Comparison of the effects of three sprue designs on the internal porosity in crowns cast with a silver-free high-palladium alloy.

This study tested the effect of bsprue design on internal porosity of a silver-frees high-palladium alloy. The designs evaluated consisted of: (1) a cylindrical sprue, (2) a cylindrical sprue with a reservoir, and (3) cylindrical sprue with a constriction at the point of attachment with the pattern. Ten identical complete crowns were made with each sprue design. The cast crowns were embedded in epoxy resin, sectioned, and polished. A total of six sites for each sample were analyzing computer. The mean amount of internal porosity from all analyzed sites for each sprue design was calculated as a percent site porosity per total site and differences between the experimental sites and groups tested. The analysis of variance found no significant differences among the sprues and no significant interaction, but determined a significant difference (p less than 0.05) among the sites analyzed. Tukey's studentized range test showed that the sprue contained a significantly greater percentage of porosity than any of the other sites analyzed.