Influence of pre- and post-sinter surface treatments on adhesion and mechanical properties of translucent monolithic zirconia

This study evaluated the effects of presinter and post-sinter surface treatments on the mechanical strength and resin bonding performance of high-translucency monolithic zirconia. A total of 110 zirconia specimens were prepared and randomly assigned to 11 groups (n = 10) based on the surface treatment protocol (airborne-particle abrasion or tribochemical silica coating), sintering stage (presinter or post-sinter), and timing of silane application. Flexural strength was assessed using a three-point bending test in accordance with ISO 6872. Shear bond strength (SBS) to a dual-cure resin cement was evaluated using a universal testing machine. Data were analyzed using the Kruskal–Wallis test followed by Dunn’s post hoc comparisons (α = 0.05). Surface treatments significantly influenced both mechanical and bonding properties (p < 0.05). The highest fracture resistance values were observed in the untreated control group, while all surface-treated groups exhibited reduced mechanical strength. In contrast, bond strength values were significantly enhanced by surface treatments. The highest SBS values were obtained in the group treated with post-sinter tribochemical silica coating combined with silane application. Groups receiving silane before final sintering exhibited lower bond strength, consistent with the expected thermal decomposition of the silane layer, whereas post-sinter silanization improved adhesion. Surface treatments improve zirconia–resin bonding but may compromise mechanical strength. The combination of post-sinter tribochemical silica coating and silane application appears to be the most effective approach for enhancing adhesion. However, the balance between improved bonding and reduced mechanical integrity should be carefully considered in clinical practice.