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

Abstract

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 14x3 x2.5 mm (L X W x 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 degrees C. A three-point bend test with a universal loading machine on notched samples was performed. 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 (alpha= 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.