Basic seminar on the general embryology with a fw slides on the growth and development of the mandible

1. GENERAL
EMBRYOLOGY,
DEVELOPMENT
& GROWTH OF
MANDIBLE
DR. IMAN ZUBAIR KHAN
JR 1
DEPT. OF ORAL MEDICINE &
RADIOLOGY1

2. CONTENTS :
 INTRODUCTION - A general aspect
 GROWTH & DEVELOPMENT
 FERTILIZATION
 CLEAVAGE
 FORMATION OF GERM LAYERS,
NOTOCHORD, NEURAL TUBE & YOLK SAC
 THE PHARENGEAL ARCHES
 FATE OF GERM LAYERS
 PRE-NATAL DEVELOPMENT OF MANDIBLE
 POST-NATAL DEVELOPMENT OF
MANDIBLE
 APPLIED ASPECTS
2

3. INTRODUCTION – GENERAL
ASPECT
 The study of formation & development of
embryo from the moment of its inception up to
the time when it is born as an infant is called
EMBRYOLOGY.
3

4.  There are 2 types cell division
MITOSIS MEIOSIS
MITOSIS : when the cell divides so that no.of
chromosomes and genetic configuration remains the
same. Daughter cells have diploid no.of
chromosomes (46).
MEIOSIS : The no.of chromosomes is halved and
the genetic information is not absolutely identical.
Gametes resulting due to meiosis have haploid no.of
chromosomes (23).
4

5. GROWTH & DEVELOPMENT
 Growth is an increase in size.
 Development is progress towards maturity.
- TODD
5

6. PERIODS OF PRE-NATAL
DEVELOPMENT
 PROLIFERATIVE PERIOD : Implantation and
enlargement of blastocyst occurs within 2 weeks
of development called proliferative period.
 EMBRYONIC PERIOD : This ranges from 3-8
weeks and is the differentiation of the three basic
tissue types and their specialization into organs
and organ systems.
 FETAL PERIOD : This is the period of growth.
6

7. FERTILIZATION
 The process of fusion of the male gamete (
sperm/spermatozoa ) with the female gamete (
ovum/oocyte ) is called FERTILIZATION.
 Fertilization takes place in the ampulla of the
uterine tube.
 This fusion results in the formation of ZYGOTE.
 As a result of fertilization
> the diploid no.of chromosomes is restored
> determination of sex takes place
> fertilized ovum begins to undergo division
7

8. 8

9. 9

10. CLEAVAGE
 The fertilized ovum undergoes a series of mitotic
divisions leading to
 3-cell stage , 4-cell stage , 5-cell stage etc.
 This process of subdivision is called CLEAVAGE.
 As this process continues the 16-cell stage is
called a MORULA.
 A cut section reveals INNER CELL MASS that is
surrounded by a layer of outer cells.
 The outer cells give rise to TROPHOBLAST & the
inner cell mass gives rise to EMBRYOBLAST.
10

11.  Fluid passes from into the morula from the
uterine cavity and separates the ICM and the
trophoblast hence the morula acquires the
shape of a cyst.
 Trophoblast cells become flat and ICM
attaches to one side of the trophoblast. This
stage is now called the BLASTOCYST & the
cavity is called the BLASTOCOELE.
 The side where ICM is attached is called
EMBRYONIC or ANIMAL pole and the
opposite side is called the ABEMBRYONIC
pole.
11

12. 12

13. 13

14. FORMATION OF GERM
LAYERS
 There is formation of a 3 layered disc as the
blastocyst develops called EMBRYONIC
DISC.
 The 3 germ layers making up this disc are
 Endoderm
 Ectoderm
 Mesoderm
14

15.  Some cells of the ICM differentiate into flat cells that
line the surface hence forming the 1st germ layer, i.e
the endoderm
 Remaining ICM cells become columnar forming the
2nd germ layer , i.e the ectoderm.
 A space appears between ectoderm & trophoblast
called AMNIOTIC CAVITY filled with AMNIOTIC
FLUID .
 The flattened cells spread & line the blastocystic
cavity . This lining is called HEUSER’S MEMBRANE ,
resulting cavity is called PRIMARY YOLK SAC.
 The cells of the trophoblast give rise to
EXTRAEMBRYONIC MESODERM . These lie
between trophoblast & flat endodermal cells .
15

16. 16

17. 17

18.  Small cavities appear in the EEM which join
together to form one large cavity called
EXTRAEMBRYONIC COELOM, thus resulting
in splitting of EEM.
 The part lining the inside of the trophhoblast
and outside amniotic cavity is called
PARIETAL MESODERM
(somatopleuric EEM or Chorionic plate)
 The part lining the outside of the yolk sac is
called the VISCERAL MESODERM.
 The developing embryo is now suspended in
the EEC and is attached to the wall of the
blastocyst by the unsplit part of EEM.
 This forms the CONNECTING STALK.
18

