Work of fracture measurements and scanning electron microscope fractographs show that both enamel and dentin can best be considered as brittle materials with anisotropic fracture properties. Enamel is highly anisotropic, with the weakest path of fracture parallel to the enamel rods. Dentin is less anisotropic, with easiest fracture perpendicular to the dentinal tubules. A model is proposed to explain the fracture behavior of enamel.
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