Slide 1

GROWTH AND DEVELOPMENT:Theories

CONTENTSIntroductionPrinciples of GrowthTheories of GrowthConclusionBibliography

Principles of Skeletal GrowthEpiphyseal Growth

Periosteal and Endosteal Growth

Sutural Growth

Remodelling

Cortical DriftTheories Of GrowthEpiphyseal Growth

Periosteal and Endosteal Growth

Sutural Growth

Remodelling

Cortical DriftEpiphyseal GrowthInitial growth of long bone Primary Ossification centre [Diaphysis]Secondary ossification centre develops on ends of diaphysisAt junction of epiphysis and diaphysis(epiphyseal plate) - major growth in length occursCartilaginous nature of plate lost at growth termination Continuous long bone formed

EPIPHYSEAL PLATE CLOSURE

Periosteal and Endosteal GrowthNormal bone Ext Periosteal layer Int Endosteal layerApposition of bone on selective periosteal surfaces and selective resorption GrowthEndosteal resorption and addition from within also necessary for appropriate thicknessBalanced apposition and resorption facilitates proper growth

Sutural GrowthExplains that growth occurs at suturesNot due to innate potential of sutures to proliferateResponse to tension from adjacent soft tissues9RemodellingOccurs concurrently with increasing bone size so that functional shape and proportion maintained

(i) Surface remodellingLeads to change in topography

(ii) Structural remodellingChange in inherent architecture

A type of surface remodelling where surface elevation/fins develop for the attachment of muscles and tendons to the pterygoid plates

Structural remodelling where alignment of the trabeculae along the lines of force can be appreciated

Cortical DriftBone/surface moves through space by selective deposition and resorption on cortical surfacesSame cortical bone one side deposition other side resorption

Whole maxilla translates showing definitive cortical drift pattern

THEORIES OF GROWTH1.Genetic theory :BRODIE 1946All growth pre planned and under genetic influenceMorphologic traits transmitted between generationsMechanism of trait transmission, nature of heredity, mode of heredity were not known till 20th century

Factors in support of genetic theory: About two-thirds of genes play a role in the craniofacial developmentGenetic factors affecting size and form of the final skeleton is clearly seen in many familial developmental anomaliesMore assumed theory than provenperhaps this part is genetically controlled while that is notthis part is more controlled by heredity than thatFactors against genetic theory:Homeobox genes- Dlx-5 and Dlx-6 gene in Drosophila play a role in appendage development Mice severe craniofacial deformities detected Msx gene muscle segment Sonic hedgehog- Its role is in patterning of facial mesenchyme. Decrease in hedgehog pathway- failure of nose to develop

He concluded that - bones of the face show wide variability in the rate and time of growth, sequence and size attainment, but the growth of the pattern is proportional, meaning a disharmony, if any, is present before birth and becomes neither better nor worse hello21COL2A1 Stickler Cleft palateGLI3 Greg Premature closure of cranial sutures, extra digits IRF6 Van der Wounde Cleft lip/plate, with lip pits IRF6 Popliteal pterygium Cleft lip/palate, webbing across joint MSX1 - Cleft lip/palate, missing teeth . TP63 Ectodermal dysplasia Limb, teeth, hair defects PAX9 Oligodontia Missing teeth TBX22 - Ankyloglossia, cleft palate TCOF1 Treacher Collins Mid face hypoplasia, small jawDHCR7 Smith-Lemli-Optiz Mental retardation, multiple organ defect Rahul Raman Doshi And Amol Somaji Patil. A Role Of Genes In Craniofacial Growth . Iioabj; Vol. 3; Issue 2; 2012: 1936 Genes causing various human birth defects2.Remodelling TheoryBRASH 1930Bone only grows appositionally at the surfacesGrowth of jaws deposition of bone at posterior surface of maxilla and mandible(Hunterian growth)Calvarial growth bone deposition ectocranial sidebone resorption endocranial side

3. Sutural TheoryWEINMANN & SICHER - 1940The connective tissue and cartilaginous joints principal location intrinsic, genetically regulated , primary growth of bone.Paired parallel sutures that attach facial areas to the skull and the cranial base region push the naso-maxillary complex forwards to pace its growth with that of the mandible.

