Effect of the physical properties of acrylic resin of overnight immersion in sodium hypochlorite solution

Objectives: This study evaluated colour stability, surface roughness and flexural strength of microwave-polymerised acrylic resin after overnight immersion in sodium hypochlorite, simulating 180 days use. Materials and methods: Forty disc-shaped (15 mm x 4 mm) and 40 rectangular specimens (65 mm x 10 mm x 3 mm) were prepared from microwave-polymerised acrylic resin. The specimens were immersed in 0.5, 1% sodium hypochlorite, Clorox/Calgon and distilled water. Colour measurements (Delta E) were determined by a portable colorimeter. A surface analyser was used to measure roughness (mu m). The flexural strength (MPa) was measured using a three-point bending test in a universal testing machine. Data were evaluated by one-way anova, followed by Student-Newman-Keuls test (alpha = 0.05). Results: Statistical analysis found significantly higher colour changes (SNK, p < 0.001) for the 1% sodium hypochlorite, but mean Delta E value quantified by National Bureau of Standards was classified as slight. When comparing the surface roughness, no statistical significance was found among the solutions (anova, p = 0.637). The 1% sodium hypochlorite presented significantly lower flexural strength compared with the control group (SNK, p = 0.034). Conclusion: It was concluded that immersion in 1% sodium hypochlorite solutions for 8 h does influence the colour stability and flexural strength of microwave-polymerised acrylic resin, during the simulated period of 180 days.