LAUSR

OBJECTIVES To compare the effects of particle abrasion medium and pressure on shear bond strength and biaxial flexural strength of three generations of zirconia (Lava Frame, Lava Plus, and Lava Esthetic) with the goal of optimizing the bond to zirconia. METHODS 280 discs (14 mm diameter; 1 mm thickness) of each zirconia were milled and sintered. Specimens of each material were randomly distributed into 14 groups (n=20); half were tested for shear bond strength and half were tested for biaxial flexural strength. The specimens were particle abraded on one surface by 2 different media (50 μm alumina particles or 50 μm glass beads) for 10 seconds at three different pressures (15, 30, and 45 psi or 0.1, 0.2, 0.3 MPa). Untreated specimens served as positive control. A tube (1.50 mm diameter) filled with dual cured resin cement (Panavia SA) was placed onto the surface and light cured. Specimens were stored in water (37°C for 24 hours) and shear bond strength was measured in a universal testing machine (Instron). Biaxial flexural strength of each specimen was measured according to ISO 6872. Shear bond strength and biaxial flexural strength were compared individually with a 2-way analysis of variance (ANOVA) for factors surface treatment and zirconia composition. RESULTS Significant differences were seen between surface treatments (p<0.01), zirconia composition (p<0.01) and their interaction (p<0.01) for both bond strength and flexural strength. With alumina particle abrasion, higher pressure produced higher bonds for Lava Frame and Lava Plus zirconia while the bond of Lava Esthetic declined with increased pressure. Higher pressure (>0.2 MPa or 30 psi) with alumina decreased biaxial flexural strength with Lava Esthetic zirconia. CONCLUSIONS Particle abrasion with alumina produced a significantly better combination of bond strength while maintaining biaxial strength of three zirconia materials than particle abrasion with glass beads. The bond strength also depended upon the pressure of particle abrasion and the generation of zirconia used.