Gypsum-bonded Investment and Dental Precision Casting (II) Investment for the Quick Casting Technique

概要

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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 30 min in three investments, two rapid heating and one conventional types. Under a comparable measuring pressure a common laboratory measurement (5℃/min) gave significantly lower expansions of 1.32-1.36% at 700℃ for the same investments (p<0.01). The shrinkage observed at 350-400℃ 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.
日本歯科理工学会の論文