Why? Lactic acid.
All teeth are the same. The gene for welcoming bacteria that make lactic acid often runs in families. And that's what dooms teeth. So trying to keep the mouth free of lactic acid has been the Holy Grail for dentistry - but the lactic acid kills cancer cells too.
Until this was figured out most dental pros thought a dirty mouth led to cavities, gum disease and great sex.
So now what? Get in there and start licking the pavement? Switch to a hair brush and go light on the toothpaste? Gargle with toilet water?
Does it ever end?