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A cementoblast is a biological cell that forms from the follicular cells around the root of a tooth, and whose biological function is cementogenesis, which is the formation of cementum (hard tissue that covers the tooth root). The mechanism of differentiation of the cementoblasts is controversial but circumstantial evidence suggests that an epithelium or epithelial component may cause dental sac cells to differentiate into cementoblasts, characterised by an increase in length.〔Ten Cate's Oral Histology, Nanci, Elsevier, 2013, page 207〕 Other theories involve Hertwig epithelial root sheath (HERS) being involved.〔Luan, X., Ito, Y. and Diekwish, T.G.H. Evolution and development of Hertwig's Epithelial Root Sheath. Dev. Dyn. 2006, 235: 1167-1180 at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2734338/〕 ==Process and structure== Cementoblasts lay down the organic matrix of cementum called cementoid which later gets mineralized by minerals from oral fluids. Thus the cementoblasts lay down collagen and secrete osteocalcin and sialoprotein. Osteocalcin and sialoprotein are bone morphogenetic proteins (also known as BMPs) that are often linked to the development and mineralization of periodontal tissues. They possess all the organelles associated with protein synthesis such as RER and Golgi apparatus. More specifically, bone morphogenetic protein-2 (BMP-2) acts on the cementoblasts in the periodontal tissue. The effect of BMP-2 on cementoblasts reduces gene expression of collagen and mineralization. Noggin (protein) is a BMP inhibitor that correlates with BMP-2 to regulate gene expression and mineral nodule formation. BMP-2 also regulates mRNA levels that are associated with the process of bone formation in the cells. The initially formed cementum in coronal two-thirds of the root is acellular, but when the cementoblasts get trapped in lacunae in their own matrix like bone cells (see further discussion below), the cementum is called cellular or secondary cementum and is present only in the apical third of the root. Thus cementoblasts resemble bone-forming osteoblasts but differ functionally and histologically. The cells of cementum are the entrapped cementoblasts, the cementocytes. Each cementocyte lies in its lacuna (plural, lacunae), similar to the pattern noted in bone. These lacunae also have canaliculi or canals. Unlike those in bone, however, these canals in cementum do not contain nerves, nor do they radiate outward. Instead, the canals are oriented toward the periodontal ligament (PDL) and contain cementocytic processes that exist to diffuse nutrients from the ligament because it is vascularized.〔Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 171〕 The progenitor cells also found in the PDL region contribute to the mineralization of the tissue. Once in this situation, the cementoblasts lose their secretory activity and become cementocytes. However, a layer of cementoblasts is always present along the outer covering of the PDL; these cells can then produce cementum if the tooth is injured (see hypercementosis). 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「cementoblast」の詳細全文を読む スポンサード リンク
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