Porosity in the base metal removable partial denture casting alloys relative to observable metallographic features.

A series of tensile test pieces of the dimensions stated in the American Dental Association Specification No. 14 were produce using both nickel-base and cobalt-base removable partial denture casting alloys. Normal dental casting techniques were employed. Appropriate sections from each specimen were sectioned to half of their original thicknesses, embedded in heat-and pressure-cured conducting mounts, and polished for metallurgical examination. A double electrolytic etching technique was used, employing serially two solutions, in order to maximize the amount of metallographic detail visible. The method proved particularly valuable in the case of the nickel-base alloy as it indicated the presence of considerable interdendritic segregation. The incidence of porosity was evaluated throughout all sections of the specimens and, although found to be especially prevalent in those regions where gross shrinkage effects might be expected to occur, it was also shown to have a diffuse intergranular and interdendritic distribution.