1) The development of the face and oral cavity involves the merging and fusion of five processes - the frontonasal, two maxillary, and two mandibular processes. Failure of merging or fusion can result in cleft lip and/or cleft palate. 2) Cleft lip occurs when the maxillary processes fail to fuse with the medial nasal or frontonasal processes. Cleft palate occurs when the lateral palatine shelves fail to fully fuse, resulting in an opening in the roof of the mouth. 3) Environmental factors like infections, radiation, and some drugs during pregnancy can increase risks of congenital anomalies like cleft lip and palate by disrupting normal facial

1. Welcome back
Embryology
part 2
by
DR. RANA NAGAH
LECTURER OF ORAL BIOLOGY

2. Objectives:
1) Stages of human
development:
 prenatal development
 postnatal development.
2) Early development &
formation of germ layers.
3) Neural tube formation.
4) Development of primitive
oral cavity.
5) Branchial arches.

3. 1- Development of Nose.
2-Formation of the upper and
lower lips.
3-Formation of the palate.
4- Formation of the tongue.

4. Five Building blocks
• Early face develop from 5 processes surrounding
the primitive oral pit.
• Mesenchymal enlargement delineated by grooves
& most of them are not completely separated.
 The frontonasal process (prominence)
Forming upper boundary of oral pit.
 Two maxillary processes (prominences)
Bilateral to the oral pit forming lateral boundaries.
 Two mandibular process (prominences)
Bilateral to the oral pit forming lower boundaries.
 Max. & mand. Processes arise from 1st
branchial arch

6. 1) Nasal placodes
• Develop at 5th wiul.
• Bilateral ectodermal thickenings at lower part of the
frontonasal process
2) Nasal pits (nostrils):
• Mesenchymal proliferations at lower margins of
each nasal placode convert it into horse-shoe
shaped structure surrounding “Nasal pit” at 6th wiul.
• So Each placode is divided into
 Medial nasal process
 Lateral nasal process
3) Lateral nasal process
• Separated from maxillary
process by nasolacrimal groove
• Give rise to sides ( alaa) of nose.

7. Nasolacrimal groove
 Ectoderm at depth of
groove proliferate to form a
cord
 The cord buries itself into
underlying mesenchyme &
detaches itself from surface
 It extends downward &
canalizes to form the
nasolacrimal duct.
 Then the groove
disappears.

8. 4) The two medial nasal processes
Merge to form Intermaxillary segment
or“Globular process” & GIVE RISE TO
- The center and tip of the nose
- The inward growth gives the nasal
septum
Frontonasal process give rise to
- Forehead
- Apex and dorsum of the nose

10. 1)Intermaxillary segment at 6th wiul:
 Formed by merging of the two medial
nasal processes
 Give rise to:
1. Philtrum (center of upper lip) Defined in
adults by 2 vertical ridges under nostrils.
2. Anterior alveolar process (carrying 4
incisors)
3. Primary palate (region of hard palate
just posterior to the upper incisors)
 Bilaterally separated from Max.
processes by fissures.

11. 2) Maxillary processes
 Give rise to:
1. Lateral thirds of upper lip
2. Horizontal part of cheek
3. Lateral palatine processes
of 2ry palate
 If union failed, it causes
cleft lip

12. Mandibular processes
 Grow toward each other and merge
together at their medial end to give :
1. Lower lip.
2. Mandiblular mesoderm
3. Lower part of check
4. Body of the tongue
Failure Median cleft of the mandible.

13. https://www.youtube.com/watch?v=FhhWG3XzARY

15. Def: the tissue ( ) oral & nasal
cavities.
It develops from two parts:
1) Primary palate
• Called Median palatine
process or Pre-maxillary bone
• Supports the 4 incisors.
• Developed at beginning 6th
wiul from post. part of
intermaxillary segment as
horizontal wedge shaped mass
( ) maxillary processes.

16. 2) Secondary palate:
 Developed at end of 6th wiul
 From medial edges of max.
processes (laterally bounding
stomodeum) forming “lateral
palatine processes ( shelves)”
 Shelves grow medially, then
downward beside tongue.
 By now, Tongue is narrow & high ,
filling oronasal cavity reaching the
nasal septum

17. 3) Shelves elevation:
- At about 8.5 wiul, shelves develop enough
strength to roll over tongue.
- This elevation is due to combination of
shelf movement & tongue displacement by
mandibular growth bringing the tongue
downward & forward.
- The tongue's posterior end is attached to
the floor, so elevation start at posterior
parts pressing the tongue downward &
forward to release the anterior parts.
- The tongue broaden & occupy the lateral
space previously occupied by the shelves.