19. 19

20.  Two important structures are formed at this
stage
 CHORION: the trophoblast & underlying
somatopleuric mesoderm form chorion
 AMNION: the cells forming the wall of the
amniotic cavity form the amnion.
Due to EEM & EEC the yolk sac becomes
smaller and is now called the SECONDARY
YOLK SAC.
The lining cells now become cubical.
20

21. 21

22.  At one circular area near the margin of the disc,
the cubical cells of the endoderm become
columnar forming the PROCHORDAL PLATE.
 Some ectodermal cells near the tail end proliferate
& form an elevation that bulges into amniotic
cavity . This elevation is PRIMITIVE STREAK.
 The cells that proliferate pass sideways, pushing
between the ectoderm & endoderm forming the
INTRAEMBRYONIC MESODERM.
 This process of formation of primitive streak & IEM
is called GASTRULATION.
22

23. 23

24. 24

25. 25

26. 26

27.  Cranial end of the primitive streak enlarges to form the
PRIMITIVE KNOT.
 A depression appears in this structure called
BLASTOPORE, which later converts into NOTOCHORDAL
CANAL.
 Cells of the primitive knot multiply & pass cranially to form a
rod like structure reaching up to the prochordal plate. This
is the NOTOCHORDAL PROCESS.
 The notochordal process undergoes changes to convert it
into a canal and then a plate and finally into a rod like
structure called NOTOCHORD.
 Wide strip of ectoderm overlying the notochord becomes
thickened and forms the NEURAL PLATE which forms the
brain and spinal cord.
 Process of formation of the neural tube is called
NEURALISATION.
27

28. 28

29.  The IEM shows 3 subdivisions
 PARA-AXIAL mesoderm: mesoderm next to midline which
undergoes segmentation to form SOMITES.
 LATERAL PLATE mesoderm: mesoderm in the lateral
part of the embryonic mesoderm.
Cavity called INTRA EMBRYONIC COELOM appears in
the lateral plate mesoderm and splits it into
SOMATOPLEURIC & SPLANCHOPLEURIC layer.
 INTERMEDIATE mesoderm: layer betwen para-axial and
lateral plate mesoderm.
 The embryonic disc undergoes foldings at the cranial and
caudal ends called HEAD & TAIL FOLDINGS.
29

30. 30

31.  Lateral folds also appear and the endoderm is
converted into a gut that is divisible into
foregut, midgut & hindgut.
 After formation of the head fold, the gut is
closed cranially by the prochordal plate, which
is now called the BUCCOPHARENGEAL
MEMBRANE.
 Caudally the gut is closed by the CLOACAL
MEMBRANE.
31

32. 32

33. 33

34. 34

35. 35

36. THE PHARENGEAL ARCHES
 The foregut is bound ventrally by the pericardium,
dorsally by the developing brain, cranially it is at first
separated from the stomatodeum by the
buccopharengeal membrane.
 When this membrane breaks down, the foregut opens to
the exterior through the stomatodeum.
 Rod like thickenings of the mesoderm present in cranial
most part of the foregut are called PHARENGEAL
ARCHES.
 The endodermal wall of foregut is separated from the
surface ectoderm by a layer of mesoderm.
 Soon the mesoderm arranges in the form of 6 bars that
run dorsoventrally in the side wall of the foregut.
36

37.  Each of these bars grow ventrally in the floor of the
developing pharnyx and fuses with the corresponding
bar of the opposite side to form a PHARENGEAL
ARCH.
 In the interval between two arches, the endoderm
(lining the pharynx) is pushed outwards to form a
series of pouches called PHARENGEAL ARCHES.
 Opposite each pouch the surface ectoderm dips
inwards forming an ECTODERMAL CLEFT.
 There are 6 branchial arches.
1st BA- Mandibular Arch
2nd BA-Hyoid Arch
3rd 4th 5th 6th BA’s have no special names and the 5th BA
soon dissapears after its formation.
37

38.  Structures formed in mesoderm of each arch :
 Skeletal Element – this is cartilaginous in the
beginning . It may develop into bone , may disappear
or may remain cartilaginous.
 Straited Muscle- This is supplied by the nerve of the
arch. It may or may not retain the attachment to the
skeletal elements or may divide to form a no.of
distinct muscles.
 Arterial Arch-ventral to foregut is the VENTRAL
AORTA and dorsally there is DORSAL AORTA. A
series of arterial arches/aortic arches connect these
two aorta. One such arterial arch lies in each
pharengeal arch.
38

