Development of face, palate and jaw

seminar on development of face palate and jaw

1. DEVELOPMENT OF FACE, PALATE AND JAWS Presented by: DR. KALPAJYOTI BHATTACHARJEE

2. CONTENTS General embryology Pharyngeal arches Development of head Development of skull Development of face Derivation of different parts of face Development of mouth Development of palate Development of mandible Development of maxilla Development of teeth Development of tongue Development of salivary glands

3. GROWTH Increase in size, change in proportion and progressive complexity- Krogman An increase in size- Todd Change in any morphological parameter which is measurable- Moss

4. DEVELOPMENT Development is the progress towards maturity- Todd(1931) Differentiation is the change from a generalized cell or tissue to one that is more specialized. It is change in quality or kind.

5. INTRODUCTION Embryology is the study of the development of an individual before birth. Fertilization is the fusion of male and female germ cells to form a zygote. It takes place in the ampulla of the uterine tube. During the first two months the developing zygote is called an embryo and after that it is called a fetus .

6. The human embryo contains 46 chromosomes, called as diploid number. Out of which 44 chromosomes are autosomes and remaining 2 are sex chromosomes, designated as X and Y chromosomes. The sex chromosome in female are XX chromosome and in male XY chromosome.

7. THE PROCESS OF FERTILIZATION The male gamete (sperm) fuses with the female gamete (ovum)

8. Prenatal development Embryonic stage :- 1 st four weeks- cellular proliferation and differentiation. next 4 weeks- major external and internal structures form. Fetal stage: - growth and maturation of embryo.

9. Formation of Blastocyst Fertilized egg undergoes rapid division Morula Fluid seeps into morula B lastocyst

10. Bilaminar disc At about day 8 of gestation, embyoblast cells differentiate , into a 2 layered disk called bilaminar germ disk. ectodermal cells are columnar and reorganize to form amniotic cavity.

11. Extraembryonic mesoderm Cells of trophoblast give rise to mass of cell called EEM. Lie between trophoblast and the flattened hypoblast cells lining the yolk sac. Does not give rise to any tissue of the embryo itself.

12. Prochordal plate During the time the axis of the embryo is established and is represented by a slight enlargement of the ectodermal and endodermal cells at the head end of the embryo in a region known as prochondral plate .

13. Primitive streak Floor of the amniotic cavity is formed by ectoderm, and within it primitive streak develops along the midline. The rostral end of streak finishes in a depression called primitive node . Multiplying cells move into the interval between ectoderm and endoderm to form mesoderm.

14. Notochord Cells of ectoderm divide at the node, migrate between ectoderm and endoderm to form a solid column that pushes forward in the midline as far as the prechondral plate. Through canalization of this cord of cells, notochord is formed to support the embryo.

15. Somite

16. Neural Crest cells A group of cells separate from the neuroectoderm on the lateral aspect of the neural plate. Undergo epithelial-mesenchymal interactions. BMP and FGF are the inducing agents. Embryonic CT derived from mesoderm- mesenchyme Head- neuroectoderm- ectomesenchyme Form all tissues of tooth except enamel. Treacher Collins syndrome .

17. Folding of the Embryo In 2 planes: rostrocaudal axis and lateral axis. Head fold critical in formation of oral cavity. Stomatodeum separated from the gut by the buccopharyngeal membrane.

18. Sequence of events 8 th day – bilaminar disc 14 th day- prochordal plate and primitive streak 16 th day- intraembryonic mesoderm 17 th day- notochord 23th day- neural tube

19. PHARYNGEAL ARCHES Rod-like thickenings of mesoderm in the foregut. At first 6 arches. 5 th arch disappear, only 5 remains. The ventral ends of the arches of the right and left sides meet at the middle line in the floor of the pharynx. They bring about elongation of the region between the stomatodeum and the pericardium forming neck. In the interval between any two adjoining arches, endoderm extends outwards to form a series of pouches. They are called endodermal or pharyngeal pouches ..

