Abstract
The problem of the concavity, which occurred on the corner of the inner surface of cast crown, was studied using a K metal under various casting conditions.
1)The incomplete castings and the concavity were eliminated for thick sprue, high mold temperature and many turns of the spring, in the case of a gypsum-bonded investment and centrifugal casting.
2)In the case of a phosphate-bonded investment and centrifugal casting, the concavity was eliminated at higher mold temperature, than in above-mentioned case.
3)No concavity occurred in pressure casting (air pressure:4kg/cm2, pressing time: 30 sec), in spite of a phosphate-bonded investment and low mold temperature.
4)The incomplete castings and the concavity occurred for a short pressing time in pressure casting.
