THEORIES OF GROWTH IN ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS

THEORIES OF GROWTH,ORTHODONTICS

1. THEORIES OF GROWTH Dr. ANZA SALIM FIRST YEAR PG

2. CONTENTS INTRODUCTION DEFINITIONS OF GROWTH THEORIES OF GROWTH Remodelling theory of craniofacial growth - Brash(1930) Genetic theory – Allen Brodie(1941) Sutural dominance theory- Sicher and Weinnman (1952) Cartilagenous theory- Scott Functional matrix hypothesis- Melvin Moss(1967) Van Limborgh’s theory Servosystem theory - Petrovic

3. OTHER GROWTH RELATED THEORIES & CONCEPTS 1. Expanding V principle - Enlow 2.Counterpart principle - Enlow 3. Neurotrophism - Moss 4. Growth Relativity Hypothesis -John C Voudouris (2000) CONCLUSION REFERENCES

4. INTRODUCTION It is a truth that growth is strongly influenced by genetic factors, but it can also be significantly affected by the environment,in the form of nutritional status, degree of physical activity, health or illness and a number of similar factors. Since a major part of the need for orthodontic treatment is created by disproportionate growth of the jaws,it is necessary to learn how the skeletal growth is influenced and controlled to understand the etiologic process of malocclusion and dentofacial deformity. Growth theories are trying to find out where exactly is growth controlling mechanism (growth centre) located in craniofacial skeleton.

5. DEFINITIONS RELATED TO GROWTH There is no universally accepted definition of growth, various clinicians have defined growth in different ways. “The self multiplication of living substance.”- J S Huxely “Increase in size, change in proportion and progressive complexity.” – Krogman “An increase in size.”- Todd “Entire series of sequential anatomic and physiological changes taking place from the beginning of prenatal life to senility”- Meredith “Quantitative aspect of biologic development per unit time.”- Moyers “Change in any morphological parameter, which is measurable.” – Moss “Growth refers to an increase in size/number.” - Profitt

6. REMODELLING THEORY OF CRANIOFACIAL GROWTH ( Brash – (1930) Vital staining by JOHN HUNTER helped BRASH to postulate the first general theory. Three fundamental tenets of the theory are : Bone grows only by apposition at the surface. Growth of jaw takes place by deposition of bone at the posterior surfaces of maxilla and mandible. This is described as Hunterian growth. Calvarium grows through bone deposition on the ectocranial surface of cranial vault and resorption of bone on the endocranial surface.

7. BONE REMODELLING THEORY concluded that the craniofacial skeletal growth takes place by bone remodelling-selective deposition and resorption of bone at its surfaces.

8. GENETIC THEORY Allen Brodie –(1941) The genetic theory simply stated that genes determine and control the whole process of craniofacial growth. But the mechanism of action by the genetic unit and the mechanism by which the traits are transmitted were not understood until recently. Gregor Mendel (1822- 1884) opened up the field of genetics, notably regarding the mechanism of inheritance and transmission. The field of genetics consists of two principle areas of interest: 1. " Transmission genetics " involved only in explaining possible method of transmission. It is based on Mendelian laws and did not explain about genes or its characteristics.

9. Transmission genetics could not explain all the changes taking place in craniofacial growth(role of environment). Eg : Thumb sucking causes projection of premaxilla. So the focus shifted to molecular genetics. Developmental and molecular genetics. This field has undergone profound development and discoveries following extensive research. Growth controlling genes- Homeobox gene Sonic hedgehog Transcription factor IHH (Indian Hedgehog Homolog / Drosophila)

10. THE SUTURAL HYPOTHESIS/SUTURAL DOMINANCE THEORY ( Sicher and Weinnman )—1952 Sicher and Weinnman , two great anatomists, introduced the sutural hypothesis. Essence of the Theory : According to Sicher , the sutures are the primary determinants of craniofacial growth. The craniofacial skeleton enlarges due to the expansible forces exerted by the sutures as they seprate .

11. He believed that the primary event in sutural growth is the proliferation of the connective tissue between the two bones. Proliferation of the connective tissue creates the space for appositional bone growth between the borders of two bones. Increase in the size of the cranial vault takes place via primary growth of bone at the sutures, which forces the bones of the vault away from each other.

