Tooth development

tooth development

1. DEVELOPMENT OF TOOTH

2. DEVELOPMENT OF TOOTH

3. Introduction Initiation of Tooth Development Tooth development Developmental Stages Root development Histophysiology Crown Pattern Determination Nerve & Vascular supply during early development CONTENTS

4. Formation of Permanent Dentition Hard Tissue Formation Formation of Supporting Tissues Tooth Eruption References

5. Tooth development (ODONTOGENESIS ) is the complex process by which teeth form from the embryonic cells, grow, and erupt into the oral cavity. For human teeth to have healthy oral environment, enamel, dentin, cementum & the periodontium all must develop during appropriate stages of fetal development. INTRODUCTION

6. Entire primary dentition is initiated between 6 th and 7 th weeks of embryonic development. Successional permanent teeth initiated between 20 th week in utero and 10 th month after birth. Permanent molars between 20 th week in utero (first molar) and 5 th year of life (third molar).

7. The primitive oral cavity is called stomodeum – lined by stratified squamous epithelium - oral ectoderm. The oral ectoderm contact the endoderm of the foregut to form the buccopharyngeal membrane. At about 27 th day of gestation buccopharyngeal membrane ruptures and the primitive oral cavity establishes a connection with the foregut. Initiation of Tooth Development

8. Most of connective tissue cells underlying the oral ectoderm are of neural crest. These cells induce the overlying ectoderm to start tooth development. Which begins in anterior portion of what will be the future maxilla and mandible and prooced posteriorly

9. About 37 days of development – continuous band of thickened epithelium forms around the mouth presumptive upper and lower jaws. Bands are roughly horse shoe shaped and correspond in position of the future dental arches. PRIMARY EPITHELIAL BAND

10. Thickening of epithelial band occurs due to change in orientation of mitotic spindle & cleavage plane of dividing cells. Each band of epithelium is called PRIMARY EPITHELIAL BAND. Quickly give rise to 2 subdivisions - vestibular lamina - dental lamina

11. Lingual (inner) process of primary epithelial band . Primordium for the ectodermal portion of deciduous teeth. Permanent molars arise from distal extension. Successional lamina: lamina from which permanent teeth develop. Fate: Remnants of dental lamina persists as epithelial pearls or islands within the jaw as well as gingiva -- Cell Rest of Serres . DENTAL LAMINA

12. Maxillary Process Dental Lamina Mandibular Process

13. Buccal (outer) process of primary epithelial band. Lip Furrow Band Cells rapidly enlarge. Becomes the vestibule between the lips and cheek & the tooth-bearing area . VESTIBULAR LAMINA

14. formation of dental and vestibular lamina

15. 10 small swellings develop in the region of future primary teeth. They form enamel organ and give rise to the enamel of the teeth. FORMATION OF ENAMEL ORGAN TOOTH DEVELOPMENT

16. Peripheral condensation of ectomesenchymal cells around enamel organ forms dental papilla Surrounding dental papilla and enamel organ is dental follicle or sac DENTAL PAPILLA AND SAC

17. Tooth germ is formed by Enamel organ enamel + Dental papilla pulp and dentin + Dental sac cementum and PDL

18. MORPHOLOGIC PHYSIOLOGIC STAGES PROCESS STAGES OF TOOTH DEVELOPMENT 1.Initiation 2.Proliferation 3.Histodifferentiation 4.morphodifferentiation. 5.apposition 1.Bud Stage 2.Cap Stage 3.Bell Stage *Early Bell Stage *Advanced Bell Stage

19. The epithelium of the dental lamina is separated from the underlying ectomesnchyme by a basement membrane. The cells of the epithelium proliferate faster than the adjacent cells. The enamel organ consist in this stage peripherally located low columnar cells & centrally located polygonal cells BUD STAGE

20. The next step is mitosis of cells of tooth bud and surrounding mesenchyme . As a result of increased mitotic activity and migration of neural crest cells in to the area of the ectomesenchymal cells surrounding the tooth bud condense. The area of ectomesanchymal condensation immediately adjacent to enamel organ is called dental papilla. The condensed ectomesenchyme that surround the tooth bud and dental papilla is the dental sac . Both dental papilla and dental sac become more well defined as enamel organ grows into the cap and bell shapes.

