Prenatal growth craniofacial

“Growth is an increase in size”-
TODD
“The self multiplication of living
substance”- J.S HUXLEY
“Increase in size, change in
proportion and progressive
complexity”-KROGMAN
www.indiandentalacademy.
com

“Entire series of sequential anatomic and
physiologic changes taking place from the
beginning of prenatal life to senility” –
MERIDITH
“Quantitative aspect of biologic development
per unit of time”-MOYERS
“Change in any morphological parameter
which is measurable”- MOSS
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I PERIOD OF OVUM fertilization to 14th
day
II PERIOD OF EMBRYO 14th
to 56th
day
III PERIOD OF FOETUS 56th
to 270th
day (birth)
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1.Embryonic period.
From fertilization to eighth week of development.
2. Fetal period
From 9 weeks to term
• Weeks 4 to 8 especially important.
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•Spermatozoon fertilizes an oocyte – ZYGOTE.
Ocurs in the ampulla of uterine tube ( oviduct)
•Zygote undergoes cleavage resulting in cells called blastomeres.
•Blastomeres form a ball of cells by adhering to each other –
MORULA.
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A fluid filled space ( blastocele / cavity ) develops within the
morula – BLASTOCYST.
Six days after fertilization – two distinct cell types:
trophoblast ( outer covering of single layer)
embryoblast ( cluster of cells )
End of first week:
•Blastocyst adheres to endometrium – implantation.
•Inner cell mass ( embryoblast ) form BILAMINAR DISK.
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• On 8th
day cell of embryoblast
differentiate into two layered disk so
called BILAMINAR GERM DISK
• So second week of development is also
called BILAMINAR DISK STAGE
• Trophoblast differentiate into layer
1] outer multinucleate
syncytiotrophoblast
2] inner cytotrophoblast
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• Syncytiotrophoblast invade
endometrial connective tissue and
erode capillaries.this eroision of
endometrial blood vessel cause
maternal blood to flow into cavities
within synytiotrophoblast.this blood
flow represent uteroplacental
circulation.
• Bilaminar disk comprise of
a] epiblast
b] hypoblast
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• Epiblast: a] ectodermal cell
b] columnar cell
c]
separated from cytotrophoblast by
amniotic cavity
• Hypoblast: a] endodermal cell
b] squamous or
cuboidal cell adjacent to blastocyst cavity
known as primitive yolk sac
• Extra embryonic mesoderm [EEM] consist
of loose CT located b/w outer surface of
primitive yolk sac inner surface of
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• Lacunae filled with fluid develop in
EEM. This lacunae fuse and form
chorionic cavity or extraembryonic
coelom [EEC]
• EEC surrounds the yolk sac &
amniotic cavity except where
bilaminar disk is attached to
cytotrophoblast by connecting stalk.
Later connecting stalk become
umbilical cord.
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• Hypoblast produce additional
cell that migrate along inside of
primitive yolk sac, squeezed off
& its remnant form secondary or
definitive yolk sac.
• By end of 2nd
week hypoblast
form localised area of
thickening called prohordal
plate at cranial end of bilaminar
disk. www.indiandentalacademy.
com

GASTRULATION:
.Called Trilaminar Disk stage.
•Bilaminar disk –changes to trilaminar disk.
•Gastrulation begins with formation of primitive streak in the
midline of epiblast.
•.cells of the epiblast migrate to primitive streak - detach and
grow beneath epiblast – Invagination.
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Some invaginating cells displace hypoblast –
Endoderm.
Between endoderm and epiblast- Mesoderm.
Remaining cells in epiblast - ectoderm.
EPIBLAST forms all three embryonic germ
layers.
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• This str. is a narrow trough with
slightly bulging sides develop in
midline of epiblast toward the
caudal end.
• Primitive pit surrounded by
elevated Primitive node is located
at cranial end of primitive streak.
• Rest explained from fig.www.indiandentalacademy.
com

