Servosystem /certified fixed orthodontic courses by Indian dental academy


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Servosystem /certified fixed orthodontic courses by Indian dental academy

  1. 1. SERVOSYSTEM THEORY OF FACIAL GROWTH INDIAN DENTAL ACADEMY Leader in continuing dental education
  3. 3. INTRODUCTION    Last 20 years have seen an increasing awareness of the potential of functional appliances as a valuable tool in the armamentarium of orthodontists. In late 1960’s Petrovic & co-workers produced first rigorous demonstration that condylar cartilage’s growth rate & amount can be modified by using appropriate functional & orthopedic appliances. Later he employed the model of cybernetics & control theory to describe craniofacial growth patterns & method of operation of functional & orthopedic appliances.
  4. 4.   The term “CYBERNETICS” (Greek kybernetes means steersman) was coined by mathematician Norbert Wiener in 1948 to encompass the entire field of control and communication theory, whether in the machine or in the animal. Cybernetics is concerned with scientific investigation of systematic processes of a highly varied nature, including phenomenon such as regulation, information processing, storage, adoption, self organisation and strategic behavior.
  5. 5.   It grew out of Shannon's information theory – designed to optimise transmission of information through communication channels and the Feed back concept used in engineering control systems. The concept of cybernetics and control theory was put forth by Petrovic (1977,1982) to describe craniofacial growth mechanisms and the method of operation of functional and orthopedic appliances.
  6. 6.   The theory refines orthodontic concepts by demonstrating a qualitative and quantitative relationship between observationally and experimentally collected findings. Helps in a broader understanding of orthodontic problems as the language of cybernetics is compatible with the rapidly expanding use of computers among clinicians.
  7. 7. Phylogenetic explanation for the peculiarities of condylar cartilage Reptiles Articular Quadratus Squamosal In mammals condylar Dentary coronoid angular
  8. 8.   According to Symons, in mammalian embryo, the condylar cartilage develops independently of the chondrocranium. The response of the condylar cartilage growth to local factors may explain the extraordinary success of the phylogenetically new mammalian joint between the skull and the lower jaw.
  9. 9.    Condylar cartilage growth is integrated into an organised functional whole that has the form of a servosystem and is able to modulate the lengthening of the condyle so that the lower jaw adapts to the upper jaw during growth. In the absence of such an adjustment the forces of occlusion would expose the pdl structures to repeated trauma and loss of teeth. This adjustment hence allows proper mastication and facilitates high basic metabolism.
  11. 11.    Cybernetics is based on the communication of information. Any cybernetically organized system operates through signals that transmit information (which may be physical, chemical or electromagnetic in nature). Any cybernetic system, when provided an input (or stimulus), processes such an input and produces an output. The output is related to the input by a transfer function that characterizes the physiologic system.
  12. 12. Input Transfer function Output
  13. 13.
  14. 14. PHYSIOLOGIC SYSTEM OPEN LOOP CLOSED LOOP No feedback loop Or Comparator REGULATOR THE SERVO SYSTEM Main input constant or follow up system Comparator detects Main input not constant disturbances It is –ve feedback
  15. 15.  In an open loop, the output does not affect the input. There are no feed back loops or comparators.  In a closed loop system, a specific relation is maintained between the input and output and are characterized by a feedback loop and a comparator.
  17. 17.  The input is fed into a comparator which analyses the input and judges the degree to which the transfer function needs to be carried out to obtain a certain output.  The output is fed back to the comparator (through a feed back loop) and is analyzed for its adequacy. If found inadequate, the transfer function is carried out once again.  The feed back loop can have a positive or enhancing affect or a negative or attenuating affect.
  18. 18.  A regulator type of closed loop is one in which the input is constant. Any disturbance in the input will cause the comparator to initiate a regulatory feedback system, which will restore the input to its normal state.  Eg. The temperature regulation system of the bodyAny change in body temperature acts as the input into the comaparator (the hypothalamus), which causes an action (pilorection and shivering) which ultimately brings the body temp back to normal.
  19. 19.  Servosystem in this the main input is constantly changing with time and the output is constantly adjusted in accordance to the input.
  21. 21.  Craniofacial growth is an extremely complex process involving a multitude of factors.  The connections between constituents are complex, although the constituents themselves are not.  The identification and analysis of the feed back loops (regulation processes) is among the main tasks in the field of craniofacial growth.
