Growth and Development:Pre & Post natal development of CRANIUM& FACE

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“There must be a beginning on any great matter ,but the continuing unto the end until it be thoroughly finished, yields the true glory’’ -Sir Francis Drake(1587)

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Growth and Development

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Contents Definition of growth and development Critical period Signalling Growth factor Pre natal development 1)Pre implantation period 2)Embryonic period a)Pre somite b) Somite c)Post somite period 3)Fetal period Post natal development Terminologies

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Contents cont’d Osteogenesis Endochondral Intramembranous Basic growth movements Remodelling Displacement Calvaria Growth of calvaria Theories of Growth Growth Spurts Importance

Growth and Development:

Contents cont’d Normal features of growth and development -Pattern a. Proportionality -Differential Growth - Cephalocaudal gradient of growth b. Predictability -Variability c)Timing, Rate & Direction Formation of Face Abnormal development

Contents:

“There must be a beginning on any great matter ,but the continuing unto the end until it be thoroughly finished, yields the true glory’’ -Sir Francis Drake(1587)

Contents cont’d:

Definition Growth may be defined as a developmental increase in mass. In other words it is a process that leads to increase in the physical size of cells ,tissues ,organs or organisms as a whole (STEWART 1982) Growth refers to increase in size or number(PROFITT 1986) Growth may be defined as the normal changes in the amount of living substance (MOYER 1988)

Contents cont’d:

Growth is an increase in the size of a living being or any of its parts, occurring in the process of development (STEDMAN 1990) Growth refers to increase in size ( TODD) Growth signifies an increase ,expansion or extension of any given tissue (PINKHAM 1994)

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Development Development is increase in complexity (TODD 1931) Development is used to indicate an increase in skill and complexity of functions( Lowrey 1951) Development is in complexity ( Profitt 1986) The act or process of natural progression from a previous, lower, or embryonic stage to a later , more complex or adult stage(STEDMAN 1990) Development addresses the progressive evolution of a tissue(PIKNHAM 1994)

Definition:

Correlation between growth and development Growth is basically anatomic phenomenon and quantitative in nature. Development is basically physiologic phenomenon and qualitative in nature. 9

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Critical periods Genes orchestrate the phenomena of normal growth and development Stage at which individual has reached a particular age is referred as Maturatinal /Biologic age *CRITICAL PERIOD (Smith .D .W and Bierman.E.L,The Biologic Ages of Man, Philadelphia1973,W.B.Saunders Co)

Development:

Critical periods Eg : Most brain cells have been formed by 6 months of age, whereas Bone & Cartilage continue to divide for atleast 15-20years,as a consequence, brain is highly susceptible to phenomena producing growth deficiency disorders during fetal and early infancy,but the skletal is susceptible to both ,during prenatal and throughout childhood and adolescence.

Correlation between growth and development :

Signaling Growth factors Signaling centre: Group of cells that regulate the behavior of surrounding cells by producing positive and negative intercellular signals. Growth factors stimulate cell proliferation and differentiation by acting through specific receptors on responsive cells. They assume different roles at different times at different places. Most of these factors are present and active throughout the life

Critical periods:

PRENATAL DEVELOPMENT PRE SOMITE 8 TO 21 DAYS SOMITE 21 T0 31 DAYS POST SOMITE 32 TO 56 DAYS

Critical periods:

PREIMPLANTATION PERIOD Initial stages of embryogenesis, depicting cell division Morula

Signaling Growth factors:

PREIMPLANTATION PERIOD After approximately 3 days of fertilization cells of the embryo divide to form a 16 cell morula CLEVAGE

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PREIMPLANTATION PERIOD The morula transforms into a blastocyst containing a cavity called blastocoele .

PREIMPLANTATION PERIOD:

PREIMPLANTATION PERIOD

PREIMPLANTATION PERIOD:

PREIMPLANTATION PERIOD CHORIONIC CONNECTION [7 th day]

PREIMPLANTATION PERIOD:

Embryonic period Pre somite – 8 – 21 days Somite – 21 – 31 days Post somite – 32 – 56 days

PREIMPLANTATION PERIOD:

Pre somite period An embryo in any stage of development before the appearance of the first pair of somites (segments), which in humans usually occurs around 19 to 21 days after fertilization of the ovum

PREIMPLANTATION PERIOD:

On day 15, a groove, called the primitive streak , appears on the surface of the midline of the dorsal aspect of the ectoderm of the embryonic disc. By day 16, a primitive knot of cells, the Henson’s node , appears at the cephalic end of the primitive streak. This knot gives rise to the cells that form the notochordal process.

