Growth Development Of Face And Oral Cavity


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  • the most common missing tooth is third molars followed by upper lateral incisors then 2nd premolars and then lower incisor. The permanent teeth erupt lingual to the deciduous because of the lingual positioning of the dental lamina for the permanent teeth
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  • hi, any one can answer these two questions please 1) what is the most comon missing tooth in the oral cavity? 2) why in a mixed dentition the erupting permanent teeth are lingual to their adjecent exfoliating primary teeth?
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    “ From the conjugation of the blood and semen ,embryo comes into existence. After the period of conception, it becomes kalada (one day old embryo), after remaining seven nights it becomes a spherical mass, after two months the head is formed, after three months limb region is formed”
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Growth Development Of Face And Oral Cavity

  1. 2. <ul><ul><ul><ul><ul><li>Dr shabeel pn </li></ul></ul></ul></ul></ul>
  2. 3. Ancient growth and development concepts <ul><li>“ From the conjugation of the blood and semen ,embryo comes into existence. After the period of conception, it becomes kalada (one day old embryo), after remaining seven nights it becomes a spherical mass, after two months the head is formed, after three months limb region is formed” </li></ul>
  3. 4. Definition of Growth <ul><li>“ Developmental increase in mass.’’- Stewart.(1982) </li></ul><ul><li>“ An increase in size or number.” - Profitt. (1986) </li></ul><ul><li>“ Normal changes in amount of living substance.’’- Moyers (1988) </li></ul><ul><li>“ Growth signifies an increase, expansion or extension of any given tissue.” - Pinkham.(1994) </li></ul>
  4. 5. Definition of Development <ul><ul><li>Development is a progress towards maturity” – Todd(1931) </li></ul></ul><ul><ul><li>“ Development connotes a maturational process involving progressive differentiation at the cellular and tissue levels” – Enlow. </li></ul></ul>
  5. 6. <ul><ul><li>“ 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(1988) </li></ul></ul>
  6. 7. Normal features of Growth & Development <ul><li>Pattern </li></ul><ul><li>-Differential Growth </li></ul><ul><li>-Cephalocaudal gradient of growth </li></ul><ul><li>Variability </li></ul><ul><li>Timing, rate & direction </li></ul>
  7. 8. PATTERN <ul><li>Pattern in growth represents proportionality .It refers not just to a set of proportional relationships at a point in time, but to a change in these proportional relationships over time. </li></ul><ul><li>The physical arrangement of the body at any one time is a pattern of spatially proportioned parts. </li></ul>
  8. 9. DIFFERENTIAL GROWTH <ul><li>Different organs grow at different rates amount and at different times. </li></ul><ul><li>Scammon’s curve of growth- Richard Scammon. </li></ul><ul><li>Lymphoid tissues attain a 200% growth by the age of ten and then regress afterwards. </li></ul><ul><li>Neural tissue attains full growth by the age of six and then stops. </li></ul><ul><li>General tissues follow a sigmoid growth pattern. </li></ul><ul><li>Genital tissue grow significantly only at puberty and achieve full growth at about 20 yrs of age. </li></ul>
  9. 10. CEPHALOCAUDAL GRADIENT OF GROWTH <ul><li>This simply means that there is an axis of increased growth extending from the head towards the feet. </li></ul><ul><li>At about 3 rd month of IU life, the head takes up 50% of total body length. By the time of birth, the proportion of head decreases to 30%. </li></ul><ul><li>This proportion steadily declines till in adult, the proportion of head is only 12%. </li></ul>
  10. 11. Normal features of Growth & Development <ul><li>Pattern </li></ul><ul><li>-Differential Growth </li></ul><ul><li>-Cephalocaudal gradient of growth </li></ul><ul><li>Variability </li></ul><ul><li>Timing, rate & direction </li></ul>
  11. 12. Variability <ul><li>No two individuals with the exception of siamese twins are like. </li></ul><ul><li>Hence it is important to have a “normal variability” before categorizing people as normal or abnormal </li></ul>
  12. 13. Timing of Growth <ul><li>One of the factors for variability in growth. </li></ul><ul><li>Variations in timing arise, because the biologic clock of different individuals is different. </li></ul><ul><li>It is influenced by: </li></ul><ul><li>genetics </li></ul><ul><li>sex related differences </li></ul><ul><li>physique related </li></ul><ul><li>environmental influences </li></ul>
