So? They were using clothing as well, doesn't mean they weren't transmitting infections to one another willy-nilly.
> as I understand it, a lot of modern man's issues with dental health are due to our grain righ diets anyway.
Maybe. I never heard of that theory myself. Bu regardless of diet, foragers still eat a lot of fruit with sugar. That's bad for teeth regardless of how well the tribe's toothbrush is passed down.
Not sure what you mean by "the tribe's toothbrush" being passed down. You can make toothbrushes (that don't last very long) from small branches by feathering out the end. You can also use toothpicks (e.g. made from bone).
Anecdote: My dad was not really good at brushing his teeth at all. "Forgot" about it quite often. He was "always" using a toothpick though. He'd be watching TV and you'd see him poking around with his toothpick. Sitting in front of the computer doing something and he's be poking around with his toothpick etc. He never had a single filling done or any issues with his teeth whatsoever. Try it some time. When the wooden toothpick is new, it can be used to get larger sticky things out from in between your teeth, which is only a problem if you have something sticky to eat in the first place. Once the toothpick has "feathered out" naturally from that, it can be used like a mini toothbrush and you can get your teeth squeaky clean little by little. I guess it's not a 3 minute brushing ritual, more of a lazy do-something-with-your-idle-hands while doing something else but hey.