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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.

This study evaluated various techniques for forming ceramic margins on metal-ceramic restorations. Marginal openings were measured using a scanning electron microscope on replicas derived from elastomeric impressions. Ceramic margins formed with a platinum foil backing showed significantly better fit than those formed with direct-lift techniques. With the platinum foil method these ceramic margins displayed a marginal fit comparable to that obtained with cast metal margins.