2. 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.
3. 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.
4. 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.
5. 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.
6.
7. 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.
8. 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.
9.
10. 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.
11. Secondary Growth Cartilages
Further growth of mandible till birth is influenced by formation of three
secondary cartilages.
Secondary
cartilages
Condylar Coronoid Symphyseal
12. 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.
13. 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.
14. 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.
