Effect of investment and flask closure on the denture accuracy

Objectives: The purpose of this study was to verify the denture base adaptation influenced by investment material and flask closure.

Methods: Sixty stone cast-wax pattern base sets were randomly assigned to 6 groups (n=10 each) and invested in metallic flasks, to receive the treatments: (1) stone investment and flask closure with traditional clamp; (2) stone investment and flask closure with RS system; (3) stone investment and flask closure with screws; (4) silicone investment and flask closure with traditional clamp; (5) silicone investment and flask closure with RS system; and (6) silicone investment and flask closure with screws. The polymerization of the Classico acrylic resin was in a water bath at 74^oC for 9 hrs. The resin bases were fixed on stone casts with instantaneous adhesive, and transverse cuts were made in the canine, first molar, and posterior palatal regions. Dimensional linear change between resin base and stone cast was verified with an Olympus microscope with accuracy of 0.0005 mm at 5 referential points in each section. Data were submitted to ANOVA and Tukey's test (a = 5%).

Results: Silicone investment showed an adaptation mean of 0.177 mm, with a statistically significant difference when compared with that of stone (0.207 mm). The RS system showed an adaptation mean of 0.166 mm, with a statistically significant difference in relation to traditional cramp (0.200 mm) and flask with screws (0.211 mm). Adaptation values for canine (0.141 mm), first molar (0.185 mm), and posterior palate (0.250 mm) were statistically significantly different. In all flask closures, there was a statistically significant difference, in which the best adaptation occurred with the silicone investment.

Conclusion: Denture base adaptation was influenced by investment material and metallic flask closure method. Better base accuracy was demonstrated for the RS system with silicone investment. The flask closure method and investment material should be considered for stability and comfort of the patient during clinical serviceability of the denture.