Generally a peroxide based agent is used in the whitening gels. The peroxide reacts with such stain producing substances thereby oxidizing and removing them completely. The gums and lips need to be protected during the application with special barriers.

Stains may be yellow, brown, black , green, orange or white (opaque). The bleaching agents work best on yellow stains. Discoloration may be caused due to excessive intake of coffee, tobacco, tea, wine and other beverages. Smokers usually have stained teeth. Metals like iodine and fluorine also cause tooth staining. Bad oral hygiene resulting in the accumulation of dental plaque and chromogenic bacteria cause the teeth to lose their natural whiteness. The above mentioned discolorations are extrinsic and are not localized in terms of position of teeth. Some extrinsic stains may be removed with ultrasonic cleaning, rotary polishing with an abrasive paste, or air-jet polishing with an abrasive powder. However, these methods can lead to enamel removal.Enamel micro abrasion used for removal of foreign particles and stains in case of orthodental treatments may be used in conjunction with bleaching.

Localized or intrinsic discoloration is caused by factors such as mild fluorosis, mild trauma to teeth during enamel formation, periapical infection of primary tooth, traumatic injury to primary tooth or teeth, incipient caries in the teeth. Metal crown margin associated with porcelain fused to metal crow may create a black stain. Hemolytic diseases and nutritional deficiencies also cause dull teeth.

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. Such bleaching may require special techniques like laser using argon rays etc. Agents like particles of silica, aluminium oxide, calcium carbonate or calcium phosphate may be present in gels or whitening toothpastes to grind off stains. A good tooth whitening agent is that which may also remineralizes teeth.

Apart from external bleaching, bleaching the tooth internally involves drilling a hole to the pulp chamber and placing a peroxide gel into the pulp chamber so that the gel can work directly inside the tooth on the dentin layer.

Bleaching should be followed by proper care of teeth. Good oral habits like brushing twice a day with a toothpaste having whitening agents, flossing and keeping a check on staining beverages like coffee.

The only risks involved are cold sensitivity in teeth for a short period in case of weak teeth and the rare case of burning in the gums due to the chemicals in the gel if the gums and lips are not properly protected. Today, bleaching is a safe, easy, and inexpensive modality that is used to treat many types of tooth discoloration.