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ORAL HISTOLOGY
DEVELOPMENT OF TEETH
(ODONTOGENESIS)
by
dr. Suhair Majeed
BACKGROUND :
The development of the tooth involves many
complex biological processes, including epithelial
mesenchymal interactions, morphogenesis and
mineralization.
In human beings, 20 deciduous and 32
permanent teeth develop from the interaction
between the oral epithelium cells and the
underlying mesenchymal cells. The basic
developmental process is similar for all teeth but
CONT.
each developing tooth develops as an
anatomically distinct unit. Mammalian teeth
develop from oral epithelium (ectoderm) and
neural crest cells derived mesenchyme
(mesoderm).
Neural crest cells are migrate (at 3rd weeks
of the embryo) from lateral parts of neural tube
and enter in the underlying mesenchyme ,now it’s
termed as ectomesenchyme.
Vitamins, minerals and hormones affect tooth
development.
CONT.
Vitamin A is important for epithelial growth,
Vitamin C = = for connective tissue
development ,
Vitamin D is essential for calcification
DEVELOPMENTAL PHASES OF TOOTH :
Tooth development is divided into three
overlapping developmental phases ,these are:
1- Initiation :
in this phase,the sites of future teeth are
established with the appearance of tooth germs
along an invagination of oral epithelium called
dental lamina .
2- MORPHOGENESIS :
in this phase,the shape of the teeth are
determined by a combination of cell proliferation
and cell movement.
3- Histogenesis :
differentiation of cell begun during
(morphogenesis) proceed to give rise to the fully
formed dental tissues,both mineralized (as
enamel ,dentin and cementum) and
unminaralized (as pulp and periodental
ligament ).
DEVELOPMENT OF TOOTH GERM
PRIMARY EPITHELIAL BAND :
after 37 days of development,
a continuous band of thickened epithelium
forms around the mouth in the presumptive
upper and lower jaws. These bands are horse
shoe-shaped and correspond in position to the
future dental arches of the upper and lower jaws.
Each band of epithelium, called the primary
epithelial band, quickly gives rise to two
subdivisions .
CONT.
.
These are:
1- the dental lamina, which forms first,
2- the vestibular lamina, which forms shortly
afterward and is positioned just in front of the
dental lamina.
DENTAL LAMINA
DENTAL LAMINA :
The dental lamina is a band of epithelium that
has invaded the underlying ectomesenchyme
along both the horse shoe-shaped future dental
arches .
Deciduous dentition develops directly from
the dental lamina at the eighth week of fetal life,
while the permanent molars develop from a distal
extension of the dental lamina.
CONT.
Along the lamina 20 areas of enlargement
next appear,which are the forming buds of 20
primary teeth ,and the lamina continues to
develop the 32 permenant tooth buds.
The lingual extension of dental lamina is called
successional lamina ,it is responsible for the
development of permanent incisors, canine and
premolars.
CONT.
The successional lamina is active from the fifth
month in utero (for the permanent central incisor)
to ten months of age (second premolar).
BUD STAGE .
(1) ENAMEL ORGAN
(2) THE DENTAL LAMINA,
(3) SUCCESSIONAL DENTAL LAMINA,
(4) PRIMARY EPITHELIAL BAND,
VESTIBULAR LAMINA :
The vestibule forms as a result of the
proliferation of the vestibular lamina into the
ectomesenchyme soon after formation of the
dental lamina. The cells of the vestibular lamina
rapidly enlarge and then degenerate to form a
cleft that becomes the vestibule between the
cheek and the tooth-bearing area.
DEVELOPMENTAL STAGES OF TOOTH
Tooth formation is a continuous process. It is
characterized by a series of stages. Each tooth
develops through successive bud, cap and bell
stages. continues to change. During these the
dental lamina breaks up and the tooth bud loses
its connection with the epithelium of the primitive
oral cavity . Interaction of the first arch epithelium
and neural crest cell results in the development of
tooth.
CONT.
all teeth pass through similar stages of tooth
development. These stages:
A. Bud stage - Initiation
B. Cap stage - Proliferation
C. Bell stage –
a. Early - Histodifferentiation
b. Advanced - Morphodifferentiation
CONT.
The name of the stages is based on the shape
of the epithelial part of the tooth germ that is
epithelial enamel organ .
1- BUD STAGE (INITIATION) :
Bud stage is the initial stage of tooth
development. The basement membrane
separates the epithelium of dental lamina
from the ectomesenchyme.
Ten small, round or ovoid swellings
develop superficial to the basement
membrane called as tooth buds. Tooth buds
are the precursors of enamel organs.
The epithelium of the tooth bud forms
the enamel.
TOOTH DEVELOPMENT – BUD STAGE
CONT.
The supporting ectomesenchymal cells are
densely packed under the lining epithelium and
around the epithelial bud.
