A detailed description of pre-natal and post-natal development of the mandible, with a brief description of theories of growth, for education purposes by Post Graduate students of Orthodontics and Dentofacial Orthopaedics

1. DEVELOPMENT OF
MANDIBLE
Dr. KUNAAL AGRAWAL
PG STUDENT
DEPT. OF ORTHODONTICS
GDCRI, BANGALORE

2.  Introduction
 Definitions
 Prenatal growth of mandible
 Mandible at birth
 Theories of growth
 Types of ossification
 Postnatal growth
 Age changes in mandible
 Developmental anomalies
 Conclusions
 Bibliography
CONTENTS

3. INTRODUCTION
 Largest, strongest,
heaviest bone of face
 Attachment by
ligaments & muscles
only
 TMJ: ginglymo
diarthrodial joint

4. Mandible – Anatomical Features

5. Muscle Attachments – Lateral Surface

6. Muscle Attachments – Medial Surface

7. DEFINITIONS
GROWTH: Entire series of sequential anatomic and physiologic
changes taking place from the beginning of prenatal life to
senility - Meridith
DEVELOPMENT: Refers to all the naturally occurring
unidirectional changes in the life of an individual from its
existence as a single cell to its elaboration as a multifunctional
unit terminating in death - Moyers
GROWTH: Growth usually refers to an increase in size and
number – Proffit

8. GROWTH
Pre-natal
Post-natal

9. PRENATAL GROWTH
 Cartilages and bones: from embryonic neural
crest cells
 Migrate ventrally to form mandibular (and
maxillary) facial prominences
 Differentiate into bones and connective
tissues
NEURAL CREST CELLS

10.  1st structure: Mandibular division of trigeminal nerve,
preceding the ectomesenchymal condensation, forming
first (mandibular) pharyngeal arch
 Prior presence of the nerve has been postulated as
requisite for inducing osteogenesis by the production of
neurotrophic factors
 Mandible is derived from ossification of an osteogenic
membrane formed from ectomesenchymal condensation
at 36 to 38 days of development
 This mandibular ectomesenchyme must interact initially
with the epithelium of the mandibular arch before primary
ossification can occur; the resulting intramembranous
bone lies lateral to Meckel’s cartilage of the first
(mandibular) pharyngeal arch

11. Developing brain & the pericardium (4th week IUL)
2 prominent bulges on the ventral aspect of the embryo
(separated by stomodeum)
 The floor of the stomodeum is formed by the bucco-
pharyngeal membrane, which separates it from the
foregut

12. At this stage Mandibular arch
forms the lateral wall of the
stomodeum
This arch gives off a bud from its
dorsal end --- maxillary
process
And maxillary process grows
ventro-medially, cranial to the
main part of the arch ---
mandibular process

14.  2nd bone to get ossified (after clavicle)
 6th week of IUL
OSSIFICATION

15.  From the primary center below and around the inferior
alveolar nerve and its incisive branch, ossification spreads
upwards to form a trough for the developing teeth
1° center of ossification
Inferior Alveolar Nerve
& Incisive branch
Trough for developing teeth
BELOW AROUND

16.  Spread of the intramembranous ossification dorsally
and ventrally forms the body and ramus
 The prior presence of the neurovascular bundle
ensures the formation of the mandibular foramen and
canal and the mental foramen
 From center of ossification bone formation spreads:
 Anteriorly – midline (separated by fibrous tissue)
 Posteriorly – where mandibular nerve divides into lingual
and inferior alveolar nerves
• Bone formation spreads rapidly and
surrounds the inferior alveolar nerve to form
mandibular canal
• Intramembranous ossification spreads in
anterior and posterior directions & forms the
Body & Ramus of the mandible
Ossification spreads posteriorly to form ramus of
mandible, turning away from Meckel’s cartilage

17. The mesoderm of the lateral plate of the ventral
foregut becomes segmented to form a series of
five distinct bilateral mesenchymal swelling
called as the Pharyngeal Arches
FORMATION OF PHARYNGEAL ARCHES

