1. DEVELOPMENT OF FACE TEETH AND Dr Ibrahim 1Thursday, January 09, 2014

2. CONTENTS Development of:Face lower lip Upper lip Maxilla Mandible Eye Ear Palate Teeth 2Thursday, January 09, 2014 3. DEVELOPMENT OF FACE The development of facebegins during the 4th week of intrauterine life from 4 primordia that surround a central depression representing the primitive mouth or the stomatodeum. These include the frontonasal process (a single cranially located process), the 2 bilaterally located maxillary process, and the 3 mandibular process derivedThursday, January 09, 2014 4. 4Thursday, January 09, 2014 5. By the 5th week, the nasal placodes develop bilaterally onthe lower part of the frontonasal process where they border the oral cavity. At the margins of the placodes, mesenchyme proliferates and produces medial and lateral nasal processes thus transforming the placodes into nasal pits(nostrils). By the 6th 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.5Thursday, January 09, 2014 6. 6Thursday, January 09, 2014 7. On each side, the lateral nasal process is separatedfrom the maxillary process by a groove called the nasolacrimal groove. This groove will eventually disappear , but before it disappears, the epithelium at its depth first forms a solid rod and later will canalise , and form the nasolacrimal duct.7Thursday, January 09, 2014 8. The point of contact ofthe epithelium covering medial nasal process and maxillary processes is termed the nasal fin. This vertically positioned epithelial sheet under each nostril separates the medial nasal and maxillary processes; and when the fin disappears, the two 8 processes will fuse.Thursday, January 09, 2014 9. DEVELOPMENT OF LOWER LIP The mandibular9process appears initially as a partially divided bilateral structure but soon merges at the median line. This process will give rise to the lower lip and the lowerThursday, January 09, 2014 10. DEVELOPMENT OF UPPER LIP AND MAXILLA During the 6thweek, each maxillary process grows medially and fuses, first with the lateral nasal processes and then with the medial nasal process. The medial and lateral nasal processes also fuses with each other ; thus closing the nasal pits to the stomatodeum. The mesoderm of the lateral part of the lip is formed from theThursday, January 09, 2014 11. The maxillary processesundergo considerable growth while the frontonasal process becomes narrower bringing the anterior nares closer together. The mesoderm of the median part of the lip(philtrum), is formed from the frontonasal process. The ectoderm of the maxillary process overgrows this mesoderm to meet that of the opposite maxillary 11 process in the midline.Thursday, January 09, 2014 12. Maxilla Develops from center of ossification in the 12mesenchyme of maxillary process. No arch cartilage associated with maxillary process. Center of ossification appear in the angle between the division of infraorbital nerve. Bone formation spreads posteriorly below orbit toward developing zygoma, anteriorly towards future incisor region, superiorly to form frontal process- bony trough around infraorbital nerve. Ossification also spreads into the palatine process to form hard palate. A secondary cartilage-zygomatic or malar cartilage appear in the developing zygomaticThursday, January 09, 2014 process and adds to the development of maxilla. 13. Mandible At 6th week the Mecklescartilage extends as a solid hyaline cartilagenous rod, surrounded by a fibrocellular capsule,from developing ear region to the midline of fused mandibular processes. Two cartilages separated by thin band of mesenchyme. The mandibular nerve begins 2/3rd of the way along the length of the cartilage. Mandibular nerve divides into lingual and inferior alveolar branch running along medial and lateral aspect of cartilage. 13 More anteriorly inferiorThursday, January 09, 2014 14. During 6th week condensation of mesenchyme in thearea of division of inferior alveolar nerve. During 7th week, intramembranous ossification begins in this condensation.,spreads rapidly anteriorly to the midline and posteriorly to a point of division of mandibular nerve. The spraed of new bone forms a trough that consists of lateral and medial plates that unite beneath the incisor nerve. The trough of bone extends to midline to come in approximation with similar trough from opposite side The two ossification remain separated at symphysis until short after birth. Thursday, January 09, 2014 14 15. Similarly a backward extension of ossificationproceeds to a point where mandibular nerve divides into inferior alveolar nerve and lingual nerve resulting in the canal formation around the inferior alveolar nerve. The ramus develops by rapid spread of ossification posteriorly into mesenchyme of first arch turning away from Meckles cartilage. This point of divergence is marked by lingula in adult mandible, the point at which the inferior alveolar nerve enters the body of mandible.15Thursday, January 09, 2014 16. Further growth influenced by appearance of threesecondary cartilages Condylar cartilage-appear during 12th week as cone shaped cartilage that occupies most of the developing ramus. This quickly undergo endochondral ossification except for a thin layer of cartilage on the condylar head. The coronoid cartilage-appears at 4th month, surmounting the anterior border and top of the coronoid process. This is a transient cartilage and disappears long before birth. The symphysial cartilage- 2 in number, that ossify to form the mental ossicles. 