I'd always assumed (and was told) that it was not possible to cure tooth decay, that cavities could not heal, and the only way to
fix oral health problems was through modern dentistry.
Like the rest of our body, our teeth and
oral health systems are a living, changing environment that is, but just treating from the outside alone (brushing and flossing), won't
fix oral problems unless you address the inside too, though these are still very important.