Hist 3

Early tooth
development
BY:dr.Nafha Shihab.
(Periodontist)
2015
Feb-16 1oral histology lab. by:dr.Nafha Shihab

. Morphological stages of tooth
development
Feb-16 2
oral histology lab. by:dr.Nafha
Shihab

MORPHOLOGICAL
1. Dental lamina
2. Bud stage
3. Cap stage
4. Early bell stage
5. Advanced bell stage
6. Formation of enamel and dentin matrix
PHYSIOLOGICAL
Initiation
Proliferation
Histodifferentiation
Morphodifferentiation
Apposition
Feb-16 3
Shihab

Tooth
development can
be divided into 3
stages:
1. Bud Stage
2. Cap Stage
3. Bell Stage
Feb-16 4
Shihab

1.Bud Stage
Feb-16 5
Shihab

BUD STAGE
PROLIFERATION• This is the initial stage of tooth
formation where enamel organ
resembles a tooth bud
• The enamel organ consists of
peripherally located low
columnar cells & centrally
located polygonal cells
• The surrounding mesenchymal
cells proliferate, which results in
their condensation in two areas
• The area of condensation
immediately below the enamel
organ is the dental papilla
• The ectomesenchymal
condensation that surrounds the
tooth bud & the dental papilla is
the tooth sacFeb-16 6
Shihab

• The dental papilla as well as the dental sac
are not well defined during the bud stage,
they become more defined during the cap &
bell stages
• The cells of the dental papilla form the
dentin and pulp while the dental sac forms
cementum & periodontal ligament
Feb-16 7
Shihab

•Epithelial outgrowth called
Enamel Organ because it will
form the enamel
•Dental Papilla:Ball of
condensed ectomesenchymal
cells (it will form dentin and
pulp).
•
•Epi.condensation is poor
morphodifferentiated &
histodifferentiated.
•The cells of tooth bud have
high RNA +enzymatic
activity with low glycogen
content
Enamel Organ
Dental Papilla
Feb-16 8
Shihab

2. Cap Stage
Feb-16 9
Shihab

 : as the epithelial bud continues to
proliferate into the ectomesenchyme,
morphogenesis has progressed, the
deeper surface of the enamel organ
invaginate to form a cap-shaped
structure. A greater distinction
develops between the more rounded
cells in the central portion of the
enamel organ and the peripheral cells
which are becoming arranged to form
the outer and inner dental epithelia.oral histology lab. by:dr.Nafha
Shihab
Feb-16 10

In the late cap stage of tooth
development, the central cells of
the enlarging enamel organ have
become separated. The resulting
tissue is termed the stellate
reticulum- is a group
of cells located in the center of
the enamel organ of
a developing tooth.
Shihab
Feb-16 11

 These cells are star-shaped and
synthesize glycosaminoglycans. As
glycosamingoglycans are
produced, water is drawn in between
the cells and stretch them apart. The
cells of the outer enamel epithelia
remain cuboidal, where as those of
inner enamel epithelia become more
columnar.
Shihab
Feb-16 12

The adjacent ectomesenchymal
cells are continue to prolipherat
and surround the enamel organ.
The part of the ectomesenchyme
lying beneath the inner enamel
epithelia is called dental papilla.
The ectomesenchymal tissue
surrounding both enamel organ and
dental papilla is called dental sac
or dental follicle.
Shihab
Feb-16 13

Dental follicle or dental sac is the condensed
ectomesenchymal tissue surrounding the
enamel organ and dental papilla. This gives rise
to cementum and the periodontal ligament
Dental follicle or sac
Enamel organ
Enamel knot
Dental papilla
Feb-16 14
Shihab

OUTER & INNER ENAMEL
EPITHELIUM
• The peripheral cells of
the cap stage are
cuboidal , cover the
convexity of the cap &
are called the outer
enamel epithelium
• The cells in the
concavity of the cap
become tall columnar
cells & represent the
inner enamel epithelium
Feb-16 15
Shihab

