A simple 3-point flexural method for measuring fracture toughness of the dental porcelain to zirconia bond and other brittle bimaterial interfaces

Abstract

Purpose: Porcelain fused to zirconia prostheses are widely used, but porcelain chipping, fracture, spalling and delamination are common clinical problems. Conventional bond strength testing is inherently un- suited for studying interfacial failure by cracking in brittle materials. Instead, fracture toughness is a more meaningful parameter because it can assess the robustness of the interface when subjected to loading, but fracture mechanics approaches have only rarely been used. Our purpose was to develop a novel, sim- ple, 3-point flexural methodology and mathematical analysis to measure the fracture toughness of the porcelain to zirconia interface.
Methods: Equations were derived to estimate the fracture toughness of the bond by computing the inter- facial energy release rate for a novel simple 3-point flexural test model. The test was validated using two different configurations of layered zirconia/porcelain beams ( n = 10), approximating the dimensions of a fixed dental prosthesis, fabricated from a tetragonal polycrystalline zirconium dioxide partially stabilized with yttria and a feldspathic dental porcelain.
Results: Cracking along the bimaterial interface was produced and measured as a discrete event. Frac- ture toughness means (standard deviations) computed from the measured energy release rate, for the porcelain to zirconia interface in two different specimen configurations were 7.9 (1.3) and 5.3 (1.6) J/m 2 .
Conclusions: Equations were derived to measure interfacial fracture toughness of brittle materials using a novel simple 3-point flexural test method. The test was then validated; estimates for the fracture tough- ness for the porcelain to zirconia bond, overlapped with previously published data derived from more complex 4-point notched tests.