20. ARCH NERVE OF THE ARCH DERIVATIVES First ( mandibular arch) Mandibular Muscles of mastication, anterior belly of digastric , tensor tympani, tensor palati , meckels cartilage, sphenomandibular ligament, anterior ligament of malleus . Second (hyoid arch) Facial Stapes, styloid process, stylohyoid ligament, smaller cornu of hyoid bone, superior part of body of hyoid bone, occipitofrontalis , platysma , posterior belly of digastric , auricular muscle . Third Glosso -pharyngeal Stylopharyngeus , greater cornu of hyoid bone, lower part of hyoid bone. Fourth Superior laryngeal Muscles of larynx and pharynx. Fifth Recurrent laryngeal

21. Fate of endodermal pouches 1 st pouch: ventral part obliterated by formation of tongue. dorsal part – tubotympanic recess proximal – auditory tube, middle ear cavity, tympanic antrum . 2 nd pouch: tonsil, tubotympanic recess, 3 rd pouch: inferior parathyroid glands, thymus. 4 th pouch: superior parathyroid glands, thyroid glands 5 th pouch: ultimobranchial body.

22. Development of head Anterior portion of the neural tube expands greatly as forebrain, midbrain & hindbrain form but a small amount of mesenchyme always remains between the developing brain and the surface epithelium. Hindbrain forms 8 bulges - rhombomeres Paraxial mesoderm : lateral to neural tube 7 Somatomeres - rostrally Somites - caudally

23. Craniofacial development- migration of the neural crest cells from the midbrain & first two rhombomeres in 2 streams:- 1 st stream : Migrates forward. Intermingles & reinforces the mesenchyme beneath the expanding forebrain. Connective tissue of the face. 2 nd stream directed towards the first branchial arch.

24. Development of the skull Skull can be divided into 3 components: 1)The cranial vault 2)the cranial base 3) the face Membranous bone, formed directly in mesenchyme with no cartilaginous precursor, forms the cranial vault and face Cranial base → endochondral ossification. Membrane formed bones may develop secondary cartilages to provide rapid growth.

25. DEVELOPMENT OF FACE The basic morphology of the face is created 24 th and 38 th day of gestation - development & fusion of the prominences:- Frontonasal prominence Maxillary swellings Mandibular swellings At 24 days, maxillary process & mandibular process are formed.

26. Early development is dominated by proliferation and migration of ectomesenchyme involved in the formation of primitive nasal cavities. At about 28 days, localized thickening develop within ectoderm of the frontal prominence - olfactory or nasal placodes . Rapid proliferation of mesenchyme - Horse shoe shaped ridge - nasal pits.

27. Lateral arm of horse shoe - lateral nasal process and middle arm - medial nasal prosess. Region of frontal prominence where nose develop - frontonasal process. The median nasal processes of both sides, together with the frontonasal process, give rise to the middle portion of the nose , middle portion of the upper lip , anterior portion of maxilla and the primary palate .

28. Maxillary process grows medially and approaches the lateral and medial nasal processes but remains separated from them by distinct groove- naso -optic and bucconasal groove . Maxillary processes grow medially - pushing the medial nasal process towards midline and merges anatomic counterpart.

29. Upper lip - by maxillary process of each side & medial nasal process. Lower lip – merging of the ectomesenchyme of the mandibular processes.

30. Derivations of the parts of the face

31. CHEEKS: After formation of upper and lower lips, the stomatodaeum is very broad. On the lateral side it is bounded above by maxillary process and below by mandibular process. The maxillary and mandibular processes fuse to form the cheeks . EYES: The eyes develop from the lens placode which are ectodermal thickenings present lateral and cranial to the nasal placode . EYELID: Eyelids are derived from folds of ectoderm that are formed above and below the eyes, and by mesoderm enclosed within the folds.

32. PINNA: The pinna (auricle) is formed by the fusion of the mesodermal thickenings on the mandibular and hyoid arches. NASOLACRIMAL DUCT : Nasolacrimal duct is formed by fusion between the lateral nasal & maxillary processes, separated by a deep groove. The epithelium in the floor of the groove between them forms a solid core that separates from the surface and eventually canalizes to form nasolacrimal duct.

