And whoever in the open field touches one who is slain with a sword, or a dead body, or a bone of a man, or a grave, shall be unclean seven days.
Torah Temimah: Niddah 55a — Everything in a corpse conveys impurity except the teeth, the nails and the hair, as it is written “or a bone” — similar to a bone: just as a bone was created with him and its stock does not regenerate, so everything that was created with him and whose stock does not regenerate. This excludes the teeth, which were not created with him, and hair and nails, which, although created with him, their stock regenerates.
English: Everything in a corpse conveys impurity except the teeth, the nails and the hair… This excludes the teeth, which were not created with him, and hair and nails, which, although created with him, their stock regenerates.
Exclusion based on creation-with and non-regeneration criteria.
Teeth, nails and hair of a corpse do not convey corpse impurity.