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Amelogenesis by Dr. Sadia (13-04-2020 to 20-04-2020).pptx

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Amelogenesis by Dr. Sadia (13-04-2020 to 20-04-2020).pptx

  1. 1. DISCIPLINE; BSC (HONS) DENTAL TECHNOLOGY MODULE NAME; ORAL HISTOLOGY CLASS; SECOND YEAR LECTURE TITLE; ENAMEL: COMPOSITION, FORMATION & STRUCTURE (chapter 7) DELIVERED BY; DR. SADIA AWAIS LECTURE DATE; 13-04-2020 to 20-04-2020
  2. 2. AMELOGENESIS INTRODUCTION AMELOGENESIS is the process of formation of enamel by cells called “ameloblasts” which originate from the embryonic germ layer known as ectoderm.
  3. 3. DEVELOPMENT OF TOOTH  stomatodeum lined by stratified squamous epithelium covering connective tissue which originates from neural crest called ectomesenchyme  at 27th day stomatodeum connected with forgut by rupture of buccopharyngeal membrane
  4. 4. PRIMARY EPITHELIAL BAND  AFTER 37 DAYS OF DEVELOPMENT  THICKENED EPITHELIAL BAND FORMED INCREASD PROLIFERATIVE ACTIVITY CHANGE IN ORIENTATION OF CELLS  two subtypes I. DENTAL LAMINA II. VESTIBULAR LAMINA
  5. 5. ORAL EPITHELIUM PRIMARY EPITHELIAL BAND DENTAL LAMINA
  6. 6. DENTAL LAMINA TWO OR THREE WEEKS AFTER RUPTURE OF BUCCOPHARANGEAL MEMBRANE BASAL CELLS OF ORAL ECTODERM PROLIFERATE MORE RAPIDLY THAN ADJACENT CELLS FORMATION OF DENTAL LAMINA DISTAL LINGUAL EXTENSION EXTENSION PERMANENT REMAINING MOLARS TEETH
  7. 7. VESTIBULAR LAMINA  CELLS RAPIDLY PROLIFERATE INTO ECTOMESENCHYME AND DEGENERATE  DEVELOP LABIAL AND BUCCAL TO DENTAL LAMINA  ALSO TERMED LIP FURROW BAND
  8. 8. DENTAL & VESTIBULAR LAMINA At 7th week of I.U.L… A- vestibular lamina B- dental lamina
  9. 9. STAGES OF TOOTH DEVELOPMENT I. BUD STAGE II. CAP STAGE III. BELL STAGE
  10. 10. BUD STAGE  8th week of I.U.L… Epithelium of dental lamina Separated from ectomesenc hyme by basement membra- ne. Round oval swellings arise from basement membrane at 10 points leading to initiation of tooth germ  Peripheral cells low columnar; central polygonal
  11. 11. CAP STAGE 11th weekof I.U.L… EARLY CAP STAGE: Peripheral cuboidal cells- -- Outer Enamel Epithelium Tall columnar cells in the concavity --- Inner Enamel Epithelium Rounded cells in the central portion
  12. 12. CAP STAGE 12th weekof I.U.L… LATE CAP STAGE: Peripheral cuboidal cells--- Outer Enamel Epithelium Tall columnar cells in the concavity --- Inner Enamel Epithelium Polygonal cells b/w Outer & Inner EE form a cellular network--- Stellate Reticulum
  13. 13. ENAMEL KNOT/CORD/NICHE Enamel knot : localized thickening in internal dental epithelium at centre of tooth germ. Enamel cord/septum : strand of cells running from knot to external dental epithelium FUNCTION: as reservior of cells; determine initial position of 1st cusp formation; express genes for many signalling molecules eg. BMP which direct growth of surrounding epithelium and mesenchyme. Enamel niche: apparent structure in histological section as concavity filled with CT
  14. 14. ENAMEL CORD
  15. 15. ENAMEL NICHE
  16. 16. BELL STAGE 14th week of I.U.L… 4 distinct layers: .Outer Enamel Epithelium .Stellate reticulum .Stratum intermedium . Inner Enamel Epithelium Early Bell Stage
  17. 17. OEE: Cells Flattened To Low Cuboidal Form with High Nuclear /Cytoplasmic Ratio. IEE:  Consists of a single layer of cells that differentiate prior to amelogenesis into tall columnar cells called ameloblasts.
  18. 18. Attached to each other by junctional complexes laterally & to the stratum intermedium by desmosomes. They have an organizing influence on the mesenchymal cells of the dental papilla which differentiates into odontoblasts.
  19. 19. Before enamel formation begins the stellate reticulum collapses reducing the distance between the ameloblasts & the capillaries between the OEE. : Formed by differentiation of epithelial cells between the IEE and s. reticulum.
  20. 20. Closely attached by desmosomes and gap junctions. Well-developed cytoplasmic organelles, acid mucopolysaccharides, high glycogen content. Basement membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called MEMBRANA PREFORMATIVA.