Endoderm :
•epithelial lining of digestive , respirat.,urinary tracts , auditory
tube, tympanic cavity.
•Parenchyma of liver, pancreas, thyroid,tonsils.
Mesoderm
•Skull ,some connective tissue of head.
•Some muscles of head and neck.
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Ectoderm;
•Surface ectoderm : tooth enamel, epidermis, nails.
•Neural crest ectoderm : pharyngeal arch cartilage,
bone and muscle
Dentin, cementum
Central and peripheral nervous system
•Neural tube ectoderm :
CNS, retina , neurohypophysis
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The neural tube - primordium of CNS.
anterior region – forebrain, midbrain, hindbrain.
8 bulges (rhombomeres) develop in hindbrain.
Neural crest cells: arise from folds of neural tube.
migrate, differentiate throughout body to form
numerous, varied structures.
Provide mesenchyme (embryonic connective tissue)
for craniofacial development.
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For face and 1st
pharyngeal arch - from midbrain and
1st
two rhombomeres.
NCC from rhombomeres express homeobox genes
(HOX)
HOX genes imp. for determining identity and spatial
arrangement of body parts, pattern and position of
developing structures.
Mutations of homeobox genes – craniofacial anomalies.
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• Early in 3rd
week invaginating
cell in primitive pit & node
region grow cranially until they
reach prochordal plate.
• They form cellular rod called
Notochordal Process that
longitudinally in midline.
• Primitive pit extend into this &
form Notochordal canal.www.indiandentalacademy.
com

• The canal disappear & leaving
solid cylinder called
Notochord.This represent early
midline axis of embryo.
• By end of 3rd
week mesoderm
separate ecto & endoderm
everywhere except cloacal
membrane in caudal area &
prochordal plate in cranial area.www.indiandentalacademy.
com

