The damage tolerance of teeth: modelling the growth of cracks and prediction of bite load capacity

[Truncated abstract] This thesis is concerned with the fracture analysis of cracks in the teeth of different species. The main focus is on finding a link between the resistance to failure by fracture and the key geometrical features of the tooth, with particular reference to its radius, height and enamel thickness. The analysis is applied to short, rounded 'bunodont' molars typical of humans and other primates; elongated, columnar 'hypsodont' molars of ruminants and the elongated, tapered canine teeth of predators. Fracture morphologies include longitudinal cracks resulting from direct occlusal loading on bunodont and hypsodont crowns, and transverse cracking of the canine resulting from lateral loading. The study was carried out by applying numerical (extended finite element method (XFEM)), experimental and analytical fracture mechanics analyses resulting in simplified analytical equations for failure load in terms of the key parameters. The ability to model the failure of a particular tooth structure allows us to predict the maximum biting force that can be applied by the animal. The existing fracture patterns in the dentition of extant animals and also in fossil records show particular damage patterns that can also be analysed to determine the magnitude and type of load that caused the damage. Hence, the result of this research can be applied by anthropologists and paleoanthropologists help understand the evolutionary route of the species. Although the geometrical features of teeth in different mammalian species vary widely, available data suggests that the mechanical properties for the component materials (enamel, dentin) do not vary greatly. Nevertheless, the impact of microstructure cannot be neglected. The modelling has therefore also tested the relevance of local spatial variations in material properties within the enamel (stiffness and toughness) and material anisotropy.