Maxilla is attached to the cranium by frontomaxillary, ZM, ZT & pterygopalatine sutures, which are parallel to each other.Thus growth at these areas would serve to move maxilla forward & downward

POINTS IN FAVOUR OF THEORYPeriosteal remodelling of bone is under strong local influences by the functional environment. Theory was consistent with the understanding of the importance of the cartilaginous structures & skeletal joints in development & postnatal growth of bones.

POINTS AGAINST THEORYSuture transplanted to other locations does not continue to grow Growth occurs in untreated cases of cleft palateMicrocephaly and Hydrocephaly cases

4.Cartilagenous Theory/Nasal Septum TheoryJAMES H SCOTT- 1956Intrinsic growth controlling factors were present only in cartilage and periosteumProposed sutures play no direct role merely permissive, secondary and compensatoryPrimarily Scott analysed only the Nasal Septum as most active and important

AccordinglySpheno-occipital synchondrosis - responsible for growth of cranial base.Nasal septal cartilage responsible for growth of naso maxillary complexCondylar cartilage responsible for the growth of mandible

Spheno-occipital SynchondrosesSynchondroses : Remnants of cartilage between bone junction which is later replaced by bone and act as growth centers of the cranial base

Nasal septal cartilageAnteroinferior growth of nasal septal cartilage , drives the midface downward and forward

Two kinds of experiments have been carried out to test the idea that cartilage can serve as a true growth center:Transplanting nasal cartilage to cultural medium did not give equivocal results, that is sometimes it grew, sometimes it did not. Indicating doubtful growth potential of the nasal septal cartilage whereas,

If a piece of the epiphyseal plate of a long bone is transplanted, it will continue to grow in a new location,

Indicating that these cartilages have innate potential. Spheno Occipital SynchodrosisCartilage from here also grows when transplanted, but not as wellDifficulty in obtaining cartilage from cranial base to transplant

Condylar Cartilage and Mandibular Growth:-Its being hypothesized that condylar cartilage is the growth center for the growth of mandible. Experiments of transplanting condylar cartilage showed little or no growth potential. Mandibular condyle thus do not have innate growth potential and not a growth center.

Effect of removal of the nasal septal cartilage on forward growth of the snout in the rabbit.2. Evaluation of the effect of growth on removing cartilage at early age

Profile view of man whose cartilaginous nasal septum was removed at age 8, after an injury. 5.Functional Matrix HypothesisMELVIN MOSS 1962Melvin Moss was inspired by the ideas of Van der Klauuw (1952) that bones were in reality , composed of several FUNCTIONAL CRANIAL COMPONENT, the size, shape & position of which were relatively independent of each other.

Bones do not grow ; Bones are grown 4.FUNCTIONAL MATRIX HYPOTHESIS:-

by Melvin Moss.Most accepted theoryMelvin Moss was inspired by the ideas of Van der Klaauw (1952) that bones were in reality , composed of several FUNCTIONAL CRANIAL COMPONENT , the size , shape & position of which were relatively independent of each other. He experimentally verified & expanded on these concepts & incorporated them with his own in 1962

Bones do not grow ; Bones are grown THE ORIGIN, GROWTH AND MAINTAINANCE OF ALL SKELETAL TISSUES AND ORGANS ARE ALWAYS SECONDARY, COMPENSATORY AND NECESSARY RESPONSES TO CHRONOLOGICALLY MORPHOLOGICALLY PRIOR EVENTS THAT OCCUR IN SPECIFICALLY RELATED NON-SKELETAL TISSUES ORGANS OR FUNCTIONAL SPACES (FUNCTIONAL MATRICES) MOSS said that Head is a composite structure, operationally consisting of a number of relatively independent functions

