theories of growth and development- orthodontics

theories of growth and development

1. Theories of growth and development Guided by Presented by dr m karthi mds Dr m harivadhani Professor I st year PG Dept of orthodontics dept of orthodontics 1

2. CONTENT INTRODUCTION GROWTH RELATIVITY HYPOTHESIS MODERN COMPOSITE THEORY RATE LIMITING HYPOTHESIS VON LIMBORGH’S COMPROMISE THEORY CHANGING PARADIGMS OF CRANIOFACIAL BIOLOGY BONE REMODELLING THEORY SUTURE DOMINANCE THEORY SCOTT’S HYPOTHESIS FUNCTIONAL MATRIX THEORY SERVOSYSTEM THEORY REFERENCES CONCLUSION 2 BIOELECTRIC SIGNALS - FROST ENLOW-HUNTER EQUIVALENT GROWTH THEORY NEUROTROPHISM

3. INTRODUCTION Growth is defined in different ways. “The self multiplication of living substance.” ( J.S.Huxley ) “Increase in size, change in proportion and progressive complexity.” ( Wilton.M.Krogman ) “Quantitative aspect of biologic development per unit of time” (Moyers RE) “Change in any morphological parameter which is measurable.” (Melvin L Moss) “Growth usually refers to an increase in size or number.” ( William.R.Proffit ) 3

4. NEUROCRANIUM MIDDLE CRANIAL FOSSA POSTERIOR CRANIAL BASE (SPHENO-OCCIPITAL SYNCHONDROSIS) ANTERIOR CRANIAL FOSSA ANTERIOR CRANIAL BASE MIDDLE FACE OROPHARYGEAL CAVITY ETMOMAXILLARY COMPLEX (NASAL CARTILAGE) LOWER FACE RAMUS (CONDYLE) CORPUS SUTURES CARTILAGE REPLACEMENT APPOSITION RESORPTION DRIFT vs DISPLACEMENT POSTERIOR GROWTH ANTERIOR DISPLACEMENT “ V” PRINCIPLE MECHANISM OF BONE GROWTH ANATOMICAL DIVISONS AND COUNTERPARTS PRINCIPLES OF BONE GROWTH THE ESSENTIALS OF CRANIOFACIAL GROWTH REFERENCE: SYNOPSIS OF CRANIOFACIAL GROWTH DON M. RANLY 4

5. 5 NEUROCRANIUM VISCEROCRANIUM

6. CHANGING PARADIGMS OF CRANIOFACIAL BIOLOGY David S Calson has classified the changing paradigm into three eras: 1920 to 1940 1940 to 1960 1960 to 1980 6

7. REFERENCE: HANDBOOK OF ORTHODONTICS MOYERS pg 49 7

8. Sir John Hunter  first scientific research on craniofacial growth The various theories of growth are: 8

9. Bone Remodeling Theory of Craniofacial Growth by Brash (1930) Three fundamental tenets of this theory are: Bone grows only by apposition at the surfaces Growth of jaws  posterior surfaces of the maxilla and mandible. "Hunterian growth“ Calvarium growth  ectocranial surface of the cranial vault and resorption of bone on the endocranial surface Reference : Sridhar PremKumar : Textbook of Craniofacial growth 9

10. The Sutural Hypothesis ( Sicher and Weinnman )—1952 Sutures, cartilages and periosteum are all responsible for facial growth Reference : Sridhar PremKumar : Textbook of Craniofacial growth REFERENCE: SYNOPSIS OF CRANIOFACIAL GROWTH DON M. RANLY 10

11. two differing views on the structure of the suture two differing views on the function of the suture Koski, Cranial growth centers: Facts or fallacies? -AJO, 1968;566-83 11

12. Evidences against Sutural Theory Trabecular pattern in the bones at the suture change with age, indicating the changes in the direction of growth Subcutaneous autotransplantation of the zygomaticomaxillary suture in the guinea pigs has not been found to grow (Watanabe M Laskin ) Extirpation of facial sutures has no appreciable effect on the dimensional growth of the skeleton ( Sarnat , 1963) Shape of sutures have been found to depend on functional stimulus (Moss & Salentejin , 1969) Closure of suture appears to be extrinsically determined (Moss ML). Sutural growth can be halted by mechanical force like clips placed across the sutures ( Leitunen , 1956) 12

