Influence of Water Temperature on Flexural Strength of Acrylic Resins

Objective: The purpose of this study was to investigate the change in mechanical properties of autopolymerizing acrylic resins when storage in air or water with different temperature during polymerization.

Methods: Two autopolymerizing methyl methacrylate resins (Provinice First, PV, Shofu; Unifirst III, UF, GC) were used. Resin mix was prepared according to manufacturers' instructions and condensed into the mold (2 x 2 x 25 mm) between two matrix strips, and pressed with a glass plate under compression (5 N). The then specimens were placed following conditions, in air at 23°C, or storage in water at 23°C, 40°C, and 80°C. Six specimens per test groups were subjected to the three-point bending flexural strength test with a cross-head speed of 1.0 mm/min. From these tests, the peak breaking stress, and the modulus of elasticity were determined from the stress-strain curve using the computer software interfaced to the testing machine. The data were analyzed for significance at the 0.05 level by two-way ANOVA and the Tukey HSD test.

Results: Two-way ANOVA revealed that there was a significant interaction between materials and polymerization environment (P<0.001). For PV, a significant decrease in flexural strength was found when the specimens were stored in water, but no significant differences were found among water storage groups. For UF, flexural strengths increased with increase in water temperature.

Conclusion: Though the method of placing acrylic resin in hot water during polymerization was useful for one material, adversely affect was found for the other material.