Concepts of Growth & Development PDF

Concepts Of Growth & Development Nayanika Priyam I year Post Graduate Contents Introduction Components of Growth: - Growth Mechanism - Growth Pattern & Variability - Growth Timing M...

Concepts Of Growth & Development Nayanika Priyam I year Post Graduate Contents Introduction Components of Growth: - Growth Mechanism - Growth Pattern & Variability - Growth Timing Mechanisms of growth: - Growth processes - Growth fields - Growth movements Concepts and hypotheses of craniofacial growth Conclusion Introduction Growth Growth is a general term implying that something changes in magnitude Growth refers to increase in size” - Todd “Growth may be defined as the normal change in the amount of living substance”- Moyers “Growth usually refers to an increase in size and number” – Proffit “Change in any morphological parameter which is measurable”- Moss “Self multiplication of living substance”- J.S.Huxley  – Development is a progress towards Development maturity” – Todd – “Development refers to all naturally occurring progressive, unidirectional, sequential changes in the life of an individual from it’s existence as a single cell to it’s elaboration as a multifunctional unit terminating in death” – Moyers – “Development connotes a maturational process involving progressive differentiation at the cellular and tissue levels” – Enlow  Major Themes of Development Changing complexity Shifts from competent to fixation Shifts from dependent to independent Ubiquity of genetic control modulated by environment  Changing Complexity Takes place at all level of organization from the sub-cellular to the whole organism Normally complexity increases with development. Most complex period of developing dentition is transition of dentitions.  Shifts from competent to fixation Undifferentiated cells once differentiated become fixed. Shifts from dependent to independent Development brings greater independence at most levels of organization.  Ubiquity of genetic control modulated by environment Genetic control of development is constantly being modified by environmental interactions  Growth Growth is largely an anatomic and phenomenon and quantitative in nature. Development Development is a physiologic and behavioral phenomenon and qualitative in nature. The two processes rely on each other and under the influence of the morphogenetic pattern, “the three fold process”- self multiplication, differentiation and organization, time being the fourth dimension. Components of Growth  Craniofacial growth may be divided into: growth mechanism growth pattern growth timing  Growth Mechanism  At the cellular level, there are three possibilities for growth: Soft – Increase in the size of individual cells : hypertrophy Tissues – Increase in the number of cells : hyperplasia – Secretion of extracellular material Hyperplasia is the main mechanism hypertrophy occurring secondarily Secretion of extracellular material also contributes to growth in soft tissues and uncalcified cartilage But different for hard tissue growth as it does not mineralize  Tissue growth generally connotes an Bone increase in size. Growth Bone cannot enlarge by proliferation and/or hypertrophy of existing cells or intercellular material because of its calcified, rigid nature. Therefore, the calcification process compels bone to grow by specifically adapted growth mechanisms which do not involve interstitial expansion: -Intramembranous -Endochondral  Undifferentiated cells in a connective tissue Intra- membrane form a cluster membranous Bone Primary center of ossification – small spicules of bone are formed (Site of initial ossification) Formation Osteoblasts form organic matrix - subsequently ossifies Meshwork of delicate bony trabeculae Formation of osteoid which rapidly calcifies  Hypertrophy of chondrocytes and matrix calcifies Endochondral Bone Cells degenerate Formation Invasion of blood vessels and connective tissue cells. Osteoblasts differentiate and produce osteoid tissue. Osteogenic tissues replace degenerating cartilage. Osteoblastic tissue calcifies.  Primary cartilage- local factors do not influence as there is a cartilagenous matrix Ex: spheno-occipital synchondrosis, nasal septal cartilage Secondary cartilage- local factors do influence and modulate growth Ex: Condylar and Coronoid cartilage  Growth Deposition: Addition of new Processes bone Resorption: Removal of bone The surface facing toward the direction of progressive growth receives new bone deposition (+). The surface facing away undergoes resorption(-) Direction Of Growth Growth Fields Outer and inner surfaces of a bone blanketed by a mosaic-like pattern of "growth fields“ Either depository or resorptive activity: If a periosteal growth field is resorptive, the opposing endosteal field is depository and vice versa These combinations produce the drift of all parts of an entire bone.  