[Comparative study of the capacity of elastomers in reproduction and transmission of details to gypsum models].

The authors studied the ability of three elastomeric impression materials in reproducing and transmitting three grooves, engraved in the polished surface of a stainless steel model, to gypsum models. The grooves were 17, 21 and 25 micrometers wide, and the fails in reproducing, as well as in transmitting the minor details to gypsum, were also investigated as to the effects of gypsum particle size, proportional relation water/powder and plasticity of the mixture. The three elastomeric impression materials used were a polysulfide, a silicone and a polyether, and the six gypsum products were two improved stones type IV, two dental stones type III and two dental plasters type II. Scores 3, 2 and 1 were attributed respectively to the 17, 21 and 25 micrometers grooves reproduced in the molds, as well to the same grooves transmitted to the gypsum models. The results showed that all the impression materials tested were able to reproduce in the molds all the three grooves present in the steel model. Nevertheless, when gypsum models were examined, it was verified that the grooves so well reproduced in the molds were neither equally nor uniformely registered in the respective models, the best results being achieved by the polysulfide and the silicone, an the worst by polyether, As to the gypsum products, the type II gypsum presented the most unfavorable results.