SEATTLE (Reuters Health) - Dentists are now warning that you should not buy teeth whiteners or bleaches over the Internet or from other over-the-counter sources without first talking to your dentist or dental hygienist. They say individuals may have cavities, root exposures or other flaws that could cause problems after tooth bleaching.

Further, many advertisements are now overselling what their products can do in terms of whitening a person's teeth, according to some dentists who attended the 2001 Pacific Northwest Dental Conference here last week.

"The public may think that they can just go out and buy something over-the-counter and all of a sudden their teeth are going to be white. Well, they may have some discolorizations that aren't going to whiten as well or a variation in color that they aren't going to be pleased with; and secondly the concentrations (of bleaching agents) they can buy over-the-counter are much lower than what they can get through the dentist's office," said Dr. Susan Hollinsworth, a dentist in private practice in Seattle, Washington.

She said patients have complained to her that they wasted their money when buying some over-the-counter bleaching products. She suggested that patients should have a dentist set up a planned program.

Dr. Dennis Riendean, a dentist from Lewistown, Idaho, said many people are over-bleaching their teeth and ending up harming their overall oral health.

Individuals with tooth decay, heat or cold sensitivity, composite fillings or crowns may experience problems with certain bleaching agents, he said. Composite fillings may not bleach along with the other teeth and so the teeth may end up looking uneven in terms of color. A porcelain crown will also not lighten with the rest of the teeth. The whitening agents also may make some existing problems worse, according to Riendean and other dentists.

"Most of us think a supervised program with a dentist or dental hygienist is far superior to buying it from infomercials. I have people back on a regular basis while they are bleaching to check that the tray (containing the bleaching agent) itself is not irritating the gum tissue and they are not getting a reaction with the gum tissue or teeth," said Dr. Clifton Caldwell, a dentist from Spokane, Washington.