Elastic Recovery of Polyether Impression Materials

Objectives: To evaluate and compare the effects of induced strain, time of straining, and straining rate on the elastic recovery of two polyether impression materials and a vinyl polysiloxane reference material. Methods: Specimens of the light and heavy-bodied types of the polyether materials P2 (P2L/H; Heraeus Kulzer) and Impregum (IML/H; 3M ESPE) and of the vinyl polysiloxane impression material Flexitime (FLC/H; Heraeus Kulzer) were loaded in a cone-plate rheometer, previously described by Joergensen (Scand J Dent Res 1976;84:175-82) with tensile strains between 16.4 and 60%, at different times after mixing, and at straining rates between 1 and 10 seconds. The resulting permanent deformation was determined from creep curves. For each material and each variable condition six specimens were tested at ambient laboratory atmosphere. Regression analyses and ANOVA (p<0.05) were used for statistical data analysis. Results: Both induced strain, time of straining, and straining rate were significantly associated with the resulting permanent deformation of all materials, except FLC when loaded in the well-set stage between 1 and 10 seconds straining rate at 37.4% induced tensile strain (p<0.001). Apart from P2 the heavy-bodied impression materials showed significantly higher secondary creep (p<0.05) than their corresponding light-bodied versions. Conclusion: Permanent deformation resulting from removal of impressions from undercut tooth areas is of clinical interest. The new polyether impression material P2 responds even on high strain and low strain rate with low permanent deformation and is in this respect a suitable alternative to conventional elastomeric impression materials.