Effect Of Resveratrol On Orthodontic Tooth Movement And Associated Root Resorption In Rats

Orthodontic tooth movement(OTM),a biological process characterized by remodeling of periodontal tissue as well as alveolar bone,is on account of bone resorption at the compression side as well as bone formation at the tension side[1].Osteoclasts are the main functional cells for bone resorption at the pressure side while osteoblasts are the main functional cells for bone formation on the tension side.The process of OTM is activated by the onset of osteoclasts,and the extent of OTM is dependent upon the number of osteoclasts on the pressure side[2].Orthodontic induced root resorption(OIRR),a potential complication of OTM,is a common undesirable outcome of orthodontic treatment[3].The prevalence of root resorption appears to be high,at 80%～90%,according to various research conducted[4-5],which affects oral health as well as function of patients,and creates challenges for dentists.Previous studies demonstrated that OIRR was caused by odontoclasts[6].In fact,as a result of their similarity in not only morphological but also functional characteristics,some researchers even categorize odontoclasts the same as osteoclasts in essence[7].Resveratrol(3,5,4’-trihydroxy-trans-stilbene,RSV)is a naturally occurring phytoalexin found in grapes,blueberries,peanuts,and other food products derived therefrom(e.g.,wine)[8].This compound has received worldwide attentions and been regarded as a potential drug candidate for a wide range of chronic diseases because of its biological effects.Studies carried out on RSV have shown that it has benefits with regards to the cardiovascular system[9],autoimmune disease[10],age-related disease[11],and cancer therapy[12].Moreover,it has been observed that RSV could affect bone metabolism by reducing osteoclasts formation and promoting osteoblasts formation[13].This indicates that RSV has application potential in the clinical orthodontic.However,so far,data on the effect of RSV on OTM and OIRR are scarce in literature.Objective:By establishing OTM rat models and feeding rats with different concentrations of RSV solution,we explored the effect of RSV on the distance of OTM,the degree of OIRR,the related indicator-tartrate resistant acid phosphatase(TRAP)-of bone metabolism,as well as the related factor-Receptor Activator of Nuclear Factor-κ B Ligand(RANKL),Osteoprotegerin(OPG),Runt-Related Transcription Factor 2(RUNX2),and Osteocalcin(OCN)-of bone metabolism in this study.This may provide a theoretical possibility for the clinical application of RSV.Methods:1.Establishment of animal model.Thirty-six male eight-week-old Wistar rats used in this study were randomly divided into three groups(the high concentration group,the low concentration group,and the control group)of 12 animals each.To establish OTM rat models,two incisors in the maxilla were tied and bonded in order to reinforce anchorage and minimize the distal movement of the incisors.Then,a nickel-titanium(Ni-Ti)closed-coil spring was fixed between the first molar and incisors,producing a 50 g orthodontic force to move the right first molar.2.Application of RSV.The high concentration group and the low concentration group were given RSV,dissolved in Carboxymethylcellulose(CMC)at a dosage of 10 mg/kg/d or 5 mg/kg/d respectively by gavage while the control group were fed the same volume of CMC with no RSV.3.Acquisition of specimens.On day 14 after the insertion of orthodontic appliance as well as the application of RSV,all the rats were sacrificed by heart perfusion.Each of the three groups was randomly divided into two subgroups,where one subgroup was used to acquire maxilla to measure the distance of OTM,and to prepare paraffin sections while another was used to acquire the right first maxillary molar for scanning electron microscopy(SEM)observation.4.Procession and measurement of specimens.Subgroup 1 was used to measure the distance of OTM and assessed by hematoxylin and eosin(HE)staining,TRAP staining,as well as immunohistochemical(IHC)staining to observe the periodontal tissue changes,compare the number of TRAP positive cells as well as the expression of RANKL,OPG,RUNX2,and OCN.Subgroup 2 was used to analyze the ratio of root resorption area via SEM photos as well as Image J software.Results:1.The OTM distance of the control group was significantly higher than that of RSV groups(p<0.01),and the OTM distance showed a dose-dependent relationship with RSV concentration(p<0.05).2.According to HE staining result,the more obvious periodontal destruction as well as larger and deeper detin resorption lacunae could be observed on the surface of root in the control group,followed by that of the low concentration group.The high concentration group showed less extent of damage of periodontal tissue and root resorption.3.According to TRAP staining result,the control group was where the most TRAP positive osteoclasts and odontoclasts exist,which was significant compared with the other two groups(p<0.01).Within the two RSV groups,the amount of TRAP positive cells in the low concentration group was remarkably more than that of the high concentration group(p<0.05).4.According to IHC staining results,the highest mean optical density(MOD)value of RANKL could be observed in the control group,followed by that of the low concentration group(p<0.01).The high concentration group showed the lowest MOD value of RANKL(p<0.05).In contrast,the highest MOD values of OPG,RUNX2,and OCN could be observed in the high concentration group,followed by that of the low concentration group(p<0.01).The MOD values of OPG,RUNX2,and OCN in the control group were the lowest(p<0.01).5.According to SEM observation results,the root resorption ratio of the control group was significantly higher than that of RSV groups(p<0.01)and the root resorption ratio showed a dose-dependent relationship with RSV concentration(p<0.01).Conclusion:1.RSV could remarkably reduce the distance of OTM.2.RSV could remarkably reduce the ratio of OIRR.3.RSV could remarkably reduce the number of TRAP positive cells in periodontal tissue.4.RSV could remarkably inhibit the expression of RANKL,but promote the expression of OPG,RUNX2,and OCN in periodontal tissue.5.The effect of the high concentration group was more obvious than that of the low concentration group.6.The inhibitory effect of RSV on OTM and OIRR may partly because of its inhibitory effect on osteoclasts as well as the promoting effect on osteoblasts.