Dimensional accuracy and surface detail reproduction of two hydrophilic vinyl polysiloxane impression materials tested under dry, moist, and wet conditions.
STATEMENT OF PROBLEM: A major limitation of vinyl polysiloxane (VPS) impression materials is their hydrophobicity. There are 2 aspects to this problem, the wettability of the polymerized impression by dental gypsum materials and the ability of the unpolymerized material to wet intraoral tissues. To address this problem, manufacturers have added surfactants and labeled the new products as hydrophilic vinyl polysiloxane. PURPOSE: The purpose of this investigation was to compare dimensional accuracy and surface detail reproduction of 2 hydrophilic VPS impression materials, when used under dry, moist, and wet conditions. MATERIALS AND METHODS: A total of 102 impressions were made of stainless steel metal dies similar to those described in American Dental Association (ADA) specification 19. The dies had 2 vertical and 3 horizontal lines inscribed on their superior surfaces. Impressions were made under dry, moist, and wet conditions. Dimensional accuracy was measured by comparing the average length of the middle horizontal line in each impression to the same line on the metal die, by use of a measuring microscope with an accuracy of 0.001 mm. A 2-way analysis of variance and least significant difference post hoc test were used to compare mean dimensional changes (alpha=.05). Surface detail reproduction was evaluated in 2 ways: (1) by use of criteria similar to ADA specification 19 for detail reproduction, continuous replication of at least 2 of the 3 horizontal lines, and (2) by use of a method developed for this study that categorized the impressions as satisfactory or unsatisfactory based on their surface characteristics: presence of pits, voids, or roughness. Pearson chi(2) (alpha=.05) was used to compare detail reproduction results. RESULTS: Conditions (dry, moist, and wet) did not cause significant adverse effects on the dimensional accuracy of either material. The mean dimensional change and SD were 0.005% +/- 0.002% or less. With both surface detail analyses, dry, moist, and wet conditions had a significant effect on the detail reproduction of both materials (P<.05). Only under dry conditions did both impression materials continuously replicate at least 2 of the 3 horizontal lines 100% of the time. Under moist conditions, 82% of the Aquasil impressions and 100% of the Reprosil impressions were judged satisfactory, while under wet conditions, only 47% Aquasil and 11% Reprosil impressions were satisfactory. With the additional surface detail characterization, only under dry conditions were impressions produced with clinically acceptable surface quality (Aquasil 77% and Reprosil 100% satisfactory). CONCLUSIONS: Dimensional accuracy of both materials tested was well within ADA standards. Best surface detail results were obtained only under dry conditions for both materials.