Embryonic period:

Pre cordal plate Precordal plate: is an endodermal thickening ,appears in mid-cephalic region as a consequence of Sonic hedgehog(SHH) signalling Prechordal plate prefaces the development of the orofacial region giving rise later to endodermal layer of oropharyngeal membrane. It is believed to form head orgainising function

Pre somite period:

Primitive streak The Resultant bulge is called prim’ streak From primitive streak, the rapidly proliferating tissue known as mesenchyme ,forms intraembryonic mesoderm c migrates in all dir’ betwn ectoderm and endoderm,except at sites of oropharyngeal membrane Appearance of mesoderm converts the bilaminar disk into trilaminar structure

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PRIMITIVE STREAK

Pre cordal plate:

Neural tube Dev of ectoderm into its cutaneous and neural portions occurs at 20 days by infolding of neural plate ectoderm at the midline forming NEURAL FOLDS, this creates a NEURAL GROOVE,. At 22days,neural folds fuse in region of third to fifth somites ,the site of the future occipital region, Initial closure proceeds cephalically and caudally to form NEURAL TUBE

Primitive streak:

Fate of germ layers Ectodermal cells will give rise to the nervous system; the epidermis and its appendages (hair, nails, sebaceous and sweat glands); the epithelium lining the oral cavity, nasal cavities and sinuses; a part of the intraoral glands, and the enamel of the teeth. Endodermal cells will form the epithelial lining of the gastrointestinal tract and all associated organs. The mesoderm will give rise to the muscles and all the structures derived from the connective tissue(e.g., bone, cartilage, blood, dentin, pulp, cementum and the periodontal ligament). The embryonic disc will soon become altered by bends and folds necessary for further development.

PRIMITIVE STREAK:

STOMATODEUM This membrane is devoid of  mesoderm , being formed by the apposition of the stomodeal ectoderm with the fore-gut endoderm; at the end of the third week it disappears, and thus a communication is established between the mouth and the future  pharynx

Neural tube:

FRONTONASAL PROCESS Mesoderm Proliferates-downward projection

Fate of germ layers:

SOMITE PERIOD When the buccopharyngeal membrane breaks down at the 4 th week, the foregut communicates with the exterior through the stomatodeum A series of mesodermal thickenings in the wall of the cranial most part of the foregut- pharyngeal / branchial arches . In the interval between any two adjoining arches, the endoderm extends outward to form the endodermal pouch to meet the ectoderm which dips into this interval as an ectodermal cleft .

STOMATODEUM:

PHARYNGEAL ARCHES Developing pharyngeal arches that appear in the 4 or 5 th week of development .

FRONTONASAL PROCESS:

SOMITE PERIOD Structures in pharyngeal arhces

SOMITE PERIOD:

The neural crest cells that originate in the neuroectoderm of the forebrain, midbrain and hindbrain migrate ventrally into the pharyngeal arches.

PHARYNGEAL ARCHES:

categorization of portions of the  central nervous system Rhombencephalon Prosencephalon RHOMBENCEPHALON The rhombencephalon can be subdivided in a variable number of transversal swellings called  rhombomeres . In the human embryo eight rhombomeres can be distinguished, from caudal to rostral : Rh7-Rh1 and the  isthmus

SOMITE PERIOD:

Prosencephalon The  prosencephalon  (or  forebrain ) is the  rostral -most (forward-most) portion of the  brain . The prosencephalon , the  mesencephalon  (midbrain), and rhombencephalon  (hindbrain) are the three primary portions of the brain during early  development  of the  central nervous system

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Derivatives of Pharyngeal arches ARCHES NERVE MUSCLES SKELETAL ARTERY I Maxillary arch Trigeminal MOM Mandible, Maxilla,incus , malleus Maxilary II Hyoid Facial Muscles of facial expression Stapes, styloid process,lesser cornu & upper part of body of hyoid, Stapedial (embryonic) Corticotympanic (adult) III Glossopharyngeal Stylopharyngeus Gr. Cornu & lower part of body of hyoid Common carotid IV & VI Sup laryngeal & recurrent laryngeal Intrinsic muscles of larynx, pharynx, levetor palatini Thyroid, cricoid , arytenoid , corniculate , cuneform IV- rt subclavian VI - pulmonary

categorization of portions of the central nervous system:

Derivatives of Pharyngeal pouches

Derivatives of Pharyngeal arches:

Branchial Arch Cartilages The initial skeleton of the branchial arches develops from the mesenchymal tissue as cartilaginous bars.

