FUNCTIONAL MATRIX HYPOTHESIS
INDIAN DENTAL ACADEMY
Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
â–şIntroduction Malocclusion and dentofacial deformities arise through variations in the normal developmental process, and so must be evaluated against perspective of normal development. Because orthodontic treatment often involves manipulation of skeletal growth, clinical orthodontics requires an understanding not only of dental development but also of more general concepts of physical growth and development www.indiandentalacademy.com
â–ş Even
for those who never work with children, it is difficult to comprehend condition observed in adults without understanding the developmental process that produced these problems. For those who interact professionally with children it is important to distinguish normal and pathologic processes. Since orthodontists are heavily involved in development of not only dentition but entire dentofacial complex he might have to manipulate facial growth for benefit of patient. Obviously it is not possible to do so without understanding mechanisms underlying it www.indiandentalacademy.com
Theories of growth ► Sutural
theory by Seicher ► Cartilagenous theory by Scott ► Functional matrix by Melvin Moss ► Multifactorial theory by Van Limborgh ► Servo system by Petrovic
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The sutural theory ► This
theory implies that the genetic control is expressed directly at the level of bone ► Sutures cannot be called growth centre. But it can be called a growth site. However sutures have been called growth centre and regarded as being homologous to epiphysial growth plate ► That considerable amount of growth occurs in sutures has been proved by many authors ► But is growth here primary? www.indiandentalacademy.com
► Now
it is clear that sutures are not at all similar to epiphysial growth plate ► Experiments by Watanabe, Laskin and Brodie of subcutaneous autotransplants of zygomaticomaxillary suture did not grow which clearly speaks against autonomous growth potential in suture. ► Extirpation of facial sutures appears to have no effect on dimensional growth of skeleton www.indiandentalacademy.com
â–ş Sarnat
(AO 1963) showed it was possible to bring growth to halt by mechanical forces using metal clips applied across sutures â–ş From the evidence presented one comes to a conclusion that sutural tissues are unlikely to have tissue separating forces and hence are not considered a growth centre
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Cartilagenous theory â–ş This
theory implies that the genetic control resides in the cartilage and the bone responds passively Cranial base synchondrosis â–ş Most authors consider this, especially sphenooccipital synchondrosis as growth centre â–ş There is no doubt of structural similarity with epiphysial growth plate and considerable growth occurs here www.indiandentalacademy.com
► Koski
and Ronning, transplanted cranial base synchondrosis to a nonfunctional sites and found not enough growth to effect growth of adjacent bone as seen in situ ► Powel and Brodie found sphenooccipital synchondrosis to close much earlier than once thought, at about 11-16yrs ► At present there is no direct evidence to support the claims that synchondrosis are growth centers www.indiandentalacademy.com
Cartilage of nasal septum â–ş Endochondral
ossification at septoethmoidal junction and area of proliferation at vomeral edge all suggest its role to provide thrusting force to push maxilla downward and forward â–ş Sarnat and Wexler, showed excision of nasal septum affected growth of upper facial growth considerably www.indiandentalacademy.com
by Latham and Burston 1966 concerning arrhinencephalic 9 month old with missing nasal septum, states that height of upper face was not greatly affected although middle one third sagittal development retarded. â–ş On the basis of the present evidence we may conclude that septo-ethmoidal junction possibly acts as growth centre during postnatal life, although direct evidence of this is lacking and may indeed be difficult to obtain â–ş Report
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Condylar cartilage of mandible â–ş Most
authors in the 60s accepted the opinion that growth at condyle moved mandible forward and downward, so condyle is indispensable for normal vertical growth of face â–ş It was also claimed growth of condyle caused antero-posterior growth of mandible
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the contrary Scott had opinion that cartilage grow upward and backward so as to maintain contact at TMJ as mandible is carried downward and forward by growth of upper facial skeleton ► Research works shows that condylar cartilage are latecomers, secondary cartilage with different embryological precursor as that of epiphysial cartilage ► Condylar cartilage is highly responsive to mechanical stimulus ► On
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► Transplanted
condylar cartilage in nonfunctional site it did not behave like condylar cartilage in situ (koski and Ronning) ► Tissue culture study have also demonstrated lack of growth ► Even bilateral condylectomy or congenital absence of ramus (Kazanjian) have no appreciable effect on growth of rest of mandible ► Thus the information available appears to very strongly point towards its subordinate role as site of growth not growth centre www.indiandentalacademy.com
► If
the sutures and cartilages do, indeed lack independent growth promoting potential, what are the factors responsible for craniofacial skeletal growth? ► Several students of craniofacial growth have proposed concepts regarding it. ► Early 1960s marked the development of alternate paradigms and thus beginning of a period of scientific revolution in craniofacial biology ► And this is almost completely associated with one individual Melvin L Moss www.indiandentalacademy.com
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Melvin L Moss
Moss came to Columbia in 1943 where he yearned a DDS at the school of dental and oral surgery He got a part time apprenticeship in Department of anthropology at American museum of natural history Moss then began his graduate work in Anatomy at Department of Anatomy , Columbia university 1948 to 1951 He got his PhD in graduate school of arts and science
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► The
functional matrix hypothesis was first articulated by Moss and Young in 1960 in article published in Am J of physical anthropology ► Moss introduced FMH to clinical orthodontic community in 1962 in vistas of orthodontics (Kraus and Reidal) ► Moss introduced his FMH as a formal, alternative conceptual scheme for understanding normal and abnormal craniofacial growth www.indiandentalacademy.com
â–ş FMH
explicitly claims that the origin, growth, and maintenance of all skeletal tissue and organs are always secondary, compensatory, and obligatory responses to temporally and operationally prior events or processes that occur in specifically related nonskeletal tissues, organs, or functioning spaces (functional matrices). â–ş This statement is a modern restatement of the central position of Wilhelm His, who enunciated the doctrine of the "physiology of the plastic,'' indicating that the biologic structure was alterable and could be intentionally changed. â–ş This concept was extended by Wilhelm Roux (and by Hans Driesch) www.indiandentalacademy.com
