Prenatal growth and development in orthodontics /certified fixed orthodontic courses by Indian dental academy

PRENATAL GROWTH
AND DEVELOPMENT

INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education

www.indiandentalacademy.com

 According to Aristotle
“He who sees things
grow from the beginning will have the
finest view of them”

www.indiandentalacademy.c
om

Human development
from ovulation to
fertilization
Human development begins at
fertilization when a male gamete or
sperm unites with a female gamete
or oocyte to form a single cell _
ZYGOTE

This highly specialized totipotent
cell marked the beginning of each
of us aswww.indiandentalacademy.c
a unique individual
om

Primordial germ cells
Gametes are derived from
“primordial germ cells” that are
formed in the epiblast during the
second week and that move to the
wall of the yolksac

om

During the fourth week these cells
begin to migrate from the yolk sac
toward the developing gonads ,where
they arrive by the end of fifth week
.mitotic divisions increase their
number during their migration and
also when they arrive in gonad

om

These primordial germ cells undergo
“GAMETOGENESIS” and
“CYTODIFFERENTIATION” to
complete their maturation

om

GAMETOGENESIS
 Gametogenesis {gamete formation}is the
process of formation and development of
specialized generative cells _
”GAMETES”
 This maturation process is called
spermatogenesis in males and oogenesis
in females
 During gametogenesis the chromosome
number is reduced to half by a process
called “meiosis”
om

Cell divisions
There are two types of cell division
MITOSIS
“ It is the process by
whereby one cell divides ,giving rise to
two daughter cells that are genetically
identical to parent cell”
Before a cell enters mitosis ,each
chromosome replicates its DNA
om

MEIOSIS
It is the cell division that
takes place in the germ cells to
generate male and female gametes
(egg & sperm) respectively
Meiosis requires two cell divisions to
reduce the number of chromosomes to
haploid number
MEIOSIS I
MEIOSIS II

om

MEIOSIS
1. SYNAPSE FORMATION
2. CROSSOVER
3.INTERCHANGE OF CHROMATID
SEGMENTS
4. CHIASMA FORMATION

om

FERTILIZATION
 It is acomplex sequence of
coordinated molecular events that
begins with contact between a sperm
& oocyte & ends with intermingling
of maternal &paternal chromosomes
at metaphase of first mitotic
division of zygote ,a unicellular
embryo
Usual site of occurrence of
fertilization is ampulla of uterine
om

Cleavage of zygote
zygote {after 30hrs after fertilization}

Repeated mitotic divisions
Two blastomeres

Four blastomeres

Eight blastomeres

om

 COMPACTION

After the nine cell stage ,blastomeres
change their shape and tightly align
themselves against each other to form a
compact ball of cells .

This phenomenon is called “compaction”

om

Morula
when there are 12 to 32 blastomeres ,the
developing human is called morula {mulberry}
It was given its name because it resembles a mulberry
or black berry

om

Formation of blastocyst
 Shortly after morula enters uterus [about 4days
after fertilization} a fluid filled space appears
inside the morula

 As the fluid increases in the blastocystic cavity ,it
separates the blastomeres into two parts
a. trophoblast {outer cell layer}
b. embryoblast {inner cell mass}

At this stage of development the conceptus is
called a blastocyst
om

 During cleavage the zygote is within thick zona
pellucida
 After free blastocyst has floated in the uterine
secretions for two days the zona pellucida
degenerates and disappears
 Shedding of zona pellucida permits the
blastocyst to increase rapidly in size about six
days after fertilization the blastocyst attaches to
endometrial epithelium
om

 TROPHOBLAST (as blastocyst attaches to the
endometrial epithelium)
a. Inner layer of cytotrophoblast
b. outer mass of syncytiotrophoblast

om

During second week of human
development
 Formation of amniotic cavity
 Formation of embryonic disk
 Formation of yolk sac

om

Formation of amniotic cavity
 After implantation of blastocyst

small space appears in embryoblast

This space is the primordium of amniotic
cavity lined by amnioblasts

om

Morphological changes occur in embryoblast that
result in formation of flat almost circular
bilaminar plate of cells,this embryonic disk has
two layers

