Higher concentrations of hydrogen peroxide, a bleaching agent used in many whiteners, can be delivered in a dentist’s office, so those procedures tend to be quicker than drugstore aids. But tooth sensitivity and gum irritation can occur, and the higher the concentration of the peroxide used, the more severe these side effects are likely to be.

More aggressive treatment isn’t necessarily more efficacious, either. A randomized trial of 90 patients found that use of a home bleaching tray with a 10 percent carbamide peroxide gel for two weeks offered the same degree of whitening as two in-office sessions using 35 percent hydrogen peroxide with light, which some dentists use because it supposedly activates bleaching agents.

Some dentists also use heat or even lasers to activate bleaching agents. But a 2007 systematic review of evidence in the journal Dental Materials found no added benefit from heat, light or lasers and suggested these methods “may have an adverse effect on pulpal tissue,” the soft material in the tooth’s center. If pulp is injured, it may require a root canal to fix.