DEVELOPMENTAL STAGES
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DEVELOPMENTAL STAGES
The developmental history of
a tooth is divided into several
morphologic “stages” for
descriptive purposes.
While the size and shape of individual
teeth are different, they pass through
similar stages of development.
They are named after the shape of the
enamel organ (epithelial part of the tooth
germ), and are called
the bud,
cap,
and bell stages.
1-B
UD
STAGE
:
with the differentiation
of each dental lamina,
round or ovoid
swellings arise from
the basement
membrane at 10
different points,
corresponding to the
future positions of the
deciduous teeth. These
are the primordia of
the enamel organs,
the
tooth buds.
The dental lamina is shallow, and
microscopic sections often show tooth
buds close to the oral epithelium.
Since the main function of certain
epithelial cells of the tooth bud is to
form the tooth enamel, these cells
constitute
the enamel organ
,
which is critical to normal tooth
development
The area of
ectomesenchymal
condensation immediately
subjacent to the enamel
organ is
the dental
papilla
The condensed
ectomesenchyme that
surrounds the tooth bud
and the dental papilla is
the dental sac
.
Both the dental papilla
and the dental sac become
better defined as the
enamel organ grows into
the cap and bell shapes.
C
AP
STAGE
:
which characterize by a shallow
invagination on the deep surface
of the bud
The peripheral cells of the cap
stage are cuboidal, cover the
convexity of the “cap,” and are
called the outer enamel (dental)
epithelium.
The cells in the concavity of the
“cap” become tall, columnar cells
and represent the inner enamel
(dental) epithelium.
The outer enamel epithelium is
separated from the dental sac,
and the inner enamel epithelium
from the dental papilla, by a
delicate basement membrane.
The enamel organ
may be seen to have a
double attachment of
dental lamina to the
overlying oral
epithelium enclosing
ectomesenchyme
called enamel
niche
between them.
This appearance is
due to a funnel-
shaped depression of
the dental lamina.
S
TELLATE
RETICULUM
:
Polygonal cells located in the center of the
epithelial enamel organ, between the outer and
inner enamel epithelia,
begin to separate due to water being drawn into
the enamel organ from the surrounding dental
papilla as a result of osmotic force.
exerted by glycosaminoglycans contained in the
ground substance.
This gives the stellate
reticulum a cushion
like consistency and
acts as a shock
absorber that may
support and protect
the delicate enamel-
forming cells.
The cells in the center
of the enamel organ
are densely packed
and form
the enamel
knot.
This knot projects in
part toward the
underlying dental
papilla, so that the
center of the epithelial
invagination shows a
slightly
knob like
enlargement that is
bordered by the labial
and lingual enamel
grooves.
At the same time a
vertical extension of
the enamel knot,
called the
enamel
cord
occurs .
When the enamel cord
extends to meet the
outer enamel
epithelium it is termed
as enamel septum, for it
would divide the
stellate reticulum into
two parts.
The outer enamel
epithelium at the point
of meeting shows a
small depression and
this is termed
enamel
navel
as it resembles
the umbilicus.
These are
temporary structures
(transitory structures) that disappear
before enamel formation begins.
The function of the enamel knot and cord
may act as a reservoir of dividing cells for
the growing enamel organ.
Recent studies have shown that enamel
knot acts as a signaling center as many
important growth factors are expressed by
the cells of the enamel knot and thus they
play an important part in determining the
shape of the tooth.
D
ENTAL
PAPILLA
:
Under the organizing influence of the
proliferating epithelium of the enamel organ, the
ectomesenchyme (neural crest cells) that is
partially enclosed by the invaginated portion of
the inner enamel epithelium proliferates.
It condenses to form the dental papilla, which is
the formative organ of the dentin and the
primordium of the pulp.
The changes in the
dental papilla occur
along with with the
development of the
epithelial enamel organ.
The dental papilla shows
active budding of
capillaries and mitotic
figures, and its
peripheral cells adjacent
to the inner enamel
epithelium enlarge and
later differentiate into
the odontoblasts.
D
ENTAL
SAC
(
DENTAL
FOLLICLE
):
Is a marginal
condensation in the
ectomesenchyme
surrounding the enamel
organ and dental papilla.
Gradually, in this zone, a
denser and more fibrous
layer develops, which is
the primitive dental sac.
3-B
ELL
STAGE
:
As the invagination of the epithelium deepens
and its margins continue to grow, the enamel
organ assumes a bell shape.
In the bell stage crown shape is determined.
The shape of the crown is changed due to the
pressure exerted by the growing dental papilla
cells on the inner enamel epithelium.
