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Tooth whitening (termed tooth bleaching when utilizing bleach), is either restoration of natural tooth shade or whitening beyond natural tooth shade, depending on the definition used. Restoration of the underlying, natural tooth shade is possible by simply removing surface (extrinsic) stains (e.g. from tea, coffee, red wine and tobacco) and calculus (tartar). This is achieved by having the teeth cleaned by a dental professional (commonly termed "scale and polish", see debridement and polishing), or at home by various oral hygiene methods. Calculus is difficult to remove without a professional clean. To whiten the natural tooth shade, bleaching is required. It is a common procedure in cosmetic dentistry, and a number of different techniques are used by dental professionals. Many different products are also marketed for home use. Techniques include bleaching strips, bleaching pen, bleaching gel, and laser tooth whitening. Bleaching methods generally use carbamide peroxide or hydrogen peroxide. There are claims that carbamide peroxide is less effective than hydrogen peroxide, but also has less side effects. Common side effects of bleaching are increased sensitivity of the teeth and irritation of the gums. Occasionally individuals develop an unhealthy obsession with tooth whitening akin to body dismorphic disorder, termed "bleachorexia". ==Natural tooth shade== The perception of tooth color is the result of a complex interaction of factors such as lighting conditions, translucency, opacity, light scattering, gloss and the human eye and brain. Teeth are composed of a surface enamel layer, which is whiter and semitransparent, and an underlying dentin layer, which is darker and less transparent. These are calcified, hard tissues comparable to bone. The natural shade of teeth is best considered as such; an off-white, bone-color rather than pure white. Public opinion of what is normal tooth shade tends to be distorted. Portrayals of cosmetically enhanced teeth are common in the media. In one report, the most common tooth shade in the general population ranged from A1 to A3 on the VITA classical A1-D4 shade guide. Females generally have slightly whiter teeth than males, partly because females teeth are smaller, and therefore there is less bulk of dentin, partially visible through the enamel layer. For the same reason, larger teeth such as the molars and the canine (cuspid) teeth tend to be darker. Baby teeth (deciduous teeth) are generally whiter than the adult teeth that follow, again due to differences in the ratio of enamel to dentin. As a person ages the adult teeth often become darker due to changes in the mineral structure of the tooth, as the enamel becomes less porous and phosphate-deficient. The enamel layer may also be gradually thinned or even perforated by the various forms of tooth wear. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tooth whitening」の詳細全文を読む スポンサード リンク
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