Mechanical properties of conventional versus microwave-polymerized denture base acrylic resins

Abstract

New denture base acrylic resins have been introduced that are specifically formulated for microwave polymerization. Microwave polymerization is a time-efficient procedure, but few studies have evaluated how these new acrylic resin formulations compare with conventionally processed acrylic resins. The purpose of this in vitro study was to compare the stiffness and strength of denture base acrylic resins formulated for microwave polymerization with conventionally processed acrylic resin. Rectangular beams were fabricated from 2 microwave-polymerized denture base acrylic resins, microwave-specific resin (Nature-Cryl MC), resin with the option of microwave polymerization (Diamond D), and a conventionally processed resin as a control (Lucitone 199). Specimens (n=10) were stored in water for 1 week and subjected to a 3-point bend test to determine the flexural modulus (stiffness) and flexural strength before (initial properties) or after 120 000 load cycles. The load cycles, conducted between 5 and 25N at 2Hz, simulated 6 months of mastication. Data were analyzed by using 2-way ANOVA, followed by pairwise comparisons (α=.05). The initial flexural modulus (mean ±standard deviation) was conventionally processed resin, 2.65 ±0.33GPa; microwave-specific resin, 3.01 ±0.20GPa; and microwave-option resin, 2.63 ±0.04GPa. After load cycling, the mean flexural modulus was conventionally processed resin, 2.34 ±0.32GPa; microwave-specific resin, 2.69 ±0.20GPa; and microwave-option resin, 1.96 ±0.11GPa. The initial flexural strength was conventionally processed resin, 77.6 ±11.0MPa; microwave-specific resin, 83.6 ±3.5MPa; and microwave-option resin, 78.9 ±2.6MPa. After load cycling, the mean flexural strength was conventionally processed resin, 68.7 ±9.0MPa; microwave-specific resin, 73.3 ±3.3MPa; and microwave-option resin, 65.5 ±3.5MPa. Resin and loading state significantly affected the stiffness and strength (P<.01); the interaction resin×state was not significant (P≥.558). Microwave-polymerized denture base acrylic resins were comparable in stiffness and strength with conventionally processed acrylic resin. All acrylic resins decreased in stiffness and strength after load cycling. The microwave-specific resin was significantly stiffer and stronger than the other denture base acrylic resins, initially and after 120 000 load cycles.