HYPOBLAST
EPIBLAST
om

EPIBLAST
forms floor of amniotic cavity

HYPOBLAST

forms the roof of exocoelomic cavity and is
continuous with thin exocoelomic membrane

Yolk sac
exocoelomic membrane +hypoblast

om

Prechordal plate
Prechordal plate develops as a
localized thickening of hypoblast,
which indicates the future cranial
region of embryo and the future site of
mouth. Prechordal plate is also an
important organizer of head region

om

Formation of germ layers
third week
 GASTULATION

A. it is formative process by which the three germ
layers and axial orientation are established in
embryos.

B. during gastrulation the bilaminar
embryonic disc is converted into trilaminar
embryonic disc.

C. first sign of gastrulation is appearance of
primitive www.indiandentalacademy.c
streak.
om

Primitive streak
 Primitive streak results from proliferation and
migration of cells of epiblast to median plane of
the embryonic disc

 Primitive streak appears “caudally in the median
plane of the dorsal aspect of the embryonic
disc”

 It is possible to identify the embryos craniocaudal
axis, its cranial and caudal end, its dorsal and
ventral surfaces and its right and left sides.
om

 PRIMITIVE NODE

As the primitive streak elongates by
addition of cells to its caudal end ,its cranial end
proliferates to form a primitive node .

Concurrently a narrow groove primitive
groove develops in the primitive streak that is
continuous with a small depression in the primitive
node - primitive pit

om

 primitive streak {cells leave its deep
surface and form }

mesenchyme{ a tissue consisting of
loosely arranged cells suspended in a
gelatinous matrix}

some mesenchyme forms intra
embryonic or embryonic mesoderm

om

 Cells from epiblast displace the hypoblast forming the
intraembryonic or embryonic endoderm

 Cells remaining in the epiblast form the intra embryonic
or embryonic ectoderm

 Reasearch data suggest that signaling molecules of
the transforming growth factor{TGF-B}superfamily
induce ,the mesoderm

 TGF-B{nodal},T-box transcription factor{veg-t}
and Wnt signalling pathway appear to be involved in
specification of endoderm
om

Fate of primitive streak
Primitive streak diminishes and becomes
insignificant structure in
sacrococcygeal region of embryo by
end of fourth week

om

Notochordal process and
notochord
 Some mesenchymal cells migrate cranially from
the primitive node and pit forming a median
cellular cord ,the notochordal process

the primitive pit extends into the notochordal
process forming a notochordal canal

om

 Notochordal process is a cellular tube extends
cranially from the primitive node to the prechordal
plate

 The floor of notochordal process fuses with the
underlying embryonic endoderm

 The fused layers gradually undergo degeneration
resulting in the formation of openings in the floor
of the notochordal process ,which brings the
notochordal process into communication with the
yolksac
om

The openings rapidly become
confluent and the floor of the
notochordal canal disappears ,the
remains of notochordal process form a
flattened ,grooved notochordal plate

om

Intrinsic signals from the primitive streak
region induce notochordal precursor cells
to form the notochord

Beginning at the cranial end of the
embryo ,the notochordal cells proliferate
and the notochordal plate infolds to form
the notochord

om

NOTOCHORD
 It is an intricate structure around which the
vertebral column forms

 It extends from the oropharyngeal membrane to
the primitive node .

 The notochord degenerates and disappears as
the bodies of the vertebrae form but it persists
as the nucleus pulposes of each intervertebral
disc www.indiandentalacademy.c
om

• Notochord functions as the primary
inductor in the early embryo

• The developing notochord induces the
overlying embryonic ectoderm to
thicken and form the “neural plate”
[the primordium of central nervous
system]

om

NEURULATION :FORMATION OF
NEURAL TUBE
 The process involved in the formation of
the neural plate and neural folds and
closure of the folds to form the neural
tube constitute neurulation.
 These processes are completed by the
end of fourth week

om

Neural plate and neural tube
As the notochord develops the embryonic
ectoderm over it thickens to form an
elongated ,slipper like plate of thickened
epithelial cells ,the NEURAL PLATE
NEURAL PLATE appears cranial to
primitive node ,dorsal to notochord and
mesoderm adjacent to it .