► The
focus of the FMH is not the skeletal tissues but the factors that influences their growth and development ► A decades study on the regulatory roles of intrinsic (genetic) and extrinsic (epigenetic) factors in cephalic growth evolved into the FMH ► The advent of structuro-functional approach within craniofacial biology led to development of a new paradigm that conflicted with traditional genomic paradigm, which was called functional paradigm www.indiandentalacademy.com
Genetic thesis ► Almost
all active clinical and laboratory scientists were taught that the neo-Darwinian synthesis satisfactorily explains the regulation of both ontogenetic and phylogenetic processes. ► This synthesis unifies the data and concepts of Darwinism and classic Mendelian genetics ► It postulated (a) that small, random, gradually accumulated mutations spontaneously occurred at specific points in the genome ► (b) that the ontogenetic product of the genome was subjected to the processes of natural selection, assuring selective survival of better ontogenetic adaptations of the species to new ecologic conditions www.indiandentalacademy.com
Implicit in this synthesis is the concept that at fertilization the diploid genome contains all the information necessary to regulate (or "cause'') individual ontogenesis, requiring only an appropriately permissive and supportive environment for full genomic expression to occur â–ş In this thesis, morphogenesis is but the predetermined reading-out of an intrinsic and inherited genomic organismal blueprint where, in addition to molecular synthesis, the genome also regulates the geometric attributes of cell, tissue, organ, and organismal size, shape, and location â–ş
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► This
thesis claims that prenatal craniofacial development is controlled by two interrelated, temporally 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. ► And "single regulatory (homeobox) genes can control the development of complex structures ► Indicating that single genes can determine the morphology of at least some complex structures," including "how characteristic noses or jaws are inherited from generation to generation www.indiandentalacademy.com
Data unconformable with the genomic hypothesis. Consider the relationship between genotype and phenotype of man and the great apes. ► In terms of chromosomes (not genes), man and the great apes show close karyotypic relationships ► Therefore the differences observed at the chromosomal level between man and chimpanzee appear to be of no consequence to their phenotype. ► Some argue that it is the genic and not the chromosomal structure that is significant. www.indiandentalacademy.com
In the overwhelming number of skeletal "genetic diseases," the chromosomes are normal, and it is urged that the defect lies in the genes. â–ş But again, note that the polypeptides (a product of genomic activity) of man and chimpanzee are 99 percent identical, while the two species display great anatomic and physiologic differences, an example of great observable phenotypic difference and little genetic difference. â–ş Further, sibling species of Drosophila, and of certain mammals, show genetic differences an order of magnitude greater, an example of little observable phenotypic difference and great genomic difference â–ş
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► To
better understand the epigenetic antithesis and the shortcomings of genetic thesis , Moss recommended analysis the following terms ► Hierarchy ► Emergence ► Causation ► Epigenetics
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Hierarchy. â–ş Biological
structures are hierarchically organized, with structural and functional complexity increasing "upward" from the ever-expanding family of subatomic particles to protons, electrons, atoms, molecules, sub cellular organelles, and on to cells, tissues, organs, and organisms. â–ş Any arbitrary developmental state (or stage) of an organism may be described by certain attributes. The next higher, more complex state not only incorporates all of the attributes of the several lower states but, importantly, now creates newer attributes that come into being concomitantly with creation of this newer complexity. www.indiandentalacademy.com
Emergence. â–ş This
phenomenon occurs in all natural hierarchies. It consists of the appearance, at each successively higher and structurally and/or operationally more complex level, of new attributes or properties, not present in the lower levels, whose existence or functions could not in any way be predicted, even from a complete knowledge of all of the attributes and properties of any or all of the preceding lower organizational levels. www.indiandentalacademy.com
â–ş For
example, full knowledge of all the attributes and properties of an osteocyte does not permit prediction of the attributes and properties of any type of bone tissue. â–ş And full knowledge of all attributes and properties of all constituent bone tissue types does not permit prediction of the form (size and shape), growth, or functions of a macroscopic "bone." â–ş Emergence is not genomically controlled. Instead, the integrated activities of all the attributes in a given hierarchical level self-organize to produce the next higher level of complexity www.indiandentalacademy.com
â–ş Thus,
the phenotype is not (as the neoDarwinians see it) merely a surface manifestation of the genotype â–ş Rather, the phenotype is the result of a hierarchy of self-regulatory processes that integrate epigenetic and genomic factors into an orderly sequence
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Causation ►A
classic categorization of causation, is useful . The four primary causal types answer corresponding questions: ► (1) What is acted upon? (material); ► (2) by what set of rules? (formal); ► (3) what was the immediately preceding event? (efficient) ► (4) for what purpose? (final). www.indiandentalacademy.com
Biologically, the answers could be ► (1) a set of cells and extracellular substance (material); ► (2) a program encoded in the genome (formal); ► (3) an immediately antecedent, epigenetic event (efficient); ► (4) some consequent use (final). www.indiandentalacademy.com
An analogy may clarify this categorization. ► An extrinsic finger pushes a button (efficient), immediately causing a bell to ring (the event observed). ► Prior to the act of pushing, the building and streets must be intrinsically wired and a generator must be constructed and connected (formal). ► Further, electrical blueprints and the "laws'' of electricity (for example, Ohm's law) must exist (formal). ► Clearly while both extrinsic and intrinsic causes are necessary, neither alone is sufficient; only their combination can cause a bell to ring. www.indiandentalacademy.com
► These
