My teenager just got her braces off and wants to get her teeth whitened. Is that OK?

"We like to wait until the child has reached the age of dental maturity," says Dr. Ronald Kosinski, chief of pediatric dentistry at Cohen Children's Medical Center of New York in New Hyde Park. That means that the roots of the child's teeth have completely formed. "Everyone reaches the age of maturity at a different rate. That's just the way genetics are," he says.

The rule of thumb for girls is 14 or 15 and already menstruating, Kosinski says. For boys, the age is more likely from 14 to 17. A dental X-ray will indicate whether your child's roots are formed. Before then, "we don't know what the potential side effects could be. There are no long-term studies," Kosinski says. This applies to bleaching in a dentist's office or with take-home bleach trays from a dentist, where the bleach is stronger than with over-the-counter products.

Kosinski suggests waiting until roots are fully formed even with drugstore products, though the companies selling them may not be as strict. According to the Crest website, "No Crest 3D White Whitestrips product is intended for use in children under the age of 12." Says Alissa Hammond, spokesman for Procter & Gamble, which makes the product: "We've done more than 100 clinical tests over the past decade to determine the safety of the product." Those tests included teens, she says. Parents should supervise teens to be sure they follow the directions for use.