Sybairs' Teeth are the teeth of the dragon Sybaris.
The Founding of Thebes
The legend of the dragon's teeth originates with the founding of Thebes. The Phoenician prince Cadmus followed a sacred cow at the oracle at Delphi's urging, which lead him to the place where Thebes would sit. Once the cow stopped its travels he sought to sacrifice it to sanctify the spot and sent his men to fetch water from a nearby spring. The spring was guarded by a dragon, which killed all of Cadmus' men before he was able to slay it. However, the dragon was sacred to Ares.
The goddess Athena took the teeth from the dragon and gave Cadmus half. At her suggestion, he planted them and fierce warriors, sons of Ares, grew from where they were placed. He threw a jewel into their midst and they killed each other off until only five remained. These five helped him found the city of Thebes, but Cadmus was forced to be a slave to Ares for one year because he killed the dragon.
Jason and the Argonauts
During the search for the Golden Fleece, Aeetes - king of Colchis - forced Jason to plant the remainder of the teeth and defeat the warriors that sprang up to prove his worth. Jason planted the teeth, then threw a stone into the warriors midst. The warriors, thinking that one of them threw the stone, fought and killed each other.
The General used them to make the Skeleton Warriors, which he sent to hunt down Percy, Thalia, Zoë, and Bianca. Not able to tell the difference between Sybaris's teeth and other fossilized teeth, the mortals mistakenly planted Saber tooth tiger teeth which grew into kittens.
As a gift, Mars gives Frank a spear tipped with a Sybaris tooth. When stabbed into the ground, a Skeleton Warrior named Gray climbs out of the ground and follows Frank's orders. The spear can only be used three times and the tooth takes about a day to grow back after each use.