Gwowth cranial base /fixed orthodontic courses

PRE-NATAL
&
POST-NATAL
GROWTH
OF
CRANIAL BASE
www.indiandentalacademy.com

INDIAN DENTAL ACADEMY
Leader in continuing dental education


 Introduction
 Functions of cranial base
 Anterior,middle and posterior cranial
fossae
 Individual bones of cranial base
 Pre-natal growth
 Various foramina
 Ossification in individual basicranial bones
 Cranial base flexure
 Post-natal growth
 Clinical implications
 References www.indiandentalacademy.com

INTRODUCTION
The cranial base is of considerable
importance to the orthodontist as it serves as
a reasonably stable reference structure in
roentgen-cephalometric analysis.

Growth and development of face
and the cranial base are intimately related to
each other, and has been a focus of interest to
many researchers.

For orthodontists, biologists and
anthropologists, the patterns of normal
development should be known to
serve as a basis for comparing and
understanding
abnormal
growth
patterns.

FUNCTIONS OF CRANIAL BASE:
 Basicranium supports and protects the
brain and spinal cord.
 It articulates the skull with the vertebral
column, mandible and maxillary region.
 It acts as an adaptive or buffer zone
between the brain, face and pharyngeal
region whose growth are paced differently.

 Internal surface of the cranial base
shows a natural division into anterior,
middle and posterior cranial fossae.
 The duramater is firmly adherent to
the whole area, and through the
numerous foramina and fissures its
outer layer, the endocranium is
continuous with the periosteum on the
exterior of the skull.

The anterior cranial fossa
 Limited in front and on each side by
frontal bone.
Its floor is formed by:
1. Orbital plate of frontal bone.
2. Cribriform plate of the ethmoid
3. Anterior part of the body and lesser
wing of sphenoid.

The anterior cranial fossa


1. Orbital plate of frontal bone
 Forms the greater part of the floor of the
fossa on each side of the median plane
 Separates the orbit and its contents from
the inferior surface of the frontal lobe of
the brain.
 In its antero-medial part it is split into two
laminae to contain part of an airspace, the
frontal sinus.www.indiandentalacademy.com

2. Cribriform plate of ethmoid
 Separates the fossa from nasal cavity
and forms the roof of the latter.
 Anteriorly it presents a median crest
like elevation CRISTA GALLI
which projects upwards in between
the two cerebrals hemispheres (which
is a land mark in frontal/anteroposterior cephalograms).

 The numerous small foramina which
perforate the cribriform plate of
ethmoid transmit the minute olfactory
nerves from the nasal mucosa to the
olfactory bulb.


3. The sphenoid bone
 Completes the fossa’s floor from
behind.Centrally is the anterior part of
the upper surface of its body termed
the jugum sphenoidale.
 This separates the fossae from
bilateral air spaces in the body of the
sphenoid named the sphenoidal
sinuses.

 Lateral to the jugum the floor of the
anterior fossa is formed by lesser wing
of sphenoid.
 Optic canal is located at the junction
of lesser wing and body of the
sphenoid bone.


The middle cranial fossa
 Deeper than the anterior.
 In front it is bounded by posterior borders
of the lesser wings of sphenoid and body
of sphenoid,
 Behind by superior borders of the petrous
parts of the temporal bone and dorsum
sella of sphenoid bone,laterally by the
temporal squamae,parietal bone and
sphenoidal greater wings.

su
fo
em

for

fora
Lesser pe
Greater pe

Teg


 Centrally the floor is narrower and
formed by sphenoid body.
 Optic canal is present between roots
of a lesser wing and lateral to the body
of the sphenoid. It contains the optic
nerve,
ophthalmic
artery
and
meninges.
 The chiasmal sulcus connects the
optic canals.

 Behind the sulcus the upper
sphenoidal surface is the sella
turcica,whose ant. slope bears a
median tuberculum sellae,behind
which is the hypophyseal fossa.
Posterior to it the dorsum
sellae projects up & forwards.

 Hypophyseal fossa is present in the
middle cranial fossa, which contain
the hypophysis cerebri.

 Laterally the middle cranial fossa is
deep and supports the temporal lobe
of cerebrum.

