Theories of craniofacial growth in the postgenomic era123 /certified fixed orthodontic courses by Indian dental academy

THEORIES OF
CRANIOFACIAL GROWTH IN
THE POSTGENOMIC ERA
(Seminars in Orthodontics11:172-183/2005)
www.indiandentalacademy.com
INDIAN DENTAL ACADEMY
Leader in continuing dental education

GOAL OF THE ARTICLE:-
To summarize the major concepts of
the growth of the craniofacial
skeleton,with specific emphasis on
concomitant developments in the
fields of genetics.

ORTHODONTICS,RACE & THE
CONCEPTS OF FACIAL TYPE
“Faces & occlusion should be brought into a
condition of harmony according to type.”
-Angle
“….endeavored in their treatment to increase the
maximum amount of bony tissue that nature has
preordained,rather than to straighten the amount
already predestined.
-Sir Arthur Keith

THEORIES OF
CRANIOFACIAL GROWTH
1)Genetic Theory
2)Bone Remodelling Theory-Brash(1930)
3)Sutural Theory-Weinmann & Sichers(1940)
4)Cartilaginous Theory-James Scott(1950)
5)Functional Matrix Theory-Melvin Moss(1962)
6)Servosystem Theory-Alexander Petrovic(1970)
7)Multifactorial Theory-Van Limborgh(1970)
8)“V” principle-Enlow
9)Counterpart Principle-Enlow

GENETIC THEORY
Growth is controlled
by genetic influence &
is preplanned.
• About 2/3rd
of total
genes play a role in
craniofacial
development.

1) Homeobox Genes
2) Sonic Hedgehog
3) Trascription factors
4) Indian Hedgehog

BONE REMODELING THEORY
• John Hunter’s approach on the growth of
the jaws & eruption of dentition culminated
in the research of Brash.
• Principle tenets of the theory:-
• 1)Appositional growth
• 2)Hunterian Growth
• 3)Calvarial Growth

• Hunterian Growth:-
Deposition of bone at
the posterior surface
of Maxilla &
Mandible.

• All of craniofacial
growth occurs
exclusively by bone
remodelling-selective
formation & resorption
of bone at its surfaces.

MODELING
• Bone resorption and bone formation occur on
separate surfaces (i.e., they are not coupled).
• E.g.:- long bone formation.
• Bone modeling occurs during birth to adulthood
and is responsible for gain in skeletal mass and
changes in skeletal form.

Bone Remodeling
• Remodeling is the replacement of old bone tissue by new
bone tissue which mainly occurs in the adult skeleton to
maintain bone mass. This process involves the coupling of
bone formation and bone resorption and consists of five
phases:
1. Activation
2. Resorption
3. Reversal
4. Formation
5. Quiescence

HEREDITY,GENETICS & GENES
• Mendel(1822-1884):-Mechanism of
inheritance & transmission of traits.
• Weismann:-
germ plasm determinants(pangene)
• Bateson(1909):-Genetics
• Johannsen:-Gene

SUTURAL THEORY
• Suture:- The line of
junction or an
immovable joint
between two bones,
especially of the
skull.
• E.g. sagittal suture

Connective tissue &
cartilaginous joints of
the facial skeleton are
principle locations at
which intrinsic .
genetically regulated ,
primary growth of
bones takes place

• Maxilla is hafted to the
cranium by
Frontomaxillary,Zygom
aticamaxillary,Zygomat
icotemporal &
Pterygopalatine
sutures,which are
parallel with each
other.thus growth at
these areas would serve
to move maxilla
forward & downward

“the role of proliferating sutural
connective tissue in the cranial
growth………..is identical to that of
proliferating cartilage in the basal
synchondrosis.”
-Sicher

• According to
Wienmann &
Sicher condyle is a
major growth
centre of mandible
& is endowed with
an intrinsic genetic
potential.

POINTS IN FAVOUR OF THEORY
• 1)Periosteal remodeling of bone is under
strong local influences by the functional
environment.
• 2)Sutural theory was consistent with the
contemporary understanding of the
importance of the cartilaginous structures &
skeletal joints in the development &
postnatal growth of bones.

A number of points were raised against
this theory…..
• 1)Extirpation of facial sutures has no
appreciable effects on dimensional growth
of facial skeleton.
• 2)Growth take place in untreated cases of
cleft palate even in the absence of sutures.