39. 39

40. 40

41. 41

42. FATE OF GERM LAYERS
42
ECTODERM
• Lining Epithelia, Glands, Others
ENDODERM
• Lining Epithelia, Glands
MESODERM
• Connective Tissue, Muscles,
Specialised Connective Tissue, Organs

43. 43

44. 44

45. PRE-NATAL DEVELOPMENT OF
MANDIBLE
 Mandibular arch gives off a bud from its dorsal end
called MAXILLARY PROCESS.
 It grows ventro-medially cranial to main part of the arch
which is called the MANDIBULAR PROCESS.
 Mandibular process of each side grow towards each
other and fuse in midline to give rise to mandible.
 First structure to develop in lower jaw :
 Mandibular division of Trigeminal nerve.
Neurotrophic factor produced by nerve induces
osteogenesis.
45

46. 46

47. 47

48.  Primary cartilage of first pharyngeal arch is
Meckel’s cartilage & it helps in formation of lower
jaw.
 Meckel’s cartilage first appears at 6th week IUL.
 It is a solid hyaline cartilaginous rod surrounded by
fibrocellular capsule.
 Ossification starts at the division of mental and
incisive branch of inferior alveolar nerve lateral to
meckel’s cartilage around 6th week IUL.
48

49.  From center of ossification bone formation
spreads:
 Anteriorly - midline
 Posteriorly - where mandibular nerve divides
into lingual and inferior alveolar branch.
 Bone formation spreads rapidly and
surrounds the inferior alveolar nerve to form
mandibular canal.
 Intramembranous ossification spreads in
anterior and posterior direction forms the
Body & Ramus of the mandible.
49

50. 50

51.  Anteriorly bone extends towards midline and comes in
approximation with similar bone forming on opposite
side.
 These two bones remain separated by fibrous tissue
mental symphysis untill shortly after birth.
 Continued bone formation increases size of mandible
with development of alveolar process to surround the
developing tooth germ.
 Ossification spreads posteriorly to form ramus of
mandible, turning away from meckel’s cartilage.
 This point of divergence is marked by lingula in adult
mandible.
51

52. 52

53.  FATE OF THE MECKEL’S CARTILAGE :
 Lacks enzyme phosphatase found in ossifying
cartilage thus precluding its ossification.
 Greater part of meckel’s cartilage degenerates
without contributing formation of mandible by 24th
week.
 Most posterior extremity forms incus and malleus of
inner ear.
 Fibrocellular capsule persists as sphenomandibular
ligament.
 Small part of its ventral end forms accesory
endochondral ossicles.
 Gets incorporated in the chin region of the mandible.
53

54.  SECONDARY CARTILAGES:
 Further growth until birth is influenced by appearance of
secondary cartilage .
 Between 10th and 14th week three secondary cartilages
develop:
 Condylar cartilage – largest and appears beneath the
fibrous articular layer of future condyle.
 Coronoid cartilage - seen associated with coronoid
process.
 Symphyseal cartilage – in the mandibular symphysis
region.
 Mandible develops largely by intramembranous
ossification and by endochondral ossification in
 Condylar process
 Coronoid process
 Mental region
54

55. CONDYLAR PROCESS
 Develops from condylar cartilage & appears as
separate area of mesenchymal condensation along
developing mandible around 8th week.
 This area develops in cone-shaped cartilage around
10th week.
 By the 14th week first evidence of endochondral bone
formation appears in condylar region.
 Cartilage fuses with mandibular ramus around 4th
month.
 Cartilage replaced by bone but upper end persists in
adulthood acting as Growth and Articular cartilage.
55

56. 56

57. CORONOID PROCESS
 Secondary cartilage appears in coronoid
process around 10-14th week.
 Cartilage grow as a response of developing
temporalis muscle.
 Coronoid cartilage becomes incorporated into
expanding intramembranous bone of ramus
and disappears before birth.
57

58. MENTAL REGION
 Throughout intrauterine life left and right
mandible are not fused at midline.
 Joined by connective tissue at midline.
 On either side of symphysis, symphyseal
cartilage appears between 10th & 14th week
post conception.
 Ossifies in the 7th month to form mental
ossicles in fibrous tissue of symphysis.
 Mental ossicles fuse with mandibular body at
the end of first year after birth.
58

59. POST-NATAL DEVELOPMENT
OF MANDIBLE
 Of the facial bones, the mandible undergoes
the largest amount of growth post-natally and
also exhibits the largest variability in
morphology
 The basal bone or the body of mandible
forms one unit, to which is attached the
alveolar process, the coronoid process, the
condylar process, the angular process, the
ramus, the lingual tuberosity and the chin.
59

