Development And Growth Of Mandible And Maxilla

Ass. prof. Dr. HEBA M. Eltohey

Steps of Mandible Development 1- Meckel’s cartilage. 2- Mandibular nerve. 3- development of body of the mandible.

4- Development of the ramus. 5- Secondary cartilage.

Development Of The Mandible • It develops by INTRAMEMBRANOUS ossification.

• Meckel’s cartilage has ONLY a close relation to the dense fibrocellular membrane but does not contribute in mandibular development.

Meckel’s  Cartilage

• It develops at 6th week IU as a Solid Hyaline cartilagenous rod, surrounded by fibrocellular capsule.

•  It extends from ear region to the midline of fused mandibular process.

• They are separated at the midline with mesenchymal band.

Fate of Meckel’s Cartilage 1- Mental ossicles and Lingula represent the remaining part of the cartilage in the developed mandible.

2- Major portion of two ear ossicles (mallus and incus).

3- Sphenomandibular ligament & anterior ligament of the mallus develop from fibrous capsule of the cartilage.

4- Spine of sphenoid bone.

The Mandibular Branch of Trigeminal Nerve • At the junction of dorsal and middle thirds, it divides into Inferior alveolar nerve and Lingual N.

• At the junction of middle and ventral thirds, It divides into Incisive And Mental N.

Body of the Mandible • At 7th week IU on the lateral aspect of Meckel’s cartilage a condensation in the mesenchyme occurs in the angle between incisive and mental nerves.

• From this center of ossification, Bone formation extend Backward along the nerve till the junction of inferior

alveolar and lingual nerves forming lateral & medial plates then canal is formed for the nerve by bone formation over the nerve.

• Tooth germs develop within the canal then separated by bone partitions.

The Ramus

• It occurs by rapid spread of ossification posteriorly to the condensed ectomesenchymal membrane of the 1st arch.

2ry Cartilage • Condylar Cartilage: It appear at 12th week IU as a carrot shaped occupies most of the developing ramus (endochondrial ossification).

• At 20 week IU only a thin layer of cartilage persists for head growth. It disappeared by the end of the 2nd decade of life.

Coronoid Cartilage: •  It appears at 4th month of development at the anterior border and top of coronoid process.

• It disapeared long before birth. Symphysial cartilage ( two in number) • They appear in the CT in the midline. They are ossified within the 1st year after birth.

The Mandible at Birth 1- Obtuse angle. 2- Small sized ramus. 3- Poorly developed chin. 4- Large coronoid process. 5- open shell body of the mandible.

6- lower mandibular canal.