Influence of simulated microwave disinfection on complete denture base adaptation using different flask closure methods

Abstract

Denture microwave disinfection may result in dimensional changes that may distort the acrylic resin base, causing discomfort to the patient. The purpose of this study was to determine the effect of simulated microwave disinfection on maxillary denture base adaptation using 2 different flask closure methods. Forty stone cast-wax base sets were prepared for flasking by the traditional flask closure (TFC) and Restriction System flask closure (RSFC) methods (n=20). The RSFC consists of 2 iron plates to hold the flask during definitive flask closure, maintaining the flask in a closed position after release of pressure. Acrylic resin (Classico) was prepared according to the manufacturer's instructions. After polymerization in water at 74 degrees C for 9 hours, the bases were removed following flask cooling and submitted to conventional finishing with abrasive stones and pumice slurry. Ten bases for each TFC or RSFC method (n=10) were submitted to simulated disinfection (SD) in 150 mL distilled water in a microwave oven at 650 W for 3 minutes; control bases for each TFC or RSFC method (n=10) were not disinfected (ND). Three transverse cuts were made through each stone cast-resin base set, corresponding to the distal of canines, mesial of first molars, and posterior palatal region. Measurements were made in the bases using an optical micrometer at 5 points for each cut to determine adaptation: left and right marginal limits of the flanges, left and right ridge crests, and midline. Collected data were submitted to 3-way ANOVA followed by the Tukey HSD test (alpha=.05). Dimension gap values (mm) for ND denture bases prepared by the RSFC method were significantly lower (0.16 +/- 0.05) when compared to the TFC method (0.21 +/- 0.05) (P<.027). Simulated disinfection statistically improved the base adaptation in bases prepared by the TFC method (0.17 +/- 0.03), compared to the ND bases (0.21 +/- 0.05) (P<.027). Simulated disinfection statistically significantly improved base adaptation (P<.0001) only in the distal of canines (ND=0.13 +/- 0.01; SD=0.11 +/- 0.03) and the posterior palatal region (ND=0.25 +/- 0.04; SD=0.21 +/- 0.01) when bases were prepared by the TFC method. Simulated disinfection by microwave energy improved denture base adaptation when the TFC method was used, but did not statistically alter base adaptation for the RSFC method.