Polymerization Cycles on Hardness and Surface Gloss of Denture Bases

Objectives: The aim of this study was to evaluate different polymerization cycles on the hardness and surface gloss of acrylic resins for denture bases.
Methods: Samples of Classico and Vip Cril Plus acrylic resins were made in dental stone molds. Powder-liquid ratio and resin manipulation were carried out according to the manufacturers’ instructions, and the mass was pressed in metallic flasks. The polymerization cycles were: A- hot water bath at 74ºC for 9 hours; B- hot water bath at 74ºC for 8 hours + 100ºC for 1 hour, and C- hot water bath at 74ºC for 2 hours + 100ºC for 1 hour. After polymerization, the samples were deflasked and submitted to finishing and polishing procedures, and stored in water at 37ºC for 24 hours. Knoop hardness values for acrylic resins were assessed using a hardness indenter with load of 25 gf for 10 seconds. A glossmeter was used to evaluate the surface gloss using a light incidence of 60 degrees. Data were submitted to ANOVA and Tukey’s test (α=0.05).
Results: Hardness: significant differences were found between resins, regardless of polymerization cycles (Classico=22.28 and Vip Cril Plus=25.83); significant differences were observed among polymerization cycles, regardless of resins (A=25.83, B=24.64 and C=21.73), and there was similarity for the resin and cycle interaction (Classico: A=24.51, B=22.68 and C=19.65; Vip Cril Plus: A=27.15, B=26.53 and C=23.81). Surface gloss: significant differences were shown between resins, regardless of polymerization cycle (Classico=57.26 and Vip Cril Plus=49.38) and between polymerization cycles, regardless of resin (A=48.82, B=53.46 and C=57.68). Statistical differences were also found for the resin and cycle interaction (Classico: A=52.32, B=63.79 and C=55.67; Vip Cril Plus: A=45.32, B=43.14 and C=59.69).
Conclusions: Different polymerization cycles showed similar effects on hardness and different effects on the surface gloss of denture base acrylic resins.