{{Refimprove, date=September 2014 Dentinogenesis is the formation of

dentin Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...

, a substance that forms the majority of

teeth 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, tear ...

. Dentinogenesis is performed by

odontoblast In vertebrates, an odontoblast is a 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 formation of dentin, the substance beneath the tooth enamel on t ...

s, which are a special type of

biological cell The cell is the basic structural and functional unit of life forms. Every cell consists of a cytoplasm enclosed within a membrane, and contains many biomolecules such as proteins, DNA and RNA, as well as many small molecules of nutrients an ...

on the outer wall of

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 centr ...

s, and it begins at the late bell stage of a

tooth development Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate stag ...

. The different stages of dentin formation after differentiation of the cell result in different types of dentin: mantle dentin, primary dentin, secondary dentin, and tertiary dentin.

Odontoblast differentiation

Odontoblasts differentiate from cells of the dental papilla. This is an expression of signaling molecules and growth factors of the inner enamel epithelium (IEE).

Formation of mantle dentin

They begin secreting an organic matrix around the area directly adjacent to the IEE, closest to the area of the future cusp of a tooth. The organic matrix contains collagen fibers with large diameters (0.1-0.2 μm in diameter). The odontoblasts begin to move toward the center of the tooth, forming an extension called the

odontoblast process An odontoblast process (also called Tomes's fibers or Tomes fibers, or by a dated term Tomes's fibrils) is an extension of a cell called an odontoblast, which forms dentin in a tooth. The odontoblast process is located in dentinal tubules. It forms ...

. Thus, dentin formation proceeds toward the inside of the tooth. The odontoblast process causes the secretion of hydroxyapatite crystals and mineralization of the matrix (mineralisation occurs due to matrix vesicles). This area of mineralization is known as mantle dentin and is a layer usually about 20-150 μm thick.

Formation of primary dentin

Whereas mantle dentin forms from the preexisting ground substance of the dental papilla, primary dentin forms through a different process. Odontoblasts increase in size, eliminating the availability of any extracellular resources to contribute to an organic matrix for mineralization. Additionally, the larger odontoblasts cause

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...

to be secreted in smaller amounts, which results in more tightly arranged, heterogeneous nucleation that is used for mineralization. Other materials (such as

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

phosphoprotein A phosphoprotein is a protein that is posttranslationally modified by the attachment of either a single phosphate group, or a complex molecule such as 5'-phospho-DNA, through a phosphate group. The target amino acid is most often serine, threonin ...

s, and phospholipids) are also secreted. There is some dispute about the control of mineralization during dentinogenesis. The dentin in the root of a tooth forms only after the presence of Hertwig epithelial root sheath (HERS), near the

cervical loop The cervical loop is the location on an enamel organ in a developing tooth where the outer enamel epithelium and the inner enamel epithelium join. The cervical loop is a histologic term indicating a specific epithelial structure at the apical s ...

of the enamel organ. Root dentin is considered different from dentin found in the crown of the tooth (known as coronal dentin) because of the different orientation of collagen fibers, as well as the possible decrease of phosphophoryn levels and less mineralization. Maturation of dentin or mineralization of predentin occurs soon after its apposition, which takes place two phases: primary and secondary. Initially, the calcium hydroxyapatite crystals form as globules, or calcospherules, in the collagen fibers of the predentin, which allows for both the expansion and fusion during the primary mineralization phase. Later, new areas of mineralization occur as globules form in the partially mineralized predentin during the secondary mineralization phase. These new areas of crystal formation are more or less regularly layered on the initial crystals, allowing them to expand, although they fuse incompletely. In areas where both primary and secondary mineralization have occurred with complete crystalline fusion, these appear as lighter rounded areas on a stained section of dentin and are considered globular dentin. In contrast, the darker arclike areas in a stained section of dentin are considered interglobular dentin. In these areas, only primary mineralization has occurred within the predentin, and the globules of dentin do not fuse completely. Thus, interglobular dentin is slightly less mineralized than globular dentin. Interglobular dentin is especially evident in coronal dentin, near the DEJ, and in certain dental anomalies, such as in dentin dysplasia.Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 156-157

Formation of secondary dentin

Secondary dentin is formed after root formation is finished and occurs at a much slower rate. It is not formed at a uniform rate along the tooth, but instead forms faster along sections closer to the crown of a tooth. This development continues throughout life and accounts for the smaller areas of pulp found in older individuals.

Formation of tertiary dentin

Tertiary dentin Tertiary dentin (including reparative dentin or sclerotic dentin) forms as a reaction to stimulation, including caries, wear and fractures. Tertiary dentin is therefore a mechanism for a tooth to ‘heal’, with new material formation protecting th ...

is deposited at specific sites in response to injury by odontoblasts or replacement odontoblasts from the pulp depending on the severity of the injury. Tertiary dentin can be divided into reactionary or reparative dentin. Reactionary dentin is formed by odontoblasts when the injury does not damage the odontoblast layer. Reparative dentin is formed by replacement odontoblasts when the injury is so severe that it damages a part of the primary odontoblast layer. Thus a type of tertiary dentin forms in reaction to stimuli, such as

attrition Attrition may refer to *Attrition warfare, the military strategy of wearing down the enemy by continual losses in personnel and material **War of Attrition, fought between Egypt and Israel from 1968 to 1970 **War of attrition (game), a model of agg ...

dental caries Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...

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