The visible ivory tusks on elephants are made primarily of dentine and include small amounts of enamel. Tusk length varies among African and Asian elephants and is hereditary. The upper incisors may grow to 10 feet or more.
One-third of the tusk's length is actually hidden from view in the animal's skull and is technically a pulp cavity comprised of tissue, blood and nerves. Primarily used in defense against predators, the tusks are also used in battle against other elephants and to aid in foraging for food. The prized ivory has made the elephant a popular target of poachers and landed the African elephant on the International Union for Conservation of Nature and Natural Resources' Vulnerable list, as well as landed the Asian elephant on the Endangered list of animals.