[Dimensional change and deformation on stone dies for full cast crowns. Differences according to impression methods...

In order to reconfirm the efficiency of an individual tooth tray, an apparatus and method were developed for measuring dimensional changes and observing over all deformation on a stone die for a full cast crown. The stone dies, which were made by combination impression methods I, II and double impression (individual tooth tray use) with vinyl silicone impression materials, were measured and compared. The results were as follows: 1. It made no difference what kind of vinyl silicone impression materials were used. 2. As to the dimensional changes: for combination impression method I, irregular results were found for the stone dies with the differences between +1 standard deviation (SD) and -1 SD being large. The variations of the other two methods were quite small, indicating that the stone dies were made accurately. 3. Observing to magnified images with the naked eye, there were no clear differences between the three methods on the marginal parts, but at the top corners of the stone dies there were good results with the double impression method. 4. It was possible to grasp easily the general aspect of dimensional changes in the stone dies using this newly developed measuring method.