The irregularity is a response to the varied functions imposed on the bone by various attachments. The operation of the growth fields is carried out by membranes surrounding the hard tissue. The various depository and resorptive fields do not have the same rate of activity. The growth movement of the bone follows the pace setting movement of the overall growth field.  It is important to understand the plan of distribution of the major growth fields as these patterns can show us if we are working with or against growth. Ex. Distalization of maxillary molars putting them into a depository field or labial placement of lower anteriors into a resorptive field. Variations in the facial structure can be due to a change in- -Pattern of the fields. -Placement of the boundaries. -Rates and amounts of deposition and resorption. -Timing of growth activity among different fields.  Growth Site Growth Center Growth fields having special According to Baume growth role in the growth of the center can be described as particular bone are called ‘Places of endochondral growth sites ossification with tissue Areas of periosteal/ sutural separation force’ bone formation Force, energy or motor for - mandibular condyle bone growth (tissue - maxillary tuberosity separating capacity) resides - synchondroses of the primarily within its growth basicranium center - sutures Areas of primary - the alveolar process cartilaginous/ endochondral ossification A growth site is merely a location where growth occurs Center is a location where independent growth occurs All centers of growth are also sites, but the reverse is not true  The basic phenomena involved in the growth mechanisms: Conversion of cartilage - synchondroses - nasal septal cartilage - condylar cartilage Sutural deposition Periosteal remodeling Synchondroses Temporary bands of cartilage at the junction of bones of endochondral origin Regarded as growth center & pacemaker of cranial base Only a few persist postnatally in the midline of basicranium Spheno-occipital synchondrosis Inter-sphenoidal synchondrosis Spheno-ethmoidal synchondrosis  Nasal Septal Plays an important role in the prenatal and very early postnatal growth of the middle face Cartilage According to Scott, the septal cartilage occupies a unique location for pushing the whole maxilla forward and downward But functional matrix by Moss, suggests that the nasal septal cartilage is a locus of secondary, compensatory, and mechanical growth for a prior passive displacement of the midfacial bones Condylar Secondary cartilage- participates in growth Cartilage early in human life and absorbs pressure forces later in life The condyle and its cartilage participate in regional adaptive growth; the condyle has a great capacity to adapt to mandibular displacement during growth Thus not a major growth center for the whole mandible Sutures Displacement growth is made possible by the craniofacial sutures Ossifies when cranial growth ceases The main biologic function of the sutural tissue: – To unite bones -allows minor movement – To act as areas of growth – To absorb mechanical stress -protecting the osteogenic tissues of the bone There are two schools of thought regarding the growth at sutures: Sutures are 3 layered structures having two bones separated by a single layer of connective tissue. The connective tissue layer acts as the proliferating zone. Implies tissue separating forces in the sutural tissue. Sutures are 5 layered with the 2 bones on either side having 2 layers of periosteum with a 5th intervening connective tissue layer. The role of this fifth layer is seen in allowing for slight adjustments between the bones during growth, while the active proliferating role is played by the cambial layers of the periosteums of each bone. Periosteum Considered an osteogenic zone The influence of the periosteum is of greatest significance for the change in size and shape of the bones Matrix-producing and proliferating cells are subject to mechanical influence; If the pressure exceeds a certain threshold level, osteogenesis ceases and osteoclasts appear leading to resorption but if exposed to tension, it responds with bone deposition Growth Growth pattern refers to the change in the size and shape of the bone. Pattern Bone grows by two fundamental physiologic processes: - Modeling - Remodeling  Modeling According to Roberts et al-modeling and remodeling are 2 distinct phenomena. In bone modeling independent sites of resorption and formation change the form (shape, size or both) of a bone. Bone remodeling is a specific, coupled sequence of resorption and formation occurring to replace previously existing bone.  