Veneer Versus Core Failure in Adhesively Bonded All-Ceramic Crown Layers
James J. Lee, Jae-Young Kwon, Sanjit Bhowmick, Isabel K. Lloyd
Joining a brittle veneer to a strong ceramic core with an adhesive offers benefits over current fabrication methods for all-ceramic crowns. However, such joining introduces the possibility of subsurface radial cracking in the veneer as well as in the core, from enhanced flexure in occlusal loading. Critical conditions to initiate veneer and core fractures were investigated in model crown-like layer structures consisting of glass veneers epoxy-joined onto alumina or zirconia cores, all bonded to a dentin-like polymer base. The results showed a competition between critical loads for radial crack initiation in the veneers and cores. Core radial cracking was relatively independent of adhesive thickness. Zirconia was much less susceptible to fracture than alumina, attributable to a relatively high strength and low modulus. Veneer cracking did depend on adhesive thickness. However, no significant differences in critical loads for veneer cracking were observed for specimens containing alumina or zirconia cores.