Cybernetics /certified fixed orthodontic courses by Indian dental academy

The unit within the system with the most
behavioral responses available to it
controls the system.
1st Law of Cybernetics
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

A Seminar on
By
Pavan Kancherlawww.indiandentalacademy.com

Contents
Introduction
Cybernetic features
Understanding of cybernetics approach
Servosystem theory
Condylar cartilage
Control of maxillary growth
Control of mandibular growth
Three level arborization
Mode of action of functional appliances
Conclusion

Introduction
Last 10 years have seen an increasing awareness of potential
of functional appliances as valuable tool in armamentarium
of orthodontists.
In late 1960’s Petrovic & co-workers produced first rigorous
demonstration that condylar cartilage’s growth rate &
amount can be modified by using appropriate functional &
orthopedic appliances.
Later he employed the model of cybernetics & control theory
to describe craniofacial growth patterns & method of
operation of functional & orthopedic appliances.

“Cybernetics is the study of communication
and control within and between humans,
machines, organizations and society.”

Cybernetics
The term itself originated in
1947 when Norbert Wiener
used it to name a discipline
apart from, but touching
upon, such established
disciplines as electrical
engineering, mathematics,
biology, neurophysiology,
anthropology, and
psychology.
Wiener, Arturo
Rosenblueth and Julian
Bigelow
Greek word kybernetes
meaning "steersman"

Cybernetics
Cybernetics, interdisciplinary science dealing with
communication and control systems in living organisms,
machines, and organizations was first introduced by the
mathematician Wiener in 1948, as the science of
communication and control in the animal and the
machine (to which we now might add: in society and in
individual human beings).
Shannon’s theory

Cybernetics
Cybernetics developed from investigations into
how information is transformed into desired
performance

Cybernetics
The principle, known as feedback, is the fundamental
concept of automation.
Purposive behavior in humans or in machines requires
control mechanisms that maintain order by counteracting
the natural tendency toward disorganization.

Cybernetics
Cybernetic concepts are used to link biological and
technological functions. The use of feedback information as
an important part of system development, helps scientists in
the field of biology and technology understand cause and
effect.

Cybernetics
This complex idea relating to feedback can be translated
into simpler terms of input and output. Input and output
are components of a completed cycle of feedback. Input is
placed into a system in order to receive a predicted output.
In biological terms this would mean that a certain stimuli is
placed upon an organism with the intent of inducing a
certain predictable response from that organism.

Cybernetics
“A distinguishing feature of the broad based field of
Cybernetics is the use of feedback information to adapt or
steer the entity toward a goal.”

Cybernetics
Cybernetic Approaches
Cause System Effect
Standard Approaches

Cybernetics
Cybernetic Approaches
The (practical) Cybernetic view

Cybernetics
Petrovic’s four types of explanation on craniofacial growth &
orthodontic influence-
1. Deductive:
used for description & classification of observations & for
forecast of future events, including degree of possibility. A
deductive explanation requires a logically organized framewor
of knowledge ( e.g. cybernetic diagram containing precise
quantitative data)
2.Deductivoprobabilistic:
used to assess the relationship between description,
classification of observations & events to be explained.
This type of explanation is most common in medicine &
orthodontics .It forms basis of differential diagnosis &
prognosis. e.g.-computer based orthodontics diagram
3.Functional:
corresponds to goal seeking description of technological
systems. Various components of system that control
craniofacial growth & development interact & provide
feedback in precise, causal interdependence &
responsiveness.

Cybernetics
4.Phylogenetic:
1st step is setting out of a sequence of major events
through which system has evolved.
2nd step is discovery of events that are casually
pertinent for the transformation of system.
3rd step is presentation of reasons for
transformation.
4th step is elucidating the successfulness of
transformation.

Cybernetic features

Cybernetic features
Craniofacial growth is an extremely complex
process.
To explain method of operation of orthopedic
& functional appliances, the following set of
approaches is useful:

Cybernetic features
Discoveries may be related by placing observations next to
each other- outdated
Diagrams displacing qualitative relations between
observations can be constructed.
Diagrams may be improved by using matrices in
mathematical language.
Cybernetics based on communication & information
theory-based on feedback-useful approach

Catastrophe theory- Rene Thom (1972)
A topologic concept to describe discontinuities. In
cybernetics models ,discontinuities corresponds to
sudden changes in references of control system.

• Catastrophe is defined as a sudden change or jump after a
smooth progress. The theory therefore studies and classifies
phenomena that are characterised by sudden shifts in
behaviour arising from small changes in circumstances. These
sudden changes are called "catastrophes" and the theory was
developed as a method of analysing and classifying these
changes. The catastrophe theory has been defined as a
mathematical treatment of continuous actions producing a
discontinuous result.

