Tensile secondary creep rate analysis of a dental veneering porcelain

Abstract

Near-interface chipping of the porcelain veneer is now widely accepted as the primary failure mode of Yttria Partially Stabilised Zirconia (YPSZ) prosthesis. The origin of these failures is believed to be the complex interaction between YPSZ phase transformation, thermal expansion mismatch and other microstructural effects which induce high magnitude residual stresses within the first few microns of the interface. Recent studies have also provided evidence that these stresses, in combination with the applied sintering temperatures, are sufficient to induce tensile creep (and the associated voiding damage) within the near interface porcelain region.In order to improve understanding of this creep rate behaviour, tensile creep has been performed on representative dental feldspathic porcelain (Vitablocs® Mark II for Cerec®) at the temperatures (650–800°C in 50°C increments) and stresses (50–125MPa in 25MPa increments) typically encountered in the near interface porcelain. Limitations on porcelain sample size meant that conventional ceramic secondary creep rate testing could not be implemented in this study and therefore a new approach based on applying multiple stresses and temperatures to a single sample was developed.The four values of activation energy and stress rate exponent determined in this study were found to be consistent to within the 95% confidence intervals of each value. Average values and 95% confidence intervals for each parameter were determined to be Q=243.0±3.1kJmol−1 and n=1.32±0.08. These values compare well with published values of creep rate behaviour in silica and alumina based ceramics.The quantitative values obtained in this study form a foundation for future studies into tensile creep induced voiding in porcelain as well as facilitating the development of improved models of the YPSZ-porcelain interface. The new single sample, tensile creep experimental approach also has potential for use in ceramic tensile creep testing of samples of limited size.