Transcript 6e430d442f8069e

The knowledge about growth and development is
very important for the orthodontist since during
this period any disturbances may give rise to
certain congenital
malformations,
malocclusion and
facial deformities … etc.
It's important to study the development of the face:
1-We must understand the variability that can occur in the facial form.
2-We must have awareness that the human face and oral cavity among
the area that most susceptible to oral formation.
We know that developing human pass through three period:
1-Proliferative period (0-2 weeks) (ovum, morula & blastocyte)
2-Embryonic period (2-8 weeks)
3-Fetus period (8weeks-9months)
Primitive oral mouth cavity:
In 3-4th weeks old primitive mouth cavity stomodeum
is a narrow slit like space lined by ectoderm. It is
bounded above by the under surface of brain capsule,
and below by the upper surface of preicardial sac. The
developing mandibular processes form a rim-like
elevation bounding the cavity at the sides. At the back
of the cavity there is a thin oral membrane forming a
septum, which at this stage separates the primitive
mouth from cavity from the pharynx. Later, this
membrane will breakup so the stomodeum becomes
directly continuous with the foregut (at end of third
week of I.U.L)
The head and neck are developed from the branchial apparatus, which consists of branchial arches,
pharyngeal pouches, branchial grooves, and branchial membranes. Branchial arches are derived
from the neural crest cells and begin to develop early in the 4th week, as the neural crest cells
migrate into the future head and neck region. By the end of the 4th week, four pairs of branchial
arches are visible. The fifth and sixth pairs are too small to be seen on the surface of the embryo.
The branchial arches are separated by the branchial grooves, which are seen as prominent clefts in
the embryo.
The branchial arches contribute to formation of the face, neck, nasal cavities, mouth, larynx, and
pharynx, with the muscular components forming striated muscles in the head and neck.
The face develops from the tissues surround the oral pit during the
second period & between 3-7 weeks, so:
-At the 3rd week:
Pros-encephalon overhangs the developing oral
groove to form the stomodeum, the oral groove
deepens and oral plate & buccopharyngeal
membrane which consists of ectodermal floor of
stomodium & endodermal lining & forgout ruptures
to form oral opening.
The face develops from the tissues surround the oral pit during the
second period & between 3-7 weeks, so:
-At the 4th week:
Above the oral pit is the covering of brain termed
frontal process from which forehead develop, lateral
to oral pit are 2 maxillary processes and below is
the mandibular arch which form the lower jaw and
inferior to it second branchial arch (hyoid bone)
which contribute in face development..
The face develops from the tissues surround the oral pit during the
second period & between 3-7 weeks, so:
-At the 5th week:
Fusion of the medial end of mandible & in the midline to form
chin, lower lip. Any failure in fusion leads to cleft
(uncommon) the epithelium covering the brain capsule has
thickening in 2 places on each side of head, the more ventral
thickening is the nasal placode that develop into nostrils &
the more dorsal is the lens placode from which eye lens
develops.
At this stage the frontal becomes frontonasal process, as the
the tissue around the nasal placode grow resulting in 2
opening in the oral pit and nastrial becomes deeper & the
tissue lateral to it termed lateral nasal process & tissue
medial to it termed medial nasal process.
The face develops from the tissues surround the oral pit during the
second period & between 3-7 weeks, so:
-At the 6th/7th week:
The lateral part of the face expand, this will change
the eye from the lateral of the head toward the
medial location.
The maxillary process move to each other & fuse in
the mid-line to form the intermaxillary segment
which will give rise to :
1-Philtrum (middle portion of upper lip)
2-prelabium.
3-Collumella.
4-Nasal septum.
5-Primary palate & anterior part of palate.
6-4 incisors, alveolar bone & gingiva.
The face develops from the tissues surround the oral pit during the
second period & between 3-7 weeks, so:
-At the 6th/7th week:
The union between the medial nasal & maxillary process give rise:
1-Maxilla
2-Palate
3-upper lip
4-lower central part nose.