This pressure however was shown to be opposed
equally by the pressure exerted by the fluid
present in the stellate reticulum
. The folding of enamel organ to cause different
crown shapes is shown to be due to differential
rates of mitosis and differences in cell
differentiation time.
Cells begin to differentiate only when cells cease
to divide.
The inner enamel epithelial cells which lie in the
future cusp tip or incisor region stop dividing
earlier and begin to differentiate first.
The pressure exerted by
the continuous cell
division on these
differentiating cells from
other areas of the enamel
organ causes these cells to
be pushed out into the
enamel organ in the form
of a cusp tip.
The cells in another
future cusp area begin to
differentiate, and by a
similar process results in
a cusp tip form.
The area between two cusp tips, i.e. the cuspal
slopes extent and therefore of cusp height are due
to cell proliferation and differentiation occurring
gradually from cusp tips to the depth of the
sulcus.
Cell differentiation also proceeds gradually
cervically, those at the cervix are last to
differentiate.
1-T
HE
INNER
ENAMEL
EPITHELIUM
IN
BELL
STAGE
consists of a single layer of
cells that differentiate
prior to amelogenesis into
tall columnar cells called
ameloblasts.
These elongated cells are
attached to one another by
junctional complexes
laterally and to cells in the
stratum intermedium by
desmosomes .
.
The cells of the inner
enamel epithelium exert
an organizing influence
on the underlying
mesenchymal cells in the
dental papilla, which
later differentiate into
odontoblasts.
The junction between
inner and outer enamel
epithelium is called
cervical loop
and it is
an area of intense
mitotic activity
A few layers of squamous
cells form the stratum
intermedium, between the
inner enamel epithelium
and the stellate reticulum.
These cells are closely
attached by desmosomes
and gap junctions.
Desmosomal junctions are
also observed between cells
of stratum intermedium,
stellate reticulum and
inner enamel epithelium.
This layer seems to be
essential to enamel
formation.
3-S
TELLATE
RETICULUM
OF
BELL
STAGE
:
The stellate reticulum
expands further, mainly
by an increase in the
amount of intercellular
fluid.
The cells are star
shaped, with long
processes that
anastomose with those
of adjacent cells
.Desmosomal junctions
are observed between
cells of stellate
reticulum, stratum
intermedium and outer
enamel epithelium.
Before enamel formation begins, the stellate
reticulum collapses, reducing the distance
between the centrally situated ameloblasts and
the nutrient capillaries near the outer enamel
epithelium.
Its cells then are hardly distinguishable from
those of the stratum intermedium.
This change begins at the height of the cusp or
the incisal edge and progresses cervically
4-O
UTER
ENAMEL
EPITHELIUM
OF
BELL
STAGE
:
The cells of the outer enamel epithelium flatten
to a low cuboidal form.
At the end of the bell stage, primary to and
during the formation of enamel, the formerly
smooth surface of the outer enamel epithelium is
laid in folds.
Between the folds the adjacent mesenchyme of
the dental sac forms papillae that contain
capillary loops and
thus provide a rich nutritional supply for the
intense metabolic activity of the avascular
enamel organ.
This would adequately compensate the loss of
nutritional supply from dental papilla owing to
the formation of mineralized dentin.
D
ENTAL
LAMINA
The dental lamina is seen to
extend lingually and is
termed successional dental
lamina as it gives rise to
enamel organs of permanent
successors of deciduous teeth
(permanent incisors, canines
and premolars).
The enamel organs of
deciduous teeth in the bell
stage show successional
lamina and their permanent
successor teeth in the bud
stage.
D
ENTAL
PAPILLA
IN
BELL
STAGE
:
The dental papilla is enclosed in the invaginated
portion of the enamel organ.
Before the inner enamel epithelium begins to
produce enamel, the peripheral cells of the
mesenchymal dental papilla differentiate into
odontoblasts under the organizing influence of
the epithelium.
First, they assume a cuboidal
form; later they assume a
columnar form and acquire
the specific potential to
produce dentin.
The basement membrane
that separates the enamel
organ and the dental papilla
just prior to dentin formation
is called the
membrana
preformativa.
D
ENTAL
SAC
IN
BELL
STAGE
Before formation of dental
tissues begins, the dental sac
shows a circular arrangement
of its fibers and resembles a
capsular structure.
With the development of the
root, the fibers of the dental
sac differentiate into the
periodontal fibers that become
embedded in the developing
cementum and alveolar bone.
A
DVANCED
BELL
STAGE
This stage is characterized by
the beginning of
mineralization and root
formation.
During the advanced bell
stage, the boundary between
inner enamel epithelium and
odontoblasts outlines the
future dentinoenamel
junction.
