system
Given the following post, respond as if you're commenting on Reddit:
human
Why do flesh, tissue, muscle, bone, skin all heal on their own but Teeth don't?

You break a bone and it will heal. Tear a Ligament or muscle, it will heal. Cut skin, it heals. Why do bad/cracked teeth not heal and go back to normal after a while?
gpt
There are two cell types responsible for making teeth. The ameloblasts and the odontoblasts. The ameloblasts make the hard enamel that protect your teeth and the odontoblasts make the softer dentin that makes up the core of your tooth. 

Enamel is deposited on your tooth like frosting. Inside-> outside. This means that the ameloblasts are on the outside of the tooth when it erupts. As a result, they all die, and you lose your ability to generate new enamel.  The odontoblasts live on after eruption, so you can generate new dentin, but it is the enamel which makes your teeth what they are, so if you lose that, you are SOL.