NASAL SEPTAL THEORY
• Osteogenic layers within the suture are
actually continuations of periosteum & dura
within the cranial vault & of the periosteum
in facial sutures.
-James Scott

• Scott assume that,intrinsic
growth controlling factors
were present only in
cartilage & in the
periosteum,with sutures
being only secondary.
• Acccording to this
theory,nasal septal
cartilage act as a space
maker for the growth of
entire naso-maxillary
complex

• The mandible is
considered as a
diaphysis of a long
bone,bent into a horse-
shoe shape with
epiphysis removed so
that there is cartilage
constituting half an
epiphyseal plate at the
ends which are
represented by
condyles.

Points in favour of nasal septum
theory
If a part of an epiphyseal plate is
transplanted to a different location , it will
continue to grow in new location . This
indicates innate growth potential of
cartilage.

• Experiment on
rabbit involving
removal of nasal
septal cartilage
demonstrate
retarded mid-facial
development.

STRUCTURAL BASIS OF GENE
& GENE ACTION
• 1)Double helix model of DNA provided a model for
the understanding of gene replication.
• 2)Operon thery explains how genes operate within
common regulatory sequence that can be turned on
or off to control transcription of m-RNA & gene
expression

PARADIGM SHIFT IN CRANIOFACIAL
BIOLOGY
GROWTH SITE
• 1)These are a growth fields
that have a special
significance in the growth of
a particular bone.
• 2)Growth occurs as a
secondary,compensatory
effect.
• 3)Lacks direct genetic
influence.
• 4)All growth sites are
growth centres.
GROWTH CENTRE
• 1)These are special growth
sites,which control the
overall growth of the bone.
• 2)Growth is primarily under
the control of heredity.
• 3)Have intrinsic genetic
potential.
• 4)All growth centres are not
always growth site.

FUNCTIONAL MATRIX
THEORY
• Most accepted theory.
• Melvin Moss was inspired by the ideas of
Van der Klaauw (1952) that bones were in
reality , composed of several
“FUNCTIONAL CRANIAL COMPONENT” ,
the size , shape & position of which were
relatively independent of each other. He
experimentally verified & expanded on
these concepts & incorporated them with
his own in 1962.www.indiandentalacademy.com

FUNCTIONAL CRANIAL
COMPONENT
• Head is a composite structure, operationally consisting
of a number of relatively independent functions;-
• Digestion,
• Respiration,
• Vision,
• Speech,
• Equilibrium,
• Neural Integration,
• Olfaction,
• Audition www.indiandentalacademy.com

Each function is carried out by a group of
soft tissues which are supported &/or
protected by related skeleton elements.
Taken together the soft tissues & skeleton
elements related to a single function are
termed as ‘FUNCTIONAL CRANIAL
COMPONENT

Functional Cranial Component
Functional Matrix Skeletal Unit
Periosteal Capsular Microskeletal Macroskeletal
Matrix Matrix
Neurocranial Oro-Facial

FUNCTIONAL MATRIX
• The totality of the soft tissues
associated with a single function is
termed as a functional matrix.
Functional matrix includes;-
1)Muscles
2)Nerves
3)Vessels
4)Glands
5)Functioning spaces- Nasopharynx
& Oropharynx

FUNCTIONAL MATRICES
PERIOSTEAL MATRIX
• It acts directly & actively
upon their related skeletal
units.
• Alterations in their
functional demands produce
a secondary compensatory
transformation of the size or
shape of their skeletal units
by inter-related processes of
bone deposition &
resorption.
CAPSULAR MATRIX
• It acts indirectly & passively
upon their related skeletal
units producing a secondary
compensatory translation in
space.
• These alterations in spatial
position of skeletal units are
brought about by the
expansion of oro-facial
capsules within which the
facial bones arise,grow & are
maintained.

SKELETAL UNIT
MICRO-SKELETAL UNIT
• Bone is comprised of
several contiguous skeletal
units.
• E.g.:-
1)Mandible:-Alveolar,
gonial, condylar, coronoid
2)Maxilla;-Orbital,
pneumatic, palatal
MACRO-SKELETAL UNIT
• Adjoining portions of a
number of neighbouring
bones are united to a
function as a single cranial
component.
• E.g.:-
Entire endocranial surface
of calvarium

SERVOSYSTEM THEORY
• Proposed by Alexandre Petrovic in 1970.
• Characterized by 2 principal factors;-
• 1)The hormonally regulated growth of the
midface & anterior cranial base which provides a
constantly changing reference input via the
occlusion.
• 2) The rate - limiting effect of this mid-facial
growth on the growth of mandible.

MULTIFACTORIAL THEORY
• Proposed by Van Limborgh in 1970
• Functional Matrix Theory + Sutural Theory
+ Genetic Theory = Van Limborgh’s
Theory

1] Chondrocranial growth is controlled mainly by
intrinsic genetic factors
2] Desmocranial growth is controlled by a few
intrinsic genetic factors
3]Cartilaginous part of skull-as growth centre.
4]Sutural growth is controlled mainly by influences
originating from skull cartilages & adjacent skull
structures.
5]periosteal growth largely depends upon growth of
adjacent structures.