  22. 22.  Cybernetic language has been the best to accurately describe the intricacy and complexity of craniofacial morphogenesis and the means to influence it clinically.  The following set of approaches may be useful in relating scientific findings and the method of operation of orthopedic and orthodontic appliances.
  24. 24.  COMMAND :a signal established independent of the servosystem and is not affected by the output of the system. It tells the system what has to be done.  REFERENCE INPUT : is a signal established as a standard of comparison.  REFERENCE INPUT ELEMENTS :establish the relationship between command and the reference input.
  25. 25.  COMPARATOR (PERIPHERAL) :It is a component that analyses the reference input and judges the performance of the system through performance analysing elements.   CENTRAL COMPARATOR : the performance judging elements then transmits a deviation signal to the central comparator which sends a signal to various components – the actuator, coupling system and the controlled system. This ultimately brings about an output/controlled variable.
  26. 26.
  28. 28.    Stutzman (1976) emphasized the following PRIMARY CARTILAGE - dividing cells, differentiated chondroblasts, are surrounded by a cartilaginous matrix synthesized by them, that isolates them from local factors able to restrain or stimulate cartilaginous growth. Chondroblasts undergo maturation and are later transformed into hypertrophied chondroblasts. Deeper in the cartilaginous matrix, calcium is deposited and endochondral ossification begins.
  29. 29. Seen in 1. 2. 3. 4. 5. Epiphysial cartilages of long bones Cartilages of synchondroses of cranial bones. Nasal septal cartilage. Lateral cartilaginous masses of ethmoid Cartilage between greater wings and body of sphenoid
  30. 30.   1. 2. 3. SECONDARY CARTILAGES the dividing cells, prechondroblasts, do not synthesize a cartilaginous matrix, hence are not isolated from local factor influences. Once they mature into chondroblasts, they become surrounded by cartilaginous matrix and do not divide. Seen in Coronoid and condylar cartilage Mid palatal suture cartilage Post fracture callus
  31. 31.
  32. 32.
  33. 33.
  34. 34.    According to studies carried out by Chartlier, Petrovic and Stutzmann on organ culturesDividing chondroblasts (in primary cartilages) are more susceptible to general extrinsic factors, especially growth hormone, stomatomedin, and sex hormones. The cartilaginous matrix surrounding the mature chondroblasts, isolates them from the effects of local factors. Local biomechanical factors can only modify the direction of growth and not the amount of growth at these sites.
  35. 35.   In the secondary cartilages, where prechondroblasts are the dividing cells, general and local extrinsic factors can affect the growth. The amount of growth of these cartilages can be affected by altering the local extrinsic factors.
  36. 36. Condylar Cartilage   Adaptive to both extrinsic & local biomechanical & functional factors. Condylar cartilage growth is integrated into an organized functional whole that has form of Servosystem & able to modulate lengthening of condyle so that lower jaw adapts to upper jaw during growth
  37. 37. Specific features of condylar cartilage 1. 2. 3. 4. 5. Fibrous capsule -fibroblasts and type I collagen. Zone of growth (mitotic compartment) –skeletoblasts and prechondroblast type II, not surrounded by the cartilaginous matrix with type I collagen. Zone of maturation - functional and hypertrophied chondroblasts. Zone of erosion Zone of endochondral ossification.
  38. 38. Correlation between growth direction of condyle & sagittal distribution of dividing cells in condylar cartilage
  39. 39.   Anatomic, microscopic and histologic studies have shown that the growth direction of the condyle coincides in general, with the axis of individual trabeculae, located just inferior to the central part of condylar cartilage. Hence the condylar growth direction can be determined by measuring the main axis of endochondral bone trabeculae in the condyle and the angle it forms with the mandibular plane.
  40. 40.  A histologic & radioautographic study was made of distribution of dividing cells in a sagittal section of condylar cartilage of juvenile rats.  Condylar cartilage divided into 4 equal sections from anterior to posterior & cells counted.  Each experimental group was subjected to specific orthopedic treatment.
  41. 41.  Results showed that both treatment with the postural hyperpropulsor & with the growth hormone produced significant increase in growth rate of condylar cartilage compared to control group (Charlier et al, 1968, 1969; Petrovic et al , 1975)
  42. 42.
  43. 43.
  44. 44.  Condylar growth is not exclusively a result of the lengthening of pre-existing endochondral bone trabeculae under condylar cartilage but also a result of growth of bone trabeculae (mesenchymal cells) that are formed in parallel & posteriorly oriented in condylar cartilage.
