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CYBERNETICS INDIAN DENTAL ACADEMY Leader in continuing dental education

Greek word KYBERNETES (art of steering) Plato & Ampere Norbart Weiner 1948 “ Science of control & communication in animal & machine” ART OF ENSURING THE EFFICACY OF ACTION. Once regarded as pointless sophistication in accounting for biologic & biomedical findings.

ďƒ˜ Cybernetics is the science that studies the abstract principles of organization in complex systems. It is concerned not so much with what systems consist of, but how they function. The cybernetic theory postulates that everything affects everything & therefore organized living systems never operate in an open-loop manner

• Based on communication & information theory : particularly on feedback control system. • Has bought new concepts eg –ve & +ve feedback,self regulation,reference input ,open & close loop

CYBERNETICS The science of control and communication in biological, electronic and mechanical systems. This includes analysis of feedback mechanics that serve to govern or modify the actions of various systems. TABER’S CYCLOPEDIC MEDICAL DICTIONARY 16TH ED

• Permits display of qualitative and quantitative relationship between observed and experimental findings (what I see is what I report) • Broader understanding of orthodontic problems, and action of appliances • Rigorous language of cybernetics is the most app way to lead to the current use of computers

Cybernetic features: 1 Placing observations next to each other 2.diagram displaying qualitative relations b/w observations. 3.mathematical language to describe interactions among various parts of morphophysiologic system. 4.cybernetics based on communication & information theory : mainly on feedback control system is also a useful research approach


Transfer of Information

• Cybernetic systems operate through transfer of information •




Black box concept Input

Black Box



Transfer function


Black box is the physiologic system under study

Input Orthodontic, Functional, & orthopedic appliances

Black Box Genetically determined & cybernetically organized biologic features of Phenomena characterizing, inducing, or controlling spontaneous & appliancemodulated growth relative To the following: •Max. lengthening & •Widening •Mandible lengthening •Teeth movements

Output Correction of malocclusion & Intermax. malrelation

• Identification & analysis of feedback loops are among main tasks in craniofacial growth . • So far, cybernetic language has been the best tool to render accurately the intricacy & complexity of craniofacial morphogenesis & the means to influence it clinically.

Pavlovian concept of accommodation in biological systems  Conditioning  Reinforcement  Habituation Living animals respond passively to stimuli

Morphophysiologic system Open loop

closed loop

Open Loop Output

has no effect on the input

Refutations 1. Steiner & Brown “The North Carolina chain gang�

2. Post retention Relapse

Principle of optimality Feedback controlled behavioral Pattern is assessed. Deviation b/w given state of system + desired optimal state of system is fed back as input : system then take action to reduce this deviation to a min.

Closed Loop Relationship maintained between input and output

Closed Loop systems Input

Regulation of effect

Measure of effect

Return of modified information

Closed Loop

Morphophysiologic systems

Open loop

closed loop Regulator


These concepts of cybernetics : 1.Mechanism of craniofacial Growth 2.Method of operation of orthopedic & orthodontic appliance.

• Theory of facial growth based on these concepts of cybernetics is servosystem

Control of maxillary growth • Direct effect : STH preosteoblast • Indirect effect : thr intermediaries

Types of Cartilage Primary

Types of Cartilage Secondary

Double differentiating potential of skeletoblasts

Primary Cartilage: Epiphysis,


Nasal Septum, Ethmoid Sphenoid Secondary Cartilage: Condyle, Coronoid, Mid Palatal Suture, Fracture Callus

Factors influencing Growth

Primary Cartilage

Secondary Cartilage




Local Factors No

Orthopaedic appliances

Yes (Pre-

(Chondroblasts surrounded by matrix)

chondroblasts not surrounded by matrix)

