Everybody knows that tea contains caffeine, which has some negative impact on the body but not on the teeth. There is a lot less fluorine in tea than caffeine, but it does a lot of harm to your teeth. Fluorine is necessary for the human body, but when there is too much of it, it affects the health of bones and teeth. To be safe, don’t drink more than 4 cups a day, and don’t drink cheap bagged tea.