Role of investment interaction layer on strength and toughness of ceramic laminates

Objectives: The aim of this study was to test the hypothesis that the interaction of a core ceramic with investment material can significantly reduce the flexural strength and the fracture toughness of core/veneer ceramic laminates. Methods: Ceramic composites were prepared from experimental core and experimental veneer and Empress 2 core and Empress 2 veneer ceramics. Four divesting techniques were used for each bilayer ceramic group. Core surfaces were etched with 1% HF solution for 15 or 30 min and grit blasted with 100 μm Al2O3 particles for 15 or 30 s. The effect of treatment on strength was analyzed statistically by means of two-way ANOVA. A linear regression graph was made for each group to analyze the relationship between flexural strength and the dimensions of critical cracks. Results: The four surface divesting treatments produced no significant differences (p>0.05) between the mean flexural strengths and the mean fracture toughnesses. However, groups with different core/veneer combinations showed statistically significant differences (p≤0.05) between the mean flexural strengths and between the mean fracture toughnesses. The Empress 2 core/experimental veneer combination exhibited the greatest fracture toughness values. The Empress 2 core/Empress 2 veneer combination exhibited the lowest mean fracture toughness and lowest mean flexural strength. Significance: The investment interaction layer does not have a significant effect on the flexural strength and fracture toughness of the bilayer ceramic laminates for interfaces that are coherent and well bonded. However, the core/veneer combination of materials does affect the strength of bilayer ceramic laminates. The existence of global residual stress is the most likely reason for the observed strength increases.