Surface properties and biological characteristics of glazed zirconia ceramics: in-depth analysis of different treatment methods

To investigate the effects of common clinical surface pretreatments on the surface properties, microhardness, and bacterial adhesion of glazed zirconia ceramics. Glazed zirconia specimens were assigned to 5 groups: control (C), ground (G), ground+polished (GP), grit-blasted (GB), and acid-etched (AE). Surface characteristics were evaluated via roughness/contact angle measurement, microscopy, X-ray diffraction, and Micro-Vickers hardness test. Streptococcus mutans and human whole-saliva biofilm adhesion were assessed by colony counting, CCK-8 assay, and 16 S rRNA gene sequencing. Grinding and grit-blasting significantly increased surface roughness (Ra up to 1.186 μm) and microhardness (from 626 MPa in the control to 1739 MPa in the GP group, P < 0.01), and induced tetragonal-to-monoclinic phase transformation (up to 12.35%); polishing reduced the monoclinic fraction to 3.43%. Bacterial adhesion showed a trend consistent with surface roughness; polishing reduced bacterial colonization and microbial diversity, while the grinding group had the highest adhesion and species richness. Notably, 16 S rRNA gene sequencing revealed that grinding uniquely enriched Fusobacterium, a key bridging pathogen in dental plaque biofilms. Surface pretreatments markedly affect the mechanical/surface properties and bacterial adhesion of glazed zirconia. Polishing optimizes clinical performance by removing the deformed surface layer, reducing roughness and bacterial colonization, whereas grinding and grit-blasting increase roughness and bacterial adhesion. This study clarifies that polishing after grinding optimizes surface smoothness and reduces bacterial adhesion on glazed zirconia, helping to lower caries and periodontal risks. It supports standardized surface protocols for durable, safe CAD/CAM restorations.