18. Mechanism of palatal shelves elevation
1) Tongue displacement by the growth of the
mandible downward & forward.
2) Presence of contractile force of the
fibroblasts in the palatal processes
(myofibroblast)
3) High mucopolysacharides (GAGs) content of
the shelves which attract water makes the
shelves more turgid.

19. When shelves become horizontal, they
grow & contact at midline.
A point of initial fusion of lateral palatine
processes first occur post. To median
palatine process (at the incisive foramen).
From point of initial contact with ant.
palate, the lateral palatine processes fuse
with median palatine process anteriorly
(Ant. Fusion)
From the same point post. Merging take
place gradually ( ) the two lateral palatine
processes over the next few weeks .
Nasal septum fuses with the shelves
except posteriorly (soft palate& uvula
remain free)

20. Palate is invaded by:
 Bone to form the hard palate
anteriorly
 Muscles posteriorly to form the soft
palate and uvula.
- Improper fusion of the lateral
palatine processes with the primary
palate or with each other results in
cleft palate.

21. https://www.youtube.com/watch?v=4LQJIf0XLP0&t=55s

23. Def: Sac of mucous membrane filled with
muscles
 Formed of two parts of different origin and
different structure
By naked eye: Composed of 2 parts:
A. Anterior 2/3 or Papillary portion
• The body of the tongue.
• Covered by lingual papillae.
• It is Ectodermal in origin.
B. Posterior 1/3 or lymphoid portion
• Base or root of the tongue
• Contains lymphoid tissue (lingual tonsils)
• It is Endodermal in origin.

24.  Junction ( ) 2 parts is
marked by a V- shaped
groove called terminal
sulcus, with a shallow
depression at V’s apex
called foramen cecum.
 Body is formed by union of
2 bilateral parts represented
by central longitudinal line
on dorsal surface called
median sulcus

25. Origin: 1st , 2nd , 3rd & part of 4th
arch & occipital myotomes’ muscle
fibers.
Ant 2/3:
 Local mesenchymal proliferation
give 3 elevations at ventromedial
aspect of “Mandibular arch”
1. Two lateral lingual swellings on the
internal surface of the two
mandibular processes on each side
of the median plane.
2. A small median elevation called
tuberculum impar just posterior to
two lateral lingual swelling.

26.  The two Lateral lingual swellings grow rapidly backward and forward &
medially to merge with each other and overgrow the tuberculum impar
forming a large mass that later form the mucous membrane of the
anterior 2/3.
The line of union between the two lateral lingual swellings is indicated
externally by median sulcus and internally by median raphae.

27.  Mesenchymal proliferation makes 2 swellings:
1) Copula formed at ventromedial aspect of the 2nd arches.
2) Large hypobranchial eminence from the mesoderm of 3
rd and part of 4th arches (immediately caudal to copula).
 Hypobranchial eminence rapidly overgrows the copula
which disappears.
 Gives the mucosa covering the posterior one third.
 The posterior one third become fused with the anterior
two thirds of the tongue, the site of fusion is marked by
the V shaped sulcus terminalis.
 N.B: Lingual tonsils appear as lymphocytic
aggregations around lingual crypts in post 1/3 of
tongue.

29.  At first tongue is fused to the floor of
the mouth
 2 grooves separate the sides of
tongue from alveolar ridge
 Then, the grooves extend forward
to meet each other in front of
tongue to form lingual sulcus & give
tongue mobility
 Except anteriorly where lingual
frenum still attach it to the floor

30.  Arise at 2nd miul (9th wiul)
 From the occipital somite
myotomes.
 Migrated from developing
brain forward into the
tongue area
 Carrying with them their
nerve supply, the 12th
cranial nerve (hypoglossal
nerve)

31. Def: Epithelial capped C.T structures found on
the tongue dorsal surface;
Four types:
1. Circumvallate and foliate (embedded in
tongue) appear first at 9th wiul
Developed as a ring of epi. that proliferate
down into the underlying mesoderm, then
invaginate forming a trench separating lateral
walls of papillae, not elevated from the surface
2. Fungiform and filliform (protruded above
surface) appear at 10th wiul.
Develop by mesenchymal proliferation
raising the corresponding epithelium.

