| ObjectiveThis study was designed to evaluate adhesion of Streptococcus mutans and electrochemical behavior of cobalt chromium alloy and titanium fabricated by selective laser melting,milling and casting with adhesion of Streptococcus mutans,to explore the difference in adhesion and corrosion resistance between three techniques and the effects of streptococcus mutans on the corrosion resistance of metal,and to provide reference for clinical application.Materials and Methods1.Preparation of specimens:Twelve pieces of cobalt-chromium alloy and titanium were fabricated by selective laser melting,milling and casting technologies,respectively.Computer aided design software was used to design the model with dimension of 10mm×10mm×2mm.The designed model was imported into the selective laser melting machine and milling machine of cobalt-chromium and titanium to complete the production.For casting specimens,the model was imported into the milling machine to cut the wax blocks,wax blocks were embedded in phosphate embedding material and put in high frequency centrifugal casting machine to complete the production.The working surface of specimens were sandblasted,polished with silicon carbide sandpaper and diamond.After cleaning and drying,the surface roughness and contact angle of specimens in six groups were tested.2.Bacterial adhesion:The copper wires were bonded on the back of eight specimens from each group by conducting resins,all the specimens were embedded into silicon rubber light body on sides and back,only the polished face was exposed.The strains of streptococcus mutans were recovered,then the specimens were cultivated in prepared bacterial solution for forty-eight hours after sterilization.Half of the specimens bonded to the copper wire were placed in the bacterial solution for forty-eight hours,and the other half were immersed in the artificial saliva of the control group for forty-eight hours.The bacterial adhesion morphology was observed by scanning electron microscope,the amounts of adhesion was measured by crystal violet staining method?the pH of medium before and after adhesion was measured.3.Electrochemical experiments:The three electrode system was used in this experiment,the saturated Ag/AgCl electrode was used as reference electrode,platinum electrode was used as auxiliary electrodes,the polished face of specimen was used as working electrode,Fusayama artificial saliva was used as electrolyte,electrochemical workstation was placed in a constant temperature water bath at 37?,then dynamic polarization curves experiments were performed on material in six groups with streptococcus mutans adhesion and immersed in artificial saliva.Results1.The surface roughness of selective laser melting-cobalt chromium,milling-cobalt chromium,casting-cobalt chromium,selective laser melting-titanium was(0.219±0.017)?m,(0.224±0.015)?m,(0.227±0.02)?m,(0.23±0.007)?m,the surface roughness of milling-titanium and casting-titanium was(0.251±0.007)?m,(0.253±0.008)?m,the roughness of the latter two groups was higher than roughness of the former four groups with statistical difference(P<0.05).and there was no difference in surface roughness between the other groups(P>0.05).2.The contact angle of selective laser melting-cobalt chromium,milling-cobalt chromium,casting-cobalt chromium respectively was(81.33±1.99)°,(78.75±3.25)0,(81.42±3.68)°,and the contact angle of selective laser melting-titanium,milling-titanium,casting-titanium respectively was(60.0±1.41)°,(59.92±3.15)°,(61.17±1.47)°.The contact angle of cobalt-chromium alloy in any group was significantly higher than angle of titanium in any group with statistical difference(P<0.001).and there was no significant difference in contact angle between three processes of cobalt chromium and titanium(P>0.05).3.The images of scanning electron microscope showed that streptococcus mutans aggregated into clusters of different sizes on the material surface,or several streptococcus mutans arranged in a chain pattern.The surface of milling-titanium and casting-titanium with pits and pores on the surface was relatively rougher than the other four groups.The optical density of adhesion of milling-titanium and casting-titanium was(0.288±0.011)/cm2,(0.294±0.013)/cm2,the optical density of the other groups respectively was(0.241±0.007)/cm2,(0.243±0.015)/cm2,(0.247±0.021)/cm2,(0.251±0.013)/cm2.The adhesion amounts of milling-titanium and casting-titanium were higher than those of the other four groups with statistical difference(P<0.05),there was no difference between milling-titanium and casting-titanium,nor the other four groups(P>0.05).4.The pH of prepared bacterial medium before adhesion was(7.09±0.14),pH of medium after adhesion for forty-eighty h in cobalt chromium and titanium fabricated by selective laser melting,milling,casting was(5.79±0.17),(5.76±0.18),(5.70±0.24),(5.66±0.14),(5.58±0.15),(5.53±0.15),pH of groups after adhesion was lower than before adhesion with statistical difference(P<0.05).The results showed that there was no statistical difference between six groups after adhesion(P=0.453).5.The polarization resistance of selective laser melting-cobalt chromium,milling-cobalt chromium,casting-cobalt chromium with streptococcus mutans respectively was(12.171±1.105)×105?,(12.036±0.956)×105,(8.917±0.886)×105?the resistance of cobalt chromium in artificial saliva respectively was(15.267±1.410)×10?,(15.040±1.555)×105?,(11.973±0.898)×5?,the resistance of cobalt chromium with streptococcus mutans were lower than that immersed in artificial saliva with statistical significance(P<0.05).The resistance of selective laser melting-cobalt chromium was higher than resistance of milling-cobalt chromium with no statistical difference(P>0.05),the resistance of casting-cobalt chromium was lower than that of the other two groups with statistical difference(P<0.05).The polarization resistance of selective laser melting-titanium,milling-titanium,casting-titanium with streptococcus mutans with streptococcus mutans was(14.423±0.808)×105?,(8.452±0.635)×105?,(6.903±0.591)×105?,the resistance of titanium immersed in artificial saliva was(18.651±1.348)×105?,(11.518±0.981)×105?,(9.164±0.730)×105?,the resistance of titanium with streptococcus mutans were lower than that immersed in artificial saliva with statistical significance(P<0.05),the resistance of selective laser melting-titanium was higher than that of the other two groups with statistical significance(P<0.05),the resistance of milling-titanium was higher than that of casting-titanium with statistical significance(P<0.05).The results of the order of corrosion current was in reverse with the order of polarization resistance.Conclusion1.Cobalt chromium alloy and titanium fabricated by selective laser melting technique have stable and great corrosion resistance.Selective laser melting and milling techniques improves the metal production quality and corrosion resistance compared with the casting technique.2.After the same polishing process,the milling titanium and casting titanium have larger surface roughness and more adhesion than that of other groups,there is no difference between the three groups of cobalt chromium alloy and titanium on wettability.3.Streptococcus mutans negatively affect the corrosion resistance of cobalt chromium and titanium. |
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