An Experimental Study Of Simvastatin Inhibiting The Relapse After Orthodontic Tooth Movement

The aim of orthodontic treatment is harmony,stable and aesthetic.Most people pay more attention to the stability after orthodontic toothmovement. The relapse of moved teeth is a physiologic response of thesupporting tissues to force appliance. To prevent such relapseclinically, the most commonly advocated measure is careful retention.Retention is an necessary period in orthodontic treatment, however,it is so long for retention that many adult and periodontitis patientsneed retainers lifetime. It takes difficult to keep orthodontic effectand patients'cooperation. Therefore, it is important to accelerateteeth stable soon in the new position, decrease the extent of relapseafter tooth movement, shorten retention time for adult andperondontitis patients clinically.Numerous reports have described the pharmacological control oftooth movement, such as non-steroidal anti-inflammatory drugs, vitaminD3, local administration of prostaglandins,osteocalcin,PTH,bisphosphonates, local OPG gene transter to the periodontal tissue.Many studies have proved that pharmacological administration by systemor lacal injection can control orthodontic tooth movement. However moststudies have effect on tooth movement through the regulation ofosteoclasts. We believe it is one of the effective methods to preventtooth relapse through stimulating bone formation of periontal tissue.Recently, Stewart DR et al. investigated the use of relaxin inpreventing relapse in a dog incisor rotated model. Relaxin by gingivalinjection was found to stimulate collagenase production to speed toothmovement and preventing relapse. This experiment aims to look forappropriate medicine, administration method and suitable dose as thevalid assistance method of orthodontic retention period.Statins promoting bone formation caused the concern of medicalscience. The statins have been shown very few side effects, receivedmore attention in clinical. In 1999, Mundy et al. examined more than30 000 compounds from a collection of natural products and firstly foudstatins are only to active osteoblast and increase expression BMP-2in vivo. Furthermore, stimulate markedly the formation of new bone inorgan cultures of murine calvarial bone in vitro. Sugiyama et al. havefound statins increase expression of BMP-2 mRNA, and suggsted thatstatins mediate their effect on bone by enhancing expression of BMP-2.Simvastatin ,the rate-limiting enzyme, hepatic hydroxymethylglutarylcoenzyme A(HMG-CoA) reductase inhibitors, inhibits the mevalonatepathway. Many reports have shown statins and aminobisphonates sharethe ability to interfere with the mevalonate pathway from differentlocation. So few people believe that statins and aminobisphonates havesimilar inhibition effect on osteoclast.Bone morphogenetic protein-2 (BMP-2) is the most effectivecytokine in bone formation, and participates bone remodeling inorthodontic tooth movement;Osteoprotegerin (OPG) and receptoractivation of NF-kB (RANKL), expressed by osteoblastic cells, directlycontrol osteoclasts. RANKL/OPG serve as the final common effectorsystem in bone remodeling. OPG/RANKL/RANK compose of key regulationsystem in osteoclast formation and activity. ZhangDing et al. havefound periodontium cells participate alveolar bone remodeling throughOPG and RANKL pathway.Objective:The purpose of the present study is to examine (1) theeffects of simvastatin by system administration for bonemetabolizition,through the extent of relapse after rats experimentaltooth movement, maxillary bone mineral density, body weight, serum boneformation biochemical index.(2)the change of BMP-2,OPG and RANKLexpression in periodontal tissue,at the same time, discuss the effectand molecule mechanism of simvastatin in periodontal tissue remodeling.Provide a dependable medicial assistance to promote movcd tooth stableand shorten rentention time in clinic.Method: Orthodontic tooth movement of upper first molar wasperformed in 40 Wistar male rats with coil spring for 21 days.40 ratswere randomly allocated into 5 groups: basic control group,simvastatin groups (2.5mg·k-1g,5.0mg·kg -1and 10.0mg·kg-1) andnegative control group.The basic control group were killed on the 21day.The experimental groups were administered simvastatinintraperitoneally daily at 1 day before appliances removed.Thenegative control group received the isotonic saline instead. Measurethe interdental distance between the first and second maxillarymolars,separately when appliances were removed and 1 week,4 weeks afterremoval.At the same time,measure all rats' body weights gain. 4 weekslater all animals were deeply anesthetized and perfused with afixative solution,taken vein blood 2ml and upper first molar includingperiodontal tissue.Mesure BMD,stain the sections with HE andBMP-2,OPG,RANKL immunohistochenmical method,the observe with a lightmicroscope. The result is analyzed by the Computer Image AnalyzingSystem and treated by statistics test.Results :(1)There is no significant change on the bodyweights(P>0.05).