13. Scott Hypothesis/ Cartilagenous Theory Sutures play little or no direct role in the growth of the craniofacial skeleton Cartilagenous part under tight genetic control  dominate postnatal facial growth Nasal septum is mostly active and vital Latham elaborated Scott's ideas 13

14. According to Scott there are two suture systems: Posterior suture system Anterior suture system Reference : Sridhar PremKumar : Textbook of Craniofacial growth 14

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16. FUNCTIONAL MATRIX THEORY "form follows function" was first proposed by Vander Klaaw (1948-52) Melvin Moss and his co-workers developed the form and function concept into the "functional matrix hypothesis“ apart from initiating the process of development, heredity and genes play no active role in growth of skeletal structures in general and craniofacial skeleton in particular ‘the origin, growth and maintenance of all skeletal tissues and organs are secondary and compensatory responses to events and processes, occurring in related non-skeletal tissues, organs and functioning spaces, called the functional matrices’. 16

17. Epigenetic, nonskeletal factors or process are the prior, proximate, extrinsic and primary cause of all adaptive, secondary responses of skeletal tissues and organs. Reference : Sridhar PremKumar : Textbook of Craniofacial growth 17

18. head is a composite area of individual encapsulated areas within which specific functions like respiration, digestion, olfaction, vision, neural integration are performed. totality of all the skeletal structures, soft tissues and functioning spaces (nasal, oral, etc.)  specific function is collectively called a " functional cranial component ". Each functional cranial component:  skeletal unit  functional unit Reference : Sridhar PremKumar : Textbook of Craniofacial growth 18

19. FUNCTIONAL MATRIX The functional matrix refers to all the soft tissues and spaces that perform a given function. The periosteal matrix corresponds to the immediate local environment. The growth process that occurs due to periosteal matrix stimulation are called "transformation" The " capsular matrix " is defined as the organs and spaces that occupy a broader anatomical complex They do not alter the size or shape of the skeletal units; instead they change their location in space. This type of growth process is called "translation" Reference : Sridhar PremKumar : Textbook of Craniofacial growth 19

20. SKELETAL UNIT The skeletal unit refers to the bony structures that support the functional matrix and these are necessary or permissive for that function There are two types of skeletal units: 1. Microskeletal 2. Macroskeletal units Microskeletal units are parts of the bone whose growth is modulated by the periosteal matrices--- intraosseous growth or transformation Macroskeletal units are made of the core of maxilla, mandible and neurocranium. Total growth change is termed "interosseous growth" by Moss. 20

21. NEUROTROPHISM Nervous control of skeletal growth, assumedly by transmission of a substance through the axons of the nerves, has been hypothesized for years and is called neurotrophism Neurotrophism could act indirectly by the nerves inducing and affecting soft-tissue growth and function, which in turn would control or modify skeletal growth and morphology Types of neurotrophism : Moss classifies neurotrophism into three types arbitrarily: 1. Neuromuscular 2. Neuroepithelial 3. Neurovisceral Neurotrophism  non-impulsive conductive function of neurons. "Axoplasmic streaming" or transport is the term used to describe this function of nonimpulsive conduction of neurons 21

22. 22 Neuromuscular trophism : Embryonic myogenesis is not under the control of nerves and neurotrophism . Neural innervations are established at the myoblast stage of differentiation. Moss states that after this stage, skeletal muscle ontogenesis cannot proceed without innervations Neuroepithelial Trophism The neurological work of neurotrophism first began in the field of dermatology. The factors which contribute to neuroepithelial trophism are: • Local mechanism operating in areas of high mitotic activity. • Epithelial growth factors. • Type of feedback mechanism between dermis and epidermis. Neurovisceral trophism : In the orofacial region, salivary gland is partially trophically regulated. Increase or decrease of mature salivary gland, under neurotrophic influence have been experimentally demonstrated.

