Servosystem Theory / Cybernetic Theory by Petrovic

Cybernetic Theory by Petrovic. The PPT is made from Graber, Petrovic and Rakosi Chapter -2 . Department of Orthodontics and Dentofacial Orthopedics.
The servo-system theory of growth was given by Alexandre Petrovic, Charlier, and Jeanne Stutzmann of Louis Pasteur school of Medicine in the late 1960s.
It is based on factorial qualitative analysis and describes the craniofacial growth mechanisms and the modulus operandi of functional and orthopedic appliances.
The servo-system theory relies on the principle of cybernetics to describe the growth of the craniofacial complex.

1. Presented by: Dr. Aditi Jain 1 st year PG Servo system Theory : Petrovic Popper (1963) Science is not a static acceptance of truth but rather the permanent search of truth. Department of Orthodontics and Dentofacial Orthopedics  Santosh Dental College, Deemed to be University

2. Introduction The servo-system theory of growth was given by Alexandre Petrovic, Charlier , and Jeanne Stutzmann of Louis Pasteur school of Medicine in the late 1960s. It is based on factorial qualitative analysis and describes the craniofacial growth mechanisms and the modulus operandi of functional and orthopedic appliances. The servo-system theory relies on the principle of cybernetics to describe the growth of the craniofacial complex. Alexander Petrovic 1923-2003 (France) “I worship contradictory discussions.”

3. Cybernetics The term "CYBERNETICS (comes from greek word kybernetes which means steersman) was coined by mathematician Norbert Wiener in 1948 to encompass the entire field of control and communication theory, whether in a machine or in an animal. Cybernetics is concerned with scientific investigation of systematic processes of a highly varied nature, including phenomenon such as regulation, information processing, storage, adaptation, self organization and strategic behavior.

4. Cybernetically organized biological features Input Orthodontic and orthopedic appliances. Black Box Output Correction of malocclusion and intermaxillary relation. Genetically determined and cybernetically organized biologic feature of phenomena characterizing, including, controlling spontaneous and appliance-modulated growth relative primarily to the following:- Maxillary lengthening and widening. Mandible lengthening. Teeth Movement. The physiological system under investigation is represented by BLACK BOX.

5. Cybernetically Organised System operated Physiological signals Transmits information Physical Electromagnetic Chemical Information Processing Production, Perception, Transmission, And Storage Of Information. Not static Sophisticated ADVANTAGES Positive & negative feedback loops Self regulation INPUT OUTPUT

6. Physiological Cybernetic System OPEN LOOP CONTROL SYSTEM CLOSED LOOP Regulator Servosystem Feedback Comparator Positive Negative Central Peripheral

7. Open loop Control System Environmental Stimulus Receptor Reflex Transmission Perception Passive Response INPUT OUTPUT

8. CLOSED loop Control System Transfer Function INPUT OUT PUT COMPARATOR FEEDBACK

9. Regulatory type of closed loop Constant Input.

10. Servosystem type of closed loop Control of movements Neural Integration Organic Control Receptor Environmental Stimulus Stimuli Control Receptor Control Feedback Input is not constant

11. SERVOSYSTEM THEORY 1977 Shannon’s information theory (1948) - designed to optimize the transmission of information through communication channels The feed back concept used in engineering control systems. Petrovic and Charlier (1967-1969) – Jaw growth rate and direction can be modified through functional appliances. Chronobiological aspects of cartilage and bone growth Jeanne Stutzmann 1976 The role of LPM & postural hyperpropulsor temporomandibular frenum mediator role.

12. The face as a Servosystem Input- Any Changes In Maxilla (outward and forward growth) Out put- Adjustment of the position of mandible

13. Components of a SERVOSYSTEM COMMAND Reference Input COMPARATOR PERFORMANCE Coupling System Controlled System (Controlled Variable) OUTPUT CONTROLER Performance Analyzing Elements ACTUATOR Constantly Changing Input Reference Input Elements Central Comparator/Sensory Engram Deviation Signal Peripheral Comparator GAIN

14. Command The command is a signal established independent of the feedback system in scrutiny and is not affected by the output of the system. It affects the behavior of the control system without being affected by the consequences of this behavior. For instance, the secretion-rates of growth hormone-somatomedin, testosterone, and estrogen do not seem to be modulated by variations of craniofacial growth.