60. RAMUS & BODY OF MANDIBLE
 The ramus moves progressively posterior by a
combination of deposition and resorption
 Resorption occurs on the anterior part of the ramus
while bone deposition occurs on the posterior region.
This results in drift of ramus in a posterior direction
 Body of the mandible lengthens as the ramus exhibits
bone deposition on the posterior aspect and
resorption on the anterior aspect
60

61. 61

62. ANGLE OF MANDIBLE
 On the lingual side of the angle of the mandible,
resorption takes place on the posterio-inferior aspect
while deposition occurs on the antero-superior aspect
 On the buccal side, resorption occurs on the anterio-
superior part while deposition takes place on the
postero-inferior part. This results in flaring of the angle
of the mandible as age advances
62

63. 63

64. LINGUAL TUBEROSITY
 The lingual tuberosity moves posteriorly by
deposition on its posterior facing surface
 Lingual tuberosity protrudes noticeably in a lingual
direction and that it lies well towards the midline of
the ramus.
 The prominence of the tuberosity is increased by the
presence of a large resorption field just below it.
 The resorption field produces a sizeable depression,
called the LINGUAL FOSSA.
64

65. 65

66. ALVEOLAR PROCESS
 As the teeth erupt the alveolar process develops and
increases in height by bone deposition at the margins
 The alveolar process adds to the height and
thickness of the body of the mandible
 In case of absence of teeth, the alveolar bone fails to
develop and it resorbs in the event of tooth extraction
66

67. THE CONDYLE
 The role of condyle in the growth of mandible has
remained a controversy. There are 2 schools of
thought regarding the role of the condyle:
 It was earlier believed that growth occurs at the
surface of condylar cartilage by means of bone
deposition.
 It is now believed that the growth of soft tissues
including the muscles and connective tissues carries
the mandible forward & away from the cranial base
(carry away phenomenon).
67

68. 68

69. CORONOID PROCESS
 The growth of the coronoid process follows the
enlarging “V” principle
 Viewing the longitudinal section of the coronoid
process from the posterior aspect, deposition occurs
on the lingual surfaces of the left and right coronoid
process
 Viewing it from the occlusal aspect, the deposition on
the lingual of the coronoid process brings about a
posterior growth movement in the “V” pattern.
69

70. 70

71. THE CHIN
 The chin is associated with a generalised cortical
recession in the flattened regions positioned between
the canine teeth.
 The process involves a mechanism of endosteal
cortical growth.
 Prominence of mental protuberance is accentuated
by bone resorption that occurs in the alveolar region
above it, creating a concavity.
71

72. APPLIED ASPECTS
DEFECTS
CONGENITAL ACQUIRED
Microsomia
Macrosomia Micrognathia
Goldenhar Syndrome Macrognathia
Treacher Collin Syndrome
72

73.  Micrognathia - Small jaw size
 Macrognathia - Big jaw size
 Agnathia - Total failure of development
 Microstomia - Excess fusion of the maxillary and
mandibular processes may result in microstomia.
 Macrostomia - Inadequate fusion of the maxillary
and mandibular processes with each other may lead
to an abnormally wide mouth. Lack of fusion may be
unilateral leading to lateral facial cleft.
73

74. 74

75.  Hemifacial microsomia –
Also called goldenhar syndrome
Due to lack of mesenchymal tissue or neural crest
cells resulting in underdeveloped mandible
75

76.  Midline mandibular cleft
Persistance of furrow between 2 mandibular
prominences
76

77.  Mandibular Dysostosis –
also called Treacher-collins syndrome
Due to disturbance in origin, migration &
interaction of neural crest cells.
Hypoplasia of mandible
77

78.  Pierre-Robin Syndrome -
Mandible is underdeveloped
Small body
Posteriorly placed condyle
Cleft palate
78

79.  Bifid condyle –
Rare
Most of them have a medial and lateral head
that is divided by an antero posterior groove.
Some condyles may be divided into an anterior
and posterior head
Cause is uncertain
79

80.  Condylar hyperplasia –
Excessive growth of one of the condyles.
Cause is unknown, but local circulating
problems, endocrine disturbances, and trauma
have been suggested as possible etiologic
factors.
80

81. REFERENCES
 HUMAN EMBRYOLOGY - I.B.SINGH
 ESSENTIALS OF ORAL HISTOLOGY & EMBRYOLOGY
- AVERY
 ESSENTIALS OF HUMAN EMBRYOLOGY -
B.S.PANDE
 TEXTBOOK OF ORTHODONTICS - BALAJI
 TEXTBOOK OF ORTHODONTICS -
GURKHEERAT SINGH
 Enlow DH, Harris DB – A study of the postnatal growth
of the human mandible, - Am J Orthod,1964;50:250-64
 Sicher H - The growth of the mandible - Am J Orthod,
1947;33:30-35
81

82. 82