Corrosion Effect And Mechanism Of The Interaction Between Candida Albicans And Streptococcus Mutans On Titanium-nickel Alloy

Titanium and its alloys are widely used in the field of oral cavity restoration due to the excellent biocompatibility,light weight,strong resilience and good corrosion resistance.However,oral cavity with a large number of microbial species is the second large-microbe host environment in human body.In the complex multi-group microbial environment,the surface of the oral titanium implant is easy to form plural-group biofilms.These plural-group biofilms can cause peri-implant inflammation and accelerate the corrosion of the implant.With the increase of biofilm thickness and biomass,it even leads oral implant surgery to fail.Streptococcus sp.are the principal microorganisms of oral cavity,in which streptococcus mutans(s.mutans)is the largest species of the streptococcus sp..Based on reports,the co-biofilm formed by s.mutans and candida albicans(c.albicans)is one of the main components of oral plaque,and it also is the primary responsibility of dental caries.Moreover,the co-culture of s.mutans and c.albicans in the medium also have synergistic symbiosis and form co-biofilm,whereas the co-biofilm structure and the metabolic products are significantly different from that of the single-species.However,there are relatively few literatures about the corrosion effect of this co-biofilm on titanium materials in oral cavity,and the corrosion mechanism is not clear.Therefore,the corrosion effects of control,c.albicans,s mutans and mixed-species on titanium-nickel alloy were studied by using microbial biomass analysis,microbial metabolic pH analysis,surface corrosion morphology analysis,corrosion dynamics analysis,extracellular electron transfer analysis,and the possible corrosion mechanism was put forward according to the experimental data.The results of microbial biomass analysis showed that c.albicans had a longer period of activation and growth than s.mutans,while the biological increment was larger than s.mutans.This phenomenon was consistent with the reproduction characteristics of fungi(c.albicans)and bacteria(s.mutans).In addition,the lag phase of mixed-species was shorter and the biomass was larger in stationary phase than that of the single species,which indicated that the growth of c.albicans and s.mutans was coordinated,and the metabolism velocity of the mixed-species was strong.The results of microbial metabolites pH analysis showed that c.albicans,s.mutans and mixed-species were mainly acid metabolized in artificial saliva.The acid-producing ability of mixed-species was the strongest,s.mutans was the second,and c.albicans was the weakest.The results of surface corrosion morphology analysis showed that c.albicans,s mutans and mixed-species could adhere to the surface of TiNi alloy.C.albicans adhered to the alloy surface with yeast phase and hyphae;s,mutans adhered to the alloy surface by chain ball;the mixed-species were mainly that c.albicans adhered to the alloy surface first,and s.mutans adhered to the surface of c.albicans,then formed the'hill'shape of s.mutans enclosing c.albicans.After removing the biofilm on the alloy surface,it was observed that the surface corrosion of mixed-species was the most serious,s.mutans was the second,and c.albicans was the weakest.The corrosion kinetics analysis showed that c.albicans,s.mutans and mixed-species all reduced the electrochemical impedance,shifted the corrosion potential negative,and increased the corrosion current density of TiNi alloy.These show that both the single species and the mixed-species can accelerate the corrosion of TiNi alloy.The corrosion of TiNi alloy was the most serious with mixed-species,followed by s.mutans and c.albicans.The results of extracellular electron transfer analysis showed that c.albicans,s.mutans and mixed-species all had the effect of strengthening extracellular electron transfer.The ability of mixed-species was the strongest,s.mutans was the second,and c.albicans was the weakest.The results of surface corrosion products analysis showed that the corrosion products of c.albicans,s.mutans and mixed-species were basically the same,mainly the complexes of titanium ions,nickel ions and the lactic acid in the microbial metabolites.