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Tooth discoloration (also termed tooth staining) is abnormal tooth color, hue or translucency.〔 External discoloration is accumulation of stains on the tooth surface. Internal discoloration is due to absorption of pigment particles into tooth structure.〔 Sometimes there are several different co-existent factors responsible for discoloration. ==Normal tooth shade== The appearance and perception of a tooth is the result of a complex interaction of factors such as lighting conditions, translucency, opacity, light scattering, gloss and the human eye and brain. Of these, the intrinsic pigmentation of a tooth is the most influential,〔 which in turn is determined by genetic and natural factors. Light hitting a tooth undergoes reflection, absorption and transmission by varying degrees in each tissue layer of the tooth substance.〔 The reflected light which is detected by the human eye determines the perceived appearance of a tooth.〔 Teeth have a thin enamel layer on their outer surface. The enamel layer is whiter and semitransparent, and contributes blue, pink green tints to the tooth color.〔 The underlying dentin layer is darker than enamel, yellow-brown in color, and less transparent.〔 Dentin forms the bulk of the tooth substance, and contributes most to the overall tooth color.〔 At the core of the tooth is soft connective tissue termed the dental pulp. The pulp is pink/red due to its vascularity, but is rarely visible through the overlying enamel and dentin unless the thickness of these layers is reduced by tooth wear (or rarely internal resorption). 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. Tooth color varies according to race, gender and geographic region.〔 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. 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 discoloration」の詳細全文を読む スポンサード リンク
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