Microporous zirconium-coated titanium surfaces for dental implant application: Surface characterization, bioactivity and effect on the oral biofilm formation

Implantable materials based on titanium have been widely used in medical and dental care due to favorable mechanical properties and biocompatibility. However, when compared to ceramics, titanium surfaces are more susceptible to bacterial adhesion and colonization by periodontopathogenic species. Peri-implant infections are the major cause of implant failure and development of implantable materials with surface properties effective in minimizing bacterial colonization is still a challenge. Plasma electrolytic oxidation (PEO) provides porous ceramic coatings of high durability and stability on titanium. Incorporating metals with antimicrobial effects may contribute to minimizing microorganism adhesion on titanium. This study developed a novel zirconium-coated titanium surface using PEO and compared the composition of oral biofilm with machined or double acid etched surfaces in situ. SEM analysis showed pores and micro-pores, respectively for PEO and zirconium coatings, with surface roughness lower than acid etching while maintaining moderate levels (Ra/Sa: 1.0-2.0 µm). Chemical composition analysis showed predomination of TiO₂ on the most superficial layer of all groups with phosphorous and calcium incorporated into PEO coatings; calcium was replaced by a relevant amount of zirconium after anodization. Both PEO and zirconium coatings presented reduced values of surface free energy and less wettability than control and etched surfaces. DNA Checkerboard hybridization analysis showed that zirconium coatings significantly reduced the total microbial counts on the formed biofilms with lower counts of opportunistic and pathogenic species. In conclusion, PEO and zirconium coatings have substantially modified the microbial colonization pattern of biofilms, with preferential colonization by commensal Streptococci on zirconium surfaces.