21. Shallow invagination on the deep surface of the bud. Peripheral cells are cuboidal , cover the convexity of the cap– Outer Enamel Epithelium. Cells in the concavity of the cap become tall, columnar– Inner Enamel Epithelium CAP STAGE

22. Polygonal cells located between the outer and inner enamel epithelia. They begin to separate as more intercellular fluid is produced and form a cellular network called the stellate reticulum. The cells assume a branched reticular form. The spaces in this reticular network are filled with a mucoid fluid that is rich in albumin, which gives the stellate reticulum a cushionlike consisstency that may support and protect the dellicate enamel-forming cells. Stellate reticulum

23. Organizing influence of proliferative epithelium of enamel organ Papillary cells proliferate Budding of capillaries and mitotic figures Later differentiate – odontoblasts – dentin Dental papilla

24. marginal condensation in the ectomesenchyme surrounding the enamel organ and dental papilla. in this zone a denser and more fibrous layer Develops primitive dental sac formation of cementum and the periodontal ligament Dental sac

25. Temporary structures , disappear before enamel formation begins . Enamel Niche : Enamel organ has double attachment of dental lamina to the overlying oral epithelium enclosing ectomesenchyme . Transitory Structures:

26. The center of enamel organ contains densely packed cells & are called enamel knot. They extend slightly into the dental papilla & form knob like projection Enamel knot

27. A vertical projection is seen from this knot known as enamel cord. Both knot & cord are temporary structures. Function : both acts as a reservoir of dividing cells. Enamel cord

28. Enamel Septum : Enamel cord extends to meet outer enamel epithelium. Enamel Navel : (resembles umbilicus) Outer enamel epithelium at a point of meeting shows small depression

29. Enamel organ resembles a bell. Undersurface of the epithelial cap deepens. Continuation of histodifferentiation ( ameloblasts and odontoblasts are defined) & beginning of morphodifferentiation (tooth crown assumes its final shape). BELL STAGE

30. Consists of four distinct layer: Inner Enamel Epithelium Stratum Intermedium Stellate Reticulum Outer Enamel Epithelium Early Bell Stage

31. Consists of a single layer of cells differentiate prior to amelogenesis into tall columnar cells Ameloblasts Inner Enamel Epithelium

32. The cells of the inner enamel epithelium exert an organizing influence on mesenchymal cells in the dental papilla later differentiate into odontoblasts .   .

33. Formed by a few layers of squamous cells between the inner enamel epithelium and the stellate reticulum. The well-developed cytoplasmic organelles acid mucopolysaccharides , and glycogen deposits indicate a high degree of metabolic activity. This layer seems to be essential to enamel formation. It is absent in the part of the tooth germ that outlines the root portions of the tooth that does not form enamel. Stratum intermedium

34. The stellate reticulum expands further mainly by an increase in the amount of intercellular fluid. The cells are star shaped, with long processes that anastomose with those of adjacent cells. Before enamel formation begins, the stellate reticulum collapses, reducing the distance between the centrally situated ameloblasts and the nutrient capillaries near the outer enamel epithelium. This change begins at the height of the cusp or the incisal edge and progresses cervically .   Stellate reticulum

35. These cell flatten to a low cuboidal form. At the end of the bell stage, the formerly smooth surface of the outer enamel epithelium is laid in folds. Between the folds the adjacent mesenchyme of the dental sac forms papillae that contain capillary loops and thus provide a rich nutritional supply for the intense metabolic activity of the avascular enamel organ. Outer enamel epithelium

36. Extends lingually . Successional Dental Lamina as gives rise to enamel organs of permanent successors of deciduous teeth (permanent incisor, canines & premolars). Dental Lamina:

37. The dental papilla is enclosed in the invaginated portion of the enamel organ. Before the inner enamel epithelium begins to produce enamel, the peripheral cells of the mesenchymal dental papilla differentiate into odontoblasts under the organizing influence of the epithelium. First, they assume a cuboidal form; later they assume a columnar form and acquire the specific potential to produce dentin Dental papilla

38. The basement membrane separates the enamel organ and the dental papilla just prior to dentin formation membrana preformativa  

39. Before formation of dental tissues begins the dental sac shows a circular arrangement of its fibers and resembles a capsular structure. With the development of the root, the fibers of the dental sac differentiate into the periodontal fibers that become embedded in the developing cementum and alveolar bone. Dental sac

40. This point is where the cells continue to divide until the tooth crown attains its full size. The inner epithelium begins at the point where the outer epithelium bends to form the concavity into which the cells of the dental papilla accumulate. The region where the internal and external dental epithelia meet at the rim of the enamel organ is known as the zone of reflexion or cervical loop . Cervical loop Cervical loop

