Servo system in orthodontics

SERVOSYSTEM
IN
ORTHODONTICS
www.indiandentalacademy.com

INTRODUCTION
Over many years various theories of growth have been
proposed for the craniofacial complex.
The Genetic theory, Scott’s Hypothesis, Sicher’s Sutural
Dominance theory, Functional matrix theory attempt to explain
the growth of the cranofacial complex with different growth
determinants and have their own limitations.
The Servosystem theory of growth is based on a factorial
qualitative analysis which takes into account various factors
which determine a coordinated growth of the craniofacial
complex as a whole.
The Servosystem theory attempts to explain craniofacial
growth and the modus operandi of Functional appliances.

GROWTH THEORY’S
GENETIC CONTROL THEORY:
• Genotype supplies all the
information required for
phenotype expression.
• Does not address the question
of local and general factors
modifying gene expression.

GROWTH THEORY’S
SICHER’S SUTURAL DOMINANCE THEORY:
• He believed that craniofacial
growth occurs at sutures.
• Paired parallel sutures which attach
the facial bones to the cranial base
and skull push the nasomaxillary
complex forwards to compare with
mandibular growth.
• Acknowledges the genetic influence
on growth at the sutures.
• Transplantation of sutures to
another site showed that there was no
innate growth potential.
• Cases of Microcephaly and
Hydrocephaly. www.indiandentalacademy.com

GROWTH THEORY’S
CARTILAGE DIRECTED GROWTH THEORY:
• James Scott- 1953, 1954, 1967
• Cartilage has intrinsic growth potential.
• Role of Periosteum and sutures only
secondary.
• All cartilages through out the skull are
primary centres of growth.
• Growth of the maxilla is attributed to the
growth of the Nasal septal cartilage.
•Nasal septal carrtilage is the pacemaker
of growth for the nasomaxillary complex.
•The mandible is like the diaphysis of a
long bone bent with epiphyseal cartilages
at both ends. www.indiandentalacademy.com

GROWTH THEORY’S
CARTILAGE DIRECTED GROWTH THEORY:
• Epiphyseal cartilages cartilages
transplanted to a different area will
continue to grow - innate growth
potential.
• Nasal septal cartilages also grow
when transplanted to another site.
•Removal of nasal septal cartilages
gives rise to retarded midface
development.
• Petrovic’s studies have shown that
only primary cartilages grow in organ
culture and not secondary cartilages.

GROWTH THEORY’S
FUNCTIONAL MATRIX THEORY:
• Melvin Moss 1960, 1962, 1997.
• A Hypothesis substantiated in the
revisited theory’s.

SERVOSYSTEM THEORY
Alexandre Petrovic, Charlier,and Jeanne Stutzmann of Louis
Pasteur School of Medicine.
SERVOSYSTEM
THEORY
Study’s in Otosclerosis by Petrovic
revealed that cartilage surrounding the
cochlea never grew in organ culture but
epiphyseal cartilages grew well.
Petrovic and Charlier in
1967-69- Jaw Growth rate
and direction can be
modified by functional
appliance.
Jeanne Stutzmann-1976 The
role of LPM and retrodiscal
pad -mediator role
Petrovic and
coworkers:Chronobiological
aspects of cartilage and bone
growth

SERVOSYSTEM THEORY
OVERVIEW
MANDIBULAR
GROWTH
HORMONAL STATUS
MAXILLARY
GROWTH AND
SAGGITAL
POSITION
LATERAL
PTERYGOID AND
RETRODISCAL PAD
FUNCTIONAL
APPLIANCES
STABLE
OCCLUSION
MALOCCLUSION

SERVOSYSTEM THEORY AND
CYBERNETICS
Craniofacial growth is a multifaceted process where the
connections and interrelationships are complex with interactions
and feedbacks.
The Servosystem theory uses the Cybernetic language of
information and communication as a tool to explain the influence
of various factors - extrinsic and intrinsic on Craniofacial growth.

CYBERNETICS
CYBERNETICS:
• “the language used to describe
control and communication in man
and machine.”
• Study’s the role of information and
the technique of measuring and
transmitting it.
• “Cybernetics” derived from a greek
word meaning ‘steersman’ by
Dr.Rosenbleuth and Norbert Weiner
and others in 1947.