12. Growth of the midface takes place via intrinsically determined sutural expansion of the circummaxillary suture system. Bone growth within the various maxillary sutures produces pushing of bone which results in downward and forward movement of maxilla.

13. Mandibular growth takes place via intrinsically determined growth of the cartilage of the mandibular condyle, which pushes the mandible downward and forward. Evidences against Sutural Theory Subcutaneous auotransplantation 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). Sutural growth can be halted by mechanical force like clips placed across the sutures ( Leitunen , 1956)

14. Conclusion Present evidences indicate sutures as adaptive growth sites. Sutural tissues have no tissue separating force and they are not comparable to growth centers.

15. SCOTT HYPOTHESIS / NASAL SEPTUM THEORY / CARTILAGENOUS THEORY / NASOCAPSULAR THEORY (1950) James H Scott, an Irish anatomist proposed the nasal septum theory. Essence of Theory According to the nasal septum theory, sutures play little or no direct role in the growth of the craniofacial skeleton. The cartilaginous development is under tight genetic control and viewed it as primary centres of growth. According to Scott, Synchondroses of cranial base, nasal septal cartilage of midface,condylar cartilage of mandible act as growth centres.

16. Scott concluded that nasal septum is mostly active and vital for craniofacial growth both prenatally and postnatally. The anteroinferior growth of the nasal septal cartilage which is buttressed against the cranial base "pushes" the midface downward and forward. This results in the separation of the midfacial suture system, which then fills via secondary,compensatory sutural bone growth.

17. Thus it allows bone growth to take place at Frontomaxillary Frontonasal Frontozygomatic Fronto -zygomaticomaxillary sutures. According to Scott, bone separation must precede before the adaptive sutural bone growth occurs The bone separation, he feels, is because of growth of organs like brain, eyeball or cartilage

18. Evidences Supporting the Theory : Sarnat in 1988, from experiments on rabbit snout concluded that deformity of snout after resection of nasal septum was the result of lack of growth.

19. Burstone emphasized the importance of the ‘septal growth impulse’ to maxillary growth in cleft palate cases. Failure of the underdeveloped maxillary segment to unite with nasal septum in complete unilateral clefts deprives of the growth impulse. The normal contralateral side on the other hand, attained normal growth. Latham and Burstone (1966) concluded that nasal septum has a role in determining anteroposterior growth of upper face .

20. Evidences Against the Theory; Moss and Bloonberg (1968), Brigit Thilander (1970) found only slight deformity after extirpation of septal cartilage. They concluded that septal cartilage provides only mechanical support for the nasal bones and is not a primary growth center. Melson (1977) stated that downward sliding of vomer in relation to anterosuperior part of nasal septum takes place throughout craniofacial development making it unlikely that cartilaginous septum could push the maxillary complex forward as suggested by Scott. Moss stated that malformation in snout following excision of nasal septum is due to trauma following surgery. Burstone and Latham reported a case with missing nasal septum. The child had normal resorption and deposition of palate, height of upper face. Only sagittal development was affected.

21. Conclusion At present, nasal septum theory is still accepted as a reasonable explanation for craniofacial growth. Nasal septum may be important for anteroposterior growth of face because of endochondral growth process occurring at its posterior border. It is not considered to be an active contributor for vertical development of face.

22. FUNCTIONAL MATRIX THEORY In 1962 Melvin Moss introduced the functional matrix hypothesis into the orthodontic world. Definition : T he origin, form, position, growth and maintenance of all skeletal tissues and organs are always secondary,compensatory and necessary responses to chronologically and morphologically prior events or processes, that occur in specifically related non- skeletal tissues,organs or functioning spaces called ( functional matrices ) Essence of the theory: Skeletal growth occurs in response to functional stimuli and neurotropic influences. It was developed complimentary to the original concept of functional cranial component by Van der Klaauw (1952).

23. Functional cranial component Head is an area where several functions are carried out independently such as neural integration,olfaction,vision,hearing etc. Each function is carried out by a functional cranial component . The totality of all skeletal structures, soft tissues and functioning spaces known as functional cranial component Any function is actually performed by the functional matrix, while the skeletal unit provides the necessary biochemical role of providing protection and support to the soft tissue matrix.

