Theroies of growth /certified fixed orthodontic courses by Indian dental academy

THEORIES OF
GROWTH
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

CONTENTS
1. Paradigms in craniofacial biology
2. Various theories of growth
--The Genetic theory
--Sicher’s Sutural Dominance theory
--Scott’s hypothesis
--Moss’ functional matrix hypothesis
--Van Limborgh’s theory


Hypothesis
-- An assumption not proved by experiment or
observation.
-- It is assumed for the sake of testing its soundness
or to facilitate investigation of a class of
phenomena.


Theory
--A supposition or an assumption based on certain
evidence or observations but lacking scientific proof.
When a theory becomes generally accepted & firmly
established, it is called a doctrine or principle
… Theory requires a basis of sound evidence,

while hypothesis is thoughtful conjecture of the
meaning of incomplete evidence

 Kuhn

defined the terms:
“ Normal Science” &“Paradigms”
as pertaining the field of craniofacial
biology.


Normal Science: defined as research
findings generally agreed to be basic to a
scientific field.
Paradigm:It is a conceptual scheme that
encompasses individual theories and is
accepted by a scientific community as a
model and foundation for further research.

 Scientific

revolution
--A change in paradigm brought about by
inconsistencies within the old scheme or by
technologic developments that permit
scientists to ask new questions & gain new
data is called a scientific revolution


EVOLUTION OF VARIOUS PARADIGMS

g

As new paradigms emerge ,a new normal
science for the field emerges.
:Kuhn &
Carlson

PARADIGMS IN CRANIOFACIAL BIOLOGY

THE GENETIC PARADIGM
 BRODIE

,assumed facial configuration
under genetic control
 Research focussed on growth sites for
this control: the sutures ,craniofacial
cartilages and periosteum
 Assumption was made that cartilages and
facial sutures were under genetic control
and brain determined the vault
dimensions

 In

1940’s 2 events reflected changing
ideas about dominant genetic paradigm :
 1)marked increase in use of animals in
craniofacial research
 2)introduction of jaw and facial
electromyography
Other developments included the use of
radioopaque implants, vital dyes & in vivo,in
vitro transplantations.

GENOMIC PARADIGM


Functional Paradigm


Rise of functional paradigm was when
Melvin Moss adopted van der Klauuw’s ideas &
published a paper in American Journal of physical
anthropology in 1960 and called it the “functional
matrix hypothesis”.
(Moss & Young)



Moss suggested skeletal tissues were passive and
under direct control of functional components to
which craniofacial skeleton adapted.

 It

focused on craniofacial growth from exactly
opposite view as genomic paradigm.

 Emphasized

the epigenetic interaction of intrinsic
and extrinsic factors that result in variation in
craniofacial form.

 Also

placed emphasis on potential of modification
of craniofacial growth & form using principles of
orthodontics and dentofacial orthopedics.

The Functional Paradigm


 Change

of concepts with time regarding the cranial
differentiation in embryonic skull and later
regarding the chondrocranial & desmocranial
growth

(from Limborg,j.v.: A new view on the control of the
morphogenesis of the skull, Acta morph ,Neer
Scand, 1970)

Cranial differentiation in embryonic skull


Sicher’s sutural dominence theory


Scott’s hypothesis


Moss hypothesis


Interrelation of all control factors


The Genetic Theory
 Simply

said genes determine all

 These

are primary controls for
initiation & formation of facial
structures.

 These

genes are same in all
animals.

 Intrinsic

genetic information necessary
for the differentiation of cranial
cartilages and bones is supplied by
neural crest cells.



Importance of intrinsic genetic factors
in controlling craniofacial differentiation
is considerably high

 Primary

genetic control determines certain
initial features
 From investigations two conclusions seen
a) inheritance of facial dimensions - polygenic
b) no more than one fourth of variability of any
dimension in children be explained by that
dimension in parents


Sutural Dominance Theory
(Sicher)
 Sicher

introduced that sutures were causing
most of growth

 Primary

event in sutural growth - connective
tissue proliferation between the two bones.



This creates the space for oppositional
growth at the borders of the two bones.

 The

connective tissue in sutures of both the
nasomaxilary complex and vault produced
forces which separated the bones.