Input & output- represented by arrows
Each arrow represents a signal; at some point it
may become a message.

The translation of message from one language to
another is called transcodage
% of data that are not indispensable to message
but contribute to reliability of its transmission is
called redundancy

Open loop
No feedback loop
Or Comparator
Closed loop
Regulator
Main input constant
Comparator detects
disturbances
It is –ve feedback system
Servosystem or follow up system
Main input not constant
Physiologic system represented by black box

Input
Orthodontic
Functional
&
Orthodontic
Appliances
Output
Correction
Of
Malocclusion
And
Intermaxillary
Relation
Genetically determined
& cybernetically
organized
Biologic features of
Phenomena
characterizing,
Inducing or controlling
Spontaneous & appliance
Modulated growth
Relative primary to
following:
Mandible lengthening
Maxillary lengthening
Teeth movements
Research design
clinical versus biologic approach

Servosystem theory
(Alexander Petrovic 1970)

Servosystem Theory
It is considered to be the last major theory of craniofacial
growth to emerge within 20th century, developed by
Alexander Petrovic & his colleagues at University of
Strasburg in 1970’s
. Development of Servosystem theory was
initiated because of interest in growth &
development of connective tissue & effect of
intrinsic & extrinsic factors particularly on
condylar cartilage.

Servosystem Theorywww.indiandentalacademy.com

Servosystem Theory
A further step in understanding mechanism of
craniofacial growth was made when Charlier,
Petrovic & Stutzmann detected in organ culture the
following dissimilarities concerning different growth
cartilages-

PRIMARY AND SECONDARY GROWTH CARTILAGE

Servosystem Theory
According to the Servosystem theory, the sagittal position
of the upper dental arch is cybernetically the “constantly
changing reference input”. This position depends on the
growth in length of the upper jaw, which is controlled by
STH and somatomedin as well as by septal cartilage
growth and by tongue growth. The effect of septal
cartilage growth on the forward growth of the maxilla is
mediated through a direct thrust, through labionarinary
muscles and through the superior labial frenum and
septopremaxillary ligament.

Servosystem Theory
NASAL SEPTAL CARTILAGE
GROWTH IN WIDTH OF UPPER JAW

Servosystem Theory
The sagittal position of the lower dental arch
is cybernetically, “the controlled variable”

The “operation of confrontation” between the upper and
lower dental arches is, cybernetically, the “peripheral
comparator” of the Servosystem.

With time, the increased activity of the lateral pterygoid muscle and,
consequently, the amplified solicitation of the retrodiscal pad
induces, first, a posterior growth rotation of the mandible and,
second, a supplementary growth rate and amount of the condyle.

During the facial growth, everything occurs as if, in the
Servosystem controlling mandibular morphogenesis, the shape
is – in cybernetic language – the “reference input,” and the
rat and amount of growth are “controlled variables.” An
important quantitative aspect of the functioning of the
Servosystem should be pointed out: the greater relative retro
position of the lower dental arch, i.e., the greater the
“deviation” between the inferior and superior dental arches,
the greater the “deviation signal” arising form the “peripheral
comparator” and the “detectors” of occlusal adjustment.

This increased deviation will, in turn, lead to
increased supplementary activity of the lateral
pterygoid muscle and of the retrodiscal pad and will
result in increased supplementary growth of the
condylar cartilage.

The Servosystem controlling the growth of the
condylar cartilage comprises, in addition to the
“peripheral comparator” (occlusal relationship), a
“central comparator” located in the central nervous
system.

In sum, “unlike what seems to occurs in the so-called primary
cartilages, the physiologic effect of factors controlling the
growth of the facial skeleton, especially of the condylar
cartilage ( a secondary cartilage), is not limited to simple
commands, but includes relays implying interactions and
feedback loops, all of which form a structured system, a
Servosystem, in which the position of occlusal adjustment
plays the role of the peripheral comparator.”

Condylar Cartilage
Adaptive to both extrinsic & local biomechanical &
functional factors

Reptiles
Condylar Cartilage
QuadratusArticular

IN MAMMALS- joint formed by 2
dermal bones
Condylar Cartilage
SquamosalDentary

Condylar cartilage growth is integrated
into an organized functional whole that
has form of Servosystem & able to
modulate lengthening of condyle so that
lower jaw adapts to upper jaw during
growth
Condylar Cartilage

Condylar cartilage in growing mammal is composed
of the following zones:
Zone of growth
Zone of maturation
Zone of erosion
Zone of endochondral ossification
Specific features of condylar Cartilage
Condylar Cartilage

Condylar Cartilage

FACTORS AFFECTING CONDYLAR CARTILAGE GROWTH
Lateral pterygoid muscle & retrodiscal pad tissue
Effect of hormones
Intrinsic regulation of condylar cartilage growth rate
Other hormonal & humoral factors
c-AMP

LATERAL PTERYGOID MUSCLE & RETRODISCAL PAD TISSUE
TEMPORO MANDIBULAR JOINTwww.indiandentalacademy.com

Retrodiscal pad

Resection of LPM & retrodiscal pad
The interruption of circulatory dependence on the blood
supply originating directly from LPM & indirectly
through retrodiscal pad may contribute to inhibited
differentiation of skeletoblasts. Experimental studies on
juvenile rats were carried out in which LPM were
resected.

