You’re right that fluoride prevents cavities by strengthening tooth enamel. But even if you drink bottled water, you may be getting the chemical from other sources. Many people use tap water to make stew or coffee, for example, and lots of commercially produced beverages and foods have small amounts of fluoride. Keep in mind too that you could buy bottled water with fluoride, or use a pour-through or faucet filter (neither filters out fluoride).
As for supplements, they’re usually not necessary for adults to have healthy teeth, as long as you brush at least twice a day with toothpaste that contains fluoride. However, if you’re very cavity-prone, consume lots of sugary foods or refined carbohydrates, take medications that cause dry mouth or have receding gums or eroded tooth enamel, extra fluoride may be warranted.
“We sometimes recommend topically applied fluoride in the form of toothpaste, mouth rinses, gels or professionally applied varnishes,” says Dr. Laurence R. Rifkin, a cosmetic and restorative dentist in Beverly Hills.