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Is Carbamide Peroxide or Hydrogen Peroxide more effective?

Published by 
SmileLabs™, LLC
Written by
Zachary Hilgers, DDS (Retired)
January 13th, 2010
© All Rights Reserved


It is often asked, “What is the difference between carbamide peroxide and hydrogen peroxide, and which one works better for teeth whitening or tooth bleaching?” This monograph reviews the literature and research to find the answer to this oft-times perplexing question. There are many differing opinions put forth by various bleach manufacturers, suppliers, and cosmetic teeth whitening companies, but along with their claims of one type being superior to the other, they usually don’t show any scientific proof and research to back up their arguments.  This will set the record straight by showing what the science is behind peroxide bleach in each of its forms.  Instead of relying on hearsay and advertising hyperbole, it is this science that SmileLABS™ uses to formulate their proprietary bleaching gels.


Historically, modern cosmetic teeth whitening or teeth bleaching began in 1989 when a pioneering dentist, Dr. Van B. Haywood, invented a treatment modality for his patients that wanted whiter, brighter teeth. Using a very weak bleach, specifically 10% carbamide peroxide in a viscous gel form, he placed it in an easily made dental appliance called a nightguard (used for patients that suffered from nocturnal bruxism or teeth grinding.) His patients wore this custom-made appliance against their upper teeth for a period 10-14 days while they slept every night. Then the same treatment was done for the lower teeth. Some dentists still use this exact method as one of their treatment options for teeth bleaching.[i]

Today, two types of bleach are used to bleach or whiten teeth, the original carbamide peroxide and one that is hydrogen peroxide-based. I’ll go more into each type later in this paper. Cosmetic teeth bleaching is now performed, in various methods, either in a dental office, at home by the consumer using over-the-counter (OTC) products, or with the help of independent entrepreneurs, such as Authorized SmileLABS™ Dealers.

The actual teeth bleaching procedure is still accomplished by placing a peroxide-based (either hydrogen or carbamide) bleaching gel, via various methods, into direct contact with the teeth. This contact of bleach to teeth is made either by painting the gel directly onto the teeth or using the custom tray method. It has been shown that these two modalities will result in noticeable whitening of the teeth. The finished degree of whitening ultimately achieved is predicated on the relative type, the strength or concentration of the peroxide-based gel that is used, as well as the amount of time that the active gel is left in contact with the surface of the teeth.

If the concentration is low, a longer amount of contact time against the teeth with the active bleach is needed to achieve a satisfactory result. This meant that for the patient a number of daily treatments were needed either in the dental office or at the patient’s home for the teeth to become satisfactorily white.

Making the teeth bleaching gel concentration stronger, on the other hand, would speed the color change, but would often lead to increasingly painful tooth sensitivity, which was a very non-desirable result for both the patient and practitioner. So, experience showed that a good result could be obtained at home if the patient used either a medium peroxide concentration of bleaching gel coupled with a regimen of spacing the treatments into an hour or less per day for a number days to a week.

Alternatively, the old stand-by of all-night bleaching with a low peroxide concentration gel every night for a 10-21 day course of treatment could be still used. These two variations of the teeth bleaching processes have been done for many years with a good and predictable outcome for the patient who actually correctly completes the treatment regimen.

The only downside was that results were not immediately obtained, but were gained incrementally over a number of days or weeks. Since this type of treatment was done unsupervised at home, strict compliance with treatment guidelines was many times hard, if not impossible to maintain, and results and patient satisfaction with the treatment were many times negative.

Therefore, many a practitioner hoped for a way that could combine the shortest course of treatment, coupled with the ability to be able to supervise the entire treatment to a satisfactory conclusion, that was both easy and pain free from sensitivity to the patient.

This hope resulted in what is now known as Chairside Power Bleaching, the system used by SmileLABS™. By combining a higher concentration of peroxide gel with the use of a strong, safe wavelength of light as an accelerator or catalyst to the bleaching reaction, a much shorter time of contact between gel and tooth resulted that increased the bleaching efficiency of the gel and shortened treatment time by a very large factor, while keeping the process mostly free from sensitivity and achieved the patient’s desire of whiter teeth in minutes instead of hours or days.  The only question that now remains is how does the carbamide and hydrogen peroxides differ and what is the best form of peroxide-based gel for each type of treatment?


