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1. 1

2. Prenatal growth
&
development
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com
2

3. Contents
Embryogenesis
The preimplantation period
The embryonic period
The fetal period
Pharyngeal arches’ pouches and grooves
Craniofacial development
3

4. Contents
Prenatal development of
Mandible
Maxilla
Palate
Tongue
Odontogenesis
Teratogenic effects on embryonic development
Conclusion
References
4

5. Male & female gametes
Cells present in sex organs or gonads– carry out
reproductive function
Gonads produce highly specialized gametes
Male gonad– testis-- spermatozoa
Female gonad– ovary-- ova
Spermatogenesis & oogenesis --- Gametogenesis
One spermatozoa fuses with one ovum-fertilization
5

6. Spermatogenesis
44+x+y
Spermatogonium type A
44+x+y
Type B
44 + x +y
Primary spermatocyte
1st meiotic div
22 + x
22+x
Secondary
22 + y
spermatocyte
22+x
22+y
2nd meiotic div
22+y
Spermatids
6

7. Oogenesis
44 + X + X
Oogonium
Enlarges to form
44 + X + X
Primary oocyte
I meiotic
division
Secondary
oocyte
22 + X
22+x
I polar body
2nd meiotic
division
ovum
22 + X
22 + X
II polar body
7

8. Fertilization
8

9. Sex determination
Spermatozoa– either x or y bearing
Ova – x bearing
ovum
sperm
ovum
sperm
22 + X
22 + X
22 + X
22 + Y
44 + X + X
44 +X + Y
Female
Male
9

10. Main results of fertilization
Restoration of diploid number of
chromosomes
Determination of sex
Initiation of cleavage
10

11. 11

12. Growth & development
Post-natal
Pre-natal
Ovum
1-14th day
Embryo
14th – 56th day
Fetus
56th – 280th day
12

13. Period of Ovum
Preimplantation period ( 1st week )
Day 1– fertilization
Day 2 –2 cell stage
Day 3 – MORULA
Day 4 – early blastocyst
Day 5 -- late blastocyst
13

14. Period of Ovum
EVENTS IN PERIOD OF OVUM
Fertilization
Morulla formation
3rd day
Blastocyst
4th & 5th day
14

15. Period of Ovum
Implantation ( 8th day )
Trophoblast sticks to
uterine endometrium
Blastocyst goes deeper
into uterine mucosa until
whole of it lies in
thickness of
endometrium---interstitial
implantation
15

16. Period of Ovum
Bilaminar Germ Disc (2nd week)
Formation of ectoderm
& endoderm –
ectoderm
endoderm
Amniotic fluid (8th
day)
Primary yolksac
formation (9th day)
16

17. Days 11, 12
& 13
Secondary yolksac formation
18

18. Gastrulation: trilaminar germ disc
Prochordal plate
Embryonic disc forms prochordal plate & primitive streak
(14th day)
19

19. 20

20. Formation of 3rd germ
layer –
Intraembryonic-
mesoderm (16th day)
21

21. Period of Embryo (3rd to 8th week)
22

22. Period of Embryo
Further development of Embryonic Disc
3rd week
knot
23

23. Period of Embryo
Formation of Notochord By Day 19
24

24. Development of mesoderm into 3 aggregations
( Transverse section)
Day 17
Day 20
Day 19
Day 2125

25. Period of Embryo
Yolksac & Folding of embryo
4th week
27

26. Cephalocaudal folding at various stages of
development ( sagital midline section)
End of I
month
28

27. 5 weeks old embryo
29

28. Derivatives of germ layers & neural crest
30

29. The Fetal Period (3rd month to Birth)
31

30. Fetal Period
Monthly changes (3rd month)
Head constitutes half
of crown rump length
Face becomes more
human looking
Primary ossification
centers are present in
long bones & skull
External genitalia
develop
32

31. Fetal Period
4th to 5th month
Head size is 1/3rd of
crown heel length
Fetus lengthens
rapidly
Fetal movements can
be felt by mother
33

32. Fetal Period
6th to 7th month
Fetus obtains well
rounded contours due
to deposition of
subcutaneous fat
50% of full term
weight added
34

33. Fetal Period
9th month
Skull has the largest
circumference of all
the parts of the body
Normal weight: 3000-
3400 gms
CRL – 36 cms
CHL – 50 cms
35

