Core Veneer Bond Strength of Three All-Ceramic Restorations

Methods: Standardized core discs were fabricated using a special adjustable mold according to the manufacturer's instructions then veneered with either its recommended veneer or an experimental veneer with higher TEC. Micro-bars were obtained for the microtensile bond strength test (MTBS). The data were analyzed using ANOVA [p<0.05]. Finite element analysis (FEA) was made for the test setup. Scanning electron microscopy(SEM)was carried out at the fracture surface.

Results: The core materials had a significantly stronger microtensile bond strength than the veneering materials and the layered micro-bars which were statistically comparable. Polishing core surfaces did not result in weakening core-veneer bond strength but it increased the percentage of adhesive failure mode for the Cercon® and Vita Mark II but not for the IPS Empress 2 system. Experimental veneer with higher TEC resulted in massive fractures in both the core and veneering material. FEA and SEM explained the failure mode and mechanics of fractured specimens.

Conclusions: Core-veneer bond strength is one of the weakest links of Cercon® and Vita Mark II systems and has a significant role in their success. Despite the high strength of zirconia cores, further research work is needed to improve its bond with its corresponding veneering material.