Effect Of Simvastatin On The Expression Of BMP-2 And VEGF During Retention Stage After Tooth Movement In Rats With Periodontitis

In recent years, with Chinese economic development, People pay more attention to the appearance, the number of adult orthodontic patients is increasing rapidly. The prevalence of adult periodontitis is very high and even more than 90% in some areas. The prevalence of adolescent periodontitis is up to 80%, and still shows an ascending trend. No matter how smart and capable orthodontists are, if they ignore the patient's periodontitis, the efficacy of orthodontic treatment will be affected. Relapse after orthodontic theatment is a common problem, and furthermore, it occurs more easily in patients with periodontitis after orthodontic active treatment due to the pathological changes in periodontal supporting tissue, such as gingival recession, reduction of periodontal ligament area, and the greater destruction than repair in alveolar bone. Relapse after orthodontic active treatment will discount the satisfactory therapeutic efficacy at various degrees. The relapse is closely associated with retention. Therefore, there is very important clinical significance on study of the retention and relapse after orthodontic tooth movement in the patients with periodontitis.To decrease the extent of relapse after tooth movement, to accelerate tooth stable in the new position as soon as possible, and to shorten retention time have important clinical significances for orthodontic patients, particularly for adults and periodontitis patients. Therefore, domestic and foreign scholars have made their efforts. Firstly, scholars have put their efforts into innovating various retainers so as to retain a better orthodontic effect. However the retainers are disadvantages to appearance and dental hygiene, and need to be wore for a long time. Even some adults and periodontis patients need to wear the retainers for whole life, which brings a lot of inconvenience to patients. Secondly, some orthodontists prevent relapse of Malocclusion Through periodontal surgeries. But many patients are not willing to accept the surgeries because of surgical risks. With the development of pharmaceutical drugs, many studies have reported some pharmacologica drugs for controlling tooth movement, such as non-steroidal anti-inflammatory drugs, bisphosphonates, osteocalcin, vitamin D3, etc. Although active mechanisms of these medicines are different, the common purpose of using these drugs is to control tooth movement by regulating periodontal tissue remodeling. This experiment explored a potential drug for facilitating tooth stable after tooth movement of periodontitis patients and the active mechanism of the drug from the angle of promoting bone formation and inhibiting the relapse so as to provide a valid assistant approach for the retention of orthodontic effect in periodontitis patients.For the past few years, in vitro and vivo and animal studies, have shown that statins can promote formation of bone and osteoid, increase activity of osteoblasts, accelerate bone transformation, shorten the time of bone remodeling, etc. Simvastatin, as cholesterol-lowering drug, has been a clinically safe medicine for over 20 years, and it has few adverse reactions and has good tolerance in long-term application, so it gains the attention and praise in the clinical application.Bone morphogenetic proteins(BMP-2)increases bone formation by promoting formation and differentiation of bone and osteoid, inducing differentiation of many non-osseous tissue-origin cells to osteocytes, increasing activity of osteoblasts, promoting alkaline phosphatase activity in cells, stimulating collagen synthesis and accelerating mineralized tuberculation. Endothelial cell growth factor(VEGF) is a kind of highly specific endothelial cell mitogens, and its main functions are to promote proliferation of vascular endothelial cell, to promote angiopoiesis and maturation. It plays an important role in vascular anagenesis. The invasion of blood vessels is a prerequisite for ossification. So VEGF also impacts bone metabolism.The objective of this experiment is to study the effect of systemic administration of simvastatin on the relapse rate of tooth movement in rats with periodontitis in retentive stage after orthodontic tooth movement so that the effect of simvastatin on the inhibition of tooth relapse movement is evaluated through the comparison of tooth relapse rates; to observe the changes of BMP-2 and VEGF expression in periodontal tissue after administration of simvastatin so as to study the functional mechanism of simvastatin on promoting remodelling of periodontal tissue at orthodontic retention stage in rats with periodontitis. This may provide a reliable drug assisted treatment for promoting moved tooth stable and shorten rentention time in orthodontic clinical treatment of the patients with periodontitis.Method: 65 male Wister rats were choosen and randomly divided into 13 groups, 5 rats per group. (1)One blank control group: after establishment animal periodontitis model, the maxillary first molars under the anchorage of rats'anterior teeth were mesially moved for for 21 days; (2)Six negative control groups: after establishment animal periodontitis model, the maxillary first molars under the anchorage of rats'anterior teeth were mesially moved for for 21 days and afterwards, retainers were placed on left arches for respectively 1d, 3d, 7d, 14d, 21d