How Does Teeth Whitening Work?

Updated: Dec 16, 2020

The Hollywood smile is a dream for so many of us. Recently, we have become obsessed with having the brightest possible smile.





Why do we want white teeth?

There is always some science behind beauty, and here is why we find white teeth attractive:


Bone structure is a representation of your genome (the full set of genes you have), which is expressed through your phenotype (all your characteristics). This means that when someone sees that you have beautiful, straight, white teeth - their brain will make an assumption that you have good genetics, meaning you would be a good mate for them... but you just interpret that as "they're hot".



What causes teeth discolouration?



Food and drink:

  • Coffee

  • Tea

  • Red Wine

  • Tomatoes


Any foods or drink which contain chromogens (molecules which cause staining) will darken your teeth - especially those which are slightly acidic. Acidic foods and drinks slightly damage the enamel, making it easier for chromogens to accumulate and harder for them to be removed.



Tabaco:

I know this is supposed to be a scientific article, but if you're still smoking and you expect to be young and beautiful... you're going to have to give one of those up.


Tar is naturally dark, and when it sticks to your enamel, it's hard to remove.

Nicotine is a colourless chemical until it's mixed with oxygen - then, it turns yellow.


Age:

Under the enamel (the first layer of the teeth), we have our dentin - which is softer and yellow. The more we brush and erode our enamel - the more visible our dentin becomes.


Other factors:

There are some other factors, however there is little we can do about it, so I won't discuss it in any detail.

  • Trauma, when your teeth are ill.

  • Medication, such as early exposure to some antibiotics, chemotherapy and above the neck radiation.



The structure of enamel

Enamel is a very tough structure.


It's made up of 95-98% calcium and phosphate ions which make up hydroxyapatite crystals, making it strong enough to bite through hard foods.


Seemingly, our teeth seem smooth, but the carbonated hydroxyapatite crystals are arranged as long rods. This means, that molecules can become stuck in-between these long rods, leaving stains behind.





Types of teeth whitening:

There are two methods of whitening your teeth....


Bleach whitening

Teeth bleaching involves these two ingredients: hydrogen peroxide or carbamide peroxide (carbamide peroxide breaks down into hydrogen peroxide when in contact with water).

Bleaching involves chemical degradation of chromogens. Hydrogen peroxide is the active ingredient which releases molecules of oxygen which then break down chromogens.


Laser whitening

Laser teeth whitening is practically the same as bleaching, the difference being a heat source is applied to the chemical solution to speed up the reaction. The same ingredients are used, so the only thing that varies, is how long you have to leave the paste on for.



How does hydrogen peroxide remove stains?

Hydrogen peroxide can only remove large organic compounds which have conjugated double bonds.



^ The structure of a large organic compound with conjugated double bonds.


Hydrogen peroxide works by oxidising those double bonds.

This makes the chromogen appear lighter in colour and less visible.



^ How hydrogen peroxide oxidises double bonds.

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