Optical and Mechanical Properties of the Multi-Transition Zones of a Translucent Zirconia.

Objective: To characterize the composition, flexure resistance, and optical properties of a multilayer translucent zirconia in relation to its multi-transition zones.

Materials and methods: A multilayer zirconia (5Y/4Y) and a conventional 3 mol% yttria partially stabilized zirconia (3Y) were investigated. Bar-shaped specimens were obtained from the enamel and dentin layers, and the vertical cross-section of 5Y/4Y (N = 10). A four-point flexural (σ_f) test was performed using a universal testing machine (1.0 mm/min). Plate-shaped specimens (N = 6) were also produced from the enamel, transition 1, transition 2, and dentin layers. Translucency parameters (TP_ab and TP₀₀) were determined using a dental spectrophotometer (N = 6). X-ray fluorescence and X-ray diffraction techniques were used to analyze elemental (N = 2) and phase compositions (N = 2), respectively. Data were analyzed using analysis of variance (ANOVA) and Tukey's test (α = 0.05).

Results: The yttrium content and σ_f varied between layers of 5Y/4Y. 3Y had the highest σ_f, followed by dentin. Enamel and cross-section showed lower and statically similar σ_f. 3Y and dentin groups had similar but statistically lower TP_ab and TP₀₀ than the enamel.

Conclusions: Different layers of multilayered zirconia have distinct compositions, which affect their mechanical and optical properties. The weak enamel layer compromises the mechanical properties of cross-sectional specimens.

Clinical significance: The development of novel cubic-containing multilayer zirconia ceramics to produce monolithic restorations brings new challenges to dental clinicians and laboratory technicians. The CAD/CAM design of multilayered 5Y/4Y restorations should consider the esthetic and mechanical requirements of each clinical case, as different properties are found in the different layers of these materials.