Role of microstructure on fracture of dentin

Dentin possesses unique hierarchical structure, which has a significant influence on the mechanical properties. Understanding the relationship between structure and mechanical properties of dentin is essential for preventing and curing oral diseases, as well as, potentially for developing man-made engineering materials with superior mechanical performance. In this study, the effect of the two-layered structure, where hard peritubular dentin (PTD) containing dentin tubules are embedded in soft intertubular dentin (ITD), on the fracture behavior of dentin is investigated. A numerical model is developed, in which PTD cracking, ITD cracking and the debonding of the interface between PTD and ITD are all taken into account. Numerical simulations reveal that PTD fracture and interface debonding are the major failure mechanisms, which are consistent with experimental observation. It is identified that the cohesive strength and critical separation of interface are the key parameters controlling which of the mechanisms is active. The low cohesive strength of interface and small critical separation of interface can lead to interface debonding, while the large cohesive strength and critical separation give rise to PTD fracture. In addition, it is found that large volume fraction of dentin tubules and small volume fraction of PTD can enhance the toughness of dentin, which provides a new insight into the degraded mechanical properties of old dentin.