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Dental anatomy is a field of anatomy dedicated to the study of human tooth structures. The development, appearance, and classification of teeth fall within its purview. (The function of teeth as they contact one another falls elsewhere, under dental occlusion.) Tooth formation begins before birth, and teeth's eventual morphology is dictated during this time. Dental anatomy is also a taxonomical science: it is concerned with the naming of teeth and the structures of which they are made, this information serving a practical purpose in dental treatment. Usually, there are 20 primary ("baby") teeth and 28 to 32 permanent teeth, the last four being third molars or "wisdom teeth", each of which may or may not grow in. Among primary teeth, 10 usually are found in the maxilla (upper jaw) and the other 10 in the mandible (lower jaw). Among permanent teeth, 16 are found in the maxilla and the other 16 in the mandible. Most of the teeth have distinguishing features. == Growing of tooth == (詳細はembryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans. For human teeth to have a healthy oral environment, enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development. Primary (baby) teeth start to form between the sixth and eighth weeks in utero, and permanent teeth begin to form in the twentieth week in utero.〔A. R. Ten Cate, ''Oral Histology: Development, Structure, and Function'', 5th ed. (Saint Louis: Mosby-Year Book, 1998), p. 95. ISBN 0-8151-2952-1.〕 If teeth do not start to develop at or near these times, they will not develop at all. A significant amount of research has focused on determining the processes that initiate tooth development. It is widely accepted that there is a factor within the tissues of the first branchial arch that is necessary for the development of teeth.〔 The tooth bud (sometimes called the tooth germ) is an aggregation of cells that eventually forms a tooth and is organized into three parts: the enamel organ, the dental papilla and the dental follicle.〔 The ''enamel organ'' is composed of the outer enamel epithelium, inner enamel epithelium, stellate reticulum and stratum intermedium.〔 These cells give rise to ameloblasts, which produce enamel and the reduced enamel epithelium. The growth of cervical loop cells into the deeper tissues forms Hertwig's Epithelial Root Sheath, which determines the root shape of the tooth. The ''dental papilla'' contains cells that develop into odontoblasts, which are dentin-forming cells.〔 *University of Texas Medical Branch. "Lab Exercises: Tooth development." Page found (here ).〕 Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth.〔A. R. Ten Cate, ''Oral Histology: Development, Structure, and Function'', 5th ed. (Saint Louis: Mosby-Year Book, 1998), pp. 86 and 102. ISBN 0-8151-2952-1.〕 The ''dental follicle'' gives rise to three important entities: cementoblasts, osteoblasts, and fibroblasts. Cementoblasts form the cementum of a tooth. Osteoblasts give rise to the alveolar bone around the roots of teeth. Fibroblasts develop the periodontal ligaments which connect teeth to the alveolar bone through cementum.〔 *Ross, Michael H., Gordon I. Kaye, and Wojciech Pawlina. Histology: a text and atlas. 4th edition, p. 453. 2003. ISBN 0-683-30242-6.〕 Tooth development is commonly divided into the following stages: the bud stage, the cap, the bell, and finally maturation. The staging of tooth development is an attempt to categorize changes that take place along a continuum; frequently it is difficult to decide what stage should be assigned to a particular developing tooth.〔A. R. Ten Cate, ''Oral Histology: Development, Structure, and Function'', 5th ed. (Saint Louis: Mosby-Year Book, 1998), p. 81. ISBN 0-8151-2952-1.〕 This determination is further complicated by the varying appearance of different histologic sections of the same developing tooth, which can appear to be different stages. 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「Dental anatomy」の詳細全文を読む スポンサード リンク
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