Bleaching (Tooth whitening)
There are many causes of why teeth get dark. The most common include genetics, aging, consumption of staining substances (smoking, coffee, tea, colas), tetracycline (antibiotic) staining, excessive fluoride, and old fillings. Whitening toothpaste can remove stain that is on the outside of the teeth. Dentists call this extrinsic staining. However, whitening toothpaste and professional dental cleanings will not change the colour or intrinsic staining of the teeth. That is why tooth whitening (sometimes called tooth bleaching) is so popular.
Before	After
In tooth whitening, a whitening gel is placed in a tray that fits over your teeth. As the active ingredient in the gel (either carbamide or hydrogen peroxide) is broken down, oxygen enters the enamel and bleaches the coloured substances. The structure of the tooth is not changed - only the tooth is made lighter and whiter. Fillings, crowns, and restorations will not lighten.
Tooth bleaching can last indefinitely, but most people like to touch up the result once or twice a year. Without a touch up, your teeh will start to restain by the same things that caused them to discolour in the first place.
Bleaching is not recommended whilst pregnant or breast feeding.