Effects of Gingival Retraction Paste and Subsequent Cleaning with Hydrogen Peroxide on the Polymerization of Three Elastomeric Impression Materials: An In Vitro Study

Purpose: It has been hypothesized that there are no effects of Expasyl and subsequent cleaning with hydrogen peroxide on polymerization of selected commonly used impression materials. Therefore, the aim of this study was to evaluate the effect of Expasyl paste on the polymerization of three impression materials with and without subsequent cleaning using 3% hydrogen peroxide (H₂O₂). Materials and Methods: Nine standardized stainless steel specimens were fabricated. One hundred and eighty impressions were made using 3 materials (60 each) as follows: group I: poly(vinyl siloxane) (PVS) (Virtual); group II: polyether (Monophase); group III: polyether (Impregum). Groups were subdivided into 3 categories: control without intervention (n = 20), pre-application of Expasyl and subsequent 1-minute washing with water and air-drying (n = 20), and pre-application of Expasyl and subsequent cleaning with 3% H₂O₂ for 10 seconds (n = 20). All impressions were made by one operator using auto-mixing cartridges under standardized conditions at room temperature. Evaluation of the polymerization inhibition was blindly and independently performed by three practitioners with comparable experience using a visual scale. The observation was subjectively categorized as noninhibited or inhibited. Data were tabulated and analyzed using Fisher's exact test with significance level set at p ˂ 0.05. Results: Significant differences were found between the control group and the impressions made after contamination with Expasyl (p < 0.001). Polymerization inhibition of PVS and Impregum was similar (in 85% and 90% of the specimens, respectively) when washed with water. There was a statistically significant reduction in polymerization inhibition in both upon cleaning with H₂O₂ (p < 0.001); however, polymerization inhibition occurred in 100% of Monophase specimens when contaminated with Expasyl despite the washing technique used. Conclusions: Under these in vitro conditions, it can be concluded that the remnants of Expasyl on specimens caused a significant polymerization inhibition of the 3 impression materials tested. Subsequent cleaning with 3% H₂O₂ significantly reduced this inhibitory effect on polymerization. Expasyl should not be used with Monophase polyether material.