24. Skeletal Unit All skeletal tissues associated with single function are called “ the skeletal unit”.Composed of bone, cartilage and tendinous tissue. MACROSKELETON UNIT : Adjoining portion of number of neighbouring bones carrying out the single function is known as macro-skeleton unit. E g : the surface of calvaria, mandible , maxilla . MICROSKELETON UNIT A single bone consist of number of small skeleton units which is known as micro-skeleton units. Eg:C oronoid process, condylar, angular, alveolar, basal bone.

25. Functional Matrix This consist of soft tissues(muscles, glands, nerves, vessels, fat,) and spaces that perform a given function. It is divided into two types Periosteal matrices Capsular matrices

26. Periosteal Matrices They act directly and actively on their related micro-skeletal units thereby bringing about the transformation in their shape and size by bone deposition and resorption. Examples of periosteal matrices are muscle, blood vessels, nerve, glands ,teeth etc. Alternations in their functional demands produce a secondary compensatory transformation of the size and shape of their micro-skeletal units. For example consider the temporalis muscle and the coronoid process. The removal or denervation of temporalis muscle results in reduction in size of coronoid process also even its total disappearance in some cases. Or hypertrophy or hyperactivity of temporalis muscle increases the size of coronoid process.

27. Capsular Matrices Defined as organs and spaces that occupy a broader anatomic complex. The capsular matrices act indirectly and passively on their related macro-skeletal units producing a secondary compensatory translation in space. Capsular matrix do not act by process of active resorption and deposition. Capsule has double layered wall Each capsule is an envelope that contains series of functional cranial component, skeletal unit and their related functional matrices and is sandwiched between the two covering layers.

28. Types: Neurocranial capsule Orofacial capsule Neurocranial Capsule Capsular matrix consist of brain,leptomeninges and CSF. Periosteal matrix consist blood vessels,nerves,muscles,bones . Cover consists of skin and duramater . As the capsule enlarges, whole of included and enclosed periosteal matrices and microskeletal units are carried outward in a passive manner. The calvarial functional component as a whole are passively and secondarily translated in space.

29. Orofacial Capsule Capsular matrix consist of functional air spaces (oral cavity, nasal cavity, pharynx, and sinuses). Growth of facial bones is controlled by the alteration within the oro -facial matrix. Limiting layers are skin and mucosa. Periosteal matrix consisit of muscles,blood vessels,glands,nerves sandwitched between the two walls.

30. Skeletal growth according to functional matrix hypothesis According to Melvin moss, the primary stimulus for skeletal growth is an expansile growth of capsular matrix. When capsular matrix expands, the capsular wall is extended and the structures sandwiched between outer and inner wall moved to a wider circumference The shift in position of periosteal matrices and skeletal elements secondary to expansile growth of capsular matrix is called translation (passive & indirect) Then the periosteal matrix related to the micro-skeletal element will exert an altered influence on micro-skeletal element ( increased stretch or decreased stretch)

31. In areas where skeletal element experiences an Increased stretch bone formation. Decreased stretch bone resorption. This remodelling is called transformation (active & direct). Thus two events takes place in functional matrix are : Translation : produced by capsular matrix Transformation : produced by periosteal matrix Which together bring about GROWTH .

32. Applying the concepts of functional matrix hypothesis in mandibular growth The facial bones lie embedded in the orofacial capsule This capsule surrounds functional matrix as teeth, muscles, glands, nerves and vessels, sinus spaces and biologically real volumes of oral, nasal and pharyngeal cavities Human orofaicial capsule increases in size from the third month of pregnancy. As the child grows, there is more functional demand and child takes more air for high metabolic activity This causes an expansion of capsular matrix outward, downward and laterally , as result of which the mandible get passively and secondarily translated.

33. Mandible is translated from glenoid fossa in a downward and forward direction Periosteal matrix attached to glenoid fossa get stretched, resulting in bone formation ( condyle lengthens ) Inter occlusal space increased and alveolar bone growth occurs Altogether transformation of mandible occurs

34. Drawbacks Moss theorized that the major determinant of growth of the maxilla and mandible is the enlargement of the nasal and oral cavities, which grow in response to functional needs. The theory does not make it clear how functional needs are transmitted to the tissues around the mouth and nose. But it does predict that the cartilages of the nasal septum and mandibular condyles are not important determinants of growth, and that their loss would have little effect on growth if proper function could be obtained.

