Strength of adhesive-bonded fiber-reinforced composites to enamel and dentin substrates

To compare in vitro the bond strength of a particulate filler composite and two brands of fiber-reinforced composite (FRC) to teeth with or without the addition of flowable composite at the adhesive interphase. Physicomechanical properties that might contribute to the bonding were also evaluated.

Two hundred extracted human molars were used as substrates with a standard acid-etch and adhesive technique. FRC material [everStick (EV) or Stick (SC)] was applied on the substrate either directly or with a thin layer of flowable composite resin [Tetric Flow (TF)] and light cured for 40 s. As a control, particulate filler composite was used. The specimens (n = 10) were water stored for 24 h or thermocycled for 6000 cycles and subjected to shear bond strength testing. Fracture surfaces were analyzed with SEM and the microhardness and thermal expansion behavior of the materials at the adhesive interface were also evaluated. Multifactorial ANOVA and Tukey's post hoc tests were used at a significance level of p < 0.05.

ANOVA showed that storage condition and substrate type (p < 0.05) had a significant effect on the bond strength values. Bond strengths of FRC did not show a significant difference compared to the control (p > 0.05). For enamel, the mean bond strengths in MPa (SD) after thermocycling were: control 19.4 (3.8); EV 22.3 (3.6); SC 16.9 (4.9); EV-TF 22.8 (3.2); SC-TF 16.7 (2.7); and for dentin they were: control 15.3 (5.57); EV10.2 (2.2); SC 14.4 (4.5); EV-TF 8.85 (1.1); SC-TF 15.6 (3.6). Thermocycling increased the bond strength values typically by 10%. The presence of flow composite resin did not produce any significant effect (p > 0.05).

The bond strength of FRC did not differ from that of particulate filler composite, and the addition of flowable composite did not improve bond strength values.