Effect of surface treatment on bond strength to zirconia ceramic

Objective: This study investigated the effect of different chemical surface treatment of zirconia ceramic on the shear bond strength. Method: Yttria-stablized zirconia ceramic blocks (VITA In-Ceram YZ, VIDENT) were sectioned to 2.5mm thick, polished with 1200-grit SiC paper, and fired at 1450oC for 6 hrs. Forty fired zirconia blocks were divided into 4 groups (n=10): Control-1: no-sandblast, applying 40% phosphoric acid gel for 5s; Control-2: sandblasted with 110ƒÝm alumina at 2.5-bar pressure for 15s, then 40% phosphoric acid gel for 5s; Exp-1: no-sandblast, applying diluted Pirahna solution (80% H2SO4+30% H2O2) for 30s; Exp-2: sandblast plus diluted Pirahna solution. Contact angles on no-sandblast samples (n=3) with different treatment were measured using the Pocket Goniometer (Model PG-2, FIBRO System AB, Sweden). Cylinders (2.73mm diameter) of light-cured composite (Photo Cure, Kuraray) were bonded to the surface of treated zirconia blocks using Panavia F 2.0 (Kuraray) resin cement following manufacturer's instructions. After storage in distilled water at 37oC for 24hrs, shear bond strength was tested on Instron 5566 testing machine with 1mm/min crosshead speed. The data were analyzed using ANOVA and post hoc Tukey-HSD test (a=0.05).

Results: Contact angles (degree): untreated samples: 109.7±2.0, 40% phosphoric acid gel: 64.5±0.5, Pirahna solution: 0^o (undetectable).

Shear bond strength (MPa): Control-1: 10.69±4.70, Control-2: 15.91±2.77, Exp-1: 16.90±5.86, Exp-2: 18.50±2.10.

Treatment with diluted Pirahna solution generated a very low (undetectable) contact angle, which indicates a clean and highly hydrophilic surface. Shear bond strength on the no-sandblast samples treated with Pirahna solution is significantly higher than the no-sandblast samples treated with phosphoric acid gel (p<0.05) and similar to the samples treated with phosphoric acid gel and sandblast (p>0.05). Conclusion: treatment with diluted Pirahna solution can significantly improve the wetting on zirconia ceramic surface and may generate adequate resin bond strength without sandblast that produces microcracks. Supported by NIH/NIDCR grant 1R21DE18349-01.