Hi, I haven't read the whole thread. I will, but in the meantime, wanted to write a bit about my experience.
I grew up in a little town in the north coast of Honduras, Central America, with about 10000 inhabitants at the time. There was a river coming down from the mountain and they had a little dam and from there the water was distributed to all the town. The water was not processed at all, but the river made honor to its name which was Cristales, which means crystals, so clean was it and its water.
I grew up drinking this water and all my friends did as well. None of us had any caries until we moved to a bigger city. There was such a lack of tooth decay in town that there was no dentist available in town. He wasn't needed, lol.
My first case of caries appeared when I was about 25 or so, after like 5 or 7 years in the big city after I moved. Of course, our diet was also purely natural, lots of fish, coconut oil, rice, green bananas, plantains, sweet potatoes and so forth. Lots of fruits like mangoes, grapefruit and "Byrsonima crassifolia" which we call Nances. We didn't have money for sweets which I think helped a lot. The ONLY people who had tooth decay were the ones who were sick as kids and were given lots of medicine, which for kids normally came in the form of some syrup.
Up to this day, I get all the time the: "Wow, you have perfect teeth" and so do my friends from back then. So I do believe that one can have good teeth in the absence of fluoride, provided the diet is adequate. I do believe that the absence of fluoride and the abundance of sweets that are readily available could be a bad combination for the teeth. But on the other hand, the absence of fluoride combined with a good diet and the absence of sweets works perfectly ok as well.
That's just my opinion based on my very limited empirical data. One town in the middle of nowhere in Honduras.
Vivalavida