The formation of dentin occurs
first as a layer along the
future dentinoenamel junction
in the region of future cusps
and proceeds pulpally and
apically.
After the first layer of dentin is formed, the
ameloblast which has already differentiated from
inner enamel epithelial cells lay down enamel
over the dentin in the future incisal and cuspal
areas.
The enamel formation then proceeds coronally
and cervically, in all regions from the
dentinoenamel junction (DEJ) towards the
surface
The developmental history of a tooth is segmented into distinct stages, namely the bud, cap, and bell stages. Each stage represents critical morphological changes in tooth development, from the initial formation of tooth buds to the differentiation of enamel organs and dental papilla. Understanding these stages is essential for describing the intricate process of tooth development.
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Presentation Transcript
The developmental history of a tooth is divided into several morphologic stages for descriptive purposes.
While the size and shape of individual teeth are different, they pass through similar stages of development. They are named after the shape of the enamel organ (epithelial part of the tooth germ), and are called the bud, cap, and bell stages.
1-BUD STAGE: with the differentiation of each dental lamina, round or ovoid swellings arise from the basement membrane at 10 different points, corresponding to the future positions of the deciduous teeth. These are the primordia of the enamel organs, the tooth buds.
The dental lamina is shallow, and microscopic sections often show tooth buds close to the oral epithelium. Since the main function of certain epithelial cells of the tooth bud is to form the tooth enamel, these cells constitute the enamel organ, which is critical to normal tooth development
The area of ectomesenchymal condensation immediately subjacent to the enamel organ is the dental papilla The condensed ectomesenchyme that surrounds the tooth bud and the dental papilla is the dental sac. Both the dental papilla and the dental sac become better defined as the enamel organ grows into the cap and bell shapes.
CAP STAGE: which characterize by a shallow invagination on the deep surface of the bud The peripheral cells of the cap stage are cuboidal, cover the convexity of the cap, and are called the outer enamel (dental) epithelium. The cells in the concavity of the cap become tall, columnar cells and represent the inner enamel (dental) epithelium. The outer enamel epithelium is separated from the dental sac, and the inner enamel epithelium from the dental papilla, by a delicate basement membrane.
The enamel organ may be seen to have a double attachment of dental lamina to the overlying oral epithelium enclosing ectomesenchyme called enamel niche between them. This appearance is due to a funnel- shaped depression of the dental lamina.
STELLATE RETICULUM: Polygonal cells located in the center of the epithelial enamel organ, between the outer and inner enamel epithelia, begin to separate due to water being drawn into the enamel organ from the surrounding dental papilla as a result of osmotic force. exerted by glycosaminoglycans contained in the ground substance.
This gives the stellate reticulum a cushion like consistency and acts as a shock absorber that may support and protect the delicate enamel- forming cells. The cells in the center of the enamel organ are densely packed and form the enamel knot.
This knot projects in part toward the underlying dental papilla, so that the center of the epithelial invagination shows a slightly knob like enlargement that is bordered by the labial and lingual enamel grooves. At the same time a vertical extension of the enamel knot, called the enamel cord occurs .
When the enamel cord extends to meet the outer enamel epithelium it is termed as enamel septum, for it would divide the stellate reticulum into two parts. The outer enamel epithelium at the point of meeting shows a small depression and this is termed enamel navel as it resembles the umbilicus.
These are temporary structures (transitory structures) that disappear before enamel formation begins. The function of the enamel knot and cord may act as a reservoir of dividing cells for the growing enamel organ. Recent studies have shown that enamel knot acts as a signaling center as many important growth factors are expressed by the cells of the enamel knot and thus they play an important part in determining the shape of the tooth.
DENTAL PAPILLA: Under the organizing influence of the proliferating epithelium of the enamel organ, the ectomesenchyme (neural crest cells) that is partially enclosed by the invaginated portion of the inner enamel epithelium proliferates. It condenses to form the dental papilla, which is the formative organ of the dentin and the primordium of the pulp.
The changes in the dental papilla occur along with with the development of the epithelial enamel organ. The dental papilla shows active budding of capillaries and mitotic figures, and its peripheral cells adjacent to the inner enamel epithelium enlarge and later differentiate into the odontoblasts.
DENTAL SAC (DENTAL FOLLICLE): Is a marginal condensation in the ectomesenchyme surrounding the enamel organ and dental papilla. Gradually, in this zone, a denser and more fibrous layer develops, which is the primitive dental sac.
