Impact of Cutting Direction in CAD/CAM FRC Blanks on the Shear Bond Strength of Veneering Composites

Fiber-reinforced composites (FRCs) are increasingly utilized in computer-aided design/computer-aided Manufacturing (CAD/CAM) workflows for both definitive and provisional restorations. Veneering these materials is essential not only for achieving aesthetic outcomes, but also to prevent direct exposure of oral tissues to glass fibers. This study evaluated the short- and long-term shear bond strength (SBS) between a veneering composite and FRC (Trinia, Bicon) with varying bonding interface orientations and load directions. Specimens were sectioned into discs with 1.5° or 45° tilt with respect to material’s layering planes and veneered with a composite pin (Ceramage, Shofu Inc.). SBS was tested after 24 h and 180 days of water storage, with forces applied either parallel or perpendicular to the layer orientation seen at the bonding interface. Long-term water storage significantly reduced SBS (24 h: 23.9 MPa vs. 180 d: 18.1 MPa, p < 0.001). In contrast, neither cutting direction (1.5° vs. 45°, p = 0.584) nor loading direction (parallel vs. perpendicular, p = 0.367) significantly influenced SBS. These results suggest veneering of the tested FRC material is clinically viable regardless of interface orientation or load direction. Although aging significantly reduced SBS, this was not clinically relevant, indicating that appropriate adhesive protocols may ensure durable bonding.