Three-dimensional measurement of stone cast deformation. Part 2. Effects of types of impression material and mold on the dimensional stability of stone casts.

Abstract

Three different types of dies (straight, tapered and undercut) obtained using three types of impression materials (alginate, polysulfide and addition-curing silicone) were measured for height and the dimension of the diameter with a three-dimensional digitizer. Assuming that the value obtained by adding the amount of free-setting expansion of the die material to the dimension of the original represents the highest accuracy, the difference in dimension according to the types of impression material used would be as follows : 1. The die made with alginate : In the case of the straight type, both the height and diameter increased somewhat uniformly. In the case of the tapered type, the height was correct but the diameter was slightly larger, especially in the upper portion. In the case of the undercut type, the height was fairly large and the diameter was large in all portions, especially in the lower portion as though spreading had occurred.2. The die made with polysulfide : In the case of the straight type, the height was particularly large but the diameter was correct. In the case of the tapered type, the height was slightly larger, and the diameter was a little larger in the upper portion, correct in the central portion, but slightly smaller in the lower portion. In the case of the undercut type, the height was almost as large as that of the die made with alginate and the diameter was large on the whole, showing a form swollen in the middle.3. The die made with addition-curing silicone : In the case of the straight type, the height was slightly large and the diameter was correct in the upper portion but was slightly small in the lower portion. In the case of the tapered type, both the height and diameter were accurate but the diameter became slightly small in the lower portion. In the case of the undercut type, both the height and diameter were almost uniformly larger, although only slightly. However, in the case of the die made with silicone, the undercut recovery was found to be better than that of the dies made with the two other impression materials.