Bleaching is whitening teeth with peroxide to change the natural color of teeth. Teeth naturally yellow as they age and whitening is a cosmetic procedure that can temporarily change the color. Yellowed or slightly discolored teeth can be perfectly healthy.

Tooth enamel contains pores, which allow external stains to penetrate. Bleaching alters the light-absorbing or light-reflecting quality of teeth. In general, yellow stains bleach more rapidly than gray stains. Some areas, including artificial crowns or veneers and the roots of the teeth, cannot be whitened by bleaching.

The degree of color change that may occur depends on the types of stains present, the strength of the chemicals, the amount of time bleach remains on the teeth and how frequently it is used. Many dentists recommend bleaching gradually, until patients find the preferred shade. Teeth are not naturally pure white and bleaching to intensely white shades may look unnatural. For a natural look, teeth should be bleached no whiter than the whites of the patient’s eyes.

Different types of stains or discolorations respond variably to bleaching. These different types of discolorations include:

• Extrinsic stains. Superficial stains that extend no deeper than the tooth enamel. These stains may be caused by smoking, beverages (e.g., coffee, tea, cola, red wine) or foods (e.g., tomato sauce). Overall, these stains tend to respond very well to bleaching.
  
  
• Intrinsic stains. Deeper stains that develop in the dentin of the tooth. These may be caused by certain chemicals or medications (e.g., excessive fluoride, tetracycline) used in childhood when the teeth are developing. The use of the antibiotic tetracycline during pregnancy can also stain a child’s developing teeth. These stains may cause a gray discoloration. They may bleach very slowly or not respond to bleach.
  
  
• Age-related stains. During the aging process the teeth become stained due to both extrinsic and intrinsic factors. The enamel becomes thinner with age and dentin becomes slightly yellow. This discoloration may be visible through the enamel, which is translucent. These stains tend to respond well to bleach.
  
  
• Stains from root canal treatments. A tooth may become discolored after a root canal treatment. These stains require a different method of treatment than others, but tend to bleach well when this treatment is used.

Bleaching is not permanent and usually needs to be repeated. The whiter color may last for up to five years, depending on how much care is taken to avoid new stains.