Studies on the burn-in and devitrification of calcium phosphate crystalline ceramic crowns.

Calcium phosphate crystalline ceramics (hereafter referred to as CPCC) is a glass ceramic and the so-called castable ceramic crown. Therefore, taking up CPCC as a material to be casted, adopting phosphate-bonded investment or cristobalite investment as a casting mold, with mold temperature of 400, 500, 600 and 700°C, and using centrifugal casting or air pressure casting as a casting method, 10 specimens were made respectively to the 16 different casting conditions, so that the occurrence of burn-in and devitrification could be studied. Further, the effect of devitrification on crystalization was also studied.The following results were obtained.(1) In case of adopting phosphate-bonded investment, the occurence rate of burn-in became higher as the casting temperature increased. Concering the casting methods, the burn-in occurrence rate was higher for air pressure casting than for centrifugal casting.(2) When cristobalite investment was used, the occurrence rate of burn-in was higher for air pressure casting, while as for the mold temperature, the occurrence rate was maximum at 600°C, but conversely decreased at 700°C, roughening on the casted surface became prominent.(3) The lower the mold temperature was, the lower the occurrence rate of devitrification was and the crystalline size became smaller.(4) Crystals precipitated by devitrification became responsible for deformed crystal structure in the subsuquent crystallization.