34. Craniofacial development
36

35. Head formation
Neural tube produced by
formn & fusion of neural
folds
Anterior part of tube
expands as forebrain,
midbrain & hindbrain form
but a small amount of
mesenchyme remains–
embryonic CT
Lateral to neural tube is
paraxial mesoderm segments
to form somatomeres--somites
37

36. Part of neural tube that
forms hindbrain devps 8
bulges– rhombomeres
Migration of neural crest –
provides embryonic CT
Neural crest cells arise from
– midbrain & first 2
rhombomeres
38

37. Migrating streams of
neural crest cells
express homeobox
genes
39

38. Pharyngeal arch
During 4th week,
lateral plate
mesoderm of
ventral foregut
segments to form 5
bilateral
mesenchyme
swellings–
pharyngeal arches
40

39. Pharyngeal arches
41

40. Each PHARYNGEAL
ARCH consists of
Central cartilage rod
Muscular component
Vascular component
Nervous element
42

41. Arch anatomy
43

42. PHARYNGEAL
ARCH
NERVE
Mandibular arch
Trigeminal
N.
MUSCLES
Cranial somatomere 4
CARTILAGE
MECKEL’S:
(41st - 45th day)
Muscles of mastication
malleus & incus
Artery: Mylohyoid,
Ant.belly of digastric,
Maxilary
Tensor tympani &
sphenomandibu
Artery
lar lig.,ant.lig.of
Part of ECA Tensor palatine
malleus
Hyoid arch
Facial N.
Cranial somatomere 6
ARTERY:
Stapedial
FACIALEXPRESSION,
post.belly of digastric,
stylohyoid,
stapedius
RIECHERT’S
(45th - 48th day)
Stapes,styloid P
stylohyoid lig.
lesser horn &
upper body of
hyoid
44

43. PHARYNGEAL
ARCH
IIIrd arch
NERVE
Glossopharyngeal N.
Artery: CCA
IV th arch
Vagus N.
Superior laryngeal N.
Artery: arch of aorta
Right subclavian &
brachicephalic
MUSCLES
SKELETON
Stylopharyngeus Greater horn
&lower body of
Cranial
hyoid
somatomere 7
Cricothyroid
Laryngeal
Thyroid
levator palatine, cartilages
cartilage
constrictors of
pharynx
Occiptal somites 2,4
VI th arch
Recurrent laryngeal N. Intrinsic muscles
of larynx
Cricoid &
arytenoid
Artery: pulmonary &
Ductus arteriosum
Occiptal somites 1,2
45

44. PHARYNGEAL POUCHES
POUCH STRUCTURE FORMED
First
Second
Auditory tube,middle
ear cavity
Palatine Tonsil
Third
Inferior
parathyroids,Thymus
Fourth
Superior
parathyroids,
Fifth
Parafollicular cells of
thyroid
46

45. PHARYNGEAL CLEFTS
First cleft (dorsal)
External acoustic meatus
2nd, 3rd & 4th clefts obliterate
by caudal overgrowth of
Hyoid arch
47

46. Branchial arch anamolies
Classification:
Unilateral-- Hemifacial microsomia or
Goldenhar’s syndrome
Bilateral-- Mandibulofacial dysostosis
48

47. Hemifacial microsomia or Goldenhar’s
syndrome
Features:
i.
assymetrical
anamolies of pinna &
middle ear
ii.
Deficiencies in malar,
temporal & ramus
iii. Facial paresis
iv. Pseudomacrostomia
49

48. Goldenhar’s syndrome
Cause:
Hematoma initiated in
stapedial artery system
Displacement & destruction of
local mesenchyme
Delay in the diff of 1st & 2nd arch
structures
Asymmetrical anomalies
50

49. 51

50. Treacher collin syndrome
Pathogenesis:
Neural crest cells
syphoned away &
redistributed in a
haphazard fashion
52

51. Anamolies of pharyngeal pouches
Pharyngeal fistulae & cysts
Etiology :
o Defect in the development of the 2nd pharyngeal
pouch
53

52. Development of face
( 24th & 38th day)
End of 4th week– facial prominences appear
54

53. During 5th week nasal
placodes invaginate to
form nasal pits
Edges of each pit
raised above the
surface
Medial raised edge-MNP
Lateral raised edge-LNP
55