  21. 21. TWO IMPORTANT EVENTS 1. Dental lamina joining the tooth germ to the oral epithelium breaks up into discrete islands of epithelial cells thus separating the developing tooth from the oral epithelium . 2. IEE folds making it possible to recognize the shape of the future crown pattern of the tooth.
  22. 22. Crown pattern formation When tooth germ is growing during early bell stage cell division occurs throughout IDE Cessation of cell division at particular point Point at which IDE cell maturation 1st occur represent growth centre At cervical loop IDE constrained and there is continued proliferation of cells leading to buckle formation Gradually maturation sweeps down cusp slope
  23. 23. Crown Pattern Determination
  24. 24. VASCULAR SUPPLY  CLUSTERS OF BLOOD VESSELS AROUND TOOTH GERM ENTERING DENTAL PAPILLA DURING CAP STAGE  NO. INCREASE DURING HISTODIFFERENTIATION  MAXIMUM AT CROWN STAGE OF DEVELOPMENT  AS AGE INCREASE BLOOD SUPPLY GETS REDUCED  BEFORE DENTIN FORMATION; DENTAL PAPILLA  IN BETWEEN; GLYC OGEN STORES AND STELLATE RETICULLUM
  25. 25. NERVE SUPPLY  nerve fibre approach during bud, cap stage  Initial innervation sensory  Rich plexus around tooth germ
  26. 26. LIFE CYCLE OF AMELOBLAST Amelobasts are the cells derived from the IEE that forms enamel. Stages of life cycle- 1.MORPHOGENIC STAGE 2ORGANISING STAGE 3.FORMATIVE STAGE 4.MATURATIVE STAGE 5.PROTECTIVE STAGE 6.DESMOLYTIC STAGE
  27. 27. MORPHOGENIC STAGE  During bell and crown stage of tooth development cells of dental organ along with dental papilla form crown  Cells of internal dental epithelium are cuboidal or low columnar with centrally placed nuclei.  Golgi elements in proximal portion of the cells.  Mitochondria and other cytoplasmic components are scattered throughout.
  28. 28. ORGANISING STAGE  Connective tissue cells become odontoblasts & starts dentine formation  Cells of IEE become longer ,with nucleus contained in proximal end and centriols, golgi body towards distal end  Acidophilic granules found in proximal parts are mitochondria.  Disappearance of cell free zone
  29. 29. FORMATIVE STAGE • Odontoblast induce the cells of inner enamel epithelium to form Ameloblasts. • Ameloblast shows proximally placed nucleus and high amount of rough E.R., high amount of golgi complex, and ribosomes along the distal part of the cell. • The cells of enamel organ deriving its nutrition from adjacent dental papilla is now cut off. The cells of enamel organ have to depend for its nutrition from dental sac, hence there is proliferation of vasculature in dental sac
  30. 30. MATURATIVE STAGE  Reduction in height of ameloblast  Decrease in volume & organalle content  Ameloblast form -rough border(introduction of inorganic content) -smooth border(removal of protein &water) -
  31. 31. PROTECTIVE STAGE  Protection of newly formed enamel surface from follicular connective tissue  Ameloblast no longer differentiated from stratum intermedium & outer enamel epithelium  Formation of reduced enamel epithelium
  32. 32. DESMOLYTIC STAGE  Reduced enamel epithelium secrete enzymes that destroy connective tissue causes eruption of tooth  Premature degeneration of r reduced enamel epithelium prevents eruption of teeth
  33. 33. AMELOGENESIS  Amelogenesis has been subdivided into three main phases (Tencate) 1) Pre-secretory Morphogenetic Differentiation 2) Secretory 3) Maturation Transitional Maturation Proper
  34. 34. MORPHOGENETIC STAGE  The cells are cuboidal or low columnar, with large centrally located nuclei and poorly developed golgi apparatus in proximal part of cell, where junctional complex occur.  Mitochondria and other cytoplasmic components scattered throughout cells
  35. 35. DIFFERENTIATION PHASE THE BASAL LAMINA IS FRAGMENTED BY CYTOPLASMIC PROJECTIONS. INNER ENAMEL EPITHELIUM DIFFERENTIATE INTO AMELOBLASTS- THEY ELONGATE AND NUCLEI SHIFT PROXIMALLY. GOLGI APPARATUS, RER AND MITOCHONDRIA CLUSTER IN DISTAL REGION. SECOND JUNCTIONAL COMPLEX OCCURES IN THIS REGION. TOMES PROCESS- DISTAL EXTENSION OF AMELOBLAST, AGAINST WHICH ENAMEL FORMS.
  36. 36.  Adjacent ameloblasts are aligned closely with each other with the help of junctional complexes.  These complexes encircle the cell at their distal and proximal end.  Fine actin containing filaments radiate into cytoplasm of ameloblast. Forming distal and proximal webs.
  37. 37. SECRETORY STAGE  In this phase the cells acquire intense secretory activity. The golgi complex is extensive and surrounded by numerous cisternae of RER.  m-RNA for enamel proteins are translated by ribosomes on the membrane of Endoplasmic Reticulum, modified by the Golgi and packaged into secretory granules.  These granules migrate to the distal extremity of cell, that is into tomes process.
