Teeth Whitening

A Lesson On Natural Acid Base Reactions

The Acids and Bases

There are two types of acids involved in teeth whitening:


  1. Hydrogen Peroxide H2O2
  2. Carbamide Peroxide CH6N2O3


The bases in this reaction are the organic compounds found on the teeth. They are created naturally through the foods we eat.

The Acids

Hydrogen Peroxide
  • H2O2
  • Pure hydrogen peroxide has a pH of 6.2; thus it is considered to be a weak acid. The pH can be as low as 4.5 when diluted at approximately 60%
  • Due to its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent.


Carbamide Peroxide

  • CH6N2O3
  • The majority of bleaching products contain carbamide peroxide which breaks down into hydrogen peroxide and urea.
  • The active bleaching agent is hydrogen peroxide, H2O2. This compound is a weak acid with strong oxidizing properties.






H2O2 V. CH6N2O3

•H2O2 systems start and finish the oxidation process quicker than the CH6N2O3 systems.

•H2O2 is also roughly three times more concentrated than CH6N2O3, with a 7% H2O2 gel being equivalent to a 22% CH6N2O3 and 12% H2O2 equivalent to 35% CH6N2O3.

•CH6N2O3 systems, because they take longer to undergo full oxidation, cause less sensitivity to the teeth and gums than the H2O2, but require more frequent applications over a number of sessions.


What Is the Reaction?

  • The reaction is a redox reaction using either hydrogen peroxide or carbamide peroxide as the oxidizing agent.
  • The basic premise of chemical teeth whitening procedures, known as tooth bleaching, is the chemical breakdown of a gel that releases oxygen, called oxidation, which in turn causes surface stains on the teeth to undergo a chemical process known as reduction.
  • This chemical reaction is said to penetrate a little below the surface of the enamel as well to remove deeper staining that the ordinary micro-abrasion technique (teeth cleaning) fails to reach.
  • A bleaching agent is a substance that can whiten or decolorize other substances. Colored substances generally contain groups of atoms, called chromophores , that can absorb visible light having specific, characteristic wavelengths, and reflect or transmit the part of light that is not absorbed.
  • Bleaching agents essentially destroy chromophores (thereby removing the color), via the oxidation or reduction of these absorbing groups. Thus, bleaches can be classified as either oxidizing agents or reducing agents.
  • During this oxidation process, the acids are both reduction agents.



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The Reaction


  • Hydrogen peroxide is frequently used as an oxidizing agent in organic chemistry. Due to the fact that the organic compounds on everyone's teeth vary, a different application for this oxidation reaction is with thioethers to sulfoxides.
  • For example, methyl phenyl sulfide can be readily oxidized in high yield to methyl phenyl sulfoxide:

· Ph−S−CH3 + H2O2 → Ph−S(O)−CH3 + H2O



What Is Teeth Discoloration?


Many different factors can cause teeth discoloration including, but not limited to consuming certain foods and beverages like coffee, tea, soda drinks, red wine, and berries, discoloration caused by aging, tooth damage, and more. Smoking is also a large contributor to teeth discoloration. Also, if the stains are due to antibiotics (such as tetracycline) or fluoride overdoses, they will be very hard to whiten. You will recognize such teeth by their greyish / brownish tint.



How Does It Work?


  • The purpose of the teeth whitening gel is to break up the substances that create stains on the teeth, essentially lifting them out so that light can shine on the actual surface of the teeth, rather than the stain. This permits more light to pass through and creates a whiter appearance.
  • The most common way of starting this oxidation process is by the utilisation of a peroxide-based gel.
  • Peroxides undergo oxidation in the presence of moisture, oral tissues, light and/or heat.
  • The reason for the "activation" of the bleaching process by some dentists with an intense light source, or other means.
  • The peroxide molecules are small enough to enter the miniscule crevices in the teeth where stains are usually found.
  • The surface of the teeth contains millions of microscopic pores, and over the years, organic compounds from food, drink and tobacco penetrate these pores causing discoloration.
  • Hydrogen peroxide attacks and destroys the coloured substances that cause stains. Oxidizing agents steal electrons and since electrons are the “glue” that hold atoms together in molecules, the molecules that cause stains to fall apart.
  • Teeth whitening occurs when hydrogen peroxide breaks down into oxygen molecules, which penetrate through the enamel and go into the dentin, which is directly under the enamel. These molecules go into the tiny pores of the enamel and dentin and bleach the colored substances.
  • After a teeth whitening treatment, the pores generally remain open for around 24 hours. This is why it is important for in-office treatments to perform them consecutively.
  • The same process applies when using carbamide peroxide.
  • When the water reacts with carbamide peroxide (an active ingredient in some bleaching solutions) it releases hydrogen peroxide, which in turn whitens the teeth.
  • The hydrogen peroxide goes through the teeth surface and oxidizes the organic composites (these composites actually cause the teeth staining) that exist in the tooth enamel.
  • The oxidation of the organic composites results in smaller remaining molecules that are much lighter in color compared to the original organic composites thus leaving "whiter" teeth.



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Actual Teeth Whitening v. Teeth Dehydration

  • In the same manner that the hydrogen peroxide molecules enters the enamel tooth, fluids flow out of the tooth.
  • During the teeth whitening process, the chemical reaction of the peroxide breaking down generates some slight heat (which the person does not feel) inside the tooth, and this heat causes the pulp and dentin to expand.
  • This expansion pushes water out of the tooth, essentially dehydrating it.
  • The result of this may be that the teeth lose water or dehydrate and appear whiter temporarily, usually for around 72 hours.
  • After that they begin to recover and absorb water from the saliva and regain some of their color.


Teeth Whitening Procedure

How Long Does It Take?

