AZUZ: In the early 1900s, Frederick McKay became known for his research into what? Fluoride and teeth, compression and engines, X-rays and bone health or telegraph and wiring. McKay was a dentist who’s work examined the effects of fluoride on teeth.

He noticed that too much fluoride caused stains on the teeth of children in part of Colorado, but it also protected their teeth from decay. A debate over this continues to this day. The U.S. Food and Drug Administration is considering a lower limit on the amount of fluoride that’s allowed in bottled water. Fluoride is often added to bottled and tap water to prevent cavities and this is in addition to the fluoride that's added to toothpaste and mouthwash and provided at dentist offices. Currently the FDA allows bottled water with added fluoride to contain between 0.8 and 1.7 milligrams per liter. The new standard would limit that to 0.7 milligrams of fluoride per liter.

But too much fluoride, especially for children who’s adult teeth are still forming, can lead to a problem called dental fluorosis when white patches form on teeth. In extreme cases, this can cause pits in the teeth. And some studies outside the U.S. have suggested that pregnant women with higher amount of fluoride in their bodies can have children with lower IQ scores. Some scientists say the new FDA limits on bottled water with fluoride don’t go far enough, that the limit should be lower. The American Dental Association, which supports adding fluoride to water, says the FDA’s proposal would still work to prevent tooth decay. The new rule has not been finalized yet.