 Communicates anteriorly with the
orbit through the superior orbital
fissure, which is bounded above by
the lesser wing ,below by the greater
wing and medially by the body of the
sphenoid.
 Transmits the terminal branches of
ophthalmic nerve, ophthalmic veins,
occulomotor, trochlear and abducent
nerves.

 Foramen Rotundum pierces the
greater wing of the sphenoid and leads
forwards into the pterygopalatine
fossa to which it conducts maxillay
nerve.

 Foramen ovale lying post. to
F.rotundum leads downwards into the
infra-temporal fossa and transmits the
mandibular nerve.

Foramen spinosum transmits the

middle meningeal artery and is located
near the posterolateral margin of
foramen ovale.

Foramen lacerum is located at the
posterior end of the carotid groove
and posteromedial to the foramen
ovale. It contains the internal carotid
artery
and
its
accompanying
sympathetic and venous plexuses.

The Posterior cranial fossa
 The largest and deepest of the cranial
fossa.
 Surrounded by dorsum sella, posterior
part of the body of the sphenoid and
basilar part of the occipital bone
anteriorly;
 Behind by the lower portion of the
occipital squamae.

 On each side by the petrous and
mastoid parts of temporal bone and
lateral parts of occipital
 Above & behind by the mastoid
angles of the parietal bones.
 It contains the cerebellum,pons and
medulla oblongata.

The posterior cranial fossa


 The foramen magnum – It is in the
floor of the fossa and surrounded by
the parts of the occipital bone.
Somewhat ovoid in shape
communicates with the vertebral canal
where the medulla oblongata becomes
continuous with the spinal cord.

 The jugular foramen sited at post. end
of petro-occipital fissure, provides a
passage to the glossopharyngeal,
spinal accessory and vagus nerves and
internal jugular vein,.


 Above the anterior part of the jugular
foramen the internal acoustic meatus
runs transversely in a lateral direction.
It allows facial and vestibulocochlear
nerves, the nervus intermedius and
labyrinthine vessels.
 Hypoglossal canal is present lateral to
the foramen magnum and contains
hypoglossal nerve.

BONES FORMING THE
CRANIAL BASE


The occipital bone
 It forms much of the back and base of
the cranium.
 Trapezoid in shape,concave internally.
Contains 3 parts:
 Squamous part.
 Basillar part.
 Lateral / condylar part.


The sphenoid bone
 It is in the base of the skull,wedged
between the frontal and the temporal
bones and basilar part of occipital
bone.
 Has a shape of a bird with wings
stretched out .

The sphenoid consists of:
1.
2.
3.
4.

Central portion or body
Greater wings (2)
Lesser wings (2)
Pterygoid processes (2)
Each has:
Lateral pterygoid plates (2)
Medial pterygoid plates (2)

The temporal bones
 This paired bone forms the sides and
base of the skull.
 Each consists of 4 parts:
•
•
•
•

Squamous part.
Petromastoid part.
Tympanic.
Styloid process


The frontal bone
 It is an irregular cap like bone which forms
the region of the forehead
 On each side it has a horizontal orbital part
which forms most of the roof of the orbital
cavity.
 The portion of the bone which projects
downwards between the supraorbital
margins is named as the nasal part.

The ethmoid bone
 It is cuboidal and extremely light in build.
 Situated at the anterior part of the
basicranium and assists in forming the
medial walls of orbits, the nasal septum
and roof and lateral walls of nasal cavity.
It consists of 3 parts:
 Cribriform plate (perforated one)
 A perpendicular plate
 Lateral masses (labyrinths)

The Inferior nasal conchae
 These are curved laminae, which lie
horizontally in the lateral walls of
nasal cavity.


PRENATAL
DEVELOPMENT OF
CRANIAL BASE


Cranium can be divided into 2 parts:
 Neurocranium:
It protects and supports the brain
and sense organs.
 Viscerocranium:
Which is related to alimentary,
respiratory tracts, face, maxilla and
mandible.

 Basicranium or cranial base is related
to the both neural and visceral
components.
 At cellular level, bones of cranial base
develop by the following processes:
 Hyperplasia (Prominent feature
of all forms of growth)
 Hypertrophy(sec. Factor)
Secretion of extracellular
material

Chondrification:
Earliest evidence of formation of
cranial base is seen in the late somite
period i.e. 4th – 8th week of intrauterine
life.


Mesenchyme derived from primitive
streak,neural crest and occipital
sclerotomes
condenses around the developing brain
“ectomeningeal capsule”
basal portion

future cranial base
.


