Fluoride is like any mineral, too much and it can be bad. There is nothing synthetic about fluoride, it is naturally occurring in the ground and ground water and is also in fruit and other plants. The most effective means of strengthening your teeth with fluoride is not by eating or drinking it. Fluoride strengthens teeth most effectively by topical contact with them where an exchange of ions occurs to form a harder less soluble mineral. Using fluoride toothpaste and mouth-rinses topically will achieve the best results.