Teeth Whitening or Bleaching
Dental bleaching, also known as tooth whitening, is a common procedure in general dentistry but most especially in the field of cosmetic dentistry. 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. Certain antibiotic medications (like tetracycline) can also cause teeth stains or a reduction in the brilliance of the enamel.

Upper jaw after 1 week bleaching with custom made tray. The lower jaw has not been treated yet to enable the Patient to see the difference.

There are two main methods of gel bleaching—one performed with high-concentration gel, and another with low-concentration agents. High-concentration bleaching can be accomplished either in the dental office, or at home. Performing the procedure at home is accomplished using high-concentration carbamide peroxide, which is readily available online or in dental stores and is much more cost-effective than the in-office procedure.

Whitening is performed by applying a high concentration of oxidizing agent to the teeth with thin plastic trays for a short period of time, which produces quick results. The application trays ideally should be well-fitted to retain the bleaching gel, ensuring even and full tooth exposure to the gel. Trays will typically stay on the teeth for about 15–20 minutes. Trays are then removed and the procedure is repeated up to two more times. 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) to reduce the risk of chemical burns to the soft tissues.

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 between 10% and 44% carbamide peroxide, which is roughly equivalent to a 3% to 16% hydrogen peroxide concentration.
Low-concentration whitening is far less effective, and is generally only performed at home. Low-concentration 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.

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. Dentists as well as some dental laboratories can fabricate custom fitted whitening trays that will greatly improve the results achieved with an over-the-counter 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.

Case studies have been performed on people with tetracycline stained teeth. They used custom bleaching trays every night for 6 months and saw dramatic results and improvement. White-spot decalcifications may also be highlighted and become more noticeable directly following a whiting process, but usually calm back down with the other parts of the teeth becoming more white.

The white spots become less noticeable, with the other parts of the teeth becoming more white. Bleaching is not recommended if teeth have decay or infected gums. It is also least effective when the original tooth color is grayish and may require custom bleaching trays. Bleaching is most effective with yellow discolored teeth.

However, whitener does not work where bonding has been used and neither is it effective on tooth-color filling. Other options to deal with such cases are the porcelain veneers or dental bonding.

Laser or Zoom Whitening"

A recent study showed that nearly half the initial change in color provided by an intensive in-office treatment (i.e., 1 hour treatment in a dentist's chair) may be lost in seven days. 

Rebound is experienced when a large proportion of the tooth whitening has come from tooth dehydration (also a significant factor in causing sensitivity). As the tooth rehydrates, tooth color 'rebounds' back toward where it started.