Effect of casting atmosphere on the quality of Ti-crowns.

Ti has a strong affinity to elements like O, N, and C. During melting a non-reacting crucible and vacuum and/or Ar-gas protection therefore have to be used. If the impurity content becomes too high, the material turns hard and brittle. In the present work vacuum/Ar-pressure casting of crowns has been carried out at different air pressure levels. Recording of hardness on cross-sections of the castings and the degree of mold filling show that an air pressure level less than 1 torr in the melting chamber and less than 10 torr in the mold chamber is sufficient to obtain sound castings of a small size like a crown.

A binary dental gold-cobalt alloy of eutectic composition.

A new dental gold alloy was investigated for the casting of prosthetic restorations. The binary alloy is composed of 10 weight-percent Co and 90 wt% Au. Studies of the structure of the alloy revealed a rod-eutectic structure with Co rods in Au matrix. By special heat treatment (solution treatment and precipitation treatment) the hardness was increased up to 280 Hv. The hardening effect caused by Co atom groups in the Au matrix was studied by transmission microscopy. Casting experiments were performed using conventional dental casting procedures. Metallographic studies revealed no Co rods in the surface layer of the castings after the heat treatment.