33. Developmental anomalies of the face Harelip Oblique facial cleft Macrostomia Lateral facial cleft Retrognathia Agnathia Mandibulofacial dysostosis Hypertelorism Congenital pits and fissure on lips proboscis

34. OBLIQUE FACIAL CLEFT HARELIP PROBOSCIS

35. DEVELOPMENT OF MOUTH The mouth is derived partly from the stomatodeum (ectodermal) and partly from the foregut (endodermal). After the disappearance of the buccopharyngeal membrane the stomatodeum communicates with the foregut. Epithelium lining the lips, cheek, palate; teeth and gums are ectodermal in origin.

36. Epithelium of the tongue is endodermal. In the region of the floor of the mouth; the mandibular process forms the lower lip, lower parts of cheek, lower jaw and tongue.

37. Development of palate From each maxillary process, a plate-like shelf grows medially; called palatal process . The palate is formed from the 3 components: The two palatal processes The primitive palate formed from the frontonasal process.

38. The mesoderm in the palate undergoes intramembranous ossification to form the hard palate . Ossification does not extend into the posterior portion; called as soft palate . The part of the palate derived from frontonasal process forms the premaxilla ; which carries the incisor teeth.

39. After the development of secondary palate distinction between the oral and nasal cavity is possible. Development 7-8 weeks and completes around the 3 rd month of gestation. 3 outgrowths appear one nasal septum and two palatine shelves. They converge and fuse in the midline. Displacement of tongue from between the palatine shelves by the growth pattern of the head is a contributing factor closure of palate.

40. Developmental anomalies of lips and palate Congenital lips Commissural pits and fistulas Van der woude syndrome Cleft lip and cleft palate Chelitis glandularis Chelitis granulomatosa

41. Cleft lip and cleft Palate

42. DEVELOPMENT OF MANDIBLE Meckels cartilage f orms the lower jaw in primitive vertebrates. In humans, Meckel’s cartilage has a close positional relationship to the developing mandible but makes no contribution to it. At 6 weeks of development this cartilage extends as a solid hyaline cartilaginous rod, surrounded by a fibrocellular capsule, from the developing ear to the midline of the fused mandibular processes.

43. The two cartilages of each side are separated in the midline by a thin line of mesenchyme. The nerve of first arch has a close relationship to meckels cartilage. During 6 th week; a condensation of mesenchyme occurs in the angle formed by the division of inferior alveolar nerve At 7 th weeks; intramembranous ossification begins in this codensation forming the first bone of the mandible.

44. From this centre of ossification, bone formation spreads rapidly anterior to the midline and posteriorly to a point where mandibular nerve divides into its lingual and inferior alveolar branches. Further growth of mandible till birth is under the influence of the secondary cartilages:- Condylar , Coronoid, Symphyseal cartilages

45. DEVELOPMENT OF RAMUS Rapid spread of ossification posteriorly into the mesenchyme of the 1 st arch. Point of divergence is marked by the lingula in the adult mandible. Spread of mandibular ossification away from meckels cartilage at the lingula.

46. DEVELOPMENT OF MAXILLA The maxilla develops from a center of ossification in the mesenchyme of the maxillary process of the first arch. Center of ossification is closely associated with the cartilage of the nasal capsule. Bone formation spreads : From center Posteriorly below orbit towards forming zygoma Anteriorly future incisor region Superiorly frontal process

47. Bony trough forms for the infraorbital nerve and from this trough downward extension forms lateral alveolar plate. Ossification spreads to the palatine process and forms hard palate. Median alveolar plate forms from the junction of the palatal process & the main body of the forming maxilla. A secondary cartilage; zygomatic or malar cartilage appears in the developing zygomatic process.

48. DEVELOPMENT OF MAXILLARY SINUS Forms around 3 rd month of intra-uterine life. Develops by expansion of nasal mucous membrane into maxillary bone. Later enlarges by resorption of internal wall of maxilla.

