Tea plants accumulate fluoride in their leaves. In general, the oldest tea leaves contain the most fluoride. Most high quality teas are made from the bud or the first two to four leaves—the youngest leaves on the plant. Brick tea, a lower quality tea, is made from the oldest tea leaves and is often very high in fluoride. Symptoms of excess fluoride (i.e., dental and skeletal fluorosis) have been observed in Tibetan children and adults who consume large amounts of brick tea. Unlike brick tea, fluoride levels in green, oolong, and black teas are generally comparable to those recommended for the prevention of dental caries (cavities). Thus, daily consumption of up to one liter of green, oolong, or black tea would be unlikely to result in fluoride intakes higher than those recommended for dental health. The fluoride content of white tea is likely to be less than other teas, since white teas are made from only the buds of the tea plant.
It has been found that not only fluoride but the polyphenols in tea also act to reduce tooth decay. Recent studies have further revealed that tea inhibits the growth of other harmful microorganisms in the oral cavity.