The document summarizes the histogenesis of tooth tissues including dentin, cementum, pulp, and periodontal ligament. It describes how: 1) Odontoblasts differentiate from dental papilla cells and secrete predentin which mineralizes to form dentin around the pulp. 2) Cementoblasts differentiate from dental follicle cells and secrete cementum on the root surface. 3) Periodontal ligament fibers are produced that attach the cementum to alveolar bone, anchoring the tooth. 4) The dental papilla cells develop into the pulp tissue enclosed within the formed dentin.

1. HISTOGENESIS OF THE TOOTH TISSUES
Brillante, Charmagne
Busto, Treblig
Cambe, Estephanie
De Leon, Janine
De Los Santos, Andrea Laura
Macainag, Mary Louisse Christine
DOH 121- DBA

2. Dentinogenesis
Dentinogenesis is the formation of dentin by the odontoblasts. It begins at late
bell stage. The presence of preameloblast will induce the peripheral cells of the dental
papilla to differentiate. This peripheral cells are star-shaped, have rounded nuclei and
have small cytoplasmic volume. Their nuclei gradually migrate toward the cell pole. They
will now change in shape and become short columnar cells. They move closer together at
the periphery of the papilla. This is now the preodontoblasts, which are columnar cells
which exhibit also short cytoplasmic processes on their distal poles.
The membranapreformativa, (basal lamina) the basement membrane between
the preameloblast and dental papilla, will thicken. The outer side of the wavy basal
lamina follows the cytoplasmicmembrance of the preameloblast, while the inner side
lines against the fibrillar material. The wavy basal lamina will determine the later
contour of the dentino-enamel junction.
The Terminal Bar Apparatus, formed at the distal pole, keeps the individual
preodontoblasts in contact with one another and seal off the intercellular spaces. As it
moves towards the center, towards the pulp, it will become a highly specialized cell,
Odontoblasts, now a slender columnar cell with thick cytoplasmic processes called
odontoblastic processes.
High RNA content and marked oxidative and hydrolytic enzyme activity
The cells will have well-developed endoplasmic reticulum, golgi apparatus with
numerous mitochondria, with many vascular structure and well-developed
microtubular system
Odontoblast changes from oval to columnar, length is 40µm, width is 7µm
The first dentin formed is at the incisal or cusp area of the tooth that progresses in a
rootward direction.
Production of collagen by the cellular elements of the sub-odontoblast layer:
The collagen molecules link together extracellulary so that distinct fiber bundles,
fibers of von Korff (Alpha Fibers), appear to spiral between the odontoblast and
are described as ‘fanning out’ against the basement of the lamina of the internal
enamel epithelium where they form the organic matrix of the first formed dentin
o This fibers contain type III collagen associated initially by fibronectin
o With the formation of the von Korff fibers, the odontoblasts and sub-
odontoblast cells move away from the basement membrane.
o The odontoblast leave behind one or more slender cytoplasmic
odontoblast processes.
o Initially, daily increment is 4µm per day

3. While the collagen fibers are being formed, the ground substance of the dentin
matrix may either be contributed by acid mucopolysaccharide (noncollagen elements
such as phosphoprotein and other glycoaminoglycan like chondroitin sulfate) from the
dental papilla which becomes progressively smaller with continued dentin formation or
alternatively, and more likely, be secreted by the Beta Fibrils by the Odontoblast.
The von Korff fibers and ground substance form the organic matrix of the dentin
which, in its non-mineralized state, is termed predentin.
Mineralization of the mantle dentin is thought to be initiated by matrix vesicles.
These membrane bound organelles are budded off from the odontoblast. They contain a
variety of enzyme (including alkaline phosphatise) and other molecules that lead to the
formation of the first mineral crystals of hydroxyapatite within the vesicles. The crystals
then break out of the vesicles and subsequent mineralization of the remainder of the
dentin occurs without the presence of matrix vesicles. Similar matrix vesicles have been
implicated in the initial mineralization of bone and calcified cartilage.
Once the initial thin layer of mantle dentin has formed collagen fibrils that is
being formed will be oriented parallel to the dentino-enamel junction. This is the
formation of the circumpulpal dentin. When the predentin reaches a thickness of about
10-20µm it attains a state of maturity that will allow it to mineralize. The fully
differentiated odontoblast continue moving pulpward, trailing out an odontoblast
process around which the odontoblast continues to secrete the predentin associated
with circumpulpal dentin.

