Biologic Response Of Mini-screw Implant Anchorage Combined Corticotomy-assisted Orthodontic Treatment To Premolar Intrusion In Beagle Dogs: Histological And Immunohistochemical Analysis

The intrusion of molars is a familiar tooth movement, and the intrusion of molars is a Gordian knot. Since the mini-screw implant anchorage(MIA) occurred, the intrusion of molars becomes easy, controlled and continuous. However, animal experiments suggested that there may be some risks of the intrusion of teeth, such as apical root resorption, periodontal tissue’s hyalinization. At the same time, the conventional molar intrusion requires a long duration, which increased high risks of caries, external root resorption, and decreased patient compliance. Hence, orthodontists need some ways to accelerate tooth movement and reduce the above risks.A systematic review showed as follows: corticotomy is more effective and safe to accelerate orthodontic tooth movement than others assistant ways. Alveolar corticotomy is a kind of alveolar surgery. Recently, most of the animal experiment researches about corticotomy-assisted orthodontic treatment have focused on the retrusion and the sagittal tooth movement. There are no relevant researches about the influence of corticotomy-assisted orthodontic treatment to root resorption and alveolar reconstruction during intrusion. Therefore, our study established an animal experiment model of mini-screw implants combined with corticotomy-assisted segmental intrusion for beagle dogs, and then elucidated the resorption of apical root and the remodelling of periapical tissues during the premolar intrusion.Objective: The purpose of this study was to evaluate the root resorption and bone remodeling of accelerating tooth movement with corticotomy-assisted orthodontic treatment to premolar intrusion in beagle dogs.Methods: Eight male beagle dogs were randomly divided into 4 groups; each dog was assigned bilateral sides of the mandible as the experimental side and the control side at random. Experimental side using MIA and corticotomy assisted intrusion of the third premolar(P3) and fourth premolar(P4), while the control side using MIA to directly intrusion. After 2(T2), 4(T4), 8(T8) and 12(T12) weeks, execute two dogs each time and obtain the specimens. Specimen slices were analyzed with hematoxylin-eosin and Masson’s trichrome staining and osteocalcin(OCN) and receptor activator for nuclear factor-κ B ligand(RANKL) immunohistochemistry.Results: 1. Apical alveolar bone resorption on the experimental side was always more active, and more osteoclasts were existed in bone resorption lacunae.2. The apical area on the control side occured hyaline degeneration at T2,and hyalinization area was cleared at T4.However, hyalinization was not observed on the experimental side.3. At the same point, the number and area root resorption lacunae after corticotomy were less than those on the control side.4. The OCN expression reached the maximum at T4 on the both side. During the whole observation period, OCN expression of the experimental side was higher than the control side(P<0.05).5. The RANKL expression reached the maximum at T2 on the experimental side, but that reached the maximum at T4 on the control side. During the whole observation period, RANKL expression of the experimental side was higher than the control side(P<0.05).In conclusion, more active periapical tissues remodeling may be the reason of the acceleration of tooth intrusion, and reduce the amount of root resorption after corticotomy. Corticotomy could decrease the risks of root resorption in beagles. Therefore, corticotomy may serve as a potential treatment for tooth intrusion.