  45. 45.
  46. 46.    Stutzmann angle- the angle formed between main axis of endochondral bone trabeculae in condyle with mandibular plane as viewed on lateral cephalogram. In anterior growth rotation there is closing of angle as seen in treatment with growth hormone. In posterior growth rotation there is opening of angle as seen in treatment with postural hyperpropulsor
  47. 47.
  48. 48. FACTORS AFFECTING CONDYLAR CARTILAGE GROWTH 1. 2. 3. 4. 5. Lateral pterygoid muscle & retrodiscal pad tissue Effect of hormones Intrinsic regulation of condylar cartilage growth rate Other hormonal & humoral factors c-AMP
  50. 50. Retrodiscal pad
  51. 51. Resection of LPM & retrodiscal pad  Experimental studies on juvenile rats were carried out in which LPM were resected.  The interruption of circulatory dependence on the blood supply originating directly from LPM & indirectly through retrodiscal pad may contribute to inhibited differentiation of skeletoblasts.  It was observed that growth of condylar cartilage & lengthening of mandible continued but significantly decreased.
  52. 52.
  53. 53.
  54. 54. Intrinsic regulation of condylar cartilage growth rate   A “negative feed back signal” originates from the proximal part of the chondroblastic zone and exerts a restraining effect on the prechondroblastic multiplication rate. This concept can help explain the effects of some orthopedic and orthodontic appliances and of a hormone such as thyroxine.
  55. 55.   The earlier commencement of chondroblastic hypertrophy and the subsequent decrease in the prechondroblastic division-restraining signal are important intermediary steps in growth stimulating effects of class II elastics, mandibular hyperpropulsar etc. The acceleration of the chondroblastic maturation rate is similarly an intermediary step for the growth rate – stimulating effect of thyroxine. (Stutzmann, Petrovic, 1975, 1979)
  56. 56.
  58. 58.      Increase in length of maxilla Is caused by growth at the premaxillomaxillary and maxillopalatine sutures and by subperiosteal deposition of bone in the anterior region. Increase in width of maxilla Is due to growth at the mid palatal suture and bone deposition along lateral areas of alveolar ridge. Mid palatal suture - secondary cartilage.
  59. 59. Mechanisms controlling growth of the upper jaw   STH-somatomedin, testosterone and estrogen play primary roles in extrinsic control of post natal growth of the upper jaw. They have direct and indirect effects.
  60. 60. Direct effects    Represents almost the entire influence of the hormones on growth of spheno-occipital synchondrosis and nasal septal cartilage. Small part of the effect of hormones on growth of cranial sutures is direct. Effects the responsiveness of preosteoblasts to regional and local factors, stimulating the skeletal cell multiplication. In secondary cartilage - effect seen in multiplication and responsiveness of prechondroblasts
  61. 61. Indirect effect  1. 2. 3. Forward growth of nasal septal cartilage. Thrust effect Septomaxillary ligament traction effect. Labionarinary muscle traction effect.
  62. 62.
  64. 64.  The variation in direction and magnitude of condylar growth is partly a quantitative response to changes in maxillary length.  Variation in maxillary growth can be induced through resection of nasal septal cartilage or administration of growth hormone or testosterone or by orthopedic appliances.  As long as growth alteration does not exceed a certain limit, no significant changes in saggital relationship of dental arches occurs.
  65. 65.    The physiologic adaptation of mandibular length to maxillary length occurs through a variation in both growth rate and direction of growth of condylar cartilage. Growth hormone- somatomedin affects the lengthening of mandible (through condylar growth) to a greater extent than its affects on the lengthening of maxilla. If this hormonal effect remains within physiological limits, the occlusion is not significantly altered, as concomitant reduction an angle between ramus and corpus of mandible, decreases the length of the mandible.
  66. 66.     The release of somatomedin represents the command (command to grow). Reference input elements are the nasal septal cartilage, septopremaxillary frenum, labionariary muscles and premaxillary and maxillary bones. The position of maxillary dental arch is constantly changing reference input of the servosystem. Lower arch is controlled variable. The “operation of confrontation” between the upper and lower dental arches is the “ peripheral comparator” of the Servosystem.
  67. 67.