During this period:

The occipital sclerotomal mesenchyme
Concentrates around the notochord
underlying the developing hindbrain
Cephalic extension
Floor of the brain.

 Approximately 40th day of intrauterine
life mesenchyme starts converting into
cartilage marking the onset of cranial
base formation.
 Chondrification centers form in the
following regions:
1.
2.
3.
4.

Parachordal
Hypophyseal
Nasal
Otic


Parachordal region
 Chondrification centers forming around the
cranial end of the notochord are
appropriately called the parachordal
cartilages.
 Fuse with the sclerotomes arising from
occipital somites.


 The sclerotome cartilage is considered to
be the first part of the skull to develop and
it forms the boundaries of foramen
magnum, providing the anlagen for basilar
and condylar parts of the occipital bone.


Hypophyseal region
 Oropharyngeal membrane closes off the
stomadeum.
 Just cranial to this membrane the
hypophyseal pouch (Rathke’s pouch)
arises from the stomodeum.

Anterior lobe of pituitary gland
(Adenohypophysis) lying cranial to
notochord termination.

Two hypophyseal
or polar
or post sphenoid cartilages
Either side of the hypophyseal stem

Sella turcica and posterior part
of the body of the sphenoid bone.

Cranial to the pituitary gland fusion of
the two presphenoid
or trabecular cartilages
Precursor to the presphenoid bone
Anterior part of the body of the
sphenoid bone.

 Laterally the chondrification centers of the
orbitosphenoid
(lesser
wing)
and
alisphenoid (greaterwing) contribute later
to the sphenoid bone.
 Most anteriorly, the fused presphenoid
cartilage forms a vertical cartilaginous
plate called the mesethmoid cartilage
Perpendicular plate of the ethmoid bone
and crista galli.

 The capsules surrounding the
nasal, otic sense organs chondrify
and fuse to the cartilages of the
cranial base.


Nasal capsules:
Formed around the nasal sense organ
Chondrify in the 2nd month IU
Box of cartilage with a roof and lateral walls
divided by a median cartilage septum.
The cartilaginous nasal capsules
Ossification

Ethmoid and inferior nasal concha.

The chondrified nasal capsules
Cartilages of the nostrils &
median nasal septum
NS remains cartilaginous
except posteroinferiorly,
Intramembraneous ossification
Vomer bone
(paired initially,2 halves uniting before birth)

 In the foetus, the septal cartilage intervenes
between the cranial base above and the
premaxilla, vomer and palatine processes
of maxilla
 Postnatally the nasal septal cartilage acts as
a functional matrix in the downward and
forward growth of the midface.
 It helps in transferring compressive forces
from incisor region to the sphenoid bone.

Otic capsules:
 Formed around the vestibulocochlear sense
organs,
Chondrify & fuse with
the parachordal cartilages
Ossification
Mastoid and petrous
portions ofwww.indiandentalacademy.combones.
the temporal

N


Initial separate centers of cranial base
chondrification
Fusion
A single, irregular and much
perforated basal plate.
 This cartilaginous basal plate has
numerous perforations formed by the
establishment of blood vessels, cranial
nerves and spinal cord between the
developing brain and its extracranial
contacts.

 The height of cartilaginous skeletal
development occurs during the 3rd month
IU.
 A continuous plate of cartilage extends
from nasal capsule posteriorly all the way
to the foramen magnum
 During the 4th month IU there is an
ingrowth of vascular elements into the
various points of chondrocranium.
 These areas become centers of ossification,
at which cartilage is transformed into bone.

Various foramina

Related
nerves
and vessels

1) Perforations in Fibres of olfactory
the cribriform plate nerve (I)
of ethmoid bone.
2)
Optic
foramen
(Formed by extensions
of
orbitosphenoid
cartilage around II N.
fused with cranial part
of basal plate)

Optic nerve (II)
Ophthalmic
artery.


3) Superior orbital
fissure
(space
between
the
orbitosphenoid and
alisphenoid
cartilages)

Occulomotor (III)
Trochlear (IV)
Opthalmic (VI)
Abducens
(VI)
nerves and
Ophthalmic veins.

