Abstract
The objective of this study was to clarify the casting accuracy of the upper and lower metal frame made by using three kinds of investments.
The results obtained were summarized as follows.
1. The difference between the master casts and the frameworks showed that both phosphatebonded investments with chromium-cobalt alloy, and plaster investments with nickel-chromium alloy were better than the other two: i. e., plaster investment with silver-palladium-gold alloy, and ethyl silicate investment with chromium-cobalt alloy.
2. Dimensional changes in each part of the metal frames showed that metal frames with either phosphate-bonded investments or with ethyl silicate investments produced shrinkage.
3. All four kinds of metal alloy showed shrinkage when made using ethyl silicate investment.
4. The following two experiments were carried out in order to reduce shrinkage. The first experiment was done by using casting ring liners. The result showed that the shrinkage was greater compared to using phosphate-bonded investments.
5. The second one was done by using gypsum impressed and expanded. This experiment showed that the percentage of shrinkage of metal frames using gypsum was almost the same as that of using phosphate-bonded investments.
This method may prove to be the most effective in solving the shrinkage problem.
