How we've ended up regulating medicine to the nth degree, but when it's teeth we're like "oh well, lol", continues to mystify me.
I'm always baffled by all the discussions about flossing, as it's something that can be very easily verified empirically: one can just floss for a month, then stop doing it for another month, then resume and get a feeling for how the gums react. If they bleed or burn (lightly), then the efficacy is evident; if not... lucky person! No need for research either way.
In my case, I don't need to floss daily, but I still need to do it regularly. Two weeks without flossing, and I'll definitely feel the burn once I resume flossing.
It's the same phenomenon as something like the calluses guitar players get. If they take a few weeks off, it'll hurt a bit when they play. That doesn't mean the activity improves their health. It means if you poke a part of the body enough it handles being poked better.