DEVELOPMENT OF MANDIBLEPRESENTED BY:

HIBA HAMID OKARVI

2ND YEAR BDS

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.

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.

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.

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.

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.

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.

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.

Secondary Growth Cartilages

Further growth of mandible till birth is influenced by formation of three

secondary cartilages.

Secondary cartilages

Condylar Coronoid Symphyseal

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.

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.

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.