| The teeth and the alveolar bone have an interdependent relationship each other, the alveolar ridge will have a continuous, progressive, and irreversible bone resorption after the tooth extraction, leading to a low level or blade form of the alveolar ridge, causing some difficulties for denture restoration and implant planting. The residual ridge resorption (RRR) leads to many aesthetic and functional problems in edentulous patients, insufficient masticatory function impacted the blood supplying of such critical organs as the heart and brain. These problems will be more obvious following with an aging population. It has clinical significance to develop a new method and material that can promote the healing of tooth socket at early stage and prevent alveolar bone resorption.In order to prevent the atrophy of the residual ridge, the research was mainly concentrated on such methods as allografts, autografts, immediate dental implants and the guided bone regeneration technique, but secondary lesions, immunologic rejection and poor long-term results of these treatments limited their clinical applications. There was few reports about the treatment of alveolar ridge by using medicine. Recent studies have shown that statins had the function of stimulating in-vivo bone formation and increasing expression of BMP-2 in bone cells. Simvastatin was one of the widely used statins, the research showed that it could increase the bone density of menostasis woman and aged people obviously and decrease the incidence rate of bone fracture. So we assumed that whether we could promote bone formation in the early stage after tooth extraction by simv- astatin. Because simvastatin underwent extensive first-pass extraction in the liver after oral administration, the availability of the drug to the general circulation limited in bone tissue; its local concentration is too low to induce bone .It needs a great quantity of simvastain to get the effect of bone restoration for bone fracture and defective by local injection, in this way, it can cause cytotoxicity, on the other hand, it required injecting repeatedly to have the ideal pharmacodynamic action, for the low molecular weight of statins diffuse quickly and having a short half life period, this method can not be accepted by patients easily. So, it is very important to optimize the administration route of simvastain, which increase the effect of bone formation and decrease the side effects.According to some studies, it is a practicable method to use simvastain carried by carrier to promote the restoration of the bone defective. Our team had prepared the simvastain carried by poly (DL-lactic-co-glycolic acid, PLGA) scaffold by dissolvent volatilization technique, explored the effect of simvastatin on the bone restoration in the mandible incisor extraction socket. The results showed that the drug released slowly from the scaffold could induce the expression of BMP-2 in periodontal ligameng cell (PDLC) and mesenchymical cell in the tooth extraction socket, it could also differentiate themselves to osteo- blast to induce new bone formation. The bone mass increased obviously in the tooth socket comparing with that in control group. But there were some limitations to use the homogenous material, the PLGA has the disadvantage in the poor hydrophilism, weak cell adsorbability and the acidity degradation which leaded to some aseptic inflammation. Considering the human tissue consisting of inorganic and organic compound ingredients, therefore from the angle of biomimetic, inorganic and organic compound biological material as the simvas- tatin drug carrier will be better. The calcium phosphate cements (CPC) has a satisfactory biocompatibility and higher mechanical strength, it can be molded randomly according to the shape of the bone defective and binded with the human bone tightly in its application. CPC can be solidified and molded freely in the environment and temperature of human body, its final degradation material is hydroxyapatite (HA) that is similar to the inorganic principle of human bone tissue. The CPC used as the inorganic biological activity material get more attention day by day, it has been used as the bone replacement material in clinical renovation. The base material after the degradation of CPC can neutralize the acid that was generated by the degradation of PLGA, the CPC also can enhance the mechanical strength of PLGA scaffold. There are no reports on the composite of PLGA and CPC used as the carrier of simvastain to repair bone defective in domestic and abroad up to now.We divided the experiment into three groups by adjusting the quality ratio of the HMW and LMW PLGA and CPC. The method to prepare the composite is called the freeze drying and dissolvent volatilization technique. We choose the best matching propotion as the carrier for simvastain according to the result of scanning electron microscope (SEM) and the change of pH in the imitation humor, at last, the optical density (A) of simvastatin was obtained by UV spectroscopy at 238 nm and the drug release curve was drew. The results showed that this scaffold had suitable strength and integrality pore, the average aperture size was 120μm, these pores communicated to each other by micro pores, so this satisfied the requirement of scaffold about pore diameter. Adding CPC into the composite could inhibit the descent of pH that was caused by the degradation of PLGA, the pH would stabilize at 6.5 at 8 weeks, these improved the performance obviously compared with the simple PLGA scaffold. The composite had a dramatic delayed releasing effectiveness, it would last more than 48 days for the drug to release. So we drew the conclusion that the composite consisting of simvastatin carried by PLGA/CPC satisfied the requirement of bone tissue engineering (BTE), this study could bring some meaning for the bone repair of the residual ridge.The new creativity of this study was to prepare the simvastatin carried by PLGA/CPC scaffold with slow releasing ability, and applied two different molecular weight PLGA to prepare the composite for the first time.
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