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

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 × ∼18 mm) with a V notch (length = ∼1.8 mm) (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.