4) Foramen
rotundum

Maxillary
(V2)

nerve

5) Foramen ovale

Mandibular
(V3)

nerve


6) Foramen spinosum
(Junction
between
thealisphenoid
and
polar cartilages)

Middle
artery

meningeal

7) Foramen lacerum
(At the junction of
alisphenoid
and
postsphenoid cartilages
and otic capsule)

Internal
artery

carotid

8) Internal acoustic Facial (VII)
meatus
(Nerves Vestibulocochlear
passes through otic (VIII)
capsule)

9) Jugular foramen
(Passage of nerves
and vessels between
the otic capsule and
the
parachordal
cartilage)

Glossopharyngeal
(IX)
Vagus (X)
Spinal accessory (XI)
Internal jugular vein

10) Hypoglossal /
anterior
condylar
canal (Nerve passing
between the occipital
sclerotomes)

Hypoglossal
(XII)

11) Foramen magnum

nerve

Lower
end
of
medulla,meninges,
spinal arteries,

Ossification in individual
basicranial bones:


Occipital bone:
 Ossified from 7 centres, which are 2
intramembranous 5 endochondral.
 The supranuchal squamous portion
ossifies
from
a
pair
of
intramembranous ossification centers
in the 8th week of intrauterine life.

 The Infranuchal squamous portion
ossifies from a pair of endochondral
ossification centers at the 10th week.

 The basilar part ossifies appearing in
11th wk IU
Anterior portion of
occipital condyle & ant. boundary of
foramen magnum.

 A pair of endochondral ossification
centres appears in the 12th wk forming
the lateral boundary of foramen
magnum & posterior portion of
occipital condyles.
 An occasional centre appears in the
post. Margin of the foramen magnum
in 16th wk-KERCKRING’s CENTRE
which unites with the rest of squamae
before birth.

The temporal bone
 Ossifies
both
endochondrally
and
intramembraneously from 21 ossification
centres.
 Squamous and tympanic elements
Intramembranous ossification
 Petrosal and styloid elements
Endochondral ossification

 The squamous portion ossified
intramembranously from a single
center appearing in the 8 week, the
zygomatic process extends from this
ossification center.
 The tympanic ring surrounding the
external acoustic meatus ossifies from
4 intramembranous centers starting in
the 12th week I.U.

 The petrosal part ossifies endochondrally
in the otic capsule from about 14 centres,
these centers start to appear in the 16 th
week and fuse during the 6th month I.U.
when the contained inner-ear, labyrinth has
reached its final size.
 Styloid process ossifies from 2 centres in
the hyoid (2nd) branchial arch cartilage; the
upper center appears just before birth and
the lower center just after birth.

 At 22 weeks of I.U. the petrous and
tympanic ring fuse incompletely, leaving
the petrotympanic fissure.
 At birth the tympanic ring fuses
incompletely with the squamous part of
temporal bone.


 The petrous, squamous and proximal
styloid process-parts fuse during the 1 st
year of life.
 The mandibular (Glenoid) fossa is only a
shallow depression at birth facing laterally,
deepening with development of articular
eminance
and
ultimately
facing
downwards.

Ethmoid bone:

This wholly endochondral bone, which
forms the median floor of the anterior
cranial fossa and forms parts of the
roof, lateral walls and median septum
of the nasal cavity, ossifies from 3
centres.

A pair of centers for the lateral labyrinths
appears in the nasal capsular
cartilages at the 4th month I.U.
A single median center in the mesethmoid
cartilage forms the perpendicular plate and
cristagalli just before birth.
At two years of age the perpendicular
plate unites with the lateral labyrinths to
form a single ethmoid bone.

Inferior nasal choncha:
Single center in the cartilage of
lateral part of the nasal capsule
(5thmonth I.U)
Endochondral ossification
Inferior nasal concha
Detaches from the capsule
Independent bone.

The sphenoid bone:
 Sphenoid bone has up to 14 ossification
centers
(intramembranous
and
endochondral)
 Until the 7th or 8th month IU,sphenoid body
has a presphenoid part anterior to
tuberculum sellae,with which the lesser
wings are continuous ; and a postsphenoid
part ,comprising sella turcica and dorsum
sellae,and integral with the greater wings
& pterygoid processes.

 Lesser wing: Endochondral ossification in
the orbitosphenoid cartilage.
 Greater wing and lateral pterygoid plate: 2
intramembraneous ossification centres seen
in alisphenoid cartilage.A part of G.wing
ossifies endochondrally.
 Medial pterygoid plate:Ossifies
endochondrally from a secondary cartilage
in the hamular process.

