STATEMENT OF PROBLEM: Denture microwave disinfection may result in dimensional changes that may distort the acrylic resin base, causing discomfort to the patient. PURPOSE: 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. MATERIAL AND 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). RESULTS: 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. CONCLUSION: 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.
STATEMENT OF PROBLEM: Denture microwave disinfection may result in dimensional changes that may distort the acrylic resin base, causing discomfort to the patient. PURPOSE: 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. MATERIAL AND 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). RESULTS: 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. CONCLUSION: 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.