Effect of degradation of filler elements on flexural strength for dental cad/cam resin composite materials in water

Abstract

Purpose: This study aimed to evaluate the effects of degradation on the strength of computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite blocks (RCBs) by subjecting them to accelerated degradation in water and conducting biaxial flexural strength tests. Methods: Six commercial RCBs were tested. The RCBs were cut into disks, after which the disks were immersed in purified water. For the aging experiment, the samples were subjected to heat treatment at 37, 60, 70, and 80 °C, in a constant temperature oven and stored statically for 30 d. After the aging experiment, the elements released from the RCB fillers were measured by inductively coupled plasma atomic emission spectroscopy. In addition, the biaxial flexural strength of the RCB fillers was measured after accelerated degradation at 70 °C. Results: Si (the main component of the filler) was detected in all the RCB solutions after the aging experiment; however, the type and amount of other elements differed considerably among the RCBs. The flexural strength of some of the RCBs decreased by approximately 20–40% after the accelerated degradation. For most materials, the Weibull coefficient decreased or remained unchanged after the test, whereas it increased in some materials. Conclusions: The strength of all the RCBs decreased after the accelerated degradation tests; however, this behavior differed among the materials. In addition, the release of elements from the filler of some of the materials into the water correlated with the decrease in the strength of these materials. These findings indicate that the evaluation of the degradation behavior of RCBs in water is essential for their long-term usage.