Revealing the structural and mechanical characteristics of ovine teeth

The survival and function of dentition over the lifetime of an animal depends upon the ability of the teeth to resist wear and chemical erosion, and to withstand occlusal loading conditions without suffering debilitating fracture. Understanding how geometrical factors (radius, height, enamel thickness) and mechanical properties of the dental tissues (Young's modulus E, hardness H and toughness KIC of enamel and dentin) combine to ensure the survival of an animal's teeth can provide great insight into the evolutionary history of the animal and its dietary adaptation. While the geometrical factors are beginning to be understood, the range of animals for which measurements of dental tissue properties are available is very narrow, being restricted almost entirely to humans and other primates. The absence of comparative data across a broader range of species makes it impossible to draw conclusions with any certainty. The present study expands knowledge of mammalian dental tissue properties by reporting the Young's modulus and hardness of ovine (sheep) enamel and dentin measured using nano-indentation. We found that sheep molar enamel Young's modulus and hardness are both lower than those of human enamel, by approximately 30%, and 9% respectively, while the properties of dentin are similar. The combination of E and H makes the ovine enamel approximately 30% more resistant to wear than human enamel, which is an imperative in ruminant dentition. The results of this study are interpreted in terms of the ovine feeding ecology, and the structure of the ovine molar and its occlusal surface.