Teeth sends out a wave of small projectiles in a conical shape in front of the caster. At higher levels, its wide radius of effect can be useful for clearing out large swaths of monsters. However, unlike similar spells such as the Sorceress' Charged Bolt skill, only one projectile can damage a monster per cast, which significantly reduces its damage potential. Points spent in Teeth are typically intended to boost the damage of the other bone spells, Bone Spear and Bone Spirit, through their synergies. Teeth itself is not frequently used as an offensive tool for the Bonemancer.
One of the first gifts of Rathma, this skill allows the Necromancer to summon forth the Den'Trang, or Teeth of the Dragon Trang'Oul*. The Necromancers believe that Trang'Oul is the beast on whose back the world lies. In the balance of all things, it is thought that Trang'Oul is the fulcrum point. He is the closest thing the cult of Rathma has to a deity and this spell is the manner in which he protects his chosen.
Trang'Oul has since the Diablo II manual was written been renamed to Trag'Oul.
↑Diablo II Manual, page 73. Blizzard Entertainment, 2000.