Fracture toughness and brittleness of novel CAD/CAM resin composite block.

Abstract

To evaluate the fracture toughness and brittleness of a newly developed CAD/CAM resin composite block and compare it with five other resin composite blocks and one polymer-infiltrated ceramic block. Fracture toughness was determined through single-edge notched beam (SENB) method according to ASTM D5045-14. Parallelepiped specimens (thickness × width × length = 1.8×3.6×∼18mm) with a V notch (length=∼1.8mm) (n=10) were made from block materials using a low-speed water-cooled diamond precision saw and razor blade. Brittleness index (BI) was calculated from Vickers hardness and fracture toughness. Data were analyzed using one-way ANOVA and post-hoc Tukey tests (p≤0.05). The experimental block showed significantly higher fracture toughness than all commercial block materials (p<0.001) and has a brittleness index similar to most commercial blocks (p>0.05) which have significantly lower brittleness index than Vita Enamic (p<0.001). A moderate or strong correlation was observed between fracture toughness and flexural strength (Pearson's correlation coefficient R=0.66) or diametral tensile strength (R=0.86) or filler loading (R=0.66), and between brittleness and Vickers hardness (R=0.87). The new composite block exhibited significantly higher fracture toughness and lower brittleness among the commercial CAD/CAM composite block materials tested, indicating a lower tendency to fracture and marginal chipping, and better machinability. The new composite block with higher fracture toughness and lower brittleness is suitable to use in the fabrication of CAD/CAM indirect restorations with potential long-term clinical success.