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Dental germ

Dental germ

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Dental germ

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  1. Dental germ

  2. Morphological and biological characteristics of the tooth germ

  3. Origin of teeth • Teeth have a dual origin: • Ectodermal; • Mesodermal: • Ectomesenchymal.

  4. EPITHELIUM-ECTOMESEMCHYME INTERACTION IN THE TOOTH DEVELOPMENT • Combine tissue type (neural crest cells + mesenchyme) is called ectomesenchyme. • In tooth development, an interaction occurs between oral ectoderm and ectomesenchyme to initiate the process. • Cellular interactions, between epithelium+ectomesenchyme:Formation of dentine, enamel and cementum as well as crown;

  5. The processes involved in tooth development • Morphogenesis is stimulated by molecular signals that control: • Cell growth; • Migration; • Cell fate and differentiation. • For every developmental event a complex and intricate cascade of gene expression take place to direct the cells to the right place and onto the proper differentiation pathway; • Many of these pathways all result from epithelial-mesenchymal interactions in which essentially the same molecular mediators are implicated.

  6. Embryonic terms to considerInduction • First process to occur during embryogenesis; • Interaction between developing embryonic cells.

  7. Morphogenesis • May also be called morphodifferentiation; • Development of form and specific tissues; • Results from migration of embryonic cells and inductive interactions between these cells.

  8. Specification of the embryo through segmentation; • Patterningisboth a spatialandtemporaleventasexemplifiedbyregionaldevelopment of incisors, canines, premolars, andmolars, whichoccursatdifferenttimesandinvolvestheclassicalprocesses of induction, competence, anddifferentiation. • Process of specialization of embryonic cells. Patterning Differentiation

  9. interstitial growth • Growth deep within a tissue of organ; • As opposed to appositional growth – growth at the periphery through the addition of additional cell layers;

  10. Stages of development • Initiation; • Proliferation; • Histodifferentiation; • Morphodifferentiation; • Apposition; • Maturation; • Eruption.

  11. Initiation of toothdevelopment

  12. Iniciation of tooth development • The newly formed stomadeum is lined by a primitive two- or three-cell-thick layered epithelium covering an embryonic connective tissue that, because neural crest cells have migrated in it, is termed ectomesenchyme; • The ectomesenchyme consists of a few spindle-shaped cells separated by a gelatinous ground substance.

  13. PHASE 1-initiation phase • Formation of primary epithelial thickening, dental lamina, tooth bud & the cap, bell stage cannot take place in absence of dentally active ectomesenchyme which becomes concentrated in regions of presumptive tooth development; • Inner epithelium of enamel organ induces ectomesenchyme of dental papilla to become orientated towards the intervening basal lamina and differentiate into odontoblasts.

  14. Iniciation of tooth development • Thickening of the epithelium.

  15. Stages of the initiation • Primary epithelial band; • Vestibular lamina; • Dental lamina.

  16. Primary epithelial band • A continuous band of thickened epithelium forms around the mouth in the presumptive upper and lower jaws; • This bands are roughly horseshoe shaped and correspond in position of the future dental arches of the jaws; • Each band of epithelium quickly gives rise to two subdivisions: • The vestibular lamina and • The dental lamina just behind it.

  17. The position of the primary epithelial band

  18. Initiation of the tooth development

  19. Upper epithelial band tongue lower epithelial band

  20. Upper and lower epithelial bands

  21. The reason for epithelial thickening • The formation of these thickened epithelial bands is the result not so much of increased proliferative activity within the epeithelium as of a change in orientation of the mitotic spindle and clevage plane of dividing cells.

  22. Sagittal section through the head of an embryo. A. Primary epithelial bands; B. The same structure at higher magnification; C The change in plane of clevage.

  23. Development of the epithelial proliferation Upper epithelial band Lower Epithelial band

  24. Deepening of the epithelial proliferation

  25. Vestibular Lamina • Thefirstsubdivision of theprimaryepithelialbandisvestibularlamina; • The vestibule forms as a result of the proliferation of the vestibular lamina into ectomesenchyme; • Itscellsrapidlyenlargeandthendegenerate to form a cleftthatbecomesthevestibulebetweenthecheekandtooth-bearingarea.

