PURPOSE: This study investigates the modulus of elasticity, yield strength, the strain at yield point, and the tear energy of nine elastomeric impression materials. MATERIALS AND METHODS: The values of the first three variables were computed from a tensile load test of 10 dumbbell-shaped specimens of each impression material. Tear energy was calculated from the results of a standard trousers tear test on 10 specimens of each impression material. RESULTS: A general descending order of modulus of elasticity (rigidity) follows: poly(vinyl siloxane) putty > polyether > polysulfides and the poly(vinyl siloxane) tray and syringeable materials. The descending order of yield strength was: poly(vinyl siloxane) putty > polyether and most poly(vinyl siloxane) tray and syringeable materials > one poly(vinyl siloxane) and the two polysulfides. The general descending order in strain at yield point (strain tolerance) was: two poly(vinyl siloxane) syringeable materials > four poly(vinyl siloxane) materials of various viscosities > polyether and the two polysulfides. Tear energy followed a general descending order of: polysulfides > polyether > poly(vinyl siloxane). CONCLUSION: The difficulty of removing impressions made of the putty or the polyether, and the increased risk of die breakage could be associated with the higher rigidity of these materials. The high strain tolerance of the poly(vinyl siloxane) impression materials allows their removal without distortion from appreciable tissue undercuts. The high tear energy of polysulfides indicates their superiority over other impression materials in their resistance to tear in thin sections.
PURPOSE: This study investigates the modulus of elasticity, yield strength, the strain at yield point, and the tear energy of nine elastomeric impression materials. MATERIALS AND METHODS: The values of the first three variables were computed from a tensile load test of 10 dumbbell-shaped specimens of each impression material. Tear energy was calculated from the results of a standard trousers tear test on 10 specimens of each impression material. RESULTS: A general descending order of modulus of elasticity (rigidity) follows: poly(vinyl siloxane) putty > polyether > polysulfides and the poly(vinyl siloxane) tray and syringeable materials. The descending order of yield strength was: poly(vinyl siloxane) putty > polyether and most poly(vinyl siloxane) tray and syringeable materials > one poly(vinyl siloxane) and the two polysulfides. The general descending order in strain at yield point (strain tolerance) was: two poly(vinyl siloxane) syringeable materials > four poly(vinyl siloxane) materials of various viscosities > polyether and the two polysulfides. Tear energy followed a general descending order of: polysulfides > polyether > poly(vinyl siloxane). CONCLUSION: The difficulty of removing impressions made of the putty or the polyether, and the increased risk of die breakage could be associated with the higher rigidity of these materials. The high strain tolerance of the poly(vinyl siloxane) impression materials allows their removal without distortion from appreciable tissue undercuts. The high tear energy of polysulfides indicates their superiority over other impression materials in their resistance to tear in thin sections.