(because the solution is not as strong)—usually two to three weeks of wearing a bite plate at night or during the day—and your teeth have to be touched up periodically. The cost ranges from $200 to $500. Bleaching works best if teeth have yellowed or browned due to external stains; internal or gray stains are not much improved.

Skip the mail-order, at-home tooth-whitening systems. "You should never try to bleach your teeth without a dental exam first," says Christine Dumas, D.D.S., a cosmetic dentist in Marina del Rey, California. "If you have cavities, exposed roots or periodontal disease, the solution can cause irreversible damage."

Reshape Your Smile

Cosmetic contouring, using a small grinding polisher, reshapes teeth to resolve discrepancies in shape, length and position. Contouring can also be used to alter age-related changes in teeth. As we get older, the edges of the front teeth get flatter and the angles more square. "Teeth can be reshaped by as much as one millimeter (about ten times the thickness of this page) without causing sensitivity or damaging the nerve," says Dr. Lowenberg. Contouring is often combined with bleaching to improve a smile.