Prenatal growth and development in orthodontics /certified fixed orthodontic courses by Indian dental academy


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Prenatal growth and development in orthodontics /certified fixed orthodontic courses by Indian dental academy

  2. 2.  According to Aristotle “He who sees things grow from the beginning will have the finest view of them” www.indiandentalacademy.c om
  3. 3. Human development from ovulation to fertilizationHuman development begins at fertilization when a male gamete or sperm unites with a female gamete or oocyte to form a single cell _ ZYGOTEThis highly specialized totipotent cell marked the beginning of each of us aswww.indiandentalacademy.c a unique individual om
  4. 4. Primordial germ cellsGametes are derived from “primordial germ cells” that are formed in the epiblast during the second week and that move to the wall of the yolksac www.indiandentalacademy.c om
  5. 5. During the fourth week these cells begin to migrate from the yolk sac toward the developing gonads ,where they arrive by the end of fifth week .mitotic divisions increase their number during their migration and also when they arrive in gonad www.indiandentalacademy.c om
  6. 6. These primordial germ cells undergo “GAMETOGENESIS” and “CYTODIFFERENTIATION” to complete their maturation www.indiandentalacademy.c om
  7. 7. GAMETOGENESIS Gametogenesis {gamete formation}is the process of formation and development of specialized generative cells _ ”GAMETES” This maturation process is called spermatogenesis in males and oogenesis in females During gametogenesis the chromosome number is reduced to half by a process called “meiosis” www.indiandentalacademy.c om
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  10. 10. Cell divisionsThere are two types of cell division MITOSIS “ It is the process by whereby one cell divides ,giving rise to two daughter cells that are genetically identical to parent cell”Before a cell enters mitosis ,each chromosome replicates its DNA www.indiandentalacademy.c om
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  12. 12. MEIOSIS It is the cell division that takes place in the germ cells to generate male and female gametes (egg & sperm) respectivelyMeiosis requires two cell divisions to reduce the number of chromosomes to haploid number MEIOSIS I MEIOSIS II www.indiandentalacademy.c om
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  15. 15. FERTILIZATION It is acomplex sequence of coordinated molecular events that begins with contact between a sperm & oocyte & ends with intermingling of maternal &paternal chromosomes at metaphase of first mitotic division of zygote ,a unicellular embryoUsual site of occurrence of fertilization is ampulla of uterine www.indiandentalacademy.c om
  16. 16. Cleavage of zygotezygote {after 30hrs after fertilization} Repeated mitotic divisions Two blastomeres Four blastomeres Eight blastomeres www.indiandentalacademy.c om
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  18. 18.  COMPACTION After the nine cell stage ,blastomeres change their shape and tightly align themselves against each other to form a compact ball of cells .This phenomenon is called “compaction” www.indiandentalacademy.c om
  19. 19. Morula when there are 12 to 32 blastomeres ,the developing human is called morula {mulberry} It was given its name because it resembles a mulberry or black berry www.indiandentalacademy.c om
  20. 20. Formation of blastocyst Shortly after morula enters uterus [about 4days after fertilization} a fluid filled space appears inside the morula As the fluid increases in the blastocystic cavity ,it separates the blastomeres into two parts a. trophoblast {outer cell layer} b. embryoblast {inner cell mass} At this stage of development the conceptus is called a blastocyst www.indiandentalacademy.c om
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  22. 22.  During cleavage the zygote is within thick zona pellucida After free blastocyst has floated in the uterine secretions for two days the zona pellucida degenerates and disappears Shedding of zona pellucida permits the blastocyst to increase rapidly in size about six days after fertilization the blastocyst attaches to endometrial epithelium www.indiandentalacademy.c om
  23. 23.  TROPHOBLAST (as blastocyst attaches to the endometrial epithelium) a. Inner layer of cytotrophoblast b. outer mass of syncytiotrophoblast www.indiandentalacademy.c om
  24. 24. During second week of human development Formation of amniotic cavity Formation of embryonic disk Formation of yolk sac www.indiandentalacademy.c om
  25. 25. Formation of amniotic cavity After implantation of blastocyst small space appears in embryoblast This space is the primordium of amniotic cavity lined by amnioblasts www.indiandentalacademy.c om