The enamel organ of bud stage contains two
types of cells :
1. Polygonal cells, which are centrally situated
2. Low columnar cells, which are peripherally
situated
CONT.
The centrally situated cells rapidly divide and
grow and condensed and formed the dental
papilla.
Tooth pulp and dentin are formed from dental
papilla.
The ectomesenchyme that surrounds the tooth
bud and dental papilla forms the dental sac.
Cementum and periodontal ligament are formed
from the dental sac.
CAP STAGE (PROLIFERATION) :
The epithelial bud continues to proliferate
into the ectomesenchyme. Immediately adjacent
to the epithelial ingrowth, the cellular density
increases. This process is known as the
condensation of the ectomesenchyme.
When the embryo is 20 weeks old ,deciduous
dentition is at various stages of development.
After continuous division and differentiation, the
size and shape of the enamel organ changes from
knob-like to cap like.
EARLY CAP STAGE OF TOOTH DEVELOPMENT
CONT.
This developmental stage is called as the cap
stage. Invagination on the inner surface of
tooth bud results from unequal division leading to
cap stage. Cap stage is characterized by
- the outer and inner enamel epithelium
- the stellate reticulum.
OUTER AND INNER ENAMEL EPITHELIUM
The cells of the outer enamel epithelium are
cuboidal and cover the convexity of the cap
whereas the cells of the inner enamel epithelium
are tall, columnar and cover the concavity of the
cap.
Basement membrane separates the inner
enamel epithelium from the dental papilla and
outer enamel epithelium from the dental sac or
dental follicle.
STELLATE RETICULUM (ENAMEL PULP)
Polygonal cells present in the center of the
enamel organ between the inner and the outer
enamel epithelium . The proteinaceous fluidcontaining albumin gives a cushion-like
consistency to the stellate reticulum that supports
and protects the delicate enamel-forming cells .
Although it is not fully developed untill the late bell
stage.
THE CENTER OF E.ORGAN SHOWING STELLATE
RETICULUM.
1-PERIPHRAL ENAMEL EPITHELIUM
2- ECTOMESENCHYME CONDENSED AROUND
E.ORGAN
CAP STAGE OF TOOTH DEVELOPMENT
Enamel organ
Dental papilla
Dental follicle
DENTAL PAPILLA
The proliferating epithelium of the enamel
organ exerts influence on the ectomesenchyme
(neural crest cells) to proliferate. The
ectomesenchymal cells are partly covered by the
invaginated portion of the inner enamel
epithelium. On condensation, it is called as the
dental papilla. It is the primordium of the pulp and
is responsible for the formation of dentin and
pulp.
CONT.
In dental papilla, mitotic cell division takes
place along with proliferation of new blood
capillaries. The peripheral cells near the inner
enamel epithelium increase in size and
differentiate to form the odontoblasts.
DENTAL SAC (DENTAL FOLLICLE)
Along with the development of enamel organ
and dental papilla, their surrounding areas at the
margins,showed cell division resulting into
condensation and fibrous development in this
zone. This results in the formation of the dental
sac.
The cells of dental sac are responsible for the
formation of the cementum and the periodontal
ligament. The entire tooth and its supporting
structures are formed by epithelial enamel organ,
the dental papilla and the dental sac.
CONT.
Dental sac is the capsular structure consisting
of circular arrangement of fibers . These fibers
with root development are differentiated into
various types of periodontal fibers, which on one
end are embedded in the alveolar bone and the
other end in the developing cementum.
TRANSITORY STRUCTURES :
During the early stages of tooth development
,three transitory structures may be seen , they are:
1- enamel knot :
it’s a localized mass of cells in the center of
inner E. epith., E. Knot thought to play a role in
the formation of crown pattern by outlying the
enamel fissure.
E.Knot soon disappears and seems to
contribute cells to the E.cord , although it’s
transitory, recent studies of E.Knot suggest
ENAMEL KNOT
CONT.
it may represent an important signaling center
during tooth development. unlike adjacent cells,
those within E.Knot are non proliferative and
produce molecules associated with signaling in
other sites .
2- Enamel cord :
it’s a strand of early bell stage of
development. it arises in the increasingly high
enamel organ as a vertical extension of the
E.Knot ,it’s termed E. septum when E. Cord
extend from E. knot to outer E. epith.
3- ENAMEL NICHE :(CORNER.SLIT)
it’s an apparent structure in the histologic
section, created because the dental lamina is a
sheet rather than a single strand and often
contains a concavity filled with C.T., a section
through this arrangement creates the
impression that tooth germ has a double
attachment to the oral epithelium by two
separate strands.
