Relativity Of MMPs In GCF And Orthodontic Root Resorption Of Rats In Different Age Groups

Root resorption is one of the most common complications during orthodontic treatment.Severe root resorption may result in root shortening,loosening of tooth, and even falling off.It is difficult to deal with it in clinic practice.At present,we usually detect root resorption by X-ray film.However,it has such a low precision that it is difficult to detect tooth resorption in time and clearly.In addition, patients will receive radiation.Thus,it is necessary to find a new method to detect the development of root resorption.The matrix metalloproteinases family can degrade all extracellular matrixes of all tissues including bone.Recently,it is indicated that matrix metalloproteinases are the major enzymes during the rebuilding of periodontal tissues,and may be relevant to root resorption.Gingival crevicular fluid is secreted from the gingival crevicular areas and consists of many components,including matrix metalloproteinases.Its composition is variable with the changes of surrounding tissues.As it is easy,harmless,and quick to be detected,the gingival crevicular fluid has been used by periodontists to diagnosis,observe the diseases,and monitor the treating effects now.ObjectiveThe study aimed to establish the animal model of orthodontic root resorption in rats,and determine whether MMP-1 and MMP-9 in gingival crevicular fluid could serve as prognostic factors for orthodontic root resorption in different age groups. We hope to look for a clue to detect the development of root resorption in clinic.Methods48 female Wistar rats were selected to prepare the animal orthodontic root resorption model,in which there were 28 6-week-old rats and 20 12-week-old rats, whose weights were 160-180g and 200-230g respectively.The orthodontic appliances were fixed onto the maxilla of the rats after general anesthesia by peritoneal injection of 2%ketamine hydrochloride.The maxillary first molar in experimental side was drawn medially by applying an excess force of 50g,with both of the maxillary central incisors as anchorage.In the control side,the maxillary first molar was winded around the dental cervix with ligature wire.The appliances were strengthened every week.Two 6-week-old rats were killed at the 1st,2ed,4th and 7th week respectively,and the histological slices were made to observe the root resorption.The gingival crevicular fluid of the other 40 rats was collected every week,and MMP-1 and MMP-9 were assayed in quantitation by using the biochemistry techniques of SDS-PAGE,Western blot and Gel Doc quantitative analysis system.The rats were divided into adolescent group and adult group by age.The data was analyzed with the statistics software SPSS 11.0.Results1.The orthodontic root resorption of the maxillary first molar in Wistar rats was evident by histological features at the 2ed week after the appliances were fixed. The absorption lacunas and macrophages were found in the histological slices, and the root resorption was more and more serious with the time.2.The quantity of GCF after the appliances were fixed was higher than that of before(P＜0.05).There was no statistical significance of the quantity between the weeks after the appliances were fixed(P＞0.05).The quantity of GCF in experimental side was higher than that in the control side(P＜0.05).The quantity of GCF of the adult rats was higher than that of the adolescent rats(P＜0.05). 3.The contents of MMP-1 and-9 in GCF increased at the 1st week in both groups and both sides,and increased greatly at the 2ed week.It reached the peak at the 3rd week,and fell back from the 4th week.At the 7th week,the contents were the least,but more than that before the appliances were fixed.4.There was statistical significance in the contents of MMP-1 between experimental side and control side at the respective week in both of adult group and adolescent group(P＜0.05),and the experimental side was more than the control side.But no statistical significance was showed in the content of MMP-9 between the two sides(P＞0.05).5.No statistical difference of the original content of MMP-1 and MMP-9 in GCF was found between adolescent group and adult group(P＞0.05),but the adult group's contents were a little more than adolescent group's.And it's the same with the 1st week's content.The content of MMPs in adult group changed more obviously than that in adolescent group.At the beginning of the experiment, the MMPs' increasing speed of adult group was higher than that of adolescent group.But at the end,the rate of descent of adult group was lower than that of adolescent group.Conclusions1.It is scientific,simple and reliable to establish the animal orthodontic root resorption model with the improved orthodontic appliances on Wistar rats to draw the maxillary first molar medially by applying an excess force of 50g, with the central incisor as anchorage.2.The root resorption was discovered in the histological section at the 2ed week of the experiment.3.MMP-1 and MMP-9 in GCF play some roles in orthodontic root resorption. MMP-1 may be more sensitive than MMP-9 to reflect the happening and development of root resorption.4.It is more serious of the orthodontic root resorption in adult group than in adolescent group.