(2)Between the three different dose experimentalgroups and the negative control group,the total amount of relapse,the anteriors are lower than the latter(P <0.05);and the percentageof relapse,the anteriors are significantly lower than the latter indose dependent manner(P <0.01).The lower dose,the less relapseextent .Among the three group,the percentage of low-dosegroup'relapse is the lowest in experimental groups(53.38%).(3)Between experimental groups and the negative control group,theamount of ALP and BGP ,the anterior are higher than the latter(P<0.05),with dose independed.AND the amount of ALP and BGP are highestin the low-dose group(2.32+0.26 ng/m and 232.50+27.99 U/L);and theamount of Ca and P,there are not obviously difference ingroups(P>0.05).(4)Maxillary BMD,the basic group significantlydecrease (P<0.001)compared with other groups;the negative group aresignificantly smaller than the low dose group(P <0.05);amongexperimental groups,BMD of the low dose group are higher than that ofthe high dose group(7.046+0.003 g/cm2).(5)Histologic examinationreveals, the phenomenon of bone formation of the experimental groupare more significant than that of the negative group,such as the numberof osteoblasts,blood vessels,hematoxylin stained line,periodontalligament.(6)Immunohistochenmical examination reveals,there are BMP-2expression in the periodontium,especially expressed stronger near thealveolar bone and cementum.BMP-2 is mainly found in the plasma offibroblast,osteoblast,cementocyte and odontoblast separately.Thelocation of OPG and RANKL is mainly in periodontium,marked in the plasmaof odontoblasts , dental pulp-cells and osteoblasts on the surface ofalveolar bone and in the medullary cavity of bone and periodontalligament fibroblasts near the alveolar bone.(7)The result analyzed bythe Computer Image Analyzing System ,the expression of BMP-2 on boththe compression and tension side of PDL,the basic group is strongest(164.47±0.74和165.50±0.55 );the experimental group are strongerthan the negative control group,among three groups the low dose groupis strongest(154.43±1.07和155.85±0.85);BMP-2 in PDL,the tensionside is slightly stronger than the compression side(P >0.05).(8)theexpression of OPG on both the compression and tension side of PDL,thebasic group is strongest ( 164.47±0.74 和 165.50±0.55 );theexperimental group are stronger than the negative control group,among three groups the low dose group is strongest(152.78±2.42和154.61±1.64);OPG in PDL,the tension side is slightly stronger thanthe compression side(P >0.05).(9)the expression of RANKL on both thecompression and tension side of PDL,the basic group is strongest(164.47±0.74和165.50±0.55 );the experimental group are lower thanthe negative control group,among three groups the low dose group islowest(121.75±2.05 和121.46±1.17);RANKL in PDL,the compressionside is slightly stronger than the tension side(P >0.05).(10)the ratioof OPG/RANKL in both the compression and tension side of PDL ,thenegative group is less than 1;the basic group and experimental groupare more than 1,among them the ratio of the low dose group is thebiggest.Conclusion : The study indicates that 1. a single systemicadministration of simvastatin has no effect on rat body weight.2.simvastatin by system administration increasing BMD and serum boneformation biochemical index,may promote system boneformation;reducing the extent of the moved tooth relapse, and theeffect of the low dose is most significant.simvastatin may be a usefulagent for the pharmacological assistance of retention period.3.pickout the appropriate dose--2.5mg/kg/d by intrapertoneallyadministered.4.simvastatin enhances BMP-2 expression to increase boneformation,and regulate the ratio between OPG and RANKL(OPG/RANKL) toinfluence osteoclasts.That might be the molecular mechanism ofsimvastain to accelerate PDL remodeling.