WHAT IS AN ODONTOBLAST??
• An odontoblast is a biological cell of neural
crest origin that is a part of the outer surface of
the pulp and whose biological function is
dentinogenesis,which is a creation of dentine.
• Dentine forming cells
• 2nd most prominent cell in the pulp
• Large columnar cells
• Arranged in a palisading pattern at the pheriphery
of the pulp
• Rich in ER, Golgi complex
• Unidirectional secretory pattern
• Interconnected by Macula adherens and gap
• No. of odontoblast = no.of dentinal tubules
• 59,000 -76,000/sqmm
• Deposits 4µm of dentine everyday.
• Morphologic variations of odontoblasts :
-Tall columnar cells in the crown of the tooth
-Low columnar cells in the middle of the tooth
-Flattened cells at the apex
Life cycle of odontoblast
• PRE-ODONTOBLAST STAGE:
-Preodontoblasts have a small ovoid cells with small
- few strands of dense fibrillar material radiating from the
- few orgenells
-The cells are located around the growing tip of the root
-BMP ,GDf11 , BSP genes
• SYNTHETIC / ACTIVE STAGE:
-Tall columnar cells
-Large basal nucleus with a basophilic cytoplasm
-Numerous endoplasmic reticulum, mitochondria
-Well developed golgi complex
- Abundant synthetic orgenelles
-Numerous secretory granules.
• TRANSITIONAL / INTERMEDIATE STAGE:
-Shows features of synthetic cells but orgenells are less in
number and less prominent.
-Nucleus shows condensation of chromatin with orgenells
distributed around the nucleus.
• RESTING / AGED ODONTOBLAST STAGE:
-Dark close faced nucleus
-Secretory granules are absent
STRUCTURal DEVELOPMENT OF ODONTOBLASTS
PREODONTOBLASTS - ↑NUCLEUS-CYTOPLASMIC
RATIO & few cisterns of rough endoplasmic
reticulum , small golgi apparatus and few
1ST SIGN OF ODONTOBLAST DIFFERENTIATION- apical
point of dental papilla during early bell stage.
↑Aperiodic fibrils ̃15-20nm in diameter and 0.5-
1µm long are perpendicular to basal lamina.
• Cytoplasmic Processes Of The Adjascent
Preodontoblasts Become Closely Associated
With The Aperiodic Fibrils And Contact The
• Simultaneously polarisation of preodontoblasts
• It has been suggested that receptor-ligand
interactions involving substrate adhesion
molecules among the aperiodic fibrils serve to
orient and immobilize the preodontoblasts,
inducing them to begin differentiation.
• AND ODONTOBLASTS ARE THUS FORMED.
Golgi apparatus,RER basement membrane
Nucleus proximal end
↑number of RER
↑size of Golgi complex
↑number of mitochondria
Numerous matrix vesicles
Thus Odontoblasts exhibit cylindrical shape.
STRUCTURE OF An ODONTOBLAST
• Approx 5-7µm in diameter
• 25-40µm in length
• Adjacent cells are connected by junctional
• Shape of odontoblast ἀ Degree of Activity
• Cytoplasmic extensions at the apical end
continue as Odontoblastic processes.
• The endoplasmic reticulum is a membrane-
bound structure that is a part of every
-Synthesis of various proteins and carbohydrates
-Transports the vesicles to the golgi complex
• As the proteins travel through the organelle, they create small
-These pockets pinch off from the organelle and form vesicles.
-The vesicles transport the proteins to the Golgi complex, where
they are processed and distributed to different cells.
• Their number increases from from pre-odontoblast stage to
active stage and further reduces as the cells reach quinesence.
• The golgi complex appears as an aggregation of
smooth walled vesicles and cisternal profiles
organised into distinct and separate groups
*Synthesis of complex carbohydrates
*Sulfation of proteins.
• Site of initial mineralization.
• They are small membrane bound structure that
buds off from the cell to form an independent unit.
*They contain alkaline phosphatase,
proteoglycans , sulfur and calcium.
• *Microanalysis of Matrix vesicles indicates
CALCIUM and SULFUR PEAK of matrix
vesicles are higher than the odontoblast
• Tomes fibres
• Is the secretory pole of odontoblast
• Form the major content of dentinal tubules
• 3-4 microns in diameter at pulpal end and taper to
1 micron near the periphery.
• Cytoplasmic orgenells are also present close to
the cell body.
• Their extension into the dentinal tubules varies
• Enamel spindles
•They play a
major role in
granules on these
processes are the
• Coated vesicles and Coated pits reflect
pinocytotic activity along the odontoblastic
process at the level of predentine close to cell
• A well-developed system of microtubules is present both
within the cell body and the odontoblast process.
