Biocorrosion behavior of high-purity Mg and Mg-Zn-Zr-Nd alloy during exposure to Porphyromonas gingivalis.

Biodegradable magnesium (Mg) materials are attractive for guided bone regeneration, but oral exposure may trigger microbiologically influenced corrosion. This study compared the early corrosion behavior of high-purity Mg (pMg) and Mg-2Zn-0.5Zr-0.5Nd (Mg-Nd) during anaerobic exposure to Porphyromonas gingivalis. Disk specimens were immersed in supplemented brain-heart infusion medium with or without P. gingivalis for 1, 3, and 7 days. Corrosion was evaluated by ICP-MS, pH monitoring, gravimetric mass loss, SEM/EDS, XRD, XPS, 3D optical profilometry, electrochemical impedance spectroscopy, and potentiodynamic polarization. Bacterial survival was assessed by CFU counting and Live/Dead imaging. Both materials rapidly alkalinized the medium and released Mg during immersion. P. gingivalis increased early mass-loss corrosion rates for both substrates and limited the development of a high-resistance interfacial state, with the strongest effect observed for Mg-2Zn-0.5Zr-0.5Nd. After 7 days, the alloy exhibited a substantially lower polarization resistance in the biotic condition than in the sterile control (700 versus 6250 Ωcm2). Surface deposits in all groups were dominated by Mg- and O-containing species, but bacterial exposure altered deposit morphology and spatial distribution. Profilometry showed reduced maximum pit depth in the presence of P. gingivalis despite sustained electrochemical activity, consistent with redistribution rather than simple amplification of localized attack. Mg-2Zn-0.5Zr-0.5Nd reduced bacterial viability in suspension relative to pMg, but this antibacterial effect did not correspond to electrochemical stabilization. These findings indicate that P. gingivalis remodels the early corrosion interface of Mg-based biomaterials and should be considered in the preclinical evaluation of oral Mg devices.