 The

theory held sutures, cartilage and
periosteum responsible for facial growth and
assumed all under tight intrinsic genetic
control.

Shortcomings of Sutural theory
.It is clear now that sutures are not

primary determinants of growth. Two
evidences in support are:

1)Sutures & periosteal tissues lack innate
growth potential,proved by transplanting
a suture
2)Growth at sutures responds to outside
influences,as compression and tension.

 For

eg. If cranial or facial bones are
pulled apart at sutures, new bone fills in
and if suture is compressed the growth
will be impeded.
 Sutures are thus areas that react-not
primary determinants.
 Thus sutures are growth sites,not
growth centres.

Growth Center:
Those areas of craniofacial skeleton that have:


tissue seperating capabilties

 innate
 not

growth potential

influenced by external factors

 e.g.Synchondrosis

and nasal septal cartilage.


Growth Site:
Locations at which active skeletal growth occur
but as a secondary ,compensatory effect
 lacking

direct genetic influence

 effected

 e.g.

by external influences.

sutures and periosteum

Scott’s Hypothesis


Held that cartilaginous portions of head,
nasal capsule, mandible and cranial base
dominate facial growth.



Specifically emphasized how the cartilage of
nasal septum paced the growth of maxilla.



Sutural growth came in response to growth of
other str. including cartilaginous structures.
Scott,1954

Condylar cartilage as
growth determinant


Growth at nasal septum causes
downward & forward translation of
maxilla


Growth of maxilla on basis of Scott’s theory
-Nasomaxillary complex grows as a unit.
-Cartilaginous nasal septum serves as pacemaker for
maxillary growth
-Cartilage is so located so that its growth leads to
forward and downward translation of maxilla.
-Forces from the growing cartilage pulled apart the
sutures which then responds by new bone formation
leading to growth.

Experiments to verify Scott’s
theory
 Two

kinds of experiments carried out to test
the theory:
 1. Transplantation experiments
 2. Removal of cartilage.
Transplantation experiments
 not all skeletal cartilage act same when
transplanted.

 Epiphysis

plate of long bone continued to
grow in new location.
 Spheno-occipital synchondrosis also grows
when transplanted, but not as well.
 Nasal septal cartilage found to grow nearly as
well as others.
 No growth found when mandibular condyle
transplanted.

Cartilage removal experiments
 Extirpating

a young rabbits septum
causes a considerable deficit in growth
of midface.

 Gilhuus-

Moe and Lund demonstrated
that after fracture of condyle in a child
there was an excellent chance that it
would regenerate to app. its original
size

Effect of removing nasal
septum on forward
growth of mid face

Mid face deficiency in a
man whose nasal septum
was removed at age of 8


Shortcomings of Scott’s
Theory


Transplantation experiments have revealed
that condyle has no innate growth potential.



It is a growth site and not a growth center



Influenced by local factors



growth at condyle is entirely reactive

FUNCTIONAL MATRIX HYPOTHESIS
(Melvin Moss)


Bone & cartilage lack growth determination



They grow in response to intrinsic growth of
associated tissues,since the genetic coding for
craniofacial skeletal growth is outside the bony
skeleton.



These associated tissues are termed,functional
matrices.

THE ORIGIN, GROWTH AND MAINTENANCE OF ALL
SKELETAL TISSUES AND ORGANS ARE ALWAYS
SECONDARY, COMPENSATORY AND OBLIGATORY
RESPONSES TO TEMPORALLY AND OPERATIONAL
PRIOR EVENTS OR PROCESSES THAT OCCUR IN
SPECIFICALLY RELATED NON-SKELETAL TISSUES,
ORGANS OR FUNCTIONING SPACES
1981


 The

head is a region within which certain
functions occur.
 Every function is completely carried out by a
functional cranial component.

Functional
Matrix

Skeletal
Unit

.

All growth changes in the size, shape, and
spatial position and, indeed, the very
maintenance in being, of all, skeletal units
are always secondary to temporally primary
changes in their specific functional matrices.


