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Tooth bleaching

Tooth bleaching, also known as tooth whitening, is a common procedure in general dentistry but most especially in the field of cosmetic dentistry. Many people consider white teeth to be an attractive feature of a smile. A child's deciduous teeth (milk teeth) are generally whiter than the adult teeth that follow. As a person ages the adult teeth often increase in value, that is to say they become darker. This darkening is due to changes in the mineral structure of the tooth, as the enamel becomes less porous. Teeth can also become stained by bacterial pigments, foodstuffs and tobacco.

As white teeth are subconsciously associated with youth, they have become desirable. This has been made more apparent with the spread of American culture worldwide, where an especially white smile is coined, a "Hollywood smile". The procedure to bleach teeth uses oxidising agents such as hydrogen peroxide to lighten the shade of the tooth. The oxidising agent penetrates the porosities in the rod-like crystal structure of enamel and oxidises interprismatic stain deposits, over a period of time, the dentine layer, lying underneath the enamel, is also bleached.

There are two main methods of bleaching. The first involves applying a high concentration of oxidising agent for a short period of time (the so called office bleach). This produces quick results but risks chemical burns to the soft tissues. The bleaching agent here is carbamide peroxide, which breaksdown in the mouth forming hydrogen peroxide.

The alternative method involves using a thin mouthguard to hold a low concentration of oxidising agent next to the teeth for several hours a day for a period of some weeks. This is known as the home or nightguard bleach. This is slower but has lower risks to the soft tissues.

A typical course of bleaching can produce dramatic improvements in the cosmetic appearance of most stained teeth, however some stains do not respond to bleaching. Tetracycline staining may require prolonged bleaching, as it takes longer for the bleach to reach the dentine layer. White-spot decalcifications may also be highlighted and become more noticeable.

Recently, efforts have been made to accelerate the bleaching process by the use of light. Studies have shown varying results as to the efficacy of light-activated bleaching.

Side effects of tooth bleaching are: Chemical burns if high concentration oxidising agent contacts unprotected tissues; sensitive teeth, and overbleaching to produce what are known in the profession as "Fridge-door teeth". Rebound, or teeth losing the bleached effect and darkening, is also an issue, with few studies showing the rebound effect over 30 days. A recent study by Kugel et al, has shown that as much as 4 shades of lightness can be lost over 30 days with light-activated/office bleaching.