2. Introduction
Prenatal Embryology Of Mandible
Meckel’s Cartilage
Endochondral Bone Formation
Post-natal Growth Of Mandible
Reference
3. Definition of GROWTH:
“ The self multiplication of living substance” (J.S.
Huxley)
“An increase in size” (Todd)
“Quantitative aspect of biological development per
unit of time” (Moyers)
Definition of DEVELOPMENT:
“Development is progress towards maturity” (Todd)
4. About the 4th week of IUL, the developing brain and the
pericardium form 2 prominent bulges on the ventral
aspect of embryo.
These bulges are separated by the primitive oral cavity
or the stomaodeum.
The floor of the stomatodeum is formed by the buccopharyngeal membrane, which separates it from the
foregut.
5. The pharyngeal arches are laid down on the lateral and
ventral aspect of the cranial most part of the foregut
that lies in close approximation with the stomadeum.
Initially there are 6 pharangeal arches, but the 5th one
usually disappears as soon as it is formed leaving only 5.
They are separated by 4 branchial grooves.
The 5th arch is called the mandibular arch and the 2nd
arch, hyoid arch
6. Each of these 5 arches contain:
1.
2.
3.
4.
A central cartilage rod that forms the skeleton of the arch.
Muscular components termed as branchiomere.
A vascular component.
Neural element.
The mandibular arch form the lateral wall of the
stomodeum.
It gives off a bud from its dorsal end, bud is called
maxillary process.
It grows ventro-medially, cranial to main part of the arch,
which is now called a mandibular process.
The mandibular process of both sides grow towards each
other and fuse in the midline.
They now form the lower border of the stomodeum i.e. the
lower lip and the lower jaw.
7.
8. It is derived from the 1st branchial arch around the 41st-45th
day of IUL.
It provides a template for guiding the growth of the
mandible.
A major portion of the meckel’s cartilage disappears during
growth and the remaining part develops into:
1. The mental ossicles.
2. Incus and malleus.
3. Spine of the spenoid bone.
4. Anterior ligament of the malleus.
5. Spheno-mandibular ligament.
9.
10. The ossifying membrane is located lateral to the
meckel’s cartilage and its accompanying neurovascular
bundle.
From this primary centre, ossification spread below
and around the inferior alveolar nerve and its incisive
brand and upward to form a trough for a
accommodating the developing tooth bud.
Spread of the intramembraneous ossification dorsally
and ventrally forms the body and ramus of the
mandible.
11. CONDYLAR PROCESS:
About the 5th week of IUL, an area of
the mesenchymal condensation can
be seen above the ventral of
developing mandible.
This develops into a cone-shaped
cartilage by about 10th week and
starts ossification by 14th week.
Then migrates inferiorly and fuses
with the mandibular ramus by about
4th month.
12. CORONOID PROCESS:
Secondary accessory cartilages appear in the region of
the coronoid process by about 10-14th week of IUL.
MENTAL REGION:
In this region, on the either side of the symphysis, one
or two small cartilages appear and ossify in the 7th
month of IUL to form a variable numbers of mental
ossicles in the fibrous tissue of the symphysis.
13. While the mandible appears in the adult as single
bone, it is developmentally and functionally divisible
into a several skeletal sub-unit.
Basal bone forms one unit, to which is attached the
alveolar process, coronoid process, condylar process,
angular process, the ramus, the lingual tuberosity and
the chin.
14. RAMUS:
It moves progressively posterior by a combination of
deposition and resorption. Resorption occurs on
anterior part of ramus while bone deposition occur on
the posterior region.
This result in a “drift” in posterior direction.
Functions of the remodelling of ramus are:
1. Accommodate the increasing mass of the masticatory
muscles inserted into it.
2. To accommodate the enlarged breadth of the
pharyngeal space.
3. To facilitate the lengthening of the mandibular body,
which in turn accommodates the erupting molars.
15. CORPUS OR THE BODY OF THE
MANDIBLE:
Displacement of the ramus results
in the conversion of the ramal
bone into the posterior part of the
body of the mandible.
In this manner, it lengthens. Thus
additional space made available
by means of resorption of the
anterior border of the ramus is
made use of to accommodate the
erupting molar.
16. ANGLE OF THE MANDIBLE:
On the lingual side of the angle of the mandible,
resorption take place on the posterio-inferior aspect
while deposition on the anterio-superior aspect.
On the buccal side, resorption occur on the anteriosuperior part while deposition takes place on poseriosuperior part.
This results in flaring of the angle of mandible as age
advances.
17. LINGUAL TUBEROSITY:
It moves posteriorly by deposition on its posteriorly
facing surface.
It protrudes noticeably in a lingual direction and that
it lies well toward the midline of ramus.
The prominence of the tuberosity is increased by the
presence of the large resorption field just below it.
18. ALVEOLAR PROCESS:
It develops in response to the presence of tooth buds.
As the teeth erupt, it develops and increases in height
by bone deposition at the margins.
19. THE CHIN:
As the age advances the growth
of chin becomes significant.
It is influenced by sexual and
specific genetic factors.
Usually males are seen to have
prominent chin as compared to
females.
Mental tuberosity forms by bone
deposition during childhood.
20. THE CONDYLE:
The head of the condyle is covered by the thin
layer of cartilage called the condylar cartilage.
The presence of conylar cartilage is an adaptation
to withstand the compression that occurs at the
joint.
It is believed that the growth of the soft tissues
including the muscles and the connective tissues
carries the mandible forward away from cranial
base. Bone growth follows secondary at the
condyle to maintain constant contact with cranial
base.
The condylar growth rate increases at puberty
reaching a peak between 121/2-14 years. The growth
ceases around 20 years of age.
21.
22. THE CORONOID PROCESS:
The growth follows the enlarging ‘V’ principle.
Viewing, the logitudinal section of coronoid process
from posterior aspect, it can be seen that deposition
occurs on the lingual (medial) surfaces of the left and
right coronoid process .
Although additions take places on the lingual side, the
vertical dimension of the coronoid process also
increases. This follows the ‘V’ principle.
Viewing from the occusal aspect, the deposition on
lingual of coronoid process brings about posterior
growth movement in ‘V’ pattern
23.
24.
25. The textbook of orthodontics
S.I. Bhalajhi (fourth edition)
