Experimental Study Of Lanthanum-hydroxyapatite Composite Coating On The Osseointegration Around Titanium Implant

Objective: The immediate implant model was established by extracting the 4 incisors both in maxillary and mandibular of rabbits.The titanium screw with lanthanum-hydroxyapatite composite coating or only hydroxyapatite coating were used respectively to be immediately implanted in the extraction sockets,then it is to be observed and detected the osseointegration between implant and bone tissue around,the effect of lanthanum-hydroxyapatite composite coating on osseointegration of the bone around titanium screw.Methods:1 The preparation of coating in titanium screw surface:Preparated the hydroxyapatite coating in the surface of 36 titanium screws through electrochemical deposition method,then 24 screws were soaked into lanthanum nitrate solution,the concentration was 0.1mol/L,to prepare lanthanum-hydroxyapatite composite coating.2 The animal grouped in this experiment:Nine healthy adult New Zealand rabbits,male and female unlimited,were randomly divided into 2 groups,the 6rabbits as the experimental group,while other 3 rabbits as the control group.After implanted titanium implant,2 rabbits in experimental group and 1in controlled group would be killed respectively at 4th,8th and 12 th.3 The preparation of animal immediate implant model:Extracted rabbit's maxillary and mandibular 4 incisors through step by step grinding method.After local anesthesia,incisors were ground off 2-3mm from cut ridge to cervix in each time,and this procedure would be repeated once a week for four times,one in one week,then those incisors could be extracted easily under general anesthesia.4 Implant surgery:After rabbit's maxillary and mandibular 4 incisors extracted,all sockets were filled with xenogeneic freeze-dried bone,whichcould made the titanium screw acquiring primary stability.In experimental group,the titanium screw with lanthanum-hydroxyapatite composite coating was implanted into socket immediately.Then gingiva was sutured to cover the screw.In control group,the titanium screw with hydroxyapatite coating was taken the same procedure as in experimental group.After operation,all experimental animals were given intramuscular injected of 40 units gentamicin everyday in 7 days to prevent infection.5 Observation results:Experimental animals were executed by air embolism method respectively at 4 weeks,8 weeks and 12 weeks after operation,which 2 in experimental group,and 1 in control group for each time.Dissected and obtained rabbit's bilateral maxilla and mandible specimens,generally observation was made to observe whether titanium screws became loose or fell off,and the situation of bone tissue around them;X-ray examination was to observe the osseointegration between titanium screw and surrounding bone tissue;bone density was then counted through the gray value of osseous tissue around screw;screw bone integrate strength was measured by torque test.At last,all the data be collected and analyzed by statistical analysis software;bone specimens obtained after the titanium screws removed would be sectioned,stained by HE,and observed for osteogenesis around screws in light microscope.Results:1 Viviperception:After operation,all the experimental animals were healthy without death,wounds healing well,and no screw exposure.The tissue around the titanium screws did not show any redness,pus discharges etc.2 General observation of specimens:In the experimental group,all titanium screws were stable and with certain retention force,no screw became loose or fell off.The titanium screws were surrounded by bone tissue closely.While in the control group at 4th week,some of screws became loose but did not fall off,there were gaps between the titanium screws and the surrounding bone tissue.3 X-ray observation:All titanium screws were steady in specimens,andthe density of bone around screws increased with the extension of time.Bone density of experimental group were higher than control group at each time point of 4th,8th and 12 th week after operation.4 Bone density analysis:At the same time point of 4 th,8th,12 th week after operation,gray value of regenerated osseous tissue around titanium screw in experimental group was higher than that of control group,the results were significantly different,and were statistically significant(P< 0.05).5 Torque test:At the same time point of 4th,8th,12 th week after operation,the average of torque peak values of titanium screw in experimental group was higher than that of control group,the results were significantly different,and were statistically significant(P< 0.05).6 Histologic analysis: Overall,at all measured time points,the regenerated osseous tissue in experimental group shows an earlier formation and higher maturity of the lamellar bone than that in control group.At the 4th week,a large amount of osteoblasts,bone lacuna and fibrous bone could be found in experimental group,and bone trabecula showed a network structure.However,less osteoclasts was observed in control group,and bone trabecula did not show any network structure.At the 8th week,the lamellar bone could be observed in the experimental group while in the control group less lamellar bone was observed.At the 12 th week,osteoblasts were substituted for a large amount of osteocytes and the lamellar bone became thicker,while less osteocytes were observed in the control group and the lamellar bone was much thinner than that in the experimental group.Conclusion:1 In immediate implant,lanthanum-hydroxyapatite composite coating and hydroxyapatite coating both contribute to the bone regeneration and osseointegration between titanium screw and bone tissue around.2 Compared with hydroxyapatite coating,lanthanum-hydroxyapatite composite coating has better biocompatibility and biological stability,which may promote osteogenesis between titanium screw and bone tissue around.