Meh, doing all the stuff you're supposed to while being too poor to afford dental care will result in teeth eventually falling out anyway.

I've made it like 7 years so far but being as autistic and thorough as possible about tooth cleaning still doesn't hold it forever. If you could figure out post-apocalyptic/extra-societal molar fillings you could maybe make it last forever. Build a meth lab and use it to make high fluoride "prescription" toothpaste instead of meth while you're at it.