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Development of mandible
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Development of mandible


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  • 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. 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.
  • 7. 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.
  • 8. 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.
  • 9. Secondary Growth Cartilages Further growth of mandible till birth is influenced by formation of three secondary cartilages. Secondary cartilages Condylar Coronoid Symphyseal
  • 10. 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.
  • 11. 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.
  • 12. 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.