Growth Theories-ppt

GROWTH- THEORIESGROWTH- THEORIES

LEARNING OBJECTIVESLEARNING OBJECTIVES

• Growth and its role in orthodontic patient management.

• Various concepts in growth and Development.

• Theories of growth and their description.

Theories of growthTheories of growth

• THEORIES OF GROWTH : INTRODUCTION

It is fact that the growth is strongly influenced by genetic factors, but it also can be significantly affected by environment, in the form of factors like nutritional status, degree of physical activity, health or illnesses etc.

Important theoriesImportant theories

1. Genetic Theory. Brodie (1941)

2. Sutural Theory, by Sicher (1945)

3. Cartilagenous Theory, by Scott (1953)

4. Functional matrix Theory, by Moss (1962)

5.Neurotropism by, Moss (1971)

6. Servosystem Theory by, Petrovic (1982).

7. Functional matrix theory revisited

-Melvin Moss 1997

Genetic theory, Brodie 1941Genetic theory, Brodie 1941

• The genetic theory simply implies that genes determines all, i.e. all growth is controlled by genetic influence and is preplanned.

• Although called a theory it was more assumed than proves.

• One can often conclude that all resemblance in families are genetic. But such similarities like facial expressions, mode of laughter may be learned as a result of living together.

• Undoubtly there are primary controls for initiation and formation of facial structures. But what we sometimes assume to be genetic may be acquired and superimposed on genetic foundation common to patients and progeny.

• In addition to multiple genes there are the effects of the environment on the product of the genetic control during formation.

• This was one of the earliest theories put forward. Only some part of this theory is accepted.

Sicher’s Sutrual Theory:1955Sicher’s Sutrual Theory:1955

According to Sicher the craniofacial growth occurs at the sutures.

From the many studies using vital dyes he deduced that, sutures are causing most of the growth. If the sutural connective tissue proliferates it creates the space for appositional growth at the borders of the two bones.

• This connective tissue in sutures of both the nasomaxillary complex and vault produced forces which separates the bones, just as syncondroses expanded the cranial base and epiphyseal plates lengthened long bones.

• According to him, paired parallel sutures that attach facial areas of the skull and the cranial base region push the nasomaxillary complex forwards to pace it’s growth with that of the mandible.

• Fig of synchondroses

• Sicher believed that both the condrocranium and the desmocranium grow under rather strong genetic control.

• He held sutures, cartilage and periosteum all responsible for facial growth and assumed all were under tight intrinsic genetic control.

• Growth, in his view , was the result of the expression at all these sites of a genetic program. The translation of maxilla, therefore, was the result of pressure created by growth of the sutures, so that bones are pushed apart.

• Rejection of Theory :• The theory has been largely rejected for the

reason, that the suture is essentially a tension – adapted tissue. The presence of any unusual pressure on a suture triggers bone resorption, not deposition. The sutural membrane can not withstand any undue amount of compression because pressure affects it’s vascular and cellular components. It is believed that the stimulus for sutural bone growth is the tension produced by the displacement of that bone.

• It is clear now that sutures, and the periosteal tissues more generally, are not primary determinants of the craniofacial growth because :

When the area of suture between two facial bone was transplanted to another location, the tissue does not continue to grow. This indicates lack of innate growth potential in sutures.

Growth takes place in untreated cases of cleft palate even in the absence of suture.

Microcephaly and hydrocephaly raised. Doubts about the intrinsic genetic stimulus of the sutures

Thus sutures must be considered areas that react not primary determinants. The sutures of the maxilla are the sites of the growth and not and not growth centers.

Scott’s Cartilaginous Scott’s Cartilaginous Theory :1953Theory :1953

• Scott assumed that the primary controlling factors in craniofacial growth are found only in the cartilage and the periostium, and the sutures are secondary and passive. He viewed that cartilaginous sites throughout the skull as primary centers of growth.

– Cartilage is specifically adapted to certain pressure-related growth sites, because it is special tissue uniquely structured to provide the capacity of growth in the field of compression. Cartilage is present in the ‘epiphyseal plate of long bones, in the ‘synchondroses of the cranial base, and the mandibular condyle, where it provides linear growth by endochondral proliferation.