Digestion, Respiration, Speech, Olfaction, Balance, VisionEach function carried out by a group of soft tissues which are supported and/or protected by related skeletal elements. Taken together the soft tissues & skeletal elements related to a single function are termed as FUNCTIONAL CRANIAL COMPONENTFunctional cranial componentSkeletal unitFunctional matricesMacroskeletalE.g. MANDIBLEMicroskeletalCoronoid Process Of MandiblePeriostealE.g.-Teeth andMuscles

CapsularE.g.- orofacial, neurocranial

Each Such Component Is Composed Of Two Parts 1. FUNCTIONAL MATRIX- which actually carries out the functions. It includes- muscles, nerves, vessels, glands, functioning spaces (nasopharynx/ oropharynx)

2. SKELETAL UNIT- whose biomechanical role is to protect and/ or support its specific functional matrixA functional matrix includes soft tissues like muscles, glands, vessels, nerves fat, etc,.

Teeth are also a functional matrix.

Functional matrices are basically 2 types. Periosteal matrix Capsular matrix.Periosteal matrix:-Acts directly and actively on their related skeletal unitsCorresponds to immediate local environment, typically muscles, blood vessels, and nerves.E.g. Coronoid process is a microskeletal unit and its Periosteal matrix is temporalis muscle.

Removal, denervation of temporalis muscle - decrease in the size or total disappearance of coronoid process.Functional hypertrophy/hyperactivity of temporalis muscle- increase in size and change in shapeHence in simple terms it can be stated- Coronoid process does not grow itself first.

Capsular matrix:Include masses and spaces that occupy a broader anatomical complex.It acts indirectly and passively in their related skeletal unit producing a secondary translation in space. These alterations in spatial position of skeletal units are brought about by the expansion of oro-facial capsules within which the facial bones arise, grow & are maintained.

Neurocranial capsule:

1.In neurocranial capsule these covers consist of skin and duramater whereas in orofacial capsule it is the skin and mucosa2.The composition of this capsule (from outward to inward) - 5 layers of scalp, bone and duramater.

Orofacial capsule:1.This capsule surrounds and protects the oro nasopharyngeal functioning spaces. 2.It is the volumetric growth of these spaces which is the primary morphogenetic event in facial skeletal growth.

SKELETAL UNIT

All the skeletal tissue associated with single function is called skeletal unit. Composed of bone, cartilage and tendinuous tissueMICRO SKELETAL UNIT- Bone consist of number of small skeletal unit.MACROSKELETAL UNIT- When adjoining micro skeletal units work to carry out single cranial component.MAXILLA-orbital -pneumatic-basal-nasal-alveolar

Microskeletal Units Of Mandible:

Coronoid- related to functional demands of temporalis

Angular- related to activity of masseter and medial pterygoid.

Basal unit- to inferior alveolar neurovascular triad.

Alveolar unit related to presence/absence of teeth.

Functional matrix theory revisited

Revisit 1 The role of MechanotransductionRevisit 2 The role of Osseous Connected Cellular NetworkRevisit 3 The genomic thesisRevisit 4 The epigenetic antithesis and the resolving synthesis

Melvin moss in 1997 proposed continuation of his classical FMH with the new concept. He published series of articles in AJO-DO in 1997. MECHANOTRANSDUCTIONAll vital cells are irritable- respond to alteration in their external environmentMechano-sensing helps cell to respond to external stimuli by Mechano-reception and Mechano- transductionThe former transmits extracellular physical stimulus into a receptor cellThe latter transforms this information to intracellular signal, mechanochemically or electrically

Melvin L. Moss. The functional matrix hypothesis of mechanotransduction 1997American Journal ofOrthodontics and Dentofacial Orthopedics Osseus Mechanotransduction- whenever a load/ stimuli is applied on bone, it tends to deform both extracellular matrix and bone cell when it exceeds threshold valueUnique in 4 ways-Most mechanosensing cells are cytologically specialised but bone cells are notOne loading stimulus can evoke 3 responses, others only 1Osseus signal transmission is aneuralEvoked adaptational responses are confined in each bone organ independently