  13. 14. Growth spurts <ul><li>Defined as periods of sudden growth acceleration </li></ul><ul><li>Sex-linked </li></ul><ul><ul><li>Normal spurts are </li></ul></ul><ul><ul><li>Just before birth </li></ul></ul><ul><ul><li>1 year after birth </li></ul></ul><ul><ul><li>Infantile spurt – at 3 years age </li></ul></ul><ul><ul><li>Mixed dentition growth spurt – 7-9 years (females); 8-11 years (males) </li></ul></ul><ul><ul><li>Pre-pubertal spurt – 11-13 years(females); 14-16 years (males) </li></ul></ul>
  14. 15. Factors Implicated in the Craniofacial Development <ul><li>Growth Factors: Growth factors are peptides, which usually transmit signals between cells and thereby modulate their activity. </li></ul><ul><li>GF is an inductive agent and regulate cell activity at cell to cell level. </li></ul><ul><li>GF have very short half life and are secreted in very small amounts. </li></ul><ul><li>A GF produced by one cell and acting on other cell is called paracrine regulation , whereas the process of cell that recaptures its own products is called autocrine regulation . </li></ul><ul><li>Transforming GF- TGF b , BMP, GDF </li></ul><ul><li>Epidermal GF- EGF, TGF a, amphiregulin, Heparin binding EGF </li></ul><ul><li>Fibroblast Growth Factor (FGF) </li></ul><ul><li>Insulin like Growth Factor (IGF) </li></ul><ul><li>Platelet derived Growth Factor (PDGF) </li></ul><ul><li>Neurotrophins- Nerve Growth Factor(NGF), Brain Derived Neurotropic Factor(BDNF),Neurotrophin </li></ul>
  15. 16. <ul><li>Homeobox Genes: A group of genes with shared nucleotide segment that are involved in bodily segmentation during embryonic development. They are considered the key regulators of embryogenesis. </li></ul><ul><li>Homeobox is a stretch of DNA sequence that contains about 180 base pairs that encode transcription factors which typically switches on cascades of other genes. </li></ul><ul><li>HOX genes- These genes function in patterning the body axis and determine where limbs and other body segments will grow in developing foetus. </li></ul><ul><li>Msx genes- Control cellular process of differentiation and proliferation during development. </li></ul><ul><li>Dlx genes- Control development of ectodermal tissues derived from lateral border of the neural plate. </li></ul><ul><li> -Control differentiation of a subset of GABA ergic neurons of the basal ganglia and the cerebral cortex. </li></ul><ul><li>-Control patterning of the branchial arch skeleton </li></ul><ul><li>-Also expressed in developing bone and regulate limb development. </li></ul><ul><li>4. Shh (Sonic hedgehog) genes- Plays an important role in the early induction of facial primordium </li></ul>
  16. 17. Growth broadly subdivided as <ul><li>a. Prenatal growth </li></ul><ul><li>Period of ovum: From time of fertilization till 1 week. </li></ul><ul><li>Period of embryo: from 2 nd week till 8 th week </li></ul><ul><li>Period of foetus: from 9 th week onwards till birth </li></ul><ul><li>b. Postnatal growth </li></ul><ul><li>c. Maturity </li></ul><ul><li>d .Old age </li></ul>
  17. 18. Origin of Human Embryo <ul><li>Human prenatal development begins with processes involved in the ovarian cycle and fertilization. </li></ul><ul><li>Fertilization occurs in the fallopian tubes. </li></ul><ul><li>Fusion of the female and male pronuclei culminate the fertilization process. </li></ul><ul><li>The fertilized ovum, termed a zygote undergoes cleavage or division as it moves towards the uterine cavity. </li></ul>
  18. 19. Morula: 4th day <ul><li>The fertilized ovum, termed a zygote, undergoes cleavage or division as it moves toward the uterine cavity. </li></ul><ul><li>The cells formed during cleavage are called blastomeres, which soon begin to rearrange themselves in order to differentiate into various groups and layers. </li></ul><ul><li>By the 4th day, when the zygote reaches the uterus, it is a many celled mass called a morula . </li></ul>
  19. 20. Blastocyt stage: 5th day <ul><li>As the cell mass divides, it enlarges and gains a fluid filled inner cavity termed the blastocele. </li></ul><ul><li>The blastocele separates the cell into 2 parts: </li></ul><ul><li>An outer cell layer, the trophoblast , and </li></ul><ul><li>An inner cell mass, the embryoblast. </li></ul>
  20. 21. Implantation: 6th day <ul><li>The trophoblast attaches to the sticky endometrial surface on the posterior wall of the body of the uterus. </li></ul><ul><li>The surface cells of the trophoblast produces enzymes that digest the uterine endometrial cells, which allows a deeper penetration of the cell mass. </li></ul>
