Materials Design of Ceramic Based Layer Structures for Crowns
Brian R. Lawn, Y N. Deng, Isabel K. Lloyd, E D. Rekow, Victoria Thompson
Explicit fracture mechanics relations for the onset of critical damage in crown-like ceramic layers on soft polymeric substrates subjected to contacts loads are presented. Damage modes include cone cracking and quasiplasticity at the top surfaces, and (comparatively deleterious) radial cracking at the lower (inner) surfaces. Critical load experiments using spherical indenters on flat layers of selected dental ceramics bonded to polycarbonate bases confirm the validity of the fracture mechanics relations. A case study on a monolithic crown ceramic (Dicor) on dentin is used to demonstrate how these relations may be used to provide simple a priori predictions of failure in any given ceramic/substrate bilayer, given essential geometrical variables (layer thickness, contact radius) and material parameters (modulus, strength, toughness, hardness).