Effects Of Simvastatin On The Rats’ Palatal Suture After Rapid Maxillary Expansion

Malocclusion,a kind of common disease of modern,which has a great influence on beauty,occlusion,psychology ect;Usually,the osteomalocclusion attracts more attention.Clinically,orthopedic force extending palatal suture is widely used to the growing children due to maxillary transverse deficiency,which is usually called Rapid Maxillary Expansion(RME).Both tooth-borne and tooth-bone-borne rapid maxillary expansion have good treatment for the maxillary transverse deficiency.For another,some drawbacks are observed in the RME:external root resorption,microtrauma of the temporomandibular joint,as well as post-expansion relapse.The curative effect of the RME was not stable and a high relapse rate was following.Researches found that the soft and skeletal tissues as well as the relative rigidity can offer immediate resistance to the expansion force,in addition,the resorption of new bone formed in the tension area can also lead to relapse.It’s significant to explore some effective approaches to promote new bone formation and mineralization in the mid-palatal suture after the RME,which will be helpful to inhibite the retractive force produced by surrounding tissue and to maintain the stability of the maxilla structure,shorten the retention period,and prevent orthodontic relapse.Objective:The curative effect of the RME is not stable and a high relapse rate is following.With the rapid maxillary expansion bow device extending rat maxillary palatine raphe,we take the group,RME following simvastatin,as experimental group.Comparative study on the gross and histological RME,RME following simvastatin effects on rat palatal raphe.And guiding the clinical application of simvastatin of accelerating the deposition and calcification of bone after the RME.Following expecting lessening bone absorption afte rthe RME,shorting the retention time,and providing some ex-perimental basis for reducing recurrence.Methods:36 male 6-week-old Wistar rats were randomly divided into three groups:a con-trol group(A),an expansion only group(B)and an expansion plus simvastatin group(C),and each group had 12 rats.Neither expansion nor simvastatin was given to the group A;On the 1st day,each rat in groups B and C was set an orthodontic appliance with an initial expansive force of 100g.During the experiment,rats in group C were administered with some simvastatin(10mg·kg-1 body weight)each day after the RME.Meantime,rats in groups A and B were dministered with comparable amount of the CMC-na.In the 1st week,the circlet of orthodontic appliance has been fixed by light-cured resin,going into the retention.And then all rats were randomly euthanized in batches on weeks 1,2,and 3.Measuring width of all rats’ upper jaw.Histologi-cal observation was used for the sections of rats.Application the software of SPSS 19.0 for data analysis and processing,one-way ANOVA and LSD comparing differ-ences among the groups.Significance level,bilateral alpha =0.05.Results:1.Generally observed No mucosal infection or weight decreased obviously in rats during the experiment.All rats conform to the requirements of this experiments,and incorporated in the experiment.During the experiment,The average body weight of rats in group A increased steadily.Body weight of rats in groups B and C fell slightly on days 2 and 3,but started to grow steadily on days 4.Maxillary width of rats had no significant change in group A(P>0.05);With the force,maxillary palatine raphe of rat in groups B and C were expanded.Width of upper jaw widened(P<0.05),which were greater than group A(P<0.05).Groups B and C has no significant differ-ence(P>0.05).2.HE staining A relatively small amount of chondrocytes,osteoblasts and red dyed fibrous tissue lived in the rat’s palatal suture that belonged to group A and so do mesenchymal cells.Different sizes and numbers of chondrocytescells showed in the rat’s palatal suture in group B and C.Bone edge approached palatal suture is crenulate.Different numbers of osteoblasts,scattered or zonal distribution,and most present a short column.Osteoid filled among part of osteoblasts.Meanwhile,red dyed fibrous tissue,vascular engorgement and tissue edema,increased spindle fibroblasts.3.Immunohistochemical staining Immunohistochemical staining was taked to detect the expression of BMP-2:during the experiment,the BMP-2 and IOD of rats’mid-palatal suture in group A,expressed weakly positively,and there is no obvious difference(P>0.05).The expression of BMP-2 and IOD in group B,on weeks 1 and 2,was positively;but that was weakly positively on week 3(P<0.05).The expression of BMP-2 and IOD in group C was strong positively(P<0.05).Conclusion:1.The RME could expand the mid-palatal suture and maxillary width of the growing rats.2.The RME could promote the deposition and calcification of new bone.Simvastatin with the RME could further promote calcification,which could be help-full to maintain the expansion effects and reduce the relapse.3.the RME can enhance the expression of BMP-2 and IOD;with the RME,simvastatin could enhance more expression of BMP-2 and IOD,promote deposition and calcification of new bone.