Microwave-assisted sintering of dental porcelains

An investigation was made of hybrid microwave-assisted sintering of dental porcelains, using five commercial ceramic frits employed in the production of dental porcelains. The powders were characterized, transformed into prismatic test specimens, and subjected to conventional and microwave sintering. Microwave sintering was performed at a frequency of 2.45 GHz, using a susceptor material and in the absence of vacuum. The apparent density and apparent porosity of the sintered samples were characterized based on the Archimedes principle. They were also analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their flexural strength and microhardness were determined by the Vickers method. The powders, which showed a broad particle size distribution with a high fraction of particles of dimensions larger than 30 μm, were composed of amorphous phase and leucite particles. Microwave sintering yielded ceramic bodies whose apparent porosity (t-test, p<0.05) was the same or very similar to that of the conventionally sintered samples, while the apparent density (t-test, p<0.05) of most of the microwave sintered samples was the same or slightly lower. Although the microwave sintered samples showed larger average pore sizes (t-test, p<0.05), four of the five samples used in this study showed the same flexural strength (t-test, p<0.05) and all the ceramics under study showed the same surface microhardness (t-test, p<0.05).