Action of MechanotransductionIonic processStretch activated channelsElectrical processesElectromechanicalElectrokineticElectric field strengthMechanical processesBONE AS OSSEUS CONNECTIVE CELLULAR NETWORKAll bone cells except osteoclasts are extensively interconnected by gap junction that form an osseous CCN. Vertically gap junctions connect periosteal osteoblasts with preosteoblastic cells and these in turn are similarly interconnected.Gap junctions -electrical synapses- they permit bi-directional signal trafficThey permit intercellular transmission of ion and small molecules and electrical and fluorescent dye transmission. Mechanotransductively activated bone cells can initiate membrane action potentials capable of transmission through interconnecting gap junctions. A CCN is operationally analogous to an artificial neural network in which massively parallel or parallel distributed signal processing occurs. The network output informational signals move hierarchically upward to regulate the skeletal unit adaptational responses of the osteoblastsGENOMIC THESISDNA sequence of an individual determines the overall phenotypeOnly 10 % genome related to phenotypic ontogenesis

The Genomic thesis in orofacial biology Genomic thesis claims that prenatal cranio facial development is controlled by two inter related, temporarily sequential processes: 1. Initial regulatory (Homeobox) gene activity. 2. Subsequent activity of two regulatory molecular groups: growth factor families and steroid/thyroid/retinoic acid super family.

In the genomic thesis, morphogenesis is reduced to molecular synthesis. It proposes no pathways from molecules to morphogenesis.

It is claimed that regulatory molecules can (1) alter the manner in which homeobox genes coordinate cell migration and subsequent cell interactions that regulate growth (2) be involved in the genetic variations causing, or contributing to the abnormal development of relatively common cranio facial malformations perhaps modifying box gene activity.

Specific implications of the genomic thesis poorly coordination control of form and size of structures or group of structures (e.g. teeth, jaws) by regulator genes explain the mismatches found in malocclusions and other dentofacial deformities. And single regulatory (Homeobox) genes can control the development of complex structures indicating that single genes can determine the morphology of atleast some complex structures including How characteristic noses or jaws are inherited from generation to generation. EPIGENETIC ANTI THESISEpigenetics- entire series of interaction, among cells and cell products which lead to morphogenesis and differentiation

Epigenetic factors- all factors which impinge on vital structures

MECHANISM : It is the fundamental physical or chemical process involved in an action/ reaction.

The genomic thesis is denied because it is both reductionist and molecular; descriptions of the causation (control, regulation) of all hierarchically higher and structurally more complex morphogenetic processes are reduced to explanations of mechanisms at the molecular (DNA) level.

Eg: the genomic thesis of craniofacial ontogenesis passes directly from molecules to morphogenesis: directly from DNA molecules to adult morphology, ignoring the roles of many epigenetic processes and mechanism competent to control (regulate, cause) the large number of intervening and increasingly more structurally complex, developmental stagesRESOLVING THESISThis is required as it is clear that both genomic and epigenetic processes were necessary to explain growth and development Genomic factors - intrinsic epigenetic factors - extrinsic

The fundamental argument of this resolving synthesis based on an analysis of causation argues that morphogenesis is regulated (controlled, caused) by the activity of both genomic and epigenetic processes and mechanisms. Both are necessary causes; neither alone are sufficient cause; and only their integrated activities provides the necessary and sufficient causes of growth and development.

