Corticotomy-assisted orthodontics

Abstract

The aims of the present study were to evaluate the root structure changes in untreated and buccal orthodontic tooth movement groups, with or without adjunctive flap surgery or corticotomy in an animal model, using Micro-CT. The null hypothesis was that there are no differences in the root structure following orthodontic tooth movement, flap surgery, corticotomy or combinations of orthodontic tooth movement and surgery compared with a control group, in both experimental and contralateral sides. Thirty six male Sprague-Dawley rats were randomly divided into six groups (three control and three experimental): 1. Nil intervention 2. Flap surgery 3. Corticotomy procedure only 4. Tooth movement only 5. Flap surgery and tooth movement 6. Corticotomy with tooth movement The right maxillary first molar was chosen as the experimental tooth. In the tooth movement groups, a customised appliance was constructed which delivered a constant buccal force of 0.1N to the upper right first molar, over the 7 days of the experiment. In the surgery groups, a full thickness flap was raised on the buccal aspect using elevators and, in the corticotomy groups, cortical bone was perforated using a round slow speed bur. Following the corticotomy procedure, the raised flap was repositioned using a tissue glue. All animals were sacrificed seven days after appliance insertion. This was followed by dissection of the maxilla, resin embedding and Micro-CT scanning. Micro-CT slices were assessed and the area of interest outlined. This consisted of the five roots of the maxillary right and left molar teeth from cemento-enamel junction to the apex of the tooth. Reconstructed images showed morphological root structure changes which were further quantified by volumetric analysis. The results from reconstructed images showed changes in all three experimental groups; however, the greatest change was in the root structure in the “Tooth movement with flap” and “Tooth movement with corticotomy” groups. The three control groups showed minimal to nil macroscopic change, in both experimental and non-experimental sides. Volumetric analysis reflected changes witnessed in reconstructed images, with a statistically significant reduction in volume of root structure in the “Tooth movement with flap” and “Tooth movement with corticotomy” groups, as compared with the other four groups. When assessing the contralateral side in these groups, similar changes in morphology and volumetric analysis were found. In conclusion, when assessing reconstructed images of corticotomy-assisted initial tooth movement in a rat model, morphological changes in root structure were evident. These changes were reflected as decreased root volume when comparing orthodontic tooth movement alone with orthodontic tooth movement with corticotomy and flap procedures. These changes were observed in both experimental and non-experimental sides. The results suggest that, although surgical intervention in conjunction with tooth movement may reduce mineral bone density and bone fraction in these groups, and thus assist in initial phase of tooth movement, it may not prevent root resorption. Furthermore, the combination of surgical intervention and tooth movement has the capacity to cause systemic root structure changes in the rat model.