| Dental implant prosthesis is a widely accepted treatment for patients with dentition defect and dentition loss.However,the incidence of senile and postmenopausal osteoporosis is very high,and implant failure is very easy to occur in the early stage of implant treatment.Therefore,how to enhance the osteointegration of implants in patients with osteoporosis has become a hot topic in the field of implantation.Titanium surface treated by micro-arc oxidation has micron pore roughness and surface morphology characteristics similar to "crater" holes,which is conducive to the adsorption of bone-induced proteins,significantly enhance the adhesion,proliferation and differentiation of osteoblasts,reduce stress shielding,and achieve physical and chemical bonding with bone tissue.At the same time,Ca and P elements in the electrolyte can be introduced into the coating to form a crystalline HA with biological activity,giving the coating biological activity.In addition,osteogenic drugs or molecules can be directly integrated into the porous titanium oxide film and released efficiently at the implant site.Strontium(Sr)is one requisite trace element in human body which can boost the proliferation,survival,differentiation and mineral formation of osteoblasts,inhibit the differentiation and activity of osteoclasts,and induce osteoclast apoptosis.Sr-containing hydroxyapatite has better histocompatibility,(?)osteoconductive ability and biodegradability.Simvastatin is a commonly used drug to reduce blood lipid.Studies have found that it can enhance the expression of BMP-2 in osteoblasts,promote bone formation and inhibit bone resorption.Therefore,we speculate that Sr-HA coating prepared by micro-arc oxidation combined with simvastatin adsorption can effectively promote bone formation and bone regeneration around implants,and whether it can enhance bone bonding in osteoporosis remains to be studied in vivo.In this study,crystalline hydroxyapatite and Sr-doped hydroxyapatite oxide film were formed on the surface of pure titanium by micro-arc oxidation.The morphology,roughness,element composition,phase composition and hydrophilicity of the coating were observed and analyzed.With the property of porous morphology of the membrane,simvastatin can be absorbed physically.The model of osteoporosis in rabbits was established quickly,and the effect of implants with this coating on osteoporosis in rabbits was studied dynamically,which provided a new idea for the success rate of osteoporosis implantation.Part I:Rapid establishment and validation of a rabbit model of osteoporosisObjectives:To establish and validate a rabbit model of osteoporosis for implant-bone analysis.Materials and Methods:The present study included 20 female New Zealand rabbits aged 5-6 months.Ovariectomy was performed on 10 of the rabbits(OVX group),whereas the remaining 10 were sham-operated as a control group(Sham).At one week post-surgery,the OVX group started treatment with dexamethasone at a dose of 0.5 mg/kg,twice weekly for 8 weeks,while the Sham group received injections with an equivalent volume of normal saline.At the end of the treatment period,densitometric measurements were performed and serum biochemical markers of bone metabolism were detected.Results:Ovariectomy followed by treatment with dexamethasone induced a quick decrease in bone mineral density(BMD)of 32%from baseline,and the results before and after treatment were significantly different.The BMD value in OVX group was significantly lower than that of the control group.Moreover,blood concentrations ofALP in the OVX group were significantly increased.There were no statistically significant differences in blood Ca and P content among the two groups.Conclusions:Ovariectomy and dexamethasone injection are able to experimentally induce osteoporosis in rabbits in a short period of time.Part II:Preparation of Sr-HA coating by MAO and characterization analysisObjective:To observe the micro-morphology,roughness,element composition,phase composition and hydrophilicity of Sr-HA coating prepared by micro-arc oxidation,and compare it with HA coating prepared by micro-arc oxidation and smooth surface to evaluate its material properties and characteristics.Materials and Methods:Titanium samples with smooth surface were randomly divided into three groups:A,B and C.Group A were not given any treatment.Group B and C were treated with MAO for 10 minutes in electrolyte solution containing calcium acetate and sodium dihydrogen phosphate,and strontium acetate hemihydrate was contained in electrolyte solution of Group C.After treatment,the samples were analyzed by SEM observation,EDS,XRD,roughness and hydrophilicity testing.Results:1.SEM showed that the surface morphology of B and C samples changed,forming a"crater" like structure,the holes with different diameter were connected with each other.The main components of surface in group A were Ti,while those in group B were Ti,O and Ca.In group C,besides Ti,O and Ca,there was a certain proportion of Sr.2.The roughness of group A,B and C were 0.106±0.007p?m?0.476±0.755?m?0.786±0.108?m