effect of the processing cycle on dimensional changes of heat-polymerized denture base resins

background: the second processing cycle for adding the artificial teeth to heat-polymerized acrylic resin denture bases may result in dimensional changes of the denture bases. the aim of thisstudy was to evaluate the dimensional changes of the heat-polymerized acrylic resin denture bases with one and two-cycle processing methods. materials and methods: a metal edentulous maxillary arch was used for making 40 stone casts. maxillary complete dentures were made with heat-polymerized acrylic resins (meliodent and acropars)with one and two stage processing methods (n = 10 for each group). linear dimensional changes in anteroposterior and mediolateral distances and vertical changes in the first molar region were measured following each processing cycle, using a digital caliper. mean percentage of the dimensional changes were subjected to two-way analysis of variance and tukey honest significant difference tests (α= 0.05). results: postpolymerization contraction occurred in both anteroposterior and mediolateral directions in all studied groups; however, the vertical dimension was increased. acropars acrylic resin showed the highest dimensional changes and the second processing cycle significantly affected the measured distances (p< 0.05). meliodent acrylic resin was not significantly in fluenced by the  processing method. conclusion: reheating of the acrylic resin denture bases for the addition of denture teeth result  in linear dimensional changes, which can be clinically significant based on the acrylic resin used. key words: acrylic resins, denture bases, polymers