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It's universal. It's contagious. So it's no wonder that people spend time, money, and effort to brighten their smiles. Teeth-whitening is among the most common procedures in cosmetic dentistry.

Did you know? Surveys show that about one-third of the population is dissatisfied with the appearance of their teeth or tooth colour.

Tooth colour is determined by the light-scattering properties of the enamel and dentin which forms the tooth, as well as stains accumulated from eating. Therefore, children's milk teeth are generally whiter than adult teeth, and adult teeth tend to become darker as the mineral properties of the tooth change and stains accumulate with age. And while a purely white smile is a purely unnatural one, many people remain dissatisfied with the colour of their teeth and want to do something about it.

Did you know? Enamel, dentin, cementum, and dental pulp are the four major tissues that make up a tooth, the first two which contribute to determine tooth colour.

The organic compounds that give enamel and dentin their colour are called chromophores and contain long chains of alternating single and double chemical bonds which give them their light-scattering properties. All teeth-whitening technologies are based on breaking these bonds so that the chromophores lose their colour-producing properties. One way that these bonds are broken is through the chemical process of oxidation, or the addition of oxygen to a compound. Therefore, oxidizing agents, which are compounds that promote the process of oxidation, such as hydrogen peroxide and carbamide peroxide are common ingredients in teeth-whitening products.

Since teeth-whitening is based on chemical reactions, its effectiveness depends on several factors that influence all chemical reactions: temperature, concentration, and time. At a dentist's office, oxidizing agents are applied to the tooth surface at high concentration and therefore the results can be seen as quickly as 15 — 20 minutes. Laser bleaching uses light energy to accelerate this process. Other sources of light energy have also been developed to minimize side effects, such as risk of burns in such dental procedures. For those of you who still have dentist-phobia, the increasing availability of teeth whitening strips, gels, and toothpastes means that teeth bleaching can also be carried out in the comfort of your own home. These products usually contain much lower concentrations of oxidizing agents and therefore it may take up to two weeks before you start seeing an effect.

Did you know? Tooth-whitening and household bleach work by the same principle — through the chemical process of oxidation, which involves the addition of oxygen to a compound.

Of course, the starting components of the chemical reaction — the type of bleach and type of chromophore — will also determine the success of the treatment. Some oxidizing agents are stronger than others while some chromophores are just harder to break apart than others. And since chromophores are organic compounds, teeth-whitening techniques based on breaking chromophore chains only work on natural tooth surfaces and not fillings.

But wait, if it's so easy and convenient, why isn't everybody using it? Just as with any other treatment, cosmetic or medical, tooth-whitening is associated with some side effects, including: increased teeth sensitivity and gum irritation. The use of teeth-whitening products is deemed safe in many countries, but some experts argue that the harmful chemical ingredients of these products, even at low concentrations can have more serious consequences. For example, the release of radicals — atoms with unpaired electrons — as a byproduct of oxidation reactions has been suggested to cause some oral cancers in the long run. So, if you are thinking of trying tooth-whitening, make sure you learn about the method before you start and always follow the instructions included with your teeth-whitening product!

Learn More!

The bleaching of teeth: a review of the literature. Journal of Dentistry (2006) 34: 412-419

Hydrogen peroxide tooth-whitening (bleaching): review of safety in relation to possible carcinogenesis. Oral Oncology (2006) 42: 668-674

Health Canada - The Safe Use of Home Tooth Whitening Kits

Teeth Whitening - The Canadian Dental Association

Irene is a graduate student at the University of British Columbia who works in a diabetes research lab and likes hiking, photography, and travel.

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