Can Oral Bacteria and Mechanical Fatigue Degrade Zirconia Dental Implants in Vitro?

Zirconia (ZrO₂) is an emerging alternative to titanium for dental implant systems due to its material properties including high mechanical strength and chemical stability. However, oral environmental factors such as bacterial adhesion and mechanical fatigue may trigger low-temperature degradation of ZrO₂, leading to reduced mechanical strength and potential implant fracture. Although failure modes of ZrO₂ in orthopedic applications have been studied, they have yet to be thoroughly investigated in the context of dental implant systems. Thus, the goal of the present study was to assess the surface of ZrO₂ dental implants for signs of degradation after exposure to oral bacteria and oral bacteria in combination with mechanical fatigue. ZrO₂ dental implants were subjected to 30-day immersion in (i) early or (ii) late colonizing oral bacteria or (iii) were mechanically loaded for 2 × 10⁶ cycles with oral bacteria in circulation. Optical microscopy, Raman microscopy, and X-ray photoelectron spectroscopy (XPS) were used to evaluate the surface morphology, phase composition, and chemical composition, respectively. Post-immersion, all implants exhibited minimal changes in surface features, and all loaded implants survived cyclic fatigue tests. All implants had <1% monoclinic phase at the collar, junction, and screw regions, excluding the screw threads, for which monoclinic phase was significantly higher but <10%. XPS revealed an increase in carbon- and nitrogen-based organic debris on the implants exposed to early colonizers as compared to those immersed in late colonizers or synergistically with mechanical loading. Within the limitations of the present study, ZrO₂ is a suitable alternative material for dental implant systems based on its ability to resist both physical and chemical degradation imposed by oral bacteria and applied cyclic loads.