Growth theories /certified fixed orthodontic courses by Indian dental academy

THEORIES OF
GROWTH
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INDIAN DENTAL ACADEMY
Leader in continuing dental education



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Great strides have been made in recent years
in improving understanding of growth control
.
A no. of hypotheses of craniofacial growth
have been formulated which are often
encountered in textbooks, where they are
sometimes called theories
Theory requires a basis of sound evidence
,while hypothesis is thoughtful conjecture of
the meaning of incomplete evidence

3

These efforts have not been successsful due
to the complicated nature of craniofacial
growth.
For elucidation of the same,Kuhn defined
the terms:
“ Normal Science” &“Paradigms”
as pertaining the field of craniofacial biology.

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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.

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EVOLUTION OF VARIOUS
PARADIGMS

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

THE GENETIC PARADIGM
•BRODIE ,assumed facial configuration
under genetic control
•Researches focussed on growth sites for this
control:the sutures ,craniofacial cartilages and
periosteum
•Assumption made that cartilages and facial
sutures under genetic control and brain
determined the vault dimensions

7

•In 1940’s events reflecting changing ideas
about dominant genetic paradigm :
1)marked increase in use of animals in
craniofacial research
2)introduction of jaw and facial
electromyography
3)Other developments included the use of

radioopaque implants,vital dyes & in vivo,in
vitro transplantations.

8

GENOMIC
PARADIGM


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Functional Paradigm
Rise of functional paradigm was when Melvin
Moss adopting 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.

10

It focussed 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.

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The Functional Paradigm


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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.

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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

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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

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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.

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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 all responsible for facial growth
and assumed all were under tight intrinsic
genetic control.

17

.

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.

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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.

19

Growth Center:
Those areas of craniofacial skeleton that
have:
tissue seperating capabilties
innate growth potential
not influenced by external factors
e.g.Synchondrosis and nasal septal cartilage.

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Growth Site:
Locations at which active skeletal growth
occur but as a secondary ,compensatory
effect
lacking direct genetic influence
effected by external influences.
e.g. sutures and periosteum

21

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.

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.
Condylar cartilage as
growth determinant

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Growth at nasal septum causes
downward & forward
translation of maxilla

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Latham elaborated on Scott’s ideas about nasal
septum and maxillary growth
Emphasized role of septopremaxillary ligament
beginning in the later part of foetal period
Felt that maxillary sutures began as sliding joints
adapting to initiating growth forces else where
but later manifest increasing osteogenesis
Thus combines ideas of Scott,Sicher,Moss

25

Growth of maxilla on basis of Scott’s theory
nasomaxillary complex grows as unit
that cartilaginous nasal septum serves as a
pacemaker for maxillary growth
cartilage growth leads to forward and
downward translation of maxilla.
sutures which serve as reactive areas
respond by new bone formation leading to
growth.

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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.

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Epiphyseal 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.

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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

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Effect of removing
Mid face deficiency in a man
nasal septum on
whose nasal septum was
forward growth of mid
removed at age of 8
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face

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

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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.

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THE ORIGIN,GROWTH AND
MAINTENANCE OF ALL SKELETAL
TISSUES AND ORGANS ARE ALWAYS
SECONDARY,COMPENSATORY AND
OBLIGATORY TO TEMPORALLY AND
OPERATIONAL PRIOR EVENTS OR
PROCESSES THAT OCCUR IN
SPECIFICALLY RELATED NON-SKELETAL
TISSUES,ORGANS OR FUNCTIONAL
SPACES
1981
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Head is a region with in which certain
functions occur
Each function is completely carried out by a
functional cranial component
Each component of a functional matrix
performs a necessary service- such as
Respiration, Balance, Digestion, Vision
mastication , Olfaction, speech

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the skeletal tissues support and protect the
associated functional matrices.
It maintains that heredity and genes play no
significant role in growth of skeletal
structures in gen. and craniofacial skeleton in
particular
The major determinant of growth of the
maxilla and mandible is the enlargement of
nasal and oral cavities which grow in
response to functional needs

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Functional Cranial Component
Functional Matrices

Skeletal unit

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


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Macroskeletal unit

Microskeletal unit


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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

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MATRICES
Periosteal matrix :
immediate local functional environment
,typically associated with muscles,blood
vessels and nerves
Capsular matrix :
organs and spaces that occupy a broader
anatomical complex

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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

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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

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 All responses of skeletal units to

periosteal matrices brought about by
complementary and inter related processes of
osseous depositon and resorption
They act by bringing transformation of the
related skeletal units
E.g – coronoid process and temporalis
muscle

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CAPSULAR MATRICES
All functional cranial components
(functional matrices plus skeletal units ) are
organized in the form of capsular matrices

Each of these is an envelop containing a
series of functional cranial components that
is functional matrices and skeletal units

43

Sandwitched between two covering
layers(capsule)
Capsules expands due to volumetric increase
of capsular matrix
All spaces between functional components
and limits of capsule filled with loose
connective tissue

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NEUROCRAINAL CAPSULE
Capsule’s covering layers are made up of
skin and dura matter.
Acts to surround and protect neurocranial
capsular matrix (brain, leptomeninges, csf)
 Consists of:

-5 layers of scalp
-2 layered dura matter.


