Many societies that have extremely low sugar consumption have fairly healthy teeth. Also, in many countries people brush with fluoridated toothpaste. Either o

Many societies that have extremely low sugar consumption have fairly healthy teeth. Also, in many countries people brush with fluoridated toothpaste. Either of those might explain your ex's teeth. Fluoride in tap water was basically a large-scale public health solution for populations that didn't have alternatives. we have enough data to show fairly convincingly that as a health intervention it's not particularly effective compared to alternatives, and can contribute to the risk of fluorosis.