33. Tongue innervation is derived from nerves of
branchial arches contributing to tongue development
Anterior 2/3
• Lingual branch of mandibular division of
trigeminal (V) nerve for general sensation
• Chorda tympani branch of the facial (VII) nerve
for taste sensation
Posterior 1/3
• Glossopharyngeal nerve ( IX cranial nerve ) for
general and taste sensation.
• Internal laryngeal (branch of vagus X).
Muscles
• Hypoglossal nerve (XII cranial nerve)(motor nerve).

34. https://www.youtube.com/watch?v=fp3Z_Y--0jo&t=156s

35. MERGING VS. FUSION OF FACIAL PROCESSES
• Most facial processes begin as two separate
swellings separated by a groove.
• Merging is the process by which the groove
between two facial processes is eliminated.
• The tissues in the depth of groove proliferate
more rapidly than the surrounding tissues,
causing the groove to become shallower &
disappear.
Examples of merging are:
 Merging of the 2 mandibular processes (the
former mandibular arch) in the midline.
 Merging of the 2 medial nasal processes in the
midline.
 Merging of lateral nasal and maxillary processes.
 Merging of mandibular and maxillary processes.

36.  Fusion is the process by which two
facial processes, that were initially
separated by a space, grow together.
 Example of fusion:
o The formation of the 2ry palate
where two palatal shelves grow
toward each other, touch each other
and, then fuse in the midline.
o In fusion, unlike merging, the
epithelium is broken down where the
two processes meet.

37. Teratology
Embryology branch that deal with
abnormal development
Teratogen
Agent that cause or increase
incidence of developmental
anomalies
Anomalies

38. Anomalies
I-Congenital Malformation
A. Hereditary causes
B. Environmental causes
Hereditary causes
1-Chromosomal causes
- Decreased number (45 chromosomes) is
usually fatal (monosomy)
- Increased number in one chromosome is
teratogenic
 Results in a condition known as trisomy 21
or Down’s syndrome (mongolism)

39. Down’s syndrome is characterized by
a)Mental retardation
b)Flat nasal bridge
c) Fissured protruding tongue
d)Macroglossia
e) Delayed tooth eruption

40. 2- Genetic causes
 Disturbance in migration and distribution of
the neural crest cells.
 '‘Mandibulo-facial dysostosis'' or Treacher
Collin Syndrome Defects of structures that
are derived form the 1st and 2nd branchial
arches
1. Underdeveloped facial bone
2. Face appear dropping
3. Malformed Ear
4. Lower border of the mandible concave
5. Cleft palate
6. Dentinogenesis imperfecta.

41. 1-Infectious agent
 Viral infection like Rubella virus germane measles
 cleft palate and malformed teeth.
2-Radiation
 X-ray embryo cleft palate
3-Drugs
 Thalidomides (hypnotic) cause partial or total absence of
limbs.
 Tetracyclines during 2nd or 3rd miul
permanent brownish discoloration and hypoplasia of enamel .
 Chloropromazine (largactil; antiemetic & tranquilizer)
hypocalcification of teeth and skeleton
B. Environmental causes

42. 4-Hormones
- Teratogenicity is not definite.
- Cortisone causes cleft lip and palate in some experimental animals.
5-Nutritional disorders
- Not teratogenic in man.
- However, vitamin A deficiency or increase is teratogenic in animals.
- Increased vitamin D and C may cause malformation in man.
6--Smoking, Alcohol and Caffeine
- Increase incidence of cleft lip and palate in infants.
- Alcohol taking during pregnancy leads to
 Mental retardation
 Growth deficiency
 Maxillary hypoplasia
- Caffiene may cause developmental defects.

43. Note: The embryonic period (2w-8w) is the
most critical period because during this period,
the differentiation of major organs and systems
takes place.