may be categorized as either intrinsic (material and formal) and extrinsic (efficient); ► Material and formal causes are intrinsic because they reside within vital structure (either intracellularly or intercellularly); ► efficient causes are extrinsic—they represent the entire spectrum of epigenetic processes, mechanisms, and events capable of being imposed on vital structures. www.indiandentalacademy.com
Epigenetics Epigenetic factors include â–ş (1) all of the extrinsic, extraorganismal, macroenvironmental factors impinging on vital structures (for example, food, light, temperature), including mechanical loadings and electromagnetic fields, â–ş (2) all of the intrinsic, intraorganismal, biophysical, biomechanical, biochemical, and bioelectric microenvironmental events occurring on, in, and between individual cells, and cells and extracellular substances. www.indiandentalacademy.com
Epigenetic antithesis ► Some
of the principal strengths of this antithesis come from precise definitions of what a gene is and is not. For example: ► (a) Gene. The unit of heredity: one or more nucleic acid sequences incorporating information necessary for the generation of a particular peptide or RNA product ► (b) enough is known about the genetic machinery. the only kind of information which polynucleotide molecules are inherently capable of has nothing about which proteins will be expressed in which cells at what time and in what quantities. www.indiandentalacademy.com
► The
genomic thesis is denied because it is too molecular; that is, 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. ► For example, the genomic thesis of craniofacial ontogenesis passes directly from molecules to morphogenesis: directly from DNA molecules to adult gross morphology, ► All ontogenesis exhibits developmental "cascades," with multiple branching points where decisions are made between alternate developmental pathways. ► Such decisions are not predetermined by encoded genetic information, but instead are responses to some epigenetic stimulus www.indiandentalacademy.com
► Recently,
the phylogenetic explanation value of the neo-Darwinian synthesis has been questioned. Concurrently, alternate hypotheses of ontogenetic regulation emerged. ► they suggest that the postfertilization genome does not contain sufficient information to regulate all subsequent development. ► It is postulated that additional necessary epigenetic information is self-generated concomitant with the attainment of increasing structural and functional complexity. www.indiandentalacademy.com
â–ş In
terms of clinical orthodontics, and of the FMH, all therapy is applied epigenetics, and all appliances (and most other therapies) act as prosthetic functional matrices. Clinical therapeutics includes a number of epigenetic processes, whose prior operations evoke a number of corresponding epigenetic mechanisms. These latter, in turn, underlie the observed processes of tissue adaptations by both skeletal units and functional matrices.
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► Few
examples of epigenesis are ► Neurotrophic regulation of the muscle cell genome is a type of epigenetic information. ► Recently, in studies of skeletal muscle fiber following motor denervation, marked changes in many of the RNA sequences present in the muscle cells were noted. ► These data give strong support to the hypothesis that the motor neurons are able to control gene expression of muscle fibers.
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Position or location of a cell within a developing organism is a significant source of epigenetic information ► Here instructive interactions between cells, and the length of time a cell or cell mass occupies a specific location, are among the factors held capable of locally providing epigenetic information capable of regulating genomic expression of cells in the immediate neighborhood. ► For example, typical pentadactyl appendage is not a phenotypic expression of genomic information totally encoded in the fertilized ovum. ► In a very real sense, the activation of a given mesenchymal cell mass to chondrogenesis, at this specific site, for that period of time, and to produce that amount of cartilage in that direction, is viewed as epigenetically regulated ►
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► Mechanical
loading is known to influence gene expression. Of clinical (and FMH) interest, extrinsic musculoskeletal loading can rapidly change ► (1) both articular cartilage intercellular molecular syntheses and mineralization ► (2) osteoblastic (skeletal unit) gene expression. Epigenetic loading processes include gravitational variations that evoke unique mechanisms of molecular synthesis. www.indiandentalacademy.com
â–ş Extracellular
matrix deformation. Musculoskeletal tissue loading inevitably deforms an extracellular matrix (ECM). Rather, in several ways, ECM regulates the formation, development, and maintenance of its included cells that synthesize the ECM. Further, ECM can regulate multicellular tissue morphogenesis and contribute to genomic regulation of its enclosed cells. www.indiandentalacademy.com
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Resolving synthesis â–ş It
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 causes; 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 www.indiandentalacademy.com
Functional matrix Functional matrix
Skeletal unit Capsular matrix
Periosteal matrix
microskeleton
macrosketeton
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Functional cranial analysis ► The
HEAD is a composite structure operationally consist of a number of relatively independent function- olfaction, respiration, speech, vision, digestion, audition, equilibration and neural integration ► Each function is carried out by a group of tissues which are supported and/or protected by related skeletal elements ► Taken together, the soft tissues, organs, functional spaces and the skeletal elements related to a single function are termed functional cranial component www.indiandentalacademy.com
Functional matrix ► Any
function per se actually is performed by the operational component – the matrix ► The term functional matrix is by no means equivalent to what is commonly understood as ‘the soft tissue’ that is muscles, glands, nerves, vessels, fat etc , although all of these are obviously included within the concept www.indiandentalacademy.com
â–ş Teeth
is also a functional matrix, indeed orthodontic therapy is based on the fact that when this functional matrix is moved, the related skeletal unit ie , alveolar bone responds appropriately to this morphogenetically primary demand â–ş The term functional matrix is more inclusive still. there exist a group of matrix in which functional spaces of oro-naso-pharyngeal cavities figure importantly www.indiandentalacademy.com
Skeletal unit â–ş The
totality of all the skeletal elements related to a single function is termed as skeletal unit â–ş It may be composed of bone, cartilage and tendinous tissues â–ş The necessary biomechanical role of providing protection and support to the functional matrix is assumed by skeletal unit ie, functional matrix are rendered morphologically and spatially secure by their specifically associated skeletal unit www.indiandentalacademy.com
â–şA
Macroskeletal unit