16Thursday, January 09, 2014 17. 17Thursday, January 09, 2014 18. DEVELOPMENT OF EYE The eyes develop during the 5th week. The first external sign of eye development is theappearance of the lens placodes between the maxillary and frontonasal processes at the lateral sides of the face.18Thursday, January 09, 2014 19. The lens placode sinks below the surface and iseventually cut off from the surface ectoderm. The developing eyeball now presents as a bulge facing laterally. With the narrowing of the frontonasal process, they come to face forwards. The eyelids are derived from folds of ectoderm that are formed above and below the eyes, and by mesoderm enclosed within the folds.19Thursday, January 09, 2014 20. DEVELOPMENT OF EAR The external ear is formed around the dorsal partof the 1st ectodermal cleft. A series of mesodermal thickenings (tubercles or hillocks) appear on the mandibular and hyoid arches where they adjoin this cleft. The pinna is formed by fusion of these thickenings. 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 20Thursday, January 09, 2014 21. 21Thursday, January 09, 2014 22. DEVELOPMENT OF PALATE By the 6th week of development, the primitive nasal22cavities are separated by a primitive nasal septum and partitioned from the stomodeum by a primary palate.The formation of secondary palate commences between 7 and 8 weeks and is completed around the 3rd month of gestation. 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. The shelves are directed first downward on each side of the tongue. Thursday, January 09, 2014 23. 23Thursday, January 09, 2014 24. 24Thursday, January 09, 2014 25. After the 7th week of development, thetongue 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.25Thursday, January 09, 2014 26. 26Thursday, January 09, 2014 27. For the fusion of palatine shelves tooccur, 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. Surface epithelial cells are sloughed off as they undergo physiologic cell death to expose the basal epithelial cells. These cells have the carbohydrate rich surface coat that permits rapid adhesion and the formation of the junctions to achieve fusion of the processes. 27Thursday, January 09, 2014 28. A midline seam is thus formed of twolayers of the epithelial cells. This midline must be removed to permit ectomesenchymal continuity between the fused process. 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. The basal lamina surrounding these cells is lost and the epithelial cells transforms into mesenchymal cells. 28Thursday, January 09, 2014 29. PALATAL SHELF ELEVATION Several mechanisms have been proposed to account for the movement of the palatal shelves from vertical to the horizontal position. The closure of the secondary palate may involve an intrinsic force in the palatine shelves the nature of which has not been determined yet. The extrinsic forces derived from the growth of the mandible and a change in degree of flexion of fetal head- the tongue drops down from the path of developing palatine processes. The high content of glycosaminoglycans , which attract water and make the shelves turgid, has also been suggested. 29Thursday, January 09, 2014 30. PALATAL SHELF ELEVATION30Thursday, January 09, 2014 31. 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.31Thursday, January 09, 2014 32. DEVELOPMENTAL DEFECT OF PALATE Cleft palate: Less common than cleft lip. Itmaybe 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.32Thursday, January 09, 2014 33. 33Thursday, January 09, 2014 34. CLEFT LIP AND PALATE34Thursday, January 09, 2014 35. OVERALL SUMMARY OF DEVELOPMENT OF FACE35Thursday, January 09, 2014 36. DEVELOPME NT OF TEETH36Thursday, January 09, 2014 37. The primitive oral cavity, or stomodeum, is lined by stratified squamous epithelium called the oral ectoderm. The oral ectoderm contacts the endoderm of the foregut to form the buccopharyngeal membrane Tooth formation occurs in the 6th week of intrauterine life with the formation of primary epithelial band. At about 7th week the primary epithelial band divides into a lingual process called dental lamina & a buccal process called vestibular lamina. All deciduous teeth arises from dental lamina, later the permanent successors arise from its lingual extension & permanent molars from its distal Extension.37Thursday, January 09, 2014 38. Membrane ruptures at about 27th day of gestation and the primitive oralcavity establishes a connection with the foregut Most of the connective tissue cells underlying the oral ectoderm are of neural crest or ectomesenchyme in origin3= Connective tissue cells These cells instruct the overlying ectoderm to start the tooth development, which begins in the anterior portion of the future maxilla & Thursday, January 09, 2014 38 mandible and proceeds posteriorly 39. 