Also know as tooth whitening or teeth 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 are generally whiter than the adult teeth that follow. As a person ages the adult teeth often become darker 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.
The procedure to bleach teeth uses oxidizing agents such as hydrogen peroxide or carbamide peroxide to lighten the shade of the tooth. The oxidizing agent penetrates the porosities in the rod-like crystal structure of enamel and oxidizes interprismatic stain deposits; over a period of time, the dentin layer, lying underneath the enamel, is also bleached. The effects of bleaching can last for several months, but may be shortened by cigarette smoking, and tea and coffee consumption.
There are two main methods of bleaching--one performed by dentist and one performed by the teeth-bearer him- or herself. A dentist applies a high concentration of oxidizing agent for a short period of time, which produces quick results. In order to reduce the risk of chemical burns to the soft tissues, most in-office bleaching procedures use a light-cured protective layer that is carefully painted on the gums and papilla (the tips of the gums between the teeth). The bleaching agent is either carbamide peroxide, which breaks down in the mouth to form hydrogen peroxide, or hydrogen peroxide itself. The bleaching gel typically contains up to 35% carbamide peroxide which is roughly equivalent to a 12% hydrogen peroxide concentration.
At-home whitening involves purchasing a thin mouthguard or strip that holds a relatively low concentration of oxidizing agent next to the teeth for as long as several hours a day for a period of 5 to 14 days. This is known as take-home or over-the-counter bleaching. Results can vary, depending on which application is chosen, with some people achieving whiter teeth in a few days, and others seeing very little results or no results at all. Whitening is potentially better at a dentist because the strip or mouth-guard does not completely conform to the shape of the teeth, sometimes leaving the tips of the teeth (near the gumline) unbleached. The bleaching agent is typically less than 10% hydrogen peroxide equivalent so irritation to the soft tissue around your teeth is minimized. Dentists as well as some dental laboratories can fabricate custom fitted whitening trays that will greatly improve the results you can achieve with an "at home" whitening method.
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. Bleaching is least effective if teeth have white spots, decay or infected gums. It is also least effective when the original tooth color is grayish. Bleaching is most effective with yellow discolored teeth.
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.
Various chemical and physical agents can be used to whiten teeth. Toothpaste typically has small particles of silica, aluminum oxide, calcium carbonate, or calcium phosphate to grind off stains formed by colored molecules that have lodged onto the teeth from food. Unlike bleaches, whitening toothpaste does not alter the intrinsic color of teeth. Bleaching solutions contain peroxide which bleaches the tooth enamel to change its color. Off-the-shelf products typically rely on a carbamide peroxide solution varying in concentration from 10% to 22%. Bleaching solutions may be applied directly to the teeth, embedded in a plastic strip that is placed on the teeth or use a gel held in place by a mouthguard. Because the concentration is typically low to avoid toxicity, whitening often takes several weeks. A tooth whitening agent that also remineralizes teeth is under development.
Whitening treatments used by dentists are much more concentrated, containing substances with more than 30% hydrogen peroxide, and require protection of the soft tissues.
Whitening teeth for aesthetic purposes has been dated back to the Ancient Egyptians, where a mixture of ground pumice and wine vinegar was brushed on the teeth with a rudimentary toothbrush. The ancient Romans used human urine by the belief that it kept the teeth white and firmly in place, a practice that continued into the eighteenth century. Whitening in the medieval ages was done by barbers, where the teeth would be filed down and nitric acid applied to the teeth. This was a dangerous procedure, considering the massive tooth damage this practice caused.