skeletal unit is not equivalent of the bones of formal and classic osteology â–ş When adjoining portions of a no. neighboring bones are united to function as a single cranial component it is termed as macroskeletal unit â–ş For example, endocranial surface of the frontal, parietal, temporal, occipital, ethmoid, and sphenoid bones form a large skeletal unit subserving one common function i.e., protection and support of the enclosed neural mass. it constitutes a macroskeletal unit www.indiandentalacademy.com
â–ş On
Microskeletal unit
the other end of the scale, a single formal osteologic bone consist of a no. relatively independent skeletal units â–ş So bones are fractionated in order to appreciate biologic significance of its total size and shape, such fractions are termed microskeletal units â–ş Continuous microskeletal units are independent of each other, changes in size and shape of the coronoid prosses in response to temporalis muscle is independent of changes in other continuous but different microskeletal units www.indiandentalacademy.com
Periosteal functional matrix ► PFM
are virtually self defining. They are best exemplified by the effect of muscles upon skl unit. ► Whether the muscles attach their tendinous portions directly into skeleletal tissues or indirectly by fusion with periosteum, they all produce rapid compensatory response by their specific skeletal unit ► All periosteal functional matrix act homologously usually by means of process of osseous deposition and resorption and such a growth is termed as transformative growth ► Almost all experimental studies like vital staining, intra osseous implants, histologic sections are capable of demonstrating the activity of only periosteal matrix www.indiandentalacademy.com
Insertion of tendon into bone
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â–ş But
when observing rapid volumetric changes of first neural and later facial skull, we are forced to accept that no possible combinations of periosteal apposition and resorption could account for either rapidity or magnitude of such growth â–ş The resolution of this seemingly perplexity was achieved when full implications of capsular functional matrix was realized
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Cranial capsules ► All
functional cranial components ie, skeletal units and functional matrix arise, grow, operate and are maintained within a series of cranial capsules ► Cranial components comprising neural region exist within neurocranial capsule, while facial region lie within orofacial capsule. ► Similarly orbital and otic capsule exists www.indiandentalacademy.com
Neurocranial and orofacial capsule
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Capsular matrix ► Both
neurocranial and orofacial capsule act to surround and protect their respective capsular matrices ► Neurocranial matrix is formed by brain, the leptomeninges and importantly cerebrospinal fluid. NCM is identical with volume of neural mass ► similarly orofacial capsule is identical with the volume of functional space of oro-nasopharyngeal cavities www.indiandentalacademy.com
â–ş When
the capsular matrix grows, the capsule expands by mitotic activity of capsular connective tissue, along with its contents that include periosteal matrix and its specific skeletal units, so there is passive and secondary translation in space â–ş It is important to note that unlike growth due to periosteal matrix, such translation occurs without necessity of selective periosteal deposition and resorption and such a growth is termed as translative growth www.indiandentalacademy.com
Translational growth ► It
Transformative growth
is caused by capsular matrix ► It is passive secondary translation in space due to volumetric increase of capsular matrix ► It does not involve osseous resorption and deposition
► It
is caused by periosteal matrix ► It is the compensatory response of periosteal matrix to translation in space ► It involves the process of deposition and resorption
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► It
is possible to demonstrate and differentiate the morphogenetic effect of capsular and periosteal matrix in a clinical material ► Longitudinal series of lateral cephalograms are taken and traced. Position of cranial base, mandibular outline, mental foramen and mandibular foramen and inferior alveolar canal are traced ► It is assumed that anterior cranial base is constant in its size and position and that mental foramen position does not change within mandible ► First and last tracings of a series are taken and superimposed www.indiandentalacademy.com
► The
two i.e., first and last tracings are superimposed on the anterior cranial base ► We observe total growth change of mandible ► It is termed and interosseous growth
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► Second
composite tracing is done by registering two mandibular outline on mental foramen ► We now observe changes in size and shape of various mandibular skeletal units ► This is termed intraosseous growth ► It is independent of the spatial position of same units with time www.indiandentalacademy.com
â–ş Third
tracing is made by superimposition of previous two tracings on the outline of the older/larger mandible â–ş We observe two distinct positions of the smaller mandible
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Translative growth â–ş The
distance between two identical earlier tracings represents the passive translative growth, that would have occurred if only capsular growth occurred
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Transformative growth â–ş However
periosteal matrix alterations have occurred and the net effect of these changes is indicated by difference between lowermost of smaller mandible and larger mandible â–ş As is seen, some of these changes are additive and some subtractive
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Neurocranial capsule â–ş The
composition of this capsule in adult is easily stated as 5 layers of scalp, then bone and double layered duramater â–ş The calvarium consists of a no. contiguous skeletal unit- the outer table, inner table, diploic space and the sinuses. each microskeletal unit has its specific periosteal matrix like muscles, vessels www.indiandentalacademy.com
Neurocranial capsule and neurocranial matrix
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Growth of calvarium â–ş Neural
mass is the capsular matrix and they are surrounded by the mesenchymal neurocranial capsule. It is with in this capsule lies several primary ossification centers for the membranous calvarial bones and chondrification centre for cartilages â–ş Neurocranial capsule encloses the neural mass and expansion of this neurocranial matrix is the primary event in expansion of neurocranial capsule. www.indiandentalacademy.com
► There
is a genetically determined volumetric growth of the entire neural mass ► The magnitude of this growth is not influenced by form of the capsule although direction of it is influenced by several environmental factors, among which degree of cranial base flexure, mode of attachment of several organized dural fibrous tracts are prominent ones ► The primary growth of neural mass causes secondary expansion of surrounding capsule as a whole. ► It is self evident that all portions within the capsule are similarly affected. www.indiandentalacademy.com
