A modified technique to determine the tear energy of impression materials

A modified method to determine tear energy of impression materials is described. Trousers-shaped specimens were prepared between two platens. They are different from those used before in that a V-shaped line is created so as to guide tear growth, and the thickness gradually increases, then remains constant and, ultimately, decreases instantaneously. The specimens were tested at ten different rates between 0.2 and 50 cm/min. lambda can be computed from the force-time diagram. Six different materials were tested: two condensation silicones, Xantopren regular (Bayer, FRG) and Xantopren light; a polyvinylsiloxane, Reprosil regular (DeTrey, Switzerland); a polysulphide Coeflex regular (Coe, USA); a polyether, Impregum (Espe, FRG); and an alginate, Cavex, Fast Set, Dust Free (Keur & Sneltjes, The Netherlands). Tear strength (in kJ/m2) variations at rates between 0.2 and 50 cm/min are as follows: Xantopren regular, 0.37-0.64; Xantopren light, 0.29-0.46; Coeflex, 1.10-5.29; Reprosil, 0.66-1.07; Impregum, 0.62-1.04; Cavex, 0.22-0.37. These values are consistent with those reported before. It might be concluded that the new test method gives reliable tear energy values.