Failure of fusion of medial nasal process & maxillary
process leads in cleft lip (unilateral or bilateral).
At the line of fusion of lateral nasal process & maxillary
process is the naso-lacrimal duct which connect the
lacrimal sac to the nasal cavity & there will be a
modification of 1st branchial groove into ear canal.
The nasal septum consists of 2 parts :
1-Anterior part form frontonasal process.
2- Posterior part form maxillary process.
Here nasal septum is free with the dorsal of tongue.
Development of the palate (6-12 weeks)
Human palate is the tissue that separate the
oral & nasal cavites .
Entire palate consists from 2structures :
1-Primary palate (premaxilla which derive from
intermaxillary segment )
2-Secondary palate (hard & soft palate ) which
derive from lateral palatine shelves of the
maxilla.
These shelves oriented in the vertical plane &
tongue between them; later the palatine
shelves elongated & the tongue becomes
small & move inferiorly, this allows the shelves
to become horizontally & fused in midline
(median palatine raphe), incisive foramen at
the junction between primary palate and lateral
palatine shelves. Failure of fusion of the lateral
palatine shelves with each other & with the
nasal septum & with primary palate result in
cleft palate (uni-, bilateral or with cleft lip)
Development of the tongue :
The mucosa of body of tongue (ant. 2/3 develop from
1st branchial arch (Mand.) & mucosa of base (Post.
1/3) of the tongue develop from 3rd branchial arch.
During tongue development there is enlargement
called tuberculum impar & 2 lateral lingual swellings
adjacent to tuberculum impar, these 3 structures
arise from 1st branchail arch & give rise to body of
tongue, the base of tongue develop from
hypobranchial eminence over grow & fused with
tuberaculum impar & lateral lingual swelling. The
line between body and base of tongue called sulcus
terminalis at which foramen cecum. Tongue may
show developmental abnormality.
Cheek and parotid gland:
Cheek consists of tissue derived from
mandibular & maxillary processes. At
the back laterally on each side of oral
cavity. The parotid salivary gland
develop as an out growth of oral
epithelium & open the opening of its
duct related to upper second molars.
Facial skeleton
Face is formed by cartilage. Meckel's cartilage develop
within mandibular arch & cartilage of nasal capsule
develops in the maxillary process & extend forward
into frontonasal process & behind , it is continues
with cartilage of cranial base (beneath the brain )
Nasal septum form septal cartilage. At later stage in
the development, the maxilla, premaxilla & lacrimal
bones develop on the outer side of cartilage of the
nasal capsule, the palatine bone develop on its inner
aspect the mandibule develops on the outer side of
Meckel's cartilage & vomer developes from septal
cartilage.
The development
of the jaws :
The jaws begins to form during the period of
early development of deciduous teeth, the first
indication of bone formation occur with the
appearance of dental lamina in the maxillary and
mandibular processes & by the time that the
deciduous tooth germs lie in cavities, the alveoli,
formed by bone of the mandible & maxilla, they
have come in to close relationship with jaws.
Development of the mandible
The mandible is formed in the lower
or deeper part of the first visceral
(mandibular) arch, & it's preceeded
the Meckel's cartilage :
Meckel's cartilage : At 6th week of
the fetal life (15mm length) , It's
attains it's fill form & then stretches
downward
&
forward
as
a
continuous
rod
from
the
cartilaginous otic capsule to the
midline, where its ventral end turns
upward in contact with the cartilage
of the opposite side, to which it's
joined by mesenchyme. The dorsal
end of the cartilage gives rise to the
malleus of the middle ear. The
remaining part of the cartilage is
largely
associated
with
the
development of the mandible which
form
the
replacing
skeletal
structure.
The mandibular nerve :
It is the nerve of first visceral arch, at
this stage of development the
Meckel's cartrilage in close relation to
it & act as a skeletal support to it.