â–ş Any
and all embedded functional cranial components are passively translated in space, i.e. neurocranial functional matrix along with related skeletal components quite literally are moved in space â–ş Even though this process does not need osseous deposition/resorption it is quite true that embedded skeletal units are simultaneously altering its form by active transformative osseous growth processes. â–ş This apposition and resorption represents response of these skeletal units to constantly altering demands of their respective functional periosteal matrix which themselves also undergoing passive spatial translation www.indiandentalacademy.com
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Hydrocephaly It is only when we examine these pathologic, or experimentally produced, situations in which periosteal matrices have been prevented from exerting their morphogenetic activity that we can observe clearly the passive, translative growth produced by the capsular matrices. ► In the neurocranium, hydrocephaly is such a condition. The expansion of the neurocranial capsule is always proportional to the increase in neural mass. ► But this same increase in intracranial pressure effectively obliterates vascular flow within the capsule and so prevents periosteal accretion of bone at sutural areas, thus producing the characteristic excessively large fontanelles and other sutural dehiscences. ►
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Hydrocephaly
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Fetal Skull
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Orofacial functional matrix ► Embryologically
there is a phase where is no orofacial functioning space yet in being. ► At about 25th day after fertilization there is a deep cleft between heart and overhanging forebrain, maxillary process springs from proximal border of 1st arch. Along with mandibular process it completes lateral boundary of oral pit ► Although oro-naso-pharyngeal space functioning space comes into being under genetic (intrinsic ) control, its subsequent growth and maintenance in being are functionally (extrinsic/ environment ) determined. www.indiandentalacademy.com
► These
3 oro-naso-pharyngeal fn spaces or rather unitary space are not haphazardly left over as it were when facial bones, muscles, glands, vessels, nerves finished their growth. ► The functional reality of respiratory and digestive system is their patency and volume of that patency is related to general metabolic demands of body as a whole ► Oral and pharyngeal regions have primary fn in maintaining patent airway. www.indiandentalacademy.com
► Bosma
AJO 1963 proposed that head and neck posture develops in relation to pharyngeal airway. ► Initial postural achievements of newborn infants are those involved in stabilization of pharyngeal airway and neck posture progressively develops upon this performance base ► The relevance of this mechanism of pharyngeal airway maintenance to orthodontist is that this mechanism is a principal determinant of antero posterior relationship between tongue tip and incisors. ► At a given moment mandibular position is relevant to both head and neck posture and pharyngeal airway www.indiandentalacademy.com
Orofacial capsule ► The
orofacial functional matrix i.e., oro-nasopharyngeal functional spaces is surrounded by orofacial capsule. The layers of this capsule are skin externally and mucous membrane internally ► Totally embedded within this capsule lie number of orofacial functional cranial components – periosteal matrix and their respective skeletal unit ► Growth of all skeletal structures in the orofacial region is a combination of two kinds of growth processes – periosteal and capsular i.e., transformative and translative growth respectively www.indiandentalacademy.com
Functional cranial analysis of human maxilla â–ş Many
osteology books fail totally to give any understanding of how maxilla participates in several relatively independent functions to which it is associated â–ş Functional point of view there is no such entity as maxilla rather we have a bone composed of several relatively independent functioning skeletal units that are associated with functions like vision, respiration, digestion, speech and protection of neurovascular structures www.indiandentalacademy.com
Osteologic maxilla
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Functional components of maxilla The microskeletal units of maxilla are ► Basal unit ► Orbital unit ► Nasal unit ► Alveolar unit
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Basal skeletal unit ► The
associated periosteal functional matrix is the neurovascular triad of which maxillary division of trigeminal nerve plays a major role ► The infraorbital foramen is the first ossification centre of human maxillary bone ► Moss and Greenberg AO 1967 studied basal bone of maxilla and showed the constancy of infraorbital canal relative to cranial base and spatial stability of IO foramen to other maxillary components so that it permits analysis of intramaxillary growth changes www.indiandentalacademy.com
► This
Nasal skeletal unit
comprises of lateral wall of the nose and its floor, and concerned with function of respiration ► Functional matrix associated with it is functional space of nasal cavity ► This matrix descends downward and increases in height. This is completed at the end of first decade of life
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Alveolar skeletal unit ► This
comprises that part of maxilla that surrounds the teeth ► The associated functional matrix of it includes the teeth ► As noted previously orthodontists work with this matrix and corresponding changes occurs in this skeletal unit ► Also evident is resorption of alveolar bone in long extracted sites www.indiandentalacademy.com
Orbital skeletal unit ► This
is the part of maxilla that forms the floor of the orbit ► The functional matrix of this unit obviously being the orbit and associated with function of vision ► Witnal has reported that this matrix reaches its adult size by 7 yrs so spatial relocation is completed by that time www.indiandentalacademy.com
â–ş In
maxilla as several splachnocranial matrix expand, maxilla would tend to be carried away from adjacent bones. â–ş The actual growth observed as in orbital floor e.g., is secondary and compensatory for such vertical lowering so that orbital cavity is not unduly expanded in this passive manner www.indiandentalacademy.com
Functional cranial analysis of mandible ► Similar
to maxilla, mandible is also a composite of several relatively independent functional cranial components ► Skeletal units corresponding to mandibular functional components includes ► Alveolar process ► Coronoid process ► Condylar process ► Angular process ► body ► chin www.indiandentalacademy.com
Formal osteologic Mandible
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Skeletal units and its corresponding functional matrix â–ş Alveolar
