Objectives : Determine the fracture toughness, Vickers Hardness, and brittleness index of a new Resin Nano Ceramic CAD/CAM material, 3M™ ESPE™ Lava™ Ultimate CAD/CAM (LVU), compared with commercially available indirect and direct materials. LVU contains about 79 wt% nanoceramic particles that reinforce a highly crosslinked polymeric matrix.
Methods : Fracture toughness was measured via the single-edge V-notched beam (SEVNB) method of ISO 6872, modified to accommodate bar sizes that could be sectioned from commercially available mill blocks. A V-notch was cut in 3mm x 4mm x 14mm bars, which were tested on a 3-point fixture with a 10mm span and a crosshead speed of 0.5mm/min. Vickers hardness was measured according to ASTM C1327-08 on mounted & polished specimens (10 indents on each material). Brittleness Index, B, was calculated from B=HvE/KIc2, where Hv is Vickers hardness, E is flexural modulus (reported in another study), and KIc is fracture toughness. Data were analyzed via ANOVA with Tukey's t-test (p<0.05).
The fracture toughness of the new resin nanoceramic material LVU is statistically higher than feldspathic glass-ceramics EMP and VM2, and composite materials MZ and TEC. Vickers hardness of EMP and VM2 is statistically higher than LVU, MZ, and TEC. The combination of high fracture toughness, low hardness, and low modulus makes LVU and the composite materials much less brittle than feldspathic glass-ceramics, as shown by the statistically significant differences in brittleness index. Low brittleness may make these materials less prone to cracking during try-in and function.
Keywords: CAD/CAM, Ceramics, Dental materials, Prosthodontics and fracture toughness
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