Functional Cranial Component
Functional Matrices

Skeletal unit

Periosteal
Capsular
Macro
Micro
I
I
I
I
(teeth,muscles) (orofacial, (endocranial (coronoid,angular
neurocranial) surface of calvaria)


FUNCTIONAL MATRIX :
 all soft tissues and spaces that perform
a given function
SKELETAL UNIT:
 bony structures that support the
functional matrix and are necessary for
that function

Skeletal units
May be compressed of bone,cartilage,or tendinous
tissues
Macroskeletal unit
 when adjoining portions of a number of
neighbouring skeletal units are united to function
as a single cranial component e.g maxilla and
mandible
Microskeletal unit
 when a bone consists of a number of skeletal units
, these skeletal units are termed microskeletal
units e.g coronoid ,condyle processes of mandible

Microskeletal unit

Macroskeletal unit

In the mandible,
•a coronoid microskeletal unit related to the functional
demands of the temporalis muscle;
•an angular microskeletal unit related to the activity of
both the masseter and medial pterygoid muscles;
•an alveolar unit related to the presence and position of
teeth; and
• a basal microskeletal unit related to the inferior
alveolar neurovascular triad matrix.

 Contiguous

microskeletal units are
independent of each other.



This implies that changes in the size, shape,
or position of the coronoid process as a result
of primary, changes in temporalis muscle are
relatively independent of such changes in
other mandibular microskeletal units.



The term functional matrix is by no means
equivalent to what is commonly understood as "soft
tissues," this is, muscles, glands, nerves, vessels,
fat, etc., although all of these are obviously included
within the concept. Teeth are also a functional
matrix. When this functional grows or is moved, the
related skeletal unit (the alveolar bone) responds
appropriately to this morphogenetically primary
demand.



Their designation as periosteal and capsular most
clearly indicates the sites of their activity.


Periosteal matrix :
 Immediate local functional environment ,typically
associated with muscles,glands,blood vessels and
nerves,fat etc
 Act directly and actively upon their related sk.units,
thereby bringing about transformation.
Capsular matrix :
 Organs and spaces that occupy a broader
anatomical complex.
 Act indirectly and passively on related sk.units,
thereby producing secondary, compensatory
translation in space.

PERIOSTEAL MATRICES
 All

non skeletal functional units
adjacent to skeletal unit form the
periosteal matrices

 All

skeletal units in formal sense,
arise, exist, grow and are
maintained while totally embedded
within their functional periosteal
matrices



All responses of skeletal units to periosteal
matrices brought about by complementary and inter
related processes of osseous deposition and
resorption



They act by bringing transformation of the related
skeletal units



E.g – coronoid process and temporalis muscle



Removal of the mammalian temporalis muscle,
or its denervation, experimentally, postinfectively,
or posttraumatically, invariably results in an actual
diminution of coronoid process size and shape or, indeed,
in its total disappearance.



Similarly, it is well established that functional hypertrophy
or hyperactivity of the temporalis muscle is productive of
increased coronoid process size and also alteration of its
shape



. The coronoid process does not grow first and thus
provide a "platform" upon which the temporalis muscle can
then alter its functions.

 While

muscles are excellent examples
of periosteal function matrices, they do
not comprise this entire category.
 Blood vessels, nerves and glands
produce morphologic changes in their
related skeletal units in a completely
homologus manner

CAPSULAR MATRICES


All functional cranial components (functional
matrices plus skeletal units ) arise, grow, operate &
are maintained within a series of cranial capsules



2 capsules– neurocranial capsule
orofacial capsule



These capsules as a whole are sandwitched
between two covering layers.
--Skin & dura mater in neurocranial capsule
--Skin & mucosa in orofacial capsule



All spaces intervening between function
components themselves, and between them and
the limits of the capsule, are filled with indifferent
loose connective tissue.

 Each

capsule surrounds and protects a capsular
functional matrix - in one case, the neural mass
which consists of the brain plus leptomeninges and
cerebrospinal fluid; in the second case, the
oronasopharyngeal functioning spaces.



The common factor in both cases is that the
capsular matrices exist as volumes.

 Capsules

expands due to volumetric increase of
capsular matrix.

NEUROCRAINAL CAPSULE
 Capsule’s

covering layers are made up
of skin and dura mater.

