Prenatal and postnatal development of mandible /certified fixed orthodontic courses by Indian dental academy

PRENATAL AND
POSTNATAL
DEVELOPMENT
OF MANDIBLE

INDIAN DENTAL ACADEMY

Leader in continuing dental education
www.indiandentalacademy.com

PRENATAL
DEVELOPMENT
OF MANDIBLE


CONTENTS
1. Period of Ovum
2. Period of Embryo
3. Period of Fetus
4. Meckel’s cartilage
5. Neonatal mandible

Period of Ovum
• 2 weeks
• 1.5 mm in length
• Cephalad differentiation not begun


Embryonal Period
• 14th to 56th day
• 3rd week- 3 mm
• 4th week- 5mm


4 week embryo

Contents of Mandibular Arch
1. Meckel’s cartilage
2. Musculature
3. Mandibular nerve
4. Maxillary and External Carotid Artery

Fetal period
• 8th week till birth
• Tremendous acceleration is the theme
• Meckel’s cartilage- precursor of
mandibular mesenchyme


Mandibular changes
•

STUDY OF HUMAN FETAL MANDIBLE
—Ingham, J. Dent. Res, 1932

• Observations:1. The alveolar plate lengthens more
rapidly than ramus
2. The ratio of alveolar plate length to total
mandibular length is reasonably constant

3. The width of the alveolar plate shows a
more rapid increase than does total
width
4. The ratio of the width between the
mandibular angle to the total width is
relatively constant during fetal life


Meckel’s Cartilage
• 41st – 45th day of IUL
• Template
• Otic capsule - Symphysis


Ossification of Meckel’s
cartilage
• Mandibular nerve

Neurotrophic
factor
Osteogenesis

cartilage
Ectomesenchymal condensation at 36-38 days

Osteogenic membrane

Primary ossification

Intramembraneous bone lateral to cartilage

cartilage
• Begins during 7th week
Woven bone

Lamellar bone

Haversian system– 5th month

Fate of Meckel’s Cartilage
1. Disappears by 24th week
2. Sphenomandibular ligament
3. Resorbs on lateral surface dorsal to
mental foramen
4. Ventrally- Accessory Endochondral
Ossicles

Fate of Meckel’s Cartilage

10th & 14th week
Sec. accessory
cartilages appear


Condylar Cartilage
Growth rate increases at
puberty(12 1/2-- 14 yrs) and
ceases by 20 yrs


Types of Ossification
•

1st one to ossify- 6th week of I.U.L

•

Two types of ossification:-

1. INTRAMEMBRANEOUS
2. ENDOCHONDRAL

Parts of Mandible derived from
• INTRAMEMBRANEOUS Ossification
1. Whole of body except anterior part
2. Ramus as far as mandibular foramen
•
1.
2.
3.
4.

ENDOCHONDRAL Ossification
Anterior part of mandible
Ramus above mandibular foramen
Coronoid process
Condylar process

NEONATAL MANDIBLE
• Low and wide ascending ramus
• Coronoid process is large
• Body- open shell
• Mandibular canal runs low

NEONATAL MANDIBLE

Differential Growth

At Birth

Fetal life
8 weeks– mandible>maxilla

Mandible retrognathic

11 weeks– mandible=maxilla

Early post natal life
Becomes orthognathic

13-20 weeks– maxilla>mandible


POST NATAL GROWTH OF
MANDIBLE


Contents
1.
2.
3.
4.
5.
6.
7.

Theories of growth
Mechanisms of bone growth
Skeletal units of mandible
Main sites of growth of mandible
Condyle and great puzzle
Current concept
Age changes in mandible

Theories of Growth
1. Genetic theory- Brodie,1941
2. Scott’s hypothesis, 1953
3. Sutural dominance theory- Sicher, 1955
4. Functional matrix theory- Moss, 1962
5. Van limborgh theory- 1970

Mechanisms of Bone Growth
1. REMODELING

2. DISPLACEMENT:• Primary displacement
• Secondary displacement


Enlow’s “V” Principle
• Growth movement
and enlargement
of many facial and
cranial bones or
parts of bones
occur towards the
wide ends of “V”


Enlow’s Counterpart Principle
• Growth of any given facial or cranial part
relates specifically to other structural and
geometric “counterparts” in the face and
cranium
Regional part

Counter part

Balanced growth

Growth Timings
•

Overall growth of mandible takes place
at different stages

•
1.
2.
3.

First there is increase in its
Width
Length
Height

Skeletal Units of Mandible


Main sites of growth of Mandible
•

Mandible undergoes largest amount of
growth postnatally and exhibits largest
variability in morphology

•

Principal growth sites are:1. Posterior surface of ramus
2. Condylar process
3. Coronoid process/ alveolar process

Symphysis Menti
• 4-12th month after birth, syndesmosis is
converted to synostosis
• No widening after fusion


Mental Foramen


Alveolar Process
• Adds to height of mandible
• Tooth absent- process fails to develop
• After tooth extraction, alveolar process
resorbs


Alveolar Process
• Buffer zone
• Adaptive
remodeling
makes
orthodontic tooth
movement
possible

Ramus
• Bridges pharyngeal
compartment
• Mandible in
occlusion with
maxilla
• Remodeled in a
posterosuperior
manner

Ramus to Corpus Remodeling
Bicondylar dimension established early
in childhood


Ramus to Corpus Remodeling
• Making room for
molars


Ramus and Middle Cranial Fossa
• Provides developmental potential for
adaptations required to place the corpus
in a continuously functional position
because of variations elsewhere in the
face and neurocranium.


