The effect of zirconia surface treatment on flexural strength and shear bond strength to a resin cement

Statement of problem: Despite the expanded applications for zirconia in restorative dentistry, there is no clear recommendation in the literature regarding surface treatment before bonding. Purpose: The purpose of this study was to evaluate the effect of mechanical surface treatment of yttria-partially stabilized zirconia on its flexural strength and the effect of mechanical and chemical surface treatments on its bond strength to a resin cement. Material and methods: For flexural strength evaluation, zirconia bars (4 × 5 × 40 mm) were prepared from zirconia blocks, finished using a diamond rotary cutting instrument, sintered, then assigned into 4 groups: (1) control (no treatment), (2) airborne-particle abrasion, (3) silicoating, and (4) wet hand grinding. After storage for 24 hours at 37°C, flexural strength was determined using a 3-point bending test, and the results were analyzed using 1-way ANOVA (α=.05). For shear bond strength evaluation, zirconia rods (2.5 × 3 mm) were prepared from zirconia blocks, sintered, and assigned into 16 groups. Each group underwent a combination of the following mechanical and chemical treatments. Mechanical treatment included: (1) control (no treatment), (2) airborne-particle abrasion, (3) silicoating, or (4) wet hand grinding. Chemical treatment included: (1) control (no treatment), (2) acid etching followed by silanation, (3) silanation only, or (4) application of zirconia primer. Dentin specimens were prepared from extracted molars stored in 0.5% chloramine-T. Zirconia rods were bonded to dentin using a resin cement (Multilink Automix), then light polymerized. After storage, the specimens were loaded to failure with the notched shear bond test method in a universal loading apparatus. For artificial aging analysis, the groups that achieved the highest bond strength values were duplicated, stored at 37°C and 100% humidity for 90 days, and thermal cycled before being loaded to failure. Results were analyzed using 2-way ANOVA (α=.05). Results: Airborne-particle abrasion and hand grinding significantly increased flexural strength. The highest shear bond strength values were achieved for the following groups: silicoated + silanated > hand ground + zirconia primer > airborne-particle abraded + silanated > zirconia primer > airborne-particle abraded + zirconia primer. Artificial aging resulted in significantly lower shear bond strength for the silicoated/silanated and the zirconia primer groups. Conclusions: Mechanical modification of the surface increased the flexural strength of Y-TZP. The resin bond to Y-TZP was improved by surface treatment. A combination of mechanical and chemical conditioning of the zirconia surface was essential to develop a durable resin bond to zirconia. (J Prosthet Dent 2010;103:210-220).