18. 4th Week Embryo

19. 4th Week Embryo

20. CONTENTS of
EACH ARCH
Skeletal Element
Striated Muscle
Nerve
Artery

21. Internal view of pharyngeal floor and cut arches

22. MANDIBULAR ARCH
1. Meckel’s Cartilage
2. Musculature
3. Mandibular Nerve
4. Arteries
 Maxillary artery
 External carotid artery

23.  41st to 45th day of
intrauterine life
 Provides a template for
development of mandible
 Extends from the otic
capsule to the midline of
mandibular symphysis
MECKEL’S CARTILAGE
Mandibular division of trigeminal nerve
Neurotrophic factors
Osteogenesis
Ossification of Meckel’s Cartilage

24. The mandible is ossified in the fibrous membrane covering the
outer surfaces of Meckel's cartilage
These cartilages form the cartilaginous bar of the mandibular arch
and are two in number, a right and a left
Their proximal or cranial ends are connected with the ear capsules,
and their distal extremities are joined to one another at the
symphysis by mesodermal tissue
Meckel’s cartilage has a
close relationship to the
mandibular nerve, at the
junction between posterior
and middle thirds, where
the mandibular nerve
divides into the lingual and
inferior dental nerve

25.  Lacks enzyme phosphatase found in ossifying
cartilage that precludes its ossification
 Malleus, Incus (from proximal ends of each
cartilage)
 Sphenomandibular ligament (as far as the
lingula)
 Perichondrium of cartilage persists as
sphenomandibular ligament
 Disappears by 24th week
FATE OF MECKEL’S CARTILAGE

26.  By 10th to 14th week of I.U.L. secondary
cartilage is seen in region of coronoid process
 Develops within temporalis muscle as its
predecessor
 Incorporated into intramembranous bone of
ramus
 Disappears before birth
CORONOID PROCESS

27. MENTAL REGION
 Secondary cartilages on either side of the
symphysis, one or two in number appear and ossify
by 7th month IUL – variable number of mental
ossicles
 By 1st year of post natal life incorporated into the
intramembranous bone and ossified completely
 Mental Ossicles

28.  5th week of IUL
 As mesenchymal condensation
above ventral part of developing
mandible
 Al about 10th week IUL, it
develops into a cone-shaped
cartilage
 Ossification: 14th week IUL
 Inferior migration and fusion with
ramus by 4th month IUL
 Replaced by bone but proximal
end persists into adulthood
acting as growth cartilage and
articular cartilage till 25 years of
adulthood
CONDYLAR PROCESS
Condylar head separated from
temporal bone by thin disc of
connective tissue – future articular
disc

29. DIFFERENTIAL GROWTH
During fetal life
8 weeks - mandible > maxilla
11 weeks - mandible = maxilla
13 – 20 weeks - maxilla > mandible
At Birth
Mandible tends to be retrognathic
Early post natal life - orthognathic
Cephalocaudal Gradient of Growth

30.  Two halves of mandible are not fused
 Joined by connective tissue at midline
 Condylar development is minimal
 No articular eminence in glenoid fossa
 Coronoid process: relatively large and
projects well above condylar process
 Two rami quite short
 Body is merely an open shell,
containing deciduous tooth buds
 Mandibular canal runs low in body
 Angle of mandible is obtuse: about 1720
 Mental foramen nearer to lower border
MANDIBLE AT BIRTH

31. THEORIES OF GROWTH
1.
• GENETIC THEORY
2.
• SUTURAL THEORY
3.
• CARTILAGENOUS THEORY
4.
• FUNCTIONAL MATRIX THEORY
5.
• CYBERNATIC THEORY

32. 1. GENETIC THEORY
 Genes determine phenotype
 More assumed than proven
 Lacked scientific
understanding
RAYE STEWART – 1950’S TO 1970’S

33. 2. SUTURAL THEORY
 “The primary event in sutural growth is the
proliferation of connective tissue between the two
bones. If sutural tissue proliferates, it creates the
space for appositional growth at the borders of the
bones”
 Functions of sutures:
 To unite bones
 To absorb forces
 To act as joints
 To act as growth sites, not centers
SICHER – 1955