CYBERNETICS
CYBERNETICS:
• Used to explain Systems and
Circuit analysis.
• Can also be used in Biological
Biomedical sciences to explain
negative and positive feedback
loops, self regulation, gain and in
the process explain physiological
processes.

CYBERNETICS
CYBERNETICS:
• A Cybernetically organised system
operates through signals transmitting
information.
• Signals can be physical, chemical or
electromagnetic in nature and of low
energy.
• Advantages: not static,
sophisticated.
Tr - RH
TSH
THYROXINE
T3,T4

CLASSIFICATION OF CONTROL SYSTEMS
PHYSIOLOGICAL
SYSTEMS
CLOSED
LOOP
CONTROL
SYSTEM
OPEN LOOP
CONTROL
SYSTEM
REGULATOR
SYSTEM
SERVOSYSTEM

CONTROL SYSTEMS
CLOSED LOOP SYSTEM:
• A specific communication
between output and input is
present
• A feed back loop with a
comparator is present.
• eg: feed back loops
maintaining hormone levels,
blood sugar etc
• Two types: Regulator and
Servosystem.
Tr - RH
TSH
THYROXINE
T3,T4

CYBERNETIC ORGANISATION OF
CRANIOFACIAL GROWTH
INPUT(STIMULUS)
ORTHOPEDIC AND
FUNCTIONAL
APPLIANCES
BLACK BOX
•GENETICALLY
DETERMINED AND
CYBERNETICALLY
ORGANISED GROWTH
•MAXILLA
LENGTHENING AND
WIDENING
•MANDIBLE
LENGTHING WIDENING
•TEETH MOVEMENT
OUTPUT
CORRECTION OF
MALOCCLUSION
AND
INTERMAXILLA
Y RELATION

COMPONENTS OF THE CRANIOFACIAL SERVOSYSTEM
CONTROLLED SYSTEM:
• Located between the controlled variable and the actuating
signal.
• Condylar cartilage.
CONTROLLER
ACTUATOR
REFERENCE INPUT
ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

COMMAND:
• A signal established independent of the Servosystem.
•It affects the behaviour of the control system without being
affected by the consequences of the behaviour.
• Growth hormone, Testosterone, Oestrogen.
CONTROLLER
ACTUATOR
REFERENCE INPUT
ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

REFERENCE INPUT:
• A signal established as a standard of comparison.
• Ideally should be totally independent of the feed back.
• The sagittal position of the maxilla.
REFERENCE INPUT ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
CONTROLLER
ACTUATOR
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

REFERENCE INPUT ELEMENT:
• They establish the relationship between the COMMAND(Growth hormone) and the
REFERENCE INPUT(Saggital position of the maxilla).
• Septal cartilage, Septopremaxillary frenum, Labionarinary muscle, Premaxilla and
Maxilla.
REFERENCE INPUT
ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
CONTROLLER
ACTUATOR
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

RELATIONSHIP BETWEEN THE COMMAND,
REFERENCE INPUT AND THE REFERENCE INPUT
ELEMENTS.
THRUST EFFECT
LIGAMENT
TRACTION
MUSCLE
TRACTION

COMPARATOR:
REFERENCE INPUT
ELEMENT
COMPARATO
R
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
CONTROLLER
ACTUATOR
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT
•Serves to establish the relationship between the REFERENCE INPUT and the
CONTROLLEDVARIABLE.
• The “operation of confrontation”- Occlusal contact between the upper and lower jaw.
• Any deviation from optimal occlusal contact detected by the comparator leads to
correction signals to reestablish optimum occlusal contact.www.indiandentalacademy.com

THE CONTROLLER:
• Located between the deviation signal and the actuating signal.
• Lateral pterygoid muscle and the Retrodiscal pad.
REFERENCE INPUT
ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
CONTROLLER
ACTUATOR
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

ROLE OF THE LATERAL PTERYGOID MUSCLE AND
RETRODISCAL PAD.
• Blood supply
•Increase in open loop factors
• Reduction in negative feed back
factors
• Biomechanical