ENAMEL NICHE
EARLY BELL STAGE OF TOOTH DEVELOPMENT
BELL STAGE
is known for histodifferentiation and
morphodifferentiation that takes place.During
this stage , tooth crown assumes it’s final shape
(morphodifferentiation ),and the cells that will be
making the hard tissues of crown (Ameloblasts
and odontoblasts ) acquire their distinctive
phenotype (histodifferentiation ).
the dental organ is bell – shaped during this
stage,majority of it’s cells are called stellate
reticulum because they have star –shaped
appearance.
CONT.
bell stage is divided into:
1- early bell stage
2- late bell stage
Cells on the periphery of enamel organ
separate into four important layers :
a. Inner enamel epithelium
b. Stratum intermedium
c. Stellate reticulum
d. Outer enamel epithelium
BELL STAGE
1- EARLY BELL STAGE :
A- INNER ENAMEL EPITHELIUM :
consists of a single layer of tall columnar
cells, which differentiate into specialized cells
called ameloblasts, before amelogenesis . These
are characterized by high glycogen content.
Ameloblasts are attached by junctional
complexes laterally and to stratum intermedium
by desmosomes. Ameloblasts exert an organizing
influence on the underlying ectomesenchymal
cells , which differentiate into odontoblasts .
B- STRATUM INTERMEDIUM :
a layer of squamous cells present in between
the inner enamel epithelium and stellate
reticulum. These cells are intimately attached by
desmosomes and gap junctions. They have a high
degree of metabolic activity due to developed
cytoplasmic organelles, acid
mucopolysaccharides, glycogen deposits and an
enzyme, alkaline phosphatase ,which is important
in the mineralization of the enamel .
CONT.
The cells of this layer concern in the transport
of materials to and from E. forming cells in inner
E. epith. (ameloblasts ). it’ is essential for the
formation and calcification of enamel.
It is absent in the root part of the tooth. Inner
enamel epithelium and stratum intermedium are
considered as a single functional unit.
BELL STAGE: DECIDUOUS MANDIBULAR FIRST
MOLAR TOOTH GERM /(L.S.)
C- STELLATE RETICULUM :
The star-shaped cells of the stellate reticulum
have long processes, which anastomose with the
processes of adjacent cells. There is continuous
expansion in the size of the stellate reticulum
because of increased amount of intercellular fluid.
Just prior to the beginning of enamel formation, at
the height of the cusp or incisal edge, the stellate
reticulum collapses and gets mixed up with the
cells of the stratum intermedium.
VARIOUS LAYERS OF EPITHELIAL ENAMEL
ORGAN
CONT.
This decreases the distance between the
ameloblasts, which are centrally situated, and the
blood capillaries situated near the outer enamel
epithelium. This change, which starts at the
height of cusps shows gradual cervical
progression . The main function of stellate
reticulum is mechanical one,this relate to the
protection of underlying dental tissues against
physical disturbance and the maintenance of
tooth shape.
CONT.
It has been suggested that hydrostatic pressure
generated within stellate reticulum is in
equilibrium with that of the dental papilla
,allowing the proliferative pattern of the
intervening inner E.epith. to determine crown
morphogenesis, although ,a change in either of
these pressures might lead to change in the
outline of the inner E. epith. And this could be
important for crown morphogenesis.
D- OUTER ENAMEL EPITHELIUM
In the initial stages of development of enamel
organ, the cells of the outer enamel epithelium
are single-layered, and cuboidal in shape. Before
enamel formation begins, outer enamel
epithelium is folded. The capillary network
develops in between the folds from the dental sac
and provides a rich blood supply to the avascular
enamel organ.
CONT.
This rich nutritional blood supply is required
for the intense metabolic activity of the avascular
enamel organ. The dental papilla is mesenchymal
in nature. Under inductive influences of
epithelium, the dental papilla develops the
odontoblasts. The development of odontoblasts
occurs and laying down of dentin starts before the
inner enamel epithelium lays down the first layer
of enamel matrix .
CAPILLARIES (C) ARE IN INTIMATE CONTACT OF
CELLS OF OUTER ENAMEL EPITHELIUM (OEE).
STELLATE RETICULUM (SR).
DENTAL LAMINA
The dental lamina proliferates lingually at its
deep end and gives rise to the enamel organ of
the permanent teeth.
FUNCTION OF DENTAL LAMINA :
functional activity of dental lamina and it’s
chronology may be considered in three phases :
1- first phase concerned with initiation of the
entire deciduous dentition that begins at 6 weeks
of intra- utrine life of embryo.
2-second phase deals with inititation of the
successors of the deciduous teeth.It’s preceded
by growth of free end of the dental lamina,lingual
to 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.
CONT.
3- 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.
FATE OF DENTAL LAMINA :
1- dental lamina is functional in developing 52
teeth from 6 prenatal weeks until 4 years after
birth (development of third permanent tooth ).
2- the dental lamina degenrates by
mesenchymal invasions in late bell stage.