  38. 38. WHEN ENAMEL FORMATION BEGINS, TOMES PROCESS COMPRISE ONLY A PROXIMAL PORTION. SECRETORY GRANULES MIGRATE & ITS CONTENTS RELEASED AGAINST NEWLY FORMED MANTLE DENTINE TO FORM INITIAL LAYER OF ENAMEL THAT DOES NOT CONTAIN ENAMEL RODS. AS INITIAL LAYER FORMED AMELOBLAST MIGRATE AWAY FROM DENTINE, AND DEVELOP DISTAL PORTION OF TOMES PROCESS AS AN OUTGROWTH OF PROXIMAL PORTION.
  39. 39. PTP(PROXIMAL TOMES PROCESS) EXTENDS FROM THE DISTAL JUNCTIONAL COMPLEX TO THE SURFACE OF THE ENAMEL LAYER. THE DTP(DISTAL TOMES PROCESS) INTERDIGITATES INTO THE ENAMEL BEYOND THE INITIAL LAYER THAT IS FROM PTP. THE CYTOPLASM OF BOTH PROCESSES IS CONTINUOUS WITH THAT OF THE BODY OF THE AMELOBLASTS.
  40. 40.  On establishment of tomes process enamel protein secretion confined to two sites  First site –formation of enamel matrix wall.walls enclose pit into which tomes process fits  Second site-fills this pit with matrix later walls-become interrod enamel ;infilling becoming rod
  41. 41. The dTP lengthens as the enamel layer thickens & thinner as the rod grows in diameter. dTP eventually squeezed out of existence creating a narrow space along the most of circumference between rod and interrod enamel that fills with organic materials and forms rod sheath.
  42. 42. BEFORE THE SECRETION OF FINAL FEW INCREMENT, AMELOBLASTS LOOSE THEIR TOMES PROCESS. sO, ENAMEL RODS ARE NOT PRESENT IN THIS LAYER. HENCE IN CONCLUSION, THE PRISMATIC ENAMEL LAYER IS SANDWICHED BETWEEN THE INITIAL PRISMLESS LAYER AND FINAL PRISMLESS LAYER OF ENAMEL.
  43. 43. MATURATION-TRANSITIONAL PHASE  Reduction of Ameloblast height and a decrease in their volume and organelle content.  Ameloblasts undergo progressive cell death (apoptosis ) upto 50% to permit orderly morphogenesis.  Just after completing the transitional phase, ameloblasts deposit a basal lamina at their flattened apex .
  44. 44. MATURATION PROPER  Ameloblasts become involved in the removal of water and organic material to introduction of additional inorganic materials.  Characterized by - cyclic creation, loss and recreation of highly invaginated ruffle-ended apical surface.
  45. 45. Significance of modulation is unknown – could be related to maintain an environment that allows accretion of mineral content and loss of organic matrix. Ruffle ended ameloblasts show endocytic activity and contain numerous lysosomes,calcium binding proteins, membrane associated calcium adenosine triphosphatases that appear to promote the pumping of calcium ions into maturing ename Smooth ended ameloblast-leak small proteins
  46. 46. RUFFLE ENDED AMELOBLASTS POSSES LEAKY PROXIMAL JUNCTIONS AND TIGHT DISTAL JUNCTIONS WHEREAS SMOOTH ENDED AMELOBLASTS HAVE LEAKY DISTAL JUNCTIONS AND TIGHT PROXIMAL JUNCTIONS.
  47. 47. Withdrawal of matrix is attributed to the action of bulk degrading enzymes that act extracellularly to digest the various matrix proteins into fragments small enough to be able to leave the enamel layer.
  48. 48.  Mineralization of enamel matrix takes place in two stages, although the time interval between them is very small.  In first stage an immediate partial mineralization in matrix segments and interprismatic substance.  Nucleation is initiated by the apatite crystallites of dentine on which enamel is laid.
  49. 49.  Chemical analysis indicate that the initial influx may amount to 25% to 30% of total mineral content.  Studies have shown that initial mineral is octacalcium phosphate, it acts as template for hydroxyapatite. It is unstable and convert into 2 units of hydroxyapatite
  50. 50.  Second stage or maturation is characterized by gradual completion of mineralization.  The process of maturation starts from height of crown and progresses cervically.  However at each level, maturation begins at the dentinal end of rod.  Thus integration of two process: each rod matures from depth to the surface, and sequence of maturing rods is from cusp or incisal edge towards cervical line.
  51. 51. Microradiographic view  Mineralization of enamel originally involve four stages-  STAGE 1- 30% mineralized enamel formed throughout (enamelin forms 8µm highly & heavily mineralized enamel near DEJ .)
  52. 52.  STAGE 2- Increase in mineralization starts at surface sweeping into deeper layer until inner 8µm is reached.  STAGE 3- From inner layer to outer layer. A 15µm surface layer distinguished to be mineralized slowly.  STAGE 4- Outer layer of 15µm mineralize rapidly and heavily so most mineralized

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