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1 st arch In the 1 st arch ,bilateral Meckel’s cartilages arise. The malleus and incus develop and ossify at the dorsal end of Meckels cartilage. The rest of the cartilage gradually disappears, leaving part of the perichondrium as the sphenomalleolar ligament (ant. Ligament of malleus ) and part as the sphenomandibular ligament. 2 nd ARCH In the, Reichert’s cartilage develops. It gives rise to the stapes, styloid process, lesser horn and upper part of the body of the hyoid. The stylohyoid ligament is formed by the perichondrium at the site of disappearance of this 2 nd arch cartilage

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The 3 rd arch cartilage forms the greater horn and lower part of the body of the hyoid. The 4 th arch cartilage forms the thyroid cartilage. The 5 th arch cartilage has no adult derivatives. The 6 th arch cartilage forms the laryngeal cartilages.

Branchial Arch Cartilages:

POST SOMITE PERIOD 2 ND MONTH OF DEVELOPMENT Facial features become more recognizable as human. The external appearance of the embryo is changed by an increase in head size and formation of limbs, face, ears, nose and eyes.

1st arch:

FETAL PERIOD (7 Months)

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FETAL PERIOD The period from the beginning of ninth week to birth is called FETAL PERIOD. Growth in length is particularly striking during the 3 rd , 4 thand 5 th months while an increase in weight mainly occurs during the last two months. The length of pregnancy is considered to be 38 weeks or 266 days after fertilization .

POST SOMITE PERIOD:

FETAL PERIOD At the beginning of the 3 rd month,the head constitutes half of overall length. Beginning of 5 th month, head is one third of the total length and At birth it is one fourth of the total length.

FETAL PERIOD (7 Months):

POST NATAL GROWTH What is post natal growth?? Post natal growth is the first 20 years of growth after birth. How does it defer from prenatal growth?? Prenatal growth is characterized by a rapid increase in cell numbers and fast growth rates Postnatal growth is characterized by declining growth rates and increasing maturation of tissues.

FETAL PERIOD:

Terminologies Primary cartilage Secondary cartilage Growth centre – location at which independent growth occurs Growth site – mere location at which growth occurs

FETAL PERIOD:

Terminologies Cortical drift – relocation of bone by simultaneous deposition and resorption processes on the opposing periosteal and endosteal surfaces Displacement – movement away from a certain position or place Primary displacement- occurring in conjunction with bone’s own growth Secondary displacement – caused by enlargement of adjacent or remote bones or soft tissues; but not of the bone itself

POST NATAL GROWTH:

Remodeling – reshaping of the outline of the bone by selective resorption of bone in some areas and deposition in other areas Relocation – relative movement in space of a bony structure, due to bone deposition on one side and resorption on the other side

Terminologies :

OSTEOGENESIS Def’n Two basic type of cells capable of osteogenesis A) Undiffentiated mesenchymal cells B)Cells in bone marrow tissue Mechanisms of bone formation It takes place by two ways 1) Endochondral 2)Intra-membranous

Terminologies :

Endochondral ossification Precursor cartilage Occurs mainly in tubular bones cuboid bones base of the skull vertebral bodies part of the pelvis. Largely responsible for elongation of individual bones ,thus constitutes mainly for increase in “Height” or “Growth’’

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Membranous ossification Occurs primarily in -the Calvarium , -the clavicles -body of mandible -spinal process of the vertebrae, -part of pelvis Thus increase in width of bones is largely due to menbranous ossification Final shape is due to osteoclastic resorption

OSTEOGENESIS:

BASIC GROWTH MOVEMENTS A)REMODELLING B)DISPLACEMENT Eg : In a joint, bone enlarges in a given direction within the joint, it is simultaneously displaced in the opposite direction.

Endochondral ossification :

A) REMODELLING Biochemical remodeling Secondary reconstruction of bone by haversian system and rebuilding of cancellous trabaculae . Regeneration and reconstruction of bone following disease or trauma.

Membranous ossification:

REMODELING process of reshaping and resizing each level within a growing bone as it is relocated sequentially into a succession of new levels.

BASIC GROWTH MOVEMENTS :

The surface that faces the direction of growth is depository. if rates of deposition and resorption are equal, the thickness of the cortex remains constant .

A) REMODELLING:

B) DISPLACEMENT Is a movement of the whole bone by a physical force that carries it away from its contacts with other bones A)Primary displacement The amount of displacement equals the amount of new bone deposition. The respective directions are always opposite B)Secondary Displacement Not related to its own growth. Anterior growth of the middle cranial fossa and temporal lobes secondarily displace the nasomaxillary complex anteriorly and inferiorly

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The Calvaria The endocranial surface of the calvaria is predominantly depository. The lining bony surface of the cranial floor is mainly resorptive . Circumcranial reversal line

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Main function to protect the brain. Growth occurs by utilizing the sutural system and small deposits occur on the ectocranial and endocranial sides. Cranial vault is one of the first regions of the craniofacial skeleton to achieve full size. Ossification begins at the7-8 th week of gestation and continues into adulthood.