Genomic factors - intrinsic and prior causes; Epigenetic factors- extrinsic and proximate causes.Van Limborgh- 1970

Funtional matrix theory+ Sutural theory+ Genetic theory= Van Limborghs Theory

1] Chondrocranial growth controlled mainly by intrinsic genetic factors 2] Desmocranial growth is controlled by a few intrinsic genetic factors 3]Cartilaginous part of skull- growth centre. 4]Sutural growth controlled mainly by influences originating from skull cartilages & adjacent skull structures. 5]periosteal growth depends upon growth of adjacent structures. 5.VAN LIMBORGHS MUTIFACTORIAL HYPOTHESISVAN LIMBORGHS HYPOTHESISCraniofacial growth is controlled by 5 factors. They are: 1)Intrinsic Genetic factors: Genetics factors inherent to the skull tissues. They exert influence within the cells and determine the characteristics of cells and tissues. 2)Epigenetic factors: are those which outside of the cells and tissues in which they are produced. 2 types-Local epigenetic factors- Genetically determined influences originating from adjacent structures(brain, Eyes etc)General Epigenetic factors- Genetically determined influences originating from distant structures (Sex and growth hormones)4)Local environmental factors- local non genetic influences originating from the external environment (local external pressure, muscle forces).5)General environment factors -General non genetic influences originating from external environment (food, oxygen supply).

Neurotrophism It is the nervous control of skeletal growth by transmission of a substance through the axonsGuth defines Neurotrophism as an interaction between nerves and cells which initiate or control molecular modification in the cells.Types of neurotrophism:-Depending upon target cells and tissues there are 3 types:Neuromuscular.Neuroepithelial.Neurovisceral.

NEUROMUSCULARThe normal contractility of skeletal muscle depends upon ability of a neuron to transmit an efferent impulse. The physiological , morphological and biochemical parameters of skeletal muscle depend on neurotrophic function.Embryonic myogenesis, in vivo and in vitro, is independent of neural innervation and so of trophic control . Approximately at the stage of differentiation, neural innervation is established without which further myogenesis cannot continue.If muscle tissue is experimentally prevented from becoming efferently innervated, motor end plates will never develop. Also it is experimentally shown that muscle receptors, muscle spindles and tendons require afferent innervation for their development.NEUROEPITHELIALDuring early growth ,epithelium grows in spurts, which is thought to occur immediately following repetitive sensory nerve contact.

If such processes were absent/ deficient, we can expect orofacial hypoplasia, or malformation.

Maxilla and mandibular hypoplasia are found associated with a wide variety of intra oral and intra nasal sensory deficits.

The nerve supplying the taste bud not only carries afferent impulses but also is responsible for maintenance of existing epithelial taste buds.

NEUROVISCERALPeriosteal functional matrices regulate the size and shape of specifically related skeletal unit.

It is apparent that genetic control of structural functional and chemical attribute of these same matrices can not reside in the matrices them selves, but rather reflect constant neurotrophically regulated homeostatic control of genome. It is also clear that similar trophic control probably exits for capsular matrices which passively regulate position of both skeletal unit and periosteal matrices. Some degree of visceral neurotrophic control is probable. Eg: salivary glands are trophically regulated.first structure to develop in the region of lower jaw is the mandibular division of trigeminal nerve.

The prior presence of the nerve has been postulated as requisite for inducing osteogenesis by production of neurotrophic factors.

A study was done by Behrents and Johnston to evaluate the role of trigeminal nerve in the regulation of facial growth. they created lesions in the root, ganglion or major sensory branch of the nerve to find out role of the nerve. They concluded- it may exert some trophic influence on the craniofacial complex, but they failed to support a major role of the nerve.

6.Bioelectric theory:-The most familiar form of bioelectricity is that related to neuromuscular activity. But bone and other tissues like cartilage generate electric potential in response to mechanical strain or deformation.

These strain generated potentials serve as a mechanism that permits bone to be remodeled in response to mechanical stresses

Basset defines piezoelectricity as electricity resulting from pressure on certain crystals. In polycrystalline materials (bone) piezo-electricity results from a summation of charges produced by aggregation of the oriented regions within the material.Direct pieizo-electric effect is generation of a charge in response to pressure. Indirect piezoelectric effect is one in which the material undergoes deformation, when it is placed in an electric field.

