Effect of Airborne Particle Abrasion Protocols on the Shear Bond Strength and Surface Hardness of High-Translucent Zirconia Under Thermocycling: An In-Vitro Study

High-translucent 5Y-PSZ zirconia offers superior esthetics but reduced mechanical strength, complicating resin–zirconia bonding and durability under thermocycling. This in vitro study evaluated the effect of airborne-particle abrasion (APA) protocols on the shear bond strength (SBS) and surface hardness (SH) of high-translucent zirconia (Shofu ZR Lucent) under thermocycling. Thirty CAD-CAM specimens were divided into three groups (n = 10) based on the APA protocol: control, 50 µm Al₂O₃, and 100 µm glass microbeads. Fifteen square specimens (n= 5 per group with dimensions 8 × 8 × 3 mm) were bonded with primer (AZ Primer) and resin cement (ResiCem) for SBS testing, and fifteen discs (n= 5 per group with dimensions 15 × 1.2 mm) were used for SH evaluation. All samples underwent 25,000 thermocycles between 5-55 °C. SBS values did not differ significantly among groups (control: 5.64 ± 1.49 MPa; 50 µm Al₂O₃: 6.49 ± 1.59 MPa; 100 µm glass microbeads: 6.42 ± 4.05 MPa; ANOVA p = 0.852), with 100% adhesive failures at the resin–zirconia interface. In contrast, SH differed markedly (control: 876.34 ± 25.10 VHN; 50 µm Al₂O₃: 1747.26 ± 37.37 VHN; 100 µm glass microbeads: 1246.94 ± 33.81 VHN; ANOVA p < 0.001), with all pairwise comparisons significant (Tukey p < 0.001). These findings indicate that while APA does not improve SBS, but it substantially enhances surface hardness, particularly with 50 µm Al₂O₃, which may strengthen the zirconia surface and improve long-term wear resistance.