FACTORS CONTROLLING
GROWTH
• 1)Intrinsic Genetic Factors
• 2)Local Epigenetic Factors
• 3)General Epigenetic Factors
• 4)Local Environmental Factors
• 5)General Environmental Factos

ENLOW’S EXPANDING ‘V’
PRINCIPLE
• Many facial bones or parts of bone have a ‘V’
shaped pattern of growth.
• The growth movements & enlargements of
these bones occurs towards the wide end of the
‘V’.
• Simultaneously resorption on inner arm of ‘V’
and deposition on outer arm of ‘V’ takes place.

Bone deposition occurs on
inside of maxillary arch and
resorption occur on whole
anterior part of maxillary arch
increase in width of palate and
the palate becomes wider
and results in ‘V’

• Bone deposition occurs on
lingual side of coronoid
process
• Growth proceeds Superiorly
• Vertical lengthening of
coronoid process
• Increased vertical ramus
dimension
• ‘V’ oriented vertically

• Bone deposition occur on
lingual side of coronoid
process and brings about
posterior direction of
growth movement
•
• Backward movement of
two coronoid processes
• Expanding ‘V’ principle
with ‘V’ oriented
horizontally

ENLOW’S COUNTERPART
PRINCIPLE
• Growth of any given facial or cranial part
relates specifically to other structural &
other geometric counterpart in the face &
cranium.
• If each regional part & its particular
counterpart enlarge to the same extent ,
balanced growth occurs.

• E.g.
1)Bony maxilla &
corpus of mandible
are mutual
counterparts.

GENETICS & CRANIOFACIAL GROWTH
THEORIES IN MODERN ERA
• At the time of remodeling theory by Brash in
1920 , concept of heredity was just a beginning ,
with no real knowledge of nature of gene & its
actions.
• In1940,during the beginning of sutural theory ,
Waddington & others combined principles of
transmission genetics & embryology to develop a
hypothesis about how genes might act on specific
phenotypic traits.-Foundation for future advances.

Nasal septum theory arise at that time , when
structure of genes & it’s actions were described .
However , it was not clear , what was being
inherited . What is the exact size & shape of the
face?
Later on Functional Matrix theory of Moss
came with conclusion that sutures are secondary
sites & soft tissue & functional factors controlling
growth .It shifts , the paradigm from genetic
predetermination to role of epigenetic factors in
craniofacial growth.www.indiandentalacademy.com

• Servosystem theory, emphasized an
approach to craniofacial growth research on
cell physiology & integrated biology.

GENETICS,CRANIOFACIAL BIOLOGY &
ORTHODONTICS IN THE POST GENOMIC ERA
• Craniofacial biology has strongly
emphasized research on postnatal
craniofacial growth as this is the period
when dentofacial orthopedics might be
attempted to correct a developing
malocclusion & skeletal discrepancy

• Developmental biology is a combination of
heredity-genetics & embryology with
emphasis on intrinsic , genetic & epigenetic
factors.
• Until 1970, genetics of craniofacial
development was a black box , to
experimental morphologists outside the
field of developmental biology.

• Stages of prenatal development were well
described by classical embryology & the
effects of teratogens on the craniofacial
complex were empirically understood.
• By mid 1970 to 1980, transforming growth
factor & homeobox genes were discovered
which have significant effect on
morphogenesis & development of
craniofacial complex

• Now in post-genomic era , 3 issues seems to be
clear-
• 1)There are number of factors that have profound
effects on cranio-facial growth.
• 2)These factors operate in epigenetic milieu.
Genes are turned on & off during critical times of
development.
• 3)There is evidence from experimental
embryology ,teratology & functional morphology
that morphogenesis , prenatal development &
postnatal growth can be modified.

However this does not mean that , craniofacial
growth can be modified in a predictable &
controlled way.
• With next several decades orthodontists will be
using molecular kits , to diagnose growth related
problems & to determine precisely each patients
developmental status as well as presence &
absence of key polymorphisms for growth factors
& signaling molecules.

CONCLUSION
Majorly influenced by embryological and less
by genetics, craniofacial growth & development,
malocclusion & treatment concepts were known till
now taking advantage of that orthodontists are now
well positioned to enter a new era of genetics and
molecular biology through the incorporation of the
principles of developmental molecular genetics into
treatment of developing malocclusion and growth
related jaw discrepancies in a new way…

THANK YOU
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