<ul><li>A vascular </li></ul><ul><li>Forms the bulk of each tooth crown & root . </li></ul><ul><li>Cellular (contains odontoblast processes ) </li></ul><ul><li>some capacity for repair by deposition on its pulpal surface . </li></ul>Histology of Dentin
<ul><li>harder than bone & cementum </li></ul><ul><li>softer than enamel </li></ul><ul><li>-> less resistant to attrition </li></ul><ul><li>occlusal and incisal attrition </li></ul><ul><li>-> less resistant to abrasion </li></ul><ul><li>toothbrush & other abrasion </li></ul><ul><li>-> less resistant to acid attack </li></ul><ul><li>caries erosion </li></ul>
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.
<ul><li>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. </li></ul><ul><li>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. </li></ul>
<ul><li>Circumpulpal dentin: The layer of dentin around the outer pulpal wall. </li></ul><ul><li>Peritubular dentin: Dentin that creates the wall of the dentinal tubules. </li></ul><ul><li>Intertubular dentin: L ocated between the dentinal tubules </li></ul><ul><li>Interglobular dentin: A reas of unmineralized or hypomineralized dentin </li></ul><ul><ul><li>where globular areas of mineralization have failed to fuse . </li></ul></ul><ul><li>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 . </li></ul>
peritubular / intratubular dentine dentin that forms the wall of each tubule more mineral than intertubular dentin intertubular dentine dentine between the tubules
<ul><li>It consists of 35% organic material and 65% inorganic material . </li></ul><ul><li>The organic material consists of collagen fibrils and ground substance( mucopoly saccharides ) </li></ul><ul><li>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. </li></ul>
<ul><li>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 . </li></ul><ul><li>Odontoblasts are large columnar cells arranged in a well defined layer , sending their odontoblastic process through dentin . </li></ul><ul><li>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. </li></ul><ul><li>Each odontoblast sends one odontoblastic process that run inside the dentinal tubule, where both traverse the dentin thickness . </li></ul><ul><li>A long its course the process sends out several lateral branches enclosed in the canaliculi . </li></ul>
Odontoblasts and process Odontoblast cells Odontoblast process Dentin Pulp
Dentinal Matrix Dentinal matrix Hole for dentinal tubules
Dentinal tubules <ul><li>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 . </li></ul>
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. Brannstrom’s Theory.