• The one way to visualize the mandible is by imagining that, it is like diaphysis of a long bone, so that there is cartilage representing ‘half an epiphyseal plate’ at the ends, which represent the mandibular condyles. Considering this, cartilage at the mandibular condyle should act as a growth center, behaving basically like epiphyseal growth cartilage.

diaphysis

epiphysis

• Although there is no cartilage in maxilla itself, there is a cartilage in the nasal septum, and the nasomaxillary complex grows as a unit. cartilaginous theory hypothesize that the cartilaginous nasal septum serves as a pacemaker for other aspects of the maxillary growth.

the basis for the theory is that the pressure-accompanying expansion of the nasal septum provides a source for the physical force that displaces the maxilla anteriorly and inferiorly. If the sutures of the maxilla served as a reactive, as they seem to do,

• then they would respond to this translation by forming new bone when the sutures were pulled apart from the forces from the growing cartilage.

• Two kinds of experiments have been carried out to test the idea that cartilage can serve as a true growth center :

Analysis of the results of transplanting cartilage.

An evaluation of the effects on growth of removing cartilage at an early age.

• Transplantation experiments demonstrate that not all skeletal cartilage acts the same when transplanted. If a piece of a epiphyseal plate of a long bone is transplanted, it will continue to grow, indicating that these cartilages do have innate potential ,

• cartilage from the spheno-occipital synchondrosis of the cranial base also grows when transplanted, but not as well.

• transplanting cartilage from the nasal septum give equivocal results : sometimes it grew, sometimes it did not .

• Experiments to test the effect of removing cartilages are also informative. The removal of the nasal septal cartilage from young growing rabbit’s nose shows considerable deficit in the growth of the midface (Sarnat and McNamara 1976).

• Ohyma in1969 did experimental study on rats and supported scotts hypothesis

Fact against scott cartilaginous hypothesis

It is seen that in 75% to 80% of human children who suffers from condylar fracture resulting loss of the condyle does not impede the mandibular growth.

• In summary it appears the epiphyseal cartilage, the cranial base synchondrosis, and the nasal septal cartilage can and do act as independently growing center. Neither tranplantation nor the cartilage removal experiment lend any support to the idea that the cartilage of the condyle is an important center.

It appears that growth of the condyle is more analogue to growth of the sutures of maxilla – entirely reactive – than to the growth of the epiphyseal plate

At present the cartilaginous theory is still accepted by no. of investigators, although it is universally realized that, much more needs to be understood.

Functional matrix theory-Melvin Functional matrix theory-Melvin Moss1962Moss1962

• Introduction:

The concept of functional matrix as introduced by professor Melvin.L.Moss has revitalised the studies of growth and development and had established a rationale for the orthodontic application of orthopaedic forces . Proff. Moss has taken a quantum leap with his functional matrix hypothesis to explain growth and development-

• Definition :

As in Am.j.orthodontics june 1969,vol 55,number 6. by Melvin.l Moss and Salentine

“all responces of the osseous portions of skeletal units to periosteal matrices are brought about by the complimentary and interrelated process of osseous deposition and resorption, the resultant effect of this is to alter their size and /or their shape”.

• Definition acc. to AJO vol july 1997 by Melvin .L. Moss “The developmental origin of all cranial skeletal elements (e.g., skeletal units) and all their subsequent changes in size and shape (e.g., form) and location, as well as their maintenance in being, are always, without exception, secondary, compensatory, and mechanically obligatory responses to the temporally and

operationally prior demands of their related cephalic nonskeletal cells, tissues, organs, and operational volumes (e.g., the functional matrices).

this theory is based on functional cranial component concept of Van Der Klaauw 1948.

• Principles of functional matrix theoryFunctional matrices are the primary

design mechanisms in craniofacial growth, i.e functional matrices grows and skeletal tissue responds.

Effects of genes are mainly exerted on the functional matrices , rather than on skeletal tissue themselves.

Changes in size, shape and location are epigenetically ( i.e causally related series of processes or changes in external and internal environment) related.

The interaction of both genomic and epigenetic factors is required o regulate or cause development

Functioning muscle influences developmental changes in the form of skeletal tissue to which they are attached through muscle-bone interface.

Functional cranial component ( tissues, organs, spaces, skeletal part )

skeletal unit functional matrix (bone, cartilage tendons periosteal capsular

micro skeletal unit macro skeletal unit

Functional matrix

Periosteal matrices Capsular matrices( muscles, vessels, nerves, ( neurocranial capsule & glands ) orofacial capsule )

Acts directly on skeletal unit Acts indirectly

Produce a secondary compen- Produce a secondaryatory transformation by translation in spaceDeposition & Resorption by expansion

Skeletal unit :

All skeletal tissues associated with a single function.

Micro skeletal unit: when bone is comprised of several contiguous skeletal units, they are termed micro skeletal unit.

Macro skeletal unit :when adjoining portions of a number of bone are united to function as a single cranial component.

Skeletal units may be composed variably of bone, cartilage, or tendinous tissues.

To a variable extent, contiguous microskeletal units are independent of each other.

