Long-term corrosion evolution of titanium and Ti5Cu alloy in the oral environment driven by Streptococcus mutans

Oral biomedical materials are susceptible to microbiologically induced corrosion (MIC) during long-term service, which may compromise their clinical performance and therapeutic efficacy. Herein, a 90-day experimental model was established to systematically investigate the MIC behavior of commercially pure Ti and Ti5Cu alloy under challenge of cariogenic Streptococcus mutans. Biofilms developed progressively on both materials, whereas Ti5Cu supported markedly thinner and less mature than pure Ti, with maximum thicknesses of 41.2 ± 3.1 and 55.1 ± 4.2 μm after 90 days, respectively. Continuous electrochemical measurements revealed lower corrosion susceptibility of Ti5Cu, as evidenced by higher polarization resistance, larger capacitive arc radii, and lower corrosion current density. S. mutans biofilms induced pronounced pitting corrosion, with maximum pit depths reaching 4.3 and 3.1 μm on Ti and Ti5Cu, respectively. AFM results further revealed increased surface roughness and potential heterogeneity on Ti, suggesting enhanced micro-galvanic effects. Nevertheless, Ti5Cu effectively mitigated these effects, likely owing to its ability to suppress biofilm formation and interfacial acidification. These findings provide a theoretical basis for understanding the long-term corrosion mechanisms of titanium-based oral materials and guiding material design for their safe service.