Only Direction

Direction and Amount

Charlier, Petrovic, Stutzmann Strasburg, France

Growth of the maxilla

Growth in Length

Growth in Height

Growth in Width

Growth in Length: Traction SeptoPremaxillary ligament


Growth of Nasal Septum


Labio narinary Muscles Release of STH Somatomedin


Growth of Pre Maxillary extremity

Anterior shift Of premaxillary bones

Growth of PremaxilloMaxillary suture

Protrusion of Upper Incisors Increased size Of Tongue

Thrust Protrusion of Lower Incisors

Direct Action

Growth of Maxillo Palatine suture

Growth in Width: Growth of Lateral cartilaginous masses of Ethmoid

Release of STH Somatomedin

Outward growth Of maxillary bones

Growth of cartilage B/w greater wings & body of sphenoid

Increased size Of Tongue

Outward shift of Alveolus and molars

Direct effect

Transverse Separation of premaxillae

Growth of inter Pre Maxillary suture

Transverse Separation of Horizontal Maxilla and Palatine plates

Growth of mid Palatine suture

Outward Appositional Bone growth

Growth in height

Control of Mandibular Growth Role of Lateral Pterygoid & Retrodiscal Pad Two roles : •Blood Supply •Biomechanic

Metabolic role Increase • Blood & Lymph flow • nutritive factors Decrease • Cell catabolites • -ve feedback factors

Biomechanic role

Relationship Between Lateral Pterygoid, Retrodiscal Pad and Condyle



Somatomedin & LPM Interaction

• Definitions • Command : signals established independent of feedback system under scrutiny. • Reference input elements: establish r/lship b/w command & reference input • Reference input : signal established as a standard of comparison. • Controller : located b/w deviation & actualling signal

•Actuating signal :corresponds to output signal of the controller • Controlled system : b/w actualing signal & directly controlled variable. • control variable : output signal of the system.

Components of a Servosystem Reference Input Elements

Reference Input

COMMAND Actuator, Coupling System

Controlled system

(Controlled Variable) Performance Analyzing Elements

Central Comparator (sensory engram)


Deviation Signal


The Face as a Servosystem Input –

Maxillary dental arch

Output – sagittal position of the mandible.

The Face as a Servosystem Release of Hormones(Command)


(Coupling system) Actuating signal


Growth at condyle (Controlled System)

Position of Maxillary Dental arch (Ref Input)


Actuator (Motor Cortex) Brain (sensory engram)

Deviation Signal


(Comparator) Periodontium, Teeth Musculature Joint

Mastication (Performance)

The Sensory Engram

• Blueprint of ideal muscular function/position • Collection of feedback loops

• CNS tends to operate along these feedback loops

Other Terms Related to a Servosystem



Output Input




(Gain <1)


Cusp to fossa relation


Cusp to cusp relation


Abnormal tooth position Occlusal interferences Arthritis Muscle Inflammation Periodontitis, Pulpitis

Peripheral Comparator Before development of Occlusion:•Sensory engram not developed •Servosystem does not operate •Genetic influence on mandibular growth •Anodontia After Development of Occlusion:•Sensory engram forms •Peripheral comparator controls growth





Catastrophe Theory So , a class II molar r/l will never spontaneously revert

to class I


Importance of Discontinuities Facial growth should be accounted for by using unpredetermined & discontinous models rather continous & deterministic ones. Stability of occlusion after it is established â&#x20AC;˘ Genotype does partially influence the phenotype

Cybernetics Dr.Rekha

The Face as a Servosystem Release of Hormones(Command)


(Coupling system) Actuating signal


Growth at condyle (Controlled System)

Position of Maxillary Dental arch (Ref Input)


Actuator (Motor Cortex) Brain (sensory engram)

Deviation Signal


(Comparator) Periodontium, Teeth Musculature Joint

Mastication (Performance)

Failure of Servosystem to Control Growth • Peripheral comparator faulty – Caries, Mutilated dentition. •Discrepancy between rotation pattern (Anterior or Posterior)

and location

of comparator.

