Development of tooth power point presentation

Development of tooth power point presentation

1. Presented by K Sushmitha I MDS

2. Contents Introduction Initiation of tooth development Primary epithelial band Dental lamina Vestibular lamina Tooth developmental stages -Bud -Cap -Bell (Early & Advanced) Root formation Histophysiology Molecular insights Amelogenesis Dentinogenesis Clinical considerations Conclusion References

3. Introduction

4. Initiation of tooth development 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 bucco -pharyngeal membrane . At about 27 th day of gestation buccopharyngeal membrane ruptures and the primitive oral cavity establishes a connection with the foregut

5. Primary epithelial band

6. T h ick e n i ng of e pit he lial band o c c u r s du e t o ch ange in orientation of mitotic spindle & cleavage plane of dividing cells. Quickly give rise to 2 subdivisions vestibular lamina dental lamina

7. Dental Lamina 6 weeks old embryo - basal cells of oral ectoderm proliferates – GERMINAL BAND OF EPITHELIUM. Represents the first sign of tooth development. Primordium for the ectodermal portion of deciduous teeth

8. Permanent molars arise from distal extension of dental lamina. First permanent molar - initiated - 4 th month in-utero. 2 nd molar - first year after birth 3 rd molar - 4 th or 5 th years

9. Develops - 5 th month IUL (permanent central incisor) 10 th month of age after birth(second premolar)

10. Initiation Primary dentition 6-7 weeks of IU Successional permanent teeth 5 th month IU to 10 months after birth

11. Fate of dental lamina

12. Cell rests of Serres

13. Vestibular Lamina Lip furrow band V shaped – forms vestibular grove.

14. Tooth Development

15. Formation of Enamel Organ At certain points on DL representing -10 mandibular & 10 maxillary deciduous teeth - cells multiply still more rapidly. Forming little knobs - grow into underlying mesenchyme

16. Each of these little outgrowths represents – beginning of enamel organ of tooth bud of deciduous teeth Not all develop at same time First- mandibular anterior region Differential growth - Change in shape

17. Dental Papilla On the inside of the cap - ectomesenchymal cells increases. Tissue appears - more dense than the surrounding mesenchyme Represents the beginning of the dental papilla

18. Dental sac/ Dental follicle Surrounding - combined enamel organ & dental papilla 3 rd part of the tooth bud forms - dental sac/follicle Consists - ectomesenchymal cells and fibres that surrounds the dental papilla and the enamel organ. Dental follicle

19. Tooth germ Includes all the formative tissues for the entire toot h and its supporting structures Ectodermal component - Enamel organ -- enamel. Ectomesenchymal component Dental papilla - dentin and pulp. Dental follicle or dental sac - cementum, periodontal ligament, and part of alveolar socket

20. Development of tooth – interaction of cells. Upto 12 days- first arch epithelium - retains ability. When combined with neural crest cells in other regions. But transferred to neural crest cells as revealed in various recombinant experiments.

21. Like any other organ development –numerous & complex gene expressions – occurs to control – development process- through molecular signals. Experimental studies to understand the genetic control and molecular signalling have been done on mice as it is amenable for genetic manipulations to produce “ knock-out mice” or “null mice”

22. Stages of tooth development

23. Bud stage

24. Cap stage/ Proliferation During ninth week - as tooth bud continues to proliferate laterally. Does not expand uniformly into a large sphere Rather show differential growth leading to cap shape.

25. Characterized by a shallow invagination on the deep surface of the bud

26. 3 layers of cap stage Outer dental epithelium Inner dental epithelium Stellate reticulum

27. Stellate reticulum Polygonal cells – b/w OEE & IEE - begin to separate due to water being drawn into the enamel organ from the surrounding dental papilla. polygonal cells  star shaped Maintain contact with each other by their cytoplasmic process star shaped cells – forms cellular network- hence the name SR. Shock absorber

28. Transient structures Enamel Knot: Densely packed cells in the center of enamel organ. Center of epithelial invagination will shows a knob like enlargement. Function of enamel knot - reservoir of dividing cells for the growing EO.

29. Enamel cord : Vertical enamel knot Enamel septum : when EC meets OEE Enamel navel : small depression - attachment of enamel cord to outer dental epithelium (resembles umbilicus)

30. Bell stage As the invagination of epithelium deepens - margins continue to grow Enamel organ assumes a bell shape In this stage - crown shape is determined. Four different types of epithelial cells- Inner enamel epithelium Stratum intermedium Stellate reticulum Outer enamel epithelium

31. Consists of a single layer of cells Differentiate prior to amelogenesis into tall columnar cells- Ameloblasts(4-5 in diameter; 40 high)   The cells of the inner enamel epithelium exert an organizing influence on mesenchymal cells in the dental papilla later differentiate into odontoblasts. Inner enamel epithelium

32. Stratum intermedium Few layers of squamous cells forms stratum intermedium - between IEE and SR These cells are closely attached by desmosomes & gap junctions Cytoplasmic granules, glycogen deposits- high degree of metabolic activity. This layer seems to be essential to enamel formation.