  • If a person only applies 1 single 20-minute session, some of the whitening that they will see is most likely initial dehydration, not actual bleaching.
  • Dentists typically perform 3 or more treatments in a row (thus 1-hour bleaching) using a higher concentration of gel than at-home gels, so the typical cosmetic teeth whitening procedure is a single appointment contained of three 20-minute sessions.
  • Each session lasts 20 minutes, which is the time needed for hydrogen peroxide to fully break down. For a single treatment for longer than 20 minutes you will not be getting any improvement after this point because the gel won’t be active anymore. For a second or third treatment, the used gel needs to be removed and replaced with fresh gel before beginning the next treatment.
  • As mentioned before, for in-office treatments its important to do all three sessions within 24 hours of the first because the pores of the teeth will remain open, allowing better results.


The Different Methods

In-Office V. Take-Home
  • The faster acting and more highly concentrated and caustic H2O2 are carefully used by the dentist in their "in-office" techniques, with or without the added use of heat/light. The dentist ensures no harm comes to the patient's gums and oral soft tissues by carefully isolating them from the caustic chemicals used.
  • The slower acting and more gentle CH6N2O3 systems are best suited for "take-home" kits which often follow-on from the dentist's "in-office" procedure, or as a stand alone process separate to it and used in between dentist visits.
  • When you undergo laser teeth whitening at your dentist's office, the laser is used to activate the gel further and results in more targeted results. Your gums and lips are covered during the procedure, and your teeth undergo a cleaning first so that all plaque and bacteria are removed from the surface of the teeth.
  • The laser acts as a stimulant over the gel, and this procedure is more effective against tough stains, such as those caused by tetracycline. However, it is far more expensive to pay for laser teeth whitening at the doctor's office.
  • It is also possible to ask your doctor to prepare a specific teeth whitening gel for you to take home with you. He or she will create a mouthpiece designed especially for your mouth so the gel will coat your teeth with more accuracy. This is less expensive than the laser option, but more effective than simply purchasing an over-the-counter product. However, the materials used are largely the same.
  • Those with sensitive teeth and gums might not want to have professional laser teeth whitening because it can cause additional pain.
  • A dentist supervised teeth whitening remains one of the most popular options. The dentist will have to examine the patient first and determine if the patient’s teeth and gums are healthy.
  • The first one involves using custom trays containing bleaching agent for several weeks (the tray must be worn about an hour daily).
  • The second one is an in-office teeth whitening, done with trays containing bleaching gel. Using laser teeth whitening procedure, which involves application of light in order to activate the bleaching solution applied to the teeth, can enhance the effects of the in-office procedure. The in-office teeth whitening takes about an hour and most of the time a single visit to the dentists is all that is needed.
  • In-office whitening procedures are often the fastest because the gel is more concentrated, and the difference might be noticeable within an hour.
  • With weaker over-the-counter solutions, it might take several days to witness a perceptible change.


The Three Options

  1. (1) dentist-administered bleaching—the use of a high concentration of hydrogen peroxide (from 35 to 50%) or carbamide peroxide (from 35 to 40%), often supplemented with a heat source
  2. (2) dentist-supervised bleaching—by means of a bleaching tray loaded with high concentrations of carbamide peroxide (from 35 to 40%) that is placed in the patient’s mouth for 30 min to 2 hrs while the patient is in the dental office
  3. (3) dentist-provided bleaching—known as “at-home” or “night-guard” bleaching and administered by the patient applying from 5 to 22% solution of carbamide peroxide in a custom-made tray
  4. (4) over-the-counter products, often based on carbamide peroxide or hydrogen peroxide of various concentrations and placed in a pre-fabricated tray, or by the recently introduced strips both to be adjusted by the user.






  • A dentist is allowed to use gel concentration up to 3 times higher than in cosmetic dentistry. Thus, while someone performing cosmetic teeth whitening can use up to 16% hydrogen peroxide, dentists normally use 35% hydrogen peroxide (not to be confused with 35% carbamide peroxide, which would be the equivalent of 12% hydrogen peroxide).



The Risks


  • Tooth sensitivity has been reported to occur during the early stages of the bleaching treatment.
  • During the later stages, tissue irritation may develop causing minor discomfort. Both of these side effects will subside once the bleaching treatment ceases.
  • Unfortunately, there have been some cases in which irreversible tooth damage has occurred, usually through improper application. The time the bleaching agent is left on is critical and can best be judged by a dentist.
  • If a person has pain in a particular tooth during treatment, they may well have a cavity that they do not know about or an exposed root. This pain usually lasts only a few seconds or a few minutes at most at the beginning of the treatment, but it is difficult to convey this during the treatment.
  • If a customer actually experiences significant tooth sensitivity during the first treatment and wants a double or triple session, it may be a good idea to perform the subsequent treatments in different days, not in a row.
  • If you have, or are concerned with sensitivity we suggest that you brush your teeth with Sensodyne Toothpaste (or suitable alternative) for a couple of weeks before undergoing the teeth whitening treatment.



Irritated Gums

Bibliography

Works Cited

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"The Chemistry of Teeth Whitening." - ElementsDatabase.com. N.p., n.d. Web. 28 Oct. 2013.

"How Does Teeth Whitening Work? Advance Dental Health Supplies - Online Suppliers of Dental Health Products." How Does Teeth Whitening Work? Advance Dental Health Supplies - Online Suppliers of Dental Health Products. N.p., n.d. Web. 28 Oct. 2013.

"Office for Science & Society." Office for Science Society How Does Peroxide Whiten Teeth Comments. N.p., n.d. Web. 28 Oct. 2013.

"Understanding the Science Behind Teeth Whitening." Yahoo Contributor Network. N.p., n.d. Web. 28 Oct. 2013.