4. Higher power showing the first formed mantle dentin stained red, adjacent to pre-
odontoblasts.
Active dentinogenesis. Note pulp on the left and odontoblast layer at the periphery of the
pulp, the pale predentin layer with mineralized dentin beyond. Note the mineralisation
front with calcospherites between predentin and dentin. There is a trace of enamel at top
right.

5. Higher power of dentinogenesis. Dentin with tubules at right; note the
mineralization front with calcospherites. Observe the odontoblasts with processes
passing through the predentin into dentin. Note capillaries in the odontoblast layer.
This section shows dentin forming on the left and enamel forming on the right.
The amelodentinal junction separates the dark purple enamel on the right from the light
purple dentin on the left. Notice the ameloblast layer immediately to the right of the
enamel.

6. Higher power of dentin, pulp, odontoblasts, calcospherites, predentin.
Root dentin formation
Formation of dentin in the root portion is the same as that of the crown, with few
differences. These are the following
1. Differentiation of odontoblast in the root portion is due to the presence of
Hertwig’s epithelial root sheath.
2. The epithelial root sheath does not deferentiate and remains only as
cuboidal cells.
3. Initially, the migrating odontoblast (pulpward) does not trail behind a
process.
Hyaline layer
• A thin, initial, organic predentin layer in root dentin that will mineralize.
• Continuous with the mantle dentin of the crown.
• nontubular , structurless band which appears whitish in color.
Granular layer of Tomes
Following the formation of the hyaline layer, the migrating odontoblasts
trail behind their odontoblasticprocesss. These branch, loop and appear

7. dilated and, when the dentin matrix around them become mineralized, give
rise to granular layer beneath the hyaline cartilage
A: Granular layer of Tomes
B: Hertwig’s epithelial root sheath
C: Hyaline layer
Interglobular dentin
There are two distinct patterns of dentin that can occur: a linear or a
spherical (calcospherite) pattern.
*In calcospherites, the crystallites are arranged in a radial pattern and,
despite complete mineralization of dentin, this pattern still be discerned using
polarized light. Failure of calcospherites to fuse may result in the appearance of
interglobular dentin, representing small regions of unmineralized matrix.
Globules of Calcospherites

8. Dentinal tubules
• S shaped or straight canal that contains the odontoblastic process
• In the formation of the odontoblastic process curvatures may arise. These
curvatures are due to the following:
a) Primary curvature results from the oscillation of the odontoblast which
arises from their crowding as the volume of the pulp decreases (coronal
direction).

9. b) Secondary curvatures are hypothesized to be a result of the inequality of
the distance moved by the odontoblast and formed length of odontoblast
process in unit time. It is said that in unit time the formed length of the
odontoblast process is greater than the distance moved by the odontoblast
towards the papilla (apical direction).

10. 2 products of odontoblast
A. Peritubular dentin
Little is known about the genesis of peritubular dentin. Scientist believes
that it is form due to the presence of microtubules and vesicle in odontoblastic
process. Such structures in the odontoblastic process explain how peritubular
dentin is formed within the depths of already formed dentin. By these structures
the materials synthesized by the body of the odontoblast could pass to the site of
peritubular dentin formation.
B. Intertubular dentin
It is the primary secretory product of the odontoblast between dentinal
tubules. Not like the peritubular dentine, intertubular dentin consists of Type I
collagen fibers.

