The most effective at-home whitening treatments come in the form of paint-on whiteners, strips and trays that make use of hydrogen peroxide or carbamide peroxide. They work because they allow the hydrogen peroxide to penetrate the porous enamel of the teeth where it works on the dentin, using its free radicals to form molecules that reflect less light and make teeth appear whiter to the eye.
Paint-on whiteners allow you apply a hydrogen peroxide solution to specific stains on specific teeth. So if your teeth are mostly white and you just have a few blemishes, this might be a good choice for you. It also is a viable solution for individuals with sensitive teeth. However, because nothing prevents your saliva from washing away the solution once you close your mouth, these types of treatments tend to be the least effective in this category.
Trays and strips however, provide you the most at-home whitening power. That's because they leave the hydrogen peroxide against your teeth the longest and they both form barriers that prevent saliva from interfering with the whitening process. Using strips or trays filled with a whitening gel for 30 minutes a day for at least a week can whiten teeth five or more shades [source: Good Housekeeping]. To get the most wonderful white from these products, try to look for strips and tray/gel kits that have the highest concentrations of hydrogen peroxide. As a general guide, dentist-prescribed solutions typically contain 15 to 38 percent hydrogen peroxide, while at-home concentrations can range from 3 to 15 percent [source: ADA Council on Scientific Affairs].
When considering a tray and gel system, be aware of the fact that over-the-counter trays may not fit your mouth correctly and could lead to gum irritation. If you are unable to find one that works for you, you might want to ask your dentist to create a custom-molded tray that you can fill with a gel purchased on your own.