  26. 26. Morphological changes occur in embryoblast that result in formation of flat almost circular bilaminar plate of cells,this embryonic disk has two layers HYPOBLAST EPIBLAST www.indiandentalacademy.c om
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  28. 28. EPIBLAST forms floor of amniotic cavityHYPOBLAST forms the roof of exocoelomic cavity and is continuous with thin exocoelomic membraneYolk sac exocoelomic membrane +hypoblast www.indiandentalacademy.c om
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  31. 31. Prechordal platePrechordal plate develops as a localized thickening of hypoblast, which indicates the future cranial region of embryo and the future site of mouth. Prechordal plate is also an important organizer of head region www.indiandentalacademy.c om
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  33. 33. Formation of germ layers third week GASTULATIONA. it is formative process by which the three germ layers and axial orientation are established in embryos.B. during gastrulation the bilaminar embryonic disc is converted into trilaminar embryonic disc.C. first sign of gastrulation is appearance of primitive www.indiandentalacademy.c streak. om
  34. 34. Primitive streak Primitive streak results from proliferation and migration of cells of epiblast to median plane of the embryonic disc Primitive streak appears “caudally in the median plane of the dorsal aspect of the embryonic disc” It is possible to identify the embryos craniocaudal axis, its cranial and caudal end, its dorsal and ventral surfaces and its right and left sides. www.indiandentalacademy.c om
  35. 35.  PRIMITIVE NODE As the primitive streak elongates by addition of cells to its caudal end ,its cranial end proliferates to form a primitive node . Concurrently a narrow groove primitive groove develops in the primitive streak that is continuous with a small depression in the primitive node - primitive pit www.indiandentalacademy.c om
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  38. 38.  primitive streak {cells leave its deep surface and form } mesenchyme{ a tissue consisting of loosely arranged cells suspended in a gelatinous matrix} some mesenchyme forms intra embryonic or embryonic mesoderm www.indiandentalacademy.c om
  39. 39.  Cells from epiblast displace the hypoblast forming the intraembryonic or embryonic endoderm Cells remaining in the epiblast form the intra embryonic or embryonic ectoderm Reasearch data suggest that signaling molecules of the transforming growth factor{TGF-B}superfamily induce ,the mesoderm TGF-B{nodal},T-box transcription factor{veg-t} and Wnt signalling pathway appear to be involved in specification of endoderm www.indiandentalacademy.c om
  40. 40. Fate of primitive streakPrimitive streak diminishes and becomes insignificant structure in sacrococcygeal region of embryo by end of fourth week www.indiandentalacademy.c om
  41. 41. Notochordal process and notochord Some mesenchymal cells migrate cranially from the primitive node and pit forming a median cellular cord ,the notochordal process the primitive pit extends into the notochordal process forming a notochordal canal www.indiandentalacademy.c om
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  45. 45.  Notochordal process is a cellular tube extends cranially from the primitive node to the prechordal plate The floor of notochordal process fuses with the underlying embryonic endoderm The fused layers gradually undergo degeneration resulting in the formation of openings in the floor of the notochordal process ,which brings the notochordal process into communication with the yolksac www.indiandentalacademy.c om
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  47. 47. The openings rapidly become confluent and the floor of the notochordal canal disappears ,the remains of notochordal process form a flattened ,grooved notochordal plate www.indiandentalacademy.c om
  48. 48. Intrinsic signals from the primitive streak region induce notochordal precursor cells to form the notochordBeginning at the cranial end of the embryo ,the notochordal cells proliferate and the notochordal plate infolds to form the notochord www.indiandentalacademy.c om
  49. 49. NOTOCHORD It is an intricate structure around which the vertebral column forms It extends from the oropharyngeal membrane to the primitive node . The notochord degenerates and disappears as the bodies of the vertebrae form but it persists as the nucleus pulposes of each intervertebral disc www.indiandentalacademy.c om
  50. 50. • Notochord functions as the primary inductor in the early embryo• The developing notochord induces the overlying embryonic ectoderm to thicken and form the “neural plate” [the primordium of central nervous system] www.indiandentalacademy.c om