3-BELL STAGE: As the invagination of the epithelium deepens and its margins continue to grow, the enamel organ assumes a bell shape. In the bell stage crown shape is determined. The shape of the crown is changed due to the pressure exerted by the growing dental papilla cells on the inner enamel epithelium. This pressure however was shown to be opposed equally by the pressure exerted by the fluid present in the stellate reticulum
. The folding of enamel organ to cause different crown shapes is shown to be due to differential rates of mitosis and differences in cell differentiation time. Cells begin to differentiate only when cells cease to divide. The inner enamel epithelial cells which lie in the future cusp tip or incisor region stop dividing earlier and begin to differentiate first.
The pressure exerted by the continuous cell division on these differentiating cells from other areas of the enamel organ causes these cells to be pushed out into the enamel organ in the form of a cusp tip. The cells in another future cusp area begin to differentiate, and by a similar process results in a cusp tip form.
The area between two cusp tips, i.e. the cuspal slopes extent and therefore of cusp height are due to cell proliferation and differentiation occurring gradually from cusp tips to the depth of the sulcus. Cell differentiation also proceeds gradually cervically, those at the cervix are last to differentiate.
1-THE INNER ENAMEL EPITHELIUM IN BELL STAGE consists of a single layer of cells that differentiate prior to amelogenesis into tall columnar cells called ameloblasts. These elongated cells are attached to one another by junctional complexes laterally and to cells in the stratum intermedium by desmosomes . .
The cells of the inner enamel epithelium exert an organizing influence on the underlying mesenchymal cells in the dental papilla, which later differentiate into odontoblasts. The junction between inner and outer enamel epithelium is called cervical loop and it is an area of intense mitotic activity
A few layers of squamous cells form the stratum intermedium, between the inner enamel epithelium and the stellate reticulum. These cells are closely attached by desmosomes and gap junctions. Desmosomal junctions are also observed between cells of stratum intermedium, stellate reticulum and inner enamel epithelium. This layer seems to be essential to enamel formation.
3-STELLATE RETICULUM OF BELL STAGE: The stellate reticulum expands further, mainly by an increase in the amount of intercellular fluid. The cells are star shaped, with long processes that anastomose with those of adjacent cells .Desmosomal junctions are observed between cells of stellate reticulum, stratum intermedium and outer enamel epithelium.
Before enamel formation begins, the stellate reticulum collapses, reducing the distance between the centrally situated ameloblasts and the nutrient capillaries near the outer enamel epithelium. Its cells then are hardly distinguishable from those of the stratum intermedium. This change begins at the height of the cusp or the incisal edge and progresses cervically
4-OUTER ENAMEL EPITHELIUM OF BELL STAGE: The cells of the outer enamel epithelium flatten to a low cuboidal form. At the end of the bell stage, primary to and during the formation of enamel, the formerly smooth surface of the outer enamel epithelium is laid in folds. Between the folds the adjacent mesenchyme of the dental sac forms papillae that contain capillary loops and
thus provide a rich nutritional supply for the intense metabolic activity of the avascular enamel organ. This would adequately compensate the loss of nutritional supply from dental papilla owing to the formation of mineralized dentin.
DENTAL LAMINA The dental lamina is seen to extend lingually and is termed successional dental lamina as it gives rise to enamel organs of permanent successors of deciduous teeth (permanent incisors, canines and premolars). The enamel organs of deciduous teeth in the bell stage show successional lamina and their permanent successor teeth in the bud stage.
DENTAL PAPILLA IN BELL STAGE: The dental papilla is enclosed in the invaginated portion of the enamel organ. Before the inner enamel epithelium begins to produce enamel, the peripheral cells of the mesenchymal dental papilla differentiate into odontoblasts under the organizing influence of the epithelium.
First, they assume a cuboidal form; later they assume a columnar form and acquire the specific potential to produce dentin. The basement membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called the membrana preformativa.
DENTAL SAC IN BELL STAGE Before formation of dental tissues begins, the dental sac shows a circular arrangement of its fibers and resembles a capsular structure. With the development of the root, the fibers of the dental sac differentiate into the periodontal fibers that become embedded in the developing cementum and alveolar bone.
ADVANCED BELL STAGE This stage is characterized by the beginning of mineralization and root formation. During the advanced bell stage, the boundary between inner enamel epithelium and odontoblasts outlines the future dentinoenamel junction. The formation of dentin occurs first as a layer along the future dentinoenamel junction in the region of future cusps and proceeds pulpally and apically.
After the first layer of dentin is formed, the ameloblast which has already differentiated from inner enamel epithelial cells lay down enamel over the dentin in the future incisal and cuspal areas. The enamel formation then proceeds coronally and cervically, in all regions from the dentinoenamel junction (DEJ) towards the surface