• Each microtubule is about 25 nm wide with a wall
approximately 7-8 nm thick
• Functions of microtubules-
- transportation of intracellular substances
- stabilises cellular shape
• These cytoplasmic filaments are usually more highly
concentrated at the cell periphery, forming distinct bands just
beneath the cell membrane.
• Nuclear changes in various stages of
• a) Pre-odontoblast stage:
*These cells present moderately reticulated
nucleoli that tend to be circular in shape.
*The nucleolar area is 0.55µm
*Few strands of dense fibrillar material radiating
from the fibrillar center
*Located at the growing tips
• b) Secretory Stage :
*characterized by a large, irregular, and
*71% is occupied by dense fibrillar component.
*2 fibrillar centres.
*Prominent interstitial space
*Located at the apical region
• c) Transitional stage:
*Seen only under electron microscope
*Nucleus is displaced from the basal extremity
*Nucleolus is reduced in size
*Granular layer is clearly seggregated
*Highly condensed chromatin
*Located at the middle region
• d) Aged Odontoblast stage
• Small, compact haematoxyphilic nucleolus
• Segregated components
• Large lipid filled vacuoles in the cytoplasm
• Located at the coronal region.
• The fibrillar center remains connected on one side
to the dense chromatin that encloses the
• They possess junctional structures constituted
by – Gap
- Tight junctions
• Gap junctions and Tight junctions of focal or
macular type appear on early odontoblasts
-Occur on the lateral
surface of the cells at
reform as the function
*Freeze fracture image
of a tight junction
branched rows of
ODONTOBLAST & DENTINOGENESIS
• After the differentiation of odontoblasts, the odontoblast
starts functiong by depositing Von Korffs fibres (Type III
• They extend towards the IEE and fan out on the ground
• As the odontoblasts increase in size they deposit Type I
collagen that orient parallel to the future DEJ.
• Thus a layer of mantle dentine (15-20mm thick) is formed
• MATRIX VESICLES contain Alkaline Phosphatase -↑
concentration of phosphates + Calcium →Hydroxyapatite
Crystals- grow rapidly, rupture the matrix vesicles
The process continues …
Spread -clusters of crystallites → fuse with adjacent clusters to
form a continuous layer of mineralized matrix
Initially- on the surface of the collagen fibrils and ground substance,
later within the fibrils- aligned with collagen.
Various Matrix Proteins Influence Mineralization:
• DPP- Binds to Ca, Controls Growth of H.A Crystals
• Osteonectin- Inhibits growth of H.A crystals, promotes their
Binding to Collagen
• Gla-proteins, Phospholipids- Act as nucleators to concentrate
• Proteoglycans- inhibit premature mineralization seen in
COLLAGEN SYNTHESIS BY ODONTOBLASTS
Hydroxylation of procollagen with N- and C-
Triple helix assembly
Triple helix formation
+n of O-linked
SECONDARY AND TERTIARY DENTIN
Secondary dentin is deposited after root formation is completed and
is formed by the same odontoblasts that formed primary dentin.
Tertiary dentin is deposited at specific site in response to injury by
damaged odontoblasts/replacement cells from pulp.
Root dentine formation
• Begins once Enamel & Dentin formation reaches the future CEJ.
• Initiated by Cells of HERS- which induce odontoblast differentiation.
• Collagen fibres- parallel to CDJ.
• Less mineralized, less number of Tubules.
• Complete- 18mths after eruption-Primary
2-3 yrs - Permanent Teeth
Capillary supply in
FATE OF ODONTOBLASTS
• Life span of odontoblasts is equal to that of a viable tooth
because once differentiated they cannot undergo further cell
• Resting Odontoblasts involved in secondary dentinogenesis
is renamed as “ODONTOCYTES” because their function
and properties are similar to osteocytes.
• These odontocytes may participate during reactionary
• Gene DMP1 is involved in the differention of secretory
odontoblasts into odontocytes
• The Phosphophoryn content of the odontoblast are
retained in the sections during the specimen preparation
and stained selectively in situ.
• Various stains for dentine are:
Haematoxylin & Eosin
Modified Gallego stain
1)Pathological differences in the functional life
cyle of odontoblasts – DENTINOGENESIS
2)Pre-odontoblasts do not differentiate into odontoblasts
– Shell/ Thistle-tube teeth
3)Odontoblasts do not differentiate into Osteocytes –
4) Outward resorption of dentinal tubules by
odontoclasts results in pulpal tissue appearing pink
through the thin enamel – Pink Tooth
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• Add Odontoblast sensitivity –fluid dynamic
• Difference between tomes granular layer &