Role of substrate material in failure of crown-like layer structures.

The role of substrate modulus on critical loads to initiate and propagate radial cracks to failure in curved brittle glass shells on compliant polymeric substrates is investigated. Flat glass disks are used to drive the crack system. This configuration is representative of dental crown structures on dentin support in occlusal contact. Specimens are fabricated by truncating glass tubes and filling with epoxy-based substrate materials, with or without alumina filler for modulus control. Moduli ranging from 3 to 15 GPa are produced in this way. Critical loads for both initiation and propagation to failure increase monotonically with substrate modulus, by a factor of two over the data range. Fracture mechanics relations provide a fit to the data, within the scatter bands. Finite element analysis is used to determine stress distributions pertinent to the observed fracture modes. It is suggested that stiffer substrate materials offer potential for improved crown lifetime in dental practice.