In an adult male the four canines project from the mouth. The lower pair curve up and outward and are the fighting teeth; the upper pair, sometimes called whetters, curve up as well and sit where the lower ones sweep past them.
Both pairs have open roots and grow throughout life. The contact between them wears the lower tusk to a chisel edge along its outer face, so the weapon is maintained by ordinary jaw movement rather than any deliberate action. A boar that loses an upper tusk can end up with a lower one that overgrows and curls, because the honing surface is gone. Males also thicken the skin over the shoulder into a fibrous shield before the rut, which absorbs slashes from rivals.
Sows have much smaller canines that do not protrude. Tusk growth rate varies enough between individuals and populations that using tusk length to age a boar is unreliable, though the practice persists.