23. Von Limborgh’s Compromise Theory Von Limborgh after review of the sutural theory, cartilaginous theory and functional matrix theory has summarized the following features: • Intrinsic genetic factor controls chondrocranial growth. • Epigenetic factors originating from skull cartilages and head tissues control desmocranial growth. • Local environmental factors like tension forces and pressure influences the growth of desmocranial growth. • General epigenetic and general environmental factors are less significant in craniofacial growth. 23

24. MODERN COMPOSITE THEORY It separates the facial skeleton into Desmocranium Chondrocranium Splanchnocranium Chondrocranium is considered the dominant factor in craniofacial growth The growth of mandible seems to be controlled by both local epigenetic and local periosteal factors 24

25. REFERENCE: SYNOPSIS OF CRANIOFACIAL GROWTH DON M. RANLY 25

26. Enlow –Hunter growth equivalent theory (1960s) Four morphogenetically distinct regions in the human skull; the mandible, the middle face, the upper face and calvaria Specific horizontal and vertical equivalents that match each other in general size or position if a harmonious face is to exist. For example, the anterior cranial base, the maxilla and the body of the mandible represent growth equivalents in the horizontal direction. ‘A critical balance of growth exists between different areas, and mutual adjustments and progressive reciprocal adaptation occur between them during continued growth’. Some key morphogenetic sites exist in different regions of the face and cranium, which are directly inter-dependent and mutually inter-related in respective growth activities 26

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28. Servo System Theory: Alexandre Petrovic Alexandre Petrovic proposed a cybernetic model known as the servosystem theory According to the cybernetic view by Jean Lavergne and Alexandre Petrovic , the craniofacial growth process consists of growth signals and feedback mechanisms anterior cranial base and mid-face – intrinsic cell growth-- changes in occlusion – growth of mandible mid-face growth also serves as a rate-limiting factor for growth of the mandible Reference: Graber Vanarsdall Orthodontic current principles sixth edition 28

29. Weiner defines cybernetics as the science of control and communication in the animal and machine Feedback mechanisms:  Open loop  Closed loop Elements and organisation of servosytem theory 29

30. Elements of Servo System Theory Command is a signal established independently of the feedback system under scrutiny Reference input elements: Establish the relationship between the command and reference input Reference input is the signal established as a standard of comparison, e.g. sagittal position of maxilla The controller is located between the deviation signal and the actuating signal. The confrontation between the position of the upper and lower dental arch is the comparator of the servo system. Activity of the retrodiscal pad and lateral pterygoid constitutes the Actuating signal 30

31. Controlled system is between the actuator and controlled variable Controlled variable is the output signal of the servo system The gain: The gain of a system is the output divided by input. Gain value greater than one is called amplification and if it is less than one it is called attenuation. The disturbance: Any input other than the reference required is called a disturbance. Disturbance results in deviation of the output signal The attractor: This is the final structurally stable state in a dynamic system The repeller : This includes all unstable equilibrium states like cusp to cusp occlusal relationships 31

32. Evidences against theory Goret -Nicaise, Awn (1983), found that the resection of the lateral pterygoid muscle fails to diminish condylar growth. Whetten and Johnston (1985)  bilateral condylotomy model in young rats  test the extent to which direct muscle traction and removed the lateral pterygoid muscle unilaterally. No difference in condylar growth between the two sides. Das, Myer and Sicher (1980) found that the occlusion remained unaffected in condylectomy studies 32

33. Rate Limiting Ratchet Hypothesis (Johnson) Views the condyle as an opportunist Unable to grow when loaded but able to grow when unloaded Hypothesis is based on the finding that condyles have an inherent ability to grow and pressure will arrest their growth Therapeutic appliance that increases the amount of time a condyle is unloaded  increase the condylar growth and ultimately the length of the condyle Appliance that increases the amount of time condyle is loaded  decrease the condylar growth and thereby results in a shorter mandible 33

