Dentinogenesis - HackDentistry

Dentinogenesis

Dentinogenesis is the formation of dentin. It proceeds in two stages: secretion of an unmineralized organic matrix called predentin, followed by mineralization of that matrix.

Composition of dentin

The organic matrix consists mainly of type I collagen, with smaller amounts of type III and type V collagen. Non-collagenous proteins include dentin phosphoprotein (DPP), dentin sialoprotein (DSP), dentin sialophosphoprotein (DSPP), osteonectin, osteopontin, and Gla protein.

Organic components make up about 20% of dentin. Together with water, they account for about 30%; most of the remainder is inorganic material, chiefly hydroxyapatite.

Odontoblast differentiation

Dentin formation begins during the bell stage. Signals from the inner enamel epithelium (IEE), including transforming growth factor (TGF) and bone morphogenetic proteins (BMP), help nearby dental papilla cells differentiate into pre-odontoblasts.

Pre-odontoblasts enlarge and elongate, develop protein-secreting organelles such as rough endoplasmic reticulum and Golgi complexes, and mature into odontoblasts. As they become polarized, their nuclei shift away from the IEE.

Dentin compartments and secretion

The first dentin formed is mantle dentin, which is about 15–20 µm thick and lies near the enamel. The remaining dentin is circumpulpal dentin.

Odontoblasts secrete collagen and non-collagenous proteins toward the IEE. The initial mantle dentin matrix consists mainly of type I collagen, with some type III collagen in von Korff’s fibers.

After secreting the initial matrix, an odontoblast develops an odontoblastic process, also called a Tomes’ fiber. The process elongates as matrix is deposited and the odontoblast moves toward the pulp. In mature dentin, these processes lie within dentinal tubules. Mantle dentin does not have dentinal tubules.

The term Tomes’ process refers instead to an ameloblast extension involved in forming enamel rods and interrod enamel.

Predentin and circumpulpal dentin

Mineralization does not extend all the way to the odontoblast cell bodies. A persistent, unmineralized layer between the odontoblasts and mineralized dentin is called predentin. It is about 15–20 µm thick.

Circumpulpal dentin matrix contains type I collagen, non-collagenous proteins, and proteoglycans. The proposed pattern of matrix deposition varies by location:

• Near the odontoblast cell bodies, predentin contains collagen and proteoglycans.
• Near the mineralized dentin, at the mineralization front, non-collagenous proteins are also present alongside collagen and proteoglycans.

Thus, circumpulpal dentin includes both predentin and mineralized dentin.

Mineralization

Mineralization begins in mantle dentin and proceeds into circumpulpal dentin.

In mantle dentin, odontoblasts release matrix vesicles into the matrix. These vesicles contain enzymes and proteins, including alkaline phosphatase and metalloproteinases, that help bind calcium and phosphate and initiate hydroxyapatite crystal formation. Crystals begin growing inside the vesicles, then are released into the matrix, where they grow and join neighboring crystals to mineralize the matrix.

Matrix vesicles are not found in circumpulpal dentin. Instead, calcium is thought to travel from the sub-odontoblastic area to the mineralization front, either through or between odontoblasts. Alkaline phosphatase and Ca-ATPase activity in odontoblasts may assist this transport. Non-collagenous proteins at the mineralization front also help support mineralization.

Patterns of calcification

• Globular calcification involves rounded or concentric mineralized masses that enlarge and fuse. It is commonly associated with mantle dentin.
• Linear calcification occurs when the mineralization front is more uniform.

Circumpulpal dentin may show either globular or linear calcification.

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