 Anterior part of body of sphenoid: Ossifies
endochondrally from 5 centres(2 paired &1
in midline) in the presphenoid cartilage.
 Posterior part of body of sphenoid:
Ossifies endochondrally from 4 centres in
the postsphenoid cartilage.
 The midsphenoidal synchondrosis between
the pre and post sphenoid fuses shortly
before birth.
 The sphenooccipital synchondrosis fuses in
adolescence.

CRANIAL BASE FLEXURE
 During the embryonic and early fetal
periods,the enormous human cerebrum
expands around a much smaller enlarging
midventral segment(the medulla,pons,
hypothalamus,optic chiasma).
 This causes a bending of the whole
underside of the brain.And the flexure of
the cranial base results, in the region of the
pituitary fossa,at the spheno-occipital
junction,so that the developing face
becomes tucked in under the cranium.

Cranial Base Flexure

Early embryo
(Cranial base straight)

Fetus
(Cranial base flexed)


Cranial Base Flexure

This relates to two key features:
1. The spinal cord is now aligned
vertically,a change that permits
upright,bipedal body stance with free
arms and hands
2. As the forehead is rotated in a vertical
plane with the growth of the frontal
lobe,the superior orbital rim is carried
with it.This aligns the eyes so that they
point in the forward direction of upright
body movt. www.indiandentalacademy.com

 The body has become vertical,but the
neutral visual axis is still horizontal ,as in
other mammals.
 This cranial base flexure effectively
enlarges the neurocranial capacity and
causes downward rather than forward
displacement of face during its growth
from the cranial base.

Cranial base angulation
 The central region of the cranial base
is composed of prechordal and chordal
parts which meet at an angle at the
hypophyseal fossa (sella turcia).
 The lower angle, formed by lines from
nasion to sella to basion in the sagittal
plane varies following the growth of
embryo.

 Initially highly obtuse = 150° in 4
week old embryo (precartilage stage).
 Reduces approximately = 130° in 7-8
week old embryo (cartilage stage).
 Becomes more acute = 115-120° at 10
weeks embryo (pre-ossification stage).
 Widens to 125-130° at 10-20 weeks
(ossification stage) and maintains this
angulation postnatally.

Uneven nature of cranial base growth
 Growth of the cranial base is highly
uneven.
 The uneven growth of the parts of the
brain is reflected in the related parts of
the cranial base adapting as
compartments or cranial fossae.

 Unevenness is also seen in rate of
growth
 Eg. the anterior cranial base increases
in length and width by evenfold
between the 10th and 40th weeks
I.U. whereas,
The posterior cranial base grows
only 5 fold.

Postnatal growth
of
cranial base


 Cranial base has a potent role in the
development of structure, dimensions,
angles and placement of various facial
parts.
 Floor of the cranium is a template
from which face develops.
 Any difference in the development of
basicranium will be reflected in the
facial growth.

 Growth of the central ventral axis of
the brain and of the related body of
the sphenoid and basioccipital bones
is slow, providing a comparatively
stable base.
 Laterally,cranially and caudal to this
base, the anterior,middle and posterior
fossae expand enormously in keeping
with the growth of related parts of the
brain.

 The cranial base grows postnatally by
complex interaction between the following
growth processes:
1. Extensive cortical drift and remodelling
2. Growth of the cartilage remnants of
the
chondrocranium that persist
between the basicranial bones.
3. Expansive forces emanating from the
growing brain displacing the bones
at the suture lines (capsular
functional
matrix).

 Cortical drift and remodelling
 Endocranial surface of cranial floor
has a different mode of development
when compared with the culvaria
because of its complex structure and
curvature.
 The endocranial or neural surface of
the basicranium in contrast to the
roof is resorptive in most areas

 The reason is that the sutures do not
have the capacity to provide for the
multiple directions of enlargement and
the complex magnitude of remodeling
required.
 Remodeling
is
required
to
accommodate the massively enlarged
human brain.

Fossa enlargement:
The unidirectional sutural growth occurs at
locations 1 and 2, which is not sufficient to
accommodate the brain expansion.


