Abstract
To investigate the casting shrinkage of higher-melting dental alloys, the densities of pure nickel, the system of Ni-Cr and Ni-Cr-M (M: Si, Cu, Mo and Mn), and commercial dental casting Ni-Cr alloys were measured at temperatures ranging from room temperature to about 1, 700℃ by using an apparatus which was based on the sessile drop method. Thermal and solidifying shrinkage of dental Ni-Cr alloys were calculated from these density changes.
The voluminal shrinkage during solidification of pure nickel was 4.91 vol% and that of Ni-Cr alloys in the range of 3.96 to 5.79 vol%, which were independent of the chromium contents. The shrinkage of Ni-Cr-M alloys were from 2.70 to 5.46 vol%, and that of the Ni-Cr-Si alloys decreased with the increasing amount of silicon. The shrinkage of commercial dental casting Ni-Cr alloys were from 2.59 to 4.69 vol%.The vacancies in the cast caused by the crystal growth during solidification have direct effects upon the solidifying shrinkage. Thus the growth of dendritic structure causes many microporosities in the cast and it results in the small shrinkage. The linear shrinkage of dental Ni-Cr alloys from solidus temperature to room temperature were from 2.07 to 2.78%, which were clearly larger than those of dental gold alloys.