34.  Transplants of sutures fail to grow in culture
medium though provided with same environment
and conditions
 Extirpation of sutures has no appreciable effect on
growth of skeletal tissues
 The shape and growth within sutures is
dependent on external stimuli (growth sites)
 Microcephaly and hydrocephaly raise doubts
about the intrinsic genetic stimulus at sutures
EVIDENCES AGAINST SICHER’S THEORY

35. 3. CARTILAGENOUS THEORY
 Intrinsic growth
controlling factors
 Cartilage
 Periosteum
 Cartilagenous sites –
primary growth centers
JAMES SCOTT

36. 4. FUNCTIONAL MATRIX
THEORY
 “Growth of the face as a response to
functional need and neurotrophic influence
and is mediated by the soft tissues in which
the jaws are embedded”
MELVIN MOSS - 1969
FMT
SKELETAL UNITFUNCTIONAL MATRIX

37.  Muscles, Glands, Nerves, Vessels, Fats, etc
FUNCTIONAL MATRIX
Capsular
Periosteal
SKELETAL UNIT
Microskeletal Unit
Macroskeletal Unit
 Bones, Cartilage, or Tendinous Tissues

38. CAPSULAR M.
GROWTH OF
CAPSULAR MATRIX
EXPANSION OF THE
CAPSULE
RESPOND TO VOLUMETRIC
EXPANSION
CHANGE IN THE SPATIAL
POSITION
EMBEDDED MACRO-SKELETAL UNIT
IS PASSIVELY AND SECONDARILY
TRANSLATED IN SPACE
ALTERATION IN SIZE AND
SHAPE OF THEIR MICRO-
SKELETAL UNITS
COMBINATION OF MORPHOLOGIC EFFECTS OF
COMPRISES THE TOTALITY OF MANDIBULAR GROWTH
PERIOSTEAL M.

39.  Divided into several
skeletal subunits
 The basal bone of the
body forms one unit, to
which are attached the
alveolar, coronoid,
angular, and condylar
processes and the chin

40.  The functioning of the related tongue and
perioral muscles and the expansion of the oral
and pharyngeal cavities provide stimuli for
mandibular growth to reach its full potential
 The growth pattern of each of these skeletal
subunits is influenced by a functional matrix
that acts upon the bone:
 Teeth – alveolar unit
 Temporalis muscle – coronoid process
 Masseter & Medial pterygoid – angle & ramus
 Lateral pterygoid – condyle
Of all the facial bones, the mandible undergoes the most growth post-
natally and evidences the greatest variation in morphology

41.  Growth results from cell division of differentiated
chondroblasts ---- general extrinsic factors (somatotropic
hormone, sexual hormones, thyroxine)
 Growth results from cell division of prechondroblasts ----
local extrinsic factors
 The Servosystem theory uses the Cybernatic language
of information & communication as a tool to explain the
influence of various factors --- extrinsic & intrinsic – on
craniofacial growth
5. SERVOSYSTEM THEORY
PETROVIC & STUZMANN – 1970’s

42.  Demonstrates qualitative and quantitative
relationship between observed and
experimental findings
CYBERNATIC MODEL OF MANDIBULAR GROWTH
PETROVIC – 1977
Signals can be physical, chemical or electromagnetic in nature
Input Process Output
Transfer Function
Input OutputCYBERNATIC
SYSTEM

43. Release of
Hormones (Command)
Hormones
OCCLUSION
(Comparator)
Periodontium,
Teeth
Musculature
Joint
Mastication
(Performance)Deviation Signal
Brain
(sensory engram)
Actuator (Motor Cortex)
Output
Actuating
signal
Growth at condyle
(Controlled System)
Position of Maxillary
Dental arch (Ref Input)
LPM & RDP
(Coupling system)
GROWTH OF MANDIBLE
(SERVOSYSTEM THEORY)

44.  Multi-factorial theory
VON LIMBORGH’S THEORY -
1970
LOCAL
EPIGENETIC
GENERAL
EPIGENETIC
INTRINSIC
GENETIC
LOCAL
ENVIRONMENTAL
GENERAL
ENVIRONMENTA
L

45.  Growth and
enlargement of
bones occur towards
wide end of ‘V’ due
to differential
deposition and
resorption
ENLOW’S V-PRINCIPLE

