Microbe–crevice synergistic acceleration of degradation of biomedical 316 L stainless steel in the oral environment

Oral metallic biomaterials are vulnerable to synergistic microbial–crevice effects that compromise long-term clinical performance and induce inflammatory responses. In this study, we systematically investigated the combined effects of the cariogenic Streptococcus mutans and crevice on the corrosion behavior of 316 L stainless steel (SS) under simulated oral anaerobic conditions. Comprehensive analyses, including biofilm characterization, electrochemical measurements, surface morphology analyses, and passive-film evaluation, revealed that both microbiologically influenced corrosion (MIC) and crevice corrosion significantly accelerated degradation. Their synergistic interaction further enhanced corrosion kinetics, resulting in a two-order-of-magnitude decrease in polarization resistance compared with sterile conditions. The cooperative action of microbial biofilms and crevices altered passive-film properties and promoted pitting corrosion. Separate electrochemical tests of internal and external crevice surfaces demonstrated that the inner crevice under bacterial conditions exhibited the highest corrosion susceptibility, which was corroborated by atomic force microscopy mapping of surface potential differences (up to 39.7 mV) and topographical heterogeneity. Based on these findings, a synergistic corrosion model was proposed to elucidate the accelerated degradation mechanism by S. mutans biofilm and crevice. This work provides new mechanistic insight into the microbe–crevice interaction in oral environments and may offer guidance for designing advanced interfacial protection strategies.