  21. 22. <ul><li>During the second week, the cells of the inner cell mass of the growing blastocyst differentiate into 2 cell types: </li></ul><ul><li>Columnar shaped ectodermal cells and </li></ul><ul><li>Cuboidal shaped endodermal cells adjacent to the blastocele. </li></ul><ul><li>The amniotic cavity appears between the ectodermal cells and the overlying trophoblast. </li></ul>
  22. 23. <ul><li>Later in the developmental process, the amnion expands, filling the entire extra embryonic coelom . </li></ul><ul><li>Thus in its final form, the amnion is a free membrane enclosing a fluid-filled space around the embryo. </li></ul><ul><li>Again, cells grow from the trophoblast and the embryonic disc, to form a primitive yolk sac. </li></ul>
  23. 24. <ul><li>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. </li></ul><ul><li>By day 16, a primitive knot of cells, the Henson’s node , appears at the cephalic end of the primitive streak. </li></ul><ul><li>This knot gives rise to the cells that form the notochordal process. </li></ul>
  24. 25. <ul><li>Cells from the primitive streak and the notochordal process migrate laterally between the ectodermal and endodermal layers of the embryonic shield. </li></ul><ul><li>These cells form the third germ cell layer called the mesodermal layer . </li></ul><ul><li>By the end of the third week, the mesoderm migrates in a lateral direction between the ectoderm and the endoderm, except at the anterior prochordal plate and posterior cloacal membrane. </li></ul>
  25. 26. <ul><li>The anterior plate forms the future oropharyngeal membrane. </li></ul><ul><li>Finally, mesodermal cells of the embryonic disc migrate peripherally to join the extraembryonic mesoderm on the amnion and yolk sac. </li></ul><ul><li>Anteriorly, mesodermal cells pass on either side of the prochordal plate to meet each other in front of this region. </li></ul>
  26. 27. Fate of germ layers <ul><li>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. </li></ul><ul><li>Endodermal cells will form the epithelial lining of the gastrointestinal tract and all associated organs. </li></ul><ul><li>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). </li></ul><ul><li>The embryonic disc will soon become altered by bends and folds necessary for further development. </li></ul>
  27. 28. Development of Nervous System <ul><li>On day 18, the developing notochord and the adjacent mesenchyme induce the overlying ectoderm to form the neural plate. </li></ul><ul><li>The neural plate then bends along its central axis to form a groove, and the raised margin along both sides of this groove form neural folds. </li></ul><ul><li>The neural folds gradually approach each other in the midline where they fuse. </li></ul><ul><li>The folds remain temporarily open at the cranial and caudal ends forming anterior and posterior neuropores. </li></ul><ul><li>The neuropores close during the fourth week and the central nervous system is established. </li></ul>
  28. 29. Development of Neural Crest <ul><li>At the time of neural tube closure, a unique population of cells separate from the crest of the folds. </li></ul><ul><li>They are known as the neural crest cells . </li></ul><ul><li>These cells undergo extensive migration beneath the surface ectoderm, especially in the head and neck region and give rise to a variety of cells. </li></ul><ul><li>They form the sensory ganglia, sympathetic neurons, schwann cells, pigment cells, meninges and cartilage of branchial arches. </li></ul><ul><li>They contribute to formation of the embryonic connective tissue of facial origin which includes connective tissue dental structures(dentin, pulp and cementum). </li></ul>
  29. 30. Development of Oral Cavity <ul><li>The primitive oral cavity or stomodeum appears late in the third prenatal week as a pit or invagination of the tissues underlying the forebrain. </li></ul><ul><li>This invagination appears as a result of the growth of the forebrain anteriorly and of the enlargement of the developing heart. </li></ul><ul><li>At the deepest end of the stomodeum, the oral ectoderm lies in close contact with the foregut endoderm. </li></ul><ul><li>The wall between the oral and pharyngeal cavity is termed the oropharyngeal membrane, as it separates the stomodeum from the first part of the foregut. </li></ul><ul><li>During the fourth week of intrauterine life, the oropharyngeal membrane disintegrates to establish continuity between the two cavities. </li></ul>
  30. 31. <ul><li>As the oral cavity emerges, it includes the stomodeum and foregut and 2 important endocrine glands develop from its roof and floor. </li></ul><ul><li>From the roof, an ectodermal lined pouch called Rathke’s pouch grows dorsally into the floor of the brain and gives rise to the anterior lobe of the pituitary gland. </li></ul><ul><li>On the floor of the oral cavity, on the tongue, a second epithelial pouch develops and grows downward into the anterior neck to give rise to the thyroid gland. </li></ul><ul><li>Both of these important endocrine glands develop from the oral tissue. </li></ul>