44. 1.cleft lip
• Def: Failure of fusion ( ) processes forming
lip
• Cause: Defect in processes migration
timing, contact or fusion.
• Form: Vary from notch on vermillion
border to cleft extending into nostrils.
• May or may not be with cleft palate.
II. Developmental anomalies

45. 1.cleft lip Types:
1) Unilateral:
 Fusion failure of ONE Max. process with
intermaxillary segment.
 Lip &nasal tissues are pulled to attached side.
2) Bilateral:
 As unilateral, but at both sides
 Defects may be symmetrical or not.
3) Median:
 Failure of merging ( )2 medial nasal processes.
 Called “Hare lip”.
 Very rare.
II. Developmental anomalies

46. 2. Median cleft of the mandible
- Incidence: Rare
- Cause: Failure of the 2 mandibular
processes to merge with each other, so
mandibule develops with no midline
hard tissue union.
- Form: A chin dimple is the simplest
(slightest) form

47. 3. cleft palate
Incidence: less common than cleft lip
Causes:
1) Interference with shelves elevation.
2) Lack of growth
3) Initial fusion failure ( ) forming processes (median &
lateral palatine processes and nasal septum)
4) Interruption of fusion at any point along fusion lines
Types: 1. Cleft of primary palate
- Failure of the lateral palatine processes to fuse
with the primary palate
- May affect upper lateral or canine (missing or
malformed).
- Unilateral or bilateral.
- Always with cleft lip as bone fuse before the lip.
Diagrammatic representations of some of the
different types of clefts of the lip and palate: (a)
Normal; (b) unilateral cleft lip; (c) unilateral cleft lip
and anterior palate; (d) bilateral cleft lip and anterior
alveolus; (e) cleft of posterior palate (hard and soft);
(f) unilateral cleft of the lip and anterior and posterior
palate

48. 2. Cleft of the secondary palate
- Failure of the lateral palatine processes to
meet, from or fuse with each other and with
the nasal septum.
- Since fusion of the secondary palate extend
posteriorly, the degree of the cleft may vary
from the simplest form or “bifid uvula” to a
cleft involving both hard and soft palate.
3. Complete Cleft of both primary and
secondary palates
- Results from failure of fusion between the
three palatine processes with nasal septum.

49. Problems differ according to the extent
of the cleft
- A bifid uvula causes no discomfort.
- Cleft in soft palate causes varying
degree of speech and swallowing
difficulty.
- Clefts of hard and soft palates
produce severe feeding problems
and food may be aspirated into the
lungs.

50.  Ankyloglossia ( tongue - tie )
The tip of the tongue remains tied to the
floor of the mouth.
 Macroglossia
o Abnormally large tongue.
o Not common
o False cases appear at birth with tongue
protruding from mouth, but soon jaws
grow fast to include tongue.
o True cases seen in Mongolism.
4. Malformations of the tongue

51.  Microglossia abnormally small
tongue.
 Bifid tongue: failure of merging of the
2 lateral lingual swellings.
 Median rhomboidal glossitis
 Central papillary atrophy due to
failure of the lateral lingual swellings
to overgrow the tuberculum impar.
 Not require treatment.

52. 5. Cervical cyst and fistula
- The 2nd branchial arch caudally
overgrow the 2nd, 3rd, &4th branchial
grooves forming ectodermal lined cavity
called cervical sinus which normally
later obliterated & disappear.
- Failure of obliteration causes cervical or
branchial cyst.
- Found anywhere along anterior border
of “sternomastoid muscle” on side of
neck
- If the cyst opens to the outside, branchial
fistula develops (internal or external).

54. 6. Thyroglossal cyst and fistula:
o Usually develop from remnants of the thyroglossal duct
o Found at any point along its course in the midline of the neck.

55. 8. Macrostomia
(transverse facial cleft)
• Cause: Incomplete union ( )
max. & mand. Processes.
• Form: cleft from mouth angle
extending to a varying degree
toward ear region
• Underlying bone may be
involved.
• Unilateral or bilateral
7. Mandibulofacial dysostosis
(Treacher Collin’s Syndrome)

56. 9. Microstomia
• Very small mouth.
• Result from: Over union ( ) max. &
mand. Processes.

57. 10. Oblique facial cleft:
• Cause: lack of union ( ) frontonasal
& max. processes
• Form:
 Extend from side of philitrum &
around alaa of nose, then into the
eye’s inner canthus
 Sometimes passes laterally ending
in infraorbital foramen producing
an indentation in bone underneath