At the center of the tooth is the pulp cavity, which in life contains nerves, blood vessels, and soft tissue.

After death, this soft tissue decomposes, but the cellular material that was once the pulp — including the nucleated cells that contain DNA — can leave molecular residues that persist in the protected environment of the dentin and pulp cavity.

The root of the tooth extends below the gumline, where it was anchored in the jawbone by the periodontal ligament.

The root canal extends through the center of the root from the pulp chamber to the tip (apex) of the root, where it opens at a tiny foramen through which nerves and blood vessels entered the tooth in life.

For ancient DNA work, the root of the tooth is the most productive region to sample.