A Comparison of Failure Loads for Polycrystalline Zirconia Ceramics with Varying Amounts of Yttria, Glass-Ceramics and Polymers in Two Different Test Conditions

It is unclear how zirconia dental crowns with different yttria compositions will perform clinically, and how they will compare with crowns made of glass-ceramics and polymers. The present objective was to determine failure loads of crowns and discs made of glass ceramics or polymers as compared to yttria-partially stabilized zirconia (Y-PSZ) crowns and discs with varying yttria concentrations. Crowns of zirconia (Cercon XT, Katana UTML, BruxZir Anterior), glass ceramic (Celtra press, IPS e.max press, Lisi press), and polymeric materials (Trilor, Juvora, Pekkton) were fabricated and cemented to epoxy abutments. The total number of specimens was 135 for crowns and 135 for discs (n = 15 specimens per material type and design). A universal testing machine was used to perform compressive loading of crowns/discs to failure with a steel piston along the longitudinal axis of the abutments. Energy dispersive spectroscopy (EDS) was used to identify the yttria concentration for each zirconia brand. The data were analyzed using generalized linear models and regression analyses. The results revealed significant differences (p < 0.05) in mean failure loads for different crown materials: Trilor (6811 +/- 960 N) > Juvora (5215 +/- 151 N) > Cercon (4260 +/- 520 N) = BruxZir (4186 +/- 269 N) = e.max (3981 +/- 384 N) > Katana (3195 +/- 350 N) = Lisi (3173 +/- 234 N) = Pekkton (3105 +/- 398 N) > Celtra (2696 +/- 393 N). The general linear model revealed significant differences (p < 0.05) in mean failure loads when comparing the different materials for the discs, i.e., Trilor (5456 +/- 1748 N) > Juvora (4274 +/- 869 N) > Pekkton (3771 +/- 294 N) > Katana (2859 +/- 527 N) > Cercon (2319 +/- 342 N) = BuxZir (2250 +/- 515 N) = e.max (2303 +/- 721 N) = Lisi (2333 +/- 535 N) > Celtra (1965 +/- 659 N). EDS showed that the zirconia materials contained yttria at different concentrations (BruxZir = 5Y-PSZ, Cercon = 4Y-PSZ, Katana = 3Y-PSZ). The yttria concentration had a significant effect on the failure load of the Katana (3Y-PSZ) crowns, which revealed lower failure loads than the Cercon (4Y-PSZ) and BruxZir (5Y-PSZ) crowns, whose failure loads were comparable or higher than e.max glass ceramic. The failure load of the trilayer disc specimens did not correlate with the failure load of the respective crown specimens for the zirconia, glass-ceramic and polymeric materials.