The Expression Of Osteoprotegerin And Wnt-5a In The Tissue Surrounding Suture On The Pressure Side During The Upper Jaw Remodeling Resulting From Maxillary Protraction

Objective: To evaluate the effects of different loading occasions of orthodonticforce on osteoprotegerin(OPG) and Wnt-5a, and to explore its clinicalsignificance through the establishment of rabbits’ maxillary protraction model.RT-PCR and immunohistochemistry staining are applied to investigating theexpression of OPG and Wnt-5a in surrounding tissue of the maxillary suture onthe pressure side during the reconstruction process. Methods: Fifteen healthymale New Zealand rabbits at the growth peak were adopted and divided to10d,20d,30d group, each of four and the rest three for control group according to themaxillary protraction time. Anesthetized animals were operated the implantationof the micro-implant anchorages to the hard palate of maxillary. Both sides ofthe palate needed to be planted a micro-screw. After they achievedosseointegration, the homemade skull external fixators were fixed to the rabbits’bilateral forelimbs in order to form a stable anchorage. The Nickel-Titaniumtraction springs were connected between the micro-screws and supportingstructures and imposed100grams traction. Observed the animals’ diet andhealth every day, then we sacrificed rabbits at the10th,20th,30th day of the experiment. After maxillaries were separated from animals, we took the tissueblock specimens surrounding tissue on the pressure side, which were bounded tothe front by the transverse palatine suture and corresponds to the maxillary thirdmolars. Two rabbits of each group were used for histomorphology studies, andtwo for RT-PCR determination. HE staining was applied to observe themorphological changes of the tissue surrounding suture. At last, we detected theexpression of OPG as well as Wnt-5a in the surrounding tissue of the suture byimmunohistochemistry and RT-PCR methods. Results:①HE staining showedthat there was little osteoblasts of bone cambium of irregular shape with a smallamount of fracture of fiber in the10d group as traction time goes on. Osteoclastswere visible and then formed lacuna. Osteogenesis activity in the20d group wasobvious. We could see new bone and osteoblasts densely arranged in chain-likeconformation on the edge of bone. Moreover, the number of osteoblast,chondroblast and fibroblast significantly increased. Osteoblasts in certainregions were embedded by surrounding matrix and fibers. The new trabeculaeparallel to the traction direction stretched to the joint was visible, and the frontpart connected to each other. There were a large number of osteoblasts andfibroblasts distributed around. The osteoclasts were visible and the bone edgethat was not smooth shaped like a silkworm erosion.②Immunohistochemicalstaining revealed that the expression of target protein of OPG and Wnt-5a werepositive. Positive cells that were brown mainly located in the cytoplasm. Theexpression site of positive cells of OPG focused on the pressure side of the boneresorption parts. It showed no significant difference between the control groupand the10d group, which expressed weakly positive. The expression of OPG ofthe20d group on the pressure side had further enhanced and new boneformation was visible. The expression of OPG of the30d group gradually weakened (P<0.05). The positive cells of Wnt-5a were scattered within theosteoblasts around suture on the pressure side instead of concentrating. However,there was no evidence show those positive cells have anything to do with thetraction time (P>0.05).③The target bands of OPG and Wnt-5a emerged in theRT-PCR detection, which were consistent with immunohistochemical stainingresults. Conclusions: OPG involves in bone remodeling course throughout theorthodontic protraction process. It is a time-dependent expression in orthodonticsuture surrounding tissue on the pressure side, which provides theory for clinicalorthodontic treatment on controlling speed of movement of maxillary and boneremodeling.Wnt-5a does express on the pressure side of suture surroundingtissue at the protein level as well as molecular level. But we have not foundobvious relationship between it and protraction duration in the experiment.Therefore, its relevance with orthodontic bone reconstruction still needs furtherstudy. What effect does age factor have on bone remodeling while under theaction of the orthodontic force? Are there any differences and relations betweenthe reaction mechanism to orthodontic pressure of young and adult individuals’osteoblast? These remain to be further discussed.