An electron microscopy study of sintering in three dental porcelains

In the manufacture of yttria partially stabilised zirconia dental prostheses, layers of porcelain veneer are sintered onto zirconia copings in order to reduce surface hardness and to produce an aesthetically pleasing finish. The stress of this interfacial bond and of the near-interface porcelain layers is crucial for reducing the likelihood of chipping during use. An improved understanding of the sintering behavior and the resulting microstructure is therefore required to ensure good prosthesis performance. In this study we use scanning electron microscopy in combination with energy dispersive spectroscopy mapping to examine the impact of vacuum sintering on the microstructure and elemental distribution of three types IPS e.max® Ceram dental porcelain (Incisal, BI shade and C4 shade) over 400 x 400 pm2 regions. It was found that the powder samples showed distinct differences in the average grain size (7 - 16 pm), maximum grain size (12 - 33 pm) and elemental composition prior to sintering. Following the application of the recommended sintering regimes, clear differences could be observed between the three samples. The Incisal porcelain demonstrated a uniform surface with limited numbers of grains and no evidence for porosity. In contrast, large numbers of sodium, aluminum and calcium rich grains were observed on the surface of the shaded porcelains, along with clear evidence of voiding.".