A hunter-gatherer diet, or even an early agricultural one, full of tough fiberous foods has been known to be conducive to straight teeth, and limited evidence of tooth decay.
The trade off is that your nice straight teeth would be worn down to nubs by the time you were in your 30s, but then not many lived past forty, so not a huge handicap.
So have your kids chew tree bark and pine cones they find, it'll save you a bunch on braces.