Q: How Does Teeth Whitening Work?

By Dr. Cheryl Bresnahan


I often get asked about teeth whitening and the options available to my patients.

Teeth have different colors and yellow teeth do whiten better than grey teeth.  Grey teeth can whiten, but you may need to use additional kits to do so and you may not get a bright white, but rather a lighter shade of grey.

All teeth will discolor with time and contributing factors are drinking dark colored beverages and smoking. Teeth that have been stained by tetracycline may take up to 6 months to whiten.

To whiten teeth, you have to have a whitening gel in contact with the tooth surface for an extended period of time, usually one hour.

The gold standard or best way to whiten your teeth is professionally through the dental office. A custom tray is constructed to just fit your teeth. Every day you wear the custom tray with the whitening solution inside for about 3 weeks.  The final result provides even whitening on all the teeth in your smile zone.

Whitening toothpastes, rinses, and gel pens do not stay in contact with the tooth structure long enough to whiten teeth.  I would be very cautious of some whitening toothpastes because some do contain strong acids that can eat the surface of your tooth away.

Are There Side Effects to Whitening Teeth?

The biggest side effect is tooth sensitivity to cold while you are whitening your teeth, but that will dissipate after you have finished whitening your teeth.  Interestingly enough, the actual chemical that whitens your teeth was originally developed as a gum treatment to make the gum tissues healthier.  A side effect of that occurred is that they noticed that it whitened teeth.  Another interesting fact is that the chemical that whitens teeth inhibits plaque formation so it actually has been indicated as a cavity prevention strategy.

Natural teeth will whiten; crowns and most fillings do not.  If you have crowns on some of your front teeth, you may notice a color difference as the teeth whiten.  If the crowns have a lighter color than your teeth, whitening the teeth can make the crowns blend in better.  If the crowns are yellow and you whiten your teeth, you may have to replace the crowns after you have finished whitening your teeth.

Professional Teeth Whitening vs. At-home Products

There are two professional ways to whiten your teeth.  One way is with take-home custom trays with whitening solution, and the other way is to sit in the dental chair and have a strong whitening solution applied to your teeth.  This is known as a jump start and you are still given take-home trays to finish whitening your teeth.  Bottom line is that both ways of whitening your teeth will create the same end results.

The in-office whitening is more expensive because it involves chair time.  Some of you have seen a pretty blue light called Zoom glowing on peoples teeth in shopping areas. Be cautions of these whitening procedures because they are not being carried out by licensed professionals and the addition of the blue light has proven to do nothing to final result, but it sure grabs your attention.

The best over-the-counter whitening product is called Crest Whitestrips.  It is a 5% solution of carbamide peroxide where as our professional gel is 22% carbamide peroxide.  The Crest Whitestrip box contains strips that are a certain size, one size fits all, and the teeth will whiten just where the strip is applied.  When the box is used up, that is it.  Because we will continue to drink dark beverages, our teeth will stain again and most people “touch-up” their whitening every 2 – 3 years.  What this means is that you already have the custom fit tray and all you need to do is buy more whitening solution from us.   There is no harm in trying Crest Whitestrips first to see what kind of results you get.

My only word of caution is to not use the strips too often.  The more often you whiten your teeth, the more translucent or see through your teeth can become.  It is better to whiten your teeth every 2 – 3 years verses once a month.

Dr. Cheryl Bresnahan is a licensed dentist and the founder of Dental Perfections in Whitewater, WI. If you'd like to ask her a question, please visit the Ask Dr. Cheryl section of our Web site.