New evidence finds side effects from brightly bleached teeth.

Polishing pearly whites with certain over-the-counter products can damage gums or teeth, according to dental surgeon Dr. Guy Sutton.

"There has been case reports with damage to the surface of the enamel of the teeth," Sutton said.

Dentists say custom-made mouth trays filled with bleach cream or gel is a safe way to avoid gum trouble while whitening.

"If the peroxide gel is in contact with the gum tissue, it can cause minor ulcerations of the tissue," Sutton said.

CarbaMide peroxide is the active bleach ingredient found in nearly all teeth whiteners. Scientists say it's safe, but some over-the-counter whitening gels contain hydrogen peroxide -- which has been shown to eat away enamel when overused.

"CarbaMide peroxide is safe. Hydrogen peroxide may be increasing your risk," Sutton explained.

Tooth enamel can also become damaged if the product includes a prewhitening wash that contains acid, KNSD-TV in San Diego reported.

"Watch out for products where you put something on your teeth and it makes it feel really, really rough. That would be something acidic," Sutton said.

Cold sensitivity is only a temporary problem in about 10 percent of people who bleach.

"The bleaching solution is cleaning the tooth so thoroughly that it's opening microscopic pores in your tooth and gives you less of a buffer that usually works like a blanket," Sutton said.

But most whitening products will not damage fillings, and are even safe enough to swallow.

"If you swallow some of this, it's no problem. It breaks down into water and urea, two products your body makes naturally," Sutton said.

If you have over-whitened your teeth and want the natural color back, Sutton said not to worry. Drinking plenty of coffee, tea and red wine will re-stain your smile within a few months.