Tooth whitening is the most often-used cosmetic dentistry treatment, and Americans spend an estimated two to three billion dollars annually on either in-home treatments or in-office procedures. While few of us would doubt the desirability of a bright sparkling smile, there are some downsides and limitations to what can be done. Knowing some of these issues will help you prepare a list of questions to ask your dentist before you agree to a course of tooth bleaching.

- Sensitivity and irritation

Tooth whitening procedures can cause a degree of irritation, or increased dental sensitivity, in patients. Irritation is usually a result of bleaching agents coming in contact with soft tissue like gums, while sensitivity is caused by high levels of hydrogen peroxide or other bleaching compounds affecting the tooth itself. Neither of these problems should continue for more than a day or two.

- Varying degrees of success

Whitening is best measured as a change, rather than an absolute value. In other words, if your teeth are particularly dark to start with you are less likely to end up with brilliantly white teeth after whitening treatments. It may be possible to reach the shade that you're hoping for eventually, but it will take longer and more sustained treatments in your case.

- Remember, it's tooth whitening not filling whitening

Whether at home or in your dentist's office, the effect will only be seen on your natural teeth. Fillings, veneers, crowns, bridges and other reconstructive dentistry will not be affected. If you're planning to also have these kind of procedures done in tandem with tooth whitening, you should first have the whitening treatment. Once your natural teeth have achieved your desired shade, reconstructive elements can be color-matched to your new shade.

- Nothing lasts forever

Immediately after your treatment you can expect your teeth to darken again slightly; this is known as the rebound effect and is perfectly normal. The color will then stabilize and should remain constant for at least six months and up to a couple of years. You can maintain the color by scheduling touch-up treatments every six months or so.

- Tooth whitening systems are all similar

There are three broad categories of whitening procedures, and : In-office treatment; dentist-prescribed at-home treatment; and over the counter treatments. In-office treatment is usually the most effective, while OTC treatments are the least. The differences are primarily a result of the concentration of bleaching agent in the various treatments; your dentist will use more powerful compounds in the office than you can (or should) purchase to use at home.

None of the various brand names of in-office treatments - Zoom, Britesmile, Opalescence, etc. - are particularly more effective than the next. So long as your dentist is using the most current methods, the results should all be satisfactory.

I highly recommend that you speak to a dentist about tooth whitening, rather than using an over-the-counter treatment; professional advice can maximize the effect of this procedure, and you'll get better results overall with fewer potential side effects.