G&d maxilla (2)

Growth of Maxilla and
Mandible
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 Growth of maxilla
• Pre – natal embryology of maxilla
• Post – natal growth of maxilla
 Growth of mandible
• Pre – natal embryology of mandible
• post – natal growth of mandible

GROWTH OF MAXILLA
• Growth and development of an individual can be divided
into pre-natal and post-natal periods.
• The Pre-natal period of development is a dynamic phase
in the development of a human being.
• The post-natal period involves complex interaction of
different growth processes.

Pre-natal embryology of maxilla
Around the fourth week of intra-
uterine life, a prominent bulge
appears on the ventral aspect of
the embryo corresponding to the
developing brain.
Below the bulge a shallow
depression which corresponds to
the primitive mouth appears called
Stomodeum.

The floor of the stomodeum is
Formed by the Buccopharyngeal
membrane which separates the
Stomodeum from the foregut.
By around the 4th
week of intra-
uterine life ,five branchial
arches form in the region of the
future head and neck.www.indiandentalacademy.com

The first pharyngeal arch is called the
Mandibular arch and plays an
important role in the development of
the naso-maxillary region.
The mesoderm covering the
developing forebrain proliferates and
forms a downward projection called
Fronto-nasal process.

The Maxillary Process grows
ventro-medio-cranial to the main
part of the Mandibular arch which is
now called the Mandibular
Process.
The mandibular arches of both the sides form the
lateral walls of the stomodeum.
The mandibular arch gives of a
bud from its dorsal end called
the Maxillary Process.

Thus at this stage the
primitive mouth is
overlapped from above by
the Fronto-nasal Process,
below by the Mandibular
process and on either
side by the maxillary
process.

The ectoderm overlying the
Fronto-nasal Process shows
bilateral localized thickenings
above the stomodeum. These
are called the Nasal
Placodes.
These placodes soon sink and
form the Nasal Pits.

The formation of these Nasal
Pits divides the Fronto-nasal
process into two parts :
a.The Medial nasal process
b.The lateral nasal process

The two mandibular processes grow medially and fuse to
form the lower lip and lower jaw.
As the Maxillary Process undergoes growth the Fronto-
nasal process becomes narrow so that the two Nasal Pits
come closer.
The line of fusion of Maxillary Process and the Medial
nasal Process corresponds to the Naso-lacrimal duct.

Post-natal growth of maxilla
Maxilla develops primarily by Intra membranous
ossification.
A Primary Intra membranous ossification center appears
for each maxilla in the 8th
week of intrauterine life at the
termination of infraorbital nerve just above the canine
tooth dental lamina.

Secondary cartilages appear at the end of 8th
week IU in the regions of the zygomatic and
alveolar processes that rapidly ossify and fuse
with the primary intramembranous center.
Two further intrmembranous pre-maxillary centers
appear anteriorly one each side in the 8th
week IU
and rapidly fuse with the primary maxillary center.

The growth of the naso-maxillary complex is
produced by the following mechanisms :
• Displacement
• Growth at Sutures
• Surface Remodeling

DISPLACEMENT
Maxilla is attached to the cranial base by means of
number of sutures, thus the growth of the cranial base
has a strong influence on the naso-maxillary growth.
A passive or Secondary Displacement of the naso-
maxillary complex occurs in a downward and forward
direction as the cranial base grows.

The naso-maxillary complex is simply moved anteriorly
as the middle cranial fossa grows in that direction.
SECONDARY DISPLACEMENT OF
MAXILLA www.indiandentalacademy.com

In addition, a Primary Displacement is also seen in a
forward direction. This occurs by growth of the maxillary
tuberosity in a posterior direction. This results in the
whole maxilla being carried anteriorly.
This is a primary type of
displacement as the bone is
displaced by its own enlargement.

GROWTH AT SUTURE
The maxilla is connected to the cranium
and the cranial base by a number of
sutures.
These sutures include :
a. Fronto - nasal suture.
b. Fronto – maxillary suture.
c. Zygomatico – maxillary suture.
d. Pterygo – palatine suture.
e. Zygomatico – temporal suture.

Weinmann and sicher have pointed out that these
sutures are all oblique and more or less parallel to each
other. This allows the downward and forward
positioning of the maxilla as growth occurs at this
sutures.

As the growth of the soft tissue occurs, the maxilla is
carried downward and forward. This leads to opening
up of space at the sutural attachments. New bone is
formed on either side of the suture.
Thus overall size of the bones increases on either
side. Hence a tension related bone formation occurs
at the sutures.

