Gypsum-bonded Investment and Dental Precision Casting

(II) Investment for the Quick Casting Technique

抄録

Part I of this study presented a hypothesis that the thermal expansion of gypsum-bonded investment should become higher under heating conditions favorable for the formation of α-hemihydrate. The present study aimed at proving this hypothesis by simulating the rapid heating condition employed in the quick casting technique. The expansion values obtained were 1.72-1.93% after 30min in three investments, two rapid heating and one conventional types. Under a comparable measuring pressure a common laboratory measurement (5°C/min) gave significantly lower expansions of 1.32-1.36% at 700°C for the same investments (p<0.01). The shrinkage observed at 350-400°C in this measurement was not observed in the rapid heating. Realistically large molds prepared from the conventional gypsum-bonded investment need to be investigated for their potentially high thermal expansion.