Effects of lipopolysaccharides on the corrosion behavior of Ni-Cr and Co-Cr alloys

Statement of problem. Lipopolysaccharides (LPS) are constituents of gingival crevicular fluid and may affect the base metal alloys used in metal ceramic crowns. The role of LPS in base metal alloys is currently unknown. Purpose. The purpose of this in vitro study was to evaluate the effects of gram-negative bacterial LPS on the electrochemical behavior of Ni-Cr and Co-Cr alloys. Material and methods. Alloy specimens were divided into 4 groups according to Escherichia coli LPS concentration (0, 0.15, 15, and 150 mu g/mL) in acidic saliva (pH 5). Open circuit potential (OCP) and potentiodynamic polarization behavior were examined using a computer-controlled potentiostat. Metal ions released from the 2 alloys were measured by immersion in LPS-free solution and 150 mu g/mL LPS solution and analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). Data were evaluated using 1-way ANOVA (alpha=.05). Results. Compared with control groups, medium LPS concentration (15 mu g/mL) accelerated Ni-Cr alloy corrosion (P<.05), whereas high LPS concentration (150 mu g/mL) accelerated Co-Cr alloy corrosion (P<.05), as determined by OCP, corrosion current density, and polarization resistance parameters. After immersion in high LPS concentrations (150 mu g/mL), a slight increase in Ni ion release (P>.05) was observed for the Ni-Cr alloy, while a more significant Co ion release (P<.05) was observed for the Co-Cr alloy. Conclusions. LPS negatively affected the electrochemical behavior of both the Ni-Cr and Co-Cr alloys.