dentin
TRANSCRIPT
Dentin
Dr. Syed SadatullahAssistant Professor
1. Introduction and Chemical Composition
Dentin is a hard bone-like tissue that is present in the crown as well as in the root of teeth.
In the crown, dentin is covered by enamel and in the root it is covered by cementum
Unlike enamel, dentin is a vital tissue containing the cell processes of odontoblasts and neuron
Mature dentin has 20% organic, 70% inorganic and 10% water by weight .
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The organic matrix of dentin is collagenous
It provides resiliency to the crown which is necessary to withstand the forces of mastication
The principle inorganic component of dentin is hydroxyapatite crystals
The high mineral content of dentin makes it harder than bone and cementum but softer than enamel
The knoop hardness for dentin is approximately 68
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2. Dentinal structure and classification
Dentin is packed with dentinal tubules that traverse its entire thickness
Dentinal tubules contain odontoblastic process and nerve fibres
The odontoblastic processes have numerous side branches that exist in the lateral branches of the dentinal tubules
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Odontoblasts – peri-tubular and inter-tubular dentin has been removed
Dentine tubules – odontoblastic processes removed
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Odontoblastic process
3. Histological Features of Dentin
Depending on its time of development Dentin is classified as:
Primary dentin
Secondary dentin
Tertiary dentin
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Primary dentin
Primary dentin is the developmental dentin that is formed before and during eruption
Secondary dentin
Secondary dentine develops after the root formation has been completedDeposition of secondary dentin is continuous but much slower It has a tubular structure which is almost continuous with the primary dentin
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Types of Dentin
Tertiary dentin
Tertiary dentin is produced in reaction to stimulus, such as attrition , caries or restorative dental procedure
Tertiary dentin can be reactionary or reparative
Reactionary dentin is that type of tertiary dentin that is deposited by the pre-existing odontoblasts
Reparative dentin is deposited by newly differentiated odontoblasts
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Secondary and Tertiary Dentin
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Types of Dentin
Predentin
Mantle Dentin
Circumpulpal Dentin
Inter-globular Dentin
Sclerotic Dentin
Intra-tubular Dentin
Inter-tubular Dentin
Tomes Granular layer
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Odontoblast process in dentin tubule
Predentin
Predentin is the first deposited layer of un-mineralized matrix of dentin
Mantle Dentin
The outer layer of dentine that mineralizes first is called mantle dentin. It lies near the DEJ
Circumpulpal Dentin
The bulk of dentin underlying the mantle dentin is called circumpulpal
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Mantle Dentin – Inter-globular Dentin – Circumpulpal Dentin
Inter-globular Dentin
Dentine separating the mantle dentin and circumpulpal dentin is hypo-mineralized and is called inter-globular dentin
Interglobular Dentin
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Intra-tubular Dentin
Dentin surrounding and nearest to each tubule is hyper-mineralized and is called intra-tubular dentin or peri-tubular dentin
If there is increased mineralization of intra-tubular dentine the tubule gets occluded and the resulting dentine is called sclerotic dentin or transparent dentin
If odontoblasts die as a result of injury or old age the tubule are referred to as dead tracts
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Intra-tubular Dentin
Inter-tubular Dentin The dentinal matrix that lies between the intra-tubular dentin is inter-tubular dentin
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Inter-tubular Dentin
Tomes granular layer
In the roots near the cemento-dentinal junction there are hypo-mineralized areas of dentin around the dentinal tubule called the Tomes granular layer
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4. Histological Features of DentinIncremental growth line
The organic matrix of dentine is deposited incrementally at a daily rate of 4µm
At the boundary of each daily increment, minute changes in collagen fibre orientation is observed which manifest as incremental lines
Incremental lines run perpendicular to the dentinal tubules
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Incremental lines
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Incremental lines
Incremental lines of von Ebner
In ground section the 5-day increment can be seen as incremental or imbrications' lines of von Ebner
Counter lines Owen
Counter lines of Owen represent normal physiological alterations in the pattern of mineralization
Neonatal line represents an exaggerated counter line of Owen.
Neonatal lines are seen in all primary teeth and the first permanent molars
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Neonatal Line in Enamel and Dentin
Lines of Owen