B) DISPLACEMENT:

The non ossified articulations at birth are sutures or fontanellae depending on their size. Premature ossification of any suture or fontanelle alters the growth of the skull and thus the midface and lower face.

The Calvaria:

As the brain expands, the separate bones of the calvaria are displaced in outward directions. (Functional matrix theory) GROWTH OF CALVARIA

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Primary displacement of the bones causes tension in the sutural membranes…. deposition of bone on the sutural edges. Sutural growth predominates until 4 yrs of life.

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Deposition on ectocranial and endocranial sides The endosteal surfaces lining the inner and outer cortical tables are resorptive Increase in the overall thickness of the bone while expanding the medullary space.

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The arch of curvature of the whole bone decreases.

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Major stimulus for calvarial growth is….. Intra cranial hydrostatic pressure ….. Correlates directly with enlarging brain volume. Brain volume increases from one quarter to three quarters in the first 2 yrs of life . the final quarter of growth is completed in the next 15 years.

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The cranial cavity thus achieves 87% of its adult size by 2 years 90% by 5 years 98% by 15 years

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Theories of Growth Control

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Theories of Growth The major theories of growth are as follows Genetic Theory Remodelling Theory Sutural Theory Cartilageneous Theory Functional matrix Theory Servosystem Theory Van Limborgh’s Theory

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Other theories related to craniofacial growth are – Enlow’s expanding ‘V’ principle Enlow’s counterpart principle Neurotrophic process in oro -facial growth

Theories of Growth Control:

Genetic growth ( brodie ) It says, growth is controlled by genetic influence in all aspect. But it cannot be accepted in all cases. As it has been shown that the external factor have significant modifying effect on growth

Theories of Growth :

Remodelling theory (1930) The research by Brash on bone provided the foundation for the development of the first general theory of craniofacial growth—the remodeling theory

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The principal tenets of the remodeling theory were that- bone only grows appositionally at surfaces. growth of the jaws is characterized by deposition of bone at the posterior surfaces of the maxilla and mandible , sometimes described as “ Hunterian ” growth of the jaws. calvarial growth occurs via deposition of bone on the ectocranial surface of the cranial vault and resorption of bone endocranially

Genetic growth ( brodie):

Sutural Dominance theory ( sicher & weimann1955) According to this theory, the connective tissue and cartilaginous joints of the craniofacial skeleton, much like epiphyses of the long bones are the principal locations at which intrinsic, genetically regulated, primary growth of bones take place. Limitation : lack of growth of suture if it is transplanted Growth occurs in cleft lip and cleft palate patients even if suture not present Suture also respond to external influence Contradiction: Koski (1968)- suture does not have its independent growth potential

Remodelling theory (1930):

Cartilaginous theory(James Scott) Ex : C ondylar cartilage for mandible Nasal cartilage for maxilla ( nasomaxillary complex)

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Functional matrix theory ( melvin moss 1968)) Functional matrix comprised of 1) periosteal component 2)capsular component Functional matrix has primary control on growth of skeletal unit and bone,which respond in passive manner but it can not explain all aspects of growth

Sutural Dominance theory (sicher & weimann1955):

Schematic representation of the functional matrix hypothesis of craniofacial growth. -Primary growth of the capsular matrix (brain) results in a stimulus for secondary growth of the sutures and synchondrosis , -Leading to overall enlargement of the neurocranium ( macroskeletal unit ). -Function of the temporalis muscle exerts pull on the periosteal matrix and bone growth of the temporal line ( microskeletal unit ).

Cartilaginous theory(James Scott):

FUNCTIONAL MATRIX REVISITED.. 1. The role of mechanotransduction Melvin L. Moss 1997 July 2. The role of an osseous connected cellular network 1997 August 3. The Genomic thesis 1997 September 4. The Epigenetic antithesis and the Resolving synthesis 1997 October

Functional matrix theory (melvin moss 1968)):

The addition to the FMT, the concepts of mechanotransduction and of computational bone biology offers an explanatory chain extending from the epigenetic event of skeletal muscle contraction, hierarchically downward, through the cellular and molecular levels to the bone cell genome, and then upward again, through histologic levels to the event of gross bone form adaptational changes. Analyzing size and shape changes by reference-frame-invariant, finite element methods produces a more comprehensive and integrated description of the totality of the processes of epigenetic regulation of bone form than previously possible 1 st AND 2 nd ..