Bone modeling is the dominant process of facial growth and adaptation to applied loads such as headgears, rapid palatal expansion, and functional appliances. Modeling changes can be seen on cephalometric tracings. Remodeling changes are apparent only at microscopic level. The mechanism for internal remodeling of dense compact bone is through axially oriented cutting and filling cones.  It is a differential growth activity Remodeling involving deposition at one end and resorption at the other Basic part of the growth process. A bone remodels during growth because its regional parts move ("drift“) from one location to another as the whole bone enlarges. Relocation Progressive and sequential movement of component parts as a bone enlarges Relocation is the basis for remodeling. The mandibular ramus moves progressively posteriorly by remodeling; Resorption in the anterior border and deposition in the posterior border The whole ramus is thus relocated posteriorly, and the posterior part of the lengthening corpus becomes relocated into the area previously occupied by the ramus  In the maxilla, the palate grows downward by periosteal resorption on the nasal side and periosteal deposition on the oral side.  Types of 1.Biochemical remodeling: molecular level- Remodeling: maintains calcium levels 2.Secondary remodeling: by Haversian systems and rebuilding of cancellous bone 3.Pathologic remodeling: occurs after disease or trauma 4.Growth remodeling Functions of 1. Sequentially relocate each component of the whole bone Remodeling 2. Progressively change the shape of the bone to accommodate its various functions 3. Progressively change the size of whole bone 4. Progressive fine tune fitting of all the separate bones to each other and to their contiguous growing, functioning soft tissues. 5. Carry out continuous structural adjustments to adapt to the intrinsic and extrinsic changes in conditions.  Enlow’s V-principle One of the basic concepts in facial growth Many facial and cranial bones, or parts of bones, have a V-shaped configuration Bone deposition occurs on the inner surface of the "V“ and resorption takes place on the outer surface The direction of movement is toward the wide end of the "V"  Example with V oriented vertically and horizontally When bone is deposited on lingual side of coronoid process, growth proceeds and this part of the ramus increases in vertical dimension.  These deposits also produce a posterior direction of growth movement of the coronoid processes  V principle applied to the mandible causes increase in both posterior and superior directions  Causes an increase in the transverse dimension of the maxilla- Increases the airway space.  Growth Movements Two kinds of growth movements are seen during the enlargement of craniofacial bones: Cortical drift Displacement  Cortical Drift Drift includes both relocation and shifting of an enlarging portion of the bone by the remodeling action of its osteogenic tissues. The continuous remodeling maintains the shape and proportions of the bone throughout the growth period. As bone deposition occurs during a simultaneous breakdown of opposing bone surfaces, the bone will migrate in relation to a fixed structure. This migration through remodeling is known as drift.  As a general rule, the surface towards which growth occurs is appositional, whereas the surface facing away from the direction of growth is resorptive The two processes do not always occur with the same intensity. Rather, appositional activity normally exceeds resorption during the growth period Due to new bone deposition on one surface, all other parts of the structure will undergo shifts in relative position, a movement that is termed relocation. As a result of this process, further adaptive bone remodeling has to take place, to adjust shape and size of the bone to its new position. An example of such passive drift in the facial region is the hard palate, which subsides in relation to the overlying structures, due to resorption of the nasal floor and concomitant deposition on the roof of the palate. Relocation and structural remodeling thus are closely related to each other.  