Incidence of Tooth Breakage Among Large, Predatory Mammals

Data on the frequency of tooth breakage among nine, large carnivorous mammals suggest that the probability of an individual predator's breaking at least one tooth in its lifetime is greater than 0.25. This figure is similar to published estimates of bone-fracture incidence in primates and viverrid carnivores and indicates that the safety factors of teeth and bone are similar. Given that bones heal and teeth do not, the equivalent rates of fracture are surprising. It suggests that the cost of tooth fracture is slightly less than that of bone fracture. The highest incidences of tooth breakage (0.35, 0.40) were found in the habitual bone eaters (hyenas), and the lowest (0.15-0.24) in the felids and the African wild dog. The gray wolf, a moderately frequent bone eater, was intermediate (0.29). Eating bone appears to increase the risk of accidental fracture because it produces relatively high, unpredictable loads. The most commonly broken teeth are canines, followed by premolars, carnassial molars, and incisors. Canines are more likely to break because their shape and function tend to subject them to significant bending stresses that are unpredictable in magnitude and direction. The evolution of canine teeth with higher safety factors is probably constrained by the necessity of maintaining a functional shape and the material properties of dentine and enamel. Finally, it is suggested that mammalian predators of large prey are likely to fracture their teeth much more often than consumers of small prey or plant material because of a much greater risk of accidental fracture during the killing of large prey.