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

Growth
and
Development
of
Mandible
www.indiandentalacademy.com

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INDIAN DENTAL ACADEMY
Leader in continuing dental education


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The mandible is derived from
ossification of an osteogenic
membrane, first appearing as a
mesenchymal condensation at 3638 days of development.
The intramembranous bone lies
lateral to Meckel’s cartilage of the
mandibular(1st) Branchial arch.


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A single ossification centre for each
half of the mandible arises in the 6 th
week i.u in the region of the
bifurcation of Inf Alv N and Art into
mental and incisive branches.
The ossifying membrane is attached
laterally to Meckel’s cartilage.


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Scheme of centre of ossification of mandible
lateral to Meckel’s cartilage at bifurcation of Inferior
alveolar nerve

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The intramembranous ossification
stops dorsally at the site which will
later become the mandibular
lingula.
From this point it continues into
middle ear
where the two post. elements later
become the malleus and incus
These two bones function in the
articulation of the mandible in lower
animals and are known as the
articulare and quadrate.
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There is some evidence that
malleus and incus function to
provide a movable joint until the
mandibular condyle develops in
relation to glenoid fossa of the
temporal bone.
Then these two cartilages ossify
and function as middle ear bones.


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The first branchial arch core of
Meckel’s cart meets its fellow of
opposite side ventrally.
The dorsal end of Meckel’s cart
ossifies to form two of auditory
ossicles,
MALLEUS
INCUS
Stapes ---- Reichert’s cartilage.

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The major portion of Meckel’s cart
disappears, leaving the Mylohyoid
groove of mandible in which it lay.
The fibrous sheath surrounding the
cartilage remains as the
Sphenomandibular
Sphenomalleolar ligaments.


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So the Meckel’s cart:in all gives rise to
Mental ossicles
Incus and Malleus
Spine of Sphenoid
Sphenomandibular
ligament
Sphenomalleolar ligaments

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Accessory cartilages appear
between the 10 th and 14 th weeks i.u
to form
Head of condyle
Coronoid process
Mental protuberance


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Accessory cartilages of foetal mandible

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The condylar process
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At about the 5 th week of i.u life an
area of mesenchymal condensation
can be seen above the ventral part
of the developing mandible.
This is primordium of future condyle
By 10 th week- it develops into cone
shaped cartilage.
14 th week– ossification starts.
It then migrates inferiorly and fuses
by about 4 months

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This condylar cart serves as an important
centre of growth for ramus and body of
mandible.
Much of the cone shaped cartilage is
replaced by bone by middle of fetal life
but its upper end persists into adulthood
acting both as a growth cartilage and an
articular cartilage.
Growth at this site normally ceases at
about the 20 th year of life.

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CORONOID PROCESS
•

Secondary accessory cartilages appear
in the region of the coronoid process by
about 10-14th week of i.u life.

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This secondary cartilage of coronoid
process is thought to grow as a
response to the developing temporalis
muscle.

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This cartilage becomes incorporated
into the expanding intramembranous
bone of the ramus and disappears
before birth.

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Mental region
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In mental region, on either side of the
symphysis, one or two small cartilages
appear and ossify in the 7 th month of i.u
life to form variable numbers of mental
ossicles in the fibrous tissues of the
symphysis.
These ossicles become incorporated into
the intramembranous bone when the
symphysis ossifies completely during
first yr of post-natal life.

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Post natal growth of mandible
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Mandible undergoes the largest
amount of growth post-natally.
Exhibits largest variability in
morphology.
It is developmentally and
functionally divisible into several
skeletal sub units.

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The basal bone forms one unit, to
which are attached
The alveolar pr
The coronoid pr
The condylar pr
The angular pr
The ramus
The lingual tuberosity
The chin

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Each of these subunits is
influenced by a functional matrix
that acts upon the bone.
Teeth –the alv unit.
Temporalis –the coronoid pr
Masseter &Medial Pterygoid
muscles –angle of mandible
Lateral pterygoid –the condylar pr


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The main sites of post-natal
mandibular growth are at
condylar cart
post border of ramus
alveolar ridges
These areas account for increases
in the height, length, and width of
the mandible


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Enlow’s expanding ‘V’
principle

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Many facial bones or parts of bone
have a ‘V’ shaped pattern of
growth.
The growth movements and
enlargement of these bones occur
towards the wide ends of ‘V’ as a
result of differential deposition and
selective resorption of bone.
Deposition –on the inner side of
wide end of ’V’
Resorption –on the outer surface.

