Generally, the longer you keep a stronger solution on your teeth, the whiter your teeth become. However, the higher the percentage of peroxide in the whitening solution, the shorter it should be applied to the teeth. Keeping the gel on longer will dehydrate the tooth and increase tooth sensitivity.

There are pros and cons to each option, but before you try at-home tooth-bleaching kits, be sure to talk to your dentist. Not everyone will see good results. Bleaching will not whiten porcelain crowns or composite tooth-colored bondings.

Teeth whitening done by your dentist can get teeth brighter faster. The bleaching solution is usually much stronger than at-home kits. Also, heat, light, or a combination of the two may be used to speed and intensify the whitening process.

The most dramatic results -- teeth generally get three to eight shades brighter -- usually take several 30- to 60-minute in-office visits. Some dentists use techniques that can be done in a single 2-hour appointment (e.g. the Zoom system). The cost of in-office tooth whitening varies, but can range from $500 to $1,000.