The purpose of the present invention is to provide a high-expansion gypsum plaster composition which is obtained by enhancing the expansion coefficient of a general-purpose dental gypsum plaster material or the like easily and effectively without using any special material by adding an inexpensive additive even in a small amount to a level that a conventional technique has not achieved, more specifically, to provide a high-expansion gypsum plaster composition which exhibits a setting expansion coefficient that is suitably controlled so as to precisely accommodate the shrinkage of a used resin and which is useful in making a model to be used in making a "non-clasp denture" which is unproblematic in occlusion (fitness). The purpose is achieved by a process for manufacturing a high-expansion gypsum plaster composition, said process including: subjecting a powdery gypsum plaster composition material which comprises both calcined gypsum as the main component and gypsum dihydrate to dry copulverization； and thus manufacturing a gypsum composition having an enhanced setting expansion coefficient.本發明目的在於提供：未使用特殊材料而是使用廉價添加材，且即便較少添加量，仍可簡便且有效地獲得膨脹率提高至例如通用牙科用石膏材料等習知技術所無法達到程度之高膨脹石膏組成物；又，本發明目的在於提供：當製作例如無咬合(適合性)問題之「無牙鉤假牙」時所使用的複製模型情況下，將硬化膨脹率適當控制成為可以高精度因應所使用合成樹脂收縮的高膨脹石膏組成物。該目的係依照下述高膨脹石膏組成物之製造方法便可達成。該製造方法係在屬於主成分的熟石膏中，含有二水石膏而構成的粉末狀石膏組成物材料，藉由依乾式施行共粉碎，而製造經提高硬化膨脹率的石膏組成物。
