Histology of Dentin
The dentin is a hard tissue that forms the bulk of the tooth.
The dentin is similar to bone but is slightly harder, although softer than enamel.
Dentin is elastic, and provides protection in that it prevents fracture of the overlying enamel (enamel is hard and brittle).
The dentin has numerous dentinal tubules that run across its length. Each dentinal tubule houses the cytoplasmic process of an odontoblast (odontoblastic process).
NOTE
- An odontoblastic process is also called Tomes fiber.
- Also, do not get confused with Tomes process and Tomes fiber.
Tomes process is the distal extension of an ameloblast that is responsible for secretion of rod and inter rod enamel.
Whereas, Tome’s fiber is the cytoplasmic process of the odontoblast present within dentinal tubules in the fully formed dentin.🎥HackDentistry - YouTube
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Composition of Dentin
The organic matrix comprises mainly type I collagen with fractions of type III and type V collagen. This comprises 90% of the organic material.
The rest of the organic material is composed of Dentin phosphoprotein (DPP), dentin sialoprotein (DSP), dentin sialophosphoprotein(DSPP), osteonectin, osteopontin and Gla protein. These make up for non-collagenous proteins.
Together they make up around 20% of dentin and along with water comprise 30% of dentin.
The rest of the dentin (70%) is made of inorganic material composed of calcium hydroxyapatite crystals (inorganic component).
Histology of Dentin
🗝️Dentinal Tubules
The odontoblastic processes are housed in canaliculi called dentinal tubules.
These dentinal tubules run or traverse the entire thickness of the dentin, extending from the inner dentin (actually from the mineralization front just before the pulp) to the dentino-enamel junction (DEJ) (coronally) and cementum dentin junction (in the root portion).
A dentinal tubule is doubly curved and follows an “S” shaped or sigmoid course. These curves are called primary curvatures.
The first curve from the inner dentin (near the pulp) has its convexity rootward (towards the apex).
Dentinal tubules show numerous branches terminally towards the DEJ and cementum dentin junction. These are called terminal branches. Tubules also show lateral branches along their length.
Terminal branching of dentinal tubules is more prominent in the root dentin than in the coronal dentin.
The course of a dentinal tubule is not straight. Each tubule shows minute curvatures or minor kinks throughout its length. These curvatures or kinks are called secondary curvatures.
Dentinal tubules have a larger diameter towards the pulpal surface.
NOTE
- Terminal branching and looping of these branches give rise to the Tomes Granular layer, in the root dentin just below the cementum.
- Secondary curvatures are believed to coincide with one another to give rise to Contour lines of Owen.💡KNOW THY FACTS
The dentinal tubule housing the odontoblast process, is also known to have a thin periodontoblastic space.
This space is thought to be filled by dentinal fluid.
🗝️Peritubular dentin
As the name describes, it is the dentin immediately surrounding the dentinal tubule.
Ironically, the peritubular dentin does not actually surround the tubule but rather lines the inner wall of the dentinal tubule. Hence, it may be more appropriately termed “intra-tubular” dentin.
The peri-odontoblastic space in the dentinal tubule exists between the odontoblast process and the peritubular or intratubular dentin.
The peritubular dentin is more mineralized (by 5 – 12%) than the intertubular dentin.
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