41. Commencement of mineralization & root formation. Boundary between inner enamel epithelium & odontoblasts –- outlines future DEJ. 1 st formation of dentin. Proceeds pulpally & apically. After first layer of dentin is formed, ameloblast which has already differentiated from IEE cells lay down enamel over dentin in future incisal & cuspal areas. Proceeds coronally & cervically . Cervical portion of the enamel organ gives rise to Hertwig’s epithelial root sheath. Outlines the future root. Responsible for the shape, length, size & number of roots. Advanced Bell Stage:

42. After odontoblasts form due to organizing influence of epithelial cells, they instruct ameloblasts in turn to secrete enamel matrix (reciprocal induction) ENAMEL & DENTIN FORMATION

43. Root formation commences once the enamel and dentin formation have reached the future cementoenamel junction(CEJ). Cervical loop from the enamel organ forms the Hertwigs epithelial root sheath (HERS). HERS determines shape of the roots and inititates radicular dentin formation. HERS consists of the outer and inner enamel epithelium only. ROOT DEVELOPMENT

44. At the future CEJ, HERS turn inwardly to a horizontal plane forming the epithelial diaphragm. Plane of diaphragm remains relatively fixed during development and growth of the root. Proliferating cells of epithelial diaphragm induce proliferation and differentiation of cells of dental papilla to odontoblasts and form root dentin.

45. The cells of dental follicle proliferate and invade the root sheath dividing it in to network of strands. Degradation of the HERS allows contact of the dental follicle cells with the dentin surface and they differentiate into cementoblasts . The cementoblasts cover the root dentin and undergo c ementogenesis – laying down cementoid

46. HERS formed from inner/outer enamel epithelia

47. The first layer of dentin has been laid down the epithelial root sheath loses its structural continuity & its close relation to the surface of the root. Its remnants persists as an epithelial network of strands or tubules near the external surface of the root. These epithelial remnants are found in the periodontal ligament of erupted teeth called rests of malassez .

48. ROOT FORMATION IN SINGLE ROOTED TEETH

49. Division of root trunk in 2/3 roots is due to differential growth of epithelial diaphragm Root formation in Multirooted teeth

50. Anterior teeth, premolars and molars all begin as a single root – root trunk. Root of the posterior teeth divides from the trunk into the correct number of root branches. Differential growth of the Hertwig’s epithelial root sheath results in the division of the root trunk into two or three roots.

51. DEVELOPMENT OF TEETH WITH TWO AND THREE ROOTS

52. INITIATION The dental lamina and associated tooth buds represent those parts of the oral epithelium that have potential for tooth formation. Initiation induction requires ectomesenchymal -epithelial interaction. Lack of initiation results in absence of either a single tooth or multiple teeth, or there may be a complete lack of teeth. Abnormal initiation may result in the devalopment of single or multiple supernumerary teeth. histophysiology

53. Enhanced proliferative activity ensues at the points of initiation and results successively in the bud, cap and bell stages of the odontogenic organ. Causes regular changes in the size and proportions of the growing tooth germ. PROLIFERATION

54. Histodifferentiation is the process in which a mass of similar epithelial cells transforms itself into morphologically and functionally distinct components. Histodifferentiation begins in the late cap stage and reaches its highest development in the early bell stage. The organizing influence of the inner enamel epithelium on the mesenchyme is evident in the bell stage and causes the differentiation of the adjacent cells of the dental papilla into odontoblasts . With the formation of dentin, the cells of inner enamel epithelium differentiate into ameloblasts and enamel matrix is formed. HISTODEFFERENTIATION

55. The morphologic pattern is established by differential growth. The cells arrange themselves along the site which out lines the basic form and relative size of the future tooth. The advance bell stage is the important stage for it outlining the future dentinoenamel junction MORPHODIFFERENTIATION

56. The dentinoenamel and dentinocemental junctions which are different and characteristic for each tooth, acts as blue print pattern. Inconformity with this pattern, ameloblasts , odontoblasts and cementoblasts deposit the enamel, dentin and cementum , giving the completed tooth its characteristic form and size. Disturbances may cause supernumerary cusps or roots, loss of cusps or roots, peg tooth.