  31. 32. Branchial Arches <ul><li>The tissues bordering the oral pit inferiorly and laterally develop into five or six pairs of bars which form the lower part of the face and neck. These bars are termed branchial arches. </li></ul><ul><li>The first four branchial arches are well developed in humans. Only the first and second arches extend to the midline, and each arch is progressively smaller from first to the last. </li></ul><ul><li>The mandibular branchial arch is the first to develop. It is located just below the stomatodeum. </li></ul><ul><li>The hyoid is the second arch to develop. </li></ul><ul><li>The IIIrd, IVth and Vth arches consist of paired bars of epithelial covered mesoderm which are divided in the midline by the developing heart. </li></ul>
  32. 33. Ectodermal clefts and Endodermal pouches
  33. 34. Branchial Grooves <ul><li>The first branchial groove deepens to form the external auditory meatus. </li></ul><ul><li>The ectodermal membrane in the first groove persists and together with mesoderm and endoderm from adjacent first pharyngeal pouch, forms the tympanic membrane. </li></ul><ul><li>The external features of the 2 nd ,3 rd and4th branchial grooves become obliterated by the overgrowth of the second branchial arch. </li></ul><ul><li>This overgrowth then provides the smooth contour of the neck. </li></ul>
  34. 35. Pharyngeal Pouches <ul><li>The endodermal epithelium of the pharyngeal pouches differentiate into a variety of important organs. </li></ul><ul><li>From the 1 st pouch ,the middle ear and the Eustachian tube develop. </li></ul><ul><li>From the 2nd, the palatine tonsils originate. </li></ul><ul><li>From the 3rd pouch, the inferior parathyroid and the thymus arise. </li></ul><ul><li>From the 4 th pouch, the superior parathyroid gland forms. </li></ul><ul><li>From the 5 th pouch, the ultimobranchial body develops. </li></ul><ul><li>The thymus is relatively large at birth, continues to grow till puberty and thereafter atrophies and disappears later in life. </li></ul><ul><li>The ultimobranchial body fuses with the thyroid and contributes parafollicular cells to this gland. </li></ul><ul><li>The parathyroid gland functions throughout life in calcium regulation </li></ul><ul><li>The tonsils function in lymphocyte development and immunologic factors. </li></ul>
  35. 37. Branchial Arch Vasculature <ul><li>Each of the 5 branchial arches contains a pair of blood vessels that conduct blood from the heart to the brain and to the posterior tissues through the arch tissues. These are called aortic arches. </li></ul><ul><li>The anterior right and left aortic arches develop first and, after a week, begin to disappear as more posterior arches develop. </li></ul><ul><li>The most caudal arch vessels then enlarge and mature. </li></ul><ul><li>The 5 th arch vessels disappear next. </li></ul><ul><li>The 3 rd , 4 th and 6 th arch vessels do not disappear but are important in later functions. </li></ul>
  36. 38. <ul><li>The 3 rd arch vessels become the common carotid arteries which supply the neck, face and brain. </li></ul><ul><li>The 4 th arch vessels become the dorsal aorta which supplies blood to the entire body. </li></ul><ul><li>The vessels of the 6 th arch supply blood to the lungs as pulmonary circulation. </li></ul><ul><li>In an embryo at 4 weeks, the heart is ventral to the arches, and the blood passes dorsally to the brain and body. </li></ul><ul><li>By the 5 th week, the 1 st and 2 nd branchial arch vessels have disappeared, and then the blood supply to the face is carried out by the 3 rd branchial artery which becomes the carotid artery. </li></ul>
  37. 39. <ul><li>The common carotid artery gives rise to the external carotid and the internal carotid arteries. </li></ul><ul><li>The external carotid artery supplies blood to the ventral part of the 1 st and 2nd branchial arches. </li></ul><ul><li>The internal carotid artery supplies blood to the brain. </li></ul><ul><li>In the region of the ear, the internal carotid artery gives rise to a small vessel, the stapedial artery, which supplies most of the blood to the upper part of face and palate. </li></ul><ul><li>Blood supply to the face by internal carotid artery is a characteristic of the embryo at 6 and 7 weeks. </li></ul>