46.  ‘The growth of any given facial or cranial part
relates specifically to other structural and
geometric “counter” parts in the face and
cranium’
ENLOW’S COUNTERPART PRINCIPLE
Regional Part Counter Part
Balanced Growth

47.  Examples:
 Maxillary arch is counter part of mandibular arch
 Vertical span of the mandibular ramus, is the vertical
counterpart of orbital and nasal maxillary component
 Mandible has a coronoid process, the maxilla has a
zygomatic process
 Maxilla has a maxillary tuberosity, the mandible has
lingual tuberosity, each counterpart to each other
 Middle cranial fossa is counterpart to pharyngeal
space

48.  Ingrowth of blood vascular elements into various
parts of the cartilaginous skeleton
 These areas become the centers of ossification, at
which cartilage is transformed into bone and islands
of bone appear in the sea of surrounding cartilage
 The cartilage continues to grow rapidly but is
replaced by bone with equal rapidity
 Examples:
 Synchondroses
 Condylar cartilage
 Nasal septal cartilage
TYPES OF OSSIFICATIONS
ENDOCHONDRAL OSSIFICATION
Morphogenetic adaptation
providing continued
production of bone in special
regions that involve relatively
high levels of compression

49.  Bone forms by secretion of bone matrix directly
into the connective tissues, without any
intermediate form of cartilage
 Undifferentiated mesenchymal cells of
membranous connective tissue transform into
osteoblasts and secrete osteoid matrix
INTRAMEMBRANOUS OSSIFICATION
 Examples:
 Cranial vault
 Maxilla
 Facial bones
 Mandible, except
condyle
Occurs in areas of Tension

50.  Whole body of mandible, except anterior part
 Ramus of mandible, as far as mandibular
foramen
DERIVATIONS OF MANDIBULAR PARTS
Intramembranous Ossification
 Anterior portion of mandible (symphysis)
 Part of ramus, above mandibular foramen
 Coronoid process
 Condylar process
Endochondral Ossification

51.  Main sites: condylar cartilages, posterior
borders of rami and alveolar ridges
 Areas of bone deposition: increase in height,
width and length
 However, superimposed upon this basic
incremental growth are numerous regional
remodelling changes that are subjected to the
local functional influences involving selective
resorption and displacement of individual
mandibular elements
POSTNATAL GROWTH

53. Different aspects of growth of maxilla and mandible

54.  Increase in width: resorption on inside and
deposition on outside
 Increase in length: drift of ramus posteriorly
 Increase in height: eruption of teeth
BODY
RAMUS
 Deposition
Posterior part
 Resorption
Anterior part

56.  Superior part of
ramus below sigmoid
notch:
 Lingual – Deposition
 Buccal – Resorption
 Inferior part of ramus
below sigmoid notch:
 Buccal – Deposition
 Lingual – Resorption

57.  The lower part of the
ramus below the
coronoid process has a
twisted contour
 Its buccal side faces
posteriorly towards the
direction of backward
growth and this, has a
depository type of
surface
 The opposite lingual
side, facing away from
the direction of growth,
is resorptive

59.  Direction of growth: Upwards and
Backwards
 Direction of growth depends on
whether the patient is horizontal or
a vertical grower
CONDYLE
Why does Condyle undergo Endochondral Ossification?
 Because the condyle grows in a direction towards its
articulation of the temporal bone ---- area of direct
compression
 An intramembranous type of growth could not
operate, because the periosteal mode of
osteogenesis is not pressure adapted and has a low
threshold for compressive forces

60.  Endochondral growth
occurs only at the
articular contact part
of the condyle,
because this is where
pressure exists at
levels that would be
beyond the tolerance
of the bone’s vascular
soft tissue membrane
The real functional significance of the
condylar cartilage thus involves an
avascular and matrix firm adaptation
for regional pressure and movable
articulation
Enclosing bony cortices – are produced by
periosteal endosteal osteogenic activity;
these vascular membranes are not subject
to the compressive forces of articulation but
are under tensional forces

