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Dentists use a stronger bleaching agent than that found in commercial products, so in-office whitening treatment produces a more dramatic effect on teeth with yellow stains. Over-the-counter products with bleach provide some change in the tooth color, and whitening toothpaste works only on surface stains.
Bleaching does not leave teeth permanently white. Whitening can last from six months to a year. Sometimes teeth stay white even longer. However, smoking or consumption of food and beverages that stain can cause discoloration within one month.
Source: The Gale Group. Gale Encyclopedia of Medicine, 3rd ed.";

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