Fossa enlargement
is accomplished by
direct
remodeling
involving deposition
on the outside with
resorption from the
inside.
This is the key remodeling process that
provides for the direct expansion of
the various endocranial fossae in
conjunction with sutural growth and
growth at synchondrosis.

Various endocranial compartments are
separated from one another by
elevated bony partitions:
 The olfactory fossae are separated by
CRISTA GALLI.
 Middle and posterior fossae are
divided by the petrous elevation.

 Right and left middle cranial fossae
are separated by the longitudinal
midline sphenoidal elevation.
 Right and left anterior and posterior
cranial fossae are divided by a
longitudinal midline bony ridge.


 All these elevated partitions, unlike of
the remainder of the cranial floor are
depository in nature because as fossae
expand outward by resorption, the
partitions between them must enlarge
inward by deposition to maintain the
proportions.


 The mid ventral segments of cranial
floor grow more slowly than the floor
of the laterally located fossae.
This
accommodates
the
slower development of the medulla,
pons, hypothalamus, optic chiasma in
contrast to the massive rapid
expansion of the hemispheres.

 A markedly decreasing and tapering
gradient of sutural growth occurs as
the ventral midline is approached but
direct remodeling also occur to
provide for the varying extents of
expansion required among the
different midline parts themselves and
much faster growing lateral regions.


 Unlike the roof, the floor of the
cranium provides the passage of
cranial nerves and major cerebral
vessels.
 The process of remodeling growth in
the basicranium provides for the
stability of these nerves and vascular
passageways.

 The foramen moves by deposition and
resorption
keeping
pace
with
corresponding
movement
of
nerve/vessel.
 The foramen enclosing each cranial
nerve and major blood vessel also
undergoes its own drift process to
constantly maintain the proper
position (Relocation)

 Growth in the posterior cranial fossa is
more when compared with growth of the
spinal cord and foramen magnum.
 Differential remodeling process maintains
the proportionate placement of spinal cord,
even though the floor of the posterior
cranial fossa, which surrounds the spinal
cord expands to a considerably greater
extent than the circumference of the
foramen magnum.

 The resorption occurs from the lining
side of the forward walls of the middle
cranial fossa (1).
 Deposition on the orbital face of the
sphenoid and in the sphenofrontal
suture (2).
 Forward displacement of the anterior
cranial fossae occurs as the frontal
lobes are displaced anteriorly (3).

 The petrous elevation (4) increases by
deposition on the endocranial surface.
 Lengthening of clivus occurs by growth at
SOS (5).
 The foramen magnum is progressively
lowered by resorption on the endocranial
surface and deposition on the ectocranial
side.
Endocranial fossa enlarge by a
combination of endocranial resorption and
ectocranial deposition.

2. Synchondroses:
The midline part of the basicranium is
characterized by the presence of
synchondroses.
They are the “left over” from the
primary
cartilages
of
the
chondrocranium after the endocranial
ossification centers appear during fetal
development.

 By their interstitial growth,the
interposed cartilages or
“synchondroses” can separate the
adjacent bones as appositional bone
growth adds to the sutural edges of the
bones.

 Different synchondroses seen in
cranial base





Spheno-occipital
Spheno-ethmoidal
Intra occipital
Inter-sphenoidal

The sphenooccipital synchondrosis
 It is the principal growth cartilage of
cranial base During childhood
 As all growth cartilages are associated
with (directly) bone development, the
SOS provides a pressure adapted bone
growth mechanism unlike the sutural
areas which show tension adapted
mechanism.

Pre s

Post
sphenoid
Basi
occipital


 Because cranial base supports the
mass of the brain and face, SOS in the
midline is subjected to craniofacial
muscular forces.
 As endochondral bone growth occurs
at the SOS,the sphenoid and the
occipital bones become moved apart
by the 1° displacement process.

 At the same time new endochondral
bone is laid down by the endosteum
within each bone (Medullary fine
cancellous bone). Compact cortical
(Intramembranous) bone is formed
around this core of endochondral bone
tissue. .
 Each
bone
thereby
becomes
lengthened. Both bones also increase
in girth by periosteal and endosteal
remodeling.

 The interior of the sphenoid bone
eventually becomes hollowed to form
the sizable sphenoidal sinus.
 Sphenoidal sinus expansion does not
push the maxilla. The sinus grows
secondarily as the body of the
sphenoid bone expands around it
keeping constant junction with the
moving nasomaxillary complex.