Piezo-electric properties of bone and other biologic material were reported by Fukada and Yasuda- demonstrated Piezoelectricity in bone caused to oscillate at a low audio frequency.. Bassett and Becker showed that the specimen routinely became negative on concave side and positive on the convex.Frost suggested that deformation of bone surfaces subjected to loads generates surface signals, which causes mesenchymal cell activation. production of osteoclasts which subsequently undergo transformation into osteoblasts which cause bone depostion. A negative feedback mechanism neutralizes the signals overtime so that the resultant cell activity operates to minimize the deformation or strain which initiated the cell activity.Factors known about strain related potentialsThey are present in living organisms but are produced by inanimate matrix rather than living cells.

Exist in both dead and living bone, although they can be modified by living cells.

The potentials are generated only by changing loads

The potential difference reached for physiologically meaningful stress is of order of millivolts.Applied aspects of piezo-electric phenomenaOsteogenesis: Studies have demonstrated that bone formation occurs in electronegative regions(compression), and destruction occurs in electropositive regions (tension).

Electromagnetic fields were used by Basseett et.al.,. He found that callus formed around the stimulated femur after 7- 14 days.

Dr Alexandre G. Petrovic and Jeanne J. Stutzmann around 1969-1972

The theory demonstrates a qualitative and quantitative relationship between observationally and experimentally collected findings.

helps in broader understanding of orthodontic problems as the language of cybernetics is compatible with expanding use of computers among clinicians.

2 Principal factors-1-The hormonally regulated growth of the midface & anterior cranial base which provides a constantly changing reference input via the occlusion.2) The rate limiting effect of this mid-facial growth on the growth of mandible.

7. Servosystem theoryVarious Components of a Servo-System:-

Command- A signal established independent of the servosystem, and is not affected by the output of the system. Hence, it tells the system what is to be done. Reference Input -The input into the servo-system (which is brought about by the command). The command created a reference input through the action of a reference input element.

Comparator (Peripheral) - The input is fed into the comparator which is the component that analyses the reference input and judges the performance of the system through performance judging elements. Central Comparator- The performance transmit a deviation signal to the central comparator which sends a signal to various components the actuator, the coupling system and the controlled system This ultimately brings about an output.The Servosystem is:-COMMANDReference Input ElementsReference InputCOMPARATORPerformance AnalyzingElementsPerformanceDeviation SignalCentral Comparator(sensory engram)Actuator, Coupling System,Controlled SystemOutput(Controlled Variable)TRANSFER FUNCTIONSAny cybernetic system, when provided an input (or stimulus, processes ,produces an output. The output is related to the input by a transfer functionOTDepends on :Types of cartilage and the influence of growth factors on them,Role of the lateral pterygoid and retrodiscal pad in condylar growth.

Types of cartilage:Primary cartilageSecondary cartilageGrowth of the Face According to the Servosystem TheoryPrimary cartilages are seen in:Epiphyseal cartilages of long bonesCartilages of synchondroses of long bonesNasal septal cartilagesLateral cartilaginous masses of ethmoidCartilage between greater wings and body of sphenoid.

Secondary cartilages are seen in:Coronoid cartilageCondylar cartilageMidpalatal suture cartilage

FACE AS A SERVO SYTEM

Input Maxillary dental archGrowth in lengthGrowth in widthOutputAdjustment of the position of mandibular dental archGrowth in Length:growth ofNasal SeptumIncreased size Of TongueLabial MusclesProtrusion ofUpper IncisorsProtrusion of Lower IncisorsPost-ant shift of premaxillarybonesGrowth of PreMaxillaryextremityGrowth of PreMaxillarySuture,Growth ofMaxillo PalatinesutureRelease of STH SomatomedinSepto-PremaxillaryligamentBiomechanicalInductionTractionThrustThrustThrustDirect ActionGrowth in WidthRelease of STH SomatomedinGrowth ofLateral cartilaginous masses of EthmoidIncreased size Of TongueGrowth of cartilageB/w greater wings& body of sphenoid Outward growthOf maxillarybonesOutward shift ofAlveolus and molarsTransverseSeparation ofpremaxillaeTransverseSeperation ofHorizontal Maxilla and Palatine platesGrowth ofmidPalatinesutureOutward AppositionalBone growth86Action of Functional Appliances based on the Servosystem TheoryTwo categories of functional appliances :-

1.Appliances like the activator, class II elastics, Frankel appliance, Twin block, Bionator etc.

