Fracture toughness of nine flowable resin composites

Statement of problem. Flowable composite is used in a variety of clinical applications; however, the capacity of these materials to resist crack propagation is not well understood. Purpose. The purpose of this investigation was to compare the resistance to crack propagation of 9 flowable composites as measured by the fracture toughness. Material and methods. The composites studied include AeliteFlo, Crystal Essence, Flow-it, FloRestore, Permaflo, Revolution, Tetric Flow, VersaFlo, and Wave. Ten specimens of each composite were formed with a brass mold with a 3-mm preformed notch. The final dimensions of each specimen were 2 x 4.2 x 20 mm. All specimens were light-polymerized to manufacturer specifications and stored in air for 24 hours. The fracture toughness value, K,, (MNm(-3/2)), for each specimen was measured by use of a 3-point bending mode and a single-edge notched beam at a crosshead speed of 0.125 mm/min until fracture. The data were analyzed statistically by use of I-way analysis of variance, t tests (P<.05), and regression analysis. Results. The flowable composites tested showed a spectrum of fracture toughness values ranging from 1.15 +/- 0.10 MNm(-3/2) for Wave to 1.65 +/- 0.13 MNm(-3/2) for Permaflo (significantly different, P<.05). The remaining materials formed 1 group with intermediate K,, values not different from each other (P>.05) but significantly different from Wave and Permaflo. Comparisons of fracture toughness to the filler content by volume of each composite revealed no correlation. Conclusion. This in vitro study concluded that there was no significant difference among 7 of the 9 composites tested in their resistance to fracture. Permaflo showed the greatest resistance to crack propagation. There was no correlation between the filler content by volume and the fracture toughness of these flowable composites.