Eg, In the mandible we distinguish easily a coronoid microskeletal unit related to the functional demands of the temporalis muscle; an angular microskeletal unit related to the activity of both the masseter and medial pterygoid muscles; an alveolar unit related to the presence and position of teeth; and a basal microskeletal unit related to the inferior alveolar neurovascular triad matrix.

Functional matrix The term functional matrix is by no means

equivalent to what is commonly understood as "soft tissues," this is, muscles, glands, nerves, vessels, fat, etc

Teeth as a functional matrix. Teeth are also a functional matrix, :most orthodontic therapy is based firmly on the fact that when this functional matrix grows or is moved, the related skeletal unit (the alveolar bone) responds appropriately to this morphogenetically primary demand .

• Periosteal matrices : these are muscles, nerves, vessels, glands. They act directly on their skeletal units; bringing about a transformation in there size and shape by bone deposition and resorption

• Periosteal matrices act upon skeletal units in a direct fashion by the processes of osseous deposition and resorption (or of cartilaginous or fibrous tissue multiplication).

• Eg supporting periosteal matrix concept : There exist considerable mutually

confirmatory data showing that experimental removal of the mammalian temporalis muscle or its denervation, invariably results in an actual diminution of coronoid process size and shape or, indeed, in its total disappearance . Similarly, it is well established that

functional hypertrophy or hyperactivity of the temporalis muscle is productive of increased coronoid process size and also alteration of its shape.

• Capsular matrix:

capsules is an envelope which contains a series of functional cranial components (skeletal units plus their related functional matrices ) which, as a whole, are sandwiched in between two covering layers.

Capsular matrices act upon functional cranial components as a whole in a secondary and indirect manner.

Cause a passive translation of these cranial components in space.

The growth of the facial skull is influenced by volume and patency of these spaces.

• Neurocranial capsule:

In neurocranial capsule , covering consist of the skin and the dura mater.

The composition of this capsule in the adult is easily stated; these are the so-called "five layers" of the scalp, then the bone itself, and, finally, the two-layer dura mater.

The neural skull does not grow first and thus provide space for the secondary expansion of the neural mass. Rather, the expansion of the neural mass is the primary event which causes the secondary and compensatory growth of the neural skull.

• Orofacial matrices: In the orofacial capsule the skin

and mucosa form the limiting layers. All functional cranial components of the

facial skull arise, grow, and are maintained within an orofacial (splanchnocranial) capsule. This capsule surrounds and protects the oronasopharyngeal functioning spaces

The functional reality of the respiratory and digestive systems is their patency, and the volume of that patency is related to the general metabolic demands of the body as a whole.

The oronasopharyngeal functioning space is particularly related to the relatively dominant cranial respiratory functional space volume.

• “ Bosma concept 1969’’ Support for capsular matrix:

Bosma believes that "a recent concept is the development of head and neck posture is about this pharyngeal airway" and that the related functional cranial components are so dynamically balanced that this airway is maintained throughout the range of motion of the head and neck.

The oral and pharyngeal "regions" are said to have a primary function in maintaining a patent airway. This is accomplished by a dynamic musculo-skeletal postural balance which is termed the “ Functional airway-maintenance mechanism ”.

Cranial growth is a combination of the morphogenetically primary activity of both types of matrix.

Growth is accomplished by both spatial translation and changes in form.

Conclusion : Thus, the functional matrix concept, in

general, is established and valid, and it is basic in helping us understand the complex interrelationship that operate during facial growth.

• It is to be realized, however that this principle is not intended to explain how the growth control mechanism actually functions. This concept describes essentially what happens during growth; it does not account for the regulatory processes at the cellular and molecular level that carry it out.

Experimental works supporting Experimental works supporting functional matrix hypothesisfunctional matrix hypothesis

• Koski -Makinen experimental study 1963-64 on transplanted components of the mandibular ramus:

supported the functional matrix theory and did not agree with sicher-weinmann hypothesis .

• Sarnet and muchnic AJO1971 done experimental study on skull of rhesus monkey to see the changes after condylecomy.

• Rankow and Moss Angle Orthodont. 1968 study of young female, who was subjected to condylectomy following ankylosis.

other works were done by:

Irving and ronning 1962.

Gianelly and moorees in 1965.

Neurotrophism mechanism (Moss-Neurotrophism mechanism (Moss-1971)1971)

• Neurotrophism is a non-impulse transmitting neural function that involves axoplasmic transport and provides for long term interaction between neurons and innervated tissues that homeostatically regulates the morphological, compositional and functional integrity of those tissues.

