A document image storage system includes a control mechanism that automatically archives a document image in response to a document being produced by a peripheral device. The moving mechanism moves relatively the denture-holding table and the main body in three-dimensional coordinate directions based on grinding portion data, and the grinding tool performs grinding of the denture occlusal surface from a direction perpendicular to the occlusal surface. The semiconductor membrane layer is initially formed from a substrate of standard thickness, and all but a thin surface layer of the substrate is then etched or polished away.