Dental implants are exposed to a wide range of pH values of saliva and different concentrations of fluoride. In order to prevent plaque and caries formation, prophylactic products have been used more commonly for dental treatments. These products contain different concentrations of fluoride, for example; bucal rinses, toothpastes and gels contain 200ppm, 1000-1500 ppm and 10000-20000 ppm of fluoride respectively with the pH varying from acidic values to neutral ones. In this study, the effects of fluoride concentration and pH value on the corrosion behavior of Nb-10Ta-1Re and Ti-6Al-4V alloys in artificial saliva at 37°C were investigated by electrochemical measurements. For both alloys, electrochemical impedance spectroscopy and potentiodynamic polarization results showed that the corrosion rate increased with decreasing pH; also, increasing fluoride concentrations resulted in an increase in the corrosion rate. EIS results suggested that the oxide layer of Ti-6Al-4V alloy became porous in artificial saliva with high fluoride concentrations; on the contrary, Nb-10Ta-1Re alloy retained its compact oxide layer. Scanning electron microscopy results showed that after 5 days of immersion the oxide layer was washed away from the surface of Ti-6Al-4V alloy. For Nb-10Ta-1Re alloy; however, the polishing scratches were evident. At low pH values and high fluoride concentrations Nb-10Ta-1Re alloy showed better corrosion resistance in comparison with Ti-6Al-4V alloy.
Key words: downloadable, Niobium alloys, fluoride, electrochemical impedance, corrosion, dental implant