The role of citric acid in denture cleansing: Effects on biofilm reduction and corrosion resistance of Co-Cr alloys

This in vitro study evaluated the effects of citric acid (CA) on surface properties, biofilm removal, and electrochemical performance of Co-Cr alloys compared to common denture cleansers. Co-Cr discs were divided into five groups based on the decontamination solution: NaCl 0.9% (control), Corega Tabs®, Periogard®, and 10% CA. The surface was characterized at baseline in terms of morphology, topography, and chemical and phase composition. Surface properties, including microhardness, wettability, and roughness, were assessed before and after exposure to each solution. Microbial viability, metabolic activity, and morphology of the polymicrobial biofilm were assessed after treatment to evaluate the efficacy of the decontamination solutions. Electrochemical and morphological evaluations were performed to assess the impact of each solution on the alloy's corrosion process. No significant changes in microhardness were observed (p > 0.05). Decontamination solutions significantly increased surface hydrophilicity (p < 0.05) and roughness, though Ra values remained below the threshold for bacterial colonization. All denture cleansers significantly reduced biofilm viability compared to NaCl (p < 0.05), with no viable colonies post-treatment. The CA group showed a significant reduction in bacterial metabolic activity compared to NaCl and Periogard® (p < 0.05), indicating superior biofilm disruption. Electrochemical tests demonstrated that CA maintained a stable Cr-oxide passive layer, evidenced by nobler OCP values and lower icorr and corrosion rates compared to Periogard® (p < 0.05). SEM images revealed pitting corrosion in all groups, except CA. These findings suggest that CA is a promising and safer alternative for denture care, offering effective antimicrobial action while preserving the electrochemical integrity of Co-Cr alloys.