61.  Secondary cartilage (does not develop by
differentiation from the established primary
cartilages of the fetal skull)
Under ectopic presence of pressure
Localized ischemia and anoxia
Induce chondrogenesis from pool of
undifferentiated connective tissue cells, rather than
osteogenesis

62.  Condylar cartilage doesn’t have a measure of
intrinsic genetic programming
 But extra-condylar factors are needed to sustain
this activity
Current Concept
Extra-Condylar Factors
Physiologic Inductors
Intrinsic and Extrinsic
Biomechanical Forces

63.  Lingual and buccal
sides are resorptive –
narrow neck
 This occurs due to
periosteal resorption
combined with
endosteal deposition
 Follows Enlow’s “V”
principle
 Some influence from
Lateral Pterygoid
muscle
CONDYLAR NECK

65. RAMUS-CORPUS JUNCTION – THE ANTEGONIAL NOTCH

66.  To produce backward movement of
ramus, anterior margin of ramus &
coronoid process, must undergo
progressive removal
 Recognized by JOHN HUNTER & later
verified by HUMPHREY (1864)
 Forward facing anterior border of
coronoid process is resorptive around
temporal crest on lingual side
 Greater portion of lingual surface is
depository
 Entire buccal surface is resorptive
 Follows V-Principle
 Movement of this ‘V’ towards its wider
ends
CORONOID PROCESS

67. Bone Deposition – Inner surface
Bone Resorption – Outer
surface
Growth in upward & backward
direction

68.  Size depends upon ramus –
corpus angle
 Any change in the ramus
corpus angle results in
gonial angle changes which
is largely produced by
ramus remodeling, not the
corpus and is determined
by the remodeling direction
of the ramus with its condyle
 Selective bone remodelling
causes flaring of angle of
mandible on age
advancement
ANTEGONIAL ANGLE

69.  Buccal surface:
 Bone deposition – posteroinferior surface
 Bone resorption – anterosuperior surface
 Lingual surface:
 Bone deposition – anterosuperior surface
 Bone resorption – posteroinferior surface
Selective resorption and deposition of bone causes flaring
of angle of mandible

70.  More vertical orientation
 As long as the ramus is
actively growing in a
posterior direction, this
is accomplished by
greater amounts of
bone addition on the
inferior part of the
posterior border than on
the superior part
RAMUS UPRIGHTING

71.  In childhood as development proceeds ramus
must lengthen vertically to a much greater
extent than it broadens horizontally ---- to
accommodate the vertical nasomaxillary growth
that is taking place at the same time
 The gonial angle must undergo change in order
to prevent change in the occlusal relationship
between the maxillary and mandibular arches
Why does Ramus Uprighting occur?

72.  However, vertical
lengthening of the ramus
continues to take place
after horizontal ramus
growth slows down or
ceases, to match the
continued vertical growth of
the midface
 To achieve this, condylar
growth may become more
vertically directed and a
different pattern of ramus
remodeling can also
become operative
 The direction of deposition
and resorption reverses

73.  Grows posteriorly and
medially by
deposition
 Resorptive field ----
below lingual fossa
LINGUAL TUBEROSITY (LINGULA)

74.  Adds to the height and
thickness of the mandibular
body
 Maintains occlusal
relationship during
differential mandibular &
midfacial growth
 Maintains vertical height
 Adaptive remodeling makes
orthodontic tooth movement
possible
 Develops in response to
presence of teeth (functional
matrix)
ALVEOLAR PROCESS

75. During the descent of the maxillary arch and the vertical drift of the mandibular
teeth, the anterior mandibular teeth simultaneously drift lingually and
superiorly. This produces a greater or lesser amount of anterior overjet and
overbite

76.  Formed by mental ossicles from
accessory cartilage and ventral end
of Meckel’s cartilage
 Poorly developed in infants
 Formed by osseous deposition
during childhood
 Prominence is accentuated by bone
resorption above it, ie, suprametale
region
 Protrusive chin is a characteristic
human trait
 More prominent in males
 Cortex is thick, dense, composed of
slow growing type of lamellar bone
 Underdevelopment of chin =
MICROGENIA
MENTAL PROTUBERANCE and CHIN

