|
Amelogenesis is the formation of enamel on teeth and begins when the crown is forming during the bell stage of tooth development after dentinogenesis, which is the formation of dentin. Although dentin must be present for enamel to be formed, ameloblasts must also be for dentinogenesis to continue. A message is sent from the newly differentiated odontoblasts to the inner enamel epithelium (IEE), causing the epithelial cells to further differentiate into active secretory ameloblasts. Dentinogenesis is in turn dependent on signals from the differentiating IEE in order for the process to continue. This prerequisite is an example of the biological concept known as ''reciprocal induction'', in this instance between mesenchymal and epithelial cells. Stages Amelogenesis is considered to have three stages.〔Ten Cate's Oral Histology, Nanci, Elsevier, 2013, page 133- 148〕 The first stage is known as the inductive stage, the second is the secretory stage, and the third stage is known as the maturation stage. During the inductive stage, ameloblast differentiation from IEE is initiated. Proteins and an organic matrix form a partially mineralized enamel in the secretory stage. The maturation stage completes enamel mineralization. ==Inductive stage (or Pre-secretory Stage)== In the inductive stage, the morphodifferentiation phase the shape of the crown is determined by the bell stage of tooth development. There is a basal lamina between the IEE and the dental papilla.〔Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 58〕 At this time, the dentin is not mineralized. The IEE cuboidal or low columnar with centralized nuclei and poorly developed Golgi complexes. The differentiation phase of the Induction stage is initiated by the presence of newly formed predentin. The IEE cells then elongate and become preameloblasts. There is a shift in polarity. Each preameloblast elongate and becomes an postmitotic, polarized, secretory ameloblast. However, there are no Tomes' process yet. It is at this stage that a signal is sent from the newly differentiated ameloblasts back across the dentinoenamel junction (DEJ) to stimulate dentinogenesis. 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「Amelogenesis」の詳細全文を読む スポンサード リンク
|