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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/05/14 00:34:07」(JST)

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In vertebrates, an odontoblast is a biological cell of neural crest origin that is part of the outer surface of the dental pulp, and whose biological function is dentinogenesis, which is the creation of dentin, the substance under the tooth enamel.

Teeth in the molluscan radula are also produced by cells termed "odontoblasts".

Origin and differentiation

Odontoblasts first appear at sites of tooth development at 17–18 weeks in utero and remain present until death unless killed by bacterial or chemical attack, or indirectly through other means (e.g. being aspirated into dentinal tubules by the use of a turbine handpiece on tooth tissue above). The odontoblasts secrete dentin throughout life (secondary dentin, once root formation is complete), which may be an attempt to compensate for natural wear of the enamel.

Odontoblasts also secrete tertiary dentin when irritated. Tertiary dentin secreted by odontoblasts is often due to chemical attack, either by chemicals diffusing through the dentin and insulting the odontoblasts, or by diffusion of toxic bacterial metabolites down the dentinal tubules in the instance of a carious attack. This tertiary dentin is called reactionary dentin. This is an attempt to slow down the progress of the caries so that it does not reach the pulp. In the case of an infection breaching the dentin to or very near the pulp, or in the instance of odontoblast death due to other attack (e.g. chemical or physical), Pulpal Stem Cells can differentiate into odontoblast-like cells which then secrete the other kind of tertiary dentin, reparative dentin, underneath the site of attack. This is not only to slow the progress of the attack, but also to prevent the diffusion of bacteria and their metabolites into the pulp, reducing the probability of partial pulp necrosis.

The distinction of the two kinds of tertiary dentin is important, because they are secreted by different cells for different reasons. Reactionary dentine is secreted at varying speeds, dependant on the speed of progression of caries above. Histologically, it is easily distinguishable by its disordered tube structure, its local secretion (causing it to protrude into the pulpal cavity) and its slightly lower degree of mineralisation than normal. The tooth is often able to be saved by a simple restoration. Reparative dentine is secreted when the tooth's situation is dire. The odontoblasts are dead, forcing the differentiation of pulpal stem cells into odontoblast-like cells that try desperately to avoid pulpitis.

Morphology

Odontoblasts are large columnar cells arranged in an epithelioid sheet along the junction between dentin and pulp, all the way down to the root apex. It is rich in endoplasmic reticulum and golgi apparatus, especially during primary dentin formation, to give it a high secretory capacity (firstly collagenous matrix to form predentine, then mineral to form the complete dentine). Its nucleus is aligned away from the dentine, with its golgi and ER above it (towards the dentine) reflecting its unidirectional secretion. On initial dentine formation it moves pulpally, away from the primitive amelodentinal junction (then Inner Enamel Epithelium/dental papillary junction) leaving behind a tubular structure known as the odontoblast process. This keeps its tapered structure with cytoskeletal fibres, mainly intermediate filaments. A pulpal A-delta (noxious, short sharp pain) nerve fibre is wrapped around the base of this process, or travels a short way into the dentinal tubule with the odontoblast process (max ~0.1mm) This process lies in a tubule, known simply as a dentinal tubule. In a complete tooth, this process rarely extends beyond 1/3 the depth of the dentine, which is why the odontoblast transduction theory of dentin sensitivity is unlikely. The functions of the odontoblast process are as follows:

1. To aid in the secretion of tubular dentin (dentin surrounding tubule) which further organises and strengthens the dentine as a whole tissue

2. General maintenance of the dentinal tubule and dentinal fluid (ion/protein content etc.)

3. To secrete sclerotic dentin upon carious attack to block off dentinal tubules, slowing the progress of the attack (air space above blockage is known as a dead tract)

4. To channel signals of attack to the odontoblast cell body, initiating reactionary dentin secretion

5. To channel hydrokinetic forces of water movement to the A delta fibre wrapped around its base, maintaining dentine sensitivity

The biological tissue formed by odontoblasts is a type of hard tissue.

It has been shown that odontoblasts secrete the extracellular matrix protein reelin.^[1]^[2]^[3]

References

^ Buchaille R, Couble ML, Magloire H, Bleicher F (September 2000). "A substractive PCR-based cDNA library from human odontoblast cells: identification of novel genes expressed in tooth forming cells". Matrix biology : journal of the International Society for Matrix Biology 19 (5): 421–30. doi:10.1016/S0945-053X(00)00091-3. PMID 10980418. http://linkinghub.elsevier.com/retrieve/pii/S0945-053X(00)00091-3.
^ Bleicher F, Couble ML, Buchaille R, Farges JC, Magloire H (August 2001). "New genes involved in odontoblast differentiation". Adv. Dent. Res. 15: 30–3. doi:10.1177/08959374010150010701. PMID 12640735. http://adr.sagepub.com/cgi/pmidlookup?view=long&pmid=12640735.
^ Maurin JC, Couble ML, Didier-Bazes M, Brisson C, Magloire H, Bleicher F (August 2004). "Expression and localization of reelin in human odontoblasts". Matrix biology : journal of the International Society for Matrix Biology 23 (5): 277–85. doi:10.1016/j.matbio.2004.06.005. PMID 15464360. http://linkinghub.elsevier.com/retrieve/pii/S0945-053X(04)00081-2.

