Cybernetic Theory and Craniofacial Growth

Cybernetic TheoryCybernetic Theory
ofof
Craniofacial GrowthCraniofacial Growth
www.indiandentalacademy.com

Petrovic 1977Petrovic 1977
• Demonstrate qualitative and quantitative
relationship between observed and experimental
findings.
• Broader understanding of orthodontic problems,
and action of appliances
• Familiarity of orthodontists with cybernetics

Cybernetics Transfer of InformationCybernetics Transfer of Information
• Cybernetic systems operate through transfer of
information
• Physical, Chemical, Electromagnetic

Input Process Output
Transfer Function
CyberneticCybernetic
SystemSystem
OutputInput

Physiological cybernetic systems
Open loop Closed loop
Regulator
Servosystem
Comparator
Feedback
Central
Peripheral
Positive
Negative

Open LoopOpen Loop
Output has no affect on the input

Closed LoopClosed Loop
Relationship maintained between input and output
Input Comparator Transfer function
OutputFeedback
Loop

Regulation Type of Closed LoopRegulation Type of Closed Loop
Input is constant
Any change of the input will initiate a “regulatory
process”
Input Comparator Transfer function
Regulation of input

Servosystem Type of Closed LoopServosystem Type of Closed Loop

Components of a ServosystemComponents of a Servosystem
COMMAND
Reference Input Elements
Reference Input
COMPARATOR
Performance
Analyzing
Elements
Performance
Deviation Signal
Central Comparator
(sensory engram)
Actuator, Coupling System,
Controlled System Output
(Controlled Variable)

Growth of the FaceGrowth of the Face
According to theAccording to the
Servosystem TheoryServosystem Theory

Types of CartilageTypes of Cartilage
Primary

Types of CartilageTypes of Cartilage
Secondary

Primary Cartilage:Primary Cartilage:
Epiphysis, Synchondrosis, Nasal Septum, EthmoidEpiphysis, Synchondrosis, Nasal Septum, Ethmoid
SphenoidSphenoid
Secondary Cartilage:Secondary Cartilage:
Condyle, Coronoid, Mid Palatal Suture,Condyle, Coronoid, Mid Palatal Suture,
Fracture CallusFracture Callus

Factors influencing
Growth
Primary
Cartilage
Secondary
Cartilage
Hormones Yes Yes
Local Factors No (Chondroblasts
surrounded by matrix)
Yes (Pre-
chondroblasts not
surrounded by matrix)
Orthopaedic
appliances
Only Direction Direction and
Amount
Charlier, Petrovic, Stutzmann
Strasburg, Francewww.indiandentalacademy.com

Role of Lateral Pterygoid and Retrodiscal PadRole of Lateral Pterygoid and Retrodiscal Pad
•Blood Supply
•Bio-mechanic

Relationship Between Lateral Pterygoid,Relationship Between Lateral Pterygoid,
Retrodiscal Pad and CondyleRetrodiscal Pad and Condyle
RDP
LPM
MENISCUS

Stutzmann and PetrovicStutzmann and Petrovic
Proper function of Lateral Pterygoid andProper function of Lateral Pterygoid and
retrodicsal pad:retrodicsal pad:
• Excision of Lateral Pterygoid
• Reduced function of the Retrodiscal pad
(Rat experiments)

The Face as a ServosystemThe Face as a Servosystem
Input – Maxillary dental arch
Output – Adjustment of the position of mandibular
dental arch

Growth in
Length
Growth in
Width
Growth of the maxillaGrowth of the maxilla

Growth in Length:
Release of
STH
Somatomedin
Growth of
Nasal Septum
Increased size
Of Tongue
Septo-
Premaxillary
ligament
Labio narinary
Muscles
Traction
Protrusion of
Lower Incisors
Protrusion of
Upper Incisors
Thrust Growth of
Maxillo
Palatine
suture
Growth of
Pre
Maxillary
extremity
Induction
Growth of
Premaxillo-
Maxillary
suture
Biomechanical
Direct Action
Anterior shift
Of premaxillary
bones
Thrust

Growth in Width:
Release of
STH
Somatomedin
Growth of
Lateral cartilaginous
masses of Ethmoid
Increased size
Of Tongue
Growth of cartilage
B/w greater wings
& body of sphenoid
Outward growth
Of maxillary
bones
Outward shift of
Alveolus and
molars Outward
Appositional
Bone
growth
Transverse
Separation of
premaxillae
Transverse
Seperation of
Horizontal
Maxilla and
Palatine plates
Growth of
inter Pre
Maxillary
suture
Growth of
mid
Palatine
suture
Direct effectwww.indiandentalacademy.com

The Face as a ServosystemThe Face as a Servosystem
Release of
Hormones (Command)
Hormones Position of Maxillary
Dental arch (Ref Input)
OCCLUSION
(Comparator)
Periodontium,
Teeth
Musculature
Joint
Mastication
(Performance)Deviation Signal
Brain
(sensory engram)
Actuator (Motor Cortex)
Output
ActuatingActuating
signalsignal
LPM & RDPLPM & RDP
(Coupling system)(Coupling system)
Growth at condyleGrowth at condyle
(Controlled System)(Controlled System)