ROLE OF THE LATERAL PTERYGOID MUSCLE AND
RETRODISCAL PAD.
Petrovic’s Experiments:
I CONTROL- INTACT LPM AND
RETRODISCAL PAD
NORMAL
II BILATERAL RESECTION OF
LPM
DECREASED NO OF DIVIDING CELLS
DECREASED GROWTH RATE
OPENING OF STUTZMANN’S ANGLE
DECREASED WIDTH OF MITOTIC
COMPARTMENT
III TMF CLAMPED
BILATERALLY
SAME AS II BUT LESS INTENSE
IV TMF CLAMPED
LPM RESECTED
SAME AS II AND V
V TMF RESECTED SAME AS A II
VI LPM AND TMF RESECTED
BILATERALLY
NO CHANGE

ROLE OF THE LATERAL PTERYGOID MUSCLE
AND RETRODISCAL PAD.
Recent studies….
GROWTH RELATIVITY

ACTUATING SIGNAL:
• Output signal from the controller-actuator complex.
• Activity of the LPM and Retrodiscal pad.
REFERENCE INPUT
ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
CONTROLLER
ACTUATOR
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

CONTROLLED VARIABLE:
• Final output.
• Sagittal position of the mandible.
REFERENCE INPUT
ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
CONTROLLER
ACTUATOR
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

GAIN:
• OUTPUT DIVIDED BY INPUT.
• > 1 - AMPLIFICATION . < 1 - ATTENUATION.
• Pterygomandiibular coupling.
• Genetically determined but can be amplified by GH and Testosterone.
REFERENCE INPUT
ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
CONTROLLER
ACTUATOR
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

ATTRACTOR:
• Structurally stable steady state.
• What the Servosystem tries to achieve.
•Full interdigitation type of Class I, II, III.

REPELLER:
• a state of unstable equilibrium.
• Tries to change to a stable steady state- ATTRACTOR.
•Cusp to cusp occlusal contact.
REFERENCE INPUT
ELEMENT
COMPARATOR
COMMAND
PERFORMANCE
ANALYSING
ELEMENTS
CONTROLLED
SYSTEM
CONTROLLER
ACTUATOR
PERFORMANCE
AMPLIFIER
REFERENCE
INPUT
OPUTPUT

CYBERNETIC ORGANISATION OF MAXILLARY
GROWTH.

CYBERNETIC ORGANISATION OF MANDIBULAR
GROWTH.

BIFURCATION TYPE OF SITUATIONS
UNSTABLE
OCCLUSION
STABLE
CLASS I
STABLE
CLASS II

CONSIDERATONS IN CRANIOFACIAL
SERVOSYSTEMS
• GROWTH ROTATIONS OF THE
MANDIBLE.
• ALVEOLAR BONE TURN OVER RATE

GROWTH ROTATIONS OF THE MANDIBLE.

ALVEOLAR BONE TURN OVER RATE
TISSUE LEVEL GROWTH POTENTIAL:
“ The rank of the alveolar bone turn over rate.”
TISSUE LEVEL GROWTH RESPONSIVENESS:
“ The magnitude of increase in alveolar bone turn over rate
caaused by a 10 day wearing of Class II elastics.”

APPLICATION OF THE SERVOSYSTEM
THEORY IN CLINICAL ORTHODONTICS
• modus operandi of functional appliances.
• Role of hormones
• Development of malocclusion
• Application of recent research

APPLICATION OF THE SERVOSYSTEM THEORY IN
CLINICAL ORTHODONTICS
FUNCTIONAL APPLIANCES
INCREASED CONTRACTILE ACTIVITY OF LPM
INCREASE IN GROWTH STIMULATING FACTORS
ENHANCEMENT OF LOCAL MEDIATORS
REDUCTION IN LOCAL REGULATORS
ADDITIONAL GROWTH OF THE CONDYLAR
CARTILAGE
ADDITIONAL SUBPERIOSTEAL OSSIFICATION
SUPPLEMENTARY LENGTHENING OF THE
MANDIBLEwww.indiandentalacademy.com