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3 RD AND 4 TH .. The first two articles in this series, by emphasizing the roles of a number of biophysical and biochemical factors in the regulation of morphogenesis, implicitly argued for the correctness of the fundamentally epigenetic thrust of the FMT However, the regulatory primacy of either genomic (genetic) or of epigenetic factors and/or processes in morphogenesis continues debated, it seemed useful to re-evaluate this nontrivial matter

FUNCTIONAL MATRIX REVISITED..:

"IT IS A WIN-WIN SITUATION“ Individually both are necessary causes, but neither are sufficient causes alone. Together they provide both the necessary and sufficient causes for the control (regulation) of morphogenesis Nevertheless, epigenetic processes and events are the immediately proximate causes of development Thus they are the primary agencies.

1st AND 2nd ..:

Multi factorial theory (Van Limborgh 1970) Intrinsic genetic factor: They are the genetic control of the skeletal unit themselves. Local epigenetic factor: Bone growth is determined by genetic control originating from adjacent structures like brain, eyes etc. General epigenetic factor: Genetic factors determining growth from distant structures. Eg : Sex hormones, growth hormones. Local environmental factor: Non genetic factors from local external environment. Eg : habits, muscle force General environmental factor: They are General Non genetic influences such as nutrition, oxygen etc

3RD AND 4TH ..:

Chondrocranial growth is controlled mainly by intrinsic genetic factors. The cartilageneous part of the skull must be considered as the growth centres . Sutural growth is controlled mainly by influences originating from the skull cartilages and from other adjacent skull structures. Periosteal growth largely depends upon growth of the adjacent structures. Sutural and periosteal growth is additionally governed by local non genetic environmental influences

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Enlow’s expanding ‘v’ principle Many facial bones or part of bone have a V shaped pattern of growth The growth movements and enlargement of these bones occur towards the wide ends of the V as a result of differential deposition and selective resorption of bone. Bone deposition occurs on the inner side of the wide ends of the V and bone resorption on the outer surface.  The V pattern of growth occurs in a number of regions such as base of the mandible, ends of long bones, mandibular body, palate etc

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Enlow’s counterpart principle The growth of any given facial and cranial part relates specifically to other structural and geometric counterparts in the face and cranium The different parts and their counterparts are : Nasomaxillary complex relates to the anterior cranial fossa Horizontal dimension of the pharyngeal space relates to the middle cranial fossa . Middle cranial fossa and breadth of the ramus Maxillary and mandibular dental arch Bony maxilla and corpus of the mandible . Maxillary tuberosity and the lingual tuberosity

Enlow’s expanding ‘v’ principle:

Imbalances in the regional relationship are produced by differences in Amount Direction Time of growth between the counterparts

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GROWTH SPURTS

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Growth Spurts Refers to Sudden increase in growth of general Body. Woodside in his study of Burlington Group showed. Girls Boys Just after birth 3 yrs 3 yrs Juvenile growth Spurt 6-7yrs 7-9yrs Pubertal growth spurt 10-12yrs 12-15yrs 87

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Biological changes seen during puberty In Boys : Stage I: - Fat spurt - Initially maturing boy gains weight and becomes chubby –production of estrogen before production of testosterone . Stage II Spurt in height, development of secondary sexual characteristics. Occurs 1 year after the Stage I Stage III Occurs 8-10months after stage II and coincides with the peak velocity with gain in height At this stage auxillary hair appears and facial hair appears on upper lip. Spurt in muscle growth occurs

GROWTH SPURTS:

Stage IV: Occurs from 15-24 months after stage III Spurt of growth in height ends. Facial hair on chin and upper lip. This indicates growth is almost complete. In Girls : Stage I: Beginning of growth spurt appearance secondary sexual characteristics . Stage II: Occurs 1 year after stage I coincides with peak velocity physical growth. Stage III: Occurs 1-1½ years later stage II. marked by onset of menstruation. By this time growth spurt all but complete . 89

Growth Spurts:

Velocity curves for growth at adolescence showing different timings for Girls and boys

Biological changes seen during puberty:

Importance of Growth Spurts : Pubertal increments. Determining and understanding the predictability, growth direction&total treatment time. Orthopedic correction Growth spurts serve as excellent indicators for timing of orthodontic treatment Correlation of a. Skeletal age, b. Dental age c. Chronological age. With onset of puberty.