Growth at the Posterior Border of the RamusGrowth at the Posterior Border of the Ramus

Other Terms Related to a Servosystem
Gain = Output
Input
Attenuatation (Gain <1)Enhancement (Gain>1)
1. STH – Somatomedin
2. Small amounts of
TESTOSTERONE
3. Very small amounts of
OESTROGEN
1. Large amounts of
TESTOSTERONE
2. Small or large amounts of
OESTROGEN
3. Large amounts of
CORTISONE

Attractor Cusp to fossa relation
Repeller Cusp to cusp relation
Disturbances 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

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

DiscontinuitiesDiscontinuities
Catastrophe TheoryCatastrophe Theory
StableStable StableStableUnstableUnstable

BifurcationBifurcation

Catastrophe TheoryCatastrophe Theory

Importance of DiscontinuitiesImportance of Discontinuities
•Growth prediction , treatment planning , decision making
•Stability of occlusion after it is established
•Genotype does not directly influence the phenotype

Height of
Bifurcation
OR

The Sensory EngramThe Sensory Engram
• Collection of feedback loops
• Blueprint of ideal muscular function/position
• CNS tends to operate along these feedback loops

Optimality of FunctionOptimality of Function
•Minimum deviation signal
•CNS always tries to revert back to optimal position
•Observation of Chain gang prisoners by Jacobs (1968)

Development of Skeletal MalocclusionDevelopment of Skeletal Malocclusion
According to the Servosystem TheoryAccording to the Servosystem Theory

For every unit of Growth hormone released,For every unit of Growth hormone released,
the amount of growth in the maxilla is less thanthe amount of growth in the maxilla is less than
in the mandible.in the mandible.

Hormone levels
Increaseinlength
MAX
LPM(norm)
LPM(min)
LPM(max)
L1 N L2
PrognathismRetrognathism

Action of FunctionalAction of Functional
AppliancesAppliances

) Activator, Postural hyperpropulsor, Frankel
appliance, Twin block, Bionator, Class II Elastics(?)
) Herren activator, LSU activator, Harvold-Woodside
activator, Extra oral traction on the mandible.
Two Types of Functional Appliances:Two Types of Functional Appliances:

FIRST GROUP:
Position mandible Increased activity of
Forward LPM and RDP
Less fatigable fibres in LPM
•Oudet et al (1988)
•Carlson et al (1990)
LPM “helped to contract more” by
Functional appliances.

CELLULAR LEVELCELLULAR LEVEL
1. Precursor
Skeletoblast –
pleuripotent,
fibroblast like.
2. Prechondroblast –
faster cell cycle,
matures into
Chondroblast

Chondroblasts lost Increased
multiplication of
prechondroblasts
(hypertrophy, surgically removed)
Local control over multiplication of
prechondroblasts
Originates from chondroblastic layer
•Stutzmann and Petrovic
(1982, 1990)

Functional appliances (especially Class II elastics)
Increased activity of RDP
Increased nutrients and growth factors supplied
and inhibitors removed.
Increased mitoses and earlier hypertrophy of
chondroblasts.

Reduced negative feedback
signal reaching
prechondroblasts
Increased growth at the
condyle

Cytoplasmic junctions between skeletoblasts reduce.
Transmission of inhibitory factors reduce.
Increased mitotic rate and rate of differentiation into
prechondroblasts.

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

wo steps:
) While appliance is worn:-
Forward position
Reduction of 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 while appliance is not worn
group

CLINICAL IMPLICATIONSCLINICAL 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 – when growth
is complete.
3) If removed when growth not complete – Proper
intercuspation.

4) Understanding of when, and for how long a
particular functional appliance should be worn.
First group – Full time
Second group – Part time

5) Proper functioning of LPM and RDP important for
growth – Proper parent counseling.
6) Sensory engram poorly developed in younger
children.
7) Utilization of high hormonal activity at puberty.

DrawbacksDrawbacks
Lot of importance on condyle:
Fracture?
Peripheral comparator (occlusion)
discrepancies may be overcome by Dentoalveolar
changes.

Occurrence of Class II end on relation is seen often?
Action of reverse pull headgear on maxilla
(primary cartilage)

ReferencesReferences
Dentofacial Orthopedics with Functional
Appliances
Graber, Rakosi, Petrovic
Craniofacial Growth Series – Monograph 23
(Craniofacial Growth Theory and Orthodontic Treatment –
Edited by Carlson)

Treatment objectives and case retention:
Cybernetic and myometric considerations
R.M. Jacobs Am J Orthod, 58:552-564, 1970
Grant’s Atlas of Anatomy

Cybernetic Theory and Craniofacial Growth

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