To study the microstructures and their relationship to corrosion characteristics, seven alloys for dental castings with varying ratios of copper/silver content were each subjected to high temperature solution treatment of 1023 K and 1123 K for one hour. The corrosion examination was carried out in an environment of 3% NaCl using the anodal polarization method. Based on this study, the following results were obtained: 1. In the microstructure of the gold-silver- palladium alloy castings which varied in the quantity of their copper/silver ratios, the solutions in both heat treatments consisted of 3 phases: α₁ phase, α₂ phase, and β phase. 2. The corrosion resistance of alloys improved at 1023 K and 1123 K due to the decrease of Cu content in the a, phase and the decrease of Ag content in the α₂ phase. 3. The electric potential of the three phases in the microstructure was lowest in the α₁ phase, but increased in phases α₂ and β in that order. 4. Corrosion resistance improved when the gold in the alloy reached 20 mass % in comparison with an alloy of 12 mass% gold content. This is because the gold solution greatly increases in the α₁ phase.

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The purpose of this study was to develop a clinical procedure for a new adhesive system using a CO₂ laser. We also observed the surface of melted orthophosphate glass adhering to the sealant for dental enamel and restoration by applying the CO₂ laser. The average shear bond strength was a maximum of 3.68 MPa/3.5 W. SEM observation of the adhesive surface showed a good contact, and there was no leakage in the infiltration test. From these results, it was suggested that orthophosphate glass can be utilized as a restorative material.

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