The effect of thickness and sintering mode on the impact strength of a graded Zirconia

Background: Graded zirconia ceramics balance the high strength of 3Y-TZP with the translucency of 5Y-PSZ through their layered microstructure. However, the mechanical behavior of distinct compositional zones, particularly the transition zone, remains insufficiently characterized under dynamic loading conditions. This study aimed to evaluate the influence of different sintering protocols and thicknesses on the impact strength of graded zirconia. Material and Methods: Specimens were sectioned by layer (3Y-TZP, transition zone, 5Y-PSZ) under two thicknesses (1.0 and 1.5 mm) and two sintering protocols (conventional and speed). Impact strength testing, finite element analysis, and fractographic analysis were performed. A total of 180 bars were tested using the Dynstat method, with results analyzed via three-way ANOVA (α = 0.05). Results: The 3Y-TZP layer exhibited the highest impact strength (46.8-66.7 kJ/m²), followed by the transition zone (23.7-41.9 kJ/m²) and 5Y-PSZ (15.5-28.7 kJ/m²). A significant three-way interaction (F2,168 = 5.080, p = 0.007) was observed, with thicker 5Y-PSZ specimens showing ~45% less resistance under speed sintering. Fractographic analysis revealed intergranular fracture without delamination, confirming structural integrity. Conclusions: The 3Y-TZP layer provides superior impact resistance regardless of processing conditions, while conventional sintering is preferable for thicker 5Y-PSZ layers. These findings inform material selection and manufacturing processes for graded zirconia restorations in high-stress applications.