Displacement Displacement is a physical movement of the whole bone as a single unit Articulations are areas ‘away’ from which the displacement movements occur as the bone enlarges. Amount of enlargement equals extent of displacement. Two types of displacements: - Primary - Secondary  Primary Displacement As a bone grows by surface deposition, it is simultaneously carried away from other bones in direct contact with it. This creates the "space" within which bony enlargement takes place The new bone deposition does not cause displacement by pushing against the articular contact surface of another bone; the bone is carried away by the expansive force of the growing soft tissues surrounding  Secondary Displacement Secondary displacement is the movement of a whole bone caused by the separate enlargement of other bones, which may be nearby or quite distant The secondary displacement is not associated with growth of the bone itself but initiated by enlargement of adjacent bones and soft structures and transferred to adjacent bones.  For example, increase in size of the bones of middle cranial fossa results in a marked displacement of the whole maxillary complex anteriorly and inferiorly This is independent of the growth and enlargement of the maxilla itself  In summary, the overall skeletal growth process (displacement and remodeling) carries out two general functions: It positions each bone It designs and constructs each bone and all of its regional parts to carry out that bone's multifunctional role.  “Domino effect” growth changes can be passed on from region to region having effect at a distant site. Growth Pattern and Variability Pattern Pattern represents proportionality-not just proportional relationships at a point in time but change in these relationships over time. Can be defined as-a set of constraints operating to preserve the integration of parts under varying conditions or through time. Cephalocaudal Gradient of Growth  The accomplishment of normal human proportions is not merely due to a general slowing down. Different tissues grow at different rates at different times. The overall pattern of growth is a reflection of the growth of the various tissues making up the organism.  Differential Growth Scammon’s curves for growth A graph for four major tissues of the body -lymphoid -neural -general -genital Predictability Predictability of growth pattern is a specific kind of proportionality that exists at a particular time and progresses towards another, at the next time frame with slight variations Any change in growth pattern would indicate some alterations in the expected changes in body proportions. Variability No two individuals with the exception of monozygotic twins are alike. Clinically important to identify if an individual is at the extreme of normal variation or is outside the range. What is normal? Normality Normality refers to that which is usually expected, is ordinarily seen or typical – Moyers Normality may not necessarily be ideal so rather than categorizing as normal or abnormal, deviations from the normal pattern is considered  Age Because of variability all individual at a given chronological age are neither Equivalence of the same size or same stage of maturation It is better to compare biologic development “Developmental ages” - skeletal age and dental age are used Timing  Growth Timing One of the factors for variability in growth Timing variations arise because biologic clock of different individuals is set differently Timing is largely genetically controlled -sex related differences -physical differences -environmental  Growth spurts Periods of sudden acceleration of growth Due to physiological alteration in hormonal secretion Timing-sex linked Normal spurts are Infantile spurt – at 3 years age Juvenile spurt – 7-8 years (females); 8-10 years (males) Pubertal spurt – 10-11 years(females); 15-18 years (males)  Changing Concepts and Hypothesis of Craniofacial Growth Remodeling theory Genetic theory Sutural dominance hypothesis Scott’s hypothesis Functional matrix hypothesis FMH revisited van Limborgh’s concept Servosystem hypothesis Growth Relativity hypothesis  Bone Remodeling Theory Brash (1930) According to the theory: Bone grows only by apposition at the surface. Growth of jaws takes place by deposition of bone at the posterior surfaces of the maxilla and mandible. This is described as Hunterian growth. Brash JC- The growth of the jaws and palate. In: The growth of jaws, normal and abnormal, in health and disease. London: The Dental Board of the United Kingdom, 1924a:23-66.  Increase in the size of the cranial vault occurs by periosteal deposition of bone on the ectocranial surface and resorption on endocranial surface Growth of the jaws takes place principally via deposition of bone on the posterior surface of the maxillary complex and mandibular ramus. Sutures and cartilages play no role in the growth of the craniofacial complex.  