put an orthodontic device in place. The device comprised two steel bands. The arms of a helicoidal spring that exerted force towards palatine passed through the palatine tubes welded to the bands. The number of odontoclasts and the percentage of root resorption areas were determined histomorphometrically on bucco-palatine sections obtained at the level of the central roots. The data showed an increase in root resorption areas when the orthodontic forces were applied to molars of rats following the induction of periodontitis. The magnitude of the force was proportional to the size of the resorption areas and to the number of odontoclasts. Both these end-points exhibited smaller values when the forces were applied once the inflammatory reaction had subsided. The present study shows that the risk of development of root resorption areas in patients with periodontal disease submitted to orthodontic treatment would be lower if lighter forces were applied and treatment were delayed until the inflammatory signs have subsided.