  26. Dental lamina • The othersubdivision of theprimaryepithelialbandisdentallamina; • Dental lamina is located orally to the vestibularlamina; • Withinthedentallamina, continuedandlocalizedproliferativeactivityleads to theformation of a series of epithelialoutgrowths intotheectomesenchymeatsitescorresponding to thepositions of thefuturedeciduousteeth.

  27. Formation of the vestibule of the vestibularlamina

  28. Dental lamina, Vestibular lamina Dental lamina • Vestibular proliferationleads to the formation of the vestibular lamina; • Oral proliferation leads to the formation of the dental lamina. Vestibular lamina

  29. tongue Vestibular lamina Dental lamina

  30. Next development ofdentallamina • Begin localized proliferations; • Early in the medial part - incisors; • Then in the lateral part - canines and molars; • In the upper and lower dental laminaareformed 10 proliferations; • The process is called “the formation of tooth bud” • This is the beginning of the toothdevelopment;

  31. Initiation of toothdevelopment • Teethdevelopfromtwotyps of cells: • Oralepithelialcells; • Mesenchymalcellsfromthedentalpapilla; • Neuralcrestcells – ectomesenchymalcells; • Epithelialcellsare flat on the surface of theepitheliumand cylindrical immediately above to thebasallamina; • Theunderlyingectomesenchymalcellsaccumulatearoundtheepithelialautgrowths.

  32. Theflatandcylindrical epithelialcells, basal lamina immediately below, andectomesenchymalcells Flat cells Cylindrical cells

  33. Iniciaction of thetooth

  34. The controlling signals (BMP-7)in place of the thickened epithelium

  35. Proliferation • The proliferation is: • Multiplication of cells; • Increases the amount of tooth bud; • The proliferation is observed: • Intheepithelium; • Intheectomesenchym.

  36. Certaincells of thebasallayerbegin to proliferateat a morerapidratethendotheadjacentcells. Theseproliferatingcellscontaintheentiregrowthpotential of theteeth .

  37. Toothedevelopmentproceedsinthreestages: • Dentalbud; • Dentalcap; • Dentalbell. • Thesetermsarediscriptive of themorphologybutwehave to describethesignificantfuctionalchangesthatoccurduringdevelopment, suchasmorphogenesisandhistodifferentiation; • Becausedevelopmentis a continuousprocess, cleardistinctionbrtweenthetransitionstagesisnotpossible.

  38. Dentalbud • 1. Dental bud; • 2. Oral epithelium; • 3. Ectomesenchyme.

  39. Histodifferentiation • Histological appearance of different cellswith: • Different form; • Different size; • Differentfunction; • Than are formed differentlayers of cells : • Intheepithelium; • Intheectomesenchym.

  40. DentalLamina andVestibularLamina

  41. Morphogenesiswithmorphodifferentiation • The differentiated cells shall be arranged under differentlayers; • Each layer acquires a separate function; • Each layer takes part in creating the structures of the tooth, in determining the shape and size of thetooth.

  42. Stages in the development of tooth germ

  43. Stages in the development of tooth germ

  44. Elements of thetooth germ • Enamelorgan - epithelial; • Dentalpapilla: • Мesenchymal; • Ectomesenchymal; • Dentalfollicle: • Мesenchymal; • Ectomesenchymal.

  45. Budstage

  46. Budstage

  47. Budstage of toothdevelopment • Proliferation of epithelial cells; • Mitotic cell division; • Increasing the cells number; • Increasing the size of the cells; • Still no cells differentiation.

  48. Budstage • Thebudstageisrepresentedbythefirst epithelialincursionintotheectomesenchyme of thejaw; • Theepithelialcellsshowlittleifanychangeinshapeorfunction; • Thesupportingectomesenchymalcellsarepacked closely and around theepithelialbud.

  49. Formation and growth of tooth bud - activation of mesoderm

  50. Ectomesenchylalcells arriving directly from neural crests • Stem cells involved in the formation of thetooth bud; • This is pluripotent cell capable to become virtually any cell.