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Normal features of Growth & Development PATTERN a. Proportionality - Differential Growth - Cephalocaudal gradient of growth b. Predictability VARIABILITY TIMING ,RATE & DIRECTION

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Pattern : Pattern represents proportionality-not just proportional relationships at a point in time but change in these relationships over time Physical arrangement of the body at one time is a spatially proportioned parts . But ,there is a higher level pattern, the pattern of growth, which refers to the changes in these spatial proportions over time

Importance of Growth Spurts::

Proportionality : Can be defined as a set of constraints operating to preserve the integration of parts under varying conditions or through time - moyers

Normal features of Growth & Development:

Differential growth Not all tissue systems of the body grow at the same rate. Different tissues and different organs grow at different rates. This process is called differential growth. Eg :Muscular & skeletal – grow faster than brain and CNS as reflected in the relative decrease of head size 95

Pattern ::

Scammon’s Growth curve The body tissues can be broadly classified as Lymphoid Neural General Genital Each of this tissues grow at different times & rates

Proportionality ::

As the graph indicates growth of neural tissues is complete by 6-7 years of age General body tissue, including Muscle, Bone, Viscera show S shaped curve, with a definite slowing of growth rate during childhood and an accelertaion at puberty. Lymphoid tissues proliferate far beyond the adult amount in late childhood, and then undergo involution and at the same time that growth of the genital tissues accelerate rapidly. ( Scammon RE: The measurement of body in childhood)

Differential growth :

Cephalo -caudal gradient of growth

Scammon’s Growth curve:

Cephalo -caudal gradient of growth It simply means there is an axis on increased growth extending from head towards the feet. A comparision of body proportion of pre natal and post natal growth reveals that postnatal growth of regions of body that are away from hypophysis is more. Represents the changes in over all body proportions during normal growth and development

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In fetal life, at about the third month of intrauterine development, the head takes up almost 50% of the total body length. At this stage, the cranium is large relative to the face and represents more than half the total head. In contrast, the limbs are still rudimentary and the trunk is underdeveloped, By the time of birth, the trunk and limbs have grown faster than the head and the face, so that proportion of entire body devoted to head has decreased to about 30% 100

Cephalo-caudal gradient of growth:

The overall pattern thereafter follows the course, a progressive reduction of relative size of the head to about 12% of the adult. Thus the name Cephalocaudal gradient of growth, meaning there is an axis of increased growth, extending from head towards the feet

Cephalo-caudal gradient of growth:

At 3 rd month of IUL head 50% of total body length. At birth head 30% of total body length. At adult head 12% of total body length. Post natally , head grows larger than the cranium

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Cephalocaudal Gradient of growth

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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. Change in growth pattern : (expected changes in body proportions). 104

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Variability No two individuals with the exception of siamese twins are like. Hence it is important to have a “normal variability” before categorizing people as normal or abnormal 105

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Normality Normality refers to that which is usually expected, is ordinarily seen or typical – Moyers Normality may not necessarily be ideal. Deviation from usual pattern can be used to express quantitative variability This can be done by using “growth charts” 106

Predictability:

TYPES OF NORMALITY STATISTICAL EVOLUTIONARY FUNCTIONAL ESTHETICAL CLINICAL 107

Variability:

Timing of Growth One of the factors for variablity in growth. Timing variations arise because biologic clock of different individuals is different. It is influenced by: genetics sex related differences physique related environmental influences

Normality:

Age equivalence Because of variability and timing all individual at a given chronological age are neither 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. 109

TYPES OF NORMALITY:

The mating of male& female gametes in the maternal uterine tube initiates the development of zygote- the first identification of an individual Cell diameter: 140um

Timing of Growth:

Formation of Face At the end of the fourth week, the centre of the face is formed by the stomodeum , surrounded by the first pair of pharyngeal arches Five mesenchymal prominences can be recognized: mandibular prominences (caudal) maxillary prominences (lateral) nasomaxillary prominence(cranial) These prominences arise from the neural crest ectomesenchyme that migrate into the facial and neck regions

Age equivalence:

FORMATION OF FACE 4 th WEEK Cardiac buldge

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Nasolacrimal duct Within the grooves between the lateral nasal and maxillary prominences, solid rods of epithelial cells sink into the subjacent mesenchyme . These rods extend from the developing conjunctival sacs at the medial corners of the forming eyelids to the external nares . Later canalise to form the nasolacrimal sacs and ducts which become completely patent only after birth

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Formation of the eyes Thickened epithelial lens placodes invaginate concomitantly with formation of optic vesicles – deep set eyeballs. Medial migration of the eyes from their initial lateral position. Folds of surface ectoderm grow over the eyes - eyelids

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Formation of the ears The internal ear manifests as a hindbrain induction of surface ectodermal cells – thickened otic placode . Placode pit vesicle internal ear. The external ear develops in the region of the neck as 6 auricular hillocks surrounding the 1 st pharyngeal groove. The middle ear develops from the 1 st pharyngeal pouch.

