Fracture Toughness of Flowable and Hybrid Resin Composites

Flowable composites, which have more resin content than the hybrids, have been used in a variety of applications; however, little has been published about their ability to resist crack propagation. Objectives: To compare the fracture toughness of flowable (Charmfil, Dentkist Inc., Korea) and hybrid (Charmflow, Dentkist Inc., Korea) composites. Methods: The composite was packed into a split mold, covered with a mylar film, pressed for ±60 sec and light polymerized. The prepared specimen (30x15x2mm) has a 0.6 mm groove as a crack guide along the centre of one surface. The specimen was placed on a double-torsion test rig on a two parallel rollers and force to fracture using a mechanical testing machine with crosshead speed of 0.1 mm/min. The average value of the force was used to calculate the KIc. t-test was carried out to determine the significant difference between the KIc of flowable and hybrid composites. Results: The changes in KIc between the flowable (1.05±0.16MN/m1.5) and the hybrid composites (1.15±0.49MN/m1.5) tended to be less clear. Having more resin content, the flowable composites demonstrated insignificant (p>0.05) changes when compared to the hybrid ones; this was probably due to the high resin content in the flowable composites that may blunt the stress at the crack tip through a plastic deformation. Conclusion: No statistically difference in resistance to crack propagation (fracture toughness) between flowable and hybrid resin composites was found in the present study.