The Accuracy of Large Castings

¹ Eastman Dental Dispensary, Rochester, New York, and Northwestern University Dental School, Chicago, Illinois

Two master models made of Invar were used, and castings of a gold alloy and a cobalt-chromium alloy were made. Three different investments were used with the gold-casting process. From measurement of approximately seventy castings and a statistical analysis of these data, several general conclusions about the effects of the thermal process associated with dental casting were made.

The change in shape when the sprues were removed from castings was due to a change in the distribution of residual stress. Various influences, such as sprue shape, size, and direction in relation to the dental casting, were discussed, as well as the probable effects of differing hot strength of investments and the nature of the alloys used.

The shape of the casting itself, including sprues, reservoirs, and amount left in the crucible, would seem to determine the accuracy of large castings.

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