1983 Volume 27 Issue 2 Pages 331-355
In recent years cast plates using high-fusing alloys like cobalt-chromium alloys are being used widely in clinical work for making removable partial dentures. This has been made possible though the development of highmelting dental casting method sustaind by the development and progress of dental equipment. The author, therefore, assuming the state of the inner surface of the clasps of the cast plates made of cobalt-chromium alloys and the surface of the mucous membrane, examined how the surface roughness of the investment materials will affect the surface of the cast plates in the process of its manufacture. The author further examined how sand blasting will affect the surface roughness of the cast structures.
As a result, the author has obtained the following information:
1. Among the three types of duplicating materials, a significant difference was found between the alginate impression material and the silicone base impression material, and also between the agar-agar impression material and the silicone base impression material. The silicone base impression material showed the lowest value.
2. The effect of the duplicating materials showed a similar trend on all of the three investment materials.
3. The surface roughness of the cast structures obtained by manual casting was about the same as that of the surface of the investment material models, but with the cast structures obtained by auto casting, the effect of the penetration phenomenon was stronger than that of the duplicating operation.
4. Where the roughness was marked, sand blasting treatment reduced the roughness, but with the surface having slight roughness, it increased on the contrary.
5. In the sand blasting treatment, the surface roughness of the cast structures became almost uniform after 2 to 4 seconds of blasting, showing 12-13μm under the ten-point height roughness scale.
6. The optimum conditions in the present experiment consisted of the use of silicone base impression material as the duplicating material, manual casting and 2-4 seconds of sand blasting treatment.
