Effects Of EGCG On Orthodontic Tooth Movement And Root Resorption In Rats

Tea is not only a traditional drink in China,but also one of the oldest and most popular drinks all over the world,including several varieties such as green tea,black tea,and oolong tea.Its history can be traced back to the fiftieth century.Tea polyphenols are the major natural active ingredients in tea and are most abundant in green tea(a class of unfermented tea).Drinking tea has multiple health benefits,which have become widely accepted by the general public in the long-term applications of tea beverages.As the most abundant and active catechin in the tea polyphenol family,epigallocatechin-3-gallate(EGCG)has attracted considerable attention in pharmacological research,recently,its anti-inflammatory,antitumor,cardiovascular protective,neuroprotective and other various potencies have been confirmed in the exploration.In addition,a large number of in vitro and in vivo studies have shown that EGCG is able to act on osteoblasts and osteoclasts,affect their proliferation and differentiation,and thereby participate in the regulation of bone metabolism,effectively improve the symptoms of osteoporosis and promote the healing of bone fractures.The process of orthodontic tooth movement(OTM)is inextricably linked to periodontal tissue remodeling.When a tooth is loaded with orthodontic forces through orthopedic devices such as brackets,archwires,etc.,the periodontal membrane on one side is squeezed(pressure side)and the periodontal membrane on t he other side is stretched(tension side),then a series of complex biological reactions occur.Osteoblast mediated new bone formation mainly occurs in the tension side,involving the expression of various osteogenic factors.While bone resorption mediated by osteoclasts mainly occurs on the pressure side,which is closely related to the rank/RANKL/OPG signaling pathway.And in this process,orthodontic induced root resorption(OIRR)tends to occur simultaneously.OIRR,as the most common and difficult complication of orthodontic treatment with an incidence of up to 90%,affects the patient’s oral health and stability of teeth after orthodontics and is a challenge that patients share with clinicians.To our knowledge,substances capable of affecting bone remodeling are often also capable of affecting orthodontic tooth movement.In the field of oral medicine,EGCG has been proven to be effective for the prevention and treatment of various diseases,such as caries,gingivitis,and oral ulcers,and can well inhibit alveolar bone resorption in periodontitis model rats in in vivo experiments.However,our knowledge about the effect of EGCG on orthodontic tooth movement and root resorption is still limited.Objective:To establish an animal model and investigate the effects of EGCG on periodontal remodeling and root resorption during orthodontic tooth movement in rats,as well as to preliminarily explore the possible mechanisms involved.Methods:Thirty six male Wistar rats(6-week-old)were randomly and equally divided into three groups:control group,50 mg/kg EGCG group and 100 mg/kg EGCG group.After adaptive feeding,all rats were established the orthodontic tooth movement model,that is,the 50 g orthodontic force were loaded on the right maxillary first molars of rats by ligature wire linking nickel-titanium closed-coil spring,and the bilateral central incisors were used as anchorage teeth to pull the first molars mesially.During the experiment,rats in the two experimental groups were given EGCG normal saline solution by gavage every day according to the corresponding dose,while rats in the control group were given an equal volume of normal saline.After 14 days of orthodontic addition,the rats were sacrificed by transcardial perfusion method and their right maxillary bones,which contained three molars,were isolated.Micro-CT was taken to analyze the tooth movement distance and root resorption of the rats in each group.And paraffin sections were prepared for H&E staining,TRAP staining,and IHC staining.The basic condition of the periodontium,the number of TRAP positive cells and the expression levels of factors involved in bone metabolism(RANKL,OPG,Runx2 and OCN)were observed and compared.Results:(1)According to the analysis of Micro-CT scanning data,the orthodontic teeth of the rats in the experimental group moved less distance than the control group,and the rats in the high concentration group moved less distance than the low concentration group,with significant differences between groups(P<0.01).Compared with the control group,the area ratio of root resorption to the volume of root resorption in the experimental group both decreased,and the decrease became more significant with higher concentrations of EGCG administration(P<0.01).(2)H&E staining showed that the mesial periodontal membrane of the distal buccal root of the right maxillary first molar of rats was compressed and arranged disorderly,and the distal periodontal membrane was stretched.The periodontal tissue destruction of the specimens in the dosing group were both reduced compared with the control group,and the reduction was more obvious in the high concentration group.(3)TRAP staining observation revealed that the number of TRAP positive cells in periodontal tissues of rats decreased with increasing concentrations of EGCG administration,and the difference between groups was statistically significant(P<0.01).(4)The average optical density(AOD)values were measured after IHC staining,and the results showed that,on the pressure side,the expression level of RANKL decreased with increasing concentrations of EGCG administration,whereas that of OPG increased with increasing concentrations,with significant differences between groups(P<0.01);On the tension side,the expression levels of Runx2 and OCN in the two experimental groups were higher than those in the control group(P<0.01),and the expression level in the high concentration group was higher than that in the low concentration group(P<0.05).Conclusion:EGCG was able to inhibit orthodontic tooth movement in rats and to reduce root resorption in this process.These effects are related to its inhibition of osteoclast formation on the pressure side of the tooth root.Meanwhile,EGCG also exerted a promoting effect on osteogenesis on the tension side of the root.