Study of the physical properties of type IV gypsum, resin-containing, and epoxy die materials.

STATEMENT OF PROBLEM Little published information is available comparing the properties of recently developed resin-modified gypsum and epoxy resin die materials, which are claimed to be superior to conventional type IV gypsum die materials. PURPOSE This study compared the properties of 3 new die materials and 2 conventional type IV gypsum products. METHODS AND MATERIAL The linear dimensional change, detail reproduction, surface hardness, abrasion resistance, and transverse strength of 2 recently introduced, resin-modified gypsum die materials (Resinrock and Milestone), a new epoxy resin die material (Epoxy-Die), and 2 conventional type IV gypsum die materials (Silky-Rock and Die-Stone) were studied. RESULTS All gypsum products expanded, whereas the epoxy resin material contracted during setting. The epoxy resin exhibited much better detail reproduction, abrasion resistance, and transverse strength than the gypsum materials, which were similar in these properties. A conventional type IV gypsum exhibited the highest surface hardness, whereas the epoxy resin had the lowest value. CONCLUSION The resin-modified gypsum products were not significantly superior to the conventional type IV gypsum die materials. In general, the epoxy resin exhibited the best properties of the materials studied; however, its setting shrinkage may necessitate alterations in technique to achieve well-adapted castings.