A laboratory evaluation of detail reproduction, contact angle, and tear strength of three elastomeric impression materials

Indiana University-Purdue University Indianapolis (IUPUI)Fabrications of desirable fixed or removable dental prostheses depend upon accurate casts or dies. Recently, the most frequently used impression materials have been polyether (PE) and polyvinyl siloxane (PVS). However, both have their limitations: PVS is inherently hydrophobic, and PE is rigid. In order to take advantage of the desirable qualities of both PVS and PE impression materials, a new generation of impression material is being developed called vinyl polyether silicone (VPES, GC). The purpose of the present study was to compare the properties of hydrophilic PVS, PE, and VPES in regard to surface detail reproduction, contact angle, and tear strength. The hypotheses to be tested were: 1) VPES will show a significant superiority insurface detail reproduction compared with PVS and PE impression materials; 2) VPES will show a significant superiority in wettability compared with PVS and PE impression materials; 3) VPES will show a significant superiority in tear strength compared with PVS and PE impression materials. In order to test the surface detail reproduction, impressions were made of stainless steel dies with a parallel series of 15 different width lines on the surface and tested under dry and moist conditions. The wettability was assessed by contact angles of saturated CaSO4 aqueous solution drops on flat impression surfaces. A trouser tear test was employed to test the tear strength. The trouser-shaped specimens were prepared and tested in the Instron Universal Testing Machine. The data were analyzed by one-way ANOVA and Pearson‘s Chi square, (p < 0.05). All the materials showed better detail reproduction under the dry conditions than the moist conditions. There were no differences between the three materials in detail reproduction when impressing under either moist conditions or dry conditions. All the materials showed good wettability in the contact angle test. PVS rendered a contact angle as low as 34.19º. The contact angle of VPES was 44.84º, which was lower than 54.76º for PE. In the tear strength test, PE showed nearly two time higher tear strength than the other two impression materials. VPES showed slightly lower tear strength than PVS. The tear strength of the three materials tested in increasing order was VPES, PVS, PE. VPES showed comparable detail reproduction to PVS and PE and better wettability than PE, but showed the lowest tear strength compared with PE and PVS