In Vitro Evaluation of Shear Bond Strength and Mode of Failure of the Interface between an Indirect Composite Bonded to Fiber‐Reinforced Composite Substructures

Abstract

Failures of fixed partial dentures (FPDs) fabricated with fiber-reinforced composites (FRCs) have been attributed to veneering fractures. The aim of the present study was to investigate the shear bond strength and mode of failure between an indirect composite and FRC substructures. SR Adoro indirect composite was bonded to the following substructures: (a) flat surface made of unidirectional glass fibers (group A), (b) retentive sticks made of unidirectional glass fibers (group B), (c) flat surface made of fiber net (group C), (d) retentive sticks made of fiber net (group D), (e) nickel-chromium dental alloy (control, group E). For every group, 13 specimens were fabricated. All specimens were hydrothermocycled (5000 cycles, 5°C/30 sec, and 55°C/30 sec). A bond test was performed in a testing machine at a 0.5 mm/min crosshead speed according to ISO 10477. The failure mode was determined by examination of the fractured surfaces under an optical microscope. Selected specimens were examined with scanning electron microscope and with energy dispersive spectroscopy for compositional determination. The morphology (flat-sticks) and the type (unidirectional-net) of fibers on the bond strength were estimated. The mean shear bond strength was significantly different between groups E and A (p= 0.044), and groups A and B (p= 0.010). All FRC specimens showed cohesive failure. Group E showed predominantly adhesive failure. The bond strength was higher when sticks or fiber nets were used. Fiber nets and retentive sticks increase the shear bond strength between FRCs and indirect composite. In FPDs, the morphology and type of FRC substructures might influence the shear bond strength between the FRC substructure and the indirect veneering composite. With the proper design of these substructures, the number of veneering fractures may be decreased.