• Nurulation is process of development
of Neural Plate , Neuroectoderm ,
folding to produce Neural Tube.
• During 3rd
week notochord induce
overlying ectoderm to form Neural
Plate.
• Lateral edges of neural plate form
Neural fold
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• Neural groove appear b/w neural
fold.
• Neural fold fuse in midline.
• Fusion start in 4th
week.
• Fusion first occur in center of
neural fold.
• Last part to fuse is Ant. & Post.
Neuropore.
• Neural fold is primordium of CNS
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Flat trilaminar disc folds in two planes –
typical, cylinderic ,C – shape.
Cranio- caudal plane – growth of CNS.
latero-medial plane - growth of somites
Folding creates primordial gut
(foregut,midgut, hindgut).
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•Folding of the head region ventrally incorporates
part of endoderm – FOREGUT.
•Buccopharyngeal membrane separates foregut
from primitive oral cavity (stomodeum).
• buccopharyngeal membrane made of -
endoderm & ectoderm
•Breaks down - end of 3rd
week (approx. day 26)
allowing continuity between foregut and stomodeum.
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• Begin to develop – 4th
week i.u. (approx.
24 to 26 days)
• Rostrally lies neural plate ,caudally the
developing cardiac plate.
• brachial arches form in pharyngeal wall.
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Pharyngeal apparatus :
Bilaterally paired arches
pouches
grooves (clefts)
pharyngeal membrane.
ARE IMPORTANT AS THEY GIVE RISE TO HEAD AND NECK
STRUCTURES.
Ectoderm – mesenchyme – endoderm
(upto 3rd
week- mesoderm)
( 4th
week onwards -NCC )
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ARCH CRANIA
L
NERVE
BONE,
CARTILAGE,
LIGAMENTS.
MUSCLES
I Vth
trigemin
al
Maxilla,zygoma,zygomatic
process
Mandible,incus,malleus
Sphenomandi.ligament,me
ckle’cartilage
Muscles of
mastication,m
ylohyoid,tenso
r veli
palatini,tensor
tympani,ant.
Digastric.
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ARCH CRANIAL NERVE BONE,
CARTILAGE,L
IGAMENTS
MUSCLES
III IX
GLOSSOPHARYNGE
AL
greater horn
,inferior body
of hyoid.
stylopharynge
us
IV and
VI
X
VAGUS
Laryngeal
cartilages:
Thyroid,
cricoid,
arytenoid
Pharyngeal
constrictors
Cricothyroid
Intrinsic
muscles of
larynx.
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Pouch 1 Tympanic cavity,auditory tube,mastoid antrum.
Pouch 2 Lining of palatine tonsils
Pouch 3 Inferior parathyroids , thymus
Pouch 4. Superior parathyroids, parafollicular cells
Groove 1 Ext. auditory meatus
Grooves 2
to 4
Cervical sinus
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Arch IV and VI form in animals but poorly developed / not visible
in human embryo.
ARCH 1. MANDIBULAR ARCH
•Major contributor to development of face.
•Distinct maxillary and mandibular processes/prominences
•Neural crest mesenchyme of maxillary process
intramembranous ossification
•Maxilla, zygomatic , squamous part of temporal bone.
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Mesenchyme tissue lateral to meckle’s cartilage
intramembranous ossification
mandible
Meckle’s cartilage
dorsal end – middle ear ossicles
Middle portion - sphenomandibular ligament
Ventral part - horse shoe shaped structure (template)
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Primarily between weeks 4 to 8.
After 8 weeks – changes in proportions ,
relative position of components.
Facial development mainly –
1. Enlargement and movement of
frontonasal prominence.
2. 4 prominences of pharyngeal arch I.
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•1st
event-
fusion of medial ends of mandibular prominences – chin and
lower lip
•Inferolateral portion of frontonasal prominence – surface
ectoderm thickens – nasal placodes
•Mesenchyme along periphery of nasal placodes proliferates–
horseshoe shape ridges – medial and lateral nasal processes
•Center of nasal placodes thins – nasal pits (precursors of
nostrils and nasal cavities.)
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Mesenchyme in maxillary prominence proliferates – move
medially towards each other and medial nasal prominences.
Medial nasal prominence medial nasal prominence
intermaxillary segment.
philtrum
4 incisors, gingiva,alveolar bone
primary palate
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Maxillary prominence:
•Lateral part upper lip.
•Maxilla (upper cheek)
•Secondary palate
Frontonasal prominence:
•Forehead
•Dorsum , bridge of nose
Medial nasal prominence
•Intermaxillary segment
•Nose midline
•Nasal septum
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•Lateral nasal process
Alae of nose
•Mandibular process
Lower lip
Lower cheek
Chin
Upper lip: medial nasal and maxillary process.
Nose : frontonasal, medial, lateral nasal processes.
Nasolacrimal ducts: lateral nasal process and maxillary
process.
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• Critical period
End of 6th
week – beginning of 9th
week.
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PALATE :
• primary/primitive palate (premaxilla)
• secondary palate.
Secondary palate :
• hard and soft palate
•paired lateral palatine shelves of maxilla.
• mesenchymal connective tissue oriented in
superior- inferior plane with tongue interposed.
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•Lateral palatine shelves elongate vertically – tongue
smaller , moves inferiorly.
•Late 8th
week – within few hours – horizontal elevation
and start growing towards each other.
•Sudden change in direction ascribed to
1.biochemical transformation in connective tissue matrix.
2.variation in vasculature and blood flow.
3.rapid differential mitotic growth.
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4. Intrinsic shelf force.
5. Muscular movement.
6.high conc. Of glycosaminoglycans.
7.displaced by tongue;mouth opening reflex
Fusion:
•8th
– 12th
week
•Palatal shelves meet in midline – fusion begins
anterior 1/3 and with nasal septum.
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•Necessary to eliminate surface epithelial
covering.
cessation of DNA synthesis in epithelium abt.
24- 36 hours before (biochemical pathways)
•Underlying basal epithelial cells – glycoproteins
rich – ready adhesion.
•Midline seam – ectomesenchyme- palatal
growth pressure – basal epithelial cells transform
into fibroblasts(mesenchymal cells)
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Meanwhile, growth of lower free edge of nasal septum –
meets and fuses with upper surfaces of palatal process –
divide stomodeum into oral cavity and 2 nasal fossae.
OSSIFICATION :
• 8th
week iu.
• From primary and secondary ossification centres in
premaxilla.
Bone spread from maxilla ossificn. Centre
and from trabeculae of palatine bones.www.indiandentalacademy.
com