To answer these questions, we need to understand a few things about how teeth bleaching actually works and also look at each molecule and understand the chemical reaction(s) that takes place when the bleaching occurs. Tooth bleaching today is based upon hydrogen peroxide (HP) as the active bleaching agent. Hydrogen peroxide is noted chemically as “H₂O₂”, and is a relatively unstable molecule by itself, and will quickly disassociate into highly reactive, strong oxidizing agents through the formation of three types of free radicals (hydroxyl radicals, per-hydroxyl radicals, and superoxide anions)[ii], reactive oxygen molecules, and hydrogen peroxide anions.[iii]

Hydrogen Peroxide, in a gel substrate, may be applied directly to the teeth, or it can be produced in another chemical reaction from the more stable Carbamide Peroxide (CP) in the presence of water.[iv]  See the numbered equations in the Table[v] below for the following text:

 1.) H₂NCONH₂ • H₂O₂ in water H₂NCONH₂ + 2H₂O₂

 2a.)    H₂O₂ 2HO•

 2b.)    HO + H₂O₂ H₂O + HO•₂

 2c.)     HO•₂ H⁺ + O⁻•₂

 3.)       2H₂O₂ 2H₂O + 2{O} 2H₂O + O₂

 4.)       H₂O₂ H⁺ + HOO⁻











Carbamide peroxide has two portions, the Carbamide portion and the Hydrogen portion. In equation 1, we see the Carbamide Peroxide molecule on the left side of the arrows, which is made up of the carbamide portion (H₂NCONH₂) bonded (•) to the hydrogen peroxide (H₂O₂) portion of the molecule. In the presence of water (i.e. oral saliva) it disassociates into free carbamide and free hydrogen peroxide. Carbamide Peroxide must go through this initial step before any bleaching can occur because it is only the free HP that actually does the bleaching. This takes more time, but Carbamide Peroxide is much more stable than Hydrogen Peroxide and also has a much longer shelf life. Also, it should be noted that a 44% solution of Carbamide Peroxide disassociates into an approximately 12.6% concentration of Hydrogen Peroxide, which equates to an approximately 3.5:1 ratio of Carbamide Peroxide concentration to final disassociated Hydrogen Peroxide concentration.

It is in equations 2, 3, and 4 that we see the production of the different oxidizing agents that actually do the bleaching. In 2a, we see the formation of hydroxyl radicals (2HO•), in 2b, per-hydroxyl radicals (HO•₂), and in 2c, the result is super oxide anions (O⁻•₂). In Equation 3, water (2H₂O) and oxygen (O₂) molecules are formed, and lastly in equation 4, the final oxidizing agent products are hydrogen peroxide anions (HOO⁻).

In all of these free radicals, it is the highly unstable free oxygen component in each that reacts with, oxidizes, or if you will, attacks the long-chained, dark-colored chromophore molecules (atoms or groups in a molecule that cause color) in the patient’s teeth enamel. This attack splits the chromophore molecules into smaller, less colored, and more diffusible (dissolvable) molecules, which results in whitening of the teeth. It doesn’t really remove any stain, but it actually changes the nature and composition of the stains on the teeth. The final results of the bleaching treatment depends mostly on the concentration of the Hydrogen Peroxide available to produce the free radicals, on the amount of time the produced radicals are in contact with the teeth, and the ease in which the radicals can reach the chromophore molecules.5.1

The last factor involved in the Carbamide Peroxide versus Hydrogen Peroxide debate is that of using a very bright, blue light, in the visible spectrum, to accelerate the reaction. Does one form of peroxide or the other work better with an accelerator light? It has been shown that using a light can aid in the bleaching process that results in whiter teeth in less time.[vi] [vii] [viii] [ix]

Also, it is also seen in the literature, that by examining the studies of the light being used in teeth bleaching, it is always used with hydrogen peroxide instead of carbamide peroxide.[x] I think that there is a very good reason for this. It appears that the added light energy of visible light at 480-520 nanometers (visible spectrum blue light) helps increase the energy of activation of the peroxide molecule to form its free radicals. Carbamide Peroxide first has to break down into carbamide and hydrogen peroxide, so it takes longer for the chemical combination to become ready to accept the light’s extra energy input to help activate or catalyze the breakdown of the Hyrdrogen Peroxide into its bleaching-capable free radicals.


