Environmental Stress Cracking of Heat-cured Denture Base Resin : Effect of Environmental Solutions on Lower Limit of Stress Intensity Factor

Abstract

To investigate the effects of environmental solutions (distilled water, 3 wt% acetic acid, 5 and 30 wt% ethanol) on the lower limit of stress intensity factor (K_<10>) of heat-cured denture base resin, the measurements of both load and crack length were carried out by the constant strain rate (0.01mm/min) test in the three point bending mode using precracked specimens. The fracture surfaces were also observed by digital microscope to obtain information on the crack growth mechanism. As a result, it was found that the K_<10> was as low as about 0.3 Mpam^<1/2> even in distilled water, suggesting that, orally, environmental stress cracking would probably occur due to environmental solutions in food and bevarages. Moreover the K_<10> was further decreased as the concentration of ethanol increased, which suggests that the habit of drinking alcohol may increase the risk of environmental stress cracking. Furthermore, since the fracture surface formed by 30 wt% ethanol solution was quite different from that in lower concentrations, we speculate that there are two different mechanisms of environmental stress cracking in heat-cured denture base resin.