 The

composition of this capsule is
-- Five layers of scalp,
--then the bone itself, and finally,
--the two layered dura mater.

 The

calvarial bones consists of a number of
contiguous skeletal units : outer table, inner
table, diploic space (and variably sinuses).
Each of these microkeletal units obviously
has its specific periosteal matrix, muscles
and vessels being good examples.


Neurocranial capsule


Acts to surround and protect neurocranial
capsular matrix (brain, leptomeninges, csf)



Expansion of the neural mass is the primary event
in the expansion of the capsule.The direction of this
primary volumetric expansion is influenced by
several environmental factors--degree of flexion of cranial base
--mode of attachement of several orginised dural fiber
tracts,which underlie the major calvarial suture
systems.





The volumetric increase causes

compensatory expansion of surrounding
capsule which is brought about by mitotic
activity of the capsular connective tissues
 All

embedded functional cranial components
are passively translated in space & such
spatial relocation takes place without
involving the processes of osseous
deposition or resorption

ORO FACIAL CAPSULE


Surround and protect oronasopharyngeal space.



Skin and mucous membrane form the limiting
layers.



Embedded in this capsule are a no. of FCC,both
periosteal matrices & related sk. unit ( for eg.
Temporalis muscle / coronoid process, masseter &
medial pterygoid / angular process)



Volumetric growth of these spaces is the
primary morphogenetic event in facial skull
growth



Growth of functional spaces causes increase
in the size of capsule



Followed by passive movement of functional
cranial component


OROFACIAL CAPSULE


MANDIBULAR GROWTH
 Mandibular

condylar cartilages are not primary
sites of mandibular growth. They are the Ioci at
which secondary, compensatory periosteal growth
occurs.

Mandibular growth, is seen as a combination of
the morphologic effects of both capsular and
periosteal matrices. The capsular matrix growth
causes an expansion of the capsule as a whole.
The enclosed and embedded macroskeletal unit
(the "mandible" as a whole), accordingly, is
passively and secondarily translated in space to
successively new positions.

 In

normal conditions the periosteal matrices
related to the constituent mandibular
microskeletal units also respond to this
volumetric expansion.

 Such

an alteration in their spatial position
inevitably causes them to grow ; that is, causes
changes in their functional demands. These now
call forth direct alterations in the size and shape of
their microskeletal units.



The sum of translation plus changes in form
comprises the totality of mandibular growth.

VAN LIMBORGH’S THEORY --1970
 Multifactorial

Theory

 Van

Limborgh supports the functional matrix
theory of Moss, acknowledges some aspects of
Sicher’s theory & at the same time does not rule
out genetic involvement.


 He

suggested following five factors controls
growth :
1 -- Intrinsic genetic factors
2 -- Local epigenetic factors
Bone growth is determined by genetic
control originating from adjacent structures
3 – General epigenetic factors
Determining growth from distant structures.
eg. Hormones


4 – Local environmental factors
eg. Habits, muscle force etc
5 –General environmental factors
eg. Nutrition, oxygen etc.
He summarized his views in following six points:
1. Chondrocranial growth is controlled mainly by the
intrinsic genetic factors

2. Desmocranial growth is controlled by any
few intrinsic genetic factors.
3. The cartilaginous parts of the skull must be
considered as growth centers
4.Sutural growth is controlled mainly by
influences originating from the skull
cartilages and from other adjacent skull
structures

5.Periosteal growth largely depends upon growth of
adjacent structures
6.Sutural and periosteal growth are additionally
governed by local non-genetic environmental
influence.


CONCLUSION
 Cranial

growth is a combination of both spatial
translation and transformation.

 As

new concepts, hypothesis & theories emerges,
it may change the picture of craniofacial
development.


REFERENCES
1.Primary role of functional matrices in facial growth—
AJO,June 1969
2.The capsular matrix-AJO,nov 1969
3.Functional matrices-AJO,july 1969
4.Contemporary orthodontics—William.R.Profit
5.Handbook of orthodontics-Rorert.E.Moyers
6.Orthodontics Principles & practice-T.M.Graber
7.New vistas in orthodontics-Lysle.E.Johnston
8 Orthodontics the art and science-S.I.Balajhi

THANK YOU

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