Whiter Teeth! (Part 2)
“I don’t like the color of my teeth. There are lots of options for making teeth whiter. How do they differ?”
In our last post, “Whiter Teeth! (Part 1)”, we discussed the difference between tooth whitening and bleaching. Typically, when patients ask us to help make their teeth whiter, they are requesting a recommendation for a bleaching procedure. No matter which technique is selected, they all require that a bleaching formula be applied to the surface of the teeth to achieve the effect.
In general, one of two substances is applied in one of three ways. Let’s take a look at them to see how they differ.
Two Bleaching Compounds
Carbamide peroxide was first introduced and recommended as an effective agent for use in bleaching teeth in 1989 by Dr. Van Haywood and my AAED colleague Dr. Harald Heymann. It now is the most-studied bleaching material in history. 9 out of 10 patients have stated that they have achieved a successful whiter tooth color when using it under dentist supervision for a period of 2-4 hours a day over a period of 2-6 weeks. Different concentrations of the carbamide peroxide solution will all yield the same eventual color change—but with differing amounts of time. To work, carbamide peroxide must first undergo a chemical reaction to form hydrogen peroxide (the chemical that actually causes the whitening effect.)
Since hydrogen peroxide is the molecule that eventually bleaches teeth to achieve a lighter color, dental suppliers concluded that they could manufacture formulations of hydrogen peroxide that could be applied directly to teeth to speed up the process. It turns out that hydrogen peroxide does interact with the staining pigments that are embedded in teeth much more rapidly than carbamide peroxide. This means that hydrogen peroxide “works faster”, but there is a trade off. Simultaneously, it is “more caustic” in its potential to cause unwanted tissue irritation and tooth sensitivity side effects.
Three Bleaching Strategies
In-Office Power Bleaching uses hydrogen peroxide applied to the surface of the teeth while supervised by a team in a dental office. The highly-concentrated solution is typically applied and then reapplied in three 20-minute periods to combine for a whitening session that lasts about an hour. During the bleaching session, a bright blue light is positioned to shine on the treated teeth. Typically, bite support blocks or oval lip retractors are used to prop the mouth open while temporary rubberized barriers are used cover the surrounding gums—all in an attempt to eliminate any contact between the bleaching gel and the surrounding soft tissue to reduce the chance for unwanted irritation of the lips, cheeks, and gums.
At-Home, Dentist-Supervised Bleaching requires the fabrication of a thin shell that is custom-fit specifically for your teeth. A proper tray fit is critical to keep the bleaching gel in close contact with the surface of the teeth. The supervising dentist will give you a set of dispensing tubes that contains either carbamide or hydrogen peroxide—depending on your personal goals and individual treatment tolerance. As we discussed earlier in this post, the carbamide peroxide works slower and must be applied for a few more hours each day to achieve the desired effect. The hydrogen peroxide products work faster and can be applied for a shorter length of time each day but are also are more likely to cause unwanted tooth sensitivity in the process. Either way, daily use of the custom tray/bleach system at home can provide significant whitening results in a few weeks.
Over-the-Counter, Do-It-Yourself Bleaching uses “one-size-fits-all” trays, flexible bleach-infused strips, or paint-on applicators to place bleaching gel against your teeth. Single doses are less expensive but also less effective than other methods because the concentration available for unsupervised “over-the-counter” is fairly low. Multiple applications over a much longer period of time are required to achieve the whitening result that would be achieved with the home tray method. These products are availalble in drug stores, on the internet, or from television “infomercials”.
Factors to consider
You should know that no amount of bleaching will yield “unnaturally” white teeth. There is a limit—a plateau—in the whiteness level that can be achieved, and the maximum final result varies from patient to patient.
During the oxidation reaction that eliminates the molecules that stain and darken teeth, oxygen bubbles are formed between the crystalline column structure of the enamel that covers the teeth. Although they eventual escape, these bubbles initially cause an optical shift that temporarily exaggerates how white the teeth appear. For this reason, the true whitening results are not seen until approximately two weeks after bleaching procedure is finished. This is an important consideration if you are about to have cosmetic dental treatment done. If acrylic bonding, porcelain veneers, or other restorations will be made to your newly bleached teeth, they should not be placed until a minimum of two weeks following bleaching to ensure proper adhesion as well as shade matching.
Although bleaching does whiten tooth structure, it does not whiten restoration color. If you have existing white restorations that match your tooth color well prior to bleaching treatment, they will not match after treatment. You will most likely need to have those restorations replaced to match the new lighter color.
Gum recession can present a problem as well. A shrinking gumline will often reveal the underlying yellowish root structure that was previously hidden. The yellowish root color does not respond well to bleach and usually retains much of its original color.
Bleaching can cause teeth to become sensitive temporarily to touch and/or temperature. In fact, some patients say they experience an “electrical” discomfort that radiates through the center of the affected teeth. Two out of three patients experience some sensitivity.
Why does it happen? Studies have shown the peroxide—the active bleach ingredient—can easily penetrate to the nerve chamber in the center of the tooth in just 5-15 minutes because the molecule is so small. Teeth with associated gum recession (shrinkage), cracked walls or deteriorated restorations are often more susceptible to bleaching sensitivity since even more of the bleaching agent is able to penetrate down to the nerve of the tooth. Although the sensitivity is only temporary, it can last several days or even weeks.
With today’s dentist supervised systems, many patients with sensitive teeth can still undergo tooth whitening procedures with the use of potassium nitrate to help alleviate the sensitivity. It comes in special toothpastes that are brushed directly on the irritated teeth. It also comes in gel formulations that are intended to be used in alternating applications with a home tray system. Sensitive patients should even consider using potassium nitrate products before bleaching sessions to prevent the sensitivity in the first place.
So which product and method is the “best”? We will see what scientific research has to say and answer that question in our next post “Whiter Teeth! (Part 3)”. Stay tuned.
Copyright © 2013 Stephen R. Snow, DDS
 Matis BA, Gaiao U, Blackman D, et al: In vivo degradation of bleaching gel used in whitening teeth. J Am Dent Assoc.130(2):227-235, 1999.
 Leonard RH, Sharma A, Haywood VB: Use of different concentrations of carbamide peroxide for bleaching teeth: an in vitro study. Quintessence Int. 29(8):503-507, 1998.
 Haywood VB, Leonard RH, Nelson CF, et al: Effectiveness, side effects and long-term status of nightguard vital bleaching. J Am Dent Assoc. 125(9):1219-1226, 1994.