77.  Limited growth till fusion
 No widening post fusion
 Fuses in 18 months post
natally
SYMPHYSIS MENTI

78.  Infants ---- Laterally directed
 Adults ---- Posteriorly directed
 Due to:
 Forward displacement of mandible
 Posterior dragging of mental neurovascular bundle
MENTAL FORAMEN

79.  Relocates backward and
upward by deposition on
the anterior and resorption
from the posterior part of
its rim
 The foramen, from
childhood through old age,
maintains a constant
position about midway
between the anterior and
posterior borders of the
ramus
MANDIBULAR FORAMEN

80. MANDIBULAR NOTCH or INCISURA MANDIBULARIS

81.  Periosteal bone added - lingual surface of ramus just below
sigmoid notch continue down from condylar head around lingual
side of sigmoid notch, then extends up to the apex of coronoid
process
Periosteal bone deposition – lingual surface
Periosteal bone resorption – buccal surface
Results in shift of anterior base of neck in lingual direction

82.  Completed before adolescent growth spurt
 Intercanine width does not increase after 12 years
 Both molar and bicondylar width shows small
increase until growth in length ends
GROWTH IN WIDTH

83.  Continues through puberty
 Girls: till 14-15 years
 Boys: till 18-19 years
GROWTH IN LENGTH

84.  Continues in both sexes for a longer period
 Growth increase occurs with concomitant
eruption of teeth due to:
 development of the alveolar process
 uprighting of the ramus
 growth of condyles
GROWTH IN HEIGHT

85.  Width > Length > Height (T>S>V)
 Mandibular intercanine width is more likely to decrease
than increase after age 12
 Intercanine width is essentially completed by the end of
9th year in girls and the 10th year in boys
 Both molar and bicondylar widths show small increases
until the end of growth in length
 Growth of mandible continues at a relatively steady rate
before puberty
 On the average, ramus height increases 1-2 mm/year;
body length by 2-3mm/year
 In girls, growth in length of the jaw ceases by age 14-15
years
 In boys, it does not decline to the basal adult level until 18
years
TIMING OF GROWTH IN WIDTH, LENGTH AND HEIGHT

86. MISCELLANEOUS CONCEPTS

87.  Mental foramen – near inferior border, laterally
directed
 Mandibular canal – along lower border of mandible
 Angle of mandible – obtuse, around 1720
 Coronoid process is large and projects above level of
condyle
AGE CHANGES IN
MANDIBLEINFANTS

88.  Mental foramen –
midway between upper
and lower borders;
posterolaterally directed
 Mandibular canal – runs
parallel with mylohyoid
line
 Angle of mandible –
110-1200
ADULTS

89.  Mandibular foramen – near alveolar bone
 Mandibular canal – near alveolar bone
 Angle of mandible – about 1400
OLD AGE

90. DEVELOPMENTAL
ANOMALIESAgnathia: Congenital absence or gross deficiency of mandible
(indicating deficiency of migration of neural crest cells)
Micrognathia: Composed of several syndromes –
• Pierre Robin Syndrome
• Cri du Chat Syndrome
• Treacher Collin’s Syndrome
• Mandibulofacial Dysostosis
• Progeria
• Oculo-mandibulo dyscephaly (Hallermann-Streiff Syndrome)
• Turner Syndrome (XO)
Aplasia of mandible and hyoid bone (1st and 2nd arch syndrome):
Plus multiple defects of orbit and maxilla
Macrognathia: Hyperpituitarism, also genetic predisposition

91.  It can be concluded that the process of growth and
development of the mandible is very controversial with
many theories and hypothesis put forward, but none of
them have been able to convincingly explain the process
 The principal clinical issue in mandibular growth is the
extent to which the clinician can alter the mandibular
morphology
 An orthodontist who attempts to interrupt or redirect or
guide the growth of the craniofacial skeleton, without
knowing the mode, or direction or method of growth and
development will be like a sailor trying to cross the sea
without the help of charts to guide him through
CONCLUSIONS

92. BIBLIOGRAPHY
Craniofacial Development - Geoffery M.
Sperber
Shafer’s Textbook of Oral Pathology
Orthodontics, Principles and Practices – TM
Graber
Textbook of Orthodontics – Samir E. Bishara