system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why are teeth alive if they're just bone and can't regenerate? Why do they need blood flow and are able die?
gpt
If you look at bones, they are filled with marrow. Check out a cross-section photo. This is filled with stemcells and allows the bones to grow bloodcells. Bones are alive. All bones would rot if they were left in open air and exposed to rotting foods and sugars for years. Most are encased in live meat to protect them. For instance, the rotting tooth does not start under the gum. It spreads there.