In males the right tooth remains embedded, but the left tooth erupts, protrudes through the upper lip, and grows forward in a spiral pattern to form a straight tusk. In rare cases the right tooth also forms a tusk, but both tusks are always twisted in the same direction. Occasionally one or even two tusks develop in a female. The distal end of the tusk has a polished appearance, and the remainder is usually covered by a reddish or greenish growth of algae. There is an outer layer of cement, an inner layer of dentine, and a pulp cavity that is rich in blood.
Broken tusks are common, but the damaged end is filled by a growth of reparative dentine.
New evidence, however, supports an old view that the tusk is exactly what it appears to be, namely, a weapon. It also may serve to communicate dominance rank, or in ritualized displays, much like the horns and antlers of some ungulates. Based on knowledge of other mammals, the amount of scarring resulting from tusk-inflicted injuries would be expected to be greatest in dominant males, who must fight more often and more intensively in order to defend a harem. Females and immature males were found to have significantly fewer head scars. It is generally found in deeper waters than those used by Delphinapterus and tends to avoid shallow seas like those around Alaska.