It was observed that growth of condylar
cartilage & lengthening of mandible
continue but significantly decreased.

Intrinsic regulation of condylar cartilage growth rate

Effect of hormones
• If blood levels of STH or testosterone increases ,
lengthening of mandible greater than maxilla.
• Operation of confrontation then produces deviation
signal that decreases activity of LPM & movements
of retrodiscal pad , resulting in decrease in condylar
cartilage growth rate.
• If stimulation of retrodiscal pad is reduced
dividing cells are relocated in less posterior
direction resulting in vertical orientation of newly
formed endochondral bone trabeculae producing
closing of angle & anterior growth rotation.
• If STH or testosterone decreases then optimum
occlusal adjustment is maintained by opening of
angle.

Effect of hormones
• During transition phase as mandible is constantly moved :
1. Increased contractile activity of LPM.
2. Increase in no. of dividing cells in condylar cartilage.
3. Increased stimulation of retrodiscal pad. As a result
dividing cells located in more posterior direction producing
opening of angle or posterior growth rotation.
4. If suboptimal occlusal adjustment is achieved after jumping o
bite angle closes again.

Effect of hormones
If STH or testosterone level rises beyond
certain hormonal level :“ Jumping of
bite “ occurs.

Effect of hormones

Other hormonal & humoral factors
Insulin, glucagon, parathormone, calcitonin ,
some mitogenic peptides which corresponds to
fibroblast growth factor, endothelial cell derived
growth, etc. have stimulating effect on condylar
cartilage growth rate.

c-AMP
• Inverse relationship between it & growth rate
of skeletoblasts & prechondroblasts observed.
• Does not directly inhibits cell multiplication but
appears to be amplifier of still unknown
inhibitory signal.
• It also has a direct effect on the cell cycle
• A brief surge of endogenous c-AMP involved
with surge of Calcium in initiating the cell
division process (Stutzmann & Petrovic 1982 )

Correlation between growth direction of condyle
& sagittal distribution of dividing cells in condylar
cartilage

• A histologic & radioautography study was
made of distribution of dividing cells in a
sagittal section of condylar cartilage of juvenile
rats.
• Condylar cartilage divided into 4 equal
sections from anterior to posterior & cells
counted.

Each experimental group was
subjected to specific orthopedic
treatment.

• Results showed that both treatment with
the postural hyperpropulsor & with the
growth hormone produced significant
increase in growth rate of condylar
cartilage to control group (Charlier et al,
1968, 1969a; Petrovic et al , 1975b)

• Stutzmann angle- the angle formed between
main axis of endochondral bone trabeculae in
condyle with mandibular plane as viewed on
lateral cephalogram.
• In anterior growth rotation there is closing of
angle as seen in treatment with growth
hormone.
• In posterior growth rotation there is opening
of angle as seen in treatment with postural
hyperpropulsor

Condylar growth is not exclusively a result of
the lengthening of pre-existing endochondral
bone trabeculae under condylar cartilage but
also a result of growth of bone trabeculae that
are formed in parallel & posteriorly oriented in
condylar cartilage.

Control of maxillary growth
• Increase in length of maxilla
• Increase in width of maxilla

Control of maxillary growthwww.indiandentalacademy.com

Control of Mandibular growth
Responsive to changes in lengthening of
maxilla

Upper dental arch -- constantly changing
reference input
Lower arch -- controlled variable.

“ Operation of confrontation “ between dental
arches in certain cases elicits deviation signal
that modifies activity of LPM & other muscles of
mastication , allowing mandible to adjust to
optimal occlusal position
This change in LPM activity probably influences
growth of condylar cartilage.

• In anterior growth
rotation
- Subperiosteal ossification rate
& alveolar bone turn over is
increased
• In posterior growth
rotation
- Decreased

Peripheral comparator maintains optimal to
suboptimal occlusal relationship.
If it is disturbed can lead to topologic
bifurcation type instability.

Control of Mandibular growthwww.indiandentalacademy.com

Three level arborization
The first level, based on the quantitative determination of the
difference between maxillary and mandibular sagittal growth,
likewise has three main branches
•The second level based on variations in the direction of
mandibular and maxillary growth, affects each of the three
main branches
•The third level, based on the occlusal relationship that
functions as the peripheral comparator of the Servosystem,
has subdivisions representing either an aggravation or a
melioration of malocclusions resulting from the first
two arborizational levels.

