Mechanical Properties of New Generations of Monolithic, Multi-Layered Zirconia

New monolithic multi-layered zirconia restorations are gaining popularity due to their excellent aesthetic properties. However, current knowledge of these newest multi-layer ceramics in terms of mechanical properties is scarce. Three monolithic, multi-layered zirconia materials (Katana, Kuraray Noritake, Japan) were selected for comparison: High Translucent Multi-layered zirconia (HTML), Super Translucent Multi-layered zirconia (STML) and Ultra Translucent Multi-layered zirconia (UTML). Fifteen specimens per group were cut from pre-sintered blocs in each of the four layers (L1, L2, L3, L4) and in different thicknesses (0.4 mm, 0.8 mm and 1.2 mm). Critical fracture load (Fcf) was recorded in 3-point-bending. Flexural strength (sigma) in MPa, Vickers hardness (HV) in N/mm(2), fracture toughness (K-Ic) in MPa*m1/2, Weibull Modulus (m) and characteristic Weibull strength (sigma w) in MPa were assessed. Statistical analysis was performed using ANOVA analysis. FS and K-Ic were significantly higher (p < 0.05) for Katana (TM) HTML (652.85 +/- 143.76-887.64 +/- 118.95/4.25 +/- 0.43-5.01 +/- 0.81) in comparison to Katana (TM) STML (280.17 +/- 83.41-435.95 +/- 73.58/3.06 +/- 0.27-3.84 +/- 0.47) and UTML (258.25 +/- 109.98-331.26 +/- 56.86/2.35 +/- 0.31-2.94 +/- 0.33), with no significant differences between layers and layer thicknesses. The range of indications should be carefully considered when selecting the type of monolithic zirconia for fabrication of dental restorations, as materials widely differ in mechanical properties.