A comparative transmission electron microscopy, energy dispersive x-ray spectroscopy and spatially resolved micropillar compression study of the yttria partially stabilised zirconia - porcelain interface in dental prosthesis

Recent studies into the origins of failure of yttria partially stabilised zirconia–porcelain veneered prosthesis have revealed the importance of micro-to-nano scale characterisation of this interface zone. Current understanding suggests that the heat treatment, residual stresses and varying microstructure at this location may contribute to near-interface porcelain chipping. In this study the chemical, microstructural and mechanical property variation across the interfacial zone has been characterised at two differing length scales and using three independent techniques; energy dispersive X-ray spectroscopy, transmission electron microscopy and micropillar compression. Energy dispersive X-ray spectroscopy mapping of the near-interface region revealed, for the first time, that the diffusional lengths of twelve principal elements are limited to within 2–6μm of the interface. This study also revealed that 0.2–2μm diameter zirconia grains had become detached from the bulk and were embedded in the near-interface porcelain. Transmission electron microscopy analysis demonstrated the presence of nanoscale spherical features, indicative of tensile creep induced voiding, within the first 0.4–1.5μm from the interface. Within zirconia, variations in grain size and atomistic structure were also observed within the 3μm closest to the interface. Micropillar compression was performed over a 100μm range on either side of the interface at the spatial resolution of 5μm. This revealed an increase in zirconia and porcelain loading modulus at close proximities (