what I have read is that instead of taking plain ACV+water, its a good idea to react ACV with Baking Soda. A lot of CO2 is released in the reaction and the acetic acid and malic acid in ACV is converted in "Na-Acetate" and "Na-Malate" which are alkaline form. Also this will not hurt the stomach.
As long as body has enough bi-carbonates, it will convert the acid to alkaline form. But if one takes lot of ACV or lemon juice, it will not only harm the teeth, but make the body more acidic.
ACV has a pH of arnd 3 or something. Add BS, to raise the PH to upto 7. this is healthier than ACV alone. And your teeth will thank u for doing this. Add just enuff BS to neutralise the acid. No more.