1.development of face and teeth by dr ibrahim

DEVELOPMENT OF
FACE
TEETH AND
Dr Ibrahim
1

Thursday, January 09, 2014

CONTENTS
 Development of:Face
lower lip
Upper lip
Maxilla
Mandible
Eye
Ear
Palate
Teeth
2


DEVELOPMENT OF FACE
 The development of face

begins during the 4th week of
intrauterine life from 4
primordia that surround a
central depression
representing the primitive
mouth or the stomatodeum.
 These include the
frontonasal process (a
single cranially located
process), the 2 bilaterally
located maxillary
process, and the
3
mandibular process derived


 By the 5th week, the nasal placodes develop bilaterally on

the lower part of the frontonasal process where they
border the oral cavity.
 At the margins of the placodes, mesenchyme proliferates
and produces medial and lateral nasal processes thus
transforming the placodes into nasal pits(nostrils).
 By the 6th week of IU life, The medial and lateral nasal
processes appear as horse shoe shaped structures with
the open end of the slit in contact with the oral cavity.

5


• On each side, the lateral nasal process is separated

from the maxillary process by a groove called the
nasolacrimal groove.
• This groove will eventually disappear , but before it
disappears, the epithelium at its depth first forms a
solid rod and later will canalise , and form the
nasolacrimal duct.

7


• The point of contact of

the epithelium covering
medial nasal process
and maxillary processes
is termed the nasal fin.
• This vertically
positioned epithelial
sheet under each
nostril separates the
medial nasal and
maxillary processes;
and when the fin
disappears, the two
8 processes will fuse.


DEVELOPMENT OF LOWER LIP
 The mandibular

9

process appears
initially as a
partially divided
bilateral structure
but soon merges
at the median
line. This
process will give
rise to the lower
lip and the lower


DEVELOPMENT OF UPPER LIP AND
MAXILLA
 During the 6th

week, each maxillary
process grows medially
and fuses, first with the
lateral nasal processes
and then with the medial
nasal process.
 The medial and lateral
nasal processes also
fuses with each other ;
thus closing the nasal
pits to the stomatodeum.
 The mesoderm of the
lateral part of the lip is
formed from the


 The maxillary processes

undergo considerable
growth while the
frontonasal process
becomes narrower
bringing the anterior nares
closer together.
 The mesoderm of the
median part of the
lip(philtrum), is formed
from the frontonasal
process.
 The ectoderm of the
maxillary process
overgrows this mesoderm
to meet that of the
opposite maxillary
11
process in the midline.


Maxilla
 Develops from center of ossification in the






12

mesenchyme of maxillary process. No arch
cartilage associated with maxillary process.
Center of ossification appear in the angle between
the division of infraorbital nerve.
Bone formation spreads posteriorly below orbit
toward developing zygoma, anteriorly towards
future incisor region, superiorly to form frontal
process- bony trough around infraorbital nerve.
Ossification also spreads into the palatine process
to form hard palate.
A secondary cartilage-zygomatic or malar cartilage
appear in the developing zygomaticThursday, January 09, 2014
process and
adds to the development of maxilla.

Mandible
 At 6th week the Meckle’s

cartilage extends as a solid
hyaline cartilagenous
rod, surrounded by a
fibrocellular capsule,from
developing ear region to the
midline of fused mandibular
processes.
 Two cartilages separated by
thin band of mesenchyme.
The mandibular nerve begins
2/3rd of the way along the
length of the cartilage.
 Mandibular nerve divides into
lingual and inferior alveolar
branch running along medial
and lateral aspect of cartilage.
 13
More anteriorly inferior


 During 6th week condensation of mesenchyme in the

area of division of inferior alveolar nerve.
 During 7th week, intramembranous ossification
begins in this condensation.,spreads rapidly
anteriorly to the midline and posteriorly to a point of
division of mandibular nerve.
 The spraed of new bone forms a trough that consists
of lateral and medial plates that unite beneath the
incisor nerve. The trough of bone extends to midline
to come in approximation with similar trough from
opposite side
 The two ossification remain separated at symphysis
until short after birth.
14

 Similarly a backward extension of ossification

proceeds to a point where mandibular nerve divides
into inferior alveolar nerve and lingual nerve resulting
in the canal formation around the inferior alveolar
nerve.
 The ramus develops by rapid spread of ossification
posteriorly into mesenchyme of first arch turning
away from Meckle’s cartilage. This point of
divergence is marked by lingula in adult mandible,
the point at which the inferior alveolar nerve enters
the body of mandible.