Action of Functional Appliances

Mode of action of functional Appliances Functional appliance

LPM Retrodiscal Pad Growth stimulating factors Lengthening of mandible

Two Types of Functional Appliances

1) Activator, Postural hyperpropulsor, Frankel appliance, Twin block, Bionator, Class II Elastics(?)

) Herren activator, LSU activator, Harvold-Woodside activator, Extra oral traction on the mandible.



Forward Position


Increased activity of LPM and RDP LPM “helped to contract more” by Functional appliances.

i.e myotactic reflex & isometric contractions

CELLULAR LEVEL 1. Precursor Skeletoblast â&#x20AC;&#x201C; pleuripotent, fibroblast like. 2. Prechondroblast â&#x20AC;&#x201C; faster cell cycle, matures into Chondroblast

Chondroblasts lost removed)

(hypertrophy, surgically

Increased multiplication of prechondroblasts Local control over multiplication of prechondroblasts Originates from chondroblastic layer â&#x20AC;˘Stutzmann and Petrovic (1982, 1990)

Functional appliances (especially Class II elastics) Increased activity of RDP

Increased nutrients and growth factors inhibitors removed. Increased mitoses and earlier hypertrophy of chondroblasts.

Cytoplasmic junctions between skeletoblasts reduce.

Transmission of inhibitory factors reduce.

Increased mitotic rate and rate of differentiation into prechondroblasts.

Reduced negative feedback signal reaching prechondroblasts

Increased growth at the condyle

SECOND GROUP: Position mandible forward , open in beyond rest position. Viscoelastic property of muscle is imp No increase in activity of LPM •Herren (1953) •Auf der Maur (1978) •Yet there was an increase in growth

â&#x20AC;˘ Proponents contend that the use of myotactic reflex should be largely ignored. â&#x20AC;˘ Alveolar remodelling is obtained from the inherent elasticity of muscle,tendinous tissue, skin without motor stimulation.

wo steps:

)While appliance is worn:Forward position increase in length of LPM New sensory engram

)While appliance is not worn:New sensory engram Functioning in anterior position Increased activity of RDP

Action of first group while appliance is worn

Action of second group while appliance is not worn

A New Parameter for estimating condylar growth direction

• Growth direction of condyle coincides in general with the axes of individual trabeculae ,located just inferior to the central part of the condylar cartilage. • Stutzmann’s angle : trabecular alignment with mandibular plane.

Stutzmannâ&#x20AC;&#x2122;s angle increases at the beginning of treatment(only a transient remedial event). Closes: horizontal growth pattern. Opens : vertical growth pattern.

CLINICAL IMPLICATIONS 1)Principle of optimality of function : Less relapse tendency if post orthodontic treatment muscular activity produces a lower deviation signal.

2) Removal of functional appliance â&#x20AC;&#x201C; when growth is complete. 3) If removed when growth not complete â&#x20AC;&#x201C; Proper intercuspation.

4) Understanding of when, and for how long a particular functional appliance should be worn. First group â&#x20AC;&#x201C; Full time Second group â&#x20AC;&#x201C; Part time


Proper functioning of LPM and RDP important for growth â&#x20AC;&#x201C; Proper parent counseling.

6) Sensory engram poorly developed in younger children. 7) Utilization of high hormonal activity at puberty.

Drawbacks Lot of importance on condyle: Fracture?

)Peripheral comparator (occlusion) itself is unstable. discrepancies may be overcome by Dentoalveolar changes rather than growth of Mandible.

) Occurrence of Class II end on relation is seen often?

) Action of reverse pull headgear on maxilla (primary cartilage)

References Dentofacial Orthopedics with Functional Appliances Graber, Rakosi, Petrovic

Craniofacial Growth Series – Monograph (Craniofacial Growth Theory and Orthodontic Treatment – Edited by Carlson)

Treatment objectives and case retention: Cybernetic and myometric considerations 1970

R.M. Jacobs Am J Orthod, 58:552-564,

Grant’s Atlas of Anatomy Leader in continuing dental education

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