The main nerve comes out from the
skull medial & ventral to the dorsal
end of the cartilage & at the junction
of the dorsal & middle 1/3 of the
cartilage the nerve into direct
relationship with it & at this region &
after giving its other branches it is
divided into lingual & inferior dental
nerve. The lingual nerve pass forward
on its medial side, the inferior dental
nerve lies lateral to its upper margin
& running forward parallel to its
terminals by dividing into mental and
incisive branches, the incisive branch
continues its course parallel to the
cartilage.
The body of the mandible:
The mandible firstly appear as a band of dense fibrocellular tissue lies on the lateral side of
the inferior dental nerve & incisive nerve.
At the 7th week of the fetal life (17-18mm length) ossification occurs in the angle formed
between the mental & incisive nerve which is the site of future mental foramen.
From this center bone formation spread rapidly backward below the mental nerve & lie in a
notch on the lateral side of the inferior dental nerve. In this notch the bone grow medially
below the incisive nerve & soon afterward it goes upward between the incisive nerve &
meckel’s car. so contained in a trough channel of bone formed by medial & lateral plates
which united below the nerve.
At the same stage & by the extension of bone over the nerve from the anterior to posterior
edge of the notch, the notch contining the mental nerve converted into mental foramen.
The bony trough grows rapidly forward toward the midline where it become in close
relationship with similar bone formation on the opposite side but firstly these 2bones
separated from each other by connective tissue & the union between them occur before the
end of the first year of life.
By the growth of bone over the incisive nerve from the lateral &
medial plates the trough of bone is converted into incisive canal.
In the backward direction a similar spread of ossification which produce first a plate of
bone in relation to the lateral aspect of inferior dental nerve, then a bony trough in which
the nerve lies & very much later the canal for it.
So by these processes of growth the original primary center of ossification produce the
body proper of the mandible as for back as the mandibular foramen & as forward as the
symphysis, which is the part of mandible surround the inferior dental nerve and the
incisive nerve.
At this stage the developing tooth grows lie some little distance superficial to the
mandible & are not contained by it.
The cavities continue to increase in size with growth of the condylar & of the articular
fossa. The articular eminence is hardly apparent at birth & only begins to attain its typical
form afte the establishment of the deciduous, small areas of secondary cartilage appear
in the temporal region, they appear ;later the condylar cartilage & disappear before birth.
The alveolar bone :
When the deciduous enamel organs reach
the early bell stage. The bone of the
mandibular begins to come in close
relationship with them & this happen by the
upward growth, on each side of the tooth
germ of the tooth germ of the medial and
lateral plates above the level of the roof
which is formed for the canal of the
incisive & inferior dental nerve.
So the developing tooth come to lie in the
trough of bone, which is later divided into
separate small alveoli & this is done by the
formation of septa between its walls.
Fate of Meckels' cartilage :
The anterior part of the mandible, except in
midline, in front of the mental foramen,
include cartilage in its substance which is
firstly surrounded by bone extend from the
medial plate & then gradually resorbed &
replaced by ossification extend from the
membrane bone around it.
During the later fetal period & at least until
the time of birth one or two nodules of
cartilage are seen in the fibrous tissue of the
symphysis. Which are the remnants of the
ventral end of the cartilage.
The rest disappear completely except for a
part of its fibrous covering which persists as
the sphenomandibular & sphenomalleolar
ligaments.
The most dorsal part of the cartilage ossifies
to form the malleus, which is attached to the
sphenoidal spine by the sphenomalleolar
ligament.
The ramus:
The ramus is produced by a spread of ossification
from the body of mandible, behind & above the
mandibular foramen.
From this region the mandible diverge laterally
from the the line of the meckel's cartilage.
Just like the body of the mandible, the ramus & its
processes are firstly mapped out by an extension
of the fibrocellular condensation.
The formation of bone in this tissue occur rapidly
so that the coronoid & condylar processes are to
large extent ossified at 40mm CR (10th week). The
further growth of these processes is modified by
the appearance of secondary cartilage.
