Effect of thermal cycling on fracture toughness of CAD/CAM materials

PURPOSE: To compare the fracture toughness of four different CAD/CAM materials, (VM) Vitablocs Mark II, (IP) IPS e.max CAD, (LU) LAVA Ultimate, and (VE) Vita Enamic under long thermocycling conditions. METHODS: Each type of ceramic block was sectioned into beams (n=9) with dimensions of 14×3×2.5 mm (L × W × H). All four ceramics were submitted to different conditions: the desiccator or distilled water, each for 7 days. The third and fourth conditions involved the specimens being submitted to 60,000 and 120,000 thermocycles in water respectively. The dwelling time was 52 seconds at 5° and 55°C. A three-point bend test with a universal loading machine on notched samples was per-formed. Furthermore, a fractographic analyses was made by scanning electron microscopy (SEM) to determine if any of these conditions influenced the type of fracture. Data were analyzed by two-way ANOVA (α= 0.05). RESULTS: A significant difference in fracture toughness (P< 0.05) was found among the groups; IP (4.20±1.23) had the highest value followed by VE (2.02±0.39), which did not have a statistically significant difference from LU (1.96±0.42). The lower value and statistical difference for VM was 1.52±0.35. The ceramics performed better after they were hydrated, while the polymer-based materials had the fracture toughness means decreased after the thermocycles. CLINICAL SIGNIFICANCE: A significant difference in fracture toughness (P<0.05) was found among the groups; IP had the highest value followed by VE, which was not statistically significantly different from LU. The ceramics performed better after they were hydrated, while the polymer-based materials had fracture toughness means decreased after thermocycling.