Nasolacrimal duct:

Formation of the nose The bridge is formed from the frontal prominence. the merged medial nasal prominence forms the median ridge and the tip. The alae are formed by the lateral nasal prominence and the cartilagenous nasal capsule gives rise to the septum and nasal conchae

Formation of the eyes:

ABNORMAL DEVELOPMENT

Formation of the ears:

Abnormal Development Cleft Lip: Can be unilateral, bilateral and can vary from a notch in the vermillion border to a cleft extending into the floor of the nostril. Cleft palate: Less common than cleft lip. It maybe due to lack of growth or failure of fusion between the median and lateral palatine processes and the nasal septum or it maybe due to initial fusion with interruption of growth at any point along its course. It may also be due to interference with elevation of palatal shelves.

Formation of the nose:

Cervical Cysts and Fistulae: Caudal overgrowth of the second arch gradually covers the 2 nd, 3 rd and 4 th branchial grooves. These grooves lose contact with the outside and temporarily form an ectoderm lined cavity, the cervical sinus, which should normally disappear. Failure of complete obliteration of the cervical sinus results in a cervical cyst.

ABNORMAL DEVELOPMENT:

Cervical Cysts and Fistulae: If the cyst opens to the outside, a fistula develops. Branchial cysts or fistulae are found anywhere on the side of the neck along the anterior border of the SCM muscle. Another cause is incomplete caudal overgrowth of 2 nd arch, which leaves an opening on the surface of the neck.

Cervical Cysts and Fistulae: :

Thyroglossal cyst and Fistula

Cervical Cysts and Fistulae: :

Mandibulofacial Dysostosis or Treacher Collins Syndrome: . This results from failure or incomplete migration of the neural crest cells to the facial region. The zygomatic bone is severely hypoplastic . The face appears to be drooping, and the ears are usually malformed. The lower border of the mandible appears concave, and cleft palate is occasionally seen

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Fissural cysts Cystic cavities which arise along the fusion of various bones or embryonic processes and lined by epithelium.

Thyroglossal cyst and Fistula:

Median rhomboid glossitis It results from persistence of the tuberculum impar and characterised by a red smooth region anterior to the foramen caecum .

Mandibulofacial Dysostosis or Treacher Collins Syndrome:. :

ankyloglossia This occurs as a result of incomplete degeneration of cells while the body of the tongue is freed, so that the tip of the tongue remains tied to the floor of the mouth.

Fissural cysts:

macroglossia Macroglossia or abnormally large tongue is not common, but is seen sometimes at birth when tongue slightly protrudes from mouth. This corrects itself when the jaws grow at a rapid rate. True macroglossia is seen in mongolism.

Median rhomboid glossitis:

Bifid tongue This is a malformation common in south American infants and is the result of failure of the lateral lingual swellings.

ankyloglossia:

REFERENCES Craniofacial development by Sperber:3 rd edition Langman’s medical embryology by T.W.Sadler:8 th edition Human embryology by Inderbir singh Pediatric Dentistry, Scientific foundations and clinical practice: STEWART,WEI,BARBER A color atlas and text book of oral anatomy, histology and embryology, B.K.B Berkowitz: 4 th edition Contemporary Orthodontics: Proffit , 4 th edition Human embryology : Larsen: 2 nd edition

macroglossia:

Textbook of Pedodontics : SHOBHA TANDON,2 nd edition Oral anatomy and histology, Ten Cate 11 th edition Synopsis of orthodontics – m.s . rani Essentials of facial growth – enlow and hans The art and science of orthodontics- bhalaji Gurkeerath singh The primary role of functional matrices in facial growth - june 1969

Bifid tongue:

THE FUNCTIONAL MATRIX HYPOTHESIS REVISITED. 1. THE ROLE OF MECHANOTRANSDUCTION MELVIN L. MOSS 1997 JULY THE FUNCTIONAL MATRIX HYPOTHESIS REVISITED. 2. THE ROLE OF AN OSSEOUS CONNECTED CELLULAR NETWORK MELVIN L. MOSS. 1997 AUGUST THE FUNCTIONAL MATRIX HYPOTHESIS REVISITED. 3. THE GENOMIC THESIS MELVIN L. MOSS – 1997 SEPTEMBER THE FUNCTIONAL MATRIX HYPOTHESIS REVISITED. 4. THE EPIGENETIC ANTITHESIS AND THE RESOLVING SYNTHESIS MELVIN L. MOSS - 1997 OCTOBER ARTICLE ON THEORIES OF GROWTH BY Dr. Rajesh Gyawali Department of Orthodontics and Dentofacial Orthopaedics Institute of Medicine, Kathmandu

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Spurt in growth of jaws occurs at about same time as the spurt in height

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Schematic representation of segmentation in early embryogenesis

