Effects of 50- and 70-Gy radiation doses on polymethyl methacrylate denture bases

The aim of this study was to evaluate the flexural strength and Knoop microhardness of the polymethyl methacrylate (PMMA) used in dental prostheses after receiving therapeutic radiation doses of 50 and 70 Gy. Thirty-six acrylic resin plates measuring 65.0 × 10.0 × 3.3 mm were fabricated and polymerized using a microwave. The specimens were randomly divided into 3 groups (n = 12): group 1, which received no radiation; group 2, which received 1 fractioned dose of 2 Gy per day, 5 days per week, for 5 weeks, totaling 50 Gy; and group 3, which received 1 fractioned dose of 2 Gy per day, 5 days per week, for 7 weeks, totaling 70 Gy. All specimens remained in ballistic gel at a temperature of 37°C throughout the study. Afterward, the specimens underwent flexural strength and Knoop microhardness tests. All data were analyzed using analysis of variance and Tukey post hoc test (P < 0.05). For flexural strength, there was a statistically significant difference between groups 1 and 2 (P = 0.012) and between groups 1 and 3 (P = 0.048). For Knoop microhardness, there was a difference between groups 1 and 2 (P = 0.001) and between groups 1 and 3 (P = 0.006). For both flexural strength and microhardness, groups 2 and 3 showed greater values than group 1. Therapeutic radiation doses of 50 and 70 Gy increased the flexural strength and Knoop microhardness of PMMA used in dental prostheses.