The mechanical properties of bilayered all-ceramic materials

Objectives: All-ceramic crowns are the optimal restorations for teeth defects. Procera all-ceramic crowns (Nobel Biocare) are composed of a coping of densely pure alumina or Y-TZP with dental porcelain. The aim of this study was to investigate the mechanical properties of Procera Allceram and Allzircon all-ceramic materials. Methods: The flexural strengths of those materials were compared and the fracture mode and fracture origin of these bilayered all-ceramic materials were identified. The effects of the core/dentin thickness ratio on bending strength were tested by 3-point bending test with core layer in tension, and the fracture section was examined by optical and scanning electron microscopy. Furthermore, Finite-element-analysis was employed for examination and comparison the fracture mechanism and failure process of all-ceramic bilayered specimens in 3-point bending test. Results: The flexural strength of Procera Allzircon core ceramics (1155.20MPa) and was higher than that of Procera Allceram core ceramics (511.60Mpa, P<0.01). The flexural strength of Procera Allceram bilayered specimen was 172.29Mpa in core/dentin thickness ratio 1:1 and 204.43MPa in core/dentin thickness ratio 2:1, no statistically significant deference (P<0.05). The flexural strength of Procera Allzircon bilayered specimen was 577.05Mpa in core/dentin thickness ratio 1:1 and 637.63MPa in core/dentin thickness ratio 2:1, having no statistically significant deference (P<0.05). ANOVA showed statistically significant differences between Procera Allceram and Allzircon bilayered test groups (P<0.05). Delamination was observed in 75% Procera Allceram bilayered specimens and 100% Procera Allzircon bilayered specimens. The fracture l began with core surface in Procera Allceram bilayered model, and both core surface and interface in Procera Allceram bilayered model. Conclusion: The flexural strength of core ceramics was declined after fired of porcelain; the fracture modes and origins were dependent upon the properties of all-ceramic materials. The interface of Procera Allzircon bilayered specimens was weak.