Tensile elastic recovery of elastomeric impression materials

Statement of problem. Currently, a standard protocol exists to measure the elastic recovery of impression materials from compressive strain; however, no protocol exists for the measurement of elastic recovery from tensile strain. Purpose. The purpose of this study was to compare elastic recovery from tensile strain test with the ISO elastic recovery test for 5 vinyl polysiloxane materials (Aquasil Ultra, Examix, Genie, Imprint 3, and StandOut) and I hybrid material (Senn). Material and methods. Specimens (n=5) were fabricated in a brass mold and loaded in tension with a crosshead speed of 300 mm/min to 50% or 100% strains. Two hours following specimen elongation, the change in length of the specimens was measured. Additional specimens (n=5) were tested in tension until failure at 200 mm/min. The maximum elongation at failure was recorded. Elastic recovery specimens (n=4) were prepared for each material following ISO standard 4823. The change in dimension of these specimens was measured following a 30% compressive strain. Group means were compared using 1-way ANOVA and Tukey-Kramer HSD test (alpha=.05). Correlation between different tests was evaluated using Pearson's correlation coefficient. Results. Vinyl polysiloxane materials of varying composition demonstrated significantly different elastic recovery, and the hybrid material demonstrated the least elastic recovery in both tests. All materials exceeded a 100% elongation before failure. Significant linear correlation was found between means of the ISO method and those of a 100% tensile strain (r(2)=0.69, P=.039), but not those of a 50% tensile strain (r(2)=0.56, P=.086). Conclusions. Elastic recovery from compressive strain can only partially predict elastic recovery from tensile strain, suggesting that elastic recovery from tensile strain is a relevant test.