2.Appliances like the Herren &LSU activator - Extra oral traction on the mandible, which position the mandible forward and open it beyond the physiologic rest position.

First GroupWhen appliance is in place, there is increased activity of the LPM and RDP due to the forward positioning of the mandible.

Hence, the mandible grows forward by deposition of bone at the condyle, thus length and even direction of growth is altered.Second Group:

The appliances in this group tend to position the mandible forward as well as open it well beyond the physiologic rest position.

No increase or even a slight decrease in the activity of the LPM was seen when these appliances were worn. Yet there was in increase in growth.

This can be explained as a 2 step process.

The time the appliance is worn, the forward positioning of the mandible caused a reduction in the length of the LPM. At this time a new sensory engram is formed for this position of the mandible.

2) When the appliance is not worn, the mouth functions according to this new sensory engram. So the mandible is functioning in a more anterior position. This increases the activity of the RDP, leading to hypertrophy of chondroblasts.

Hence actual lengthening of the mandible takes place when appliance is not worn.FUNCTIONAL APPLIANCE INCREASED CONTRACTILE ACTIVITY OF THE LPM

INTENSIFICATION OF THE REPETITIVE ACTIVITY OF RETRODISCAL PAD

INCREASE IN GROWTH STIMULATING FACTORS

CONDYLAR CARTILAGE CHANGES

LENGTHENING OF MANDIBLECLINICAL IMPLICATIONS1.All orthodontic treatment must strive to reach the optimal functional situation,if not post treatment condition should be better than pretreatment condition,tendency for relapse is less.2.A functional appliance should be removed only when growth is completed,if not should achieve good intercuspal relation,ensures stable result.3.Proper functioning of LPM and RDP is important for growth4. Utilization of high hormonal activity at puberty.5.understanding of how functional appliances affect the servosystem is important to know how long the appliance is to be worn.6.Younger children respond better to functional appliance - results more stableDrawbacksThe theory places a lot of importance on the condyle as the growth centre. Hence if the condylar cartilage is lost subsequent to a fracture, growth should seize.

Lot of importance is placed on the role of hormones in controlling growth. In all probability, they do not have such a large role to play. The peripheral comparator, the occlusion, itself, is unstable. Discrepancies in the occlusion can easily be overcome by dentoalveolar changes, rather than by growth of the mandible.

According to the theory, an end on relation is a repeller. Still, end on relation of the molars and other teeth are often seen.

The theory does not explain the action of the reverse pull headgear. 8.Remodelling theory:GIVEN BY JC BRASH IN 1930

Brash provided the foundation for the development of the first general theory of craniofacial growth.

First bone is deeply stained through out by giving madder continuously from birth for sufficient time. Then it is omitted for any period during which growth of bone is to be determined.

The research by Brash provided the foundation for development of first theory of craniofacial growth - the remodeling theory.

Principal tenets of remodeling theoryBone grows only appositionally at surfaces,bone does not grow grow interstitially through mitotic activity of osteocytes. Growth of jaws is characterized by deposition of bone at posterior surface of maxilla and mandible,sometimes described as Hunterian growth of jaws. Calvarial growth occurs via deposition of bone on ectocranial side and resorption endocranially.According to this theory all of the craniofacial skeletal growth occurs mainly by bone remodelling selective addition and removal of bone at surfaces.

Schematic Representation Of The Remodeling Theory Of Craniofacial Growth Using The Cranial Vault As A ModelINCONSISTENCYThis theory created doubt about the role of unique structures like sutures, cranial base synchondrosis and mandibular condylar cartilage.