33. Stellate reticulum SR expands further due to continued accumulation of inter-cellular fluid star shaped cells,- having a large processes that anastomose with those of adjacent cells enamel formation starts – SR collapses to a narrow zone Thereby reducing distance b/w the OEE & IEE

34. Outer enamel epithelium Cells - flatten to form low cuboidal cells OEE is thrown into folds which are rich in capillary network – source of nutrition for EO

35. Dental papilla Enclosed in the invaginated portion of EO. Before IEE begins to produce enamel, peripheral cells of DP- odontoblasts. First they assume cuboidal form, then columnar. Acquires a specific potential for dentin production. BM-separating EO& DP- ‘ membrana preformativa ’

36. Cervical Loop Region where IEE & OEE meet at the rim of the enamel organ This is the point where cells continue to divide until tooth attains its full size & which after crown formation gives rise to epithelial component of root formation.

37. Advanced bell stage Characterized by commencement of mineralization & root formation. Boundary b/w IEE & odontoblasts – outlines future DEJ. Formation of dentin occurs first as a layer along future DEJ Begins at cusp tips, proceeds cervically and apically .

38. After 1st layer of dentin- ameloblasts- enamel- cusp area. Proceeds coronally & cervically from DEJ towards surface. Cervical portion of enamel organ will gives rise to “HERS“ Outlines future root; responsible for shape, length, size& no. of roots.

39. Root formation Begins after enamel & dentin formation has reached future CEJ. Enamel organ - imp role – HERS - molds shape of root and initiates radicular dentin formation. Cells of IEE & OEE - proliferate as double layered sheath from cervical loop. Devoid of SI& SR.

40. HISTOPHYSIOLOGY Initiation :- ectomesenchyme will instructs the epithelial cells to form the enamel. Proliferation :- Proliferative growth causes regular changes in size and proportions of tooth germ. Histodifferentiation :- Ectodermal and mesenchymal cells differentiated into specialized cells Morphodifferentiation :- Shape of the tooth is decided Apposition :- Formation of mineralized hard tissues. It is characterized by regular and rhythmic deposition of extracellular matrix.

41. Molecular insights in tooth morphogenesis Role of epithelial mesenchymail interactions : Interactions between epithelium and mesenchymal tissues components have particularly important function in developing teeth, as well as all other organs forming as ectodermal appendages. It takes place by the expression of the various genes. BMP- 2, 4 & 7 Msx 1, Msx 2 Shh Wnt 7 Lef-1 Pax-9 Activin-A Msx1 BMP-4 Fgf-8 + BMP-4 Pax-9

42. Patterning of dentition: The determination of specific tooth type at their correct positions in the jaw. It is remarkably a consistent process. Field theory (Butler, 1939): All tooth primordia are initially equivalent. Controlled by varying concentrations of morphogens in local environment. A number of diffusible signalling molecules may be involved which would produce periodicity along the developing dental axis. Clonal model (Osborn, 1978): Tooth primordial cells being equipped with necessary positional information. Westgaard and Ferguson: Proposed hybrid progress zone model.

43. Homeobox code model It is based on the observations of the spatially restricted expression of several homeobox genes. Msx-1 &Msx-2 restricted to distal midline mesenchymal regions of incisors & canines. Dlx-1 &Dlx-2 restricted to mesenchymal cells of multicuspid teeth. Expression of Barx-1 overlaps with Dlx-1& Dlx-2. This model proposes that the overlapping domain of these genes will provide the positional information for tooth type determination.

44. Molecular insights in bud stage: Msx-1 &Msx-2 and Dlx-1& Dlx-2 might act parallelly at lamina stage. These genes will express at different levels in bud stage due to transitions.

45. Molecular insights in cap stage: Recent studies - enamel knot- acts as signaling center E. knot-organization centre - orchestrates cuspal morphogenesis. Fgf-4 & Slit-1: best markers; both primary& sec. knots.

46. Amelogenesis Process of formation of enamel. It takes place under 3 stages. Presecretory stage - Morphogenic phase -Differentiation phase Secretory stage Maturation stage - Transition phase -Maturation proper

47. Proteins in enamel matrix: Amelogenins : Predominant and comprises about 80% of the young enamel matrix and contains high levels of amino acids proline, glutamine, histidine and leucine. Non- amelogenins : Tuftelin , sheathlin , enamelin, sulphated enamel proteins and amelotin.

48. Dentinogenesis The process of formation of dentin. Stages of dentin development: -Differentiation of odontoblasts -Deposition of organic matrix -Mineralization

49. Clinical considerations

50. Enamel pearls Cause: If the cells of the epithelial root sheath of Hertwig remain adherent to the dentin surface, they may differentiate into ameloblasts and produce enamel, called enamel pearls. They appear as small, spherical enamel projections especially at the cemento -enamel junction (CEJ) or in the furcation area in molars.

51. Bare dentine If the epithelium root sheath of Hertwig is delayed in its separation from the dentin, a zone of the root is devoid of cementum.

52. Accessory root canals Causes :- If the continuity of the epithelial root sheath of Hertwig is broken prior to odontoblastic differentiation and dentin formation As a result of disturbance in the fusion of the tongue like extension of the diaphragm. Large blood vessel may disturb the course of the root sheath lead to accessory root canal.

53. Cell rests of Serres when proliferates will lead to: Odontogenic keratocyst Lateral periodontal Cyst Gingival Cyst Glandular odontogenic Cyst

54. Conclusion

55. References Orban Oral Histology And Embryology 12 th Edition Tencate’s Oral Histology Antonio Nanci 8 th Edition Oral Development And Histology James Avery Third Edition. Inderbeer Singh: Human Embryology

56. Thank you