In vertebrates, an odontoblast is a
cell of
neural crest
The neural crest is a ridge-like structure that is formed transiently between the epidermal ectoderm and neural plate during vertebrate development. Neural crest cells originate from this structure through the epithelial-mesenchymal transition, ...
origin that is part of the outer surface of the
dental pulp
The pulp is the connective tissue, nerves, blood vessels, and odontoblasts that comprise the innermost layer of a tooth. The pulp's activity and signalling processes regulate its behaviour.
Anatomy
The pulp is the neurovascular bundle cen ...
, and whose biological function is
dentinogenesis
{{Refimprove, date=September 2014
In animal tooth development, 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 cell on th ...
, which is the formation of
dentin
Dentin ( ) (American English) or dentine ( or ) (British English) () is a calcified tissue (biology), tissue of the body and, along with tooth enamel, enamel, cementum, and pulp (tooth), pulp, is one of the four major components of teeth. It i ...
, the substance beneath the
tooth enamel
Tooth enamel is one of the four major Tissue (biology), tissues that make up the tooth in humans and many animals, including some species of fish. It makes up the normally visible part of the tooth, covering the Crown (tooth), crown. The other ...
on the crown and the cementum on the root.
Structure
Odontoblasts are large columnar cells, whose cell bodies are arranged along the interface between dentin and pulp, from the crown to the cervix to the
root apex in a mature tooth. The cell is rich in
endoplasmic reticulum
The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...
and Golgi complex, especially during primary dentin formation, which allows it to have a high secretory capacity; it first forms the collagenous matrix to form predentin, then mineral levels to form the mature dentin. Odontoblasts form approximately 4 μm of predentin daily during tooth development.
[Ten Cate's Oral Histology, Nanci, Elsevier, 2013, page 170]
During secretion after differentiation from the outer cells of the dental papilla, it is noted that it is polarized so its nucleus is aligned away from the newly formed dentin, with its Golgi complex and endoplasmic reticulum towards the dentin reflecting its unidirectional secretion. Thus, with the formation of primary dentin, the cell moves pulpally, away from the basement membrane (future dentinoenamel junction) at the interface between the inner enamel epithelium and dental papilla, leaving behind the odontoblastic process within the dentin. The odontoblastic cell body keeps its tapered structure with cytoskeletal fibres, mainly
intermediate filaments
Intermediate filaments (IFs) are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate ''Branchiostoma''.
Intermedi ...
. Unlike cartilage and bone, as well as cementum, the odontoblast's cell body does not become entrapped in the product; rather, one long, cytoplasmic attached extension remains behind in the formed dentin.
The differentiation of the odontoblast is done by signaling molecules and growth factors in the cells of the inner enamel epithelium.
Like enamel, dentin is avascular. Nutrition for odontoblasts within the dentin comes through the dentinal tubules from tissue fluid that originally traveled from the blood vessels located in the adjacent pulp tissue. Within each dentinal tubule is a space of variable size containing dentinal fluid, an odontoblastic process, and possibly an afferent axon (see next discussion). The dentinal fluid in the tubule presumably also includes the tissue fluid surrounding the cell membrane of the odontoblast, which is continuous from the cell body in the pulp.
It has been shown that odontoblasts secrete the
extracellular matrix
In biology, the extracellular matrix (ECM), also called intercellular matrix (ICM), is a network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide structural and bio ...
protein
reelin
Reelin, encoded by the ''RELN'' gene, is a large secreted extracellular matrix glycoprotein that helps regulate processes of neuronal migration and positioning in the developing brain by controlling cell–cell interactions. Besides this importa ...
.
A pulpal
A-delta (noxious, short sharp pain) nerve fibre is either wrapped around the base of this process, or travels a short way into the dentinal tubule with the odontoblast process (max ~0.1 mm) This process lies in the dentinal tubule. In primates, enamel spindles were observed where the odontoblast process reaches until the border between dentin and enamel. With the discovery of TRPC5 as cold transducer the odontoblast transduction theory has become a likely explanation of dentinal hypersensivity
The contribution of TRPC5 channels to the sensory function in odontoblasts is still controversial
It has been shown that odontoblast-neuron signal communication via Piezo1/TRPA1 channels and pannexin-1 in odontoblasts and P2X3 receptors in
A-delta neuron is involved in the generation of dentinal sensitivity/hypersensitivity. Oodontoblasts are necessary for sensory transduction to generate dentinal sensitivity as mechanosensory receptor cells.
Development
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 such as heat or trauma (e.g. during dental procedures). Odontoblasts were originally the outer cells of the dental papilla. Thus, dentin and pulp tissue have similar embryological backgrounds, because both are originally derived from the dental papilla of the tooth germ.
[Fehrenbach, MJ and Popowics, T. (2006). ''Illustrated Dental Embryology, Histology, and Anatomy'', 6th edition, Elsevier, page 67-68.]
Function
# To aid in the secretion of intertubular and peritubular dentin (the dentin surrounding odontoblastic process) that forms the dentinal tubule, which further organizes and strengthens the dentin as a whole
# General maintenance of both the dentinal tubule and dentinal fluid (ion/protein content etc.)
# 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)
# To channel signals of attack to the odontoblastic cell body, thus initiating secretion of reactionary dentin
# To act as a cellular component of the dental temperature sensing system either by sensing temperature changes directly or by detecting hydrokinetic forces of fluid movement in the tubules or a combination of both.
The odontoblasts secrete dentin throughout life, unlike enamel, which is considered secondary dentin once root formation is complete, which may be an attempt to compensate for natural wear of the
enamel. This is because of the retention of the odontoblasts within the tooth, along the outer pulpal wall.
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 with dental decay. 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), undifferentiated mesenchymal cells can differentiate into odontoblast-like cells which then secrete another type, reparative dentin, underneath the site of attack. This is not only to slow the progress of the attack, but also prevents 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 dentin is secreted at varying speeds, dependent on the speed of progression of caries in the outer dentin surface. Histologically, it is easily distinguishable by its disordered tube structure, the location of the secretion (it protrudes into the pulpal cavity) and its slightly lower degree of mineralization than normal. The tooth is often able to be saved by a simple restoration. In contrast, reparative dentin is secreted when the tooth has a poor prognosis.
Other animals
Teeth in the
molluscan radula are also produced by cells termed "odontoblasts".
See also
*
Tooth development
A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, teari ...
*
Ameloblast
Ameloblasts are cells present only during tooth development that deposit tooth enamel, which is the hard outermost layer of the tooth forming the surface of the crown.
Structure
Each ameloblast is a columnar cell approximately 4 micrometers in ...
*
Cementoblast
*
List of human cell types derived from the germ layers
This is a list of Cell (biology), cells in humans derived from the three embryonic germ layers – ectoderm, mesoderm, and endoderm.
Cells derived from ectoderm
Surface ectoderm Skin
* Trichocyte (human), Trichocyte
* Keratinocyte
Anterior pi ...
*
List of distinct cell types in the adult human body
The list of human cell types provides an enumeration and description of the various specialized cells found within the human body, highlighting their distinct functions, characteristics, and contributions to overall physiological processes. Cell ...
References
{{Tooth development
Tooth development