  51. 51. NEURULATION :FORMATION OF NEURAL TUBE The process involved in the formation of the neural plate and neural folds and closure of the folds to form the neural tube constitute neurulation. These processes are completed by the end of fourth week www.indiandentalacademy.c om
  52. 52. Neural plate and neural tubeAs the notochord develops the embryonic ectoderm over it thickens to form an elongated ,slipper like plate of thickened epithelial cells ,the NEURAL PLATENEURAL PLATE appears cranial to primitive node ,dorsal to notochord and mesoderm adjacent to it . www.indiandentalacademy.c om
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  54. 54. As the notochord elongates ,the neural plate broadens and eventually extends cranially as far as the oropharyngeal membrane ,eventually the neural plate extends beyond the notochordOn about 18th day ,the neural plate invaginates along its central axis to form a longitudinal MEDIAN NEURAL GROOVE ,which has neural folds on each side www.indiandentalacademy.c om
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  57. 57. The NEURAL FOLDS become particularly prominent at the cranial end of the embryo and are the first signs of brain development .By the end of the third week ,the neural folds have begun to move together and fuse ,converting the neural plate into NEURAL TUBE www.indiandentalacademy.c om
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  59. 59. NEURAL CREST FORMATION As the neural folds fuse to form the neural tube, some neuroectodermal cells lying along the crest of each neural fold lose their epithelial affinities and attachments to neighbouring cells As the neural tube separates from the surface ectoderm, neural crest cells migrate dorsoventrally on each side of neural tube . They soon form a flattened irregular mass, the neural crest, between the neural tube and the overlying surface ectoderm www.indiandentalacademy.c om
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  62. 62. Neural crest soon separates in to right and left parts migrate into the dorsoventral aspects of neural tube, here they give rise to sensory ganglia and cranial nerves www.indiandentalacademy.c om
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  64. 64. Neural crest cells migrate in various directions and disperse within the mesenchymeAlthough these cells are difficult to identify special laser techniques have revealed neural crest cells disseminate widely www.indiandentalacademy.c om
  65. 65.  Neural crest cells give rise to 1. Spinal ganglia 2. Ganglia of ans 3. Ganglia of cranial nerves 5,7,9,10 4. Pigment cells 5. suprarenal medulla 6. several skeletal and muscular components in head www.indiandentalacademy.c om
  66. 66. Laboratory studies indicate that BMP, Wnt,Notch,FGF are involved in signalling systems of neural crest formation and in migration and differentiation of neural crest cells www.indiandentalacademy.c om
  67. 67. PHARYNGEAL APPARATUS Pharyngeal apparatus are aslo known as Branchial apparatus The word Branchial is derived from greek word Branchia which means Gill. The head and neck regions of a 4 week human embryo resemble these regions in a fish embryo of a comparable stage of development hence the name www.indiandentalacademy.c om
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  69. 69.  Pharyngealapparatus consists of 1. Pharyngeal arches 2. Pharyngeal pouches 3. Pharyngeal grooves 4 pharyngeal membranes www.indiandentalacademy.c om
  70. 70. PHARYNGEAL ARCHESThe pharyngeal arches begin to develop early in the fourth week as Neural crest cells migrate into the future head and neck regionsFirst pair of pharyngeal arches{primodium of jaws} appear as surface elevations lateral to developing pharynx www.indiandentalacademy.c om
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  72. 72. BY the end of fourth week ,4 pairs of pharyngeal arches are visible externally . 5 & 6 pharyngeal arches are rudimentary and are not visible on surface of embryoPharyngeal arches are separated from each other by fissures known as pharyngeal groove www.indiandentalacademy.c om
  73. 73. Pharyngeal arch components Each pharyngeal arch consists of a core of mesenchyme {embryonic connective tissue}and is covered externally by ectoderm and internally by endoderm This mesenchyme is derived from mesoderm in third week ,during fourth week most of the mesenchyme is derived from neural crest cells that migrate into pharyngeal arches www.indiandentalacademy.c om
  74. 74. Neural crest cells are unique in that despite their neuroectodermal origin they make a major contribution to mesenchyme in head & neck region www.indiandentalacademy.c om