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Deposition

also takes
place at the
ends of the
2 arms of
the ’V’
resulting
in growth
movement
towards the
ends.

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Ramus
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The ramus moves post by a
combination of deposition and
resorption.
Resorption –on anterior part of
ramus
Deposition –on posterior region.
Result –drift of ramus in post
direction.
The proportion of ramus is
maintained.

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This deposition and resorption
balance extends up to the coronoid
involving the mandibular notch, and
progressively repositions the mand
foramen in a posterior direction.
The attachment of elevating
muscles of mastication to the
buccal and lingual aspects of ramus
are influential in determining the
ultimate size and proportion of
these mand elements.

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Relocation www.indiandentalacademy.com ramus
of mandibular

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While the whole ramus grows
posteriorly and superiorly, the
mandibular foramen drifts backward
and upward by deposition on the
anterior and resorption from the
posterior part of its rim.
Maintains a constant position about
midway b/w ant & post borders of
ramus.


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Functions of remodelling of
ramus:
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To accommodate the increasing
mass of masticatory muscles
inserted into it.
To accommodate the enlarged
breadth of the pharyngeal space.
To facilitate lengthening of the
mandibular body, which in turn
accommodate the erupting molars.

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Corpus or body of
mandible
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The displacement of the ramus
results in the conversion of former
ramal bone into the posterior part of
the body of mandible.
So the body lengthens by the
posterior molar region becoming
relocated anteriorly into premolar
and canine regions.

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So additional space is provided for
the later erupting molar teeth, all of
which develop in the ramus-body
junction.
Their forward migration and post
ramal displacement both lengthen
the molar region of the mandible.


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Resorption on anterior border of ramus, thus
making space for the molars

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Downward
& forward
transposition
of md.
Upward &
Backward
growth
Adult md angle
Fetal md angle

Growth of mandible with fetal md
superimposed on adult md

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Angle of mandible
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The growth and remodelling
changes occurring during infancy
and childhood serve to alter the
angle b/w the ramus and body of
mandible from about 140 to nearly
90 in adulthood.
Resorption of alveolar bone with
tooth loss results in the angle
formed by the ramus and body,
again increasing in senility.

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On lingual side of the angle of
mandible,
resorption –on the post-inf aspect
while deposition –on the ant-sup
part.
On buccal side of angle of
mandible,
resorption –on the ant-sup part
while deposition –on the post-inf
part.
Result –flaring of the angle of the

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The lingual tuberosity
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The lingual tuberosity is a direct
equivalent of max tub, which forms
a major site of growth for the lower
bony arch.
It forms the boundary b/w the ramus
&the body.
It protrudes noticeably in a lingual
direction.
Lies towards the middle of ramus.

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Moves post by deposition on its
posteriorly facing surface.
The tub is prominent due to
presence of large resorption field
just below it.
Resorptive field produces
depression
lingual
fossa
The combination of resorption in
the fossa and deposition on the
medial surface of the tub itself

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The post growth of the tub is
accomplished by continued new
deposits of bone on its posterior
facing exposure.
Part of ramus just behind the tub
grows medially.
And thus becoming a part of
corpus.

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Tub growing in an almost directly post direction.

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The alveolar process
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Alv pr develops in response to the
presence of tooth buds.
As teeth erupts the alv pr develops
and increases in height by bone
deposition at the margins.
It adds to the height and thickness
of the body of mandible.
Absence of teeth – pr fails to
develop
Tooth extraction –pr undergoes
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resorption www.indiandentalacademy.com

The chin

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A specific human characteristic
Found in its fully developed form in
recent man only.
In infancy chin is usually
underdeveloped.
The growth of chin is influenced by
sexual and specific genetic factors.
Usually males have prominent chins
compared to females.

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The mental protuberance forms by
bone deposition during childhood.
Its prominence is accentuated by
bone resorption that occurs in the
alv region above it, creating a
concavity known as Point B .
Underdevelopment of chin is known
as microgenia


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Mental foramen
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The mental neurovascular bundle
emanates from mandible at almost
right angles at birth.
In adulthood the foramen is
characteristically backwardly
directed.
This is due to forward direction of
growth that occurs in the body of
mandible, while the neurovascular
bundle drags along.

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Clinical implication
In administration of L.A to the
mental foramen.
In Infancy &childhood the syringe
needle is placed at right angles
In case of adults needle has to be
placed obliquely from behind to
achieve entry.