Moss 1971 j.Dent .res talk about the neurotrophic processes in oro facial growth and indicate three general categories:

• Neuro-epithelial trophism• Neuro-muscular trophism• Neuro-visceral trophism

A.T. STOREY AND D J.KENNY Adv Dent Res 3(l):14-29, May, 1989

There is evidence that vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide(CGRP) elaborated from sympathetic and parasympathetic neurons may have a modulatory role.

Neurotrophism Mechanisms involved in growth, development, and maturation of tissues sustained by neural cells would seem to depend on chemical interactions.

Petrovic’s servo system theory Petrovic’s servo system theory (1982 )(1982 )

• Using the language of cybernetics, petrovic reasoned that it is the interaction of a series of causal change and feedback mechanism which determines the growth of various craniofacial regions.

• Cybernetic is an organized system that operates through signals that transmit information.

• Petrovic used a cybernetic model for the physiologic phenomena involved in facial growth.

• In servo system the main input is not constant but varies with time

• According to this theory control of primary cartilage takes a cybernetic form of a command, whereas in contrast, control of secondary cartilage (e.g. mandi condyle) is comprised not only of a direct effect of cell multiplication but also of indirect effects.

• Primary cartilage growth – if growth results from cell division of differentiated chondroblasts (epiphyseal cartilage of long bones, cartilages of synchondrosis of cranial base and nasal septum), it appears to be subjected to general extrinsic factors and more specifically to somatotropic hormone, somatomedin, sexual hormone and thyroxine.

• Secondary cartilage growth : if growth results from cell divisions of prechondroblasts, (coronoid and angular cartilage of mandible, mid-palatal suture cartilage ) it is subjected to local extrinsic factors.

Command

( growth hormone, somatomedins, sex hormone, thyroxin )

In secondary cartilage In primary cartilage direct control

Indirect control Direct control Septal cartilage

saggital positioning of maxilla normal signal deviation signal

Lateral pterygoid Condylar muscle activity Cartilage Regulatory mechanism Mandibular growth

• This theory explains the mode of action of the functional appliances directed at condyle.

• The upper arch acts as a mould into which the lower arch adjusts it self, such that optimal occlusion is established.

Functional matrix hypothesis revisited 1997:1.The Functional matrix hypothesis revisited 1997:1.The role of mechanotransductionrole of mechanotransduction

• The FMH postulates two types of functional matrices. This new version deals only with the responses to periosteal matrices. It now includes the molecular and cellular processes underlying the triad of active skeletal growth processes-

-deposition - resorption - maintenance

• FMH – revisit presents seamless description between several level of bone structure and operation from genomic to organ level.

It does so by the inclusion of two complementary concepts- 1) Mechanotransduction occurs in single bone cells. 2) Bone cells are computational elements that function multicellularly as a connected cellular network.

Mechanotransduction Mechanotransduction

• Mechanosensing process enable a cell to sense and to response to extrinsic loading by using the process of mechanoreception and mechanotransduction.

mechanoreception: transmits an extra cellular physical stimulus into a receptor cell, the mechanotransduction transforms the stimulus into an intra cellular signal.

Mechanotransduction: transducing or transforming the stimulus's energetic and/or informational content into an intracellular signal. Mechanotransduction is one type of cellular signal transduction. There are 2 mechanotransductive process- 1) Ionic or electric 2) mechanical- through physical continuity of the transmembrane molecule integrin

Extracellular collagen

INTEGRIN

intracellularly with cytoskeletal ACTIN

Nuclear membrane

Intranuclear process

Regulate genomic activity

Osseous mechanotransductionOsseous mechanotransduction

Osseous mechanotransduction is unique in 4 ways-

1)Not cytologically specialized.

2) Evoke three adaptational responses

3)Osseous signal transmission is Aneural. 4)Evoked bone adaptational response are confined with in each ‘bone organ’ independently.

Functional matrix hypothesis revisited 1997: Functional matrix hypothesis revisited 1997: 2. the role of an osseous connected cellular 2. the role of an osseous connected cellular

networknetwork

• Bone as an osseous connected cellular network (CCN): All bone cells, except osteoclasts, are extensively interconnected by GAP-junction that form an osseous CCN. Each osteocyte enclosed with in its mineralized lacunae

• Gap-junction exhibit both electrical and fluorescent dye transmission, in addition to permitting the intercellular transmission of ions and small molecules.

• Mechanotransductively activated bone cells, e.g. osteocyte, can initiate membrane action potentials capable of transmission through interconnected Gap-junction.

