Why don't teeth heal? All the other bones do. Can tooth decay be reversed?

THe teeth do not heal, and to this day decay cannot be reversed. The reason for that is in their function. To be efficient, teeth are protruding out of gums, in the mouth, which means pretty much outside your body. Unlike other bones, they are not recovered by tissue. For this reason they lack access to the blood stream to bring enough ressources (cells, oxygen, calcium...). That also why they grow inside the gums before pushing out.
In fact bones not only heal but they are eaten and reformed all the time, but you need a lot of blood and cells to do that.
The only thing they could do, but don't, is keep growing, like rodents' teeth.

Last edited by Jerome Feldmann (18th Mar 2008 18:19:22)

And to add a little more:-

Very early tooth decay can be reversed. If there is a little bit of the mineral lost from the enamel (outermost layer of the tooth) then it can be replaced. Minerals can come from saliva, and fluoride can help the replacement with stronger mineral.

Once decay gets through the enamel into the dentine (next layer down) then this can't happen, and then the dentist has to remove the decay and put a filling in. The decay has to be removed because it has bacteria in it that can carry on producing the acid that cause the decay, even if a filling is put on top.

Bone can heal because the cells that can make new bone are still around. On the other hand teeth don't have this. Firstly cells that make enamel (ameloblasts) make enamel from the inside-out, the cells that make it start where the enamel and dentine meet, and work outwards towards the tooth surface. Once the enamel is made, the ameloblasts are not capable of making any more. This means enamel can't repair unlike bone.

Dentine making cells (odontoblasts) do stay around but they make the dentine from the join between enamel and dentine, and so end up in the middle of the tooth, in the pulp chamber. If dentine gets attacked by decay, this happens a long way from these cells, and they can't get to the damage through the dentine. They can start to make a bit of new dentine to try and block the decay but often this isn't fast enough to stop decay from reaching the pulp (where the nerves for the tooth are).