The shear bond strength of bidirectional and random-oriented fibre-reinforced composite to tooth structure

Objectives The objective of this study was to evaluate the bond strength and fracture pattern of fibre-reinforced composite (FRC) with two different fibre orientations and matrix compositions to dentine and enamel. Materials and methods Extracted human molars were used as substrates (enamel and dentine) with a standard acid-etch technique. Light-polymerizable FRC with two different interpenetrating polymer network matrices and random or bidirectional fibre orientations was applied to the substrate, together with the adhesive resin. As a control, particulate filler composite resin was bonded to the substrates. The substrate–composite specimens (n=10) were either stored in water for 24 h or additionally thermocycled for 6000 cycles. The shear bond strength of composite to substrate was measured and the fracture surfaces were evaluated visually and with SEM. Results Three-way factorial analysis of variance highlighted significant differences according to the substrate type, storage condition and composite material (p<0.05). Dentine specimens showed a significantly lower range of bond strength values (8.8–15.0 MPa), compared with enamel specimens (14.0–23.0 MPa). The highest mean bond strength in dentine was 15.0 MPa obtained with bidirectional FRC, whereas the highest bond strength in enamel was 23.0 MPa obtained with random-oriented FRC. Thermocycling did not identify a significant effect on the dentine bond strength, but did identify a significant decrease in enamel bond strength values (p<0.05). Several cohesive failures were observed in the tooth structure with the control material, whereas no cohesive bulk fracture of the tooth was observed when a thin layer of FRC was placed at the interface. Conclusions The addition of bidirectional or random continuous fibres did not show any significant improvement in bond strength values compared to control of particulate filler. However, the difference in the fracture patterns observed may have implications for clinical applications.