I think the two main reasons that teeth go ( besides eating acidic fruit continuously ) is the mineral imbalance excess fruit causes, and probably why some show decay and others don't is that there are certain bacteria that create acidic byproducts when feeding on sugar that tears down enamel and allows the bacteria to then start feeding on dentin. Some people harbor more of these than others, and those are the ones that really need to avoid sugar and fruit. It's not just the tooth structure that is damaged but pockets of bacteria that form under the gum and proliferate by continual feedings of sugar in the mouth. those millions of bacteria continually breeding and protected from brushing deep in pockets are like an army with unlimited reserves.