development of mandible
TRANSCRIPT
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DEVELOPMENT OF MANDIBLEPRESENTED BY:
HIBA HAMID OKARVI
2ND YEAR BDS
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Mandible ???
• From Latin “mandibula” meaning
jawbone.
• It is the largest and strongest bone
of the face.
• It houses the lower teeth.
• Consists of a curved horizontal
portion: the body, and two
perpendicular portions: the rami.
• The body and rami unite at the
angle of mandible nearly at right
angles.
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Development of Mandible
• Forms from the 1st arch within the mandibular process.
• Meckel’s cartilage (cartilage of 1st arch) forms lower jaw in primitive
vertebrates.
• In humans, it has a close relation to the developing mandible but makes
no direct contribution to it.
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Meckel’s Cartilage
• Forms at 6th week of development.
• It is a solid hyaline cartilage surrounded
by a fibro-cellular capsule.
• Extends from otic capsule to the midline
of the fused mandibular processes.
• Cartilages of each side do not meet at
midline; they are separated by a thin
band of mesenchyme.
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Meckel’s Cartilage Cont’d
• Formation of the mandibular division of trigeminal nerve begins two-
thirds along the length of the cartilage.
• It divides into two branches at this point:
Lingual nerve
Inferior alveolar nerve (IAN)
• Lingual nerve runs along the medial aspect of the cartilage.
• Inferior alveolar nerve runs along the lateral aspect of the cartilage.
• Anteriorly, IAN divides to form mental and incisive branches.
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Primary Ossification Centre
• Condensation of mesenchyme occurs
lateral to Meckel’s cartilage in the 6th week
gestation.
• This condensation begins at the angle
formed by division of the IAN into incisive
and mental branches.
• Intra-membranous ossification begins in
this condensation during the 7th week.
Ossification begins in the membrane
covering the outer surface of Meckel’s
cartilage.
• From this centre, bone formation spreads
rapidly, anteriorly to the midline,
posteriorly to the point of division of the
mandibular nerve into lingual nerve and
inferior alveolar nerve.
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Formation of Mandibular
Canal
• Ossification grows medially beneath the incisive nerve, then spreads
beneath this nerve and Meckel’s cartilage.
• Incisive nerve is contained within this trough or groove of bone formed by
lateral and medial plates which are united below the nerve.
• This trough comes in close contact with a similar trough from the opposite
side. The two fuse shortly after birth. Trough converted into canal when
bone forms over the nerve.
• Spread of ossification in the backward direction produces at first a trough-
like gutter of bone in which lies the inferior alveolar nerve up to the level of
the future lingula.
• Later this gutter is converted to bone.
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Development of Body and Ramus
BODY OF MANDIBLE
• Above bony canal, medial and lateral alveolar
plates develop.
• Odontogenic epithelium forming the tooth
germs lies superiorly.
• Medial and lateral plates develop around these
germs and they come to lie in a secondary
trough.
• Trough is partitioned by developing individual
tooth germs.
• Alveolar plates completely enclose the tooth
germs.
RAMUS OF MANDIBLE
• Ossification spreads posteriorly into
mesenchyme of the 1st arch.
• Spreads away from Meckel’s cartilage
and this point of turning away is the
future lingula.
• By 10th week, primitive mandible is
formed almost entirely by
membranous ossification.
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Secondary Growth Cartilages
Further growth of mandible till birth is influenced by formation of three
secondary cartilages.
Secondary cartilages
Condylar Coronoid Symphyseal
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Secondary Growth Cartilages Cont’d
CONDYLAR CARTILAGE
• Appears during 12th week.
• Rapidly forms cone/carrot
shaped mass occupying most
of ramus area.
• Converted to bone by
endochondral ossification.
• By 20th week, only a thin layer
of cartilage remains in the
condylar head.
• This remnant of cartilage
persists till the 2nd decade of
life.
• Provides a growth mechanism
for the mandible in the same
way as an epiphyseal
cartilage does in the limbs.
CORONOID CARTILAGE
• Appears at about 4th
month of development.
• Forms near anterior
border and top of the
coronoid process.
• It is a transient cartilage.
• Disappears long before
birth.
SYMPHYSEAL CARTILAGE
• Two in number.
• Appear in the connective
tissue between two ends
of the Meckel’s cartilage.
• Get obliterated within the
first year of birth.
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Fate of Meckel’s Cartilage
• Its posterior-most extremity forms the incus and malleus (ear ossicles)
of the inner ear, and the spheno-malleolar ligament.
• From the sphenoid to the division of mandibular nerve into its inferior
alveolar and lingual branches, the Meckel’s cartilage disappears
completely. Only its fibro-cellular capsule persists as sphenomandibular
ligament.
• From lingula to area of mental foramen, Meckel’s cartilage degenerates.
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Summary
• Mandible is a membrane bone, developed in
relation to the nerve of the first arch.
• Almost entirely independent of Meckel’s
cartilage.
• Its growth is assisted by the development of
secondary cartilages.
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