I know baking soda seems really abrasive, and I actually had the same worries as you do, and stopped using my homemade toothpaste for a while. Then while doing research for the book I happened across a scale that is used to rate the abrasiveness of dental products.
It runs from 0-200 (0 being least abrasive, 200 being most). Baking soda clocks in at a measly 7, while the closest store-bought toothpaste rates a 35! So, baking soda toothpaste? Definitely safe.
BOOM. Hippies for the win.
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