om

As the notochord elongates ,the neural
plate broadens and eventually extends
cranially as far as the oropharyngeal
membrane ,eventually the neural plate
extends beyond the notochord

On about 18th day ,the neural plate
invaginates along its central axis to form a
longitudinal MEDIAN NEURAL
GROOVE ,which has neural folds on each
side
om

The NEURAL FOLDS become
particularly prominent at the cranial end of
the embryo and are the first signs of brain
development .

By the end of the third week ,the neural
folds have begun to move together and
fuse ,converting the neural plate into
NEURAL TUBE

om

NEURAL CREST
FORMATION
 As the neural folds fuse to form the neural tube, some
neuroectodermal cells lying along the crest of each
neural fold lose their epithelial affinities and
attachments to neighbouring cells

 As the neural tube separates from the surface ectoderm,
neural crest cells migrate dorsoventrally on each side
of neural tube .

 They soon form a flattened irregular mass, the neural
crest, between the neural tube and the overlying surface
ectoderm www.indiandentalacademy.c
om

Neural crest soon separates in to right and
left parts migrate into the dorsoventral
aspects of neural tube, here they give rise
to sensory ganglia and cranial nerves

om

Neural crest cells migrate in various
directions and disperse within the
mesenchyme
Although these cells are difficult to identify
special laser techniques have revealed
neural crest cells disseminate widely

om

 Neural crest cells give rise to
1. Spinal ganglia
2. Ganglia of ans
3. Ganglia of cranial nerves
5,7,9,10
4. Pigment cells
5. suprarenal medulla
6. several skeletal and muscular
components in head

om

Laboratory studies indicate that
BMP, Wnt,Notch,FGF are
involved in signalling systems of
neural crest formation and in
migration and differentiation of
neural crest cells

om

PHARYNGEAL
APPARATUS
 Pharyngeal apparatus are aslo known as
Branchial apparatus

 The word Branchial is derived from greek
word Branchia which means
Gill.

 The head and neck regions of a 4 week
human embryo resemble these regions in a
fish embryo of a comparable stage of
development hence the name
om

 Pharyngealapparatus consists of
1. Pharyngeal arches
2. Pharyngeal pouches
3. Pharyngeal grooves
4 pharyngeal membranes

om

PHARYNGEAL ARCHES
The pharyngeal arches begin to develop
early in the fourth week as Neural crest
cells migrate into the future head and neck
regions

First pair of pharyngeal arches{primodium
of jaws} appear as surface elevations lateral
to developing pharynx
om

BY the end of fourth week ,4 pairs of
pharyngeal arches are visible externally .
5 & 6 pharyngeal arches are rudimentary
and are not visible on surface of embryo

Pharyngeal arches are separated from
each other by fissures known as
pharyngeal groove

om

Pharyngeal arch components
 Each pharyngeal arch consists of a core of
mesenchyme {embryonic connective
tissue}and is covered externally by
ectoderm and internally by endoderm

 This mesenchyme is derived from
mesoderm in third week ,during fourth week
most of the mesenchyme is derived from
neural crest cells that migrate into
pharyngeal arches
om

Neural crest cells are unique in that
despite their neuroectodermal origin
they make a major contribution to
mesenchyme in head & neck region

om

Fate of pharyngeal arches
 Pharyngeal arches contribute extensively to formation of
face , nasal cavities, mouth,larynx,pharynx&neck

 During fifth week, second pharyngeal arch enlarges and
overgrows the third and fourth arches ,forming an
ectodermal depression called cervical sinus

 By the end of 7 week the second to fourth pharyngeal
grooves and cervical sinus have disappeared giving neck a
smooth contour
om

