Effect of Original Water Content in Acrylic Resin on Processing Shrinkage

Purpose: The aim of this study was to determine the original water content of a supplied acrylic resin powder and a monomer and of dry heat-processed acrylic bars. The effect of the original water content of acrylic resin on processing shrinkage was also investigated. Materials and Methods: Ten bar specimens were fabricated using dried and as-supplied (control) acrylic resins. The resins were polymerized and cooled, then weighed and measured to determine the amount of shrinkage. The initial water content of the specimens was determined by thorough drying, and results were compared with the Student t test. Results: The initial water content and processing shrinkage of the dried acrylic resin bars were both significantly lower (P .0001) than those of the as-supplied acrylic resin bars. Conclusion: The processing shrinkage of acrylic resin made from dried constituents was significantly less than that of resin made from products as supplied by the manufacturer. However, it is not known if this change is of clinical significance.