An analysis of crack growth in dentin at the microstructural scale

Dentin is a biocomposite possessing complex hierarchical structure, which endows this hard tissue with excellent damage tolerance. In this study, crack growth in dentin at the microstructural scale is investigated and the synergistic effects of plastic deformation of intertubular dentin (ITD), elasticity and fracture properties of peritubular dentin (PTD), and fracture properties of PTD/ITD interface on the fracture of dentin are explored. A micromechanical model is developed, which captures the experimentally observed fracture process of dentin, i.e. occurrence of microcracking of PTD ahead of the main crack. It is found through numerical simulations that high relative stiffness and low cohesive strength of PTD increase the propensity of microcracking of PTD, whereas reduce the plastic dissipation and toughness of the microstructure of dentin. The microcracking of PTD can be also promoted by low toughness of PTD. The large friction angle and weak strain hardening of ITD could promote the microcracking of PTD, and simultaneously enhance the toughness of the microstructure of dentin. In addition, it is identified that the cohesive strength of the PTD/ITD interface plays a crucial role in dominating fracture mechanisms; low cohesive strength leads to fracture of interface and suppresses microcracking of PTD, which provides an explanation for the crack deflection along interface observed in experiments. Nevertheless, the toughness of interface has a negligible influence on the fracture of dentin.