15


 Further growth influenced by appearance of three

secondary cartilages
 Condylar cartilage-appear during 12th week as cone
shaped cartilage that occupies most of the
developing ramus. This quickly undergo
endochondral ossification except for a thin layer of
cartilage on the condylar head.
 The coronoid cartilage-appears at 4th
month, surmounting the anterior border and top of
the coronoid process. This is a transient cartilage
and disappears long before birth.
 The symphysial cartilage- 2 in number, that ossify to
form the mental ossicles.
16


17


DEVELOPMENT OF EYE
 The eyes develop during the 5th week.
 The first external sign of eye development is the

appearance of the lens placodes between the maxillary
and frontonasal processes at the lateral sides of the face.

18


 The lens placode sinks below the surface and is

eventually cut off from the surface ectoderm.
 The developing eyeball now presents as a bulge
facing laterally. With the narrowing of the
frontonasal process, they come to face forwards.
 The eyelids are derived from folds of ectoderm
that are formed above and below the eyes, and
by mesoderm enclosed within the folds.

19


DEVELOPMENT OF EAR
 The external ear is formed around the dorsal part

of the 1st ectodermal cleft.
 A series of mesodermal thickenings (tubercles or
hillocks) appear on the mandibular and hyoid
arches where they adjoin this cleft.
 The pinna is formed by fusion of these
thickenings.
 When first formed the pinna lies caudal to the
developing jaw. It is pushed upwards and
backwards due to later enlargement of the
mandibular process
20


21


DEVELOPMENT OF PALATE
 By the 6th week of development, the primitive nasal

22

cavities are separated by a primitive nasal septum
and partitioned from the stomodeum by a primary
palate.The formation of secondary palate
commences between 7 and 8 weeks and is
completed around the 3rd month of gestation.
 Three outgrowths appear in the oral cavity: the nasal
septum grows downwards from the frontonasal
process along the midline, and 2 palatal shelves or
processes , one from each side, extend from
maxillary process towards the midline.
 The shelves are directed first downward on each
side of the tongue.

23


24


 After the 7th week of development, the

tongue is withdrawn from between the
shelves, which now elevate and fuse with
each other above the tongue and with the
primary palate.
 The septum and 2 shelves converge and
fuse along the midline, thus separating
the oronasal cavity into oral and nasal
cavities.

25


26


 For the fusion of palatine shelves to

occur, elimination of the epithelial covering of
the shelves is necessary. To achieve this
fusion, DNA synthesis ceases within the
epithelium some 24 to 36 hours before the
epithelial contact.
 Surface epithelial cells are sloughed off as
they undergo physiologic cell death to expose
the basal epithelial cells.
 These cells have the carbohydrate rich
surface coat that permits rapid adhesion and
the formation of the junctions to achieve
fusion of the processes.
27


 A midline seam is thus formed of two

layers of the epithelial cells. This midline
must be removed to permit
ectomesenchymal continuity between
the fused process.
 The growth of the seam fails to keep
pace with the palatal growth so that the
seam first thins and then breaks down
into discrete islands of epithelial cells.
 The basal lamina surrounding these
cells is lost and the epithelial cells
transforms into mesenchymal cells.
28


PALATAL SHELF ELEVATION
Several mechanisms have been proposed to
account for the movement of the palatal shelves
from vertical to the horizontal position.
 The closure of the secondary palate may involve
an intrinsic force in the palatine shelves the
nature of which has not been determined yet.
 The extrinsic forces derived from the growth of
the mandible and a change in degree of flexion of
fetal head- the tongue drops down from the path
of developing palatine processes.
 The high content of glycosaminoglycans , which
attract water and make the shelves turgid, has
also been suggested.
29


PALATAL SHELF ELEVATION

30


Cleft Lip: Can be unilateral, bilateral and can vary
from a notch in the vermillion border to a cleft
extending into the floor of the nostril.

31


DEVELOPMENTAL DEFECT OF
PALATE
 Cleft palate: Less common than cleft lip. It

maybe due to lack of growth or failure of fusion
between the median and lateral palatine
processes and the nasal septum or it maybe due
to initial fusion with interruption of growth at any
point along its course. It may also be due to
interference with elevation of palatal shelves.

32


33


CLEFT LIP AND PALATE

34


OVERALL SUMMARY OF
DEVELOPMENT OF FACE

35


DEVELOPME
NT
OF TEETH

36


• The primitive oral cavity, or stomodeum, is lined by stratified
squamous epithelium called the oral ectoderm.
• The oral ectoderm contacts the endoderm of the foregut to
form the buccopharyngeal membrane
•Tooth formation occurs in the 6th week of intrauterine life with
the formation of primary epithelial band.
• At about 7th week the primary epithelial band divides into a
lingual process called dental lamina & a buccal process called
vestibular lamina.
•All deciduous teeth arises from dental lamina, later the
permanent successors arise from its lingual extension &
permanent molars
from its distal
Extension.

