Surface analysis and corrosion behavior of pure titanium under fluoride exposure

Statement of problem. The corrosive effects of oral fluoride products on titanium have been reported, and chronic fluorosis, which causes hyperfluoemia, is one of the world's health problems. Nevertheless, the relationship between high serum fluoride and corrosion on the titanium surface, which might have adverse effects on titanium implant osseointegration, has not been elucidated. Purpose. The purpose of this in vitro study was to investigate the corrosion behavior of pure titanium exposed to high serum fluoride with different pH values based on surface analysis. Material and methods. Pure titanium specimens, exposed to different electrolytes with 0.04 and 0.4 ppm NaF at pH 7.3 and 5.0 values, were examined for surface microstructure by using scanning electron microscopy (SEM) and for surface element composition with X-ray photoelectron spectroscopy (XPS). The corrosion behavior and metal ion release of specimens immersed in the Hanks' balanced salt solution (HBSS) containing 0.04 and 0.4 ppm serum fluoride concentrations (NaF) at 7.3 and 5.0 pH values were measured by electrochemical impedance spectroscopy (EIS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Results. Pitting holes were observed on pure titanium surfaces exposed to high serum fluoride. The surfaces became rougher with the increase of serum fluoride concentration, especially under acidic conditions. XPS analysis revealed a reduction of dominant titanium dioxide (TiO2) on the pure titanium surface under serum fluoride exposure, corresponding to an increase in the relative level of F. EIS data showed an active corrosion behavior of pure titanium exposed to high serum fluoride and gradually decreased corrosion resistance with increasing concentration of serum fluoride, which was more severe under acidic conditions. The release of titanium ions was also induced by high serum fluoride and acidic conditions. Conclusions. High serum fluoride had a negative influence on the corrosion behavior of pure titanium. The titanium oxide film barrier could be broken down in the fluoride ions condition, and the corrosion resistance of pure titanium decreased with the increasing concentration of serum fluoride. The increased corrosion susceptibility of pure titanium accelerated the release of titanium ions after exposure to high serum fluoride; this was more pronounced in an acidic environment.