  68. 68.    Owing to the forward and outward growth of maxilla, there is obvious change in relation of the teeth. What was originally a cusp to fossae relationship becomes a cusp to cusp relationship. Hence the peripheral comparator (occlusion), senses this, due to change in performance or efficiency of mastication. Due to improper mastication there is increases force on periodontium, teeth, muscles and TMJ, which serve as performance analysing elements. The performance analyzing elements send signals to the central comparator (controller) represented by the CNS. The CNS is equipped with a SENSORY ENGRAM.
  69. 69.
  70. 70.  The sensory engram is a collection of feedback loops, which record the activity of masticatory muscles corresponding to a particular habitual mandibular position.  It operates on the principle of OPTIMALITY OF FUNCTION.
  71. 71.   Any particular muscle action or mandibular position that gives the minimal deviation signal is recorded in the sensory engram. i. e. when any new mandibular position is dictated to the patient, unless the newer position causes a smaller deviation signal than the older position, the CNS will tend to make the mandible relapse to its older position, where in function was more ideal. The CNS compares the present muscular position with the ideal position stored in sensory engram and sends a deviation signal to an actuator-motor cortex to correct this discrepency.
  72. 72.     The actuator then sends an actuating signal to the coupling system of the lateral pterygoid muscle and retrodiscal pad. The LPM positions the mandible forward and the activity of retrodiscal pad induces mandibular growth at the condyle. The resultant output or controlled variable is the forward growth of mandible which results in an ideal cusp to fossa relationship. Once growth at the condyle occurs, the posterior border of the mandible becomes more concave in shape, causing a negative piezoelectric effect to develop at the posterior border of mandible and bone apposition occurs.
  73. 73.
  74. 74.  At the same time anterior border becomes more convex, positive piezoelectric current resorption of bone.  Thus length of mandible increases.
  76. 76.    It is a morphogeneticic classification of human facial development. By Lavergne and Petrovic (1983). The first level, based on the quantitative determination of the difference between maxillary and mandibular sagittal growth, has three main branches.
  77. 77.   The second level based on variations in the direction of mandibular and maxillary growth, relates to growth inclinations and growth rotations of both maxilla and mandible. The third level, based on the occlusal relationship that functions as the peripheral comparator of the Servosystem, has subdivisions representing either an aggravation or a melioration of malocclusions resulting from the first two arborizational levels.
  78. 78.
  80. 80.    Occlusal relationships play a significant role in the process of controlling facial growth. The peripheral comparator has several stable positions, each corresponding to some type of class I, II or III intercuspations. Any given occlusal relationship is stable with respect to limited fluctuations and disturbances.
  81. 81.   Each cusp to cusp unstable position corresponds to a functional discontinuity-a topologic bifurcation type instability, described by Thom(1972)and Zeemann(1976). The concept of discontinuity connotes that at critical points, the servosystem behavior goes through some basic switch, implying the existence of continuous quantitative variations that appear qualitative.
  82. 82.  Occlusal development involves two phases.  First phase consists of all morphogenetic process leading to a stable occlusion, during this phase all the parts of the servosystem are already existent and functional, but stable occlusal relationship capable of serving as a peripheral comparator has not yet been achieved. A reference point for the development of sensory engram is not possible Hence mandibular morphogenesis cannot be regulated through information originating from occlusal relationships.  
  83. 83.   The beginning of the second phase coincides with the establishment of a stable occlusion to serve as a peripheral comparator – required for the development of a sensory engram. The subsequent morphogenesis of the face is regulated to minimize possible deviations from achieved stable occlusal adjustment, regardless of whether this corresponds to a class I, II or III intercuspation.
  84. 84.    Depending on the relationship of maxilla to mandible, the dentition as a whole or in part (peripheral comparator may be located near molars or incisors, sometimes near canines.) may be operating as a peripheral comparator of the servo system. In posterior rotating mandible - molars In anterior rotating mandible - incisors and canines. The action of the peripheral comparator is an important part of both orthodontic and orthopedic treatment.
  85. 85. Clinical implications  Whenever a curative measure alters the position of group of teeth operating as a part of the peripheral comparator in a growing child (incisor – canine group in anterior rotating mandible, molar group in posteriorly rotating mandible, or whole dentition in some cases), the clinician is dealing not only with an orthodontic treatment (moving teeth) but also with an orthopedic one (modifying the rate, amount and direction of growth in facial skeleton.)
  87. 87.  Appropriate functional appliances that place the mandible in forward postural position increases condylar cartilage growth rate & amount.  Periodic increase in thickness of postural hyperpropulsor, produces increase in LPM activity & of retrodiscal pad, consequently increasing rate & amount of condylar cartilage growth.