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Primary Germ Layers Prechordal plate Ectoderm Epithelium of skin Outer membrane of Hair Oropharyngeal membrane Sweat glands Sebacious glands Lacrimal glands Rathke’s pouch Ext’ acoustic meatus & Outer layer of tympanic membrane Adenohypophysis Oral epithelium Neural tube Placodes -Enamel Neurohypophysis Olfactory : sensory -Taste buds Spinal cord :Peripheral nerves Lens : eye -Salivary gland Brain Otic:inner ear -Thyroid gland -Optic vessels : Retina -Cranial nerves

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Mesoderm Pre chordal mesoderm Paraxial somites Intermediate Prosencephalic Sclerotomes:Bassiocciput Urogenital system orgainsing centre Myotomes : Cervical , Suprahyoid Glossal muscles Dermatomes : Dermis & skin Head mesenchyme Lateral Bld vessels & Lympatics Blood &Lymph cells Connective tissue -Coverings of laryngeal muscles Cranial mesodermal derivatives

Schematic representation of segmentation in early embryogenesis:

Endoderm

Primary Germ Layers:

FORMATION OF FACE( Clefting ) Nasolacrimal groove Mesodermal penetration Other factors Shift of blood supply[7 th week] Syndromic clefts Trisomy – median nasal process Waedenberg’s synd - neural crest cell Vander Woode’s synd - failure of regression

Mesoderm:

PHASES OF DEVELOPMENT Embryogenesis is divided into three distinct phases during 280 days of gestation. The phases are Pre implantation(first 7days) Embryonic period (Next 7 weeks) Fetal period(the next calendar months)

Endoderm:

Pre natal growth Period of ovum (0-1 week) Secondary oocyte fuses with the sperm within 24hr after ovulation, forming the zygote. The zygote contains 46chromosomes,which is the diploid number. The zygote undergoes cleavage after 30hr to form the morula and finally the blastocyst, which gets implanted in the endometrium by 3-5 days Period of Embryo(1-2week) Appearance of bilaminar embryonic disc consisting of the ectoderm and endoderm. Amniotic cavity and the yolk sac are formed seperated by the embryonic disc. Prochordal plate is formed indicating the future cranial region and the primitive mouth

FORMATION OF FACE(Clefting):

3rd week First missed menstural period. Morphogenesis begins The third primary germ layer,the mesoderm appers during third week and converts bilmainar germ into trilaminar structure,. Primitive streak initiates the formation of embryo. Notochord is formed. Embryonic disc is slightly curved as the head and tail folds appear. Paraxial mesoderm condenses from the somites . By the end of 3 rd week, Cardiovascular system is the first to reach its functional stage. Head forms ½ the body length

PHASES OF DEVELOPMENT:

4 th week Neural tube is formed Embryonic disc assumes C-shape as the head, tail and lateral folds form The three primary germ layers serve as a basis for the differentiating tissues and organ systems, From the ectoderm, develop the cutaneous and neural elements of embryo Mesoderm: Cardiovascular structures ,bones, muscles, and connective tissue Endoderm: The lining epithelium of the gut between pharynx and the anus, the secretory cells of the liver and pancreas ,and the lining epithelium of the respiratory syste m

Pre natal growth:

5 th week Major development occurs in the head region. 4branchial arches present. 2 nd Pharyngeal arches overgrow,3 rd and 4 th form cervical sinuses. Upper limb differentiates into hand plates, Otic placodes and optic cesicles seen Heart beats can be detected ultrasonographically . By the end of 5 th week,42-44pairs of somites are formed

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FORMATION OF FACE 5 th Week (early)

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FORMATION OF FACE 5 th WEEK (LATE)

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FORMATION OF FACE 6 th Week

FORMATION OF FACE:

FORMATION OF FACE 7 th Week

FORMATION OF FACE:

FORMATION OF FACE 10 th Week

FORMATION OF FACE:

Physiology of Growth Growth is a product of continuous interaction btw endocrine & skeletal systems Nearly all the body’s hormones affect growth. Ex: GH, Thyroxin, Insulin, Corticosteroids influence growth rates whereas parathormone ,metabolites of Vit D3 and possibly calcitonin affect skletal ossification The gonadotropins and gonadal and adrenal steroids are of primary importance in skeletal maturation and pubertal growth spurt.

FORMATION OF FACE:

Human growth hormone( hGH ) Secreted by somatropic cells of anterior pitutary Its release is closely regulated by two hypothalamic hormones. hGH releasing hormone hGH inhibitory hormone( somatostatin ) The secretion of these hormones is inturn controlled by CNS and humoural feedback systems that influence hypothalamus

FORMATION OF FACE:

Endocrine growth axis

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