Intramembranous ossification.
Most posterior part NOT ossified – SOFT PALATE.
Fetal period:
More growth in width than length
midpalatal sutural growth
appositional growth lateral alv. margins.
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•Begins 36 – 38 days.
•From ossification of osteogenic membrane(mesenchyme
condensation)
•Lateral to and uses meckle’s cartilage as template/scaffolding.
BODY/CORPUS
•At 6 weeks –
meckle’s cartilage extends as solid hyaline cartilage rod
from ear region to midline of fused mandibular processwww.indiandentalacademy.
com

Md. nerve – close positional relation with developing mandible.
Lateral aspect of meckle’s cartilage : condensation of
mesenchyme in the angle formed by inf. alv N- incisive and
mental branches - 7 weeks :intramembranous ossification begins.
centre
anteriorly posteriorly
(to midline) (pt. of division into lingual
and inferior alv.)
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Bone formation anteriorly form of trough (medial,lateral
plates)
Bone formation posteriorly along lateral aspect of
meckle’s cartilage gutter formation
converted into canal enclosing inf. alv. Nerve.
RAMUS:
Rapid spread of ossificn. posteriorly into mesenchyme of 1st
arch
turning away from meckle’s cartilage.
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Point of divergence- LINGULA.
By 10 weeks rudimentary mandible formed – intramembranous.
Further growth:
a) 3 secondary growth cartilages
b) development of muscular attachments.
•Condylar cartilage
•Coronoid cartilage
•Symphyseal cartilage
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Condylar cartilage:
•5th
week – mesenchymal condensation above ventral
part of developing mandible.
•By 12th
week – cone/carrot shape mass occupying most
of developing ramus.
•This mass of cartilage – endochondral ossification.
•By 20 weeks – only a thin layer of cartilage remains in
condylar head.
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Coronoid cartilage:
•Appears 10 – 14 week
•Grows as a response to developing temporalis muscle
•Incorporates into bone of ramus and disappears before birth.
Symphyseal cartilage:
mental region either side of symphysis 2small cartilages
ossify 7th
month i.u. no. of small mental ossicles.
complete ossificn. 1st
year post natal
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Summary:
Mandible is an intramembranous bone,developed in
relation to nerve of 1st
arch ,but growth independent
of meckle’s cartilage
It has a neural,alveolar and muscular element . Its
growth is assisted by development of secondary
cartilages.
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• 4th
week i.u.
• In relation to pharyngeal arches in the floor of
mouth.
• Medial most part of mandibular arch
proliferates
2 lingual swellings.
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• Lingual swelling tuberculum impar lingual
swelling
(midline swelling)
• Immediately behind tuberculum impar
epithelium proliferates
thyroglossal duct.
• Site of this down growth marked by – foramen caecum.
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HYPOBRANCHIAL EMINENCE :
Another midline swelling - medial portion of 2nd
, 3rd
, 4th
branchial arches.
HYPOBRANCHIAL EMINENCE
cranial part caudal part
2nd
, 3RD
arch 4th
arch
copula epiglottis
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Anterior 2/3 of tongue:
1. Tuberculum impar
2. The 2 lingual swellings.
Thus, derived from mandibular arch.
Posterior 1/3 :
1.Copula (2nd
and 3rd
arches)
Mesoderm of 2nd
arch buried below .
‘’ 3rd
arch grows over and fuses with mesoderm of 1st
arch.
Posterior most part :
Derived from 4th
arch.
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Osteogenesis:
1. intramembranous bone
formation
2. endochondral bone formation
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I NEUROCRANIUM
desmocranium chondrocranium
(cranial vault) (cranial base)
II VISCEROCRANIUM
from branchial/ pharyngeal arches
bones of nasomaxillary complex
intramembranous bone formation.
III ALVEOLAR/SUPPORTING
invagination of oral ectoderm
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Endochondral bone formation:
• Most parts of embryo
• Cartilagenous model closely resembles bone to be
formed.
Process:
1. Mesenchymal cells become condensed at site.
2. Some mesenchymal cells differentiate into chondroblasts
– hyaline cartilage.
3. Cartilage surrounded by membrane (perichondrium )
highly vascular and contains osteogenic cells.
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4. Alkaline phosphatase secreted by cartilage cells –
surrounding intercellular substance calcified.
5. Nutrition to cartilage cells cut-off – death –
formation of empty spaces – primary areolae
6.Osteogenic cells – osteoblasts – osteoid
7.Osteoid calcifies to become a lamellae of bone.
• Calcified matrix of cartilage acts as support for
bone formation.
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• Bones of endochondral origin in craniofacial
skeleton :
1.Cranial base
2.Some bones of Calvarium
• 8th
week i.u. – 1st
evidence of endochondral
ossification occurs in craniofacial skeleton.
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Intramembranous bone formation :
• not preceded by cartilagenous model.
• Directly laid down in fibrous manner.
Process :
1. Aggregation of mesenchymal cells.
2. Mesenchymal cells lay down bundles of collagen fibres.
3. Some enlarge ,acquire a basophilic cytoplasm –
osteoblasts.
4. Osteoblasts secrete agelatinous matrix - osteoid around
collagen fibres.
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5. Deposition of calcium salt into osteoid –
bone lamellae.
•6th
week i.u. – 1st
evidence of
intramembranous ossification.
•By 8th
week , centres of ossification appear
in the facial regions .
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• 2 halves arise from a single ossification centre
each.
• Purely intramembranous.
• Developmental elements:
Neural and alveolar areas.
Frontal, zygomatic, palatal processes.
Paranasal sinuses, some part of alveolar
process, nasal capsule develop independently.
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Last half of fetal period - in height of
maxilla by bone growth between orbit and
alveolar process.
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1. MATERNAL FACTORS
a. Vascular Compromise
i. Acute Toxemia
ii. Hypertension
iii. Chronic Renal Disease
iv. Cardiac Insufficiency
v. Diabetes Mellitus
vi. Ulcerative Colitis
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b. Drugs
i. Narcotics
ii.Alcohol
iii.Tobacco
c. Malnutrition, Socioeconomic Status
d. Hypoxia
i. Altitude
ii.Sickle cell anemia
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a. Chronic Lesions
i. Abnormal insertions of cord
ii. Hemangioma
iii. Parabiotic Twinning
iv. Fibrinosis and Infarctions
b. Acute Lesions
i. Abruptio Placentae
ii. Rupture of fetal vessels
iii. Ascending Chorioamnionitis
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a. Genetic
b. Chromosomal
i. Trisomic Syndrome : 15,18,21
ii. Autosomal Deletions : 5,18,21
iii. Sex Chromosomes :
XO,XXXXY
iv. Chromosomal Breakage:www.indiandentalacademy.
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c. Infections
i. Rubella
ii. Cytomegalic inclusion disease
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i. Single umbilical artery
ii. Dysmorphic Syndrome
iii. Teratogenic agents
iv. Endocrinological causes
* Hypothyroidism
* End- organ insensitivity to
somatotropinwww.indiandentalacademy.
com

Stage of time relatedsynd.
Development
I germ layer day 17 Fetal alcohol
syndrome
II neural tube days 18 anencephaly
/oropharynx - 23
formation
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III origin ,migration, interaction days 19- 23 hemifacial microsomia
neural crest cells mandibulofacial dysostosis
IV formation of organ systems cleft lip/palate
• primary palate days 28- 38 facial clefts
• secondary palate days 42-55 cleft palate
V final differentiation of days 50 to achondroplasia,
tissues birth synostosis syndr.
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• Upper cleft lip.: maxillary process with medial nasal
process.
• Midline upper cleft lip : defective development of
frontonasal process.
• Oblique cleft lip : maxillary process with lateral nasal.
medial angle of eye – mouth
nasolacrimal duct not formed.
• Lower lip cleft : non – fusion of mandibular processes.www.indiandentalacademy.
com

Prenatal growth craniofacial

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