Tooth enamel (essentially calcium phosphate) reacts with all acids to form cavities (see any chemistry text dealing with solubilities). The proton of the acid pulls the phosphate right out of the enamel, and fast. By drinking a sip of water along with the acid during eating, the acid reacts chemically with water immediately to form hydronium ion and thus the enamel is saved. One can use milk or coffee for the same purpose, since they are both non-acidic. Dr. Albert Schatz, Nobelist who discovered streptomycin, found several decades ago that sharks' teeth with their excessive fluoride would dissolve just as readily in citric acid as ordinary non-fluoridated teeth, laying to rest the hypothesis that fluoride would stop cavities. The dental people (American Dental Association) pushed aside this discovery and Dr. Schatz' discoveries regarding excessive baby mortalities caused by fluoridation in Chili, South America as insignificant. They returned his mail 3x unopened and would not deal with him.
Some harmful acids (with pH <4) which are tart to the taste and attack the enamel include lemons, grapefruit, oranges, pineapple, kiwi fruit, tomatoes, vinegar, cider, vitamin C (especially chewable) and stomach acid. The lower the pH, the more rapidly the acids attack. Body acid (extremely weak) is insignificant in this process. Non-acid foods such as beans, bread and potatoes have no action on teeth. Worry about such foods is over. The only worry about non-acid foods is if they will crack the teeth due to their hardness.
I realize this doesn't fit with a fruitarian or vegan diet, but I'd start taking cod liver oil.