Studies In The Early Reparative Process Of Rodent Orthodontical Tooth Resorption

Background and ObjectiveInflammatory root resorption is a common side-effect during orthodontic tooth movement.During the process of orthodontic tooth movement, periodontal tissue were effected by mechanical strength, ocurred reconstruction of alveolar bone and updation of periodontal membrane,which caused varying degrees of root resorption.The root resorption caused by orthodontic tooth movement, due to its characteristics of high incidence of onset, many researches focus on root resorption and repair during orthodontic tooth movement. But the biological processes and mechanisms of root resorption and repair after orthodontic treatment are still unclear. Is resorption of the root can able to return to pre-orthodontic treatment? It is not clearly. At present, clinically, we have not particularly effective methods of prevention of root resorption during orthodontic treatment. Can we interfere with the repair process after root resorption, the root repair to achieve a better result? Therefore, it is very important to understand the nature of root resorption during orthodontic treatment and repair mechanism.In this study, we establish the early root resorption repair induced tooth resorption model, Combined with scanning electronic microscope(SEM), haematoxylin and eosin (HE) staining, tartrate-resistant acid phosphatase (TRAP) staining and immunohistochemistry, and observed the histology changes and cementoclasts in periodontal tissue, the changes and expression of BMP-2 and BSP. Preliminary understand the histology changes of the early repair process after inflammatory root resorption caused by orthodontic treatment result. Discuss the relativity of the expression of BMP-2, BSP and early root repair after root resorption caused by orthodontic treatment, to clarify the mechanism, and rich the theoretical and practical basis of early root repair after root resorption caused by orthodontic treatment.MethodsWe established the early root repair after root resorption induced tooth resorption model in experiment group, control group include the opposite side without any force. An orthodontic appliance consist of a stretched closed coil spring (0.012 inch nickel–titanium wire) , ligated between the maxillary left first molar and the incisors of SD rats, moving the molar mesially with a force of 50g. After 14 days, the appliance was removed. Rats were anesthetized, sacrificed, fixed and decalcified, on 0, 1, 3, 5, 7, 10, 14, and 28 day after withdrawl appliance. Alveolar bone around the first molars were cut for paraffin histology and prepared sagittal paraffin sections, using TRAP to count on cementoclasts, and observed the morphological changes of periodontal tissue by SEM and HE staining, the expression BMP-2 and BSP in the periodontal tissues were detected by immunohistochemistry.Results1. Successfully established the early root repair after root resorption induced tooth resorption model.2. HE staining Tip: Appeared in the experimental group of first molar: 0 day group showed significant alveolar bone and root resorption, as time elapsed, with the appliance removal, resorption gradually stoped, occurred varying degrees repairment.3. TRAP staining results: 0 day group shows that the nucleus >3and TRAP positive cementoclasts, which was mainly arranged in the resorption of root surface, one day group showed the largest number of cementoclasts, experiment 1 day, TRAP staining of multinucleated cementoclasts were decreased, and on 7days, TRAP staining on the number of multinucleated cementoclasts had gradually returned to the physiological level.4. Scanning electronic microscope showed: In the experiment group, as time elapsed, with the appliance removal, resportion lacuna on the surface of root occurred varying degrees repairment. 5. Immunohistochemical staining showed:(1) BMP-2 staining intensity on day 1 expression reached its highest peak, Compared with control group, there were significant differences, day 3 begins to drop until day 28 weakly positive were observed.(2) BSP staining intensity on day 3 expression reached its highest peak, Compared with control group, there were significant differences, day 5 begins to drop until day 28 weakly positive were observed.Conclusion1. Under 50g of orthodontic force root absorption of rats happened, absorption site were distributed in the root neck, root furcation and apical 1 / 3.2. Some degree of root resorption during orthodontic tooth movement could be repaired after removed the appliances. The resorption occurred in cementum region repaired better than dentin region. As for the repair capacity, cementum was better than dentin. The resorption occurred in the apical 1 / 3 region repaired better than root neck and root central.3. After removal of appliance, force on the termination, root resorption during orthodontic tooth movement have not completely stopped, root resorption and root repair process co-exist, after 7 days the repair process continued mainly.4. Periodontal BMP-2 and BSP expression through the tooth root repair in rats after orthodontic tooth resorption the entire process and the changes had some regularity. We presumed BMP-2 and BSP participated in the repair process after orthodontic root resorption in alveolar bone and cementum remodeling.