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Expansion of the brain i.e closed capsular
matrix volume is primary event in
expansion of the capsule.
The volumetric increase causes

compensatory expansion of surrounding
capsule which is brought about by mitotic
activity.

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Later the calvarial functional cranial
component as a whole are passively and
secondarily translated
.Such translations occur without necessity of
involving the processes of selective periosteal
apposition and resorption

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Neurocranial capsule


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ORO FACIAL CAPSULE
Surround and protect oronasopharyngeal
space.
Skin and mucous membrane form the
limiting layers.
Originates by process of enclosure.

49

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

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OROFACIAL CAPSULE


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Constraints of FMH
It provides only qualitative dynamics of
cephalic growth at gross anatomical level.
Methodologic constraint.
Macroscopic measurements,, e.g.,
roentgenographic cephalometry, permitted
only method-specific descriptions that
cannot be structurally detailed.
 Removed by techniques of the finite
element method (FEM ).

52

Hierarchical constraint.
Did not extend downward to processes at
cellular, subcellular or molecular domains
or upwards to the multicellular processes by
which bone tissues respond to lower level
signals
it could not describe how extrinsic
,epigenitic FM stimuli are transduced into
regulatory signals by individual bone

53

Functional Matrix Hypothesis :Revisited
periodic incorporation of advances in
biomedical , bioengineering and computer
sciences have created more comprehensive
revisions of FMH.
A comprehensible revision of FMH should
indicate
a)portions that are retained , extended or
discarded

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FMH claims -responses of the skeletal unit
(bone and cartilage) cells and tissues not
directly regulated by informational content
of the intrinsic skeletal cell genome .
Rather, this additional, extrinsic, epigenetic
information created by functional matrix
operations.
This new version deals only with responses
to periosteal matrices

55

It now includes the molecular and cellular
processes underlying the triad of deposition ,
resorption and maintenance

Studies show - deposition and maintenance
are functions of relatively large groups of
homologous osteoblasts, never single cells

Sharp demarcations exists between adjacent
grps of active , depository , resting osteoblasts

56

Revised statement:1997(Melvin Moss)
The developmental origin of all cranial skeletal
elements (e.g., skeletal units) and all their
subsequent changes in size and shape (e.g., form)
and location, as well as their maintenance in
being, are always, without exception, secondary,
compensatory, and mechanically obligatory
responses to the temporally and operationally
prior demands of their related cephalic
nonskeletal cells, tissues, organs, and operational
volumes (e.g., the functional matrices).

57

This newest FMH version, transcends some
hierarchical constraints and permits
descriptions from the genomic to the organ
level by the inclusion of two complementary
concepts:
(1) that mechanotransduction in single bone
cells,
(2) that bone cells function multicellularly as a
connected cellular network

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MECHANOTRANSDUCTION

All vital cells are irritable.
Respond to alterations in ext. env.
Mechanosensing process enables to respond
to ext. loadings by using
mechanoreception
EC stimulus
transmitted into
receptor cell

mechanotransductio
n
Transforms stimulus’s
energetic content into
intracellular signal


59

OSSEOUS MECHANOTRANSDUCTION

This process translates the information
content of a periosteal functional matrix
stimulus into a skeletal unit cell signal,
There are two, possibly complementary,
skeletal cellular mechanotransductive
processes:
ionic and mechanical.

60

Ionic-brought about by transport of ions
through plasma membrane resulting in
creation of electrical signal.
Two possible proceses:
a) Stretch activated channels
loading
S-A ch get activated
passage
of certain sized ions
initiate intracellular
electrical events
b) Electrical processes
• Electromechanical
• Electro kinetic
• Electric field strength

61

MECHANICAL
it is an alternative means by which stimulus is
converted into an intracellular signal.
A series of EC macromolecular mechanical
levers exist, capable of transmitting
information from strained matrix to bone cell
nuclear membrane.
One such lever is physical continuity of
transmembrane molecule INTEGRIN.

