1. Dr Jamal Naim PhD in Orthodontics Development of face and oral Cavity

2. Phases of Development Embryogenesis is divided into three distinct phases during the 280 days of gestation : the preimplantation period (the first 7 days), the embryonic period (the next 7 weeks), and the fetal period (the next 7 calendar months).

3. The start - Fertilization Beginning of life for an individual human being is the moment, when the sperm unites with the ovum and forms a fertilized egg called zygote. The process of fertilization occurs in the distal third of the fallopian tubes.

4. The preimplantation period Following 3-5 days the ovum moves towards the uterus. The ovum undergoes a series of divisions and by the time it enters the uterine cavity a solid mass of cells, known as morula, has been formed.

5. The preimplantation period Shortly, a central cavity appears inside the morula and the cells form a fluid-filled ball called the blastocyte, which becomes implanted in the mucosa of the uterus. the blastocyte Embryoblast

6. The preimplantation period

7. The embryonic period The wall of the blastocyte cavity consists of a thin cell layer, the trophoblast, which is thickened at one site where a small group of cells, the embryoblast, bulges into the cavity. the blastocyte

8. The embryonic period About the 2nd week, the embryoblast differentiate into a layer of ectoderm and endoderm. Over the next few days, two small fluid-filled cavities form in the embryoblast - the amniotic cavity and the yolk sac, the walls of which are in contact.

9. The embryonic period The circular contact area consists of a layer of ectoderm towards the amniotic cavity and a layer of endoderm towards the yolk sac and constitutes the bilaminar embryonic disc. Only the embryonic disc will give rise to the embryo, while the remaining structures of the cavities develop into fetal membranes.

11. The embryonic period By the end of the 2nd week of development an endodermal thickening known as the prechordal plate is seen at the cephalic (head) end of the now oval-shaped embryonic disc. The prechordal plate is believed to perform a head-organizing function. This plate is firmly attached to the overlying ectodermal germ layer and the whole becomes the future bucco-pharyngeal membrane.

12. The embryonic period

13. During the 3rd week of development a narrow groove, called the primitive streak, appears at the caudal (tail) end of the ectoderm layer facing the amniotic cavity. Cells of this layer then migrate along the surface of the embryonic disc towards the primitive streak, which they invaginate.

15. The embryonic period From here the cells spread forward and laterally between the ectodermal and endodermal layers and form an intermediate cell layer, the mesoderm.

17. The embryonic period Each of the three germ layers gives rise to a number of specific tissues and organs. The cutaneous and neural systems develop from the ectoderm. The mesoderm gives rise to the cardiovascular system, the locomotor system (bones and muscles), connective tissues, and dental pulp.

18. The embryonic period The endoderm develops into the lining epithelium of the respiratory system and of the alimentary canal between the pharynx and the anus, as well as the secretory cells of the liver and pancreas.

19. The embryonic period The formation of the central nervous system starts as a thickened central plate within the ectoderm layer in the cephalic end of the embryo. Differentiated growth of this plate - the neural plate - folds into a neural groove.

20. The embryonic period The margins of the groove, the neural folds, become elevated, approach each other, and fuse along the midline.

21. The embryonic period This results in a tube-like structure, the neural tube. The neural tube develops into the brain and the spinal cord. During the folding of the neural plate, a unique group of cells develops from the ectoderm along each edge of the neural groove. These cells are the neural crest cells.

22. The embryonic period The neural crest cells that come to lie parallel to and on either side of the neural tube undergo extensive migration within the developing embryo.

23. The embryonic period The neural crest cells undergo differentiation into many different cell and tissue types. The neural crest-derived mesenchyme in the head and neck - often called the ectomesenchyme - contributes to branchial arch, cartilages, bone, connective tissue proper and dental tissues such as pulp, dentine, cementum and periodontal ligament.

24. The embryonic period During the 3rd and 4th weeks of development the ectoderm and neural tube grow extensively and produce two pronounced cephalocaudal flexions of the flat embryonic disc, one in the region of the buccopharyngeal membrane and the other in the region of the cloacal membrane.