Armed with this information, one can now come to some reliable conclusions as to which form of bleach is best for whitening teeth. The answer is, they both are right for the right set of circumstances. When one is doing chairside power teeth bleaching with a light, such as how dentists do this type of treatment and how SmileLABS™ does its proprietary light bleaching, one needs a gel that is relatively strong and that gets to work, and finishes whitening the teeth, as fast as possible. Since Hydrogen Peroxide can form free radicals faster than Carbamide Peroxide and reacts to the light better, it seems that the obvious choice in this case is Hydrogen Peroxide.

On the other hand, when a fast single-treatment in one-hour-or-less is not being done, and one wants to design a take home teeth bleaching kit that is safe and very forgiving of consumer mishandling, Carbamide Peroxide is the better choice. It is much more stable and takes longer to react than Hydrogen Peroxide. It has a longer shelf life since it needs to come into contact with water before it starts to react, whereas Hydrogen Peroxide can start to react by being over-exposed to just light energy.

Also, since higher concentrations of Carbamide Peroxide actually equate to much lower concentrations of eventually formed Hyderogen Peroxide, a safer, higher concentration of Carbamide Peroxide can be utilized for take home use, where the consumer is only using it for a short time each day, i.e. 30-60 minutes per day for up to a two week daily treatment regimen.

This is exactly what SmileLABS™ uses in both of their Medium-strength and Extra-strength take home kits. Each uses a proprietary blend of Carbamide Peroxide gel. Both of SmileLABS’™ treatment modalities now available, either the chairside with a light plus Hydrogen Peroxide method, or the various take home kits with Carbamide Peroxide, work equally well. It is up to the individual to decide which is best for him/herself: either the very fast but at a higher fee ($99-$149) chairside teeth whitening system, or the lower priced ($39-$69) take home teeth whitening kits that take a longer. Either way, the consumer can always be assured that they are always receiving the right type of peroxide and the very best in Cosmetic Teeth Whitening available today.


Cited References

[i] Haywood VB, Heymann HO. Nightguard vital bleaching. Quintessence Int 1989; 20:173-6

[ii] Gregus Z, Klaassen CD. 1995; Mechanisms of Toxicity. In: Cassarett and Doull’s Toxicology, the Basic Science of Poisons. Klaassen CD, editor. New York: McGraw-Hill Companies Inc., pp 35-74.

[iii] Cotton FA, Wilkinson G. 1972;  Oxygen. In: Advances in Inorganic Chemistry. A Comprehensive Text. Cotton FA, Wilkinson G, editors. New York: Interscience Publisher, pp 403-420.

[iv] Budvari S, O’Neil MJ, Smith A, Heckelman PE. 1989; The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals. Rahway, NJ: Merck and Co., Inc.

[v] Dahl JE, Pallesen U. Tooth Bleaching-A Critical Review of the Biological Aspects. Crit. Rev. Oral Biol. Med.; 2003; 14: 292-304.

5.1 Dahl JE, Pallesen U. Tooth Bleaching-A Critical Review of the Biological Aspects. Crit. Rev. Oral Biol. Med.; 2003; 14: 292-304.

[vi] Kuk K, Tam L, Hubert M. Effect of light energy on peroxide tooth bleaching. J Am Dent Assoc. 2004; (135): 194-201

[vii] Ontiveros JC, Paravina RD. Color change of vital teeth exposed to bleaching performed with and without supplementary light. J Dent. 2009 Nov;(37): 840-847

[viii] Gallagher A, Maggio B, Bowman J, Borden L, Mason S, Felix H. Clinical study to compare two in-office (chairside) whitening systems. J Clin Dent. 2002; 13(6): 219-224

[ix] Tavares M, Stultz J, Newman M, Smith V, Kent R, Carpino E, Goodson J. Light augments tooth whitening with peroxide. J Am Dent Assoc. 2003 Feb; (134): 167-175.

[x] Strassler HE. Vital Tooth Bleaching: An Update. Mdental Cont Ed Insert U Maryland Baltimore College of Dental Surgery. 2006; Dec.: 1-12

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