Tooth Whitener for Home Use (Brush for Application) Tooth bleaching, also known as tooth whitening, is a common procedure in general dentistry but most especially in the field of cosmetic dentistry. Many people consider white teeth to be an attractive feature of a smile. A child's deciduous teeth are generally whiter than the adult teeth that follow. As a person ages the adult teeth often become darker. This darkening is 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. As white teeth are subconsciously associated with youth, they have become desirable. This has been made more apparent with the spread of American culture worldwide,[citation needed] where an especially white smile is coined a "Hollywood smile". The procedure to bleach teeth uses oxidising agents such as hydrogen peroxide or carbamide peroxide to lighten the shade of the tooth. The oxidising agent penetrates the porosities in the rod-like crystal structure of enamel and oxidises interprismatic stain deposits; over a period of time, the dentine layer, lying underneath the enamel, is also bleached. Tooth bleaching will generally last from 5 to 7 years, with variations from factors such as cigarette smoking, and tea and coffee consumption. [1]