Shear bond strength of bi-layered all ceramics systems with finite element and acoustic emission analysis

Success of all-ceramic dental restorations depends on the cohesive strength of the strong ceramic core, the esthetic veneer and the bonding of their interface. Shear bond strength and failure modes of commercially available all-ceramics systems (IPS e.max Ceram/Press and IPS e.max Ceram/Katana) with adhesively luted experimental ceramic was investigated in the study. The maximum principal stresses (MPS) in finite element analysis and the amplitude intensities during acoustic emission analysis (AE) were further correlated with their failure modes during shear bond test. Shear bond strength between the core-veneer specimens were tested with a universal testing machine at a cross-head speed of 1 mm/min with acoustic emission sensors to investigate fracture mode. Three dimensional geometric models were built to simulate shear bond test. Kruskal Wallis and Mann Whitney post hoc test were used to compare the shear bond strength and AE amplitudes between the groups. Median and interquartile ranges of shear bond strength in glass-ceramic systems were 26 MPa (10.74) and in zirconia, was 22 MPa (8.5) respectively. Cohesive core fractures in glass-ceramics and mixed mode/adhesive fractures were observed in zirconia and experimental ceramic. MPS values in glass-ceramic and zirconia groups were comparable. Statistically significant differences between initial, final fracture loads and AE amplitudes were seen within the ceramic groups. Fracture modes in glass-ceramic core-veneers suggest a strong core-veneer bonding than in zirconia. Finite element and acoustic emission analysis can be explored to predict the failure modes of bi-layered ceramics.