process - as in maxilla, teeth are the functional matrix of this process .It is evident from edentulous mandible that also looses its alveolar process along with the teeth as they are lost www.indiandentalacademy.com
â–ş Coronoid
process temporalis muscle inserted to it forms the periosteal matrix of this process. â–ş This is evident from myosection or cutting the nerve to temporalis causes regenerative changes only in the coronoid process www.indiandentalacademy.com
Effect of unilateral temporalis muscle resection in rats
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â–ş Body
– the functional matrix of body of mandible is the inferior alveolar neurovascular bundle
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â–ş Angular
process - the periosteal matrix of this process includes the pterygomandibular sling comprising of masseter laterally and medial pterygoid medially www.indiandentalacademy.com
Masseter and medial pterygoid muscle
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â–ş It
is critical to grasp the significance of real independence of each unit â–ş Any alteration in one unit causes changes in its specific skeletal unit alone â–ş So bilateral removal of condylar process causes lack of functional temporomandibular joint with loss of length of condylar process alone, making mandible suspended by muscles as hyoid bone but does not cause any regressive change in other skeletal units of mandible www.indiandentalacademy.com
Case report of bilateral condylectomy by Moss in A O 1969
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Applying the concepts of FMH 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 ► The growth of the orofacial matrix is that which furnish the primary morphogenetic force for facial skeletal growth ► Primary growth of this matrix causes the orofacial capsule to expand secondarily outward, downward and laterally www.indiandentalacademy.com
► Each
of the individual skeletal units is passively translated ► Also each of skeletal units also grow in response to altering spatial and functional demands of its functional matrix ► Direction of the skeletal growth has no correlation to direction of passive translation ► Normally mandible passively translates downward with expansion of orofacial matrix, such movement would disarticulate the TMJ if there was not a secondary compensatory growth of condylar cartilage www.indiandentalacademy.com
Constraints of the FMH â–ş Initially,
the FMH provided only qualitative narrative descriptions of the biologic dynamics of cephalic growth, at the gross anatomic level, and it had hierarchical explanatory constraint
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Hierarchical constraint
â–ş Descriptions
did not extend "downward" to processes at the cellular, subcellular, or molecular structural domains, or extend "upwards" to the multicellular processes by which bone tissues respond to lower level signals. All prior FMH versions were "suspended" or "sandwiched" as it were, between these two hierarchical levels. â–ş Explicitly, the FMH could not describe either how extrinsic, epigenetic FM stimuli are transduced into regulatory signals by individual bone cells, or how individual cells communicate to produce coordinated multicellular responses. www.indiandentalacademy.com
â–ş At
the lower cellular or molecular levels, another problem exists. Almost uniformly, experimental and theoretical studies of bone adaptation consider only the unicellular, or unigenomic levels. Accordingly, their results and derivative hypotheses generally are not extensible to higher multicellular, tissue, levels. â–ş the FMH could not describe either how extrinsic, epigenetic FM stimuli are transduced into regulatory signals by individual bone cells, or how individual cells communicate to produce coordinated multicellular responses. â–ş Consequently, in prior FMH versions, significant disjunctions exist between the descriptions at each of the several levels of bone organization. www.indiandentalacademy.com
Mechanosensing processes â–ş Mechanosensing
processes enable a cell to sense and to respond to extrinsic loadings, a widespread biologic attribute, by using the processes of mechanoreception and of mechanotransduction. â–ş Mechanoreception - transmits an extracellular physical stimulus into a receptor cell; â–ş Mechanotransduction - transduces or transforms the stimulus's energetic and/or informational content into an intracellular signal. www.indiandentalacademy.com
Osseous mechanotransduction ► Osseous
mechanotransduction is unique in four ways: ► (1) Most other mechanosensory cells are cytologically specialized ► (2) one bone-loading stimulus can evoke three adaptational responses ► (3) osseous signal transmission is aneural ► (4) the evoked bone adaptational responses are confined within each "bone organ" independently, e.g., within a femur, so there is no necessary "interbone" or organismal involvement. www.indiandentalacademy.com
â–ş This
process translates the information content of a periosteal functional matrix stimulus into a skeletal unit cell signal, for example, it moves information hierarchically downward to the osteocytes. There are two, possibly complementary, skeletal cellular mechanotransductive processes: â–ş ionic and â–ş mechanical.
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Ionic or electrical processes. â–ş This
involves some processes of ionic transport through the bone cell (osteocytic) plasma membrane. There is a subsequent intercellular transmission of the created ionic or electrical signals that, in turn, are computed by the operation of an osseous connected cellular network (CCN) â–ş These processes can be any one or possible combination of the following www.indiandentalacademy.com
Stretch-activated channels â–ş Several
types of deformation may occur in strained bone tissue. One of these involves the plasma membrane stretch-activated (S-A) ion channels, a structure also found in bone cells, and significantly in fibroblasts. When activated in strained osteocytes, they permit passage of a certain sized ion or set of ions, including K+, Ca2+, Na+ etc â–ş Such ionic flow may, in turn, initiate intracellular electrical events, for example, bone cell S-A channels may modulate membrane potential as well as Ca2+ ion flux www.indiandentalacademy.com
Electrical processes â–ş These
includes many nonspecific mechanotransductive processes â–ş 1. Electromechanical. The osteocytic plasma membrane contains voltage-activated ion channels, and transmembrane ion flow may be a significant osseous mechanotransductive process. It is also possible that such ionic flows generate osteocytic action potentials capable of transmission through gap junctions. www.indiandentalacademy.com
Electrokinetic. Bound and unbound electric charges exist in bone tissue, many associated with the bone fluid(s) in the several osseous spaces or compartments. ► Electrical effects in fluid-filled bone are not piezoelectric, but rather of electrokinetic, that is, streaming potential (SP) origin. ► The SP is a measure of the straingenerated potential (SGP) of convected electric charges in the fluid flow of deformed bone. The usually observed SPG of ±2 mV can initiate both osteogenesis and osteocytic action potential ► 2.
