Abstract
Surface defects of cast Ni-Cr crowns were studied using various casting machines.The following conclusions were obtained;
1)The defective castings with surface roughness were formed, when a gypsum-bonded investment was used.
2)The concavity on the inner surface of cast crown occurred at low mold temperature or in short holding time, when a centrifugal casting machine and a phosphatebonded investment were used.
3)No concavity on the inner surface occurred in spite of low mold temperature or short holding time, when a pressure casting machine and a phosphate-bonded investment were used.
4)In another pressure casting machine, the air in the mold was vacuumed and then the whole surface of cast ring was pressed by Argon gas.No concavity on inner surface and large surface concavity on outer surface occurred, when this casting machine and a phosphate-bonded investment were used.