37


• Membrane ruptures at about 27th day of gestation and the primitive oral

cavity establishes a connection with the foregut
• Most of the connective tissue cells underlying the oral ectoderm are of
neural crest or ectomesenchyme in origin

3= Connective tissue
cells

• These cells instruct the overlying ectoderm to start the tooth
development, which begins in the anterior portion of the future maxilla &
38 mandible and proceeds posteriorly

• 2- 3 weeks after the rupture of buccopharyngeal membrane, certain
areas of basal cells of oral ectoderm proliferate rapidly, leading to the
formation of primary epithelial band
• The band invades the underlying ectomesenchyme along each of the
horse-shoe shaped future dental arches.

39


• At about 7th week the primary epithelial band divides into an inner

(lingual) process called Dental Lamina & an outer ( buccal) process called
Vestibular Lamina

• The dental lamina serves as the primordium for the ectodermal portion

of the deciduous teeth
• Later during the development of jaws, permanent molars arise directly
from the distal extension of the dental lamina
40

• The successors of the deciduous teeth develop from a lingual extension

of the free end of the dental lamina opposite to the enamel organ of each
deciduous teeth.

41


The lingual extension of the dental lamina is named the successional
lamina & develops from the 5th month in utero ( permanent central
incisor) to the 10th month of age (second premolar)

42


FATE OF DENTAL

LAMINA

• It is evident that total activity of dental lamina exceeds over a period of atleast 5
yrs
• As the teeth continue to develop, they loose their connection with the dental
lamina
•They later break up by mesenchymal invasion, which is at first incomplete and
does not perforate the total thickness of the lamina

43


• Fragmentation of the dental lamina progresses toward the developing
enamel organ
• Any particular portion of the dental lamina functions for a much briefer
period since only a relatively short time elapses after initiation of tooth
development before the dental lamina begins to degenerate
• However the dental lamina may still be active in the third molar region
after it has disappeared elsewhere, except for occasional epithelial
remnants

44


VESTIBULAR LAMINA
• Labial and buccal to the dental lamina in each dental arch, another epithelial
thickening develops independently
• It is Vestibular Lamina also termed as lip furrow band
• Subsequently hollows and form the oral vestibule between the alveolar
portion of the jaws and the lips and cheeks.

45


• At certain points along the dental lamina each representing the location of one
of the 10 mandibular & 10 maxillary teeth, ectodermal cells multiply rapidly &
little knobs that grow into the underlying mesenchyme
• Each of these little down growths from the dental lamina represents the
beginning of the enamel organ of the tooth bud of a deciduous tooth
• First to appear are those of anterior mandibular region
• As the cell proliferation occurs each enamel organ takes a shape that
resembles a cap

46


DENTAL SAC/ DENTAL
FOLLICLE
Surrounding the combined enamel organ or dental papilla, the third part of the
tooth bud forms. It is known as dental sac/follicle and it consists of
ectomesenchymal cells and fibres that surrounds the dental papilla and the
enamel organ.

C= Dental sac
47


DENTAL PAPILLA
On the inside of the cap, the ectomesenchymal cells increase in number.
The tissue appears more dense than the surrounding mesenchyme and
represents the beginning of the dental papilla

B = Dental Papilla
48


• Thus the tooth germ consists of ectodermal
componentthe
enamel
organ,
the
ectomesenchymal components- the dental
papilla & the dental follicle

• The enamel is formed from the enamel
organ, the dentin and the pulp from the dental
papilla and the supporting tissues namely the
cementum, periodontal ligament & the alveolar
bone from the dental follicle
• During & after these developments the shape
of the enamel organ continues to change
• The depression occupied by the dental
papilla deepens until the enamel organ
assumes a shape resembling a bell
• The dental lamina becomes longer, thinner &
finally loses its connection with the epithelium
of the primitive oral cavity
49


REFERENCES
1. Avery, James K., Chiego Daniel J. : Essentials of
Oral Histolgy and Embryology. 3rd edition.
2. Gray’s Anatomy.
3. Ten Cate’s oral histology-Development
, Structure and Function. 7th edition.
4. Singh Inderbir, G.P. Pal,: Human Embryology. 8th
ed.
5. Sadler J.W. Langman’s Medical EEmbryology. 9th
ed.

50

6. Kurt E. Johnson: Human Developemental
Anatomy
7. Bhalajhi S.I., Orthodontics, The Art and
Science, 3rd ed.

THANK
YOU
51


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