The secondary (Accessory) cartilages:
The occur at various sites in the region of
membrane bone formation since they are not
part of, & have no connection with primary
cartilage (meckel's cartilage), so they called
secondary.
They differ from the primary cartilages which
are formed by Hyaline cartilage In their
behaviour & histological appearance.
Which have less inner cellular matrix than
hyaline cartilage.
Secondary cartilage increase in size by the
proliferation & trans formation of the cells of
the thick layer of the fibrocellular tissue which
covers them.
In the mandible there are 3 main
sites
of
secondary
cartilage
formation which are:
1-Condylar.
2-Coronoid.
3-Symphyseal.
1-The condylar cartilage:
cartilage in anterior older part of the tissue begins to show
Largest,1st
secondary
cartilage
& it
is of great
endochondral
ossification
& this
continue
until importance
the only areaforof the
the
growth
of mandible.
cartilage
left un resorbed in a zone immediately beneath the
1stproliferating
appearance tissue
at the 12th
week
(50mmarticular
length) at
which So
its seen
a
of the
condylar
surface.
in theas5th
fringe
of cartilage
lateral
aspects of
bone
in the
months
of fetal on
life,the
thesuperior
original &
cone
of cartilage
is the
largely
replaced
condylar
process
which
will merges
on oneside
into &
this
bone &with
on the
by bony
tubercular
which
run through
the ramus
contrast
the
other
into the bone
fibrocellular
layers which
limitsof
the
condylar
region.
membrane
of the ramus.
(The zone
the
cartilage
left behind
Bythe
additions
the of
cells
the covering
the
articularfrom
surface
the of
condyle
persistsfibrocellular
until at leasttissue,
the end
of
cartilage
a cone shaped mass which not only occupy the whole of
the 2ndfrom
decade)
theDuring
condylar
forward
& downward
ramus
thisprocess
period but
as reaches
proliferative
activity
of cells into
of itsthecovering
as fibrocellular
far as level oflayer
mandibular
grows foramen.
less, the thickness of zone of cartilage
disappear & replacing bone forms whole of condylar.
So the cartilage will increase the length of the mandible during this
period.
By 5th month a large vascular canals have appeared in the condylar
cartilage, these are still present at birth & they are related to the
nutritive requirements if the rapidly growing cartilage.
2-the coronoid cartilage:
It appear in 80 mm CR.
It forms a strip along anterior
border & submit of the coroniod
process. It is covered superficially
by thick fibrocellular layer & rests
on the membrane bone below. All
traces of it has
disappeared long
before birth.
3-the Symphyseal cartilage:
In 100 mm CR.
At each end of two halves of bony mandible ,
these enable mandible to grow in width,
while they persist it is entirely in dependent
of Meckel's cartilage & it's perichondrium.
Shortly after birth the 2 halves united & this
union obliterate these cartilage so that they
take no further part in growth of the
mandible. Small areas of secondary
cartilage, irregular in their location &
appearance may supply for a time the
growth of the alveolar bone at its margin .
At birth the mandible differs in several
respects from the adult bone. The chief
differences are
1-the absence of any definite chin
2-wide mandibular angle.
3-small size of ramus compare with the
body.
Development of Mandibular joint:
It first induced by growth of tissue condensation of the developing mandible, which
every where precedes ossification, towards the corresponding condensation for the
temporal region.
The mandibular condensation maps out the shape of the condylar.
At this stage the mandibular & temporal elements of the joint are still separated by a
wide interval. The closure approximation of the mandibular to the temporal region is
brought about by the development of secondary cartilage in the condylar process. By
the rapid growth of the cartilage of the previously wide interarticular interval is
largely obliterated. The only intervening tissue left is a strip of dense tissue
immediately above the upper surface of the condylar. This tissue appears at the same
time of as the condensation for the condylar & it's connected to the lateral pterygoid
muscle from its first appearance. The strip of tissue becomes the articular disc. The
formation of the joint cavities above & below this strip of tissue occurs as the
condyle becomes approximated to the temporal element of the joint. Joint cavity
development is virtually complete between the 65-70mm C.R. stages)
The development of maxilla:
The upper jaw (maxilla proper) excluding
the premaxilla is developed in the maxillary
process of mandibular arch.
