Status report on low-gold-content alloys for fixed prostheses. Council on Dental Materials, Instruments, and Equipment

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.

Castability of crown and bridge alloys

A special saucer-shaped wax pattern was designed to evaluate the castability of five casting machines and four casting alloys. The casting machines used included one broken arm unit, one induction unit, one resistance unit, and two vacuum air pressure units. The alloys included one base metal alloy, two high-fusing noble metal alloys, and one type III gold alloy. Results of analysis of variance showed that at the 95% confidence level there was a significant difference among casting machines and alloys, the casting machines had a stronger effect on castability. No attempt was made to evaluate the fit quality of the castings with regard to surface roughness or porosity.

Dental casting alloys with a low content of noble metals: physical properties

Several physical properties such as strength (UTS and fracture and proof stress), modulus of elasticity, strain (elastic and plastic elongation), hardness, and hardening ability were determined for five low-gold alloys and two conventional gold casting alloys (types III and IV). The composition and the structure (pores and defects) of the cast tensile test specimens were also studied. The results showed that alloys with a low content of noble metals could have properties comparable to those of the traditional types III and IV dental gold casting alloys. A marked difference was seen in the plastic elongation (ductility). A great number of defects (pores and oxide inclusions) were also observed, especially in the specimens with a high content of both palladium and silver.