Schematic representation of the remodeling theory of craniofacial growth using the cranial vault as a model. Theories of Craniofacial Growth in the Postgenomic Era- DS Carlson; Semin Orthod Vol 11:172–183, December 2005  The Genetic Theory Brodie (1941) The genotype supplies all the information required for phenotypic expression - genes determine and control the process of craniofacial growth But the mechanism of action by the genetic unit and the mechanism by which the traits are transmitted were not understood until recently  The Sutural Hypothesis Harry Sicher and Joseph Weinmann (1947) According to this theory, sutures, cartilages and periosteum are responsible for facial growth and were assumed to be under intrinsic genetic control. “The primary event in sutural growth is the proliferation of the connective tissue between the two bones. If the sutural connective tissue proliferates, it creates the space for appositional growth at the borders of the two bones”.  Sicher and Weinmann explained that growth of nasomaxillary complex in a downward and forward direction is due to growth at sutures which attach the complex to cranium which are parallel and oblique Sutures: – Frontomaxillary – Zygomaticomaxillary – Zygomaticotemporal – Pterygopalatine  Cartilaginous Dominance Theory Proposed by James Scott in 1950 According to the theory: Intrinsic growth controlling factors are present in – Cartilage – Periosteum Sutures are only secondary and dependent on extrasutural influence  Cartilaginous parts of skull responsible for cranial growth Nasal septum a major contributor in maxillary growth Condyle determines growth of the mandible Cranium Cranial base Synchondroses Pacemakers/ Growth Centers Nasomaxillary Nasal septum Complex Mandible Condyle  Hunter & Enlow’s Growth Equivalence Important principle covering the development of the facial skeleton. As the individual components of the skull develop in different directions, they must interact directly in order to compensate for the various growth activities This is achieved by growth equivalents which act in opposing directions  Functional Matrix Hypothesis Melvin Moss based on original concept by Van der Klaaus (1969) “The functional matrix is primary and the presence, size, shape, spatial position and growth of any skeletal unit is secondary, compensatory, and mechanically obligated to changes in the size, shape, spatial position of its related functional matrix” (Moss, 1968) Two types of functional matrices: - Periosteal Matrix - Capsular Matrix  Periosteal Matrix Matrix related tissues that influence the bone directly through the periosteum – Muscles – Blood vessels and nerves lying in grooves or entering or exiting through foramina Affects a microskeletal unit- sphere of influence is usually limited to a part of one bone – Temporalis - coronoid process – Tooth - alveolar bone  Capsular Matrix Includes masses and spaces that are surrounded by capsules – Neural mass with scalp and dura – Orbital mass with supporting tissues of the eyes Affects macroskeletal units-several bones are simultaneously affected – Inner surface of calvarium Theories of Craniofacial Growth in the Postgenomic Era- DS Carlson; Semin Orthod Vol 11:172–183, December 2005  Neurotrophism Neurotrophism is a non impulsive, transmitive neurofunction involving axoplasmic transport providing for long term interaction between neurons and innervated tissue, which homeostatically regulates the morphological compositional and functional integrity of those tissues Types of neurotrophism: Neuromuscular Neuroepithelial Neurovisceral  The Functional Matrix Theory- Revisited Concept of Mechanotransduction Mechanotransduction signifies cellular signal transduction Process by which macromolecular extrinsic stimuli are converted into cellular signals, which can be internalized by a cell and processed so that a suitable adaptive response can be generated. The functional matrix hypothesis Revisited-The role of mechanotransduction by ML Moss in AJO-DO -Volume 112, No. 1; July 1997  Altered external environment Vital cells are perturbed Mechanoreceptors transmits an extracellular physical stimulus into a receptor cell Mechanotransduction – transduces or transforms the stimulus into an intracellular signal Intracellular activation of oseteocytes and osteoblasts  van Limborgh’s Compromise van Limborgh (1970) According to van Limborgh, craniofacial morphogenesis is controlled by five different factors: - Intrinsic genetic factors - local epigenetic factors - general epigenetic factors - local