While both teeth and bones both rely on calcium phosphate minerals for toughness, there are a few big differences between teeth and bones. For one, teeth are covered in enamel, which is very strong and inflexible, and mostly mineral. Also, the hard part of bones still contains living cells, and so even the hard part of bone has veins with blood running through them. Most of the hard part of teeth (dentin tissue) has no cells in it, and no veins. Because of this, bones can heal themselves, and teeth mostly cannot.