Ring-on-ring Biaxial Flexure Strength of Acrylic Denture Base Resin

Objectives: Biaxial flexure test has been widely used to evaluate flexure strength of dental restorative materials, but not for that of denture resins. This study was to investigate the flexure strength of acrylic denture resin by ring-on-ring biaxial flexure test. Method: Heat-curing acrylic denture resin (Vertex RS, Vertex) disks were prepared by conventional pack and press technique. The nominal sizes of disks were 20 mm or 40 mm in diameter and 1.8 mm in thickness. All specimens were ground parallel to be flat and one side was finally polished with #2400 SiC paper. After water storage at 37ºC for 50 h, ring-on-ring biaxial flexure strength was tested by using hardened steel loading fixtures with (support-load) ring diameters in mm; (16-4), (16-8) for disks 20 mm in diameter and (32-8), (32-16) for disks 40 mm in diameter. Flexure test was conducted at 2 mm/min loading speed and eight specimens were tested for each test configuration. Ring-on-ring biaxial flexure strength was calculated by ASTM C 1499. Results: Mean biaxial flexure strength (MPa) and standard deviation values for each group were (84.7±14.4), (84.8±6.7), (111.0±18.2), and (123.3±7.9) for (16-4), (16-8), (32-8), and (32-16), respectively. Biaxial strength values of (32-8) and (32-16) were significantly higher than those of (16-4) and (16-8). However, there was no significant difference between biaxial strength values by difference in load ring diameter (Scheffe's test). Conclusions: Ring-on-ring test can be used successfully to measure biaxial flexure strength of acrylic denture base resin. However, further variation should be verified to standardize ring-on-ring biaxial test for acrylic resin materials. (Supported by NRF # 2010-0010841 and KHT # A084491)