system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't teeth heal themselves?
gpt
Tissues that can heal themselves need to be made of living cell that can divide and grow more cells from a small amount of living cells. Much of teeth is mineral that was deposited by living cells but after that initial process, teeth are mostly non-living very hard mineral or hard mostly non-cellular tissue. The cells that initially made all that mineralized hard stuff died and are no longer around to do it again.