 The synchondrosis has a series of
zones like primary cartilage :

1.
2.
3.
4.

Familiar reserve zone.
Cell division zone.
Hypertrophic zone.
Calcified zone.

 Similar to an epiphyseal plate, but unlike
the condylar cartilage, the chondroblasts in
the cell division zone are aligned in
distinctive columns that point along the
line of growth
 Unlike
the
epiphyseal
plate
the
synchondrosis has 2 major (Bipolar)
directions of linear growth.
 Structurally
the
synchondrosis
is
essentially 2 epiphyseal plates positioned
back to back and separated by a common
zone of reserve cartilage.

 SOS is the last of all synchondrosis to
fuse and starts fusing at 12-13 years
in girls, and 14-15 years in boys and
completing ossification of the
external aspect by 20 years of age.
 This prolonged growth period allows
for continued posterior expansion of
the maxilla to accommodate last
erupting molar teeth and provides
space for growing nasopharynx.

Spheno-ethmoidal synchondrosis
 A cartilaginous band between the
sphenoid and ethmoid bones.
 Believed to ossify after 5yrs of age.
Inter sphenoidal synchondrosis
 Between 2 parts of sphenoid
 Ossifies at birth
Intra occipital synchondrosis
 This ossifies by 3-5 yrs of age.

 The size, shape and characteristics of
cranial floor have evolved in direct
phylogenetic association with the brain it
supports, but the basicranium itself has
presumably developed a genetic capacity
of its own growth that is some how
independent of the brain.
 Extrinsic control factors are also involved;
but to what extent they are involved is not
fully understood, since the cranial floor
can develop to a greater or lesser extent,
even though the brain is malformed or

3. Expansive forces from brainGrowth at sutures.
Some of the sutures of cranial base:
 Spheno-frontal
 Fronto-temporal
 Spheno-ethmoid
 Fronto-ethmoid
 Fronto-zygomatic

.
 The expansion of the middle cranial
fossa and its neural contents

 Secondary displacement effect on the
anterior cranial floor , underlying
nasomaxillary complex and mandible.


 Because the posterior boundary of
nasomaxillary
complex
is
developmentally positioned to exactly
coincide with the boundary between
the anterior and middle cranial fossae
some amount of forward displacement
of both the anterior cranial fossa and
the nasomaxillary complex occurs.

 The temporal and frontal lobes have
fibrous attachments to the middle and
anterior cranial fossa.
 As both lobes expand these 2 fossae
are thus pulled away from each other.
 This set up tension fields in various
frontal, temporal, sphenoidal, and
ethmoidal sutures and this also
presumably triggers sutural bone
responses.

 At about 5 years of age, frontal lobe
growth and anterior cranial fossae
expansion are largely complete.
 The temporal and middle cranial
fossa, however continue to enlarge for
several more years


 The expansion of each temporal lobe
continues to displace the frontal lobe
forward and this in turn causes tension
in the osteogenic suture systems
between these 2 areas.
 The anterior fossae and the maxillary
complex are carried anteriorly by the
frontal lobes, which is moved forward
because of temporal lobe enlarging
behind it.

Timing of cranial base growth
1. By birth,55-60 % of adult size is
attained.
2. By 4-7 yrs,94 % of adult size is
attained.
3. By 8-13 yrs,98 % of adult size is
attained.

Clinical implications


Study:Cranial base growth for Dutch
boys and girls (AJO 1994 November))
- Monique Henneberke and
Birte Prahl Andersen
In this study growth and development of
the cranial base in children who were
treated orthodontically were compared
with children who were not.

The hypothesis tested was that there is
no difference in cranial base growth
between children with and without
orthodontic treatment.
This is a mixed longitudinal study of
*153 boys and 167 girls samples for
S-N
*116 boys and 116 girls for N-Ba and
S-Ba,
* All were of 7-14 years of age.

 Cephalometric points used in this
study.

Results:
 The effect of orthodontic therapy on
cranial base growth was apparently so
limited that no significant differences
could be demonstrated between
children with or without treatment.
 The cranial base displayed sexual
dimorphism in absolute size, timing
and amount of growth.

 All C.B. dimensions examined in this
study were greater in boys than in
girls.

 Girls did not show adolescent growth
spurts, where as all boys showed that
for S-N and N-Ba.