Transitory structures:
During the early stages of tooth
development, three transitory
structures may he seen, which are
enamel knot,
enamel cord
enamel niche.
Shihab
Feb-16 16

1-Enamel knot:
 it is a localized mass of cells in the center of
the inner enamel epithelia. The enamel knot
is a signaling center of the tooth that
provides positional information for tooth
morphogenesis and regulates the growth
of tooth cusps. The enamel knot produces a
range of molecular signals from all the
major signaling families, such as
Fibroblast Growth Factors (FGF),
Bone morphogenetic proteins (BMP)
and other signals.oral histology lab. by:dr.Nafha
Shihab
Feb-16 17

2-Enamel cord:
it’s a strand arises in the enamel
organ as a vertical extension of
the enamel knot at the early bell
stage of development. Its
termed enamel septum when
enamel cord extend from
enamel knot to the outer enamel
epithelia. oral histology lab. by:dr.Nafha
Shihab
Feb-16 18

3-Enamel niche:
it is created because the dental
lamina is a sheet rather than a
single strand and often contains a
concavity filled with connective
tissue. A section through this
arrangement creates the impression
that the tooth germ has a double
attachment to the oral epithelium
by two separate strands.oral histology lab. by:dr.Nafha
Shihab
Feb-16 19

• The cells in the center of the enamel
organ are densely packed and form the
enamel knot(EK)
•
enamel knot
Feb-16 20
Shihab

Feb-16 21
Shihab

• At the same time a vertical
extension of the enamel knot, called
the enamel cord occurs
enamel cord
Feb-16 22
Shihab

Enamel niche
Feb-16 23
Shihab

Bell stage
Continued growth of teeth germs leads to the
next stage of tooth development- the bell stage,
so called because the enamel organ comes to
resemble a bell which is in its final shape
(Morphodifferentiation). During this stage, the
cells that will be making the hard tissues of
crown (Ameloblasts and odontoblasts) acquire
their distinctive phenotype (Histodifferentiation).
•
Feb-16 24
Shihab

 Early bell stage: the enamel organ
shows four distinct layers:
 The outer enamel epithelium: is a layer of
cuboidal cells located on the periphery of
the enamel organ in a developing tooth and is
separated from the surrounding ectomesenchymal
tissue by a basement membrane of l-2µm
thickness. The outer enamel epithelial cells
contain large, centrally placed nuclei and
relatively small amounts of the intracellular
organelles associated with protein synthesis (e.g.
endoplasmic reticulum, Golgi complex &
mitochondria) and they contact each other via
desmosomes and gap junctions.oral histology lab. by:dr.Nafha
Shihab
Feb-16 25

 Involved in the maintenance of the
shape of the enamel organ and in
the exchange of substances
between the enamel organ and the
environment in order to provide
nutritional supply for the metabolic
activity of the avascular (without
blood supply) enamel organ.
Shihab
Feb-16 26

Feb-16 27
Shihab

 The stellate reticulum: is a group of star
shaped cells located in the center of
the enamel organ of a developing tooth.
These cells synthesize glycosaminoglycans,
causing water to be drawn in between the
cells and stretch them apart generating
hydrostatic pressure within the stellate
reticulum which is in equilibrium with that
of the dental papilla, allowing the
maintenance of tooth shape. Stellate
reticulum is lost after the first layer of
enamel is laid down. This brings cells in
inner enamel epithelium closer to blood
vessels at the periphery.
Shihab
Feb-16 28

 Stratum intermedium: several layers of
squamous cells closely attached by
desmosomes and gab junction, lying
between the inner enamel epithelium and
stellate reticulum. The cells of stratum
intermedium characterized by high degree
of alkaline phosphatase enzyme which is
important in the mineralization of the
enamel. This layer, along with the inner
enamel epithelium, is responsible for
the tooth enamel formation.
Shihab
Feb-16 29