• Antegonial notch• Single field of
resorption
• Mandibular foramen• Relocates backward
and upwards
• Sustains midway
location

Size of notch
depends
On angle


Lingual tuberosity
• Anatomic equivalent of maxillary
tuberosity
• Boundary between ramus and corpus
• Remodels in posterior and medial
direction
• Resorptive field below forms Lingual
Fossa

Coronoid Process
• Propeller like twist


Vertical V

Horizontal V

The Mandibular Condyle
• Historically- regarded as kind of
cornucopia
• No longer believed as a pacesetting
“master centre”
• Functions as regional field growth

The Mandibular Condyle
• Dual function1. Articular
2. Growth
Not a primary center of growth but rather
1. Secondary in Evolution
2. Secondary in Embryonic origin
3. Secondary in Adaptive responses

Condylar Growth Mechanism
• Special non vascular tissue
• Firm hydrophillic intercellular matrix
• Endochondral growth mechanism- specific
response to particular local circumstance


Histology of Condyle
• Capsular layerpoorly vascularised
• Proliferative layerprechondroblasts
closely packed with
scanty matrix
• Zone of Deposition
and Resorption

• Proliferative process
produces upward
and backward growth
movement
• Multidirectional
proliferative capacity


Neck of the Condyle
• Lingual and buccal
surfaces resorptive
• Condyle becomes
neck after
remodeling
• Endosteal surfaces
faces growth
direction
• Periosteal surface
points away from it
• V principle www.indiandentalacademy.com

The Condylar Question?
•
•

Mandibles totally lacking condyles exist
in nature
Occupy normal anatomic position and
proper occlusion

• 2 conclusions1. Not the master center
2. Displaced Anteriorly and Inferiorly
without a push

•
•
•
•

1955- Weinmann and Sicher
Major growth center
Explanation seems to be logical
Charlier and Petrovic supported this
theory
• If correct then condyle would grow by 2
mechanisms1. Interstitial proliferation
2. Appositionalwww.indiandentalacademy.com
growth

• 1962- Moss, Functional matrix Hypothesis
• Questions the primacy of Sicher theory
• Condyle is under influence of the growth
of orofacial capsular matrices
• Concept of dominance of epigenetic and
environmental factors is supported

•
•
•
•

1963- Koski et al
Transplanted mandibular ramus of the rat
Recovered tissue was same as original
Condyles with part of ramus transplantedmeasurable growth

• 1968- Rankow and Moss
• Condylectomy in young femaleimmediate downward and forward growth
seen along with basal mandibular
translation and increase in vertical height

Current concept
•
•

Enlow
Condyle does have intrinsic genetic
programming but extra condylar factors
are needed
• Extra condylar factors are1. Intrinsic and extrinsic biomechanical
forces
2. Physiologic inductors

• More recent studies involve NerveMuscle-Connective tissue pathways
• Periodontal membrane and soft tissue
matrix--- sensory input– higher centers–
motor input to muscles– repositions
mandible– affects growth and remodeling
of condyle

Adaptive Role of Condyle
• Multidirectional growth potential
• If growth of mandible were
preprogrammed within condyle, mandible
cannot fit into maxilla and basicranium


Chin
• Protrusive chin is characteristic of humans
• Males- more prominent
• Females- less prominent


Mental Protuberance
• Formed by mental
ossicles
• Poorly developed in
infants
• Forms by osseous
deposition
• Reversal line www.indiandentalacademy.com

Factors affecting mandibular
growth
•
1.
2.
3.
4.

Systemic factors
Genetic
Hormonal
Nutritional
Illness


Factors affecting mandibular
growth
•
1.
2.
3.
4.

Local factors
Ankylosis
Trauma
Birth injury
Ear infection


Anomalies of mandible
•

Syndromes associated with mandible
1. Pierrie robin syndrome
2. Treacher collins syndrome
3. Marfan’s syndrome


•

Congenital anomalies
1. Agnathia
2. Micrognathia
3. Macrognathia


•
1.
2.
3.
4.

Developmental anomalies
Torus mandiularis
Stafne’s cyst
Achondroplasia
Odontogenic cyst


Touras mandibularis

Stafne’s cyst


Age changes of Mandible
At birth

Adult

Old age

1 Mental
foramen

Near the lower
border

Midway b/n upper
& lower border

Near the upper border

2 Angle of the
mandible
3 coronoid &
condyloid
processes

Obtuse

Right angle

Obtuse

Coronoid is
larger & above
condyle

Condyle is above
the coronoid

4 Mandibular
canal

Runs little
above the
mylohyoid line
Present; two
halves united
fibrous tissue

Runs parallel to
the mylohyoid line

Condyle is above the
coronoid but in
extreme old age –bent
backwards
Runs close to the
upper border

5 Symphysis
menti

Represented by
faint ridge only in
the upper part


Not recognizable or
absent

References
1. Human anatomy- B.D. Chaurasia
2. Human Embryology- I.B Singh
3. Craniofacial embryology – SPERBER
4. CranioFacial growth – ENLOW

5. Contemporary orthodontics – PROFFIT
6. Principles and practice of orthodontics –
T.M GRABER
7. Study of human fetal mandible–
INGHAM, J Dent Resarch, 1932
8. Text book of oral pathology- SHAFER’S


There is
nothing
new under
the sun

But there are
lot of old
Things we
don’t know

Thank You

Prenatal and postnatal development of mandible /certified fixed orthodontic courses by Indian dental academy

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