environmental factors - general environmental factors  Intrinsic genetic factors - Genetic factors inherent to the tissues - exerts influence within the cells in which contained - determine the characteristics of cells and tissues Local Epigenetic factors General - Genetically determined factors effective outside the cells and tissues in which produced  Local- originating from adjacent structures ; embryonic induction influences General- originating form distant structures; sex and growth hormones Local Environmental factors General - Non-genetically determined factors Local- muscle forces General- nutrition, oxygen supply  Chondrocranial growth is controlled by intrinsic genetic factors Desmocranial growth is controlled mainly by local epigenetic factors, also by local environmental factors General epigenetic and general environmental factors have very little role to play.  Servo-System/Cybernetics theory Alexandre Petrovic (1972) Growth of various craniofacial regions is the result of interaction of a series of causal changes and feedback mechanisms According to the theory: - control of primary cartilages takes a cybernetic form of “command” - control of secondary cartilages like condyle is comprised of both direct effect of cell multiplication and also indirect effects.  The physiologic effect of factors controlling the facial growth is not limited to simple commands but includes relays, implying interactions and feedback loops (Servosystem) as follows: Position of occlusal adjustment - peripheral 'comparator' Sagittal position of the upper dental arch- 'constant changing reference input’ controlled by somatotrophin and somatomedin and by growth of septal cartilage and tongue  Sagittal position of the lower dental arch- controlled variable Signals originating from the 'peripheral comparator' of the servosystem produce an increased postural activity of the lateral pterygoid muscle enabling the lower dental arch to adjust to the optimal occlusal position This increased muscle activity induces a posterior growth rotation of the mandible and supplementary growth of the condyle  Growth Relativity Hypothesis John C Voudouris and Kuftinec Mladen (2000) States that – “with orthopaedically displaced condyle, the bone architecture is influenced by the neuromusculature & the contiguous, non–muscular, viscoelastic tissues anchored to the glenoid fossa & the altered dynamics of the fluids enveloping bone” Foundations for Growth Relativity theory: -Displacement -Viscoelasticity -Referred force (transduction)  Mandibular advancement(displacement) Synovial fluid dynamics Influx of nutrients Engorged blood vessels Stretch of non – muscular viscoelastic tissues Transduction New bone formation Improved clinical use of Twin-block and Herbst as a result of viscoelastic tissue forces on the condyle and fossa in treatment and long–term retention: Growth relativity by John C Voudouris and Kuftinec Mladen in AJO-DO 2000 Mar;117:247-66  Conclusion Malocclusion and craniofacial deformity arise through variations in the normal developmental process Planned changes of bone growth and morphology are a fundamental basis of orthodontic treatment Thus knowledge of the basic concepts of craniofacial growth is essential for sound treatment planning and desired outcome  References Enlow D.H: Essentials of facial growth- 3rd Edition Gianelly A & Goldman H: Biologic basis of orthodontics-2nd Edition, 1971 Proffit W.R: Contemporary orthodontics-3rd Edition, 2000 Moyers R.E: Handbook of orthodontics- 4th Edition Koski K. Cranial growth centers: Facts or fallacies? ; AJO 1968 Vol 54: 566-583 Sridhar Premkumar: Textbook of Craniofacial Growth  T Rakosi, I Jonas, TM Graber: Orthodontic Diagnosis DS Carlson: Theories of Craniofacial Growth in the Postgenomic Era; Semin Orthod Vol 11:172–183,Dec 2005 ML Moss and L Salentijn: The functional matrix hypothesis Revisited- The role of mechanotransduction in AJO-DO-Volume 112, No. 1; July 1997 Brash JC- The growth of the jaws and palate. In: The growth of jaws, normal and abnormal, in health and disease. London: The Dental Board of the United Kingdom, 1924a:23-66  Improved clinical use of Twin-block and Herbst as a result of viscoelastic tissue forces on the condyle and fossa in treatment and long–term retention: Growth relativity by John C Voudouris and Kuftinec Mladen in AJO-DO 2000 Mar;117:247-66 Enlow D.H., Harris D.B.: A study of the postnatal growth of the human mandible. Am J Orthod. 1964; 50: 25-50. Thilander B.: Basic mechanisms in craniofacial growth. Acta Odontol Scand 1995; 53: 144-151. Concepts Of Growth & Development Nayanika Priyam I year Post Graduate