54. Formation of lip, nose & cheeks
FNP
56

55. Development of eye
Ectodermal thickening
– lens placode
sinks below the surface
& cut of from ectoderm
Developing eyeball
produces bulging
directed laterally
57

56. 58

57. 59

58. PROMINENCE
STRUCTURES FORMED
1
Frontonasal
Forehead, Bridge of nose,
Medial & Lateral nasal
prominences
2
Maxillary (P)
Cheeks, lateral portion of
upper lip & UPPER JAW
3
Medial nasal
(P)
Philtrum of upper lip, Crest &
tip of nose
4
Lateral nasal
Alae of nose
(P)
Mandibular(P) Lower lip & LOWER JAW
5
60

59. Anomalies of face
Defects of rhomboencephalic organizing
center, which is responsible for induction of
viscerofacial skeleton ---- account for
dysmorphology of middle & lower 3rd of
face.
61

60. Anomalies of face
Facial clefts
Mandibular midline
cleft: failure of
mandibular process to
merge
Bilateral clefting of
upperlip : failure of
MNPs to merge with
maxillary prominences
62

61. Anomalies of face
Unilateral cleft lip
Median cleft lip
Oblique facial cleft
63

62. Anomalies of face
Microstomia or
macrostomia:
Merging of maxillary &
mandibular prominences
beyond or short of the site
for normal development
64

63. Anomalies of face
Fetal alcohol syndrome
Deficiency in MNPs
Features:
mandible
prognathic in reln to
midface
marked
underdevelopment of
premaxilla
65

64. Anomalies of face
The preventable tragedy:
Fetal Alcohol Syndrome
Seen in child whose mother consumes alcohol during pregnancy
66

65. Anomalies of face
Craniofacial developmental cysts
Named acc. to site in
which they develop:
1. Nasolabial cysts
2. Globulomaxillary
cyst
3. Median mandibular
cyst
67

66. Development of tongue (4th week)
Tongue arises in the ventral wall of primitive oropharynx
from first 4 pharyngeal arches
68

67. Development of tongue
69

68. Development of tongue
70

69. Development of tongue
Taste buds arise by inductive interaction
b/w epithelial cells & gustatory nerve cells
Gustatory cells- 7th wk
Taste buds– 13 -15 wks
71

70. Development of tongue
Muscles of tongue–
floor of pharynx in
occipetal somite region
Embryological
components retain
initially established
nerve supplies
72

71. Anomolies of tongue
Ankyloglossia
Microglossia
Abberant thyroid tissue
Macroglossia
Bifid / trifid
tongue
Aglossia
73

72. DEVELOPMENT OF PALATE
INTERMAXILLARY
SEGMENT:
Formed by merging of the 2
medial nasal processes
It is composed of –
a) Labial component- forms
PHILTRUM
b) Upper jaw componentcarries 4 MAX.INCISORS
c) Palatal component- forms
PRIMARY PALATE
74

73. Formation of definitive/ secondary palate
6th week– 2 lateral palatal
shelves devp
Secondary nasal septum
grows
7th week– palatal shelves
grow & lie vertically
2 peaks of DNA synthesis
occur here:
initial shelf outgrowth
vertical shelf elongation
75

74. 8th week
Stomodeum enlarges
Tongue drops
Vertically inclined
palatal shelves
become horizontal
Shelves contact each
other in midline–
forms sec. palate
By 12th week, fusion
of palatal processes is
complete
76

75. DEVELOPMENT OF PALATE
(occlusal view)
77

76. DEVELOPMENT OF PALATE
(frontal view)
78

77. THEORIES OF PALATAL SHELF ELEVATION :
EXTRINSIC FORCES
Descent of tongue
Myoneural activity with in tongue
Shelves pushed up by tongue
Mouth opening reflexes
79

78. INTRINSIC FORCES
 Hydration and polymerisation of intercellular
substance
 Differential growth on one side of palatal shelf
 Turgor produced by build up of HYALURONIC ACID
 SEROTONIN release from neural tissue.
 ACCUMULATION of HYALURONIC ACID
 Mesenchymal cell biosynthetic activity
 Changing amounts of
GLYCOSAMINOGLYCANS(GAG)
80

79. Palatal clefts
Defective fusion of various components of palate
Causes:
a.
b.
c.
d.
e.
f.
g.
Defective shelf fusion
Failure of shelves to elevate
Failure of tongue to drop from b/w shelves
Smallness of shelves
Inhibition of fusion process itself
Delayed elevation of shelves
Failure of medial edge epithelial cell death
81

