Chemistry behind Teeth Whitening

It’s no lie that over the past few years we have become more conscious about the way we look, dress, and present ourselves, so are more willing to make adjustments to our appearance. Many surveys done by dental companies have found that the first thing people notice when they look at someone is their smile. It is therefore understandable why people spend years and years perfecting it, using composite bonds, veneers and braces until they are satisfied with their shape, alignment and nowadays even colour. The once ‘natural’ colour of teeth has been overlooked with a new pristine white colour that can almost only be achieved through the use of some form of whitening, unless you are of course the woman from the Colgate adverts who only eats apples and manages to maintain the crisp, pearl white colour through just brushing her teeth. However, whilst whitening might appear to just be lightening the colour of our teeth and leaving a more pleasant colour, the act of whitening can also cause damage to your teeth if not done correctly.

There is general awareness that teeth whitening can affect the sensitivity of your teeth, however scientists have recently found that there are other risks that can occur through the process of whitening. Some of these include tooth surface roughening and softening and increased risk of demineralization especially with the enamel in your teeth.

The general process of teeth whitening often involves the chemical hydrogen peroxide (H2O2) which is also commonly found in the form of carbamide peroxide - a compound that breaks down in contact with water to release hydrogen peroxide. The tooth stains often fall into two categories, intrinsic, where the colour difference occurs within the tooth, and extrinsic, where the colour inconsistency occurs on the surface of the tooth. The actual compounds that cause the colour disparities are called chromogens which are either metal containing elements or large organic compounds that contain alternating single and double bonds. When the teeth have colour due to the latter reason, they are whitened with hydrogen peroxide which reacts with the double bond to oxidise it. This oxidation causes the chromogens to become lighter in colour. When the colouring is caused by chromogens containing metal elements, it is much harder to remove this colour so the teeth need professional products that contain chemicals like sodium hypochlorite (NaOCl). This operates in the same way that hydrogen peroxide does by reacting with the double bonds in the chromogen, however often the end result isn’t usually as white as desired so people tend to opt for veneers or composite bonds as an alternate method of achieving whiter teeth.

There are many different methods and products that can be used to achieve different levels of lightness. For lighter stains, a simple toothpaste can be used, but for more severe stains, it's best to get them professionally whitened. For the more milder cases, one might opt for whitening strips and gel, whitening toothpaste or whitening rinses. Whitening toothpastes don't contain sodium hypochlorite but in some cases they may contain low concentrations of hydrogen peroxide. Because of this, whitening

toothpastes generally only lighten the teeth by one or two shades. Whitening strips and gels are peroxide based and are often left on the teeth for a substantial period of time to see the effect of lightening - much like toothpaste this usually only lightens by one or two shades. A whitening rinse contains hydrogen peroxide or another form of oxide; however, this process generally takes a much longer time to see the same effect as some of the other methods.

Another method of achieving this highly desired white smile is through the use of blue light. This can be done in the dentist with highly specialised equipment; however, in this day and age, more will opt for an at home kit in which you are given your own small blue light machine to do the procedure yourself. This form of whitening focuses on a bleaching property of chemicals like hydrogen peroxide or carbamide peroxide in the form of a whitening gel. This is first put on your teeth and does the actual whitening of your teeth, but it is believed that the addition of using a blue light speeds up this reaction as it activates the product while on the teeth and causes an increase in the rate of chemical reactions. Typically, a higher concentration of hydrogen peroxide can be found in the gel because of its professional usage which also provides a more visible colour difference.

Researchers have found that the mild use of teeth whitening doesn't cause that much harm to the teeth however aggressive teeth whitening can cause changes to the tooth’s microstructures and restoration changes. It can cause reactions between ceramic crowns and composite restorations, in turn reducing the stability of the teeth. It can also change the microstructure of enamel crystals (which provide enamel with their mechanical properties).

The best way to avoid all this damage is to fully avoid teeth whitening which can be hard due to the chromogens which appear in coffee, red wine, cigarette smoke and many other things that we wouldn't think twice about putting in our mouths. However, the damage whitening causes isn’t believed to be that serious so dentists will continue to recommend the treatments if the patient desires them.

By Sofia Cullinane

Sources: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC 4058574/

https://www.daybreakdentalcare.com/blog/scie nce-behind-teeth-whitening