Download Development of the mandible

Development of face and oral Cavity
Development of the mandible
Development of the mandible

The mandible is the largest and strongest bone of the face
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It consists of a curved, horizontal portion, the body, and two
perpendicular portions, the rami, which unite with the ends of
the body nearly at right angles.
For better description development of the mandible will be
divided into:
1. Body of the mandible.
2. The rami
3. The alveolar process
Devel. of the mandibular body
The basic growth pattern of the mandibular body and condyle
appeared in week 7 of fertilization.
Histologically, the embryonic mandible originated in the lower
part of the first branchial arch from primary intramembranous
ossification in the fibrous mesenchymal tissue around the
Meckel's cartilage.
Devel. of the mandibular body
Devel. of the mandibular body
Meckel’s cartilage has a close, relationship to the mandibular
nerve, at the junction between poximal and middle thirds, where
the mandibular nerve divides into the lingual and inferior alveolar
nerve.
The lingual nerve passes forward, on the medial side of the
cartilage, while the inferior alverolar lies lateral to its upper
margins.
Before the begin of ossification the mandibular nerve and its
branches are developed and they ensure the formation of canals
around them.
Devel. of the mandibular body
Development of the mandible
The Ossification takes place in the membrane covering the outer
surface of Meckel's cartilage and each half of the bone is formed
from a single center which appears, in the region of the
bifurcation of the mental and incisive branches, about the sixth
week of fetal life.
From this initial ossification, the ramifying trabecular bones
developed forward, backward and upward, to form the symphysis
and the mandibular body respectively, following the path way of
the incisive and the inferior alveolar nerve.
Devel. of the mandibular body
From the proximal end of each cartilage the Malleus and Incus,
two of the bones of the middle ear, are developed.
Devel. of the mandibular body
Development of the rami
The ramus of the mandible develops by a rapid spread of
ossification backwards into the mesenchyme of the first branchial
arch diverging away from Meckel’s cartilage. This point of
divergence is marked by the mandibular foramen.
Somewhat later, accessory nuclei of cartilage make their
appearance:

A wedge-shaped nucleus in the condyloid process and
extending downward through the ramus.

A small strip along the anterior border of the coronoid process.
Development of the rami
The accessory cartilages:
1. Symphysal cartilage
2. Condylar cartilage:
3. Coronoid cartilage
Coronoid
Development of the rami
Condylar cartilage:
•
Carrot shaped cartilage appears in the region of the condyle
and occupies most of the developing rami.
•
It is the largest and most important one.
•
It appears in the 12th WIU and is rapidly converted to bone
by endochondral ossification (14th WIU).
Development of the rami
•
It gives rise to:
•
Condyle head and neck of the mandible.
•
The posterior half of the ramus to the level of inferior
alveolar foramen.
•
A thin layer of cartilage remains in the condylar head and
persists until the 20 years of life providing a mechanism of
mandibular growth.
Development of the rami
The coronoid cartilage:
•
It is relatively transient growth cartilage center ( 4th to 6 th
MIU). it gives rise to:
•
Coronoid process.
•
The anterior half of the ramus to the level of inferior
alveolar foramen.
Development of the alveolar process
•
It starts when the deciduous tooth germs reach the early bell
stage. The bone of the mandible begins to grow on each
side of the tooth germ.
•
By this growth the tooth germs come to be in a trough or
groove of bone, which also includes the alveolar nerves and
blood vessels.
•
Later on, septa of bone between the adjacent tooth germs
develop, keeping each tooth separate in its bony crept.
Development of the alveolar process
•
The mandibular canal is separated from the bony crypts by a
horizontal plate of bone.
•
The alveolar processes grow at a rapid rate during the
periods of tooth eruption.
Growth of the mandible
•
The shape and size of the mandible undergo considerable
transformation from embryonic to adult mandible.
•
The process of transformation occurs in three steps:
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Growth by accessory Cartilage
•
Growth with the alveolar process
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Subperiosteal bone apposition and bone resorption.
Growth of the mandible
Growth of the mandible
The mandible grows in all directions:
• Anterio-posterior by bone deposition along the posterior border
of the ramus.
• Vertical by growth of the condyle, along the upper border of the
ramus and the formation of the alveolar process.
• Transverse by bone deposition on the external surface and
bone resorption at the inner surface.
Growth of the mandible