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The location of mental foramen also
alters its vertical position within the
body of mandible from infancy to
childhood and old age.
When teeth are present –the
foramen is located midway b/w the
upper and lower borders of the
mandible.
In edentulous mandible –foramen is
located near the upper margin of
the thinned mandible

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The coronoid process

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The coronoid pr has a propeller like
twist, so that its lingual side faces
three general directions all at once–
posteriorly
superiorly
medially.
When bone is added to the lingual
side of coronoid pr, its growth
thereby proceeds superiorly, and
this part of ramus becomes
increased in vertical dimension

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Each coronoid pr lengthens
vertically, even though additions
are made on the medial (lingual)
surfaces of the right and left
coronoid pr.
 This is an e.g. of “enlarging V
principle”, with the V oriented
vertically.
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enlarging V principle

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The same deposits of bone on the
lingual side also bring about a
posterior direction of growth
movement.
This produces a backward
movement of the two coronoid pr,
even though deposits are added on
the lingual surface.
This is an e.g. of “expanding V
principle”, with the V oriented
horizontally.

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expanding V principle

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These same deposits of bone on
the lingual side also function to
carry the base of the coronoid pr
and the anterior part of ramus in a
medial direction in order to add this
part to the lengthening corpus,
which lies well medial to the
coronoid pr.
This, again is an e.g. of V principle.


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The condyle
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The mandibular condyle is
considered as a major site of
growth.
Initially it was believed to be the
ultimate determinant of rate &
amount of mandibular growth,
growth direction, overall mandibular
size and shape.
It is no longer believed to represent
a pace setting “master center”.

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During mandibular development,
the condyle functions as a regional
field of growth.
The condylar cartilage of the
mandible serves the unique dual
roles of an articular surface
cartilage analogous to the T.M joint,
and as a growth cartilage
analogous to the epiphyseal plate
in a long bone.

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The formation of bone within the
condylar head results in the mand
rami growing in an upward and
backward direction, with
consequent displacement of whole
bone in an opposite downward and
forward direction.
Bone resorption adjacent to the
condylar head accounts for
narrowed condylar neck.

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Direction of condylar growth

Mandibles of a neonate, a 4 yr. Child and an adult

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The attachment of the lateral pterygoid
muscle to the condylar neck, and growth
and action of the tongue and masticatory
muscles, are functional forces implicated
in this phase of mandibular growth.
Any damage to the condylar cartilage will
restrict the growth potential and normal
downward and forward displacement of
the mandible, unilaterally or bilaterally,
according to the sides damaged.


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Due to posterior
divergence of the
two halves of the
mandible (in a V
shape), growth at
the condylar
heads of the
increasingly more
widely displaced
rami results in an
eventual total
widening of the
mandibular body.

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AGE CHANGES IN MANDIBLE,
1) at Birth
At birth mandible is in two separate
halves united in the median plane
by fibrous tissue -symphysis menti.
A trace of separation near the
alveolar margin may still be visible
at the beginning of the 2nd year.

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The body elongates more especially
behind the mental foramen.

2) 1st and 2nd year
During the 1st and 2nd year as the
prominence of chin develops the mental
foramen alters in direction.
Proliferation of condylar cartilage leads
to increase in vertical height of ramus
and downward and forward growth of
mandible.

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Also the distance between the
condyle increases as the base of
skull widens.
As the mandible increases in size
bone is laid down along the
posterior borders of mandibular
ramus and the coronoid process


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and resorption of bone occurs along
their anterior borders.
This remodelling goes on until the
bone has reached the adult size
and it enables the alveolar part to
lengthen sufficiently to provide the
necessary space for the permanent
molar teeth.
3) Adults
The angle of mandible diminishes

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as the height of ramus increases
with age but contour of the angle of
mandible remains unaltered.
4) Old age
Bone is decreased in size as the
teeth are lost.
Following the loss of teeth the
alveolar part is absorbed and
consequently the mandibular canal
and mental foramen are close to the
alveolar border.

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Ramus is oblique.
Angle is 140 degrees and neck of
mandible is bent backwards.
The process of absorption affects
chiefly the thinner of the two
alveolar walls .
As alveolar ridge resorbs the
mandible widens.


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References:
1.Human embryology : Sperber

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2.Comtemporary orthodontics :Profitt

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3.Handbook of orthodontics : Moyers

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4.Facial growth : Enlow


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Leader in continuing dental education


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

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