  38. 40. Shift in Blood Supply to the Face <ul><li>An important change in the human embryo takes place in the 7 th prenatal week as the stapedial artery suddenly occludes and separates from the internal carotid artery; which discontinues its blood supply to the face and palatal tissues. </li></ul><ul><li>Many of its terminal branches fuse with the peripheral branches of the external carotid. </li></ul><ul><li>This results in the most unusual shift in the blood supply of the face, from the internal carotid to the external carotid artery. </li></ul><ul><li>The timing of this shift is very important. The vessels begin to degenerate at one site and rapidly proliferate at another. </li></ul>
  39. 41. <ul><li>If timing in the shift is not precise, there will be a period when the face is deprived of oxygen and nutrition carried by this blood supply. </li></ul><ul><li>The 7 th week is an important period of rapid growth expansion and fusion of the facial processes. The lip and palate are undergoing maximal developmental changes during this time. </li></ul><ul><li>Thus, a vascular deficiency at this time may result in oxygen and nutritional deficiency which could result in cleft lip, cleft palate or both. </li></ul>
  40. 42. Branchial Arch Cartilages <ul><li>The initial skeleton of the branchial arches develops from the mesenchymal tissue as cartilaginous bars. </li></ul><ul><li>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. </li></ul><ul><li>In the 2 nd arch, 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. </li></ul>
  41. 43. <ul><li>The 3 rd arch cartilage forms the greater horn and lower part of the body of the hyoid. </li></ul><ul><li>The 4 th arch cartilage forms the thyroid cartilage. </li></ul><ul><li>The 5 th arch cartilage has no adult derivatives. </li></ul><ul><li>The 6 th arch cartilage forms the laryngeal cartilages. </li></ul>
  42. 45. Development of Facial Muscles <ul><li>During the 5 th and 6 th weeks, myoblasts within the mandibular arch begin proliferation. They become oriented to the sites of origin and insertion of the muscles they will form. </li></ul><ul><li>By 7 weeks, the mandibular muscle mass has enlarged and cells have begun migrating and differentiating into the 4 muscles of mastication : the masseter, medial and lateral pterygoid and temporal muscles. </li></ul><ul><li>The muscle cells within the hyoid arch and in the occipital myotomes undergo proliferation and migrate anteriorly toward the floor of the mouth to form muscles of the tongue. </li></ul><ul><li>Muscle cells of the 3 rd and 4 th arch form the pharyngeal muscles : stylopharyngeus, cricothyroid, levator palatini and constrictor muscles of pharynx. </li></ul>
  43. 46. <ul><li>By the 10 th prenatal week, the mandibular arch muscle masses have become well organised bilaterally. </li></ul><ul><li>The muscle cells of masseter and medial pterygoid have formed a vertical sling inserting into the site that will form the angle of the mandible. </li></ul><ul><li>The temporalis muscle has differentiated in the infratemporal fossa and is inserting in the developing coronoid process. </li></ul><ul><li>The lateral pterygoid muscle fibres, which also arise from the infratemporal fossa, extend horizontally to the necks of the condyles and insert in the articular discs. </li></ul><ul><li>The pharyngeal constrictor muscles have differentiated and enclosed the pharynx. </li></ul><ul><li>The face will change shape considerably as it grows, and all its muscles will develop to meet the increasing functional demand. </li></ul>
  44. 47. Innervation of Facial Muscles <ul><li>By the 7 th week, the Vth nerve has entered the mandibular muscle mass, as has the VIIth nerve in the second arch mass. This means that the nerves are incorporated in these muscles very early and they follow the muscles as they migrate and differentiate. </li></ul><ul><li>The trigeminal nerve (V) supplies sensory fibres to the mandible and maxilla and motor fibres to the muscles of mastication and to mylohyoid, tensor palatini, tensor tympani, and anterior belly of digastric muscle. </li></ul><ul><li>The facial nerve (VII) follows the migration of the facial muscle mass from the neck onto the face. It also supplies the stylohyoid and stapedius muscles and posterior belly of digastric muscle. </li></ul><ul><li>The glossopharyngeal nerve (IX) supplies the stylopharyngeus and the upper pharyngeal muscles. </li></ul><ul><li>The vagus nerve (X) supplies the pharyngeal constrictor and laryngeal muscles. </li></ul>
