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Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most heterodont mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whereas armadillos have none.〔http://www.dentalcare.com/en-US/dental-education/continuing-education/ce421/ce421.aspx?ModuleName=coursecontent&PartID=2&SectionID=-1〕 ==Structure== Adult humans normally have eight incisors, two of each type. The types of incisor are: * maxillary central incisor (upper jaw, closest to the center of the lips) * maxillary lateral incisor (upper jaw, beside the maxillary central incisor) * mandibular central incisor (lower jaw, closest to the center of the lips) * mandibular lateral incisor (lower jaw, beside the mandibular central incisor) Children with a full set of deciduous teeth (primary teeth) also have eight incisors, named the same way as in permanent teeth. Young children may have from zero to eight incisors depending on the stage of their tooth eruption and tooth development. Typically, the mandibular central incisors erupt first, followed by the maxillary central incisors, the mandibular lateral incisors and finally the maxillary laterals. The rest of the primary dentition erupts after the incisors. Apart from the first molars, the incisors are also the first permanent teeth to erupt, following the same order as the primary teeth, among themselves. 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「Incisor」の詳細全文を読む スポンサード リンク
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