Bonding of Composite to Fiber-reinforced Resin – Effect of Fiber Orientation

Objectives: Fiber-reinforced composite (FRC) is promoted as a digitally fabricated alternative for the fabrication of fixed restorations. FRC blanks are layers of bidirectionally interlaced glass-fiber and resin. A composite veneering is required for FRC material to avoid antagonist wear and to improve aesthetics. The aim of this study was to evaluate the effect of fiber orientation on the shear bond strength between FRC material and veneering composite depending on the fiber orientation with respect to the interface surface.
Methods: CAD/CAM-FRC blanks (Trinia, Bicon LLC, Boston, USA) were cut to discs and divided into two groups, differing in glass-fiber orientation: The blanks were either cut at a 45° (n=33) or a 90° (n=33) angle with respect to the layering direction and along one of the main directions of an interwoven layer. The samples were ground flat, sandblasted and steam-blasted. As recommended by the manufacturer, each sample was pre-treated with the bonding (Cera-Resin Bond, CRB, Shofu Dental, Kyoto, Japan), with pre-opaquer (Universal Opaque, pre-opaque Shofu Dental) and with two layers of opaquer (Universal Opaque, opaque, Shofu Dental). A pin of light-curing veneering composite (Ceramage, Shofu Dental), with a diameter of 2.38mm, was produced onto the pre-treated samples. All samples were stored in water for 24 hours at 37°C. In a universal testing machine, shear bond strength tests were carried out until failure.
Results: The 90°-samples showed a significantly (p < 0.001) lower bond strength after 24 hours of water storage (20.5MPa±6.0MPa) compared with the 45° samples (26.7MPa±7.2). The samples failed predominantly in a mixed adhesive/cohesive mode.
Conclusions: In clinical use, the fibers of FRC material will inevitably be cut in different orientation. For future studies on bond strength of this material, however, it is important to include fiber orientation as a contributing factor.