Pertinent Data on Some Physical Properties of Different Investments used in the Casting of Gold Alloys

Abstract

Fineness, time of setting, compressive strength, linear thermal expansion, hygroscopic expansion, normal setting expansion, and surface defects of alloy castings were determined using casting investments of three types thermal inlay, hygroscopic inlay, and thermal partial denture. The use of the normal setting expansion combined with either the hygroscopic or thermal expansion to compensate for the shrinkage of casting gold alloys is discussed.
The values for significant properties of some commercial casting investments, along with the corresponding requirements of American Dental Association Specification No. 2 for Casting Investment for Dental Gold Alloy, are presented. The setting times of all the investments were in the lower or middle third of the 5 to 25 minute range permitted by the specification. Compressive strengths of most of the investments were 1¹/₂ to 2¹/₂ times the minimum specification value. Setting expansion in air was generally near the specified maximum while setting expansion in water was near or below the specified minimum.