62

Extracellular
Intracellular
Macromolecular
collagen
INTEGRIN Cytoskeletal actin
of organic matrix
connected to
Nuclear membrane
Such a chain initates intranuclear processes
regulatory of genomic activity and is able to provide
physical stimulus able to activate osteocytic genome

63

BONE AS OSSEOUS CONNECTED
CELLULAR NETWORK
 All bone cells, except osteoclasts, are
extensively interconnected by gap junctions that
form an osseous CCN.
 Each osteocyte, has cytoplasmic (canalicular)
processes, that interconnect with similar
processes of neighbouring cells.
 These processes lie within mineralized bone
matrix channels (canaliculi).

64


65

GAP JUNCTIONS
Intercellular gap junctions permit bone cells to
intercellularly transmit and subsequently process,
periosteal functional matrix information, after its
intracellular mechanotransduction.
Connexin 43 is main protein in these.
They connect:
osteocytes to periosteal and endosteal osteoblasts.

66

-Lateral connection of osteoblast
-Periosteal osteoblast with preosteoblastic
cells,which are interconnected
gap junctions : electrical synapses.
Mechanotransductively activated bone
cells like osteocytes can initiate membrane
action potentials capable of transmission
through interconnecting gap junctions

67

In CCN, cells organised into layers:
initial input
one or more intermediate or hidden layers
final output.
Operational processes are similar for all
cells in all layers.
each cell in any layer may receive several
stimuli.

68

Loadings

IC inputs summed
when
above threshold

IC signal generated
transmitted to

Hidden layers

signal goes to

Final layers

outputs determine

Site, rate, direction &
duration of adaptive response.

69

Other properties of CCN:
Information is distributed across all or part of
the network.
The CCNs show oscillation,
All the osteoblasts of a cohort engaged in an
identical adaptation process are
interconnected by open gap junctions .

70

Cybernetic Theory
of
Craniofacial Growth


71

Introduction
Petrovic employed terminology of
cybernetics and control theory to describe
craniofacial growth mecahnisms and method of
operation of functional and orthopedic
appliances.
The theory demonstrates a qualitative and
quantitative relationship between
observationally and experimentally collected
findings.

72

Cybernetic approach:
system operates through signals that transmit
information.
signal may be of physical, chemical or
electromagnetic nature.
Any cybernetic system, when provided an
input (or stimulus), processes such an input and
produces an output. The output is related to the
input by a transfer function:www.indiandentalacademy.com

73

Input

process

output

This is similar to feeding numbers into a
computer, and obtaining the sum or product of
the numbers.
The calculations performed by the computer,
correspond to the “TRANSFER FUNCTION”

74

Physiologic system can be of two types:
Physiologic system
Open loop

Closed loop

servosystem

regulator
75

Loops:
Open loop
The previous example shows an open loop.
The Output does not affect the input.
Closed loop
In a closed loop system, a specific relation is
maintained between the input and output.
Closed loops are characterized by a feedback
loop and a comparator.

76

Open Loop
Output has no affect on the input


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Input

Comparator

Tranfer func.

Output

CLOSED LOOP

78

The input is fed into a comparator which analyses
the input and judges the degree to which the transfer
function needs to be carried out to obtain a certain
output.
The output is fed back to the comparator (by a feed
back loop) and is analyzed as to its adequacy. If
found to be inadequate, the transfer function is
carried out once again. The feed back loop can have
a positive or enhancing effect or a negative or
attenuating effect.

79

TYPES OF CLOSED LOOP
A Regulator type of closed loop is one
which the input is constant.
Any disturbance in the input will cause the
comparator to initiate a “regulatory feedback
system, which will restore the input to its
normal state.

80

An Eg.of this is the temperature regulation
system of the body. Any change in body
temperature acts as the input into the comparator
(the hypothalamus), which causes an action
(pilorection or shivering) which ultimately
brings the body temperature back to normal.
Servo-system- In this, the main input is
constantly changing with time, and the output is
constantly adjusted in accordance with the input.

81

Various Components of a Servo-System
Command- A signal established independent
of the servosystem, and is not affected by the
output of the system. Hence, as the name
suggests, it tells the system what is to be done.
Reference Input- The input into the servosystem (which is brought about by the
command). The command created a reference
input through the action of a reference input
element.

82

Comparator (Peripheral) - The input is fed
into the comparator that analyses the input and
judges the performance of the system through
performance judging elements.
Central Comparator- The performance
judging elements then transmit a deviation
signal to the central comparator which sends a
signal to various components – the actuator,
the coupling system and the controlled system
This brings about output (controlled variable).