2- 3 weeks after the rupture of buccopharyngeal membrane, certain areas of basal cells of oral ectoderm proliferate rapidly, leading to the formation of primary epithelial band The band invades the underlying ectomesenchyme along each of the horse-shoe shaped future dental arches.39Thursday, January 09, 2014 40. At about 7th week the primary epithelial band divides into an inner(lingual) process called Dental Lamina & an outer ( buccal) process called Vestibular Lamina The dental lamina serves as the primordium for the ectodermal portionof the deciduous teeth Later during the development of jaws, permanent molars arise directly from the distal extension of the dental lamina Thursday, January 09, 2014 40 41. The successors of the deciduous teeth develop from a lingual extensionof the free end of the dental lamina opposite to the enamel organ of each deciduous teeth.41Thursday, January 09, 2014 42. The lingual extension of the dental lamina is named the successional lamina & develops from the 5th month in utero ( permanent central incisor) to the 10th month of age (second premolar)42Thursday, January 09, 2014 43. FATE OF DENTALLAMINA It is evident that total activity of dental lamina exceeds over a period of atleast 5 yrs As the teeth continue to develop, they loose their connection with the dental lamina They later break up by mesenchymal invasion, which is at first incomplete and does not perforate the total thickness of the lamina43Thursday, January 09, 2014 44. Fragmentation of the dental lamina progresses toward the developing enamel organ Any particular portion of the dental lamina functions for a much briefer period since only a relatively short time elapses after initiation of tooth development before the dental lamina begins to degenerate However the dental lamina may still be active in the third molar region after it has disappeared elsewhere, except for occasional epithelial remnants44Thursday, January 09, 2014 45. VESTIBULAR LAMINA Labial and buccal to the dental lamina in each dental arch, another epithelial thickening develops independently It is Vestibular Lamina also termed as lip furrow band Subsequently hollows and form the oral vestibule between the alveolar portion of the jaws and the lips and cheeks.45Thursday, January 09, 2014 46. At certain points along the dental lamina each representing the location of one of the 10 mandibular & 10 maxillary teeth, ectodermal cells multiply rapidly & little knobs that grow into the underlying mesenchyme Each of these little down growths from the dental lamina represents the beginning of the enamel organ of the tooth bud of a deciduous tooth First to appear are those of anterior mandibular region As the cell proliferation occurs each enamel organ takes a shape that resembles a cap46Thursday, January 09, 2014 47. DENTAL SAC/ DENTAL FOLLICLE Surrounding the combined enamel organ or dental papilla, the third part of the tooth bud forms. It is known as dental sac/follicle and it consists of ectomesenchymal cells and fibres that surrounds the dental papilla and the enamel organ.C= Dental sac 47Thursday, January 09, 2014 48. DENTAL PAPILLA On the inside of the cap, the ectomesenchymal cells increase in number. The tissue appears more dense than the surrounding mesenchyme and represents the beginning of the dental papillaB = Dental Papilla 48Thursday, January 09, 2014 49. Thus the tooth germ consists of ectodermal componentthe enamel organ, the ectomesenchymal components- the dental papilla & the dental follicle The enamel is formed from the enamel organ, the dentin and the pulp from the dental papilla and the supporting tissues namely the cementum, periodontal ligament & the alveolar bone from the dental follicle During & after these developments the shape of the enamel organ continues to change The depression occupied by the dental papilla deepens until the enamel organ assumes a shape resembling a bell The dental lamina becomes longer, thinner & finally loses its connection with the epithelium of the primitive oral cavity 49Thursday, January 09, 2014 50. REFERENCES 1. Avery, James K., Chiego Daniel J. : Essentials of Oral Histolgy and Embryology. 3rd edition. 2. Grays Anatomy. 3. Ten Cates oral histology-Development , Structure and Function. 7th edition. 4. Singh Inderbir, G.P. Pal,: Human Embryology. 8th ed. 5. Sadler J.W. Langmans Medical EEmbryology. 9th ed.506. Kurt E. Johnson: Human Developemental Anatomy 7. Bhalajhi S.I., Orthodontics, The Art and Thursday, January 09, 2014 Science, 3rd ed. 51. THANK YOU 51Thursday, January 09, 2014