©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

By Hesham Dameer

A vascular

Forms the bulk of each tooth crown & root .

Cellular (contains odontoblast processes )

some capacity for repair by deposition on its pulpal surface .

Histology of Dentin

harder than bone & cementum softer than enamel →less resistant to attrition occlusal and incisal attrition →less resistant to abrasion toothbrush & other abrasion →less resistant to acid attack caries erosion

Primary dentin the most prominent dentin in the tooth, lies between the enamel and the pulp chamber.

Secondary dentin is formed after root formation is complete, normally after the tooth has erupted and is functional. It grows much slower than primary dentin.The growth of this type of dentin causes the decrease in the size of the pulp chamber with age; this is why cavity preparation in young patients is risky which may lead to exposing the pulp.

Tertiary dentin is a dentin that formed as a reaction to external insult such as caries. The dentin is formed from a pre-existing odontoblast.

Tertiary dentin formation is regarded as an

important defense mechanism of the pulp-dentin complex in response to either pathological or physiological insults. The presence of tertiary dentin reduces dentin permeability.

Tertiary dentin

Circumpulpal dentin: The layer of dentin around the outer

pulpal wall. Peritubular dentin: Dentin that creates the wall of the

dentinal tubules.

Intertubular dentin: Located between the dentinal tubules Interglobular dentin: Areas of unmineralized or

hypomineralized dentinwhere globular areas of mineralization have failed to

fuse .

Granular layer of tome's: The superficial layer of dentin , adjacent to cementum, shows minute black spaces in the ground sections These are only found in the root dentin .

peritubular / intratubular dentine dentin that forms the wall of each tubulemore mineral than intertubular dentin

intertubular dentinedentine between the tubules

Interglobular DentinInterglobular Dentin

Inter-globulerdentin

DentinalTubules

DentinoEnamelJunction

Dentin

Cementum

Granular layer of Tomes

It consists of 35% organic material and 65% inorganic material .

The organic material consists of collagen fibrils and ground substance( mucopoly saccharides )

The inorganic component consists of hydroxy apatite crystals composed of several thousands of unit cells . The crystals are plate shaped and smaller than the plates of enamel.

Odontoblasts: 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 .

Odontoblasts are large columnar cells arranged in a well defined layer , sending their odontoblastic process through dentin .

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.

Each odontoblast sends one odontoblastic process that run inside the dentinal tubule, where both traverse the dentin thickness .

A long its course the process sends out several lateral branches enclosed in the canaliculi .

Odontoblast processes

Odontoblasts and processOdontoblasts and process

Odontoblast cellsOdontoblast process

Dentin Pulp

Dentinal MatrixDentinal Matrix

Dentinal matrix

Hole for dentinal tubules

Dentinal tubules

Dentinal tubules are structures that span the entire thickness of dentin and form as a result of the mechanism of dentin formation. From the outer surface of the dentin to the area nearest the pulp, these tubules follow an S-shaped path. The diameter and density of the tubules are greatest near the pulp. Tapering from the inner to the outermost surface, they have a diameter of 2.5 μm near the pulp, 1.2 μm in the middle of the dentin, and 0.9 μm at the dentino-enamel junction. Within the tubules, there is an odontoblast process .

Dentinal tubules

Dentinal tubules

Peritubular dentin Intertubular dentin

Dentinal TubulesDentinal Tubules

Coronal dentin

Root dentin

                                        

                                                  

 Brannstrom’s Theory.

Hydrodynamic theory : Fluid movements in the dentinal tubules – the tubular nature of dentin permits fluid movement to occur within the tubule when a stimulus is applied – a movement registered by pulpal free nerve endings close to the dentin.

THE END

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