Flossing also hasn't been shown to not prevent tooth decay. (I.e. there is not much data to support one way or the other.) Also, some people don't carry the bac

Flossing also hasn't been shown to not prevent tooth decay. (I.e. there is not much data to support one way or the other.) Also, some people don't carry the bacteria that create acid in their mouths, so (by chance) they don't need to floss/brush as much. Your dad might have been one of those people. If I don't brush or floss, I get like 5 cavities in 6 months. And my breath smells awful. It's like type systems and productivity: we don't have a lot of data to say whether type systems make people more productive or not, but there are ton of SWEs who think that type systems make them more productive, and they are probably right (at least for their domains). Dentists, in their anecdotal experience, probably see patients improve once they start flossing and brushing. That's why they suggest it.