  45. 48. Development of Tongue <ul><li>The tongue is composed of the body which is the movable oral part and the posterior (attached) base or pharyngeal part. </li></ul><ul><li>The tongue develops from the tissues of the 1 st , 2 nd and 3 rd branchial arches and from the occipital myotomes. </li></ul><ul><li>The body of the tongue develops from 3 elevations on the ventromedial aspect of the 1 st arch: a tuberculum impar and paired lateral lingual swellings. These lateral lingual swellings rapidly enlarge, merge with each other , and overgrow the tuberculum impar to form the oral part of the tongue. </li></ul><ul><li>A U-shaped sulcus develops in front and on both sides of this oral part, which allows it to be free and highly mobile except at the region of the frenum lingulae. </li></ul>
  46. 50. <ul><li>The base of the tongue develops mainly from the 3 rd branchial arch. Initially, it is indicated by 2 midline elevations that appear caudal to the tuberculum impar. </li></ul><ul><li>These are the copula of the 2 nd arches and the large hypobranchial eminence of the 3 rd and 4 th arches. </li></ul><ul><li>Later the hypobranchial eminence overgrows the 2 nd branchial arches to become continuous with the body of the tongue. </li></ul><ul><li>The site of union between the base and body of the tongue is delineated by a V-shaped groove called sulcus terminalis. </li></ul><ul><li>The occipital myotomes migrate anteriorly into the tongue during the 5 th to 7 th weeks. </li></ul><ul><li>Later, various types of papillae differentiate in the dorsal mucosa of the body of the tongue, whereas lymphatic tissue develop into the base of the tongue. </li></ul>
  47. 51. Innervation of Tongue <ul><li>As the occipital muscle masses migrate anteriorly, the IXth and XIIth nerves are carried along into the tongue. </li></ul><ul><li>The Vth nerve supplies sensory fibres to the body or anterior 2/3rds of the tongue. </li></ul><ul><li>The VIIth nerve supplies the taste fibres to the same part. </li></ul><ul><li>The IXth nerve supplies sensory taste fibres to the posterior 1/3 rd </li></ul><ul><li>The hypoglossal nerve supplies the intrinsic muscles (longitudinal, vertical and transverse) and the extrinsic muscles (styloglossus, hyoglossus and genioglossus). </li></ul>
  48. 52. Development of Thyroid <ul><li>In the 4 th week, the thyroid gland develops as a depression and epithelial thickening in the floor of the pharynx. </li></ul><ul><li>This appears at a point between the body and base of the tongue called the foramen caecum. From this point, the thyroid primordium descends in the neck as a bilobed diverticulum to reach in front of the trachea in the 7 th week. </li></ul><ul><li>During this migration, the gland remains connected to the floor of the oral cavity by an epithelial cord or duct, the thyroglossal duct which later becomes a cord of cells. </li></ul><ul><li>The foramen caecum remains at the site of origin. </li></ul><ul><li>The thyroid gland begins to function at the beginning of the 3 rd month when colloid containing follicles appear. </li></ul>
  49. 53. Development of Salivary Glands <ul><li>The major salivary glands (parotid, submandibular and sublingual) begin development during 6 th to 8 th week. </li></ul><ul><li>The parotid develops in the lateral aspects of the stomodeum, and the submandibular and sublingual develop in the floor of the stomodeum. </li></ul><ul><li>Each gland develops through growth from a bud of oral epithelium into the underlying mesenchyme. </li></ul><ul><li>The epithelial buds differentiate into extensive system of solid cords of cells which later form lumen and become ducts. </li></ul><ul><li>Minor salivary glands develop during the 3 rd prenatal month. They remain as separate acini scattered in the connective tissue underlying the oral mucosa. </li></ul><ul><li>Failure of canalisation of ducts before acinar secretion begins results in retention cysts. </li></ul>
  50. 54. Development of Early Face <ul><li>The face develops during the 5 th to 7 th week of intrauterine life from 4 primordia that surround a central depression called the central pit. </li></ul><ul><li>These include the frontal process (a single cranially located process), the 2 bilaterally located maxillary process, and the mandibular process derived from the first branchial arch. </li></ul><ul><li>The mandibular process appears initially as a partially divided bilateral structure but soon merges at the median line. This process will give rise to the mandible, the lower part of the face and the body of the tongue. </li></ul>
  51. 55. <ul><li>By the 5 th week, the nasal placodes develop bilaterally on the lower part of the frontonasal process where they border the oral cavity. </li></ul><ul><li>At the margins of the placodes, mesenchyme proliferates and produces medial and lateral nasal processes thus transforming the placodes into nasal pits(nostrils). </li></ul><ul><li>By the 6 th week of IU life, The medial and lateral nasal processes appear as horse shoe shaped structures with the open end of the slit in contact with the oral cavity. </li></ul>