35. VAN LIMBORGH’S COMPOSITE THEORY (1970) He suggested a composite theory combining the strong or convincing points of the genetic, sutural dominance, cartilage dominance and functional matrix theories. According to him 5 factors are responsible for controlling craniofacial growth. 1. Intrinsic genetic factors – i.e , genetically controlled skeletal growth which is not modifiable by environmental factors. Eg. Epiphyseal plate of long bones 2.Local epigenetic factors – These are genetically controlled skeletal growth that arise from adjacent structures. Eg , brain, eyes etc.

36. If brain is small the brain case remains small. If eyeball is missing the orbit doesn’t grow. 3 . General epigenetic factors- They are genetically controlled skeletal growth that arise from distant sites – eg : hormones 4. Local environmental factors – They are non genetic factors from local environment. Eg – habits 5. General environmental factors- T hey are general or systemic factors that influence growth. Eg - nutritional deficiencies.

37. Van Limborgh summarised craniofacial growth as follows- 1. I ntrinsic genetic factors controls chondrocranial growth. 2 .Sutures are considered only as growth sites. 3 . De smocranial growth is not mainly under under genetic control. E pigenetic 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. 4 . General epigenetic and general environmental factors are less significant in craniofacial growth.

38. SERVOSYSTEM THEORY ( CYBERNETIC THEORY ) Introduced by Dr. Alexander Petrovic in 1974 Petrovic was interested in the nature of cartilage growth in the craniofacial region in general and that of the mandibular condylar cartilage in particular. Based on his in vivo and in vitro research he arrived at the following two conclusions- The cartilages of the craniofacial complex ( synchondrosis and nasal septum)are primary cartilages. Like any other primary cartilage they respond to hormonal influences and behave like growth centers to some extent. They are not significantly influenced by local epigenetic factors. 2. The condylar cartilage is a secondary cartilage.Its growth is highly adaptive/secondary and is responsive to (a) extrinsic systemic factors and (b) local biomechanical & functional forces.

39. Petrovic explained the craniofacial growth using the vocabulary of cybernetics. According to Weiner, cybernetics is the science of communication in animals and machines. The cartilages of the skull base ( synchondrosis) & nasal septum are primary cartilages and they grow under the influence of hormonal factors (command) just like any other primary cartilage. Because of their growth, the mid face grows downwards and forwards taking the maxillary dental arch to a slightly anterior position.This is the first and primary event. The structures responsible for this positional change of maxilla includes the synchondrosis, septal cartilage, septopremaxillary ligament & labionarinary muscles and are collectively called as reference input elements .

40. The sagittal position of maxilla is the reference input . U pper dental arch is the constantly changing refrence input. This causes a minute discrepancy between the upper and lower dental arches (occlusal deviation) – which Petrovic calls ‘comparator’ or the ‘confrontation’ The proprioceptors in the periodontal ligament and TMJ recognise these occlusal deviations and send impulses to the CNS. According to Petrovic CNS is the controller . Impulses from the controller tonically activate the lateral pterygoid muscle and the retro discal pad,which constitutes the actuator. The activity of the actuator is initiating the actuating signal.

41. The actuator through their actuating signals act directly on the condylar cartilage.They also act indirectly by altering the blood supply to the TMJ,stimulating condyle to grow. The condyle is the controlled system . The sagittal position of the mandible is the controlled variable . The effect of actuating signal on the condylar cartilage and the responsiveness of the cartilage to the muscle function are influenced by the hormonal factors As long as the mid face-upper dental arch continue to grow forward and the hormonal and functional factors are favourable , the entire cycle is continuously activated. This affects the output signal.The output signal is the final sagittal position of mandible.

42. Synchondrosis,nasal septum,septomax . Ligament, labionarnari muscles Hormones- growth hormone, testosterone, estrogen, somatomedin command Ref. input elements Maxillary sagittal position Ref. input Confrontation or Comparator propriceptors CNS Controller Lat.pterygoid Retrodiscal pad d Actuator Condylar growth Mandi. position Controlled system Controlled variable

43. ENLOW’S ‘V’ PRINCIPLE OF GROWTH • Most of the facial bones have a ‘V’ shaped configuration. • Bone deposition occurs in the inner side of ‘V’ and resorption occurs in the outer surface.Simultaneously deposition takes place at the ends of the two arms of the ‘V’ resulting in its widening. • Due to this the bone moves in the direction towards the wide end of ‘V’.