  75. 75. Fate of pharyngeal arches Pharyngeal arches contribute extensively to formation of face , nasal cavities, mouth,larynx,pharynx&neck During fifth week, second pharyngeal arch enlarges and overgrows the third and fourth arches ,forming an ectodermal depression called cervical sinus By the end of 7 week the second to fourth pharyngeal grooves and cervical sinus have disappeared giving neck a smooth contour www.indiandentalacademy.c om
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  77. 77.  Typical pharyngeal arch contains1. aortic arch2. a cartiliaginous rod3. muscular component4. nerve www.indiandentalacademy.c om
  78. 78. Derivatives of pharyngeal arch cartilages FIRST ARCH Dorsal end of first arch cartilage [meckel cartilage] is closely related to the developing ear and ossifies to from two middle ear bones ,the malleus and incus Middle part of cartilage regresses but its perichondrium forms the anterior ligament of malleus and the sphenomandibular ligament www.indiandentalacademy.c om
  79. 79.  Second arch Dorsal end of second arch cartilage {Reichert cartilage} aslo related to developing ear,ossifies to form stapes of middle ear and the styloid process of temporal bone The part of cartilage between the styloid process and hyoid bone regresses ,its perichondrium forms stylohyoid ligament Ventral end of second arch cartilage ossifies to form lesser cornu and superior part of body of hyoid bone www.indiandentalacademy.c om
  80. 80.  Third arch cartilage ossifies to form greater cornu and the inferior part of body of hyoid bone The fourth arch cartilage and sixth arch cartilage fuse to form laryngeal cartilages,except for epiglotis www.indiandentalacademy.c om
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  82. 82.  Derivatives of pharyngeal arch muscle Derivatives of pharyngeal arch nerves www.indiandentalacademy.c om
  83. 83. Pharyngeal pouches Primordial pharynx derived from foregut widens cranially ,where it joins the primordial mouth/stomodeum and narrows caudally where it joins the esophagus. The endoderm of pharynx lines the internal aspects of pharyngeal arches and passes into ballon like diverticula called pharyngeal arches www.indiandentalacademy.c om
  84. 84.  There are 4 well defined pairs of pharyngeal pouches fifth pair is absent/rudimentary First pharyngeal pouch1. tubotympanic recess2. tympanic membrane3. tympanic cavity and mastoid antrum www.indiandentalacademy.c om
  85. 85.  Second pharyngeal pouch1. Palatine tonsil2. Tonsillar sinus Third pharyngeal pouch1. Inferior parathyroid gland Fourth pharyngeal pouch1. Superior parathyroid galnd www.indiandentalacademy.c om
  86. 86.  PHARYNGEAL GROOVES head and neck regions of human embryo exhibit four pharyngeal grooves on each side,these grooves separate the pharyngeal arches externally www.indiandentalacademy.c om
  87. 87.  Pharyngeal membrane it appears in floors of pharyngeal grooves .these membranes separate pharyngeal pouches from pharyngeal grooves www.indiandentalacademy.c om
  88. 88. Thyroid gland development It is first gland to develop after about 24 days after fertilization there appears median endodermal thickening in the floor of primordial pharynx this thickening soon forms a small outpouching Thyroid primodium www.indiandentalacademy.c om
  89. 89.  Thyroid primodium is hollow but it soon becomes solid and it divides into right and left lobes which are connected by isthmus of thyroid gland Thyroglossal duct for a short time thyroid gland is connected to tongue by a narrow tube ,the thyroglossal duct. By end of 7 weeks thyroid gland has assumed its final site in neck ,by this time thyroglossal duct has normally degenerated and disaappeared www.indiandentalacademy.c om
  90. 90. Development of face Five facial primordia appear around large primordial stomodeum early in 4 week ,they are1. single frontonasal process2. paired maxillary process3. paired mandibular processFacial development depends on the inductive influence of the prosencephalic &rhombencephalic organizing centers www.indiandentalacademy.c om
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  92. 92.  Frontonasal prominence surrounds the ventrolateral part of the forebrain Frontal part of frontonasal process forms the forehead The nasal part forms the rostral boundary of the stomodeum, primodial mouth, nose The paired maxillary prominence forms the lateral boundaries of the stomodeum The paired mandibular process forms the caudal part of primitive mouth , stomodeum www.indiandentalacademy.c om