57. Apposition is the deposition of the matrix for the hard dental structures. There is regular and rhythmic layer like deposition of the extracellular matrix resulting in additive growth. This matrix is partially calcified- serves as a frame work for later calcification proper. Disturbances can cause hypocalcified or hypomineralized enamel or dentin. APPOSITION

58. Future crown patterning -- bell stage, by folding of the inner enamel epithelium. Cessation of mitotic activity within the inner enamel epithelium determines the shape of a tooth. The point at which inner enamel epithelium cell differentiation first occurs represent the site of future cusp development. CROWN PATTERN DETERMINATION

59. Crown Pattern Formation in the Inner Enamel Epithelium

60. Vascular supply: Cap stage. Blood vessels grow in the dental follicle and enter the dental papilla. The number of blood vessels reaches a maximum at the beginning of the crown stage , and the dental papilla eventually forms in the pulp of a tooth. NERVE & VASCULAR SUPPLY DURING EARLY DEVELOPMENT

61. Pioneer nerve fibres approach developing tooth during bud to cap stage development. Nerve fibre ramify and form a rich plexus around the tooth germ in that structure. Nerve fibres penetrate dental papilla when dentinogenesis begins. Initial innervation – sensory for future p.d.l & pulp. Nerve supply

62. Arises from dental lamina. Form in essentially the same manner, though at different times. The tooth germs that give rise to permanent incisors, canines and premolars form as a result of further proliferative activity within the dental lamina, lingual to the deciduous tooth germ. The developing permanent molars have no deciduous predecessor and their tooth germs originate from the dental lamina that extends posteriorly beneath the oral epithelium after the jaws have grown. FORMATION OF PERMANENT DENTITION

63. The next step in development of tooth is terminal differentiation of ameloblast and odontoblast and formation of enamel and dentin. Until crown assumes the final shape durind cap to early bell stage,all cells of inner enamel epithelium continually divide. First layer of dentin appears at the cusp tips and progresses cervically , & the columnar cells of the inner enamel epithelium becomes elongated & show reverse polarization, with the nuclei adjacent to stratum intermediate ( ameloblasts ). HARD TISSUE FORMATION

64. Undifferentiated ectomesenchymal cells increase rapidly in size and ultimetly differentiated into odontoblast . In the absence of epithelial cells no dentin develops. As devlpoment continues ,progressive dfferentiation of cells of IEE down cusp slopes, odontoblast are differentiate begin to elaborate the organic matrix of dentin,which ultimately mineralize. As the organic martrix deposited,odontoblast move towards center of dental papilla,leaving behind the cytoplasmic extension around which dentin is formed

65. Inner enamel epithelial cells continue their differentiation into ameloblast that produce organic matrix against the newly formed dentinal surface. Organic matrix is mineralize and becomes initial enamel layer of crown. Ameloblast moving away from the dentin , leaving behind an ever increasing thickness of enamel. the differentiating odontoblasts and ameloblasts receive signals from each other n viceversa –- Reciprocal Induction . cells of enamel organ receives its nourishment from two sources-blood vessels of dental papilla. -vessels situated at periphery of OEE.

66. While roots are forming, the supporting tissues of the tooth also develop. The supporting tissues( cementum , PDL, bone) of the tooth are formed from the dental follicle . As the root sheath fragments, ectomesenchymal cells of dental follicle penetrates between the epithelial cells & lie close to the newly formed root dentin. FORMATION OF SUPPORTING TISSUES

67. These cells differentiate into cementum -forming cells- Cementoblasts . Fibers of the periodontal ligament, which will also form from the cells of the dental follicle will get anchored in the organic matrix of the cementum which later gets mineralized. Bone in which ligament fiber bundles are embedded is also formed by cells that differentiate from dental follicle.

68. After formation of root is initiated, the tooth begins to erupt. Axial movement-- from its developmental position within the jaw to its final functional position in the occlusal plane. Formation of reduced enamel epithelium. REE + oral epithelium = solid mass of epithelial cells over crown of the tooth. Central cells in this mass disintegrate–- epithelial canal–- crown of the tooth erupts TOOTH ERUPTION

69. Clinical Significance

70. TYPES OF OPEN APICES These can be of two configurations. NON BLUNDERBUSS Broadly opened apex (Cylinder – shaped root canals). BLUNDERBUSS Funnel shaped apex (Apical opening can be wider than the coronal root canal orifice (inverted root canal conicity ) BLUNDERBUSS APEX Acc to BEENA PHILIP MATHEW * MITHRA N. HEGDE **, E ndodontology .

71. Diagnosis: -visual examination -clinical examination -radiographic examination -laser doppler flowmetry -potential aid to vitality testing and pulp revascularization. Management: - apexification - apexogenesis

72. REFERENCES Ten Cate’s Oral Histology Development, Structure, and Function Antonio Nanci : 7 th edition. Orban’s Oral Histology and Embryology : 12 th edition. Inderbeer Singh: Human Embryology James k avery -oral development and histology,3 rd edition