Objectives: High temperature properties are important for fit and deformation of casts. This study was to investigate thermal expansion percentage, coefficients of thermal expansion and high temperature strengths of dental cast Au-Ag-Pd alloy up to the liquidus. Microstructure, solidification rate and its effects on microstructure in solid/liquid mixture phase were also studied. Methods: Au-Ag-Pd alloy -S12-(Ishifuku, Japan) was used. Thermal expansion and high temperature strength were measured with Thermo-Mechanical Analyzer TMA50 (Shimadzu, Japan) in N₂ gas environment. Microstructures of solid/liquid mixed phase was obtained by water-quenching from S+L phase. Results: It was found that solidus and liquidus points of S12 alloy were 83.8±2.5°C and 957.7±1.5°C, measured at 696Pa pressure. The melting expansion percentage was 0.932±0.058%. This melting expansion was sustained to 0.106±0.04%(915°C) under the measuring pressure of 1,392Pa, and furthermore the expansion cannot be measured at pressure of 2,089Pa. The microstructure of solid/liquid phase quenched from 860°C showed normal structure, but it changed to fine granular structure when quenched from 885°C. By increasing the quenching temperature, the grain size became coarser. With 960°C structure, fine structure of liquid phase and granular solid phase were completely separated. On the other hand, when the alloy was cooled slowly from 1,000°C, it revealed a huge dendritic structure. It was also found that all measured alloys were covered with oxide film which might have supported the pressure for the thermal expansion measurements. Conclusions: It was concluded that Au-Ag-Pd alloy S12 can be easily deformed at very low stress and solidification shrinkage did not show adverse effects on fit of casts.

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