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Electric field strength. Bone responds to exogenous electrical fields. ► Field strength may play an important role. A significant parallel exists between the parameters of these exogenous electrical fields and the endogenous fields produced by muscle activity. ► Bone responds to exogenous electrical fields in an effective range of 1 - 10 µV/cm, strengths that are on the order of those endogenously produced in bone tissue during normal muscle activity ► 3.
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Mechanical processes â–ş Mechanical
transductive process discussed later does not initiate action potentials, it is an alternative means by which periosteal functional matrix activity may regulate hierarchically lower level bone cell genomic functions. â–ş A series of extracellular macromolecular mechanical levers exist, capable of transmitting information from the strained matrix to the bone cell nuclear membrane. â–ş The basis of this mechanism is the physical continuity of the transmembrane molecule integrin www.indiandentalacademy.com
â–ş Integrin:
This molecule is connected extracellularly with the macromolecular collagen of the organic matrix and intracellularly with the cytoskekeletal actin. â–ş Actin, in turn, are connected to the nuclear membrane, at which site the action of the mechanical lever chain initiates a subsequent series of intranuclear processes regulatory of genomic activity. www.indiandentalacademy.com
Integrins attached to actins and intermediate filaments
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â–ş It
is suggested that such a cytoskeletal lever chain, connecting to the nuclear membrane, can provide a physical stimulus able to activate the osteocytic genome, possibly by first stimulating the activity of such components as the c-fos genes. â–ş It is by such an interconnected physical chain of molecular levers that periosteal functional matrix activity may regulate the genomic activity of its strained skeletal unit bone cells, including their phenotypic expression. www.indiandentalacademy.com
Bone as osseous connected cellular network
â–ş All
bone cells, except osteoclasts, are extensively interconnected by gap junctions that form an osseous CCN. In these junctions, connexin 43 is the major protein. â–ş Each osteocyte, enclosed within its mineralized lacuna, has many as 80 cytoplasmic (canalicular) processes, arrayed three-dimensionally, that interconnect with similar processes of up to 12 neighboring cells. These processes lie within mineralized bone matrix channels (canaliculi) www.indiandentalacademy.com
Osteocyte with three dimensional array of canalicular process
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► Gap
junctions are found where the plasma membranes of a pair of markedly overlapping canalicular processes meet. ► In compact bone, the canaliculi cross "cement lines," and they form extensive communications between osteons and interstitial regions. ► Gap junctions also connect superficial osteocytes to periosteal and endosteal osteoblasts. All osteoblasts are similarly interconnected laterally. www.indiandentalacademy.com
Gap junctions and connexons
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► Vertically,
gap junctions connect periosteal osteoblasts with preosteoblastic cells, and these, in turn, are similarly interconnected. ► Effectively, each CCN is a true syncytium, they allow both electrical and fluorescent dye transmission ► They permit bidirectional transport ► In a very real sense, bone tissue is "hard-wired” www.indiandentalacademy.com
Gap junctions - true syncytium
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Mechanism of conduction â–ş Mechanotransductively
activated bone cells, e.g., osteocytes, can initiate membrane action potentials capable of transmission through gap junctions. â–ş The ionic signals rather than secondary messengers is suggested here, because, although bone cell transduction may also produce secondary messengers that can pass through gap junctions, the time-course of mechanosensory processes is believed to be too rapid for the involvement of secondary messengers. www.indiandentalacademy.com
► CCN
is analogous to "artificial neural network" ► It processes, in a multiprocessor network mode, the intercellular signals created by an electrical type of mechanotransduction of periosteal functional matrix stimuli. ► Subsequently the computed network output informational signals move hierarchically "upward" to regulate the skeletal unit adaptational responses of the osteoblasts.
