Cybernetic theory of craniofacial growth /certified fixed orthodontic courses by Indian dental academy

Cybernetic Theory
of
Craniofacial Growth
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Petrovic 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 Information

• Cybernetic systems operate through transfer of
information
• Physical, Chemical, Electromagnetic


Input

Input

Process

Cybernetic
System
Transfer Function


Output

Output

Physiological cybernetic systems

Open loop

Closed loop

Regulator

Servosystem

Comparator

Feedback


Peripheral
Central
Positive
Negative

Open Loop
Output has no affect on the input


Closed Loop
Relationship maintained between input and output

Input

Comparator

Feedback
Loop

Transfer function

Output


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

Comparator

Regulation of input

Transfer function

Servosystem Type of Closed Loop


Components of a Servosystem
COMMAND

Reference Input Elements

Actuator, Coupling System,
Controlled System

COMPARATOR
Output
(Controlled Variable)

Central Comparator
(sensory engram)

Reference Input

Deviation Signal

Performance
Analyzing
Elements

Performance

Growth of the Face
According to the
Servosystem Theory

Types of Cartilage
Primary


Types of Cartilage
Secondary


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

Factors influencing Primary
Growth
Cartilage

Secondary
Cartilage

Hormones

Yes

Yes

Local Factors

No (Chondroblasts

Yes (Pre-

Orthopaedic
appliances

Only Direction

Direction and
Amount

surrounded by matrix) chondroblasts not
surrounded by matrix)

Charlier, Petrovic, Stutzmann
Strasburg, France

Role of Lateral Pterygoid and Retrodiscal Pad
•Blood Supply

•Bio-mechanic


Relationship Between Lateral Pterygoid,
Retrodiscal Pad and Condyle

MENISCUS

LPM
RDP


Stutzmann and Petrovic

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

The Face as a Servosystem

Input – Maxillary dental arch

Output – Adjustment of the position of mandibular
dental arch

Growth of the maxilla

Growth in
Length

Growth in
Width


Growth in Length:

Traction
SeptoPremaxillary
ligament

Induction

Growth of
Nasal Septum

Biomechanical

Labio narinary
Muscles
Release of
STH
Somatomedin

Thrust

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

Transverse
Separation of
premaxillae
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

Growth of
inter Pre
Maxillary
suture

Transverse
Seperation of
Horizontal
Maxilla and
Palatine plates

Growth of
mid
Palatine
suture

Outward
Appositional
Bone
growth

The Face as a Servosystem
Release of
Hormones (Command)

LPM & RDP
(Coupling system)

Position of Maxillary
Dental arch (Ref Input)

Hormones

Growth at condyle
(Controlled System)

OCCLUSION
Output

Periodontium,
Teeth
Musculature
Joint

Actuating
signal

Actuator (Motor Cortex)
Brain
(sensory engram)

(Comparator)

Deviation Signal

Mastication
(Performance)

Growth at the Posterior Border of the Ramus


Other Terms Related to a Servosystem
Gain

=

Output
Input

Enhancement (Gain>1)

Attenuatation (Gain <1)

1. Large amounts of
TESTOSTERONE
2. Small or large amounts of
2. Small amounts of
OESTROGEN
TESTOSTERONE
3. Large amounts of
3. Very small amounts of
CORTISONE
OESTROGEN
1. STH – Somatomedin


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.


Discontinuities

Stable

Unstable

Catastrophe Theory

Stable

Bifurcation


Catastrophe Theory


Importance 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 Engram

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


Optimality 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 Malocclusion
According to the Servosystem Theory


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


Increase in length

LPM(max)
LPM(norm)
LPM(min)
MAX

Retrognathism

Prognathism

L1

N

L2

Hormone levels

Action of Functional
Appliances


Two Types of Functional Appliances:

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

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


FIRST GROUP:
Position mandible
Forward

Increased activity of
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 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
prechondroblasts

over

multiplication

of

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 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.

Drawbacks
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)


References
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


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