So the only reason I wasn't already brushing my teeth with baking soda is that my mother told me it tasted horrible.
I can't decide whether I should excoriate her for being an idiot or me for believing her.
I was experimenting with vinegar as a cleaning compound, and I decided to have fun with the whole science-fair volcano thing. Pure vinegar really does smell like 'volcano' to me. Then I realized I'd never properly tested baking soda as a toothpaste.
The first thing I found out is that it tastes better than toothpaste. So, I got my toothbrush and started brushing. It was much more comfortable than toothpaste - it doesn't burn.
I noticed it easily equaled toothpaste as a cleaner; as in, not impressive. So I got a better payload and tried again. Success. Baking soda also cleans better than toothpaste.
Notably, baking soda is also edible, though I wouldn't recommend it. I did find swallowing some was less than awesome.
So, tastes better, cleans better, nontoxic, doesn't burn, and it is cheaper. It even says right on the box that you can use it for cleaning your teeth. So, obviously, everyone uses toothpaste. Can you say marketing coup?