| BACKGROUNDShortening the period of implant-bone osseointegration to achieve early loading even instant loading, is the main goal of research of surface modification of dental implants. Besides the effects of surface morphology and chemistry of implant surface, the recipient bone quantity and quality is also crucial factors. Since China is an aging society now, the population of osteoporotic people is increasing, as well as the need for dental implants. However, systematic osteoporosis affects the quantity and quality of jaw bones, which is considered as a contraindication of dental implant surgery. Thus, the urgent task of modern implantology is to achieve fast and solid osseointegration of titanium implants and surrounding osteoporotic bone tissue.Recently, it was reported that a kind of liposoluble statin, simvastatin, could induce the expression of bone morphogenetic protein (BMP)-2 mRNA and that, as a result, it promoted bone formation on the calvaria of mice. And some researchers demonstrated the topical application of statins improved bone formation around implants. In this context, we designed simvastatin-loaded porous titanium implant surface by immersion method and biomimetic method. The aim of this study was to investigate the feasibility of local delivery of simvastatin using these two methods and the effects of the delivery on implant osseointegration by in vitro and in vivo experiments. The study is divided into two parts:Part I Preparation of simvastatin-loaded porous titanium surfaces by immersion method on Ti-based dental implant surface and its effects on implant osseointegration in osteoporotic ratsMETHODS AND RESULTSWe got our substrate Ti surfaces by polishing, sandblasting and etching. The control group consisted of cells cultured on titanium disks without any intervention for different time intervals (4 d,7 d and 14 d), whereas the experimental groups (simvastatin-loaded groups) consisted of cells cultured on titanium disks that were pre-incubated in varying concentration (10-7M,10-6M, 11-5M and 10-4M) of simvastatin for the same time intervals of the control. Alkaline phosphatase activity (ALP), Type I collagen synthesis and osteocalcin release were used to measure the cellular osteoblastic activities.All simvastatin-loaded groups showed increased ALP activity compared to control group at every time point, especially the 10-7 M group significantly increased the activity by almost 4-fold at 4 days (P＜0.05). In the Type I collagen synthesis assay, all simvastatin-loaded groups showed an increase and the effect was inverse dose dependent (maximal at 10-1M). Furthermore, this stimulatory effect of simvastatin was also observed in osteocalcin release assay (P＜0.05, at 10-7M,10-6M, maximal at 10-7 M). Based on the in vitro results, roughened implants were divided into control groups (n=32), test 1 group (n=32), and test 2 group (n=32). Test implants were immersed into 10"7 M (Test 1 implants) or 10-6M (Test 2 implants) simvastatin solutions for drug adsorption onto implant surfaces.48 ovariectomized rats randomly received two implants in both tibiae. After 1,2,4, and 12 weeks of implantation, tibias were retrieved and prepared for histomorphometric evaluation. Bone-implant contact (BIC) and bone area around implant, as well as histological findings, were obtained. Results:New bone formation on test implant surfaces was seen after 1 week while it was seen on the control implant surface after 2 weeks. There were more bone tissue and bone-implant contact along the test implant surfaces than which along the control implant surface. The test 1 and 2 implants showed a significantly greater bone area and BIC compared to the control implant during the observation periods (p<0.05). No differences were found between the test 1 and test 2 implants after 1,2,4, and 12 weeks (p>0.05).Part II Preparation of simvastatin-incorporated coating by biomimetic method on Ti-based dental implant surface and its effects on implant osseointegration in osteoporotic ratsMETHODS AND RESULTSWe got our substrate Ti surfaces by polishing, sandblasting and etching as previously described. Simvastatin was prepared onto titanium porous surfaces by biomimetic calcium phosphate coating by adding a series of concentrations simvastation (the final concentration is 10-7M,10-6M and 10-5M) in SBF-2. FSEM, XRD and FTIR were utilized to observe the surface morphology and the crystal structure of the coatings. MC3T3-E1 cells were cultured on these disks with varying concentration of simvatatin. The total protein content, ALP activity and osteocalcin production were measured to examine the effects of coatings to the proliferation and differentiation ability.FSEM results showed that sharp crystal flakes were deposited on the control plate surface. The crystalline coating entirely covered the substrate surface. All the crystal plates were oriented more or less perpendicularly to the surface of the plates. The flake morphology and orientation did not obviously change at the low concentration of simvastatin (10-7M and 10-6M). However, the morphology and size of crystal flakes changed at the high concentration. At the 10-5M and10-4M concentration, flake-like crystals combined into sphere-like structures. The size of flakes dramaticly decreased. At the 10-3M concentration, the sphere-like structures were seen on the sample surfaces while the flake crystals disappeared. XRD and FTIR results indicated the presence of OCP in all the coatings. Simvastatin has been incorporated into the synthetic OCP coatings. What’s more, the content of simvastatin in the coating also increased with the increasing concentration of simvastatin in SBF-2 accordingly.Based on the in vitro results,10-6 M (Test implants) was chosen for the treatment of implant screws in osteoporotic animal experiments. After 4 and 12 weeks of implantation, tibias were retrieved and prepared for histomorphometric evaluation. Bone-implant contact (BIC) and bone area around implant, as well as histological findings, were obtained. New bone formation on test implant surfaces was seen earlier than control group. Also there were more bone tissue and bone-implant contact along the test implant surfaces than which along the control implant surface at 4 and 12 weeks. (p<0.05).Conclusion:These results indicate that simvastatin-loaded porous implant surface has the potential to improve implant osseointegration in the ovariectomized model, which provide scientific proof for develop novel dental implants for osteoprotic patients clinically. |
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