Anencephaly
 Characterizd by
chondrocranium
anomalies.

a short, narrow
with
notochordal

 Anencephaly patients retain the acute
cranial base flexure typical of early
fetuses.
 This suggests that brain growth contributes
to flattening of the cranial base.

 Certain forms of dental malocclusions may
be related to defects of the chondrocranium
eg. The defects that minimize the space
available for maxillary dentition
(diminished maxilla) may lead to impacted
teeth viz.third molars.


 Afflictions of cartilage growth produce a
reduced cranial base resulting in a ‘dished’
deformity of middle 13 of face which is
seen in conditions like achondroplasia,
cretinism and Down’s syndrome (Trisomy
21).
 All these produce a similar characteristic
facial deformity by their inhibiting effect
on chondrocranial growth.

Achondroplasia:


 The C.B. does not lengthen normally
because of deficient growth at the
synchondroses; the maxilla is not
translated forward to the normal
extent, and a relative midface
deficiency occurs


 Premature ossification or synostosis of
the suture between the presphenoid
and post sphenoid parts and of the
sphenooccipital suture produces a
characteristic apearance.
 This is seen in profile, and consists of
an abnormal depression of the bridge
of the nose


 Hypertelorism.
Anomalous development of the
presphenoidal elements excessive
separation between the orbits and
abnormally broad nasal bridge.


 Craniopharyngeal tumours
Coalescence of the ossification
centers in the body of sphenoid
obliterates the orohypopharyngeal
track. Persistence of the track as a
craniopharyngeal canal in the
sphenoid body gives rise to
craniopharyngeal tumours.


 Premature fusion of sphenooccipital
synchondrosis in infancy results in a
depressed nasal bridge and dished
face.
 Cleidocranial dysostosis patients with
CCD exhibit high frequencies of
anomalous traits in the cranial base.

 CCD is characterized by abnormalities
of the skull, jaws and shoulder girdle
as well as by occasional stunting of
long bones.
 In the skull, frontanelles remain open
or atleast exhibit delayed closing.
 Frontal, parietal and occipital bones
are prominent and the paranasal
sinuses are underveloped and narrow.

Study: (AJO May 1981)
 Kreiborg,Jensen, Bjork and Skieller
conducted a qualitative screening for
abnormal morphological traits in the
cranial base.
 The sample comprised 17 patients
with CCD (8 males and 9 females) 1646 yrs of age.

Results:
 The anterior and posterior cranial base
was significantly shorter and the C.B.
angle smaller in the syndrome groups
than in the control groups.
 Clivus was distorted in 82 % of
patients.

 All patients showed bulbous dorsum
sellae and many had small pituitary
fossae.
 The amount of bone resorption was
lesser than normal, so abnormalities in
remodeling pattern is seen.

 Lateral roentgenocephalometric film
of adult male patient with
cleidocranial dysostosis.
 Poor visualization of posterior
cranial base.

 Midsagittal tomogram of posterior
cranial base in a patient of CCD.
 Bulbous dorsum sellae and flexion
of clivus.

 Tracings of the posterior
cranial base from
midsagittal tomograms of
three patients with
cleidocranial dysostosis.
Note shallow pituitary
fossa in Patient 1065Z.
All three patients exhibited bulbous
dorsum sellae, flexion of clivus, and
bulbous anterior margin of foramen
magnum.

 Distortion of clivus in the syndrome
group could have arisen in a number
of ways:
• First, it could be related to an
abnormal remodeling pattern.
• Second, it could be primary anomaly
comparable to the other midline
anomalies found in the syndrome..

 Third, it could result from
displacement of the bone of the
cranial base during the development
caused by delayed or defective
ossification in the region
 It could result from any combination
of these mechanisms

References
1. Craniofacial Embryology
- G.H.SPERBER
2. Essentials Of Facial Growth
- D.H.ENLOW
3. Gray’s Anatomy
- Gray
4. Contemporary orthodontics
- W.R.PROFFIT

5. Orthodontics-The art and science-- S.I.Bhalajhi
6.Abnormalities Of Cleidocranial
Dysostosis – Kreiborg,bjork& Skeiller
(AJO May; 1981)
7. Cranial Base Growth For Dutch Boys
& Girls – M.Herneberke,b.P. Andersen
(AJO November; 1994)

Thank you
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