Esthetic Zirconia Flexural Strength after Blasting with Glass or Alumina

Objectives: Currently the most common way to condition zirconia for bonding is to blast the intaglio surface with abrasive particles, but this can lower the resistance of the zirconia to fracture. Also, instructions vary on the pressure to use. In this study, the effect of aluminum oxide or glass bead blasting on the flexural strength of several esthetic multilayered zirconia products was compared.
Methods: Zirconia blocks were milled from 98 mm discs, and bars were cut with a water-cooled low-speed diamond wafering saw and finished with 600-grit diamond discs to 25 x 2 x 4 mm³ post sinter dimensions according to ISO 6872:2015 methods. Zirconia tested included DD Cube X² ML (Dental Direkt GmbH) and Lava Esthetic (3M). Test groups (n=10, N=100 included the control finished through 600-grit diamond discs, and uniform blasting with 50 micron glass beads and 50 micron aluminum oxide at pressures of 1.5 bar and 3 bar. Bars were tested with a 1 mm/min crosshead speed and 20 mm span with a 3-point bend on an Instron 5866 universal testing machine. Means and standard deviations were determined. Data were analyzed by ANOVA. Fisher’s PLSD multiple comparison test was calculated at the 0.05 level of significance.
Results: Mean flexural strength of the 600-grit finished control group was the highest (703-748 MPa), followed by 1.5 bar glass bead blasting (624-688 MPa), 3.0 bar glass bead blasting (578-598 MPa), 1.5 bar aluminum oxide blasting (408-429 MPa), and 3.0 bar aluminum oxide blasting (343-402 MPa). There were significant differences in mean flexural strength between DD Cube X² ML and Lava Esthetic (p=0.04, critical difference=26 MPa) depending on the surface treatment.
Conclusions: The flexural strength of esthetic multilayered zirconia was adversely affected by aluminum oxide blasting and to a lesser extent by glass bead blasting.