and 28d. During retentive stage normal saline was injected intraperitoneally for once a day. (3)Six experimental groups: rats were treated in the same way as in negative control group and but simvastatin solution instead of normal sodium was injected. Plaster models of rats'upper mandible were made, and tooth relapse distance was measured and relapse rate was caculated respectively at the begain and end of tooth movement and at the end of retentive stage. At the end of retention, rats were euthanized by transcardiac perfusion and the maxillary samples were collected. Mesiodistal pathological sections were cut and stained with HE and immunohistochemistry so that the histological changes and BMP-2 and VEGF expression in periodontal tissue of moved teeth were examined.Results: The tooth relapse rates on non-retained sides in negative control groups and experimental groups were higher than those on retained sides(table 3.1, 3.2). Whether the moved teeth were retained or not, the tooth relapse rates were obviously higher in negative control groups than those in experimental groups(table 3.3, 3.4).HE staining sections showed that restorative remodeling of periodontal tissue was faster in experimental groups than that in negative control groups. On non-retained sides in both experimental and negative groups, active bone resorption occurred on the mesial and distal sides of moved teeth, and bone formation was shown mainly after 21 days. On retained sides of moved teeth, active bone resorption was rarely observed and bone formation occurred early in periodontal tissue and periodontal tissue was restoring to normal.Time and drug factors significantly impacted the expression of BMP-2 in the periodontal tissues on the mesial side of rat maxillary first molar in terms of gray values ( F=68.372, P<0.05; F=57.219, P<0.05 ) . Whether on the non-retained side(table 3.7)or retained side(table 3.8), BMP-2 expression didn't change significantly at the early stage of retention in both experimental group and negative control group, decreased in 7th day, then increased. Comparison of the experimental group and the negative control group at the same time point showed that BMP-2 expression was significantly higher in the experimental group than that in the negative control group.Time and drug factors significantly impacted the expression of BMP-2 in the periodontal tissues on the distal side of rat maxillary first molar(F=37.212, P<0.05; F=23.918, P<0.05). On the non-retained side (table 3.9), BMP-2 expression gradually increased at the early stage of retention in both experimental group and negative control group, then decreased after the 14th day, and didn't change significantly after 21st day. On retained side (table 3.10), BMP-2 expression showed an increasing trend in both experimental group and negative control group. Comparison of the experimental group and the negative control group at the same time point showed that BMP-2 expression was higher in the experimental group than that in the negative control group.Time and drug factors significantly impacted the expression of VEGF in the periodontal tissues on the mesial side of rat maxillary first molar (F=28.248, P<0.05; F=20.274, P<0.05). On the non-retained side (table 3.11), VEGF expression gradually increased at the early stage of retention in both experimental group and negative control group, then decreased after the 7th day, and gradually increased again after 21st day. On retained side (table 3.12), VEGF expression decreased at beginning of retention in both experimental group and negative control group, and gradually increased after 7th day. Comparison the experimental group and the negative control group at the same time point showed that BMP-2 expression was higher in the experimental group than that in the negative control group at all time point except the 1st day.Time and drug factors significantly impacted the expression of VEGF in the periodontal tissues on the distal side of rat maxillary first molar(F=16.469, P<0.05; F=16.408, P<0.05). On the non-retained side (table 3.13), VEGF expression increased at the beginning of retention in both experimental group and negative control group, then obviously decreased after the 7th day. Comparison at the same time point, VEGF expression was significantly higher in the experimental group than that in the negative control group. On retained side (table 3.14), VEGF expression gradually increased in both experimental group and negative control group during retention stage. VEGF expression was significantly higher in the experimental group than that in the negative control group at the same time point. Conclusion: 1. Systemic administration of simvastatin can inhibit the relapse extent after orthodontic tooth movement in rat with experimental periodontitis and can assist retainers to improve moved teeth stability in retention stage. Therefore, simvastatin have an auxiliary functionc of preventing relapse at retention stage after tooth movement in the patients with periodontitis. 2. Simvastatin can increase the expression of BMP-2 and VEGF in periodontal tissue of rat with experimental periodontitis. This increase of expression in BMP-2 and VEGF can promote angiopoiesis and maturation, the production of osteocyte, the mineralization of bone, and might be the active mechanism of simvastatin accelerating the periodontal tissue remodeling at retention stage after orthodontic tooth movement in rats with periodontitis.