Growth & development of mandi

Growth and development of
Mandible
Dept. of Orthodontics &
Dentofacial orthopedicswww.indiandentalacademy.comwww.indiandentalacademy.com

Growth andGrowth and
development ofdevelopment of
mandiblemandible
• Pre-natal embryology ofPre-natal embryology of
mandiblemandible
• Post-natal growth of mandiblePost-natal growth of mandible
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Pre – natal embryology ofPre – natal embryology of
mandiblemandible
• Around the fourth
week of intra uterine
life, a prominent bilge
appears on the
ventral aspect of
embryo
corresponding to the
developing brain.

• Below the bulge a
shallow depression
which corresponds to
the primitive mouth
appears called
Stomodeum.

• The floor of the
stomodeum is formed
by the
Buccopharyngeal
membrane which
seperates the
stomodeum from the
foregut.

• By around the fourth
week of intra-uterine
life, Five branchial
arches form in the
region of the future
head and neck.

• The first pharyngeal
arch is called the
Mandibular arch and
plays an important
role in the
development of naso-
maxillary region.

• The mesoderm
covering the
developing forebrain
proliferates and forms
a downward
projection called
Fronto-nasal
Process.

The mandibular arches of both the sides formThe mandibular arches of both the sides form
the lateral walls of the stomodeum.the lateral walls of the stomodeum.
• The mandibular arch
gives of a bud from
its dorsal end called
the Maxillary
process.

• The maxillary process
grows ventro-medio-
cranial to the main
part of the mandibular
arch which is now
called the
Mandibular process.

• Thus at this stage
the primitive mouth
is overlapped from
above by the fronto-
nasal process,
below by the
mandibular process
and on either side
by the maxillry
process.

• The two mandibular processes grow medially
and fuse to form the lower lip and the lower
jaw i,e the Mandible.

Meckel’s CartilageMeckel’s Cartilage
• The Meckel’s cartilage is derived from the
first branchial arch around the 41st
– 45th
day
of intra-uterine life. It extends from the
cartilaginous otic capsule to the midline or
symphysis and provides template for guiding
the growth of the mandible.

• A major portion of the Meckel’s Cartilage
disappears during growth and the remaining
part develops into the following structures:
1) The mental ossicles
2) Incus and malleus
3) Spine of sphenoid bone
4) Anterior ligament of malleus
5) Spheno-mandibular ligament

• The first structure to develop in the
primordium of the lower jaw is the mandibular
division of the trigeminal nerve. This is
followed by the mesenchymal condenstion
forming the first branchial arch.
• Neurotrophic factors produced by the nerve
induce osteogenesis in the ossification
centers.

• A single ossification center for each half of the
mandible arises in the 6th
week of intra-uterine
life in the region of the bifurcation of the inferior
alveolar nerve into mental and incisive
branches.

• The ossifying membrane is located lateral to
the Meckel’s Cartilage and its accompanying
neuro-vascular bundle.
• From this primary center, ossification spreads
below and around the inferior alveolar nerve
and its incisive branch and upwards to form
trough for accommodating the developing
tooth buds.
• Spread of the intramembranous ossification
dorsally and ventrally forms the body and
ramus of the mandible.

• As ossification continues, the meckel’s
cartilage becomes surrounded and invaded
by the bone.
• Ossification stops at the site that will later
become the mandibular lingula from where
the Meckel’s cartilage continues into the
middle ear and develops into the auditory
ossicles i,e Malleus and Incus.
• The spheno-mandibular ligament which
extends from the lingula of the mandible to
the sphenoid bone also forms a remnant of
the Meckel’s cartilage.

Endochondral bone formationEndochondral bone formation
• Endochondral bone formation is seen only in 3
areas of the mandible.
1) The Condylar Process.
2) The Coronoid Process.
3) The Mental Region.

Condylar ProcessCondylar Process
• At about the 5th
week of intra-uterine life, an area
of mesenchymal condensation can be seen
above the ventral part of the developing
mandible.
• This develops into a cone – shaped cartilage by
about 10th
week and starts ossification by 14th
week.

• It then migrates inferiorly and fuses with the
mandibular ramus by about 4 months.
• Much of the cone-shaped cartilage is
replaced by bone by the middle of fetal life
but its upper end persists into adulthood
acting as a growth cartilage and an articular
cartilage.