44. Palatine and alveolar process of maxilla showing V principle

45. ENLOW’S COUNTERPART PRINCIPLE There is a part-counterpart relationship between the various components in the craniofacial region. It states that growth in any one region of the skull necessarily influence the growth in others. Consequently a functional equilibrium is maintained. A balanced growth occurs if the regional part and counterpart enlarge to the same extend. Imbalances are produced due to variation in: a) Magnitude of growth between the counterparts. b) Timing of growth between the counterparts. c) Directions of growth between the counterparts.

46. Few counterparts Nasomaxillary complex - anterior cranial fossa Horizontal dimension of the pharyngeal space - middle cranial fossa. Middle cranial fossa - breadth of the ramus. Maxillary - mandibular dental arch. Bony maxilla - corpus of the mandible. Maxillary tuberosity - lingual tuberosity .

47. NEUROTROPHISM Neurotrophism is a non-impulse transmitting neural function that involves axoplasmic transport and provides for long term interaction between these neurons and innervated tissues. It is important for morphological, compositional and functional integrity of those tissues. The nature of neurotrophic substance and the process of their introduction into target tissue are unknown at present. Moss classifies neurotrophism into three types 1.Neuroepithelial trophism 2.Neurovisceral trophism 3.Neuromuscular trophism

48. GROWTH RELATIVITY HYPOTHESIS (John C Voudouris 2000) Growth relativity refers to growth that is relative to its displaced condyles from actively relocating fossae. He introduced this concept 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

49. Displacement of Condyle The displacement that takes place initially following mandibular advancement affects the fibrocartilagenous lining in the glenoid fossa to induce bone formation locally Viscoelastic Stretch Once the condyle is displaced, it is followed by the stretch of nonmuscular viscoelastic tissues. Viscoelasticity refers to all the non-calcified tissues .Viscoelasticity addresses the viscosity and flow of the synovial fluids, the elasticity of the retrodiscal tissues, the fibrous capsule and other nonmuscular tissues etc. 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 . Alteration of synovial fluid dynamic also takes place

50. 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. Thus condylar growth is affected by viscoelastic tissue forces through attachment of the fibrocartilage that covers the head of the condyle.

51. Effect of three growth stimuli (Displacement + viscoelasticity + transduction of force): Modification of growth occurs by a combination of above all the three factors Modification "first" occurs as a result of the action of anterior mandibular displacement. "Second", the condyle is affected by the posterior viscoelastic tissues anchored between the glenoid fossa “Third", displacement and viscoelasticity further stimulate the normal condylar growth by transduction of forces over the fibrocartilage cap of the condylar head Growth relativity hypothesis is more specific to condyle only when compared to functional matrix hypothesis

52. Voudoris and Kuftinec compares this process to the light bulb analogy. When the growing condyle is continuously advanced, it lights up like a light bulb on a dimmer switch. When the condyle is released from the anterior displacement, the reactivated muscle activity dims the light bulb and returns it close to normal growth activity. The resultant increase in new bone formation appears to radiate as multidirectional finger like processes beneath the condylar fibrocartilage and significant appositional bone seen in the fossa.

53. CONCLUSION It is important for the clinician to know the normal and abnormal ranges of growth for proper diagnosis, treatment planning and selecting appropriate clinical procedures. Identifying the primary trigger mechanism for the growth of maxilla and mandible will help the orthodontist to either stimulate or retard the growth of maxilla and mandible. This will prove to be the key to successful growth modification treatment in skeletal malocclusions.

54. REFERENCE Textbook of Craniofacial Growth – Sridhar Premkumar Orthodontics the art and science- S.I.Balajhi Contemporary Orthodontics 6th edition - William R. Proffit , Henry W. Fields, David M. Sarver Orthodontics Diagnosis and management of malocclusion and dentofacial deformities 3 rd edition - Om Prakash Kharbanda

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