  93. 93. FORMATION of LNP and MNP Nasal placodeBy the end of 4th week bilateral oval thickenings of surfaceectoderm develop. These are known as nasal the end of 5th week the nasal placodes invaginate to formnasal pits, in doing so they create a ridge of tissue thatsurrounds each pit and forms nasal prominencesthe prominences on the outer edge of the pits are lateral nasal prominences and those of inner ridge are medial nasal prominences www.indiandentalacademy.c om
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  95. 95. FORMATION OF UPPER LIP During the following 2 weeks the maxillary prominences due to proliferation of mesenchyme continue to increase in size and grow medially compressing the MNP towards the midline. Subsequently the cleft between the MNP and MP is lost and the 2 fuse, hence the upper lip is formed by 2 MNP and 2 MP. www.indiandentalacademy.c om
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  97. 97. NASOLACRIMAL DUCT MP and LNP are seperated by deep furrow known as nasolacrimal groove The ectoderm in this floor of this groove forms a solid epithelial cord that detaches from the overlying ectoderm After canalization the cord forms the nasolacrimal duct, its upper end widens to form lacrimal sac www.indiandentalacademy.c om
  98. 98. Lower jaw and lower lip are the first formed parts of the face to be formed.They result from merging of medial ends of mandibular prominences in the medial plane. www.indiandentalacademy.c om
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  103. 103. Formation of noseNose is formed from 5 facial prominences.Frontonasal prominence gives rise to nasal bridge.Merged medial nasal prominences provide the crest and the tip.Lateral nasal prominences form the sides or alae of the nose. www.indiandentalacademy.c om
  104. 104. Intermaxillary segment As a result of medial growth of maxillary prominences the MNP merge forming intermaxillary segment. It has 3 components:1. The labial component2. upper jaw component3. palatal component www.indiandentalacademy.c om
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  106. 106. Summary of facial development FNP forms fore head, dorsum apex of nose, LNP and MNP. LNP forms the sides of the nose MNP forms nasal septum and philtrum of upper lip. Maxillary prominences forms the upper cheek and most of upper lip. Mandibular process gives rise to chin, lower lip, lower cheek region www.indiandentalacademy.c om
  107. 107. Development of palate Palate develops from two primordia1. The primary palate2. The secondary palatePrimary palate early in the 6th week the primary palate – median palatine process begins to develop from the deep part of the intermaxillary segment of maxilla www.indiandentalacademy.c om
  108. 108. The primary palate forms the premaxillary part of maxilla .it represents only a small part of the adult hard palate www.indiandentalacademy.c om
  109. 109. Secondary palate The secondary palate is the primodium of the hard and soft parts of the palate The secondary palate begins to develop early in 6th week from two mesenchymal projections that extend from the internal aspects of maxillary prominences. Initially these structures the lateral palatine process or palatal shelves project inferomedially on each side of tongue www.indiandentalacademy.c om
  110. 110.  As the jaws develop tongue becomes relatively smaller and moves inferiorly During seventh and eighth week the lateral palatine process ascend to horizontal position superior to tongue Gradually these process approach each other and fuse in median plane they also fuse with nasal septum and posterior part of primary palate www.indiandentalacademy.c om
  111. 111.  Bone gradually develops in the primary palate forming the premaxillary part of the maxilla concurrently bone extends from maxilla and palatine bones into the lateral palatine process to form hard palate The posterior parts of these processes do not become ossified they extend posteriorly beyond the nasal septum and fuse to form soft palate ,including its soft conical projection uvula www.indiandentalacademy.c om
  112. 112. Anomalies of lip and palate1. Anterior cleft anomalies2. Posterior cleft anomalies3. Clefts involving the upperlip a. unilateral b. Bilateral c. median cleft lip4 Complete cleft palate www.indiandentalacademy.c om
  113. 113. Facial clefts INCISIVE FORAMEN is considered the dividing landmark between the anterior and posterior cleft deformities Those anterior to incisive foramen include1. Lateral cleft lip2. Cleft upper jaw3. Cleft between primary and secondary palate www.indiandentalacademy.c om
  114. 114. Anterior defects are mainly due to partial or complete lack of fusion of maxillary prominence with medial nasal prominence on one or both sides www.indiandentalacademy.c om
