Long after your teeth are fully formed, fluoride can still protect them. “It does so by becoming incorporated into the enamel, making the teeth more resistant to decay,” says the American Dental Association’s Clifford Whall. “It’s most beneficial to expose the teeth to fluoride several times a day through the use of fluoride toothpastes and mouth rinses.”

If you count on getting your fluoride through your water, take a good look at your filter, cautions Thomas Patrick Collins, a dentist in Greenbrae, California. Reverse-osmosis filters, for instance, take out much of the fluoride, but carbon filters (such as Brita) take out very little. Check with the manufacturer to find out how much fluoride your filter removes.