Tooth enamel cannot heal itself because it has no living cells.

Tooth enamel is about 96% hydroxyapatite, a hard calcium-phosphate crystal. It is the hardest substance in the human body. During early life, cells named ameloblasts lay down this mineral layer. After the tooth erupts, these cells die and never return.Because no living cells remain, enamel is acellular and has no blood supply. Skin and bone keep living cells that divide and fill damage, but enamel cannot do this.Saliva supplies calcium and phosphate that can harden tiny weak spots. This process only strengthens existing enamel and does not rebuild lost chunks. When decay passes through the surface, the hole is permanent until a dentist fills it.In 2017 researchers at King’s College London used the drug Tideglusib to help stem cells grow new dentin, not enamel. No current treatment can regrow human enamel. Sharks avoid the problem by growing new teeth again and again. Humans get only two sets of teeth, so protecting enamel is critical.