Influence of age-related changes on crack growth trajectories and toughening mechanisms in human dentin

Objectives: Dentin microstructure undergoes changes with age and its materials properties degrade over time. In the present study, we investigate the coupled influence of increased filled tubules and decreased materials properties on the fracture behavior of human dentin.

Methods: We assume degraded materials properties are linked with increased advanced glycation end-products (AGEs) crosslinks in dentin tissue. We use morphological data of human molars to create 2D and 3D models of dentin microstructure, and utilize a phase field fracture framework to study crack growth trajectories. We construct aged dentin samples (i.e., filled tubules and degraded properties) and compare the fracture results with the samples without age-related changes.

Results: The simulations show an increase in the number of filled tubules can deactivate the toughening mechanisms such as crack deflection and microcracking. In addition, filled tubules have adverse impacts on the ability of peritubular dentin to shield microcracking. We further show how the dentinal tubules' orientations affect the crack surface growth. We also investigate that an increase in the AGEs level can result in increased brittleness.

Significance: The developed model and findings of the present study provide region-dependent information on crack growth trajectories as well as more understanding of crack surface growth at the presence of filled tubules.