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2. 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
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3. Cybernetics
Transfer of Information
• Cybernetic systems operate through transfer of
information
• Physical, Chemical, Electromagnetic
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7. Closed Loop
Relationship maintained between input and output
Input
Comparator
Feedback
Loop
Transfer function
Output
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8. Regulation Type of Closed Loop
Input is constant
Any change of the input will initiate a “regulatory
process”
Input
Comparator
Regulation of input
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Transfer function
10. 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
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Performance
Analyzing
Elements
Performance
11. Growth of the Face
According to the
Servosystem Theory
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16. Role of Lateral Pterygoid and Retrodiscal Pad
•Blood Supply
•Bio-mechanic
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17. Relationship Between Lateral Pterygoid,
Retrodiscal Pad and Condyle
MENISCUS
LPM
RDP
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18. Stutzmann and Petrovic
Proper function of Lateral Pterygoid and
retrodicsal pad:
• Excision of Lateral Pterygoid
• Reduced function of the Retrodiscal pad
(Rat experiments)
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19. The Face as a Servosystem
Input – Maxillary dental arch
Output – Adjustment of the position of mandibular
dental arch
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20. Growth of the maxilla
Growth in
Length
Growth in
Width
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22. 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
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Growth of
Maxillo
Palatine
suture
23. 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
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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
24. 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
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Mastication
(Performance)
25. Growth at the Posterior Border of the Ramus
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26. 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
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27. Attractor
Cusp to fossa relation
Repeller
Cusp to cusp relation
Disturbances
Abnormal tooth position
Occlusal interferences
Arthritis
Muscle Inflammation
Periodontitis, Pulpitis
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29. 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
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30. Failure of Servosystem to Control Growth
• Peripheral comparator faulty – Caries,
Mutilated dentition.
•Discrepancy between rotation pattern (Anterior
or Posterior) and location of comparator.
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34. Importance of Discontinuities
•Growth prediction , treatment planning , decision making
•Stability of occlusion after it is established
•Genotype does not directly influence the phenotype
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36. The Sensory Engram
• Collection of feedback loops
• Blueprint of ideal muscular function/position
• CNS tends to operate along these feedback loops
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37. Optimality of Function
•Minimum deviation signal
•CNS always tries to revert back to optimal position
•Observation of Chain gang prisoners by Jacobs (1968)
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38. Development of Skeletal Malocclusion
According to the Servosystem Theory
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39. For every unit of Growth hormone released,
the amount of growth in the maxilla is less than
in the mandible.
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42. 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.
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43. 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.
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47. 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.
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49. Cytoplasmic junctions between skeletoblasts reduce.
Transmission of inhibitory factors reduce.
Increased mitotic rate and rate of differentiation into
prechondroblasts.
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50. 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
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51. 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
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52. Action of first group
while appliance is worn
Action of second
while appliance is not worn
group
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53. CLINICAL IMPLICATIONS
1) Principle of optimality of function :Less relapse tendency if post orthodontic
treatment muscular activity produces a lower
deviation signal.
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54. 2) Removal of functional appliance – when growth
is complete.
3) If removed when growth not complete – Proper
intercuspation.
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55. 4) Understanding of when, and for how long a
particular functional appliance should be worn.
First group – Full time
Second group – Part time
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56. 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.
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57. Drawbacks
Lot of importance on condyle:
Fracture?
Peripheral comparator (occlusion)
discrepancies may be overcome by Dentoalveolar
changes.
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58. Occurrence of Class II end on relation is seen often?
Action of reverse pull headgear on maxilla
(primary cartilage)
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59. References
Dentofacial Orthopedics with Functional
Appliances
Graber, Rakosi, Petrovic
Craniofacial Growth Series – Monograph 23
(Craniofacial Growth Theory and Orthodontic Treatment –
Edited by Carlson)
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60. 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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61. Thank you
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