The doubt was that if these sites are not essential for normal craniofacial growth then why they were present at all ?Enlows V principle One of the basic concepts in facial growth is the "V" principle. Many facial and cranial bones, or parts of bones, have a V-shaped configuration.

Deposition also takes place at the end of two arms of the V resulting in growth movement towards the ends.

Enlows Expanding V Principle , 1963

V Enlows counterpart principle

The growth of any facial and cranial part relates to other structural counter part in the face and cranium.

-If the regional part and its particular counter part enlarge to some extent, balanced growth occur.

-Imbalance occur when differences in amounts or directions of growth between parts and counter part is seen.Different parts and their counterpartsNasomaxillary complex- anterior cranial fossaMiddlecranial fossa and ramus breadth are counterpartsMaxillary and mandibular arches- counterpartsBony maxilla and corpus of mandibleMax tuberosity- lingual tuberosityconclusionMajorly influenced by embryological and less by genetics, craniofacial growth & development, malocclusion & treatment concepts were known till now taking advantage of that dentists are now well positioned to enter a new era of genetics and molecular biology through the incorporation of the principles of developmental molecular genetics into treatment of developing malocclusion and growth related jaw discrepancies in a new way

References:-Proffit W.R.: Contemporary Orthodontics. 5th Edition Textbook Of Orthodontics- Samir E. Bishara Enlow D.H.: Handbook Of Facial Growth. 3nd Edition.1990, W. B. Saunders Company Graber Petrovik Rakosi : Scientific Concepts & Validation Of Functional AppliancesRahul Raman Doshi And Amol Somaji Patil. A Role Of Genes In Craniofacial Growth . Iioabj; Vol. 3; Issue 2; 2012: 1936 VIRGILIO F. Ferrario, Chiarella Sforza, Graziano Serrao, Veronica Ciusa, Claudia Dellavia. Growth And Aging Of Facial Soft Tissues: A Computerized Three-dimensional Mesh Diagram Analysis. Clinical Anatomy 16:420433 (2003)Melvin L. Moss. The functional matrix hypothesis of mechanotransduction 1997American Journal ofOrthodontics and Dentofacial Orthopedics Melvin L. Moss The functional matrix 3. The genomic thesis . 1997American Journal ofOrthodontics and Dentofacial Orthopedics

Sanjay Gupta , Patnaik. V . V. Gopichand, Subhash Kaushal , Sudha Chhabra ,Vipin Garsa. CRANIAL ANTHROPOMETRY IN 600 NORTH INDIAN ADULTS. Int J Anat Res 2013, Vol 1(2):115-18. ISSN 2321- 4287Bjork A. Eur J Orthod 2005 29: i82-88Clinical othrodontics: current concepts, goals and mechanics. Ashok karad. 2nd edV.Venkatesh ,K.A.JeevanKumar,A.P.Mohan ,B.PavanKumar ,RameshKunusoth, M.PavanKumar. Achieving the Prediction Results by Visualized Treatment Objective Following Anterior Maxillary Segmental Osteotomy. A Retrospective Study. Journal of Maxillofacial and Oral Surgery June 2013, Volume 12, Issue 2, pp 188-196Brons S, van Beusichem ME, Bronkhorst EM, Draaisma JM, Berg SJ, Schols JG, et al. (2014) Methods to Quantify Soft TissueBased Cranial Growth and Treatment Outcomes in Children: A Systematic Review. PLoS ONE 9(2): e89602. doi:10.1371/journal.pone.0089602D. Verma ,T.Peltomki ,A.Hunter. Predicting vertical growth of the mandibular ramus via hand-wrist radiographs. Journal of Orofacial Orthopedics / advances orthodontics May 2012, Volume73,Issue3,pp 215-224Sagun Mathew. Assessment of Computerized Cephalometric Growth Prediction: A Comparison of Three Methods. http://hdl.handle.net/10027/9208