3- developing tooth lose it’s connection with
dental lamina .
4- sometimes remnants of dental lamina
remains in the jaws as epithelial rests of
Serres( Serre’s pearls ).
DENTAL PAPILLA ( D.P.) IN EARLY BELL STAGE
before the inner E. epith. Differentiate into
ameloblast to produce enamel( E.) ,the periphral
cells of d.p. differentiate into odontoblasts
(dentin forming cells) under the organizing
influence of inner E.epith.
Membrana performativa :
is the basement membrane, which separates
the enamel organ and dental papilla before dentin
develops
DENTAL SAC (D.S.) IN EARLY BELL
STAGE :
Befor formation of dental hard tissue begins,
d.s. shows a circular arrangement of it’s fibers
and it’s resemble a capsular structure .
with the development of the root, fibers of
d.s. Differentiate into periodontal fibers that
become embeded in the cementum and
alveolar bone.
2- ADVANCED BELL STAGE
In advanced bell stage, two more features of
tooth development are also seen .
1. Future dentinoenamel junction –
forms from the boundary present between
the inner enamel epithelium and odontoblasts.
The first layer of dentin is formed. After the
formation of first layer of dentin, enamel is laid
down over the dentin by the ameloblast .
ADVANCED BELL STAGE
CONT.
2. Hertwig’s epithelial root sheath –
develops from the cervical portion of the
enamel organ. As the crown develops, cell
proliferation continues at the cervical region of
the enamel organ, where the inner and outer
enamel epithelial cells join to form a root sheath .
When the crown is completed, the cells in this
region of the enamel organ continue to grow,
forming a double layer of cells termed the
epithelial root sheath or Hertwig's root sheath
ADVANCED BELL STAGE
CONT.
The root sheath originates at the point that
enamel deposits end. The length, curvature,
thickness, and number of roots , all depend on
the inner root sheath cells.
At the proliferating end, the root sheath bends
at a near 45-degree angle. This area called the
epithelial diaphragm , which encircles the apical
opening of the dental pulp during root
development, by the proliferation of these cells ,
root growth occur.
DEVELOPMENTAL DISTURBANCES :
anadontia : a complete lack of tooth
development .
hypodontia : lack of some tooth development .it is
one of the most common developmental
abnormalities .the absence of third molars very
common ,occuring in 20-23 % of the population,
followed in prevalence by the second premolar
and lateral incisor.also it is associated with
absence of a dental lamina ,which is
vulnerable(weak)
CONT.
to environmental forces ,like infection and
chemotherapy , medications ,and it’s also
associated with many syndroms,such as Down
Syndrome .
hyperdontia : is the development of extraneous
(external) teeth, about 86% of these cases
involve a single extra tooth in the mouth ,most
commonly found in the maxilla ,where the
incisors are located .hyperdontia is believed to
be associated with an excess of dental lamina .
CONT.
Dilaceration :
is an abnormal bend found on a tooth ,it’s
always associated with trauma that moves the
developing tooth bud. As a tooth is forming , a
force can move the tooth from it’s original
position ,leaving the rest of the tooth to form at
an abnormal angle.
CONT.
Amelogenesis imperfecta :
is an autosomal dominant disease
characterized by a defect in dental enamel
formation. Teeth are often free of enamel , small,
misshapen, and tinted brown. The cause of these
deformities is due to a mutation in enamel in
expression .
Natal and neonatal teeth :
Are a rare anomaly that involves teeth
erupting in a newborn infant’s mouth earlier
than usual.
CONT.
natal teeth are present at the time of birth,
while neonatal teeth will erupt during the first
30 days after birth. Most common location is in
the mandibular region of the central incisors .
natal and neonatal teeth are associated with
genetics, developmental abnormalities , it’s also
called baby teeth , milk teeth, precocious
dentition .
NUTRITION AND TOOTH DEVELOPMENT
nutrition has an effect on the developing
tooth,essential nutrients for a healthy tooth
include calcium , phosphorus , and vitamins A,C ,
and D.
Calcium and phosphorus are needed to properly
form the hydroxyapatite crystals , and their
levels in blood are maintained by vitamin D .
Vitamin A is necessary for the formation of
keratin , as vitamin C is for collagen.
CONT.
Flouride is incorporated into the
hydroxyapatite crystal of a developing tooth and
makes it more resistant to demineralization and
subsequent decay.
Deficiencies of these nutrients can affected on
tooth development :
--dificiencies of calcium , phosphorus , and
vitamin D, resulted in less mineralization of hard
structures of the tooth .
CONT.
--A lack of vitamin A ,can cause a reduction in
the amount of enamel formation .
--- fluoride deficiency causes high
demineralization when the tooth exposed to an
acidic environment , and also delays
remineralization.
--- an excess of fluoride during tooth
development can lead to a condition called
fluorosis.
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