Mode of action of functional appliancesPostural Hyperpropulsor
• Appropriate functional appliances that
place the rat mandible in forward postural
position increases condylar cartilage growth
rate & amount.
• Periodic increase in thickness of postural
hyperpropulsor, produces increase in LPM
activity & of retrodiscal pad, consequently
increasing rate & amount of condylar
cartilage growth.

If appliance removed after growth completed –
little or no relapse
If removed before growth completed-
no relapse if good intercuspation
Postural Hyperpropulsor

If good intercuspation not achieved-
then comparator of
Servosystem imposes an increased or
decreased growth rate until state of
good intercuspation achieved

Class II elastics
• It is seen that they are not only orthopedic
devices capable of moving teeth but also
functional appliances capable of stimulating
growth rate & amount of condylar cartilage.
• Mechanism of action-
Through mainly retrodiscal pad

Class II elastics

HERREN (L.S.U) ACTIVATOR
(Louisiana state university)
• It opens the construction bite beyond the
postural rest position.
• Acc. To Herren (1953) & Auf der maur (1978)
the wearing of appliance does not bring about
any increased activity of LPM as no free
movement of mandible possible-
Should be worn part time

HERREN (L.S.U) ACTIVATOR
2 STEP ACTION-
1. when appliance is worn-
Forward positioning of mandible is the
cause of reduced increase in length of LPM
2. When appliance is not worn-
New sensory engram
Mandible functioning in more forward
position
More stimulation of retrodiscal pad activity
• Repetitive activity of pad leads to earlier onset
of condylar chondroblasts hypertrophy
• Decrease in no of functional chondroblasts
• Decrease in prechondroblasts multiplication
restraining signal
• Increase in condylar cartilage growth

FRANKEL LATERAL VESTIBULAR SHIELD
• The appliance acts by stimulating midpalatal
suture growth & to lesser extent by increasing
bone apposition on external subperiosteal
layer of maxilla
• Buccal shield --- eruptive pathway of teeth

Mode of action of functional applianceswww.indiandentalacademy.com

Effect of various functional appliances on growth of rat
mandible

Summary of method of operation of functional appliances
1. Class II elastics, postural hyperpropulsar,
frankels regulator, Balters’ bionator , Clark twin
block all exert effects mainly through movement
of mandible. Their stimulating effects are
produced mainly during wearing of appliance.
2. Herren & L.S.U activators & extraoral forward
traction on mandible seem to exert their effects
mostly through sagittal repositioning of
mandible.

Summary of method of operation functional appliancewww.indiandentalacademy.com

Summary of method of operation functional appliance
Regardless of differences in mode of action, the
following causal chain is involved-
Functional appliance
Increase contractile activity of LPM
Intensification of repetitive activity of retrodiscal
pad

Summary of method of operation functional appliance
Increase in growth stimulating factors:
1. Enhancement of local mediators
2. Reduction of local mediators (factors causing negative
feedback effects)
• Change in condylar trabecular orientation
• Additional growth of condylar cartilage
• Additional subperiosteal ossification of posterior border
of mandible
Supplementary lengthening of mandible

Active retropulsion of mandible (chin caps)
• More orthopedic than functional.
• If growing rats subjected to active retropulsion
with chin cap therapy-
• No. of dividing cells in mandibular condylar
cartilage decreases
• Direction of growth becomes more vertical
• Closing of Stutzmann's angle
• Decrease in length of mandible markedly

Are these experimental findings relevant
to humans?

CONCLUSION
• Rat, mouse, guinea pig, rabbit, monkey,
human.
• Any claim that the responsiveness of the
condylar cartilage to functional appliances
is different in growing laboratory animals
from that in the child is, for the time being,
biologically unsupported.

CONCLUSION
• Interindividual heterogeneity in human
mandibular tissue growth and
responsiveness originates from distinct
quantitative differences at the tissue, cell,
and molecular level.
• Six biological levels and 11 corresponding
rotational types.

CONCLUSION
These results demonstrate that a
methodologically rigorous evaluation of the
effectiveness of a functional appliance must
take into account the biologic heterogeneity
of the human mandibular tissues.

CONCLUSION
So previously reported negative results in the
literature may be due not only to the
characteristics of the appliance used, but
also to errors in identifying biologic growth
category and inappropriately selected
control.

"The simplest schoolboy is now familiar with
truths for which Archimedes would have
sacrificed his life." — Ernest Renan (1823-
92), French philosopher

All human actions have one or more of these
seven causes: chance, nature, compulsion,
habit, reason, passion, and desire.

Thank you
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Cybernetics /certified fixed orthodontic courses by Indian dental academy

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