Non-human primates also eat predominantly carbs, but mostly from fruits (and not from grains, which are highly cultivated by humans).

So I guess it's good to distinguish between sugars-from-fruit and starches-from-grains.

I thought that link between agriculture and tooth decay was due to the early "milling" techniques which introduced bits of stone into the food, causing mechanical wear? I don't remember where I got this from, however.