 Inner enamel epithelium: is a layer of
columnar cells that differentiate prior to
amelogenesis into the ameloblasts; located on the
rim nearest the dental papilla of the enamel
organ in a developing tooth and are separated from
the peripheral cells of dental papilla by a basement
membrane and cell free zone about 1-2 µm wide.
The inner enamel epithelial cells rich in RNA but
unlike the stratum intermedium do not contain
alkaline phosphatase. The cells of this layer exert
an organizing influence on the underlying
ectomesenchymal cells, which differentiate into
odontoblasts.
Shihab
Feb-16 30

Dental papilla (d.p.): before the inner enamel
epithelia differentiate into ameloblast to produce the
enamel, the peripheral cells of d.p. differentiate into
odontoblasts (dentin forming cells) under the
organizing influence of inner enamel epithelium.
Dental sac (d.s.): Before formation of dental hard
tissue begins, the d.S. shows a circular arrangement of
its fibers and it resemble a capsular structure. With the
development of the root, the fibers of d.S. differentiate
into periodontal fibers that become embedded in the
cementum and alveolar bone.
Feb-16 31
Shihab

Shihab
Feb-16 32

• Advance (late) bell stage or appositional stage:
this stage of tooth development is associated with the
formation of the dental hard tissues. Dentine formation
always precedes enamel formation. During this stage
the boundary between inner enamel epithelia and
odontoblasts outlines the future dentino enamel
junction (D.E.J.). In addition, the basal margin of the
enamel organ (cervical loop) gives rise to the epithelial
root sheath.
The rim of the enamel organ where the outer
and inner enamel epithelium join is called
the cervical loop, at which there is
considerable mitotic activity.
Feb-16 33
Shihab

Function of dental lamina:
•The first phase is concerned with the initiation of the entire
deciduous dentition that begins at the 6 weeks of intra-uterin life of
embryo.
•The second phase deals with the initiation of the successors of
the deciduous teeth. It is preceded by the growth of the free end
of the dental lamina (successional lamina), lingual to the enamel
organ of each deciduous tooth, and occurs from about the fifth
month in embryo for the permanent central incisors to 10 months
of age for the second premolar
•The third phase is preceded by the extension of the dental lamina
distal to the enamel organ of the second deciduous molar and the
formation of permanent molar tooth germs.
Feb-16 34
Shihab

Fate of dental lamina
•Dental lamina is functional in developing 52 teeth from
6 prenatal weeks until 4 years after birth (development
of third permanent tooth).
•The dental lamina degenerates by mesenchymal
invasions in late bell stage.
•Developing tooth lose its connection with dental lamina.
•Sometimes remnants of dental lamina remains in the
jaws as epithelial rests of Serres ( Serres’ pearls) .
Feb-16 35
Shihab

Disturbance of epithelial-mesenchymal interactions:
Malformation of teeth related to variation in size, shape,
number or in structure:
•macrodontia (enlarge tooth).
•microdontia ( small size tooth).
•gemination( partial cleavage of tooth germ).
•fusion (union of 2 adjacent teeth).
•hypodontia (reduction in No. of teeth).
•anndontia ( complete absence of teeth).
•dens in dente( tooth within tooth).
Feb-16 36
Shihab

Malformation of teeth related to the
development of specific dental tissue:
•Amelogenesis imperfecta.
•Dentinogenesis imperfecta.
•Truma and infection of deciduous
teeth may cause malformation in
permanent teeth.
Shihab
Feb-16 37

QUIZ
Shihab
Feb-16 38

M C Q
 1. Inner enamel epithelium
 Consists of epithelial cells rich in RNA and contain alkaline
phosphatase.
 The cells of this layer exert an organizing influence on the underlying
ectomesenchymal cells, which differentiate into odontoblasts.
 located on the rim nearest the dental folicle of the enamel organ in
a developing tooth.
 is a layer of tall cuboidal cells that differentiate prior to amelogenesis
into the ameloblasts.
Shihab
Feb-16 39

M C Q
 2. Malformation of teeth related to
variation in size:
 macrodontia.
 Germination.
 fusion.
 hyperdontia
Shihab
Feb-16 40

Feb-16 41
Shihab

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