External links

Dentistry portal

MeSH Odontoblasts

UpToDate Contents

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1. 歯性感染症の疫学、病因、および臨床症状 epidemiology pathogenesis and clinical manifestations of odontogenic infections
2. 歯の解剖学的構造および発達 anatomy and development of the teeth
3. 歯の発達障害 developmental defects of the teeth

English Journal

Immunohistochemical localization of Pax6 in the developing tooth germ of mice.

Lei H1, Liu H, Ding Y, Ge L.
Journal of molecular histology.J Mol Histol.2014 Aug;45(4):373-9. doi: 10.1007/s10735-014-9564-5. Epub 2014 Jan 30.
Recent studies have reported that supernumerary teeth were observed in the maxillary incisor area in several Pax6 homozygous mutant mouse and rat strains. To date, it remains unknown whether Pax6 is expressed during tooth development in any species. The study aimed to analyze the expression of Pax6
PMID 24477661

The tick tock of odontogenesis.

Zheng L1, Ehardt L2, McAlpin B2, About I3, Kim D2, Papagerakis S4, Papagerakis P5.
Experimental cell research.Exp Cell Res.2014 Jul 15;325(2):83-89. doi: 10.1016/j.yexcr.2014.02.007. Epub 2014 Feb 25.
Although a big deal of dental research is being focused to the understanding of early stages of tooth development, a huge gap exist on our knowledge on how the dental hard tissues are formed and how this process is controlled daily in order to produce very complex and diverse tooth shapes adapted fo
PMID 24582863

Odontoblast physiology.

Bleicher F.
Experimental cell research.Exp Cell Res.2014 Jul 15;325(2):65-71. doi: 10.1016/j.yexcr.2013.12.012. Epub 2013 Dec 18.
Odontoblasts are post-mitotic cells organized as a layer of palisade cells along the interface between the dental pulp and dentin. They are responsible for the formation of the physiological primary and secondary dentins. They synthesize the organic matrix of type I collagen and actively participate
PMID 24361392

Japanese Journal

Coexpression of Ang1 and Tie2 in Odontoblasts of Mouse Developing and Mature Teeth—A New Insight into Dentinogenesis

Nakajima Kazunori,Shibata Yasuaki,Hishikawa Yoshitaka,Suematsu Takashi,Mori Masako,Fukuhara Shigetomo,Koji Takehiko,Sawase Takashi,Ikeda Tohru
ACTA HISTOCHEMICA ET CYTOCHEMICA 47(1), 19-25, 2014-02-27
… After birth, Ang1 was detected in the predentin, whereas both Ang1 and Tie2 were colocalized in odontoblasts and odontoblast processes. …
NAID 120005438944

Dentin Phosphophoryn Promotes Odontoblast Differentiation in vitro and Induction of Mineralized Tissue-like Matrix in vivo

, ,
Journal of Oral Tissue Engineering 11(3), 201-212, 2014
… MDPC-23, a rat odontoblast-like cell line was used in this study in vitro and to investigate mineralized-matrix induction ability of DPP in vivo. …
NAID 130004941112

Dental pulp cells that express adeno-associated virus serotype 2-mediated BMP-7 gene enhanced odontoblastic differentiation

, , , , ,
Dental Materials Journal 33(5), 656-662, 2014
This present study investigated the potential of adeno-associated virus serotype 2 (AAV2) mediated BMP-7 (AAV2-BMP-7) to induce odontoblastic differentiation of human dental pulp cells (DPCs) in vitro …
NAID 130004696771

Related Pictures

★リンクテーブル★

リンク元	「象牙質芽細胞」
拡張検索	「odontoblastic」

「象牙質芽細胞」

Odontoblast
	A developing tooth with odontoblasts marked.
	The cervical loop area: (1) dental follicle cells, (2) dental mesenchyme, (3) Odontoblasts, (4) Dentin, (5) stellate reticulum, (6) outer enamel epithelium, (7)inner enamel epithelium, (8) ameloblasts, (9) enamel.
Latin	odontoblastus
Code	TE E04.0.3.3.1.0.13