Tray teeth whitening: Why are some whitening gels formulated with hydrogen peroxide and others with carbamide peroxide?

The vast majority of the whitening gels manufactured for use with an at-home tray-based teeth whitening system are formulated with peroxide. And if you were to read the ingredient list of very many of these products you would soon learn that the two most common forms of peroxide that are used are carbamide and hydrogen peroxide. So why is this? Why are these two compounds used and what is the difference between them?

The science of teeth whitening is based on the action of free radicals.

The science of the matter is this. The whole process of whitening teeth is founded upon the oxidative action of molecules called as "free radicals." In the case of teeth whitening, free radicals break down (oxidize) pigmented compounds that have become trapped in a tooth's enamel layer. Because the byproducts that result from this process are colorless, a whitening effect is created.

Free radicals are produced by the degradation of peroxides.

One compound that can generate free radicals when it breaks down is hydrogen peroxide. And this is precisely why some brands of tooth whiteners are formulated with it. There is a hitch however. Hydrogen peroxide itself is a very reactive molecule and therefore breaks down and creates free radicals quite readily. This means that once a hydrogen peroxide-based tooth whitener is placed into use, the whitening process begins, and subsequently becomes spent, fairly rapidly.

Compared to hydrogen peroxide, carbamide peroxide is a relatively stabile compound. When it decomposes it degrades into hydrogen peroxide (and urea), which in turn, creates the free radicals necessary for the tooth whitening process. But since this transformation takes some time, the free radicals are created over a longer time period and at a more sustained rate.

The type of peroxide found in a whitener's formulation can have an effect on its characteristics.

This last mentioned fact can have an affect on the manner in which different types of peroxide-based teeth whitening gels are intended to be used. At least this is true historically. The relatively rapid formation of free radicals by hydrogen peroxide-based tooth whiteners suggests that these gels will become depleted of active ingredient fairly quickly. A hydrogen peroxide whitener therefore might be considered to be most appropriate for short duration bleaching treatments, such as those performed during waking hours when the duties of life often interfere with our plans. The slower, more sustained, release of free radicals by carbamide peroxide whiteners suggests that they are more suited for longer treatments, such as those performed overnight.

With modern products the distinction between these two peroxides 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 (there are a number of issues involved) and understanding this point is paramount. Not using your 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. (The information found on our pages only discusses tray-based tooth whitening technique utilized with a 10% carbamide peroxide whitening gel.)

Both carbamide and hydrogen peroxide whitening gels can be expected to give the same whitening results.

Of course there are other differences between those teeth whiteners formulated with hydrogen and carbamide peroxide but for the most part they are issues that manufacturers must deal with. With all factors being equivalent, both hydrogen and carbamide peroxide products can be expected to produce the exact same teeth whitening results and can be considered to be interchangeable products.

Dentists across the nation readily dispense both types of whitening gels.

As a point of interest, the following list contains the brand names of many of whitening gels (intended for use with tray-based teeth whitening technique) that are sold directly to dentists for use with their patients. We've divided them in to two groups as to whether the gel is formulated with carbamide or hydrogen peroxide.

Notice that there is no strong bias in the marketplace. Both types are readily available and sold to fill the exact same purpose. Also notice, as suggested above, that two carbamide peroxide whiteners have the term "Night" in their name. In similar fashion, the names of two of the hydrogen peroxide whiteners have the word "Day" in them.