Effects of low-energy electron beam irradiation on flexural properties of self-curing acrylic resin

Purpose: The purpose of this study was to confirm the effectiveness of LEB irradiation onto the polymer powder for improving the mechanical properties of self-curing acrylic resin. Methods: The polymer powder of self-curing acrylic resin was irradiated with total LEB doses of 25, 50, 75 or 100 kGy. Non-irradiated powder was used as a control. After LEB irradiation, ESR measurement, weight-average molecular weight measurement and three-point bending test were performed. Results: ESR spectrum of control had no peaks. After LEB irradiation, nine peaks were observed in each ESR spectrum, which indicates the presence of free radicals from main polymer chain. The quantity of free radicals increased linearly up to 100 kGy. Calibrated weight-average molecular weights were as follows: control, 960,000; 25 kGy, 500,000; 50 kGy, 440,000; 75 kGy, 410,000; and 100 kGy, 390,000. Molecular weight decreased with increasing LEB irradiation dose. The mean values of flexural strength (MPa) were as follows: control, 61.5 +/- 3.0; 25 kGy, 68.1 +/- 4.0; 50 kGy, 73.0 +/- 1.9; 75 kGy, 70.4 +/- 3.6; and 100 kGy, 67.7 +/- 2.3. The flexural strength of the specimens cured with the LEB-irradiated powder was significantly higher than that of control (p < 0.01). These results indicate that flexural strength of polymer materials cured with the LEB-irradiated powder increases because of increase in cross-linking structure. Conclusion: It is confirmed that LEB irradiation onto the polymer powder of self-curing acrylic resin improves the flexural strength. Crown Copyright (C) 2013 Published by Elsevier Ireland on behalf of Japan Prosthodontic Society. All rights reserved.