 Typical pharyngeal arch contains
1. aortic arch
2. a cartiliaginous rod
3. muscular component
4. nerve

om

Derivatives of pharyngeal arch
cartilages
 FIRST ARCH
 Dorsal end of first arch cartilage [meckel
cartilage] is closely related to the developing ear
and ossifies to from two middle ear bones ,the
malleus and incus
 Middle part of cartilage regresses but its
perichondrium forms the anterior ligament of
malleus and the sphenomandibular ligament

om

 Second arch
 Dorsal end of second arch cartilage {Reichert
cartilage} aslo related to developing ear,ossifies to form
stapes of middle ear and the styloid process of temporal
bone

 The part of cartilage between the styloid process and hyoid
bone regresses ,its perichondrium forms stylohyoid ligament

 Ventral end of second arch cartilage ossifies to form lesser
cornu and superior part of body of hyoid bone

om

 Third arch cartilage ossifies to form greater
cornu and the inferior part of body of hyoid
bone

 The fourth arch cartilage and sixth arch
cartilage fuse to form laryngeal cartilages,except
for epiglotis

om

 Derivatives of pharyngeal arch muscle
 Derivatives of pharyngeal arch nerves

om

Pharyngeal pouches

 Primordial pharynx derived from foregut
widens cranially ,where it joins the primordial
mouth/stomodeum and narrows caudally
where it joins the esophagus.

 The endoderm of pharynx lines the internal
aspects of pharyngeal arches and passes into
ballon like diverticula called pharyngeal
arches
om

 There are 4 well defined pairs of pharyngeal
pouches fifth pair is absent/rudimentary
 First pharyngeal pouch

1. tubotympanic recess
2. tympanic membrane
3. tympanic cavity and mastoid antrum

om

 Second pharyngeal pouch
1. Palatine tonsil
2. Tonsillar sinus

 Third pharyngeal pouch
1. Inferior parathyroid gland

 Fourth pharyngeal pouch
1. Superior parathyroid galnd

om

 PHARYNGEAL GROOVES
head and neck regions of
human embryo exhibit four pharyngeal
grooves on each side,these grooves
separate the pharyngeal arches externally

om

 Pharyngeal membrane
it appears in floors of pharyngeal
grooves .these membranes separate pharyngeal
pouches from pharyngeal grooves

om

Thyroid gland development

 It is first gland to develop

after about 24 days after fertilization there
appears median endodermal thickening in
the floor of primordial pharynx

this thickening soon forms a small
outpouching Thyroid primodium
om

 Thyroid primodium is hollow but it soon becomes
solid and it divides into right and left lobes which
are connected by isthmus of thyroid gland

 Thyroglossal duct
for a short time thyroid gland is
connected to tongue by a narrow tube ,the
thyroglossal duct.

 By end of 7 weeks thyroid gland has assumed its
final site in neck ,by this time thyroglossal duct has
normally degenerated and disaappeared

om

Development of face
 Five facial primordia appear around large
primordial stomodeum early in 4 week ,they are

1. single frontonasal process

2. paired maxillary process

3. paired mandibular process

Facial development depends on the inductive
influence of the prosencephalic
&rhombencephalic organizing centers
om

 Frontonasal prominence surrounds the
ventrolateral part of the forebrain

 Frontal part of frontonasal process forms the
forehead

 The nasal part forms the rostral boundary of the
stomodeum, primodial mouth, nose

 The paired maxillary prominence forms the lateral
boundaries of the stomodeum

 The paired mandibular process forms the caudal
part of primitive mouth , stomodeum

om

FORMATION of LNP and MNP
Nasal placode
By the end of 4th week bilateral oval thickenings of surface
ectoderm develop. These are known as nasal placodes.

by the end of 5th week the nasal placodes invaginate to form
nasal pits, in doing so they create a ridge of tissue that
surrounds each pit and forms nasal prominences

the prominences on the outer edge of the pits are lateral nasal
prominences and those of inner ridge are medial nasal
prominences
om

FORMATION OF UPPER LIP

 During the following 2 weeks the maxillary
prominences due to proliferation of
mesenchyme continue to increase in size and
grow medially compressing the MNP towards
the midline.

