Metalographic Properties And Microhardness Of Gold-Based Dental Castings

Composition and laboratory procedures have the greatest influence on the microstructure, mechanical, and electrochemical properties of dental casts. Objectives: The aim of this study was to evaluate the metallographic properties of high gold-based dental castings, Dentor S, and low gold-based dental castings, Mid or S, used for the same fixed prostehtic indication. Material and methods: Samples were centrifugally cast in a phosphate-bonded investment and cooled at room temperature. The microstructure was analyzed and photographed with light microscope and scanning electron microscope. The grain size and the percentage porosity were evaluated. The Vickers microhardness was tested. T-test for independent samples (alpha=0.05) was used for statistical analysis. Results: Micrographs showed difference in microstructure, homogeneity and grain size. Average grain size number according to ASTM112/96 of Dentor S (7.72 +/- 0.23) was significantly greater comparing with Midor S (6.26 +/- 0.19) castings. Percentage porosity of castings was calculated from average impurities and defects, where Dentor S (0.62%+/- 0,24%) was significantly more porous than Midor S (0.49%+/- 0.19%). Vickers microhardness of Midor S castings (HV0.1=169.98 +/- 10.61) was significantly greater then those of Dentor S castings (HVO.1=157.58 +/- 15.42). Conclusion: It can be concluded that composition, under the same laboratory procedures, has a critical influence on microstructure and microhardness of conventional gold-based castings. To ensure functional and technical durability of restoration, selection of the alloy should be based on its composition and mechanical properties as on the patient's bite forces.