11. Secondary dentin
Secondary dentin is formed by the same odontoblast that formed the primary
dentin, and is laid down as a continuation of the primary dentin after root formation. It is
formed the same way as primary dentin but at a much slower pace. Secondary dentin is
easily distinguished from primary dentin due to its changed in direction and also by the
presence of the demarcation line between the secondary dentin and primary dentin.
Tertiary dentin
It is a dentin that is deposited at specific sites in response to injury or trauma. Its
formation depends on the degree of the injury; the more severe the injury, the more
rapid the rate of dentin deposition. Because of the rapid deposition tubular patterns are
distorted.
*tertiary dentin is poor in collagen and enriched in noncollagenous matrix
proteins such as sialoprotein and osteopontin

12. Incremental lines
The rate of dentin formation varies, producing incremental lines. These are the
following:
a) A diurnal rhythm of formation produces short-period lines approximately 4µm
apart (von Ebner lines), resulting from slight differences in composition or
orientation of dentin matrix.

13. b) Contour lines of Owen
It is the result from coincidence of the secondary curvatures between
neighboring dentinal tubules.

14. Root Formation
Root formation occurs after the crown has completely formed and shaped. Therefore,
tooth begins to form from crown to root. It involves interactions between the Enamel
organ, Dental papilla and Dental Sac.
A. Enamel Organ
B. Dental Papilla
C. Dental Sac / Follicle
The cervical loop, derived from the region of the enamel organ, has external and
internal enamel epithelia begins to grow down into the dental sac forming a double
layered epithelial root sheath (Hertwig’s epithelial root sheath). Epithelial root sheath
proliferates apically to shape the future root except at the basal portion of the pulp
which will serve as the apical foramen. As it proliferates it will enclose the dental papilla.

15. The mesenchymal cells of the dental follicle which lies external to the root sheath
will differentiate into cementoblast that deposit cementum on the developing root, to
the fibroblast of the developing periodontal ligament and possibly to the osteoblasts of
the developing alveolar bone.
Formation of Periodontal Ligament
Formation of the periodontal ligament occurs after the cells of the Hertwig’s
epithelial root sheath have separated, forming the known as the epithelial rest of
Malassez.
This separation permits the cells of the dental follicle to migrate to the external
surface of the newly formed root dentin. Other cells of the dental follicle will
differentiate into fibroblast. Fibroblast will make the fibers and ground substances of
the periodontal ligamnet by secreting collagen. The fibers will then be embedded in the
surface of newly developed adjacent cementum and alveolar bone. The attachment of
the periodontal ligament fibers in the cementum and alveolar bone holds the tooth
securely in the socket . As the tooth errupts , the periodontal ligament fibers are
reoriented. The different orientations are alveolar crest group, oblique fiber group,
apical fiber group,horizontal fiber group and interradicular fiber group. The orientation
of the fibers is due to the occlusion with the opposing tooth.

16. The five fiber groups of periodontal ligament:
This diagram shows the location of some of the principal
fibers of the periodontal ligament.
AC: alveolar crest fibers; H: horizontal fibers; OBL:
oblique fibers; PA: periapical fibers; IR: Interradicular
fibers.
1. Interradicular fiber group

17. 2. Apical Group
3. Oblique fiber group

18. 4. Horizontal fiber group
5. Alveolar crest group
Cementogenesis
Cementogenesis is the formation of primary (acellular) cementum and the
secondary (cellular) cementum. The process begins at the cervical loop and extends
apically as the root grows downwards. It begins shortly after the fragmentation of
Hertwig’s epithelial root sheath. Figure 2 below shows the cervical root area with the
Hertwig’s epithelial root sheath and its extended diaphragm that will out line the root
formation.

