Mechanical properties of resin-ceramic CAD-CAM materials after accelerated aging

Statement of problem. The development of polymer-based computer-aided design and computer-aided manufacturing (CAD-CAM) milling bocks and the limited availability of independent studies on these materials make it pertinent to evaluate changes in their mechanical properties after simulated aging to identify strengths and limitations. Purpose. The purpose of this in vitro study was to measure the effect of thermocycling on the flexural properties of ceramic, resin, and resin-ceramic CAD-CAM materials. Material and methods. Studied materials included Lava Ultimate Restorative (LVU; 3M ESPE), Enamic (ENA; VITA Zahnfabrik), Vitablocs Mark II (VM2; VITA Zahnfabrik), and Paradigm MZ100 (MZ1; 3M ESPE). Polished 4x1.2x14 mm bars (n=45 per material) were prepared from standard-size milling blocks. The 2 distilled water baths of the thermocycling apparatus were set to 5 degrees C and 55 degrees C, with a specimen immersion time of 15 seconds and transfer time of 4 seconds. Fifteen specimens from each material group were subjected to a 3-point flexural test at 3 different thermocycling intervals: 0 (control), 5000, and 10 000 cycles. The flexural test was performed over a 12-mm span with a crosshead speed of 0.5 mm/min. Data were subjected to multiple analyses of variance and the Tukey HSD post hoc tests (alpha=.05). Results. Mean flexural strength values for 0, 5000, and 10 000 cycles were 133, 130, and 128 MPa for VM2; 175, 139, and 134 MPa for LVU; 154, 144, and 138 MPa for MZ1; and 149, 136, and 132 MPa for ENA. Mean flexural modulus values were 51, 52, and 54 GPa for VM2; 14, 13, and 13 GPa for LVU; 16,15, and 15 GPa for MZ1; and 31, 30, and 31 GPa for ENA. Mean modulus of resilience values were 0.17,0.16, and 0.15 MPa for VM2; 10.1, 0.76, and 0.72 MPa for LVU; 0.77, 0.69, and 0.62 MPa for MZ1; and 0.42, 0.31, and 0.28 MPa for ENA. A significant difference was found among the materials in the mean change of flexural strength (P<.001) and modulus of resilience (P<.05) after thermocycling. No significant difference was found among the materials in the mean change of flexural modulus after thermocycling (P=.113). Conclusions. The mean flexural strength of resin-ceramics is significantly different from that of the feldspathic ceramic control at 0 and 5000 cycles, but not at 10 000 cycles. The mean modulus of resilience of resin-ceramics varies significantly after thermocycling, unlike the feldspathic ceramic control. Conversely, the mean flexural modulus of tested materials did not vary significantly after thermocycling.