Metallographic characterization of four alternative alloys intended for fixed prostheses.

Four dental casting alloys intended as alternatives for type III gold alloys were studied with regard to their metallographic appearance. The structures of two low-gold and two silver-palladium alloys were evaluated in the as-cast and hardened conditions and in the condition achieved after annealing for 1 h at 100 degrees C below the solidus temperature. The microstructure was studied by light optical microscopy, scanning electron microscopy, electron microprobe analysis, and X-ray diffraction analysis. In addition, the hardness and the grain size of the alloys were determined. The presence of concentration gradients and dissimilar phases is discussed. It was concluded that to obtain the optimum properties of these alloys, strict and detailed instructions about the various heat treatments are needed.