Shear strength of core-veneer interface in bi-layered ceramics

Abstract

Statement of problem Delamination of veneering porcelain from underlying ceramic substrates has been reported for all-ceramic restorations. Whether this phenomenon is an inherent weakness of the veneering porcelain due to a weak interface between the veneering and the core porcelains, or merely a fracture through the veneering porcelain itself, has not been explored. Purpose The purpose of this study was to investigate the strength of the substructure and veneering porcelain interface in all-ceramic systems. Methods The all-ceramic systems tested with their respective veneering porcelains were IPS-Empress2 with Eris (IE), Procera AllCeram with AllCeram (PA), Procera AllZircon with CZR (PZ), and DC-Zircon with Vita D (DC). The veneering porcelain recommended by the manufacturer for each material was fired to the ceramic core. A metal ceramic (MC) combination was tested as a control group. Sixty specimens, 12 for each system and control, were made from 1 master die. A cylinder of veneering porcelain 2.4 mm in diameter was applied using a specially designed aluminum split mold. After firing, the specimens were placed in a mounting jig and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.50 mm/min until failure. Average shear strengths (MPa) were analyzed with a 1-way analysis of variance and the Tukey test (α=.05). The failed specimens were examined microscopically at original magnification ×20 to classify the mode of failure as cohesive in the core, cohesive in the veneer, or adhesive at the interface. Results The mean shear strengths (±SD) in MPa were MC control 30.16 ± 5.88; IE bonded to Eris 30.86 ± 6.47; PZ bonded to CZR 28.03 ± 5.03; DC bonded to Vita D 27.90 ± 4.79; and PA bonded to AllCeram 22.40 ± 2.40. IE, PZ, and DC were not significantly different from the MC control. Microscopic examination showed that adhesive failure, or complete delamination, did not occur between the compatible ceramic core and veneering materials. Failure primarily occurred near the interface with residual veneering porcelain remaining on the core. IE with Eris exhibited cohesive failure in both the core and the veneer. Conclusion The bond strengths of 3 of the tested all-ceramic materials (IE, PZ, and DC) were not significantly different from the control (MC) group.