15. Reference Input Element They establish the relationship between Command (Growth Hormone) and the Reference Input (Sagittal Position of Maxilla). Septal Cartilage, Septomaxillary Frenum, Labionarinary Muscle, Premaxillary and Maxillary bone.

16. Reference Input It is constantly changing variable. Signal established as a standard of comparison. Independent of the feedback mechanisms. Sagittal Position of maxilla.

17. Comparator Serves to establish the relationship between the reference input and controlled variable. “The operation of confrontation” – Occlusal contact between upper and lower jaw. Any deviation from optimal occlusal contact detected by the comparator leads to correction signals to reestablish optimum occlusal contact.

18. PERFORMANCE The function occurring by peripheral comparator that is occlusion of mandible and maxilla is mastication which is the performance. It is analyzed by performance analyzing elements.

19. PERFORMANCE Analyzing elements They are periodontal ligament, teeth, muscles, temporomandibular joint . Proprioceptors within the periodontal regions and temporomandibular joint perceive even a very small occlusal discrepancy and tonically activate the muscles responsible for mandibular protrusion.

20. DEVIATION SIGNAL: Any input other than the reference chosen by the researcher is considered a disturbance. The disturbance is responsible for deviation of the output signal and is thus called deviation signal. It may act on any element of the regulating system. Abnormal Tooth position, occlusal interferences, arthritis, muscle inflammation, periodontitis, pulpitis.

21. Controller The BRAIN or the Central Nervous System is the Central Compactor also called as Sensory engram or Controller.

22. Actuator The actuator is the Motor Cortex from where the signal is transferred. The actuating signal corresponds to the output signal of the controller (i.e., to the input signal of the controlled system). The activity of the Lateral Pterygoid Muscle and retro discal pad corresponds to the actuating signal.

23. COUPLING SYSTEM The coupling system is part of the control system between the actuating signal and the directly controlled variable. An example is the growth of condylar cartilage via metabolic blood interchange in retrodiscal pad.

24. CONTROLLED SYSTEM The final output of the system i.e. the OUTPUT SIGNAL. The Sagittal position of Mandible. Since it is not constant it is also controlled variable which keeps on changing with the change in input.

25. GAIN The gain of a system is the output divided by the input. Gain > 1= Amplification. Gain < 1 = Attenuation. The pterygo -condylar coupling is an example of gain. According to petrovic's investigation, the basal value of the gain is determined genetically but may be amplified by growth hormone-somatomedin and testosterone or attenuated by estrogen. This is of great clinical significance.

26. Attractor Structurally stable steady state in dynamic system. Full interdigitation of the teeth. CLASS-I, CLASS-II, CLASS-III with cusp to fossa relationship. The servosystem strives to achieve this stable form. Repeller Unstable equilibrium state. Cusp to cusp type of occlusal relationship. The comparator detects this kind of disturbance (Deviation signal) and tries to achieve the cusp to fossa relationship through servosystem. Feedback Signal The feedback signal is the function of the controlled variable that is compared to the reference input. In a regulator or servo-system, it is negative.

27. Growth of Face According to Servosystem Theory

28. TYPES OF CARTILAGE PRIMARY CARTILAGE : Nasal septum, cartilage between the body of sphenoid, epiphysis, synchondrosis, ethmoid. SECONDARY CARTILAGE : Condylar process, Coronoid process, Mid- palatal Suture, Fracture Callus

29. Growth at Cellular Level Chondroblast lost (hypertrophy or surgically removed) INCREASED MULTIPLICATION OF PERICHONDROBLAST Precurssor – SKELETOBLAST pluripotent, fibroblast like PERICHONDROBLAST faster cell cycle , matures into chondroblast Local Factors (Originates from Chondroblastic layer)

30. Functional appliances ( especially class 2 elastics) Increased activity of RDP Increased nutrients and growth factors supplied and inhibitors removed Increased mitosis and earlier hypertrophy of chondroblast Reduced negative feedback signal reaching Prechondroblasts Increased Growth at Condyle

31. Cytoplasmic Junctions between Skeletoblast reduce Transmission of inhibitory Factors reduce Increased mitotic rate and rate of differentiation into Prechondroblast

32. Local Factors affecting the condylar Cartilage Consistent transmembrane ion flux variation. Intra cellular Na ion concentration increased. Intra cellular K ion concentration is decreased. Discharge of H ions from blast cells is increased. Increased pH. Intracytoplasmic Ca++ concentration is low.

