Over recent years the dental profession has been bombarded with whitening systems many with exaggerated claims. Teeth whitening can be undertaken in surgery and therefore supervised by the dentist chairside, undertaken at home by the patient but under the prescription of the dentist or by using an over the counter preparation which is unsupervised.
The definition of tooth whitening is the removal of stains from enamel using a bleaching process. The bleaching agents diffuse into enamel causing the breakdown of complex molecules which appear as a stain.
Dark discolouration is caused by deposits of organic or inorganic molecules within the crystalline structure of the tooth or by the ingestion of chromogenic agents during tooth formation for example tetracycline stains.
The teeth are bleached by an oxidative process. Free radicals *OH are obtained from hydrogen peroxide or carbamide peroxide by heat, UV light, laser sources or chemical accelerators. These *OH radicals degrade the organic chromophores with a high molecular mass to molecules with a lower molecular mass. The former reflect light of specific wavelengths resulting in the appearance of a stain.
It has been difficult to accurately assess the effectiveness of different forms of bleaching as results vary widely. This is because the initial stain can be due to such a large range of factors and enamel and dentine vary in transluscency, thickness and colour between individuals.
Carbamide peroxide and hydrogen peroxide are used to produce the free radicals required for the bleaching process. A 10% concentration of carbamide peroxide is equivalent to a 3-3.5 % of hydrogen peroxide. CP is more stable and so citric acid or phosphoric acid can be added and the pH is maintained around 6.2 to 7.0. This makes it safe to use on enamel as enamel dissolves only at a pH below 5.
Hydrogen peroxide however works faster that CP therefore less contact time is required and in tray bleaching can be carried out more rapidly therefore the trays do not have to be worn overnight. Indeed some systems advocate a period of 30 minutes twice daily for 14 days.
Hydrogen peroxide can be supplied in a twin barrel syringe therefore stability is maintained and the 2nd barrel can contain an alkaline activator increasing the pH to 7. Initiators and activators can also be added which increase the levels of *OH and increase the rate of conversion leading to a more rapid rate of whitening. Blackburn et Al (2006) showed that by adding an amino alcohol activator the bleaching effect of hydrogen peroxide could be increased by 300%.
There are 3 main side effects of teeth whitening. These are soft tissue irritation, dentine hypersensivity and pulpal inflammation. It has been shown that upto 80% of patients experience side effects to some level but virtually all subside after 24 to 48 hours on cessation of whitening. Prevention of contact of the bleaching agent with the soft tissues and exposed dentine is imperative to reduce symptoms.