 Subsequently the cleft between the MNP and
MP is lost and the 2 fuse, hence the upper lip is
formed by 2 MNP and 2 MP.

om

NASOLACRIMAL DUCT

 MP and LNP are seperated by deep furrow
known as nasolacrimal groove
 The ectoderm in this floor of this groove forms
a solid epithelial cord that detaches from the
overlying ectoderm
 After canalization the cord forms the
nasolacrimal duct, its upper end widens to form
lacrimal sac

om

Lower jaw and lower lip are the first
formed parts of the face to be formed.

They result from merging of medial ends
of mandibular prominences in the medial
plane.

om

Formation of nose
Nose is formed from 5 facial prominences.
Frontonasal prominence gives rise to nasal
bridge.
Merged medial nasal prominences provide
the crest and the tip.
Lateral nasal prominences form the sides
or alae of the nose.

om

Intermaxillary segment

 As a result of medial growth of maxillary
prominences the MNP merge forming
intermaxillary segment.
 It has 3 components:

1. The labial component
2. upper jaw component
3. palatal component
om

Summary of facial development
 FNP forms fore head, dorsum apex of nose,
LNP and MNP.
 LNP forms the sides of the nose
 MNP forms nasal septum and philtrum of upper
lip.
 Maxillary prominences forms the upper cheek
and most of upper lip.
 Mandibular process gives rise to chin, lower lip,
lower cheek region
om

Development of palate
 Palate develops from two primordia
1. The primary palate
2. The secondary palate
Primary palate
early in the 6th week the primary palate
– median palatine process begins to develop
from the deep part of the intermaxillary
segment of maxilla
om

The primary palate forms the
premaxillary part of maxilla .it
represents only a small part of the
adult hard palate

om

Secondary palate
 The secondary palate is the primodium of the
hard and soft parts of the palate
 The secondary palate begins to develop early in 6th
week from two mesenchymal projections that
extend from the internal aspects of maxillary
prominences.
 Initially these structures the lateral palatine
process or palatal shelves project inferomedially
on each side of tongue

om

 As the jaws develop tongue becomes relatively
smaller and moves inferiorly
 During seventh and eighth week the lateral
palatine process ascend to horizontal position
superior to tongue
 Gradually these process approach each other
and fuse in median plane they also fuse with
nasal septum and posterior part of primary
palate
om

 Bone gradually develops in the primary palate
forming the premaxillary part of the maxilla
 concurrently bone extends from maxilla and
palatine bones into the lateral palatine process
to form hard palate
 The posterior parts of these processes do not
become ossified they extend posteriorly
beyond the nasal septum and fuse to form
soft palate ,including its soft conical
projection uvula

om

Anomalies of lip and palate
1. Anterior cleft anomalies
2. Posterior cleft anomalies
3. Clefts involving the upperlip
a. unilateral
b. Bilateral
c. median cleft lip
4 Complete cleft palate

om

Facial clefts
 INCISIVE FORAMEN is considered
the dividing landmark between the
anterior and posterior cleft deformities
 Those anterior to incisive foramen
include
1. Lateral cleft lip
2. Cleft upper jaw
3. Cleft between primary and secondary
palate www.indiandentalacademy.c
om

Anterior defects are mainly due to partial
or complete lack of fusion of maxillary
prominence with medial nasal prominence
on one or both sides

om

POSTERIOR CLEFTS
1. cleft palate
2. cleft uvula
Cleft palate:
Lack of fusion between palatal shelves
 Smallness of shelves
 Failure of shelves to elevate
 Inhibition of fusion process
 Failure of tongue to drop from between the shelves
because of micrognathia

om

 Anterior clefts vary in severity from a barely
visible defect in the vermillion of lip to
extension into nose
 In severe cases the cleft extends to a deeper
level,forming a cleft of the upper jaw and the
maxilla is split between the lateral incisor and the
canine tooth

om

 OBLIQUE FACIAL CLEFT

failure of fusion of maxillary prominence to
merge with its corresponding lateral nasal process
o MEDIAN FACIAL CLEFT
incomplete merging of the two medial nasal
prominences in the midline .this anomaly is usually
accompanied by a deep grove between the right and left
sides of nose

om

Development of salivary glands
During 6th, 7th, week salivary glands
development begins as solid epithelial buds
from primordial oral cavity
The club shaped ends of these epithelial
buds grow into the underlying
mesenchyme
The connective tissue in glands is derived
from neural crest cells
om