33. Thrust Effect Ligament traction Muscle traction Spheno -occipital synchondrosis Nasal septal cartilage Lateral masses of ethmoid Body and greater wing of sphenoid STH- Stomatomedin Control of the maxillary Growth Direct Effect Indirect Effect Forward Growth Of Septal Cartilage Outward Growth

34. Forward Growth of Septal Cartilage Thrust Effect Anterior Extremity of the Nasal Septal Cartilage Spreads Laterally in Anterio - Inferior Direction Penetrates into the Premaxillary Bone Thrust Effect Premaxillomaxillary Suture Maxillopalatine Suture

35. Septopremaxillary Ligament traction Growth of the Nasal Septal Cartilage Traction effect on the premaxillary bone through the septomaxillary ligament. Traction of the labionarinari muscle Traction of the premaxillary bone through this muscle. Biomechanics promotion of the forward growth of the upper jaw. Absence of labial muscle attachment on the nasal septum – cleft lip- bone deformation .

36. out ward Growth Outward growth of lateral Cartilaginous masses of the ethmoid and the cartilage between the body and greater wings of sphenoid. Produces a lateralization of right and left alveolar ridges Stimulates the growth of mid-palatal suture Outward growth of Maxilla

37. ROLE OF LPM AND RETRODISCAL PAD Blood circulation: Increase in open Loop Factors. Reduction in negative feedback factors. Biomechanical effect

38. For every unit of STH or testosterone that is released, amount of growth is maximum. Mandible > Maxilla At normal hormonal level N- good maxilla and mandible relation is maintained. At T2- hormonal level- (man> max)- LPM is reduced. Beyond T2 hormonal level – LPM activity can no longer be reduced – Prognathism The opposite happens when hormonal level is below T1 hormonal level – LPM activity can no longer be increased- retrognathism. Within levels T1- T2 , good maxilla and mandible relation is maintained outside these levels: malocclusion occurs.

39. Growth in length of maxilla

40. Growth in width of maxilla

41. Growth Hormones [STH- Stomatomedin ] Sagittal Position of maxilla OCCLUSION MASTICATION Lateral pterygoid muscle and retrodiscal pad Growth at condyle, sagittal position of mandible BRAIN Periodontium, teeth, muscles and TMJ Motor Cortex Constantly Changing Input Septal Cartilage, Septomaxillary Frenum, Labionarinary Muscle, Premaxillary and Maxillary bone Central Comparator/Sensory Engram Deviation Signal Peripheral Comparator GAIN

42. Mode of action of functional appliances 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 super periosteal ossification Supplementary lengthening of mandible

43. Functional Appliances 1 st - Group Postular hyperpropulsor Twin Block Bionator Anderson Haupl activator Class ii elastics Frankel’s Appliance 2 nd -Group Herren Activator Lsu Activator Harvold Woodside activator Extra oral traction of the mandible

44. Positions Mandible Forward Increased Activity of LPM & RDP Less fatigable fibers in LPM Oudet et el (1988) Carlson et el (1990) Positions Mandible Forward 1 st - Group 2 nd - Group Open in beyond rest position No Increased Activity of LPM. Yet increase in Growth Herren (1953) Auf der Maur (1978)

45. 2 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 Activity of 1 st Group Activity of 2 nd Group

46. Postural Hyperpropulsor

47. Class – ii Elastics Acts primarily through RDP rather LPM. Alters the intrinsic regulation of the prechondroblastic 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.

48. Twin Block Alters the occlusal inclined planes. 70˚ inclined planes alter the sensory engram and provide a horizontal component of force.

49. L.S.U. or hERREN ACTIVATOR Acts when 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 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.

50. Effect of Chin cup therapy Retropulsion of the mandible results in reduction in number of dividing cells. Dividing cells if any are found anteriorly. Resulting in anterior Growth rotation and decreased mandibular Length.

51. Clinical Implications Principle of optimality of function:- less relapse tendency if post orthodontic treatment muscular activity produces a lower deviation signal. Removal of functional appliances when growth is complete. If removed when growth not complete then we need proper intercuspation.

52. First group : full time , second group: part time . Proper functioning of LPM and RDP is important for growth – parent counselling should be done properly. Sensory engram is poorly developed in younger children. Utilization of high hormonal activity at puberty.

