Mechanical properties of 3 hydrophilic addition silicone and polyether elastomeric impression materials

Statement of problem. New "hydrophilic" elastomeric impression materials have been introduced with the goals of reducing marginal voids and distortion in the impressions and improving the quality of gypsum dies, but there are insufficient data on the mechanical properties of these materials. Purpose. Mechanical properties, including elastic recovery, strain in compression, tear energy, and tensile strength of 3 hydrophilic impression materials with low and high consistencies were compared. Material and methods. Two addition silicone impression brands (Imprint II, 3M ESPE; Flexitime, Heraeus Kulzer) and a polyether brand (Impregum, 3M ESPE) were studied. Two consistencies of each material (light-body and heavy-body) were investigated. Elastic recovery (%) and strain in compression (%) were tested according to ISO 4823; tear energy (J/m(2)) and tensile strength (MPa) were tested following Webber and Ryge's method and ASTM D412 (Test Method A), respectively. Five specimens were made for each group for a total of 24 groups and 120 specimens. Results were analyzed by 2-way analysis of variance, and Fisher's protected least significance difference intervals were calculated (alpha=.05). Correlation analysis was used to evaluate the relationships among properties. Results. P values were smaller than .0001 for material, consistency, and interaction for strain in compression, tear energy, and tensile strength. For elastic recovery, P values were smaller than .0001 for material and the interaction between material and consistency, but equal to .4150 for consistency. Strain in compression correlated with other mechanical properties (P<.05), but tensile strength and tear resistance were not correlated. Conclusions. in general, new "soft" polyether impression materials had higher strain in compression and lower tensile strength compared to new "hydrophilic" addition silicone materials. Heavy-body materials had higher tear properties and tensile strength than light-body materials. Strain in compression was correlated with elastic recovery, tear energy, and tensile strength. Tear resistance and tensile strength were not correlated.