Crack Initiation Modes in Bilayered Alumina/Porcelain Disks as a Function of Core/Veneer Thickness Ratio and Supporting Substrate Stiffness

Abstract

We hypothesize that the fracture resistance of alumina core/porcelain veneer disks increases and that crack initiation shifts from veneer to core as the core/veneer thickness ratio (tc/tv) increases from 0.5/1.0 to 1.3/0.2, or as the elastic modulus of the supporting substrate (Es) to which it is resin-bonded increases from 5.1 to 226 GPa. When supported by a low-modulus substrate, disks with low tc/tv ratios exhibited cracks in the veneer and within the core, while those with high tc/tv ratios demonstrated core cracks, but not veneer cracks. None of the disks supported by Ni-Cr alloy (E = 226 GPa) exhibited core cracks. These results support the hypothesis that the crack initiation site shifts as the tc/t v ratio increases, but the increase in Es did not affect the crack initiation site. This study suggests that the tc/tv ratio is the dominant factor that controls the failure initiation site in bilayered ceramic disks.