Loading of bone stimulate initial cells ( loading exceeds

threshold value) Intracellular signals generated transmitted to intermediate or hidden

layer cells (osteocyte) ( when exceeds

threshold value) transmission to final layer cells

(osteoblasts) Adaptive response

• A skeletal CCN displays the following attributes- 1) Developmentally: untrained

self-organized, self-adaptive and epigenetically regulated system.

2) Operationally: stable, dynamic system that exhibits oscillatory behavior permitting feed back. 3)Structurally, an osseous CCN is nonmodular.

Functional matrix hypothesis Functional matrix hypothesis revisited1997: 3. The genomic thesisrevisited1997: 3. The genomic thesis

• The initial version of the functional matrix hypothesis claiming epigenetic control of morphogenesis was based on macroscopic (gross) experimental, comparative and clinical data. Recently revised it now extends hierarchically from gross to microscopic (cellular & molecular) levels and identifies some epigenetic mechanisms capable of regulating genomic expression.

• The epigenetic /genomic problem is a dichotomy and dialectics is one analytical method for its resolution. The method consists of the presentation of two opposing views- • The genomic thesis

• An epigenetic antithesis and a resolving synthesis.

• The genomic thesis : The genomic thesis holds that the genome from

the moment of fertilization, contains all the information necessary to regulate (cause, control, direct)--- 1)The intranuclear formation and transcription of mRNA.

2) All (phenotypic) feature are ultimately determined by the DNA sequence of the genome.

Genomic thesis is denied because it is both reductionist and molecular, that is description of the causation (control, regulation) of all hierarchically higher and structurally more complex morphogenetic processes are reduced to explanation of mechanisms at the molecular (DNA) level.

The functional matrix hypothesis The functional matrix hypothesis revisited :4. The epigenetic antithesis revisited :4. The epigenetic antithesis

and the resolving synthesisand the resolving synthesis

• The epigenetic antithesis : Its Goal is to identify and describe comprehensively the series of initiating biological process and their related underlying (biochemical, biophysical) responsive mechanisms that are effective at each hierarchical level of increasing structural and operational complexity.

Craniofacial epigenetics:• Broadly speaking, epigenetics refers to the entire

series of interaction among cells and cell products which leads to morphogenesis and differentiation. thus all cranial development is epigenetic.

• In terms of clinical orthodontics, all therapy is applied epigenetics and all appliances acts as prosthetic functional matrices.

• Clinical therapeutics includes a number of epigenetic processes, whose processes of tissue adaptation by both skeletal unit and functional matrices.

A resolving synthesisA resolving synthesis• Morphogenesis is regulated (controlled, caused)

by the activity of both genomic and epigenetic processes and mechanisms.

• Both are necessary, neither alone are sufficient cause and only their integrated activities provides the necessary and sufficient causes of growth and development.

• Genomic factors are considered as intrinsic and prior causes, epigenetic factors are considered as extrinsic and proximate cause.

• Epigenetic processes and events are the immediately proximate causes of development and as such they are the primary agencies.

TAKE HOME MESSAGETAKE HOME MESSAGE• A good knowledge of growth and development

helps us to know the etiology, diagnosis and treatment planning of malocclusion and also helps us to predict the prognosis of orthodontic treatment.

• Growth modification by means of functional and orthodontic appliance gives better response before growth completion (best results during growth spurts)

• Orthognathic surgery gives best results if done after completion of growth, so as to prevent relapse.

References References • Enlow D.H. : Essential of facial growth.ed-2,Philadelphia, W.B.Saunders

company,1982.• Graber T.M. : Orthodontics: principle and practice, 3rd ed, W.B.Saunders

company,1988.• Graber T.M.,Rokosi T.,Petrovic A.:Dentofacial orthopedics with functional

appliance. 2nd ed, st.Lovis: Mosby 1997.• Kaskik A.,Odont L.,Odont D.: cranial growth centers facts or fallacies.

Am.J.Orthodont,54:566-583, august 1968.• Moss M.L.and letty salentijn:The primary role of functional matrices in facial

growth. Am. J. orthodont.,55:566-577, June 1969.• Moss M.L.and Letty salentijn: The capsular matrix. Am. J. orthodont.,56:474-

490,Nov 1969.• Moss M.L.:The functional matrix hypothesis revisited, Am.J. Orthodont, 1997.• Nepola S. Richard:The intrinsic and extrinsic factors influencing the growth and

development of the jaws: heredity and functional matrix. Am.J. orthodont,55:499-505, may 1969.

• Proffit W.R.,Fields H.W. : Contemporary orthodontics, 3rd ed. St. Louis:C.V.Mosby,2000.

• Storey A.T. and Kenny D.J. : growth, development, and aging of orofacial tissues :Neural aspect. Adv. Dent. Res.3(1):14-29, may1989.