34. Growth Relativity Hypothesis (John C Voudouris 2000) To explain the possible effect of functional appliances on condyle and the resulting growth The main foundations of growth relativity hypothesis are: • Displacement of condyle • Nonmuscular viscoelastic tissue stretch • Force transduction beneath the fibrocartilage of the glenoid fossa and condyle add new bone formation 34

35. Reference : Sridhar PremKumar : Textbook of Craniofacial growth 35

36. Viscoelastic Stretch Once the condyle is displaced, it is followed by the stretch of nonmuscular viscoelastic tissues Due to viscoelastic stretch there is influx of nutrients and other biodynamic factors into the region, through engorged blood vessels of the stretched retrodiscal tissue that feed into the fibrocartilage of the condyle Force Transduction and New Bone Formation: New bone formation takes place at some distance from actual retrodiscal tissue attachments in the fossa The glenoid fossa and the displaced condyle are both influenced by the articular disk, fibrous capsule and synovium which are contiguous 36

37. Effect of three growth stimuli (Displacement + viscoelasticity + transduction of force): Voudoris and Kuftinec The resultant increase in new bone formation appears to radiate as multidirectional finger like processes beneath the condylar fibrocartilage and significant appositional bone formation is seen in the fossa Reference : Sridhar PremKumar : Textbook of Craniofacial growth 37

38. BIOELECTRIC SIGNALS The piezo factor has been one of the great bone growth-control hopes since the mid-1960s distortions of the collagen crystals in bone, caused by minute (ultramicroscopic) deformations of the bone matrix due to mechanical strains, generate bioelectric charges in the immediate area of deformation ( i.e , the piezo effect) These altered electrical potentials appear to relate, either directly or indirectly, to the triggering of osteoblastic and osteoclastic responses two separate target categories for the mechanical actions of muscles  the cellular component of the osteogenic connective tissues  the calcified part of the bone itself, the matrix, 38

39. 39 Surface pressure  on the membrane  restrict the vascular bed with an osteoclastic result  tissue response is resorption Tension  on the membrane  osteoblastic, and the response is new bone deposition . Presumably continue until physiologic and biomechanical equilibrium is attained, whereupon the blastic and clastic activities are turned off This leads to regional changes in configuration involving localized surface convexities and concavities Reference: ENLOW AND HANS ESSENTIALS OF FACIAL GROWTH

40. 40 REFERENCE: SYNOPSIS OF CRANIOFACIAL GROWTH DON M. RANLY

41. Current views on growth at the turn of the 21st century Advances in the field of molecular biology and developmental genetics have identified a number of genes that are involved in morphogenesis of the craniofacial skeleton possibility to activate these genes and produce growth factors that may have positive, targeted and predictable effects on postnatal craniofacial growth the issue is not the fact that intrinsic factors within the genome regulate morphogenesis, but that the complex -interaction of cells and tissues with remote extrinsic factors within both the body and the environment are triggers or switches for gene expression that influences postnatal growth and responsiveness to clinical treatment. 41

42. CONCLUSION Everything is not yet known and much research is yet to be done, but clinicians must treat patients with working hypothesis of growth in mind while issues are being resolved by craniofacial biologists in their minds and laboratories In light of these technological advances, previous theories given by orthodontists over the last 80 years stand the test of time and scrutiny Genes are turned on and off by factors both within and outside the genome to produce specific traits and to influence susceptibility to variations in development and growth. New paradigms in craniofacial growth will continue to emerge. 42

43. REFERENCES: DON M RANLY; SYNOPSIS OF CRANIOFACIAL GROWTH MOYERS; HANDBOOK OF ORTHODONTICS ENLOW AND HANS ESSENTIALS OF FACIAL GROWTH GRABER AND VANARSSDALL ORTHODONTIC CURRENT PRINCIPLES SIXTH EDITION SRIDHAR PREMKUMAR: TEXTBOOK OF CRANIOFACIAL GROWTH O P KHARBANDA Orthodontics: Diagnosis and Management of Malocclusion and Dentofacial Deformities Koski, Cranial growth centers: Facts or fallacies? -AJO, 1968;566-83 43

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