Type III gold alloy complete crowns cast in a phosphate-bonded investment

A phosphate-bonded investment and a calcium sulphate-bonded investment were evaluated for the surface smoothness and marginal fit they impart to type III gold castings. The phosphate-bonded investment was used with burnout temperatures of 900 degrees F and 1,300 degrees F. The results of this study lead to the following conclusions: 1. The marginal fit with the phosphate-bonded investment method was superior to that obtained with the calcium sulphate-bonded investment. 2. Surface roughness was greater for the castings made with the phosphate-bonded investment when measured with SEM photographs and visual observation. 3. The phosphate bonded-investment increased the incidence of nodules on the surface of the castings. 4. No correlation was demonstrated between marginal fit and surface roughness or the incidence of nodules on the castings.