25. The embryonic period During this growth process the buccopharyngeal membrane becomes inverted and comes to lie on the ventral aspect of the so-called head fold. Here it is located in a depression known as the stomodeum, the primitive oral cavity.

26. The embryonic period The entrance of the newly formed stomodeum is a wide opening bounded cranially by the frontal prominence of the bulging forebrain and caudally by the pericardial swelling.

27. The embryonic period The buccopharyngeal membrane, forming the floor of the stomodeum, ruptures at the end of the 3rd week of development and disappears during week 4. In this way communication is established between the stomodeum and the cranial end of the foregut, the pharynx.

28. The embryonic period At about the same time a stream of migrating neural crest cells is responsible for the formation of the frontonasal process, a swelling of tissue in front of the forebrain. Another stream of neural crest cells migrates towards the lateral aspect of the head where they surround the mesodermal cores in the arising branchial arches.

29. The embryonic period Both the frontonasal process and the branchial arches play a large part in the formation of the face and the oral cavity.

30. The embryonic period The branchial (or pharyngeal) arches comprise six paired bar-like thickenings formed from the lateral plate mesoderm between the ectoderm and endoderm.

31. The embryonic period They expand ventrally from the lateral side of the pharynx, intervene between the stomodeum and the developing heart, and finally meet in the midline.

32. The embryonic period The first and second pair of arches, named the mandibular and hyoid, are more prominent than the others, specially the fifth and sixth.

33. Maxillary process 1. Pharyngeal arch (mandibular) 2. Pharyngeal arch (hyoid arch) 3. Pharyngeal arch 4. And 6. Pharyngeal arch Developing heart Nasal placode Frontonasal prominence

34. The embryonic period Deep furrows in which the ectoderm and endoderm are in contact separate the branchial arches. The external furrows, on the lateral surface of the embryo, are called the branchial grooves, and the internal ones, along the lateral wall of the pharynx, are the pharyngeal pouches.

35. The embryonic period groove pouch

36. The embryonic period Each branchial arch contains a cartilaginous and muscular component, a nerve and an artery. The skeletal element, the arch cartilage, is derived from the neural crest mesenchyme, while the mesoderm of the arches gives rise to striated muscle cells.

37. DEVELOPMENT OF THE FACE

38. Formation of the face The face derives from five prominences that surround the stomodeum. The prominences are: the single median frontonasal prominence and the paired maxillary prominences and mandibular prominences; (derivatives of the first pharyngeal arch)

39. Formation of the face Tissues from the mandibular arches form all the lower face and most of the midface while the other pairs of arches, including branchial grooves and pharyngeal pouches, are involved mainly in the formation of the neck region.

40. Formation of the face The mesenchyme beneath the ectodermal thickenings rapidly proliferate, causing a tissue elevation around the placode. Each nasal placode possesses an outer lateral nasal and an inner medial nasal swelling.

42. Formation of the face In the fifth week, the lateral and medial nasal swellings enlarge rapidly, with the medials advancing toward one another and eventually fusing.

43. Formation of the face The maxillary prominence is dimensionally not impressive early in development. With medial growth of its terminals and broadening of its other borders, the maxillary prominence presses onto the nasal swellings forcing their medial and lateral arms closer together.

44. Formation of the face During the following week, the medial and lateral nasal swellings unite and merge with the maxillary process. The line of fusion of the maxillary process with the lateral nasal swelling is marked by a trough, the nasolacrimal groove.

45. Formation of the face The union of the medial nasal swellings forms the intermaxillary process of the maxillary arch. The intermaxillary process produces the philtrum of the lip, the segment of the maxilla bearing the incisor teeth, and the primary palate. Fused palatal process

46. Formation of the face The lateral nasal prominences give rise to the wings or alae of the nose. The medial nasal processes produce the inferior segment of the nasal septum.

47. Formation of the face By the end of the fourth week, the two mandibular prominences have grown towards one another and merged. The mandible, the lower lip, the lower portion of the cheek, the chin, and the gingiva take their origins from the mandibular prominences. The maxillary process gives rise to the lateral portions of the upper lip and cheeks, the maxilla, and the secondary palate with its associated gingiva.