The first challenge is extraction.

The interior of a tooth — specifically the dentine, the hard tissue that forms the bulk of the tooth root and lies beneath the enamel of the crown — contains collagen, the protein that forms the organic scaffold of mineralized tissues.

Collagen is moderately resistant to degradation, more resistant than most soft tissues, and can preserve traces of DNA in the small pores of the mineral matrix even after the organic structure itself has substantially degraded.

To access this DNA, researchers drill into the tooth — typically at the cementoenamel junction or through the root surface — extracting a small amount of dentine powder.