Tray teeth whitening: Why are some bleaching gels formulated with hydrogen peroxide while others contain carbamide peroxide?

Both hydrogen and carbamide peroxide products can be can be expected to produce the same whitening results.

When comparing similar strength products (whiteners formulated so to produce a similar concentration of bleaching molecules, termed 'free radicals') both hydrogen and carbamide peroxide products can be expected to produce the same whitening end results and can be considered to be equivalent products.

This is not to say that differences between these two peroxides don't exist. They do. But, as we describe below, they are typically differences that are a greater concern for the whitener's manufacturer, as opposed to the person bleaching their teeth.

Dental professionals routinely dispense both types of peroxide whiteners to their patients.

As a point of interest, and as evidence that both of these peroxide compounds are routinely used in the formulation of whitening gels, the following lists contain the names of some of the brands of whiteners that are sold directly to dentists for use with their patients.

The two groups that we've created are based on whether the whitener is formulated using carbamide or hydrogen peroxide.

Tooth bleaching gels formulated with carbamide peroxide.

Discus Dental NightWhite, GC TiON Take Home, Life-Like Cosmetic Solutions, Natural Elegance Plus, Nupro White Take Home, Omni White & Brite, Opalescence PF, Pola Night, Sapphire Take Home, Star White, Venus White

Tooth bleaching gels formulated with hydrogen peroxide.

Beyond StayWhite, Discus Dental DayWhite, Nupro White Take Home, Perfecta Bravo, Perfecta Rev, Pola Day, Zoom! Weekender

[ Source: Dentistry Today. Guide to At-Home Whitening Systems. December 2008. ]

As you can see, there is no strong bias in the marketplace between carbamide and hydrogen peroxide tooth whitening gels. Both of these types of products are readily available. And they are sold to dentists for the exact same purpose. (Notice that some brands even manufacture both types of formulations.)

So what is the point of providing this information?

We're interested in helping consumers make appropriate decisions founded on facts. Yes, there can be various reasons why a dentist or a manufacturer might have a preference for a carbamide peroxide or hydrogen peroxide product. But making a claim that one type of product whitens more so or differently than the other because of some inherent property associated with the peroxide compound itself is not valid and we think you should be aware of this.

Why are hydrogen and carbamide peroxide used in teeth whitening products in the first place?

The vast majority of gels manufactured for use with at-home tray-based teeth whitening systems are formulated with peroxide as the bleaching agent.

And if you were to read the ingredient list of very many of these whiteners you would soon learn that the two most common forms of peroxide that are utilized are carbamide and hydrogen peroxide.

So, why is this? Why are these two compounds used and what is the difference between them?

How does whitening teeth work? - The science.

The whole process of whitening teeth is founded upon the action of a type of molecule called a "free radical." By nature free radicals are very reactive. And because of this they are able to interact with and subsequently break down (oxidize) other compounds.

In the case of stained teeth, free radicals are used to break down the pigmented compounds that have become entrapped in a tooth's enamel layer. Because the byproducts that are formed during this oxidation process are colorless, a whitening effect for the tooth is obtained.

Peroxide compounds are included in tooth whitener formulations because they release free radicals.

One type of chemical compound that releases free radicals as it breaks down is hydrogen peroxide. There is a hitch however. As a compound, hydrogen peroxide is relatively unstable. This means that it breaks down (degrades) quite readily.

Historically hydrogen peroxide proved to be a difficult compound to work with.

On a practical level (at least historically), hydrogen peroxide's high level of reactivity lead to two difficulties. One was that it was difficult for a manufacturer to create a product that had a long, predictable shelf life. The other was that once the whitener had been dispensed the whitening process would begin and subsequently become depleted fairly rapidly.

Historically carbamide peroxide offered some advantages.

In comparison to hydrogen peroxide, carbamide peroxide is a relatively stable compound. As it breaks down it first transforms into hydrogen peroxide (and urea), which in turn breaks down and produces the free radicals necessary for the tooth whitening process.

Because its transformation into hydrogen peroxide takes time, however, free radicals are produced over a longer time span and at a more sustained rate. This gives the potential for a more predictable and controlled whitening process. This lower level of reactivity also makes it easier for a manufacturer to create a stable product with a predictable shelf life.

Today both types of peroxides are routinely used in tooth whiteners.

Over time manufacturers have developed ways to minimize the difficulties associated with using hydrogen peroxide in a whitener's formulation. And because of this, as our listing of products shown above demonstrates, nowadays it is commonplace to find either type of peroxide used as the active ingredient in a bleaching gel.

( Related content: What's contained in the formulation of tooth whitening gels? )

The type of peroxide found in a whitener's formulation can influence the way it is best used.

The fact that hydrogen peroxide whiteners tend to release free radicals at a more rapid rate than their carbamide peroxide counterparts can influence the way a whitening product might most ideally be put to use.

The relatively rapid formation of free radicals by hydrogen peroxide-based whitening gels suggests that these products will become depleted of active ingredient comparatively quickly. A hydrogen peroxide whitener might, therefore, be considered to be most appropriate for short duration bleaching treatments, such as those performed during waking hours when the duties of life can easily interfere with bleaching plans.

The slower, more sustained, release of free radicals by carbamide peroxide whiteners suggests that they might be more suited for longer treatments, such as those performed overnight.

One confirmation of this theory is demonstrated by our listing of bleaching gels given above. Notice that two of the carbamide peroxide-based whiteners literally have the word "night" in their name. In similar fashion, two of the brand names of hydrogen peroxide whiteners contain the word "day."

( Related content: Which is best, performing your tray tooth bleaching sessions during the day or overnight? )

Hydrogen and carbamide peroxide whitening products may not have the same instructions set.

With the modern products of today, the distinction between carbamide and hydrogen peroxide-based bleaching gels has become less of an issue. This is not to imply, however, that all types of whiteners are intended to be used in the exact same fashion. They are not and understanding this point is paramount.

Not using a tooth whitening gel in its intended fashion can lead to significant complications with whitening side effects. In all cases you must read and follow the instructions that come with your specific tooth whitener. (When reading our pages, please realize that the information they contain describes the use of a tray-based tooth whitening technique in conjunction with 10% carbamide peroxide whitening gel.)