FUNCTIONAL APPLIANCES
• POSTURAL
HYPERPROPULSOR
• ANDERSEN HAUPL
ACTIVATOR
• CLASS II ELASTICS
• FRANKEL’S
APPLIANCE
• TWIN BLOCK
• HERREN OR L.S.U
ACTIVATOR
• HARVOLD WOODSIDE
ACTIVATOR

POSTURAL HYPERPROPULSOR:
• Simulates a more anterior position of the upper dental arch.
• A deviation signal is produced which increases LPM and
retrodiscal pad activity.
TWIN BLOCK:
• Alters the occlusal inclined planes.
• 70 degree inclined planes alter the sensory engram and
provide a horizontal component of force.

CLASS II ELASTICS:
• Act primarily through the
retrodiscal pad rather than the LPM.
• Alters the intrinsic regulation of
prechondroblast multiplication .
• Enhance the rate of hypertrophy of
Functional chondroblasts so that the
decreased amount of Functional
chondroblasts enhance
prechondroblast replication.
• Similar to the effect of Thyroxine.

L.S.U or HERREN ACTIVATOR:
• Acts when the appliance is not worn.
•Action not mediated to through the LPM but
through the Retrodiscal pad.
• Shortening of the LPM when the appliance is
worn when compared to other muscles.
• A new sensory engram is produced.
• The mandible closes in a more anterior
position.
•Stimulation of the retrodiscal pad and alteration
of intrinsic regulation of the cartilage similar to
the Class II elastics.

EFFECT OF CHIN CUP THERAAPY:
• Retropulsion of the mandible results
in reduction in the number of dividing
cells.
• Dividing cells if any are found
anteriorly.
• Resulting in anterior growth rotation
and decreased mandibular length.

ROLE OF HORMONES:
•

APPLICATION OF THE SERVOSYSTEM THEORY
IN CLINICAL ORTHODONTICS
DEVELOPMENT OF MALOCCLUSION - MALFUNCTION OF
THE SERVOSYSTEM.
MALFUNCTION AT THE LEVEL
OF THE PERIPHERAL
COMPARATOR
MORPHOLOGIC
ALLY
DEFECTIVE
INADEQUATE
REFERENCE
INHERENT LLIMITATION
OF GROWTH
MECHANISMS
ANTERIOR
ROTATION
CLAS III
SKELETAL
POSTERIOR
ROTATION
CLASS II
SKELETAL

APPLICATION OF RECENT RESEARCH
Lavergne and Petrovic grouped children who are morphogenetically
and morphophysiologically alike. Members within each group have similar
tissue level growth potential and will respond in a similar manner to functional
appliances.
I
1
BASAL SAGITTAL GROWTH
POTENTIAL OF MANDIBLE
ALMOST SAME AS THAT OF THE
MAXILLA - 70%
2
BASAL SAGITTAL GROWTH OF
THE MANDIBLE IS INFERIOR TO
THAT OF MAXILLA - 25%
3
BASAL SAGITTAL GROWTH OF
THE MANDIBLE IS SUPERIOR TO
THAT OF THE MAXILLA- 3%
II
A ANTERIORLY
ROTATING
R NEUTRAL
P POSTERIORLY
ROTATING

III
N NORMAL AP
RELATIONSHIP
OPEN BITE OB
M MANDIBLE MESIAL NORMAL N
D MANDIBLE DISTAL DEEP BITE DB

T1= Expected ML/NSL - Measured ML/NSL.
T2= Expected NL/NSL - Measured NL/NSL
T3= ANB
Expectd ML/NSl = 192-2*SNB and Expectd Nl/NSL = [(Measured ML/NSL)/2]-7

CONCLUSION
The Servosystem theory with the pharaseology of
Cybernetics gives us an insight into the complex process of
Craniofacial growth.
Though the experiments conducted by Petrovic and
coworkers were conducted on rats the biochemical and cellular
response is the same.
At the moment the Servosystem theory is the only theory
which can explain the role of intrinsic and extrinsic factors in
growth.

Servo system in orthodontics

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Servo system in orthodontics