Tensile and bond strength of putty-wash elastomeric impression materials

Abstract

n dimensional instability of elastomeric impression materials has been the subject of numerous reports.‘” The instability of these materials is a function of a number of variables, including evaporation of byproducts formed during polymerization, ability to bond to a custom tray, thickness of material within the tray, rigidity of the tray, polymerization shrinkage, and viscosity of the elastomer (light body versus heavy body). When these materials are bonded to an acrylic resin custom tray, their dimensional stability has been shown to be increased significantly.4 Usually, low-viscosity elastomers (light body, syringe, or wash material) are polymerized against high-viscosity elastomers (heavy body or tray materials), which are bonded with adhesive to acrylic resin custom trays. Cherim-AmkieS showed that lowviscosity elastomers shrink less when polymerized against high-viscosity elastomers bonded to a polymethyl methacrylate substrate-a custom tray. Davis et a1.6 found the clinical effectiveness of tray adhesives to be related to their drying time and elastomer type. Polyether elastomers were found to exhibit the greatest bond strength to trays, and polysulfide elastomers adhered better than silicone elastomers. To simulate custom trays, high-viscosity elastomers (putty materials) are used in stock trays, usually without an adhesive. An internal coating of lowviscosity material provides detail. Putty materials typically exhibit good dimensional stability because of a low polymer-to-filler ratio. Their dimensional stability is related to high polymer concentration, particularly in regard to by-product formation and polymerization shrinkage. Therefore, these materials shrink less than lower viscosity materials. The dimensional stability of the putty-wash combination materials would be expected to be related to the factors described as well as to the quality of the bond