Mechanical properties and fracture behavior of flowable fiber reinforced composite restorations

Objective: The aim was to evaluate the effect of short glass-fiber/filler particles proportion on fracture toughness (FT) and flexural strength (FS) of an experimental flowable fiber-reinforced composite (Exp-SFRC) with two methacrylate resin formulations. In addition, we wanted to investigate how the fracture-behavior of composite restorations affected by FT values of SFRC-substructure. Methods: Exp-SFRC was prepared by mixing 50 wt% of dimethacrylate based resin matrix (bisGMA or UDMA based) to 50 wt% of various weight fractions of glass-fiber/particulate filler (0:50, 10:40, 20:30, 30:20, 40:10, 50:0 wt%, respectively). FT and FS were determined for each experimental material following standards. Specimens (n = 8) were dry stored (37 °C for 2 days) before they were tested. Four groups of posterior composite crowns (n = 6) composed of different Exp-SFRCs as substructure and surface layer of commercial particulate filler composite were fabricated. Crowns were statically loaded until fracture. Failure modes were visually examined. The results were statistically analysed using ANOVA followed by post hoc Tukey's test. Results: ANOVA revealed that ratio of glass-fiber/particulate filler had significant effect (p < 0.05) on tested mechanical properties of the Exp-SFRC with both monomer systems. Exp-SFRC (50 wt%) had significantly higher FT (2.6 MPam1/2) and FS (175.5 MPa) (p < 0.05) compared to non-reinforced material (1.3 MPam1/2, 123 MPa). Failure mode analysis of crown restorations revealed that FT value of the substructure directly influenced the failure mode. Significance: This study shows that short glass-fibers can significantly reinforce flowable composite resin and the FT value of SFRC-substructure has prior importance, as it influences the crack arresting mechanism.