Prenatal And Postnatal Growth Of Mandible

Prenatal Growth of Mandible

The mandible develops from the first branchial arch or mandibular arch.
On the lateral aspect of Meckel’s cartilage, during the sixth week of embryonic development, a condensation of mesenchyme occurs in the angle formed by the division of the inferior alveolar nerve and its incisor and mental branches.
In 7th week, intramembranous ossification begins in this condensation, forming the first of the mandible.
From this center ossification, bone formation spreads rapidly anteriorly to the midline and posteriorly toward the point where the mandibular nerve divides into its lingual and inferior alveolar branches.
The spread of new bone formation occurs anteriorly along the lateral aspect of Meckel’s cartilage, forming a trough that consists of lateral and medial plates that unite beneath the incisor nerve.

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This trough of bone extends to the midline, where it comes into approximation with a similar trough formed in the adjoining mandibular process. The two separate centers of ossification remain separated at the mandibular symphysis until shortly after birth.
The tris is soon converted into a canal as bone forms over the nerve, joining the lateral and medial plates.
Similarly, a backward extension of ossification along the lateral aspect of Meckel’s cartilage forms a gutter, anis converted into a canal that contains the inferior alveolar nerve.
This backward extension of ossification proceeds in the condensed mesenchyme to the point where the mandibular nerve divides into the inferior alveolar and lingual nerves.

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From this bony canal, extending from the division of the mandibular nerve to the midline, medial and lateral alveolar plates of bone develop the forming tooth germs so that the tooth germs occupy a secondary trough of bone.
This trough is partitioned, and thus, the teeth come to occupy individual compartments, which finally are enclosed totally by the growth of bone over the tooth germ. In this way, the body of the mandible is formed.
The ramus of the mandible develops by the rapid spread of ossification posteriorly into the mesenchyme ofthe first arch, turning away from Meckel’s cartilage.

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Thus, by 10 weeks, the rudimentary mandible is formed almost entirely by membranous ossification. Thee concondylar processarts forming inin the th week. As the condylar process is not completely formed, malleus and incus bones form a temporary joint with glenoid fossa, which leads to mandibular movements.
Meckel’s cartilage is replaced by bone, and remnants of Teckel’s cartilage are the malleus, incus, and soft tissue of the sphenomandibular ligament. The center of ossification lies at the site of the future mental foramen.
Condyle of the mandible arises as separate mesenchymal condensation, which is cone-shaped in the 10th week of IUL.
As the condyle is formed, the temporomandibular joint shifts anteriorly.

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Ossification of the ramus of the mandible occurs, and the condyle is fused to the mandible in the 16th week of IUL.
During the 10 to 14th week of the IUL, the coronoid process develops from secondary cartilage. During this period, the intramembranous ossification causes the fusion of the coronoid process to ramus.
Single or two cartilaginous fragments at the mental foramen become ossified and fuse with the mandible at the 7th month of intrauterine life.
The ossification center lies at future Meckel’s cartilage on both sides. Ossification commences anteriorly as well as posteriorly from this point and stops at the site of future lingual.

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