The Corrosion Effect Of Candida Albicans On Titanium Materials In Artificial Saliva

Due to the better corrosion resistance, stronger mechanical properties and better biocompatibility, since the 1980s, dental implants and dental orthodontics made of titanium and its alloys are widely used in dental fields. As is known to all, the form of TiO2 on the surface of titanium and its alloys endows them stronger corrosion resistance. However, titanium and its alloys still have a certain ability to react, the dynamic balance between dissolution and repairation （passivation） is likely to be broken when the environment is changed. Oral cavity is a complex weak acid ecosystem, which contains viruses, protozoa, fungi, bacteria and other microorganisms. Fungi account for more than 60% of them, the existence of a large number of fungi may influence the performance of oral implant materials. Researchers have carried out a series of studies on bacteria-metal corrosion. Based on the abundant researches, the laws of bacteria-metal corrosion are summarized and a series of mechanisms are introduced. However consensuses of mechanisms is hard to get because of the complex of corrosion environment. Until now, researches about fungi-metal corrosion are rare, mechanisms between them are unknown. Candida albicans is one of the most common fungi in oral cavity, the research about the relationship between Candida albicans and titanium materials is significant for the further research of fungi-metal corrosion.Fluorescent microscope and laser scanning confocal microscope, scanning electron microscope are used to study the formation of Candida albicans biofilm on the surface of titanium and its alloys. At the same time, electrochemical methods, such as open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy are used to research the corrosion behavior of titanium and its alloys in the presence and absence of Candida albicans. Furthermore, the metabolites of Candida albicans and corrosion products are researched by ultraviolet-visible spectrometer, FTIR spectroscopy and energy dispersive spectrometer. The purpose of this research is to make the effect of Candida albicans on titanium and its alloys clear. In order to find out the corresponding corrosion mechanism. Specific results are as follows:（1） Candida albicans can form biofilms on the surface of pure titanium, Ti-6A1-4V alloys and TiNi alloys, the formation of biofilm is a process of accumulation over time. After 14 days, a certain thickness of biofilm formed on the surfaces of titanium materials. However, the morphology of biofilms on different metals is varying. Three-dimensional biofilms formed by hyphae are observed on the surface of pure titanium, while biofilms on the surface of Ti-6Al-4V alloy are made of staggered hyphae and yeasts. The biofilms on the surface of TiNi alloy are mainly composed of yeasts. The thickness of the biofilms on these three metals are ranked as:pure titanium> TiNi alloy> Ti-6Al-4V alloy, the distinction of biofilms leads to the difference of corrosion behavior.（2） Combined effect of metabolites, extracellular polymer matrix and biofilms, the electrochemical behaviors of titanium and its alloys are different. Generally speaking, the Ecorr shifts positive and icorr increases, Rct decreases, but different effect of Candida albicans is found. For pure titanium, Ecorr fluctuates and icorr increases, Rct decreases, which indicates the pitting of pure titanium. For Ti-6Al-4V alloys, icorr increases significantly, Ecorr shifts positive, which shows the accelerated corrosion of them. The icon of TiNi alloys changed little in the presence of Candida albicans and no obvious corrosion is found, which suggests Candida albicans has slight corrosive effect on TiNi alloys.（3） The presence of Candida albicans leads to the corrosion of metals. The results of ultraviolet-visible spectrometer shows that the absorption peak of pure titanium and Ti-6Al-4V alloy is stronger in the presence of Candida albicans, which indicates the corrosion of them. While the results of EDS suggests that the dissolution of Ni²⁺is more then Ti4+ and the absorption peak of titanium with Candida albicans is weaker than without Candida albicans at 260 nm, indicating the inhibited corrosion of TiNi alloy when containing Candida albicans. Combined with the SEM results, corrosion degree of these three materials is different with or without Candida albicans. The corrosion of pure titanium is most serious, and the presence of Candida albicans causes the pitting corrosion of it. Surface roughness of Ti-6Al-4V alloy increases, while no obvious corrosion is found on the surface of TiNi alloy in the presence of Candida albicans.（4） When different metals are immersed, the acid-base property of metabolites, morphology of biofilms, electrochemical corrosion behaviors of metals are different. Microbiologically influenced corrosion is a complex process, it is important to consider the effect of fungi and materials, comprehensively.