Correlation between the degree of deformation of the stone die and the amount of the master die undercut. Part 1. Single tooth die.

In order to investigate the deformation the stone die depending on the amount of undercut, 5 kinds of undercut master dies were used to take impressions using 3 kinds of impression materials (addition type silicone rubber, polysulfide rubber, alginate). The stone dies were measured for dimensional changes in shape as projected to a two-dimensional plane by means of a newly devised apparatus. The results showed that deformation of the stone dies increased, in general, in proportion to the amount of undercut of the master die. The stone dies obtained from addition type silicone rubber impression material tend to be less deformed. In the case of the polysulfide rubber impression, the deformation was very small in stone dies in the case of non-undercut master dies, but it was very large in the case of undercut master dies. The alginate impression materials gave results with wider variations.