The relationship between the microstructure and hardness of a dental casting Au-Ag-Pd alloy, which was fabricated by the liquid rapid solidification (LRS) method, subjected to re-solidification with two types of cooling rate, i.e., water-quenched and air-cooled solidifications, or a solution treatment at a high temperature after those were investigated based on the β phase precipitation behavior in this study. The following conclusions were obtained from the results. 1. The water-cooled microstructure in which a specimen without the β phase was dissolved had a tessellated structure and the β phase did not precipitate during the solidification process. The β phase did not precipitate even during solution treatment at a high temperature, and the hardness decreased. However, in the case of air-cooling solidification, β phases precipitated in the solidification structure, and the hardness improved by solution treatment at a high temperature. 2. The solidified microstructure of the water-cooled alloy (the as-received specimen containing the β phase was dissolved) had a dendritic structure and the β phase was presented in the matrix. Therefore, at a dissolution temperature of 1323 K, the β phase did not melt or solidify into the matrix. Furthermore, the β phase did not melt and the hardness improved even after solution treatment at a high temperature was subsequently provided.

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Zirconium oxide ceramics have recently been applied to all-ceramic restorations in esthetic dentistry. In this study, we evaluated the effects of surface treatments (#600, Rocatec) on the bond strength of indirect restorative composite resin (Estenia C&B ES, Epricord EP, Gradia GR) to yttrium partially stabilized zirconium oxide ceramics (Y-TZP). For the shear bond strength of zirconia, there were significant differences between indirect restorative composite resin and surface treatments (p<0.01); however, there were no significant differences in interaction between them. The maximum bond strength was 11.95 MPa in GR/Rocatec, and the minimum one was 7.70 MPa in EP/#600. From the results of this study, based on the shear bond strength for zirconium oxide ceramics, it was evaluated that the use of indirect restorative composite resin (GR) and Rocatec would be improved the safety for clinical application.

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