The Science Behind Teeth Whitening

Due to the increasing influence of social media, television and movies, more and more people are becoming aware of discoloured teeth and are consequently searching for ways to create whiter and more perfect teeth. Before you look into ways to correct tooth discolouration, it is important to understand the science behind teeth whitening and what happens to your teeth during the process.

What causes teeth discolouration?

There are 2 main causes of discolouration:

  1. Extrinsic staining

Extrinsic staining is mostly caused by external factors – things that we introduce into our mouths. These factors include smoking, highly staining foods and drinks (e.g. wine, coffee, chocolate), mouth rinses or plaque that has accumulated on the teeth.


Examples of extrinsic staining (from Carey 2014)

Extrinsic staining factors contain coloured molecules called ‘chromogens’. These molecules are released and are attracted by and adhere to the surfaces of teeth – causing discolouration.

  1. Intrinsic staining

This type of staining is caused by either systemic factors, such as:

  • Genetics
  • Excess fluoride exposure during childhood
  • Antibiotics (e.g. tetracycline)

Or by local factors, including:

  • Trauma or injury to the tooth
  • Decay
  • Root canal treatment
  • Old metallic restorations
  • Aging

In the case of intrinsic staining the chromogens are located within the enamel and dentine structure, rather than on the surfaces of teeth.

Treatment of extrinsic stains

The most common way to remove extrinsic stains is through tooth brushing where the abrasive component in toothpaste in addition to the brush bristles both act to dislodge and remove the chromogens. If staining is difficult to remove, extensive or has been present for a while, professional cleaning and polishing by a dentist will be required.

Other agents such as whitening toothpastes may be recommended that contain more abrasives compared to traditional toothpastes. They also contain additional chemicals, which act on tooth surfaces to help further removal of stains.

Getting a professional clean and polish by your dentist can get rid of extrinsic stains


Treatment of intrinsic stains

Intrinsic stains are a little more difficult to treat, as they require the removal of coloured particles within tooth structure. Generally, intrinsic stains require the use of bleaching materials containing an active ingredient called hydrogen peroxide (H2O2). This active ingredient is small enough to penetrate tooth structure and acts to break down the chromogen molecules, removing them from within the tooth.

There are a few methods that your dentist may recommend for tooth whitening including either in-office or at home treatment.

Discoloured front tooth due to root canal treatment

Tooth following bleaching treatment (from Plotino et al. 2008)








As with all kinds of procedures, tooth whitening comes with some risks and side effects. The most common side effect is increased tooth sensitivity, which usually occurs during treatment and generally lasts for a few days afterwards. Sensitivity occurs as the peroxide diffuses through tooth structure, exposing nerve endings within the deeper layers. Your dentist may recommend some things that will help to reduce the sensitivity, such as: sensitive toothpastes or chewing gum. Alternatively, they may recommend altering the treatment or stopping it completely until sensitivity subsides.

Discoloured teeth can be frustrating and can have a great impact on your confidence. It is important to talk to your dentist in order to address the causes behind the discolouration, and to determine what treatment will be most effective.



Carey, C. (2014). Tooth Whitening: What We Now Know. Journal of Evidence Based Dental Practice, 14, pp.70-76. (IMAGE 1) (2014). Tooth Discolorization – Common Causes of Tooth Discolorization. [online] Available at: [Accessed 31 Oct. 2017].

Eddis, Y. (n.d.). Sensitive Teeth After Whitening | Colgate® Oral Care. [online] Available at: [Accessed 31 Oct. 2017].

Nathoo, S. (1997). The Chemistry And Mechanisms Of Extrinsic And Intrinsic Discoloration. The Journal of the American Dental Association, 128, pp.6S-10S.

Plotino, G., Buono, L., Grande, N., Pameijer, C. and Somma, F. (2008). Nonvital Tooth Bleaching: A Review of the Literature and Clinical Procedures. Journal of Endodontics, 34(4), pp.394-407. (IMAGES A and B)

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