Corrosion Effect And Mechanism Of Two Typical Candida Fungi On Titanium Alloys

Titanium and its alloys have been widely used in oral implants because of their high chemical inertia and excellent biocompatibility.However,the corrosion of implants by microorganisms in oral cavity will lead to the dissolution of metal ions,such as Al³⁺,V⁴⁺,Ni²⁺and so on.The long-term effects of these metal ions on the human body will affect human health,like causing gingival discoloration,material implantation failure.Severely,they will cause tissue canceration.How to prevent the corrosion of titanium and its alloys and the dissolution of metal ions became a problem.In the past decades,microbiologically influenced corrosion in oral cavity has mainly focused on exploring the effects of bacteria on implant materials.However,little has been reported on the effects of oral fungi on dental implants.As a kind of prevalent microbes distributed in the oral cavity,the influence of fungi on oral implant materials can not be ignored.In addition,due to the complex oral environment and various microorganisms in oral cavity,the corrosion mechanism of oral microorganisms remains controversial.Therefore,it is of great significance to study the effect of oral fungi on implant materials.Based on this,the corrosion effects on titanium-nickel alloy and titanium-zirconium alloy in the presence of single fungus and mixed fungi were carried out in this paper.The specific experimental contents are as follows:1.The formation and electron transfer ability of biofilm of Candida tropicalis,Candida parapsilosis and mixed Candida on titanium alloys surface were investigated.The results of fluorescence microscope observation showed that Candida tropicalis,Candida parapsilosis and mixed Candida could colony on the surface of titanium-nickel alloy and titanium-zirconium alloy.With the increasing immersion time,single fungus and mixed fungi appeared yeast-like and mycelial-like transformation on the titanium alloys surface,and finally formed biofilm.For the two titanium alloys,the difference was that single fungus and mixed fungi were easier to colonize on titanium-zirconium alloy surface and form a thicker biofilm.The differential pulse voltammetry curves showed that the biofilms of Candida tropicalis,Candida parapsilosis and mixed Candida could promote the transfer of electrons from the anode to the cathode,thus accelerating the corrosion of titanium-nickel and titanium-zirconium alloys.2.The corrosion effects of Candida tropicalis,Candida parapsilosis and mixed fungi on titanium-nickel alloy and titanium-zirconium alloy in artificial saliva were investigated.Compared with the abiotic group,the electrochemical test results of the biotic group showed that the impedance of titanium-nickel alloy and titanium-zirconium alloy decreased and the corrosion current increased to a certain extent,indicating that Candida tropicalis,Candida parapsilosis and mixed Candida could accelerate the corrosion of titanium-nickel alloy and titanium-zirconium alloy.Noticeably,in the presence of mixed Candida,the impedance value was the lowest and the corrosion current was the highest,indicating that the corrosion of the two kinds of titanium alloys caused by mixed Candida was the most serious.3.The surface morphology of titanium-nickel alloy and titanium-zirconium alloy under Candida tropicalis,Candida parapsilosis and mixed Candida were observed,and the corrosion products of single fungus and mixed fungi were analyzed.After the removal of fungal biofilm,pitting spots were found on the surfaces of titanium-nickel alloy and titanium-zirconium alloy.The number of pitting spots on the surface of the two kinds of titanium alloys was the most in the presence of mixed Candida,indicating the most serious corrosion.Electrochemical test results also showed that the mixed fungi had the greatest influence on the corrosion of two titanium alloys.XPS and FTIR showed that under the condition of single fungus and mixed fungi,the corrosion products of the two titanium alloys were similar,namely metal oxides.In this paper,the corrosion effects of Candida tropicalis,Candida parapsilosis and mixed Candida fungi on titanium-nickel alloy and titanium-zirconium alloy were explored.The corrosion dynamics,surface morphology and corrosion products were analyzed.The corrosion law was summarized and the corrosion mechanism was put forward,which not only provided a reference for the study of the corrosion of mixed microorganisms,but also provided a basis for the selection of dental restoration materials in the later stage.