19. (figure 1) (figure 2)
Fragmentation of root sheath permits penetration of the connective tissue cells of the
follicle so that they come to lie between the remnants of the root sheath and the surface
of the newly formed root. Figure 3 below shows the fragmentation/disintegration of
Hertwig’s epithelial root sheath. Figure 4 below shows the penetration of connective cells.
(figure 3) (figure 4)
The ectomesenchymal cells of the follicle after penetration the root sheath differentiate
into cement-forming cells or cementoblast. Present in these cells are numerous
mitochondria, a roughed surface endoplasmic reticulum, and a prominent Golgi complex.
The factor responsible for cementoblast differentiation is unknown.
(figure 5)

20. The fibrous connective tissue in contact of the roots contributes to the first
formed cement matrix. When sufficient organic matrix has been formed it becomes
mineralized. As matrix formation proceeds, the cement-forming cells can be
incorporated within the developing cement where they become cementocytes, or may
remain on the surface of the forming cement as more rounded cells lacking processes.
Two types of cement are then recognized, cellular and acellularcementum. Cementocytes
are characterized by processes radiating towards the periodontal ligament and their
cytoplasm shows a drastic reduction in the number of organelles when compared to
cementoblast.
After eruption of the tooth the fibers of the periodontal ligament lie oblique to the
root surface and it is obvious that they must be incorporated within the cement,
otherwise no attachment would be made. Figure 6 shows the incorporation of cementum
and periodontal ligament.
(figure 6)
Once incorporated within the cellular cement they become fully mineralized and
indistinguishable from the few other fibers of cement matrix. Acellular cement serves
the purpose of anchoring the tooth in the alveolus and explains why it is found applied to

21. the coronal two-thirds of the root. Cellular cementum, in the other hand, has only few
collagen content derived from Sharpeyfibres.
(figure 7) (figure 8)
(figure 9)

22. Histogenesis of the Pulp
The central cells of the dental
papilla, which is ectomesenchymal in
origin, gives rise to the pulp.
Dental Papilla
Tooth pulp, or simply, pulp was
initially called the dental papilla. It is only
designated as “pulp” only after dentin
forms around it. The transformation of
papilla to pulp only occurs after the
formation of primary dentin, the innermost
layer of
dentin matrix, encloses the pulp cavity.
It is the area of the proliferating future papilla
that causes the oral epithelium to invaginate and form
the enamel organ in the earliest stages of tooth
development. These enlarge to enclose the dental papilla
on the center portion of the developing tooth.
The development of the dental pulp begins at
about the eighth week of embryonic life. Soon thereafter Dentin
the more posterior tooth organs begin differentiating.
The dental papilla is a well-vascularized and organized network of vessels, which appear
by the time dentin formation, begins. Capillaries crowd among the odontoblasts in the
period of active dentinogenesis.
The cells of the dental papilla appear as undifferentiated mesenchymal cells.
These cells will differentiate into stellate shaped fibroblasts. After which, the odontoblast

23. then differentiates from the peripheral cells of the dental papilla. As this occurs, it is no
longer called dental papilla; instead, it is now designated as the pulp organ. Fibroblasts
and mesenchymal cells will have a decrease in concentration during the transition of
papilla into pulp. And there will be an increase in collagen fibers. Fibroblasts came from
the undifferentiated mesenchymal cell of the papilla. Some of the original mesenchymal
cells remain in mature pulpal tissue as undifferentiated cells. These will form a reservoir
of cells, which can be used in a later
time to replace odontoblasts.
Nerves and blood vessels in
the dental papilla begin to form the
primitive dental pulp.
Once nerve fibers start to go
near the cap stage of the developing
tooth, and grow toward the dental
follicle. The nerves will then, develop
around the tooth bud and enter the
1= dentin 4= cell-rich zone
dental papilla when dentin formation
2=predentin 5= blood vessels (nerves,
and veins are not seen has already begun. These nerves never
3= odontoblastic zone here) proliferate the enamel organ.
Blood vessels is derived from the dental follicle and will enter the dental papilla during
cap stage. The number of blood vessels reaches a maximum at the beginning of the crown
stage, and the dental papilla eventually forms in the pulp of a tooth.
Bone ossification
Ossification means bone formation. Bone is a hard, dense, calcified connective
tissue that forms most of the skeleton of most vertebrae. It can be formed by two ways:
Intramembranous ossification
Endochondral ossification