Coronoid ProcessCoronoid Process
• Secondary accessory cartilages appear in the
region of the coronoid process by about the
10th
-14th
week of intra-uterine life. This
secondary cartilage of coronoid process is
believed to grow as a response to the
developing temporalis muscle.
• The coronoid accessory cartilage becomes
incorporated into the expanding
intramembranous bone of the ramus and
disappears before birth.

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

Post - natal growth ofPost - natal growth of
mandiblemandible
• Of the facial bones, the mandible undergoes
largest amount of growth post-natally and also
exhibits the largest variability in morphology.
• While the mandible appears in the adult as a
single bone, it is developmentally and
functionally divisible into several skeletal sub-
units.
• Thus the study of post-natal growth of the
mandible is made easier and more meaningful
when each of the developmental and functional
parts are considered separate.

The Ramus of MandibleThe Ramus 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 a DRIFT of the ramus in a
posterior direction.

• The functions of remodeling of the ramus
are :
1) To accommodate the increasing mass of
masticatory muscles inserted into it.
2) To accommodate the enlarged breadth of
the
the pharyngeal space.
3) To facilitate the lengthening of the
mandibular
body, which in turn accommodates the
erupting
molars. www.indiandentalacademy.comwww.indiandentalacademy.com

Corpus or Body of MandibleCorpus or Body of Mandible
• Displacement of the ramus in a posterior
direction by remodeling process results in
lengthening of the body of the mandible.
• Thus the additional space made available by
means of resorption of the anterior border of
the ramus is made use of to accommodate
the erupting permanent molars.

Angle of the MandibleAngle of the 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
antero-superior part while deposition takes
place on the postero-inferior part

The Lingual TuberosityThe Lingual Tuberosity
• The Lingual tuberosity is a direct equivalent
of the maxillary tuberosity, which forms a
major site of growth for the lower bony arch. It
forms the boundary between the ramus and
the body.
• The lingual tuberosity moves posteriorly by
deposition on its posteriorly facing surface.

• It can be noticed that the 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. This resorption field produces a
sizable depression, the lingual fossa.

The Alveolar ProcessThe Alveolar Process
• This develops in response to the presence of
the tooth buds. As the tooth erupt the alveolar
process develops and increases in height by
bone deposition at the margins.
• The alveolar bone adds to the height and the
thickness of the body of the mandible and is
particularly manifested as a ledge extending
lingual to the ramus to accommodate the third
molars.

The ChinThe Chin
• The chin is a specific human characteristic and
is found in its fully developed form in recent man
only.
• In infancy, the chin is usually underdeveloped.
As age advances the growth of the chin
becomes significant.
• It is influenced by sexual and specific genetic
factors. Usually males are seen to have
prominent chins as compared to females.

• The mental protuberance forms by bone
deposition during childhood. Its prominence is
accentuated by bone resorption that occurs in
the alveolar region above it, creating a
concavity.
• The deepest point in this concavity is known
as “Point B” in cephalometric terminology.

The CondyleThe Condyle
• The mandibular condyle has been recognised as
an important growth site. The head of the
condyle is covered by a thin layer of cartilage
called the Condylar cartilage.
• The presence of this cartilage is an adaptation to
withstand the compression that occurs at the
joint.

• The role of the condyle in the growth of
mandible has remained a controversy. There
are two schools of thought regarding the role
of the condyle.
1) It was earlier believed that the growth occurs
at
the surface of the condylar cartilage by
means
of bone deposition. Thus the Condyle grows
towards the cranial base, the entire mandible
gets displaced forwards and downwards.

2) It is now believed that the growth of soft
tissues
including the muscles and connective tissue
carries the mandible forwards away from the
cranial base. Bone growth follows
secondarily at
the condyle to maintain constant contact with
the
cranial base.

• The condylar growth rate increases at puberty
reaching a peak between 12 1/2 – 14 years.
The growth ceases around 20 years of age.

The Coronoid processThe 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, it
can be seen that deposition occurs on the
lingual (medial) 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.
• Briefly the coronoid process has a propeller
like twist, so that its lingual side faces three
general directions all at once i,e
posteriorly,superiorly and medially.

Growth & development of mandi

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Growth & development of mandi