83

Command

Reference
input
element

Reference input

Direct effect

Actuator,
coupling sys.
Central
comparator

Output

Peripheral comparator
Performance analysing
elements

Deviation signal


Performance

84

Growth of the Face – As Explained by the
Servosystem Theory
Background: types of cartilage
Primary cartilage - in this dividing cells are
differentiated chondroblasts surrounded by
cartilaginous matrix
this isolates them from local factors able to
restrain or stimulate cartilaginous growth
e.g. in axial skeleton , skull base and limbs

85

Secondary cartilage :
the dividing cells , prechondroblasts are not
surrounded by a matrix
so not isolated from local factors influences
e.g. condylar, coronoid and in small mammals
in angular processes
local factors may modify the growth rate of
secondary cartilage

86


87

 If growth results from cell division of

differentiated chondroblasts
 Subject to general extrinsic factors and more
specifically to somatotropic hormone (STH)
somatomedin, sexual hormones,and thyroxinel.
The effect of local biomechanic factors is
reduced to modulation of the direction of
growth (with no effect on the amount of
growth).

88

 If growth results from cell divisions of

prechondroblasts (secondary cartilage) -it is
subjected to local extrinsic factors.
In this case the amount of growth can be
modulated by appropriate orthopedic devices.


89

Various cybernetic terms in relation to
growth of face:
The position of dental arch forms the
REFERENCE INPUT of the servosystem
The release of somatomedin represents the
COMMAND (command to grow). The hormone
itself is the REFERENCE INPUT ELEMENT.


90

The OCCLUSION between the upper and
lower teeth forms the COMPARATOR.
The Sensory Engram :
-the optimal functional ‘blueprint’ is recorded
as the sensory engram
-The CNS serves as a central comparator for
the servosystem.

91

•The central comparator refers to what is known
as the SENSORY ENGRAM.
•The sensory engram operates on the principle
of OPTIMALITY OF FUNCTION.
•Any particular muscle action or mandible
position that gives the minimum deviation signal
is recorded in the sensory engram.

92

Growth of face
The growth of the maxilla is brought about
by the release of hormones (esp. STHSomatomedin).
These hormones have various direct and
indirect effects which result in the growth of
the maxilla
Somatomedin induces growth of primary
and secondary cartilages which results in an
outward and forward growth of the maxilla.

93

Another important action of somatomedin is
the increase in the size of the tongue, which
also facilitates the outward and forward
growth of the maxillary dental arch

Once the maxilla increases in length and
width, the position of the maxillary dental
arch is changed.

94

Forward & outward growth of maxilla
change in relation of teeth
sensed by peripheral
comparator (occ.)

inc. forces on periodontium, teeth, muscles&
TMJ (performance analysing elements)
signal sent to

CNS (central comparator)

95

Sensory engram ( record of ideal tooth
positions and muscle posture).
Compares

original muscle position with present muscle
position
sends deviation signal

Motor cortex (Actuator)
sends actuating signal

lateral pterygoid muscle (coupling sys)

96

Positions mandible forward.
Retrodiscalpad activated

mandibular growth at condyle ( output)

ideal cusp to fossa relationship attained.


97

The Face as a Servosystem
Input – Maxillary dental arch

Output – Adjustment of the position of
mandibular dental arch

98

Some other terms related to servosystem
Attractor- It is the final structural state that the
system tries to attain. i.e.:- Maximum interception.
Repeller- All the unstable states that the system
tries to avoid.i.e.:- cusp to cusp relation.
Disturbance- Any input, other than the reference
input, which tends to have an effect of the output.
E.g. - Abnormal tooth positions or occlusal
interferences can act as a disturbance to the
99
peripheral comparator

Drawbacks
1)The theory places a lot of importance on the
condyle as the growth centre. Hence if condylar
cartilage is lost subsequent to a fracture, growth
should seize. But studies done in Scandinavia
show that this does not happen.
2)The author places a lot of importance on the
role of hormones in controlling growth. In all
probability, they do not have such a large role to
play.

100

3) The peripheral comparator, the occlusion,
itself, is unstable. Discrepencies in the
occlusion can easily be overcome by
dentoalveolar changes, rather than by growth of
the mandible.
4) According to the theory, an end on relation
is a repeller. Still, end on relation of the molars
and other teeth are often seen.

101

While we may no longer seek a
synthesizing single theory for all of
craniofacial growth, we may now have,
because of Petrovic’s work, a convenient
model and a language by which to describe
and relate growth activities to one another,
thus obviating any need for another
paradigm.

102

Thank you
Leader in continuing dental education


103

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