53. Considerations of servosystem theory Growth Rotations of the Mandible Alveolar Bone Turnover Rate

54. Bifurcation Topologic Representation of increasing Hormone levels (testosterone or STH- stomatomedin ) resulting in supplementary growth of the mandible combined with lengthening of the maxilla as modulated by the comparator of the servosystem ( cuspal relief). Experimental results are expressed in terms of catastrophe theory.

55. Petrovic’s Growth Categories Growth Inequality of Bases 1 : Mandible equal to maxilla 2 : Mandible smaller than maxilla 3 : Mandible greater than maxilla Rotation of the Mandible R : Neutral P : Posterior rotation of mandible A : Anterior Rotation of Mandible Posteroanterior State N: Normal D: Distal M: Mesial Vertical State N: Normal OB: Open Bite DB: Deep Bite

56. LEVEL -1 Cell and molecular Biology Level 70% 3% 25% Mandible less than Maxilla Mandible greater than Maxilla Mandible equal to Maxilla Quantitative determination of difference between maxilla and mandible.

57. LEVEL -2 Partly on Respiration Phonation & Deglutition Anterior Posterior Neutral Relates to the Growth rotation and growth inclination of both maxilla and mandible

58. LEVEL -3 Unstable occlusion and Functional Discontinuity Distal Mesial Normal Based on the occlusal relationship

59. Growth Rotations of Mandible Morphogenetic Rotations Positional Rotations The Change in the Shape of Mandible The Change in the Position of Mandible in relation to the Adjacent Structures Lavergene & Gasson (1977)

60. Alveolar Bone Turn over rate Tissue level Growth Potential : Level of subperiosteal ossification rate and the level of alveolar bone turnover rate  Tissue level Growth Responsiveness:   The degree of augmentation of the alveolar bone turnover resulting from orthodontic treatment.

61. Auxologic Groups Six auxologic categories of the mandible. Depends on: tissue level growth potential Tissue level Growth responsiveness to orthodontic, orthopedic and functional appliances. Helps define the biologic inter-individual variation of growing mandible. Clinicians must give importance to tissue level growth responsiveness than just determining the growth direction.

62. Failure of Servosystem to Control Growth Before development of Occlusion Sensory engram not developed Servosystem does not operate Genetic influence of mandibular Growth Anodontia After Development of Occlusion :- Sensory Engram forms Peripheral Comparator Control Minimize possible deviation to achieve stable occlusion. Peripheral Comparator Faulty- Caries, Mutilated Dentition Discrepancy between rotation pattern (Anterior or Posterior) and location of Comparator.

63. Drawbacks The author places a lot of importance on the role of hormones in controlling growth. The peripheral comparator, the occlusion, itself is unstable. According to this theory, an end on relation is a Repeller. This theory places a lot of importance on condyle as growth center. If condylar cartilage is lost, growth should seize. But some studies done on Scandinavia show that this does not happen.

64. Evidences against the theory Goret – Nicaise, Awn (1983) - Resection of LPM – Fails to diminish condylar Growth. Whetten and Jhonston (1985) – bilateral condylectomy and unilateral LPM in rats – same growth on both sides. Das, Myer & Sicher ( 1980) – Occlusion remained unaffected in condylectomy studies.

65. Conclusion While we may no longer seek a single synthesizing theory for all of craniofacial growth, we now have, because of petrovic’s work, a convenient model & a language by which we can describe and relate growth activities to one another, thus obviating any need for another paradigm. The cybernetic theory of facial growth and the crucial -topologic concept of structural and functional stability and instability are highly useful in a systematic and increasingly computerized approach to clinical situations.

66. References Graber, Petrovic, Rakosi . Dentofacial orthopaedics and functional appliances, 2nd edition, 1917. Zhou, Z.; Luo, S. (1998-05-01). "[Differential expression of IGF-I and its mRNA in mandibular condylar cartilage of rat--direct evidence for servosystem theory of facial growth]".  Hua Xi Kou Qiang Yi Xue Za Zhi = Huaxi Kouqiang Yixue Zazhi = West China Journal of Stomatology .  16  (2): 164–165.  ISSN   1000-1182 .  PMID   12214426 . https://www.scribd.com/document/383886681/Petrovic .  Role of the lateral pterygoid muscle and meniscotemporomandibular frenum in spontaneous growth of the mandible and in growth stimulated by the postural hyperpropulsor J.J. Stutzmann   , A.G. Petrovic DOI: https ://doi.org/10.1016/0889-5406(90)70110-X . https://phaidrabg.bg.ac.rs/open/o:21881  

67. Thank You