Re´sume´of the expansion required to compensate for casting gold shrinkage

Abstract

Abstract 1. We feel that we have proof that setting expansion is effective in compensating for the gold alloy shrinkage. We realize that the shape of the wax pattern and its temperature during the setting stage of the investment determines the amount of setting expansion that is utilized. 2. Hygroscopic expansion, when taking place at 98 to 100 ° F., will compensate for the casting shrinkage; with its use the shape of the wax pattern has no influence on the amount of expansion required. Taking into consideration the influence of all the variables, we have obtained most consistent results when using the hygroscopic technique. 3. With the exception of pure gold, and some of the soft inlay gold alloys, we believe it is not necessary to vary the amount of expansion to compensate for the casting shrinkage of the different inlay gold alloys on the dental market. 4. We have not been able to fit a dental inlay casting to a steel die when the combined compensating expansion was 1.25 per cent. 5. It is our opinion that a combined compensating expansion of at least 1.50 per cent is necessary to compensate for the casting shrinkage of the available inlay gold alloys.