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The maxillary central incisor is a human tooth in the front upper jaw, or maxilla, and is usually the most visible of all teeth in the mouth. It is located mesial (closer to the midline of the face) to the maxillary lateral incisor. As with all incisors, their function is for shearing or cutting food during mastication (chewing). There is typically a single cusp on each tooth, called an incisal ridge or incisal edge. Formation of these teeth begin at 14 weeks in utero for the deciduous (baby) set and 3–4 months of age for the permanent set.〔Ash, Major M. and Stanley J. Nelson. Wheeler’s Dental Anatomy, Physiology, and Occlusion. 8th edition. 2003. pp. 45 and 54. ISBN 0-7216-9382-2.〕 There are some minor differences between the deciduous maxillary central incisor and that of the permanent maxillary central incisor. The deciduous tooth appears in the mouth at 8–12 months of age and shed at 6-7 years, and is replaced by the permanent tooth around 7–8 years of age. The permanent tooth is larger and is longer than it is wide. The maxillary central incisors contact each other at the midline of the face. The mandibular central incisors are the only other type of teeth to do so. The position of these teeth may determine the existence of an open bite or diastema. As with all teeth, variations of size, shape, and color exist among people. Systemic disease, such as syphilis, may affect the appearance of teeth. ==Notation== Dentistry has several systems of notation to identify teeth. In the universal system of notation, the deciduous maxillary central incisors are designated by a letter written in uppercase.〔(ADA.org: Oral Health Topics: Tooth Numbering Systems ), hosted on the (American Dental association ) website. Page accessed April 1, 2007.〕 The right deciduous maxillary central incisor is known as "E", and the left one is known as "F". The permanent maxillary central incisors are designated by a number. The right permanent maxillary central incisor is known as "8", and the left one is known as "9". In the Palmer notation, a letter is used in conjunction with a symbol designating in which quadrant the tooth is found. For the deciduous teeth, the left and right central incisor would have the same letter, "A", but the right one would have the symbol, "┘", underneath it, while the left one would have, "└". For the permanent teeth, the left and right central incisor would have the same number, "1", but the right one would have the symbol, "┘", underneath it, while the left one would have, "└". The FDI World Dental Federation notation has a different system of numbering system from the previous two.〔(FDI Two-Digit Notation ), hosted on the (FDI World dental Federation ) website. Page accessed April 1, 2007.〕 Thus, the right deciduous maxillary central incisor is known as "51", and the left one is known as "61". For the permanent maxillary central incisor, the right one is known as "11", and the left one is known as "21". 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「Maxillary central incisor」の詳細全文を読む スポンサード リンク
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