respectively.Compared with smooth surface in group A,the roughness of MAO and MAO-Sr groups had significant statistical significance,and the roughness of MAO and MAO-Sr groups also had statistical difference.3.The average value of contact angle in group A was 42.42,17.40° in group B,and 14.87° in group C.The contact angle of group B and C was significantly different from that of group A(P<0.01),but there was no significant difference between group B and C(P>0.05).4.Group B mainly consists of HA,rutile and anatase.Group C consists of SryCa(10-y)(P04)6(OH)2(0<y<10),rutile and anatase.The diffraction peak of HA shifts to a small angle(left).Conclusions:The samples treated by micro-arc oxidation have better surface morphology,roughness,hydrophilicity,higher surface energy than smooth surfaces,and the organic coatings containing HA can provide better biological activity and biocompatibility.The addition of Sr element in group C endow titanium samples with better physical,chemical and biological properties.Part III:Effect of simvastatin-loaded Sr-HA coating on implant osseointegration in osteoporotic rabbitsObjective:To evaluate the effect of Sr-HA-simvastatin coating on osteointegration in osteopprotic rabbitsMaterials and Methods:The implants were divided into three groups,10 smooth surface implants in group A,11 MAO implants in group B and 11 Sr-MAO implants in group C.Group C was soaked in 10-6 mol/1 simvastatin solution for 48 hours and dried naturally.The implants of each group were randomly implanted into the tibia of osteoporotic rabbits with two implants on one side.Tetracycline hydrochloride(30mg/kg)was injected subcutaneously 14 and 13 days before and calcein(6mg/kg)4 and 3 days before the end of the experiment.Animals were sacrificed at 4W,8W and 12W after the implantation and specimens containing implants were collected.hard tissue slices were made and observed histomorphologically by means of sequential fluorescence staining and fuchsin-methylene blue staining.histomorphological analysis were conducted through Image-pro software.The effects of osteointegration were observed.Bone-implant contact rate(BIC)and mineral apposition rate(MAR)were calculated.The tibial specimens containing implants were tested by Pull-out test to determine the quality of bone integration in each group.Results:1.The pull-out test results showed that the maximum force values of group A,B and C at 4 weeks were 20.22±3.88N?48.97±3.41N?65.43±14.73N,34.10±6.05N?72.801±4.3 5N?106.83±7.49N at 8 week,44.38±2.21N?1 09.00±2.05N?114.80±11.95N at 12 week.The results showed that the maximum pull-out force of the implants increased gradually with time(P<0.01).Compared with the other two groups in the same period,the maximum pullout force of group C was significantly higher(P<0.01).2.Fluorescence microscopy showed that the amount and speed of new bone formation in group C were significantly higher than those in group A and B,manifesting significant contact osteogenesis,while in group A,distance osteogenesis was dominant.3.The MAR values of group A,B and C were 0.794±0.064pm/d?1.19±0.046?m/d?1.326±0.033?m/d at 4 week,1.094±0.063?m/d?1.414±0.024?m/d?1.884±0.02?m/d at 8 week,and 1.59±0.036?m/d?1.98±0.037?m/d?2.252±0.155?m/d at 12 week,respectively.The MAR of each group increased gradually with the prolongation of time(P<0.01).At the same time,compared with group A and B,MAR in group C showed superiority,and MAR in group B was also significantly higher than that in group A.4.Methylene blue-fuchsin staining showed that there were fewer trabeculae around implants in group A,and the contact with bone was loose,the Harvard system was not obvious,and the process of osteogenesis was slow;Group C had the most trabeculae,and the trabeculae were relatively strong and orderly arranged.The Harvard system was obvious and close to the implant.Osteogenesis progressed from the screw surface of implants and the bone tissue simultaneously with faster speed,bone tissues contact with implants tightly;although the bone mass in group B was more than that in group A,the osteogenetic speed,the number of osteoblasts,the Haversian system and the calcified bone matrix in group B were significantly lower than those in group C.5.The BIC of group A,B and C were 20.34±1.14%?39.19±0.69%?52.13±0.92%at 4 week and 23.92±0.99%?48.27±0.56%?66.34+1.44%at 8 week,34.4±0.95%?59.71±1.59%?71.42±1.93%at 12 week,respectively.With the prolongation of observation time,BIC increased,and reached the highest level at 12 week.The increase of BIC in the same group during different observation periods was statistically significant(P<0.01).In the same period,the BIC of MAO-Sr-Simvastatin group was the highest,while that of smooth group was the lowest,and that of MAO group was the middle.The difference among the three groups was statistically significant(P<0.01).Conclusion:Simvastatin-loaded Sr-HA coating can significantly enhance the osteointegration of titanium implants under osteoporosis,and has good biocompatibility,osteoconductivity and can accelerate osteogenesis. |
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