The first appearance is a membraneous
ossification, just like the mandible, but
unlike the mandible , its further
development & growth are little affected by
the appearance of secondary cartilage.
Ossification of maxilla start slightly later
than in the mandible & center of
ossification first appears in a band of
fibrocellular tissue, which lies to the outer
side of the cartilage of the nasal capsule &
immediately lateral to & slightly below the
infra orbital nerve where its gives of its
anterior
superior
dental
branch.
Ossification center lies above that part of
the lamina from which develops the enamel
organ of the canines tooth germ.
The ossification spreads from this center backward towards
the developing zygomatic bone below the orbit & forward
infront of anterior – superior dental nerve below the terminal
part of the infra orbital nerve toward the developing
premaxilla.
At this stage the forming bone takes the shape of a curved
strip, arranged vertically with the convex side directed
medially.
From anterior extension there develops the upward directed
frontal process which, with a corresponding process of
premaxilla, forms the frontal process of the adult bone.
Early in development the developing maxilla forms a bony
trough for the infra orbital nerve & by downward growth, an
outer alveolar plate in relation to the canine & deciduous
molar tooth germs.
The growth of maxilla continues mainly upward, downward &
backward & with the development of a palatal process also
spreads towards the midline in the substance of the anterior
part of the united palatal folds.
By the appearance of secondary cartilage in the zygomatic
process & by its proliferation for a time adds considerably to
the bulk of this part of maxilla, during this period the palatal
process extends backward, at the union of the palatal process
& the main part of the developing maxilla a large mass of bone
is produced.
From this region, on the inner side of
dental lamina & tooth germs, the medial
alveolar plate develops some what later
than the lateral alveolar plate. The
trough of bone formed is later than the
lateral alveolar plate. The trough of
bone formed is later divided by septa
into alveoli.
Also some areas of secondary cartilage
may develop along the growing margins
of the alveolar plates & in the midline of
the developing hard palate between the
2 palatal processes
The maxillary sinus:
At the 4th month of the fetal life its first appearancre
as a small out pocketing of the mucosa from the
lateral wall of the nasal cavity. It is firstly separated
from the developing maxilla by the cartilage of the
nasal capsule & only comes into direct relationship
with the bone after the cartilage has atrophied.
In its gradual extension the sinus comes into relation
with the maxilla above the level of the palatal process
& hollows out the interior of the bone, so separating
its upper or orbital surface from its lower dental
region.
At birth, however, these parts are still close together &
it is only very gradually that the maxilla increases in
height with an associated increase in the size of the
sinus.
Near the time of the completed eruption of the
permanent teeth, the maxilla reaches its final height.
The sinus may increase in size however during the
adult life by extension into alveolar process.
Comparison of mandibular & maxillary development
1. both have neural and alveolar elements.
2. Both develop secondary cartilages in their back ward
extension.
3. Both commence as a centers of ossification in close relation to
a nerve at a place of bifurcation & in close relation to elements
of cartilaginous facial skeleton.
4. The condylar cartilage, however, remains active as a growth
center for along period in relation to the mandibular joint, the
zygomatic (Malar) cartilage of the maxilla is restricted in its
appearance & activity to a limited period of fetal life & in
related to the suture between it & the zygomatic bone.
5. The maxilla has no muscular processes & the mandible has no
palatal process.
6. In the growth, the maxilla depends upon surface deposition &
growth at the suture at which it articulate with the adjacent
bones, the mandible depends for its growth on the surface
growth on the surface deposition & the replacement of the
cartilage by bone.