Resin pattern material with low polymerization shrinkage.

PURPOSE: The purpose of this study was to develop a material with low polymerization shrinkage for resin patterns to improve the fit of a long superstructure to implants. MATERIALS AND METHODS: Three different chemical substances were added at 1, 2, 3, 5, 10, and 20 wt% to the liquid component of a self-curing acrylic resin. Specimens for measuring shrinkage during self curing were prepared in a metal mold that took the form of a conical cavity with slightly tapered walls. The specimens were prepared using three different methods: (1) a brush-on technique, (2) an injection method, and (3) an injection-press method. The percentage of linear shrinkage was calculated from the protrusion of the specimen from the bottom of the cavity. RESULTS: The injection-press method and the brush-on method gave the lowest polymerization shrinkage results (P 0.05). The standard deviation of the former method was smaller than that of the latter. The linear shrinkage in the injection-press method decreased with the increase of the powder-to-liquid ratio (P 0.05). All three additives reduced shrinkage to about 1/3 of the shrinkage of the basic resin using the injection-press method and a 2.00:1.00 powder-to-liquid ratio. CONCLUSION: The addition of three different chemical substances to liquid reduces linear shrinkage to about 1/3 of the shrinkage of the original self-curing acrylic resin.