49. Developmental anomalies of jaws Agnathia Micrognathia Macrognathia Facial hemihyperatrophy Facial hemiatrophy

50. Development of teeth Primary epithelial band is a band of epithelium that has invaded underlying ectomesenchyme along each of the horseshoe shaped future dental arches. At 7 th week the PE band divides into Dental lamina and vestibular lamina . The dental lamina shows a series of local thickenings- enamel organ .

51. The dental lamina is established in the sixth week of intrauterine life. The dental lamina serves as primordium of the ectodermal position of the deciduous teeth. Permanent molars arise directly from a distal extension of the dental lamina. Dental lamina extends over a period of atleast 5 years.

52. Anomalies of teeth One or more teeth are absent. Supernumerary teeth. Individual tooth abnormality. Gemination . Malocclusion. Precocious eruption. Delayed eruption. Improper formation of enamel and dentin.

53. DEVELOPMENT OF TONGUE Develops at about 4 weeks. Pharyngeal arches meet at the midline beneath the primitive mouth. Local proliferation gives rise to a number of swellings in the floor of the mouth. 2 lateral lingual swellings enlarge and merge with each other and the tuberculam impair to form a large mass, from which anterior 2/3 rd of the tongue is formed.

54. Root of the tongue arises from a large midline swelling developed from the mesenchyme of the 2 nd 3 rd & 4 th arches. Swelling consists of copula and large hypobranchial eminence. As tongue develops, hypobranchial eminence overgrows the copula. Posterior part of the fourth arch marks the development of the epiglottis.

55. Anomalies of tongue Macroglossia, microglossia, aglossia Bifid tongue Ankyloglossia Persistence of tuberculum impar Thyroid tissue within the muscles Remnants of thyroglossal duct Fissured tongue

56. Development of Paranasal Sinuses Paranasal sinuses appear as diverticula from nasal cavity . The diverticula gradually invades the bones. Enlargment of paranasal sinuses is associated with the overall enlargement of the facial skeleton including the jaws. This provide space in the jaws for growth and eruption of teeth.

57. Development of Salivary Gland The salivary glands develop as outgrowths of the buccal epithelium . The outgrowths are at first solid and are later canalized. They branch repeatedly to form the duct system. The terminal part of the duct system develop into secretory acini.

58. The outgrowths of the parotid gland arise in relation to the line along which the maxillary and mandibular processes fuse to form the cheek. It is ectodermal . The outgrowths for the submandibular and sublingual glands arise in relation to the linguo-gingival sulcus. They are endoderma l in origin. One or more salivary glands may sometimes be absent.

59. 4 TH WEEK 5 TH WEEK 6 TH WEEK 7 TH WEEK 8 TH WEEK 10 TH WEEK Frontonasal, maxillary and mandibular process can be identified. Lens and nasal placodes are also present. nasal pits are established Tubercles of the developing pinna, on each side palatal process appear. Eyelids are established. Maxillary process fuse with median nasal process. Eyes shift from lateral to frontal position. Bucconasal membrane ruptures. The palatal process and nasal septum fuse with each other.

60. Tongue starts forming Hypobranchial eminence becomes visible Dental laminae of upper and lower jaws are established Salivary glands starts developing Enamel organs are formed Enamel organ becomes cup- shaped Formation of tonsil begins Tonsil is infiltrated by lymphatic tissue Enamel amd dentine have formed considerably, tongue complete. Cementum is formed PDL formed before eruption of teeth. 4 th week 5 th week 6 th week 7 th week 8 th week 10 th week 3 months 5 months 6 months Just after birth After birth

61. REFERENCES Inderbir Singh; G.P. Pal- human embryology- seventh edition. Nanci A. Tencate’s Oral Histology- Development, Structure and Function, 8 th Ed, Mosby Missouri. Kumar GS, Orban’s Oral Histology and Embrology, 13 th Ed, Elsevier Mosby.

62. S.l Bhalajhi, orthodontics the art and science, 3 rd edition. Berkovitz BKB, Holland GR, Moxham BJ, Oral Anatomy, Histology and Embryology, 4 th Ed, Mosby, Missouri. Shafers, textbook of oral pathology, 7 th edition.

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