Composite microfiller content and its effect on fracture toughness and diametral tensile strength

Previous studies have examined the relationship between total filler content in hybrid restorative composites and some of their mechanical properties. This investigation evaluated the effect of varying the amount of microfiller in an experimental hybrid composite on fracture toughness (single edge-notch technique) and diametral tensile strength. The microfiller content in the experimental hybrid composite was varied from 0-44 wt% for seven specimen groups, while the total filler content ranged from 77-84 wt%. It was found that 9 wt% microfiller loading produced the highest mean fracture toughness (1.33 MPa.m(1/2)) and 44 wt% loading produced the lowest mean value (0.80 MPa.m(1/2)). Only the 9 wt% microfiller content group differed significantly in fracture toughness from the other specimen groups. The diametral tensile strength displayed only small differences for the range of microfiller content studied with mean values ranging from 42.1-49.6 MPa. Additional research on the viscoelastic properties of these heavily filled hybrid composites may provide some insight into the differences for the fracture toughness and diametral tensile strength results.