The document summarizes the process of dentinogenesis or dentin formation. It involves differentiation of odontoblasts from dental papilla cells, secretion of an organic matrix, and mineralization of the matrix. Odontoblasts secrete collagen fibers and matrix vesicles that initiate mineralization. Dentin is formed in mantle dentin near enamel and circumpulpal dentin further inside via continuous mineralization. Root dentin formation begins after crown completion, guided by Hertwig's epithelial root sheath.

1. Dr. Sonal Aggarwal
M.D.S. Oral Pathology & Microbiology
Dentinogenesis

2. • The dynamic process of formation of dentin
involves a chain of different mechanisms:
 Cell differentiation and interactions
 The synthesis of an organic matrix
 Mineralization of the matrix.
• It is a highly regulated and well-controlled process
that starts in the bell stage of tooth development.

3. Odontoblasts
These cells are the formative cells of dentin
They line the pulpal aspect of the dentin
They are present usually throughout the life of the tooth
Show different morphological features at different
phases of activity
The total duration of odontoblast activity is about 750
days.
The odontoblasts in the crown are larger than
odontoblasts in the root. In the crown of the fully
developed tooth.
The cell bodies of odontoblasts are columnar and
measure approximately 50 mm in height, whereas in the
midportion of the pulp they are more cuboid and in the
apical part more flattened.

4. • Dental papilla:
– The dental papilla cells are small and
undifferentiated, and they exhibit a central
nucleus and few organelles.
– There is a delicate PAS +ve membrane
between the inner enamel epithelium and
the peripheral cells of the papilla.
– Cell free zone is present
– The peripheral cells are stellate and have
large nuclei, surrounded by amorphous
ground substance rich in acid MPS mingled
with delicate fibers.
Changes preceding matrix formation

5. • Differentiation of odontoblasts
The peripheral cells get closely packed and
become low columnar, eliminate the cell free
zone.
Almost immediately after cells of the inner
enamel epithelium reverse polarity, changes also
occur in the adjacent dental papilla.
They are the pre-odontoblasts. When the pre-
odontoblasts withdraw from the mitotic cycle,
they become polarizing odontoblasts, measuring
50 μm in length
They establish a palisade- like structure forming
intercellular junctions. They finally acquire their
terminal polarization and become
dentinogenically active, secretory cells.

6. Epithelial cells
The undifferentiated
ectomesenchymal cell
(A)
This cell divides
(B), with its
mitotic
spindle
perpendicular to
the basal lamina
(pink line).
A daughter cell (C),
influenced by the
epithelial cells(D) ,and
molecules they produce,
differentiates into an
odontoblast(F).
Another daughter
cell (E), not exposed
to this epithelial
influence, persists as
a subodontoblast
cell(G).
A B
D
C
E
F
G
Odontoblast differentiation

7. • The terminal differentiation of odontoblasts, as well as ameloblasts,
seems to be dependent on specific cell membrane/cytoskeleton
interactions with BM constituents and other extracellular
components.
• The ectomesenchymal cells adjoining the acellular zone rapidly
enlarge and elongate to become preodontoblasts first and then
odontoblasts as their cytoplasm increases in volume to contain
increasing amounts of protein-synthesizing organelles.
• The acellular zone between the dental papilla and the inner enamel
epithelium gradually is eliminated as the odontoblasts differentiate
and increase in size and occupy this zone.
• These newly differentiated cells are characterized by being highly
polarized, with their nuclei positioned away from the inner enamel
epithelium.

8. Life cycle of the odontoblast
BL, Basal lamina; Ce, centriole; Col, collagen; G, Golgi complex; IEE, inner enamel epithelium; JC, junctional complex; m,
mitochondria; N, nucleus; Nu, nucleolus; Odp, odontoblast process; PD, predentin; rER, rough endoplasmic reticulum; SG,
secretory granule; Va, vacuole.

9. • In the polarizing
odontoblast, the RER
develops actively, with
numerous free ribosomes.
• With the development of
the cytoplasm, the nucleus-
to-cytoplasmic ratio
decreases.
• Mitochondria are scattered
across the cytosol and Golgi
complexes are well formed.

10. • In the junction between the odontoblast cell
body and the process, there exist junctional
complexes.
• Mostly adherent complexes and some tight
junctions.
• Permeability of this region is variable.

13. • Mantle dentin
– The young odontoblasts secrete collagen and
non-collagenous proteins
– This constitutes the predentin. After 10-20 μm of
thickness is laid, mineralization starts.
– The initial crystal formation takes place inside 100-200
nm membrane-bound matrix vesicles.
Initial Dentin Formation

14. • The first sign of dentin formation is the
appearance of distinct, large-diameter
collagen fibrils (0.1 to 0.2 mm in
diameter) called von Korff’s fibers.
• These fibers consist of collagen type III
associated, at least initially, with
fibronectin.
• As the odontoblasts continue to increase
in size, they also produce smaller
collagen type I fibrils that orient
themselves parallel to the future
dentinoenamel junction.
• In this way, a layer of mantle predentin
appears.

15. Matrix vesicles
– The Odontoblast buds off a number of small,
membrane-bound vesicles known as matrix
vesicles, which come to lie superficially near
the basal lamina.
– They provide a protected micro-environment
for crystallization and for nucleating
macromolecules, enzymes, or other essential
components.
– They display high activity of alkaline phosphatase, are constituted of phospholipids,
Ca-ATPase and other molecules.
– Capable of forming Ca-Po4-phospholipid complexes.

16. Mantle dentin formation
A concentration of large-diameter collagen fibrils (arrows) can be seen in the
forming predentin (PD) matrix near the surface of the ameloblasts. C, As this
matrix mineralizes, the fibrils become incorporated in the mantle dentin (D).

17. Mantle dentin formation

18. Circumpulpal dentin formation
• This comprises of matrix
formation and subsequent
frontal mineralization
without matrix vesicle
formation
• Described in three zones:
– Cell and cell processes
• Exocytosis and endocytosis
– Predentin
• Collagen meshwork
– Mineralized dentin

19. Mineralization
• The mineral phase first appears within the matrix
vesicles as single crystals believed to be seeded
by phospholipids present in the vesicle
membrane.
• These crystals grow rapidly and rupture from the
confines of the vesicle to spread as a cluster of
crystallites that fuse with adjacent clusters to
form a continuous layer of mineralized matrix.
• Following mineral seeding, noncollagenous
matrix proteins produced by odontoblasts come
into play to regulate mineral deposition.

20. • Only intertubular dentin is
mineralized close to the
mineralization front.
• The formation of intratubular dentin
starts at some distance away from
the predentin/dentin junction.
• The mineralization is of two types:
– Linear
– Globular
• @ 2 μm /12 hours

21. • The type of mineralization depends on the rate of
formation.
• Largest globules appear in the fastest deposition regions
• Slower deposition leads to uniform linear mineralization
• The process can occur either due to matrix vesicles or by
heterogenous nucleation
• The crystal size is 3 nm X 100 nm, three hundred times
smaller than enamel crystals

22. Root dentin
• At the end of crown formation, root
dentin formation begins.
• At the cervical loop, Hertwig‘s epithelial
root sheath develops. This initiates
odontoblast differentiation.
• The outermost layer of root dentin, the
equivalent of mantle dentin in the
crown, shows differences in collagen
fiber orientation and organization, in
part because the collagen fibers from
cementum blend with those of dentin.
A – dental papilla B – root dentin C and D – Root sheath E – epithelial diaphragm