Effect of the setting expansion of dental stone upon the die precision.

The present investigation has shown that the setting expansion of two dental stones when measured according to the ADA Specification No. 25, was lower than the expansion determined by a dial gauge method. The values from this latter test and the percentage deviation of the diameter of full crown stone dies (produced in individual silicone impressions) from the base diameter of the original preparation were identical. A reduction of the effective expansion to a value of 0.05% or less is desirable and proved possible for the stone materials studied without altering other important properties.