Microbiologically influenced corrosion (MIC) at oral biomaterial interfaces is viewed as an ecological phenomenon, yet how microbial composition and interspecies interactions shape corrosion remains unclear. Here, we investigated whether oral microbial community composition and interspecies interactions contribute to medical 316L stainless steel corrosion. Consortia-enhanced Cr and Fe release and localized surface pitting, with marked inter-subject variability. Interface-associated biofilms exhibited trends toward compositional shifts and showed enrichment of predicted pathways for fermentation and riboflavin metabolism, along with higher genome-based metabolic interaction potential than planktonic communities. Extracellular riboflavin accumulated in MIC systems and correlated positively with dissolved Cr and Fe concentrations. In perturbation assays, riboflavin supplementation increased corrosion current density (icorr) and metal dissolution, whereas roseoflavin reduced extracellular riboflavin availability and corrosion-related parameters without marked changes in the measured biofilm biomass or surface-associated ATP levels. A defined three-strain consortium (C. tsuruhatensis, R. erythropolis, and T. aromatica) reconstituted the S3 high-corrosion phenotype, including elevated icorr, extracellular riboflavin accumulation, and induced pitting, consistent with a proposed riboflavin-linked model involving species-dependent metabolic interactions. These findings suggest that extracellular riboflavin may represent a candidate redox-active factor associated with microbial community interactions and corrosion activity, providing an ecological framework for understanding microbiota-associated corrosion resistance at oral biomaterial interfaces.