  88. 88. Postural Hyperpropulsor    If appliance removed after growth completed – little or no relapse. If removed before growth completed- no relapse if good intercuspation. If good intercuspation has not been achieved before the growth is completed - then the comparator of Servosystem imposes an increased or decreased growth rate until state of good intercuspation achieved.
  89. 89. Class II elastics  Class II elastics not only move teeth but act also act as a functional appliance capable of stimulating the growth rate & amount of condylar cartilage.  The stimulating effect of the Class II elastics on the lengthening of the condyle appears to be mediated primarily through the retrodiscal pad.
  90. 90. HERREN (L.S.U) ACTIVATOR (Louisiana state university)   It opens the construction bite beyond the postural rest position. According to Herren (1953) & Auf der maur (1978) the wearing of appliance does not bring about any increased activity of LPM as no free movement of mandible possible.
  91. 91. TWO STEP ACTION • • When appliance is wornForward positioning of mandible is the cause of reduced increase in length of LPM. New sensory engram When appliance is not wornMandible functioning in more forward position More stimulation of retrodiscal pad activity
  92. 92.  Repetitive activity of pad leads to earlier onset of condylar chondroblasts hypertrophy.  Decrease in no of functional chondroblasts.  Decrease in prechondroblasts multiplication restraining signal.  Increase in condylar cartilage growth.
  93. 93. FRANKEL LATERAL VESTIBULAR SHIELD    The appliance acts by stimulating midpalatal suture growth & to lesser extent by increasing bone apposition on external subperiosteal layer of maxilla. Buccal shield --- eruptive pathway of teeth at the critical time in their development. The relief of pressure from the cheeks in the dentoalveolar area seems to allow a more downward and outward eruptive path at a time of maximal variability, permitting horizontal and vertical adjustment of osseous tissues involved.
  94. 94. Summary of method of operation of functional appliances   Class II elastics, postural hyperpropulsar, Frankel regulator, Balters bionator, Clark twin block all exert effects mainly through movement of mandible. Their stimulating effects are produced mainly during wearing of appliance. Herren & L.S.U activators & extraoral forward traction on mandible seem to exert their effects mostly through sagittal repositioning of mandible.
  95. 95.
  96. 96.  Regardless of differences in mode of action, the following causal chain is involvedFunctional appliance Increase contractile activity of LPM Intensification of repetitive activity of retrodiscal pad
  97. 97. Increase in growth stimulating factors Enhancement of local mediators Reduction of local mediators (factors causing negative feedback effects) Additional growth of condylar cartilage Additional subperiosteal ossification of posterior border of mandible Supplementary lengthening of mandible
  99. 99.    According to the principle of optimality of function, a condition which results in maximum efficiency is one that is instilled in the brain. Hence the tendency for relapse will be less if we achieve an optimal functional situation. Functional appliance therapy should be extended until growth is completed, or should achieve a good intercuspal relation, if growth is not completed. If Treatment ends with teeth in poor occlusion, during growth phase, relapse is more likely to occur.
  100. 100.  The sensory engram is poorly developed in children. Hence they respond better to functional appliance therapy.  Hormonal activity is highest during pubertal growth spurt. As hormones are very important for growth, one must take full advantage of the increased hormonal activity if any growth modulation is required.  Proper functioning of LPM-RDP, is essential for growth. (Petrovic and Stutzmann)
  101. 101. References 1. 2. 3. Dentofacial Orthopedics with Functional Appliances. Graber TM, Rakosi T, Petrovic AG. Second edition. Chapters 1-73. Petrovic A, Stutzmann JJ. Does the frankel appliance produce forward movements of the mandibular premolars? EJO 1982;4;173. Lavergne J, Petrovis A. Discontinuities in occlusal relationship and the regulation of facial growth.A cybernetic view. EJO 1983;5,269.
  102. 102. 4. 5. 6. 7. Stutzmann JJ, Petrovic A. Intrinsic regulation of the condylar cartilage growth rate. EJO 1979,1:41. Stutzmann JJ, Petrovic A, Shaye R. Relationship between mandibular growth rotation and alveolar bone turnover rate. J Dent Res 1980: 59,448. Orthodontics – Current principles and techniques. third edition. Graber, Vanarsdall. Contemporary orthodontics. third edition, Proffit.
  103. 103. Thank you For more details please visit