  115. 115. POSTERIOR CLEFTS 1. cleft palate 2. cleft uvulaCleft palate:Lack of fusion between palatal shelves Smallness of shelves Failure of shelves to elevate Inhibition of fusion process Failure of tongue to drop from between the shelves because of micrognathia www.indiandentalacademy.c om
  116. 116.  Anterior clefts vary in severity from a barely visible defect in the vermillion of lip to extension into nose In severe cases the cleft extends to a deeper level,forming a cleft of the upper jaw and the maxilla is split between the lateral incisor and the canine tooth www.indiandentalacademy.c om
  117. 117.  OBLIQUE FACIAL CLEFT failure of fusion of maxillary prominence to merge with its corresponding lateral nasal processo MEDIAN FACIAL CLEFT incomplete merging of the two medial nasal prominences in the midline .this anomaly is usually accompanied by a deep grove between the right and left sides of nose www.indiandentalacademy.c om
  118. 118. Development of salivary glandsDuring 6th, 7th, week salivary glands development begins as solid epithelial buds from primordial oral cavityThe club shaped ends of these epithelial buds grow into the underlying mesenchymeThe connective tissue in glands is derived from neural crest cells www.indiandentalacademy.c om
  119. 119. Parotid gland First to appear They develop from buds that arise from the oral ectodermal lining near angles of stomodeum These buds grow towards ears and branch to form solid cords with rounded ends Later the cords canalize develop lumina and become ducts by about 10th, weeks www.indiandentalacademy.c om
  120. 120.  Rounded ends of the cords differentiate in to acini Secretions commence at 18 weeks The capsule and connective tissue develop from surrounding mesenchyme www.indiandentalacademy.c om
  121. 121. Submandibular gland Appear late in 6th week They develop from endodermal bulbs in the floor of stomodeum ,they grow posteriorly ,lateral to tongue Acini begin to form at 12 weeks Secretory activity begins at 16 weeks www.indiandentalacademy.c om
  122. 122. Sublingual glandThey appear in 8th weekThey develop from multiple endodermal epithelial buds in paralingual sulcusThese buds branch and canalize to form 10 to 12 ducts that open inti floor of mouth www.indiandentalacademy.c om
  123. 123. Development of tongueTongue appears in embryos of approximately 4 weeks in the form of 1. two lateral lingual swellings 2. one median swelling 3. the tuberculum impar these three they arise from first pharyngeal arch www.indiandentalacademy.c om
  124. 124. A second median swelling, copula or hypobranchial eminence is formed by the mesoderm of second, third, part of fourth archA third median swellings formed by the posterior part of the fourth arch marks the development of the epiglottis www.indiandentalacademy.c om
  125. 125.  The lateral lingual swellings overgrow the tuberculum impar and merge ,forming the anterior two thirds of tongue Sensory innervation to this part of tongue is the mandibular part of trigeminal nerve Posterior part is formed from second ,third& part of fourth arch Sensory innervation to this part of tongue is glossopharyngeal nerve Extreme posterior part of tongue is innervated by superior laryngeal nerve www.indiandentalacademy.c om
  126. 126. Special sensory innervation (taste) to anterior two-thirds is chorda tympaniWhile to posterior is glosssopharyngeal nerve www.indiandentalacademy.c om
  127. 127. Molecular regulation of facial development Much of the face is mainly derived from neural crest cells that migrate into pharyngeal arches In hind brain they(NCC) orginate from rhombomeres (segmened regions) They are eight segments NCC from R1 & R2 migrate to first arch Cells from R4 go to second arch Those from R6 & R7 go to third arch Those from R8 go to fourth and sixth arches www.indiandentalacademy.c om
  128. 128.  Patterning of pharyngeal arches is regulated by HOX genes carried by migrating neural crest cells The expression patterns of HOX genes occur in specific overlying patterns The expression patterns determine the organization of cranial ganglia and nerves and pathways of neural regulation Initially crest cells express the HOX genes from their segment of origin ,but maintainence of this specific expression is dependant upon interaction of cells with mesoderm in pharyngeal arches www.indiandentalacademy.c om
  129. 129.  A host of upstream and down stream genes are involved in expression pattern SONIC HEDGEHOG may be one of the upstream regulators Retinoids can also regulate HOX gene expression in a concentration dependant manner Regulation occurs through retinioc acid response elementsIn addition to HOX gene ,OTX2 also participate in morphogenesis of first arch www.indiandentalacademy.c om
  130. 130. Thank you for Watching For more details please www.indiandentalacademy.c om