  52. 56. <ul><li>On each side, the lateral nasal process is separated from the maxillary process by a groove called the nasolacrimal groove. </li></ul><ul><li>This groove will eventually disappear , but before it disappears, the epithelium at its depth will proliferate into a solid cord which will separate from the surface, canalise , and form the nasolacrimal duct </li></ul><ul><li>The point of contact of the epithelial covered medial nasal and maxillary processes is termed the nasal fin. </li></ul><ul><li>This vertically positioned epithelial sheet under each nostril separates the medial nasal and maxillary processes; and when the fin disappears, the lip will fuse. </li></ul>
  53. 57. Formation of Upper Lip <ul><li>During the 6 th week, the 2 medial nasal processes merge in the midline to form the intermaxillary segment. </li></ul><ul><li>This will give rise to the centre of the upper lip, the primary palate, and the part of the alveolar process carrying the incisor teeth. </li></ul><ul><li>Each maxillary process grows medially and fuses, first with the lateral nasal processes and then with the medial nasal process. </li></ul><ul><li>The medial and lateral nasal processes also fuses with each other ;thus closing the nasal pits to the stomatodeum. </li></ul><ul><li>The mesoderm of the lateral part of the lip is formed from the maxillary process. The overlying skin is derived from ectoderm of the same process. </li></ul>
  54. 58. <ul><li>The maxillary processes undergo considerable growth while the frontonasal process becomes narrower bringing the anterior nares closer together. </li></ul><ul><li>The mesoderm of the median part of the lip(philtrum), is formed from the frontonasal process. </li></ul><ul><li>The ectoderm of the maxillary process overgrows this mesoderm to meet that of the opposite maxillary process in the midline. </li></ul><ul><li>As a result, the skin of the entire upper lip is supplied by the maxillary nerves. </li></ul>
  55. 59. <ul><li>The 3 sets of facial processes derive their nerve supply from 3 divisions of the trigeminal nerve. </li></ul><ul><li>The ophthalmic division supplies the frontonasal process, the maxillary division supplies the maxillary process, and the mandibular division supplies the mandibular process. </li></ul>
  56. 60. Development of Eye <ul><li>The eyes develop during the 5 th week. </li></ul><ul><li>The first external sign of eye development is the appearance of the lens placodes between the maxillary and frontonasal processes at the lateral sides of the face. </li></ul><ul><li>The lens placode sinks below the surface and is eventually cut off from the surface ectoderm. </li></ul><ul><li>The developing eyeball now presents as a bulge facing laterally. With the narrowing of the frontonasal process, they come to face forwards. </li></ul><ul><li>The eyelids are derived from folds of ectoderm that are formed above and below the eyes, and by mesoderm enclosed within the folds. </li></ul>
  57. 61. Development of Ear <ul><li>The external ear is formed around the dorsal part of the 1 st ectodermal cleft. </li></ul><ul><li>A series of mesodermal thickenings appear on the mandibular and hyoid arches where they adjoin this cleft. </li></ul><ul><li>The pinna is formed by fusion of these thickenings. </li></ul><ul><li>When first formed the pinna lies caudal to the developing jaw. It is pushed upwards and backwards due to later enlargement of the mandibular process </li></ul>
  58. 62. Development of the Palate <ul><li>By the 6 th week of development, the primitive nasal cavities are separated by a primitive nasal septum and partitioned from the stomodeum by a primary palate. </li></ul><ul><li>Both the primary nasal septum and the primary palate are derived from the frontonasal process. </li></ul><ul><li>The formation of secondary palate commences between 7 and 8 weeks and is completed around the 3 rd month of gestation. </li></ul><ul><li>Three outgrowths appear in the oral cavity: the nasal septum grows downwards from the frontonasal process along the midline, and 2 palatal shelves or processes , one from each side, extend from maxillary process towards the midline. </li></ul><ul><li>The shelves are directed first downward on each side of the tongue. </li></ul><ul><li>After the 7 th week of development, the tongue is withdrawn from between the shelves, which now elevate and fuse with each other above the tongue and with the primary palate. The septum and 2 shelves converge and fuse along the midline, thus separating the oronasal cavity into oral and nasal cavities. </li></ul>
