Why do rodents' incisors grow continuously throughout life?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A labeled cross section illustration of an adult human molar shows the tooth's crown and root, with layers including enamel, dentin, and pulp, as well as gum, cementum, blood vessels, periodontal ligament, lateral canals, and nerve. — tooth Cross section of an adult human molar.

Rodents possess rootless incisors that grow continuously throughout their lives because they lack a closed pulp cavity, which allows for perpetual growth. This evolutionary adaptation is essential for herbivores that rely on gnawing, as it compensates for the constant wear these teeth experience during daily use.12

The structure of these teeth is specifically designed to maintain functionality: the front of each incisor is coated in a hard layer of enamel, while the back consists of softer dentine. As the rodent gnaws, this differential wear ensures that the teeth are self-sharpening, creating and maintaining a perpetually sharp chisel edge. If these teeth do not wear down properly through regular chewing, they can become overgrown, which may require veterinary intervention.32