Bond strength of fiber reinforced composite substructure to restorative composites

Objectives: Fiber reinforced composite substructure (Cavity FRC, StickTech), containing short multidirectional glass fibers, is used to reinforce composite fillings and ease the clinical procedure to restore large molar cavities. For similar indications a flowable composite has recently been introduced (Surefil SDR, Dentsply). Both materials need to be bonded to the overlaying composite. In the present study bond strength of these substructure materials to commercial particulate filler composites (PFC) was compared.

Methods: Test samples were prepared by applying and light curing the studied substructure materials (either FRC or SDR) into cavities made in acrylic blocks. PFC was then added to the surface of the substructure material to form a cylindrical stub with a diameter of 3.6mm. 4 different PFCs were used (Majesty Posterior, Tetric evoCeram, Gradia direct and Grandio). Samples to test composite-composite bond strength were also made by using the same PFC in the substructure and stub. 12 samples (n) of all material combinations were made. Shear bond strength test was performed (speed 1mm/min), maximum load and stress at maximum load were calculated. Anova and Tukey's test were performed (p=0.05).

Results: All PFCs bonded similarly to both cavity FRC and Surefil SDR. Type of PFC had a significant effect on bond strength (p<0.05).

Conclusions: Studied multidirectional short-fiber composite (Cavity FRC) showed equal bonding properties to commercial restorative composites than Surefil SDR. Bond strength of the tested restorative composited varied markedly. All studied restorative composites, except Majesty Posterior, showed better bond strength to subsructure materials than to themselves.