SURFACE REMODELING
In addition to the growth occurring at the sutures,
massive remodeling by bone deposition and
resorption occurs to bring about :
• Increase in size.
• Change in shape of bone.
• Change in functional relationship.

Bone remodeling changes seen in the
Naso - maxillary complex
1) Resorption occurs on the lateral surface of
the orbital rim leading to lateral movement
of the of the eye ball. To compensate, there
is a bone deposition on the medial rim of the
orbit and on the external surface of the
lateral rim.
2) The floor of the orbit faces superiorly, laterally and
anteriorly.

3) Bone deposition occurs along the posterior margin of
the maxillary tuberosity. This causes lengthening of the
dental arch and enlargement of the antero- posterior
dimension of the entire maxillary body. This helps to
accommodate the erupting molars.

4) Bone resorption occurs on the
lateral wall of the nose leading to an
increase in the size of the nasal cavity.
5) Bone resorption is seen on the floor
of the nasal cavity. To compensate
there is a bone deposition on the
palatal side. Thus a net downward shift
occurs leading to increase in maxillary
height.

6) The zygomatic bone moves in a
posterior direction. This is achieved
by resorption on the anterior surface
and deposition on the posterior
surface.
7) The face enlarges in width by bone
formation on the lateral surface of the
zygomatic arch and resorption on its
medial surface.

8) The anterior nasal spine prominence
increases due to bone deposition. In
addition there is resorption from the
periosteal surface of labial cortex. As a
compensatory mechanism, bone
deposition occurs on the endosteal
surface of the labial cortex and
periosteal surface of the lingual cortex.

9) As the teeth start erupting,
bone deposition occurs at the
alveolar margins. This
increases the maxillary height
and the depth of the palate.
10) The entire wall of the maxillary sinus except the
mesial wall undergoes resorption. This results in
increase in size of the maxillary antrum.

11) Specifically mentioning, the vertical
growth of the maxillary complex is due
to the continued apposition of alveolar
bone on the free borders of the alveolar
process as the teeth erupt.
12) Transversely, additive growth on
the free ends increases the distance
and thus the buccal segments move
downward and outward.
The expanding ‘V’ in the
downward and forward
growth of the maxilla

DEVELOPMENT OF PALATE
The palate is formed by contribution of the :
a. Maxillary process
b. Palatal shelves given off by the maxillary process
c. Fronto-nasal process

The fronto-nasal process gives rise to the premaxillary
region while the palatal shelves form the rest of the
palate.

As the palatal shelves grow medially, their union is
prevented by the presence of the tongue. Thus initially
the developing palatal shelves grow vertically
downwards towards the floor of the mouth.
Sometimes during the seventh week of intrauterine life,
a transformation in the position of the palatal shelves
occurs.They change from a vertical to horizontal
position.

This transformation is believed to take place within
hours. Various reasons are given to explain how this
transformation occurs. They are :
a. Alteration in biochemical and physical consistency of
the connective tissue of the palatal shelves.
b. Appearance of an intrinsic shelf area.
c. Rapid differential mitotic activity

d. Alteration in vasculature and blood supply to the
palatal shelves.
e. Muscular movements.
f. Withdrawal of the embryonic face from against the
heart prominence results in slight jaw opening. This
results in withdrawal of the tongue from between
the palatal shelves and aids in the elevation of the
shelves from a vertical to a horizontal position.

The two palatal shelves, by 8 ½ weeks
of intrauterine life , are in close
approximation with each other. Initially
the two palatal shelves are covered by
an epithelial lining. As they join, the
epithelial cells degenerate.
The connective tissue of the palatal shelves intermingle
with each other resulting in their fusion.

The entire palate does not
contact and fuse at the same
time. Initially contact occurs in
the central region of the
secondary palate posterior to
the premaxilla. From this point,
closure occurs both anteriorly
and posteriorly.

The mesial edges of the palatal
processes fuse with the free lower
end of nasal septum and thus
separates the two nasal cavities
from each other and the oral
cavity.

Ossification of palate
 Ossification of the palate occurs from 8th
week of intra-
uterine life.
 This is an Intramembranous type of an ossfication.
 The palate ossifies from a single center derivedfrom
the maxilla.
 The most posterior part of the palate does not
ossify.This forms the Soft palate.
 The mid-palatal suture ossifies by 12-14 years.

G&d maxilla (2)

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