Parotid gland
 First to appear

 They develop from buds that arise from the oral
ectodermal lining near angles of stomodeum

 These buds grow towards ears and branch to
form solid cords with rounded ends

 Later the cords canalize develop lumina and
become ducts by about 10th, weeks

om

 Rounded ends of the cords differentiate in to
acini

 Secretions commence at 18 weeks

 The capsule and connective tissue develop from
surrounding mesenchyme

om

Submandibular gland
 Appear late in 6th week

 They develop from endodermal bulbs in the floor of
stomodeum ,they grow posteriorly ,lateral to tongue

 Acini begin to form at 12 weeks

 Secretory activity begins at 16 weeks

om

Sublingual gland
They appear in 8th week
They develop from multiple endodermal
epithelial buds in paralingual sulcus
These buds branch and canalize to form 10
to 12 ducts that open inti floor of mouth

om

Development of tongue
Tongue appears in embryos of
approximately 4 weeks in the form of
1. two lateral lingual swellings
2. one median swelling
3. the tuberculum impar
these three they arise from first
pharyngeal arch
om

A second median swelling, copula or
hypobranchial eminence is formed by the
mesoderm of second, third, part of fourth
arch
A third median swellings formed by the
posterior part of the fourth arch marks the
development of the epiglottis

om

 The lateral lingual swellings overgrow the
tuberculum impar and merge ,forming the
anterior two thirds of tongue
 Sensory innervation to this part of tongue is the
mandibular part of trigeminal nerve
 Posterior part is formed from second ,third&
part of fourth arch
 Sensory innervation to this part of tongue is
glossopharyngeal nerve
 Extreme posterior part of tongue is innervated
by superior laryngeal nerve
om

Special sensory innervation (taste) to
anterior two-thirds is chorda tympani
While to posterior is glosssopharyngeal
nerve

om

Molecular regulation of facial
development
 Much of the face is mainly derived from neural crest
cells that migrate into pharyngeal arches
 In hind brain they(NCC) orginate from rhombomeres
(segmened regions)
 They are eight segments
 NCC from R1 & R2 migrate to first arch
 Cells from R4 go to second arch
 Those from R6 & R7 go to third arch
 Those from R8 go to fourth and sixth arches

om

 Patterning of pharyngeal arches is regulated by HOX
genes carried by migrating neural crest cells
 The expression patterns of HOX genes occur in
specific overlying patterns
 The expression patterns determine the organization of
cranial ganglia and nerves and pathways of neural
regulation
 Initially crest cells express the HOX genes from their
segment of origin ,but maintainence of this specific
expression is dependant upon interaction of cells with
mesoderm in pharyngeal arches

om

 A host of upstream and down stream genes are involved
in expression pattern
 SONIC HEDGEHOG may be one of the upstream
regulators
 Retinoids can also regulate HOX gene expression in a
concentration dependant manner
 Regulation occurs through

retinioc acid response elements
In addition to HOX gene ,OTX2 also participate in
morphogenesis of first arch

om

Thank you for Watching
For more details please visit
www.indiandentalacademy.com

om

Prenatal growth and development in orthodontics /certified fixed orthodontic courses by Indian dental academy

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

En vedette

En vedette (20)

Similaire à Prenatal growth and development in orthodontics /certified fixed orthodontic courses by Indian dental academy

Similaire à Prenatal growth and development in orthodontics /certified fixed orthodontic courses by Indian dental academy (20)

Plus de Indian dental academy

Plus de Indian dental academy (20)

Dernier

Dernier (20)

Prenatal growth and development in orthodontics /certified fixed orthodontic courses by Indian dental academy