Effect of (-)-epigallocatechin gallate on electrochemical behavior and surface film composition of Co-Cr alloy used in dental restorations.

The aim of this study was to investigate the electrochemical behavior of Co-Cr alloy in artificial saliva containing (-)-epigallocatechin gallate (EGCG) and to characterize the composition and structure of the passive film formed by potentiodynamic polarization.Electrochemical measurements ranked the corrosion resistance of Co-Cr dental cast alloy as follows when exposed to artificial saliva containing different concentrations of EGCG: 4.0 g/L<2.0 g/L<0 g/L<0.5 g/L<1.0 g/L. This showed that the concentration of EGCG in artificial saliva affected the corrosion behavior of Co-Cr alloy. X-ray photoelectron spectroscopy (XPS) results revealed that the outermost surface layer on Co-Cr alloy was mainly composed of Cr2O3 and EGCG-Cr (III) ion complex, which were formed by redox and complex formation reactions respectively. When the redox reaction was dominant, Co-Cr alloy exhibited high corrosion resistance in EGCG-containing artificial saliva. On the contrary, when the complex formation reaction was dominant, Co-Cr alloy exhibited low corrosion resistance.