Fracture strength of type IV and type V die stone as a function of time.

STATEMENT OF PROBLEM

During the removal of casts from the impression there is the risk of stone fracture.

PURPOSE

This study evaluated the fracture resistance of four die stone materials at different time intervals.

MATERIAL AND METHODS

Additional silicone impressions were made of a maxillary master cast. Two Type V, one Type IV die stones and one Type IV resin reinforced stone were tested. A total of 80 casts were prepared, separated, and tested on the Instron Universal Testing Machine at 1/2, 1, 12, and 24 hours to measure resistance to fracture.

RESULTS

Significant differences to fracture resistance of the different die stone materials were observed at all time intervals except at 24 hours. The data were analyzed with ANOVA at alpha = 0.005 and n = 5.

CONCLUSION

It is recommended to wait at least 12 to 24 hours when separating casts from impressions to avoid fracturing casts. Residual moisture content in a stone cast may contribute to fracture.