  59. 64. <ul><li>For the fusion of palatine shelves to occur, elimination of the epithelial covering of the shelves is necessary. To achieve this fusion, DNA synthesis ceases within the epithelium some 24 to 36 hours before the epithelial contact. </li></ul><ul><li>Surface epithelial cells are sloughed off as they undergo physiologic cell death to expose the basal epithelial cells. </li></ul><ul><li>These cells have the carbohydrate rich surface coat that permits rapid adhesion and the formation of the junctions to achieve fusion of the processes. </li></ul><ul><li>A midline seam is thus formed of two layers of the epithelial cells. This midline must be removed to permit ectomesenchymal continuity between the fused process. </li></ul><ul><li>The growth of the seam fails to keep pace with the palatal growth so that the seam first thins and then breaks down into discrete islands of epithelial cells. </li></ul><ul><li>The basal lamina surrounding these cells is lost and the epithelial cells transforms into mesenchymal cells. </li></ul>
  60. 65. Palatal Shelf Elevation <ul><li>Several mechanisms have been proposed to account for the rapid movement of the palatal shelves from vertical to the horizontal position. </li></ul><ul><li>The closure of the secondary palate may involve an intrinsic force in the palatine shelves the nature of which has not been determined yet. </li></ul><ul><li>The extrinsic forces derived from the tongue and jaw movements may be responsible for this. </li></ul><ul><li>The high content of glycosaminoglycans , which attract water and make the shelves turgid, has also been suggested. </li></ul>
  61. 66. <ul><li>The developing human is least susceptible to teratogens during the proliferation period; first 2 or 3 weeks. </li></ul><ul><li>The embryonic period; end of 2 nd or 3 rd week to end of 8 th week; is most critical period because it is the period of differentiation of organs and systems. </li></ul><ul><li>During the foetal period; end of 8 th week until birth; the susceptibility to teratogens rapidly declines and may cause only minor defects. </li></ul>
  62. 67. <ul><li>Hereditary causes: </li></ul><ul><li>Chromosomal abnormalities- Trisomy 21; mental retardation, upward slanting palpebral fissures, flat nasal bridge and fissured protruding tongue. </li></ul><ul><li>Genetic abnormalities- Mandibulofacial dysostosis </li></ul><ul><li>Environmental causes: </li></ul><ul><li>Infectious agents- Rubella in pregnant women causing cleft palate, malformed teeth and congenital cataracts. </li></ul><ul><li>Radiation- Direct and indirect effect </li></ul><ul><li>Drugs- Aminopterin, tetracycline, Phocomelia by thalidomide </li></ul><ul><li>Hormones- Cortisone in experimental animals </li></ul><ul><li>Nutritional disorders- Vitamin deficiencies and hypervitaminosis A C D </li></ul><ul><li>Teratogenic habits- Smoking, alcohol and caffeine </li></ul>
  63. 68. Abnormal Development <ul><li>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. </li></ul><ul><li>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. </li></ul>
  64. 69. <ul><li>Cervical Cysts and Fistulae: </li></ul><ul><li>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. 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. </li></ul><ul><li>Another cause is incomplete caudal overgrowth of 2 nd arch, which leaves an opening on the surface of the neck. </li></ul>
  65. 70. Thyroglossal cyst and Fistula: Cysts and fistulae found along the midline of the neck usually develop from remnants of thyroglossal duct. Generally, thyroglossal cysts maybe found at any point along the course of the thyroglossal duct but it is usually found at the level of the hyoid bone and the thyroid cartilage. 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.
  66. 71. Abnormal Development <ul><li>Fissural cysts: Cystic cavities which arise along the fusion of various bones or embryonic processes and lined by epithelium. </li></ul><ul><li>Median Rhomboid Glossitis: It results from persistence of the tuberculum impar and characterised by a red smooth region anterior to the foramen caecum. </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>Bifid tongue: This is a malformation common in south American infants and is the result of failure of the lateral lingual swellings. </li></ul>
  67. 72. Developmental Anomalies <ul><li>Hare lip </li></ul><ul><li>Oblique facial cleft </li></ul><ul><li>Cleft palate </li></ul><ul><li>Macrostomia </li></ul><ul><li>Microstomia </li></ul><ul><li>Hypertelorism </li></ul><ul><li>Congenital lip pits or fistulae </li></ul><ul><li>Double lip </li></ul><ul><li>Congenital tumours in relation to the face </li></ul><ul><li>Bifid nose </li></ul>