Odontoblast
Encyclopedia
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".
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.
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
.
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
of neural crest
Neural crest
Neural crest cells are a transient, multipotent, migratory cell population unique to vertebrates that gives rise to a diverse cell lineage including melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia....
origin that is part of the outer surface of the dental pulp
Pulp (tooth)
The dental pulp is the part in the center of a tooth made up of living connective tissue and cells called odontoblasts.- Anatomy :Each person can have a total of up to 52 pulp organs, 32 in the permanent and 20 in the primary teeth....
, and whose biological function is dentinogenesis
Dentinogenesis
Dentinogenesis is the formation of dentin, a substance that forms the majority of teeth. Dentinogenesis is performed by odontoblasts, which are a special type of biological cells on the outside of dental pulps, and it begins at the late bell stage of a developing tooth...
, which is the creation of dentin
Dentin
Dentine is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...
, the substance under the tooth enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
.
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 uteroIn utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...
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
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
.
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 reticulumEndoplasmic reticulum
The endoplasmic reticulum is an organelle of cells in eukaryotic organisms that forms an interconnected network of tubules, vesicles, and cisternae...
and golgi
Golgi
Golgi may refer to:*Camillo Golgi , Italian physician and scientist after which the following terms are named:**Golgi apparatus , an organelle in the eukaryotic cell...
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
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
formed by odontoblasts is a type of hard tissue.
It has been shown that odontoblasts secrete the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
protein reelin
Reelin
Reelin is a large secreted extracellular matrix protein that helps regulate processes of neuronal migration and positioning in the developing brain by controlling cell–cell interactions. Besides this important role in early development, reelin continues to work in the adult brain. It modulates the...
.