"If there's plaque on your teeth, the bleach won't easily penetrate the enamel or lighten its color," he said. A thorough at-home brushing also will help. One caveat is that "if you have especially sensitive teeth, you may feel more discomfort if you bleach immediately after brushing, so wait 30 minutes to an hour before you use a whitener," said dentist Silvia Bilobron of Short Hills, N.J.
Soothe sensitivity • It's a common side effect that most people experience, typically for a day or two.
"The chemical reaction of bleaching opens the microscopic channels in teeth, causing discomfort," said Kantor. Using toothpaste for sensitive teeth, such as Sensodyne ProNamel, available for $6 in most drugstores, can help lessen the pain. Consuming acidic foods and beverages, such as grapefruit and orange juice, can increase sensitivity, as well, so avoid these while whitening and for up to a week afterward, adds Bilobron.
Prevent new stains • During testing, researchers ate and drank things they normally would have but for even better results, stay away from staining foods and beverages during and after whitening. The small channels in your teeth remain open for a few days afterward, which makes teeth susceptible to stains.
Avoid common culprits such as red wine, coffee, blueberries, grape juice, tea and tomato sauce: "If it can stain a white T-shirt, it's likely to stain your teeth," said Kantor.
Go electric • Swap your manual toothbrush for an electric version. "Most people don't brush properly or for long enough. A powered toothbrush with a self-timer compensates for that," said Joseph Banker, a dentist in Westfield, N.J. Although brushing alone won't give you dramatic results, "daily use of an electric toothbrush, paired with whitening toothpaste, is the most effective way to maintain whitening results," added New York City dentist Michael Apa.
Try Oral-B Professional Care Smart-Series 5000, available for around $160 in many department stores. Testers loved its timer and its pressure sensor.
Rinse, don't brush • After eating or drinking something staining, your natural inclination may be to brush right away, but you should wait at least 30 minutes. "Brushing immediately afterward can push pigments and the enamel-eroding acid in things like wine or dark soda into teeth rather than remove them," said New York City cosmetic dentist Nancy Rosen. Rinse with water, then wait. Your saliva will naturally wash away some of these elements.
Don't overdo it • In-office bleaching should be done no more than once a year, said Kantor, but given that over-the-counter products don't have the same high concentrations of bleach, you can use them regularly without any risk of damage.
Avoid the biggest smile-staining culprit • Seventy-five percent of Good Housekeeping's Facebook fans said coffee was their biggest tooth-staining vice. Can't give up the java? Sip through a straw to keep from discoloring the fronts of your teeth.