The effect of preparation order on the crystal structure of yttria-stabilized tetragonal zirconia polycrystal and the shear bond strength of dental resin cements.

OBJECTIVES: The purpose of this study was to evaluate the effect of preparation order on the crystal structure of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and the shear bond strength of dental resin cements.

METHODS: One-hundred fifty pre-sintered Y-TZP cylinders (Ø 9mm×13.5mm) were prepared and divided into three groups (control group, SBS group and SAS group). Specimens in control group were not treated. Specimens in SBS group were sandblasted and then densely sintered, and specimens in SAS group were sintered in advance, and then sandblasted. The specimens were analyzed by X-ray diffractometry, confocal laser scanning microscopy and Energy dispersive X-ray spectroscopy before and after sandblasting. All specimens were embedded in polytetrafluoroethylene (PTFE) molds using PMMA and each group was divided into five subgroups. The mixed resin cements (Clearfil SA luting cement, Zirconite, Superbond C&B, Rely-X Unicem, and Multilink) were placed onto the Y-TZP surfaces using PTFE molds with Ø 3mm×3mm, followed by storage in distilled water at 37°C for 24h, and thermocycling (5000 cycles at 5°C and 55°C with a 30s dwelling time). All specimens were tested for the shear bond strengths with a universal testing machine, and fractured surfaces were evaluated by SEM. Statistical analysis was performed using one-way ANOVA and Scheffé comparison with α=.05.

RESULTS: Sandblasting of the zirconia significantly increased shear bond strength of resin cements, but the preparation order had no significant influence on the shear bond strength in both test groups. In SEM observation, the natures of the surface faceting of the zirconia grains were totally different between SBS and SAS groups. SBS group exhibited less monoclinic structures than SAS group.

SIGNIFICANCE: Sandblasting of pre-sintered Y-TZP and then sintering may induce favorable proportion of tetragonal structures. This might have positive effect on the clinical performance of zirconia restorations.