80. Formation of organ systems especially the pharyngeal
arches and palate
28th – 38th day – Primary palate  Cleft lip &/or
palate and other Facial Clefts
42nd -55th day – Secondary palate  Cleft palate
82

81. Prenatal development of maxilla
Maxilla arises from a single centre of
ossification in the mesenchyme of the
maxillary process of the 1st arch
No primary cartilage exists in the maxillary
process
Centre of ossification is associated with the
cartilage of nasal capsule
83

82. Development of maxilla
The centre of ossification appears in the
angle between the division of an nerve (i.e.
where the anteriosuperior dental nerve is
given of from the inferior orbital nerve) just
above the canine tooth dental lamina
84

83. Developing elements of maxilla
Neural
Alveolar
Zygomatic
Palatal
Cartilaginous
85

84. As a result of bone deposition --a bony trough forms
for the infra orbital nerve
From this trough a bony downward extension forms
the lateral alveolar plate for the maxillary tooth germs
Ossification spreads in to the palatine process to form
hard palate
The medial alveolar plate develops from the junction
of the palatal process & main body of the forming
maxilla
This plate together with its lateral counterpart forms a
trough of bone around the maxillary tooth germs,
which eventually become enclosed in bony crypts
86

85. Development of mandible
Derived from
ossification of an
osteogenic membrane
at 36 to 38 days of
development
At 6th week, a single
ossifcation center for
each half of mandible
arises at bifurcation of
inferior alveolar nerve
87

86. 88

87. Fate of meckel’s cartilage
Dorsal end ossifies to
form: malleus & incus
Disappears by 24th week
after conception
Parts transform into:
sphenomandibular
ant. Malleolar ligament
Ventral end forms
accessory endochondral
ossicles
89

88. b/w 10th -14th weeks,
secondary accessory
cartilages appear to
form
head of condyle
part of coronoid
process
mental protruberance
90

89. Thus mandible is membrane bone developed in relation to the nerve of the
1st arch & almost independent of Meckel’s cartilage. The mandible has
neural, alveolar & muscular elements & its growth is assisted by the
development of secondary cartilages
91

90. Anamolies of mandible
1. Agnathia : mandible grossly deficient/
absent
cause: deficiency of neural crest tissue in
lower part of face
92

91. Anamolies of mandible
2. Micrognathia: characteristic of
Pierre robin syndrome
Treacher collins syndrome
Downs syndrome
Turner syndrome
Cause: A central dysmorphogenic mechanism of
neural crest production, migration or destruction
93

92. Anamolies of mandible
3. Macrognathia:
prognathism
inherited condition
seen in hyperpituitarism
94

93. Embryological basis of dental tissue genesis
4th week of intra uterine life
Lined by str. squ epi
i.e oral ectoderm
CT cells overlying ectoderm are
ectomesenchyme in origin,
induce tooth devp
Ruptures at 27th
day of gestation
95

94. Teratogenic effects of embryonic
development
Teratogen : any substance, agent or process
that interferes with normal prenatal
development resulting in one or more
abnormalities in children
96

95. Susceptibility to Teratogenesis
97

96. Drugs
/chemicals
Alcohol
Infections
Maternal
conditions
Cytomegalovir Age
us
General health
Rubella
Thalidomide
Diabetes
Anticonvulsants Syphilis
mellitus
Antidepressants Toxoplasmosis
Corticosteriods Varicella
Radiation
Exposure
98

97. Conclusion……..
99

98. References….
1. Craniofacial Development : Geoffrey H.SPERBER(2001)
2. Textbook Of Craniofacial Growth : MOYERS
3. Oral anatomy,histology & embryology 3rd edition :
B.K.B.BERKOWITZ
4. Langman’s medical embryology 9th edition : T.W.SADLER
5. Scientific foundations in dentistry: COHEN
6. Fundamentals of craniofacial growth(1997) : ANDREW
D.DIXON
7. Human embryology – 7th ed – Inderbir Singh
8. Ten cate’s Oral Histology – 6th ed – Antonio
9. Essentials of Facial Growth – Enlow
10. DCNA: Vol 19: (1) : 1975
100

99. THANK
YOU
101

100. Thank
you
102

101. Thank
you
103