Teeth are naturally designed to remineralize, but you have to eat healthily, making sure that you get plenty of minerals/trace minerals, stay away from processed sugar and from toothpastes which contain glycerin (which coats the enamel and takes up to a dozen brushings to completely renew). Weston Price found that tooth decay was virtually non-existent among Australian Aborigines and other indigenous peoples until sugar and the western diet was introduced. He also found where cracks in the enamel had naturally been remineralized and repaired.