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â–ş In
The network theory
network theory, these cells are organized into "layers": an initial input, a final output, and one or more intermediate or "hidden" layers. â–ş Regardless of the actual physiological stipulatory process, each cell in any layer may simultaneously receive several "weighted" inputs (stimuli) â–ş In the initial layer, these represent the loadings. Within each cell independently, all the weighted inputs are then summed. www.indiandentalacademy.com
â–ş This
sum is then compared, within the cell, against some threshold value. If this value is exceeded, an intracellular signal is generated, i.e., successful mechanotransduction occurs â–ş This signal is then transmitted identically to all the "hidden" layer cells (adjacent osteocytes) to which each initial layer cell is connected â–ş Next, similar processes of weighted signal summation, comparison, and transmission occur in these intermediate layers until the final layer cells (osteoblasts) are reached. www.indiandentalacademy.com
â–ş The
outputs of these anatomically superficial cells determines the site, rate, direction, magnitude, and duration of the specific adaptive response, i.e., deposition, resorption, and/or maintenance, of each cohort of osteoblasts. â–ş Information is not stored discretely in a CCN, rather it is distributed across all or part of the network, and several types of information may be stored simultaneously. www.indiandentalacademy.com
► state
of a CCN is a property of the state of all its cells and of all their connections. ► This assures that the network is fault or error tolerant, i.e., one or several inoperative cells causes little or no noticeable loss in network operations ► The morphogenetic primacy of periosteal functional matrices on their skeletal units is consensually accepted. ► As a muscular demand alters, e.g.,, exercise, hypertrophy, atrophy, augmentation, or repositioning, the triad of active bone growth processes correspondingly adapts the form of its specifically related skeletal unit. www.indiandentalacademy.com
â–şA
classic example is the regulation of coronoid process form by the temporalis muscle. â–ş The tension in the tendon of this contracted muscle, transmitted through intertwined periosteal fibers inserted into subjacent bone, deforms the loaded skeletal unit. â–ş Although some periosteal osteoblasts may be directly stimulated, extant data suggest osteocytic primacy in mechanosensory processes. www.indiandentalacademy.com
â–ş Anatomically,
bone cells are competent mechanoreceptors. â–ş Their three-dimensional array of extensive canalicular cell processes is architecturally well-suited to sense deformation of the mineralized matrix. â–ş Although no one mechanical parameter reliably predicts all bone adaptational or remodeling responses, strain probably plays the primary role and is a competent stimulus www.indiandentalacademy.com
► The
Strain attributes
significant strain attribute may vary with specific conditions. These include: ► (a) loading category - bone responds best to dynamic rather static loading ► (b) frequency - osteocytes may be physiologically "tuned" to the frequencies of muscle function analogous to those of specialized nonosseous sensory cells, e.g., auditory hair cells; ► (c) magnitude - relatively small microstrains (about 10-6), and strain magnitudes of 2000 ± 1000 are morphogenetically competent. www.indiandentalacademy.com
► Skeletal
muscle contraction is a typical periosteal functional matrix loading event, and frequency is one of its critical parameters. ► Although the fundamental frequency of contracting muscle is about 2 Hz, other strain-related harmonics of 15 to 40 Hz exist. ► Of particular significance to the FMH is the close similarity of muscle stimulus frequencies to bone tissue response frequencies. www.indiandentalacademy.com
â–ş These
factors strongly suggest a rather precise matching of significant operational characteristics between a contracting skeletal muscle stimulus and the ability of loaded bone cells to transduce this into signals capable of regulating their adaptive responses. â–ş In a phrase, bone appears to be closely "tuned" to skeletal muscle, i.e., skeletal units are tuned to their periosteal functional matrices. www.indiandentalacademy.com
Objections to functional matrix ► The
force exerted by neural mass is same on cranium and cranial base, but little change of base is seen as response to it. So growth of chondrocranial growth could be independent of functional stimulus ► Differential air pressure may be the activating force for expansion of the space but Moss considers it due to mitosis of connective tissues. ► According to Frankel these functional spaces do not constitute a dynamic factor and a space can increase resulting from the forces from within (neural mass), outside (air pressure) www.indiandentalacademy.com
Conclusion â–ş The
theories of ontogeny and phylogeny currently are being significantly reinvigorated by the new and evolving sciences of complexity that integrate topics from mathematics, biology and physics, while minimizing distinctions between them. Because epigenetic processes and mechanisms are best explained as examples of Complexity theory, a clear-cut demonstration of the role of CT in craniofacial ontogeny, at some point, is both necessary and possible. www.indiandentalacademy.com
â–ş Complexity
theory provides description of the behavior of complex biological systems that exists as ensembles of several tissues and organs and not as clusters of individual cells and extracellular substances â–ş Such an ensemble (identical to a functional cranial component in the FMH) is termed here as a complex adaptive system (CAS), structurally arrayed as a vital continuum
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â–ş The
operation of complexity can be suggested as follows. "Environmental factors thus play a decisive role in all ontogenetic processes. But it is the organism itself that, as an integrated system, dictates the nature of each and every developmental response .The living organism self-organizes on the basis of its own internal structuring, in continuous interaction with the environment in which it finds itself www.indiandentalacademy.com
References
1. Moss ML, Salentijn L. The primary role of the functional matrices in facial growth. Am J Orthod 1969;55:566-77. 2. Moss ML, Salentijn L. The capsular matrix. Am J Orthod 1969;56:474-90. 3. Moss ML. The functional matrix hypothesis revisited. 1. The role of mechanotransduction. Am J Orthod Dentofac Orthop 1997;111:8-11. 4. Moss ML. The functional matrix hypothesis revisited. 2. The role of an osseous connected cellular network. Am J Orthod Dentofac Orthop 1997;112:221-6. www.indiandentalacademy.com
5. Moss ML. The functional matrix hypothesis revisited. 3. The genomic thesis. Am J Orthod Dentofac Orthop 1997; 221-6 6. Moss ML. The functional matrix hypothesis revisited. 4. The epigenetic antithesis and resolving antithesis. Am J Orthod Dentofac Orthop 1997;410-7 7. Moss ML. Genetics, epigenetics and causation. Am J Orthod 1981;80:366-75 8. Moss ML, Rankow R. The role of the functional matrix in mandibular growth. Angle Orthod 1968;38:95-103. www.indiandentalacademy.com
9.Moss, M. L., and Greenberg, S.: Functional cranial analysis of the human maxillary bone. 1. Basal bone, Angle Orthodontist 37: 151-164, 1967. 10. Koski K. Cranial growth centers: facts or fallacies? AM J Orthodontics 1968;54:566-81. 11. Moss ML. Twenty years of functional cranial analysis. Am J Orthod 1972;61:479-85. 12. Bosma, J. F.: Maturation of function of the oral and pharyngeal region, AM. J. Orthodontics 49: 94-100, 1963. www.indiandentalacademy.com
13.Sarnat, B G.: postnatal growth of upper face: some experimental considerations A O 1963;33:139-161 14.Watnabe M, Laskin DM, Brodie AG: effect of autotransplantation of growth of zygomaticomaxillary suture. Am J of Anat 1957; 100:319-329
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