Strength and Mode of Failure of Unidirectional and Bidirectional Glass Fiber-Reinforced Composite Materials

Purpose: The flexural strength of two commercially available dental fiber-reinforced composites (FRC) (glass fiber-reinforced composite material), one unidirectional and the other bidirectional, were investigated. Materials and Methods: Ten uniform beams of core materials and ten beams of laminated core materials were fabricated for FibreKor and Vectris Frame. The specimens were subjected to a three-point bending test. Flexural strength for both FRC materials was determined with and without their composite laminations. The strength data were analyzed using the Weibull method. Modes of failure for both systems were determined using SEM. Results: The strength of FibreKor was significantly greater than that of Vectris Frame when comparing the core materials with and without their respective composite laminations. Mode of failure of FibreKor was predominantly debonding with fiber fracture. Vectris Frame did not exhibit debonding failure. Mode of failure for Vectris Frame was fiber fracture with delamination and matrix microfracture. Conclusion: FibreKor, a unidirectional FRC, demonstrated higher flexural strength than Vectris Frame, a bidirectional FRC. Debonding of fibers from the matrix possibly contributed to toughening mechanisms such as crack deflection, fiber pullout, and fiber bridging in FibreKor.