24. For both processes, bone tissue that appears first is primary, or immature bone. It is
a temporary tissue and will soon be replaced by lamellar, or secondary bone.
Remodeling of bones does not only occur in growing bones, but also throughout adult
life, although its rate of change is slower.
INTRAMEMBRANOUS OSSIFICATION
Intramembranous
ossification takes place within
condensation of connective
tissues, such as mesenchymal
tissues. Formation of flat
bones is derived from this
process. Examples of flat
bones are the bones of the
skull, such as the parietal
bone, temporal bone, frontal bone, the mandible, maxilla, and occipital bone.
Mesenchymal cells
differentiate into osteoblasts.
These clusters of osteoblasts
form an ossification center
that secretes organic
extracellular matrix, called
osteoid.
These mesenchymal cells
usually group together near
or around the blood vessels, and differentiate into osteogenic cells, which deposit bone
matrix. These aggregates of bony matrix are called bone spicules. The spicules will trap
osteoblasts in a lacuna, and will eventually differentiate into osteocytes.

25. As the bony spicules continue to grow, they fuse with adjacent spicules to form the
trabeculae, forming the spongy bone. The appearance of the trabeculae is the first sign of
bone formation. Trabeculae is the anastomosing bony spicules in cancellous or spongy
bone which form a meshwork of
intercommunicating spaces that
are filled with bone marrow.
These trabeculae will connect to
form the compact bone.
Intramembranous
ossification begins at about the
eighth week in the human
embryo.
ENDOCHONDRAL OSSIFICATION
Unlike,
intramembranous
ossification, cartilage is
present during
endochondral
ossification. It is also
an essential process
during the
rudimentary formation
of long bones, the
growth of the length of
long bones, and the
natural healing of bone
fractures.

26. PRIMARY CENTER OF OSSIFICATION
The first site of ossification occurs in the primary center of ossification, located in the
middle of the diaphysis. The first that will happen is the formation of the periosteum.
The perichondrium becomes the periosteum. This periosteum contains a layer of
undifferentiated cells, called osteoprogenitorcells, that will later transform into
osteoblasts. Formation of the bone collar. The osteoblasts will secrete osteoid against the
shaft of the cartilage model, which will serve as support for the new bone. Calcification of
matrix.Chondrocytes in the primary center of ossification begin to grow. Then the
calcification of the matrix occurs and apoptosis of the hypertrophic chondrocytes occur.
This will create cavities within the bone. Invasion of periosteal bud.Blood vessels will
sprout from the Osperichondrium before the chondrocytes undergo apoptosis. These
will form the periosteal bud and invade the cavity left by the chondrocytes. These blood
vessels carry hemopoietic cells, which will later on form the bone marrow, and
osteoprogenitor cells inside the cavity.Formation of trabeculae.Osteoblasts use the
calcified matrix as a scaffold and begin to secrete osteoid, forming the bone trabecula.
Osteoclasts, formed from macrophages, break down spongy bone to form the medullary
cavity.
SECONDARY OSSIFICATION CENTER
Secondary ossification appears
in each end, epiphysis, of long
bones. The cartilage between the
primary and secondary
ossification center is called the
epiphyseal plate, and continues to
form new cartilage, which is
replaced by bone, which results in
an increase in length of the bone.
The point of union of the primary
and secondary ossification centers is called the epiphyseal line.

27. During endochondral ossification, five distinct zones can be seen:
1. Zone of resting cartilage. This
zone contains normal, resting hyaline
cartilage.
2. Zone of proliferation.
Chondrocytes in this zone undergo rapid
mitosis, forming distinctive looking stacks.
3. Zone of maturation
Chondrocytes undergo hypertrophy (become
enlarged).
4. Zone of calcification.
Chondrocytes are either dying or dead, leaving
cavities that will later become invaded by
bone-forming cells, osteoblasts.
5. Zone of ossification.
Osteoprogenitor cells invade the area and
differentiate into osteoblasts, which elaborate
matrix that becomes calcified on the surface of
calcified cartilage.