The electrochemical behavior of Zr5Ti, Zr25Ti, and Zr45Ti, with and without surface modification were monitored in acidic artificial saliva (pH = 3) containing NaF concentrations 0.2, 0.5, and 1 wt.%, simulating the fluoride concentrations in dental rinses. A passive behaviour for thermally oxidized ZrTi alloys was found using EIS, and XPS data show that the protective oxide film contains both TiO2 and ZrO2, though titanium contents in the outer layer bigger than those in the base alloy result from thermal oxidation. High corrosion resistance to acidic fluoridated environments of ZrTi alloys treated using thermal oxidation in air at 500 ºC.

The electrochemical behaviour of two Ag-Pd alloys (Unique White and Paliag) used in dental prosthetics construction for crowns and bridges and one Co-Cr alloy (Vitallium 2000) was studied in artificial saliva using the polarization curves and electrochemical impedance spectroscopy (EIS). The corrosion resistance was evaluated by means of the corrosion currents value and by coulometric analysis. The open circuit potential of Ag-Pd are attributed to dealloying followed by surface enrichment with Ag and the possible formation of an insoluble AgCl surface film on the respective alloy surfaces. Our results have shown that these alloys have a somewhat good corrosion resistance in artificial saliva. The corrosion current densities of Unique White and Vitallium 2000 alloys were very low (~100 nA/cm 2 ). For Ag-Pd alloys, when increasing the content of Cu, corrosion resistance decreases. The passivation of all samples occurred spontaneously at the open circuit potential. The electrochemical properties of the spontaneously passivated electrodes at the open circuit potential were studied by EIS. The polarization resistance (R p ) and the electrode capacitance (C dl ) were determined. The polarization resistance of all the samples increases with the immersion time. The polarization resistances are largest for Unique White (Ag-Pd) and Vitallium 2000 (Co-Cr) alloys. Because the electrochemical behaviour of the Co-Cr alloy was compared with that of Ag-Pd alloy, this type of alloy may be a suitable alternative for use in the manufacture of fixed dental prostheses. The present study, though limited, has shown that electrochemical characteristics can be used to identify such alloys. Knowledge of the in vitro corrosion behaviour of these alloys may lead to better understanding of any biologically adverse effects in vitro.

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Electrochemical behaviour of Zr5Ti, Zr25Ti and Zr45Ti, with and without surface modification were investigated for dental applications. All untreated and thermal oxidized alloys in Na2CO3 at 890 °C were tested by electrochemical impedance spectroscopy (EIS) performed in 10% carbamide peroxide solution. In addition, scanning electron microscopy (SEM) was employed to observe the surface morphology before and after 8 hours immersion time in carbamide peroxide solution. The electrochemical corrosion parameters obtained from the EIS indicated a typical passive behaviour for untreated and thermal oxidized ZrTi alloys. Higher impedance values were observed for thermal oxidized ZrTi alloys compared to untreated materials. The thermal oxidized Zr45Ti alloy appears to possess superior corrosion resistance than the thermal oxidized Zr25Ti and Zr5Ti alloys in carbamide peroxide solution.

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