Development of mandible and maxilla Flashcards
What tissues from do the mandible and maxilla originate?
First brachial arch
Which cartilage forms thelower jaw?
Meckel’s cartilage
What happens at 6 weeks of development?
At 6 weeks of development, this cartilage extends as a solid hyaline
cartilaginous rod surrounded by a fibrocellular capsule, from the
developing ear region (otic capsule) to the midline of the fused
mandibular processes
How do the 2 cartilages meet?
The two cartilages of each side do not meet at the midline but are
separated by a thin band of mesenchyme.
Where does the mandibular branch of the trigeminal nerve begin in relation to mechel’s cartilage?
The mandibular branch of the trigeminal nerve (the nerve of the first
arch) has a close relationship to Meckel’s cartilage, beginning two thirds
of the way along the length of the cartilage.
• At this point the mandibular nerve divides into lingual and inferior
alveolar branches, which run along the medial and lateral aspects of the
cartilage, respectively.
• The inferior alveolar nerve further divides into incisor and mental
branches more anteriorly.
What happens at the lateral aspect of meckel’s cartilage during the 6th 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.
What occurs at 7 weeks of devlopment on the lateral aspect of of meckel’s catilage?
intramembranous ossification begins in this condensation, forming the first bone of the mandible
• From this centre of 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.
• This 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.
• 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 centres of ossification remain separated at the
mandibular symphysis until shortly after birth.
• The trough soon is converted into a canal as bone forms over the
nerve, joining the lateral and medial plates.
How is the body of the mandible formed?
Similarly, there is a backward extension of ossification along the lateral
aspect of Meckel’s cartilage to the point where the mandibular nerve
divides into the inferior alveolar and lingual nerves.
• From this point where the nerve divides to the midline, medial and
lateral alveolar plates of bone develop in relation to the forming tooth
germs subdividing the trough of bone.
• Thus the teeth come to occupy individual compartments, which finally
are enclosed totally by growth of bone over the tooth germ.
In this way the body of the mandible essentially is formed.
What factors is further growth of the mandible until birth influenced by?
The further growth of the mandible until birth is influenced strongly by
the appearance of three secondary (growth) cartilages and the
development of muscular attachments. These secondary cartilages
include:
the condylar cartilage, which is most important
the coronoid cartilage
the symphyseal cartilage
When does the condylar cartilage appear and what happens to it?
The condylar cartilage appears at 12 weeks of development and rapidly
forms a cone-shaped mass that occupies most of the developing
ramus. This mass of cartilage is converted quickly to bone by
endochondral ossification, so that at 20 weeks of development only a
thin layer of cartilage remains in the condylar head.
‣ This remnant of cartilage persists until the end of the second
decade of life, providing a mechanism for growth of the mandible,
in the same way as the epiphyseal cartilage does in the limbs.
Where does the maxilla develop from?
centre of ossification in the mesenchyme of the maxillary process of the first arch
Where does the centre of ossificaion appear from in the maxilla?
Where does bone formation spread from this centre?
appears in the angle between the divisions of a nerve
(where the anterosuperior dental nerve is given off from the inferior
orbital nerve).
• From this centre, bone formation spreads posteriorly below the orbit
toward the developing zygoma and anteriorly toward the future incisor
region.
• Ossification also spreads superiorly to form the frontal process. As a
result of this pattern of bone deposition, a bony trough forms for the
infraorbital nerve. From this trough a downward extension of bone
forms the lateral alveolar plate for the maxillary tooth germs.
• Ossification also spreads into the palatine process to form the hard
palate
What coordinates jaw patterning?
In the first branchial arch, a gradient of gene expression involving the
Dlx family of transcription factors (1-6) promotes coordinated gene
expression along the dorsoventral axis that regulates jaw patterning.
• Distinct sets of Dlx family members (homebox genes) are important for determining theidentity of the mandible (Dlx1/2/5/6) versus the maxilla (Dlx1/2).
• Lack of Dlx5/6 causes a reversal of the mandible into a maxilla,
generating an animal with two mirror image upper jaws
Which buds do the maxilla develop from?
1x frontonasal mass
2x lateral nasal prominences
2x maxillary prominences
When do the prominences oproduced by proliferation of neural crest cells occur?
All the prominences produced by proliferation of NCCs that migrate into
arches from neural crest occur during the fourth week of gestation
