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DENT 5315/DH 2215 February 8, 2008

DENT 5315/DH 2215 February 8, 2008. Dr. Sandra Myers myers025@umn.edu. What are elephant tusks made of?. Enamel Dentin Enamel & Dentin Chalk Marble. Ectoderm & Enamel. Enamel: an epithelially derived protective covering for the teeth derived from ectoderm Fig. 2-12 p. 26.

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DENT 5315/DH 2215 February 8, 2008

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  1. DENT 5315/DH 2215 February 8, 2008 Dr. Sandra Myers myers025@umn.edu

  2. What are elephant tusks made of? Enamel Dentin Enamel & Dentin Chalk Marble

  3. Ectoderm & Enamel Enamel:an epithelially derived protective covering for the teeth derived from ectoderm Fig. 2-12 p. 26

  4. Ectoderm & Enamel What happens when ectoderm fails to form or form properly?

  5. Enamel & Amelogenesis Enamel: most highly mineralized extracellular matrix 96% mineral 4% organic material & water

  6. Enamel & Amelogenesis Hard Tissue Formation Amelogenesis Structure of Enamel Clinical Correlations

  7. Hard Tissue Formation “Bell Stage” Hard Tissue Formation Amelogenesis Structure of Enamel Clinical Correlations

  8. Amelogenesis 3 Main Functional Stages: 1. Presecretory 2. Secretory 3. Maturation Presecretory Ameloblasts: Differentiate (acquire phenotype) Change polarity (nuclei) Develop enamel synthesis apparatus Morphodifferentiation (shape) Histodifferentiation (microscopic)

  9. Amelogenesis Begins first at cusp tips Then sweeps down crown slopes Stops at CEJ

  10. Amelogenesis - Secretory Stage pcw = proximal cell web dcw= distal cell web cell webs hold cells in formation

  11. Amelogenesis - Secretory Stage Hallmarks: Intense synthetic & secretory activity Secretion is continuous Secretory granules not stored Almost immediate mineralization Initial layer does not contain rods Enamel Matrix: Note Tomes’ processes & picket-fence appearance.

  12. Amelogenesis - Secretory Stage IGS = interrod, RGS = rod growth sites sg = secretory granules, ppTP = proximal dp = distal portion of Tomes process

  13. Amelogenesis - Secretory Stage Enamel crystals: What are these composed of? Initial enamel: “no rods” crystalline calcium phosphate (hydroxyapatite) substituted with carbonate ions “pits filling with enamel”

  14. Enamel - Amelogenesis (Note how trajectory of enamel rods changes)

  15. Amelogenesis - Life Cycle of Ameloblasts Functional stages in life cycle of ameloblasts: Morphodifferentiation Histodifferentiation 3. Secretory (initial) 4. Secretory (Tomes’ process) Maturation (ruffle-ended) Maturation (smooth-ended) Protective

  16. Amelogenesis - Maturation Stage Maturation Process: Removal of water & organic material Introduction of additional inorganic material Process = “Modulation” cyclic creation, loss, and recreation of highly invaginated ruffle-ended apical surface on ameloblasts

  17. Smooth-ended Ruffle-ended Amelogenesis - Maturation Stage Ameloblasts incorporation of inorganic material exit of protein fragments & water Ameloblasts

  18. Amelogenesis - Maturation Stage

  19. Ameloblast Modulation (a visually dramatic activity) regional pH variations maturing enamel (rat incisors) Large bands = ruffle-ended cells Smaller bands = smooth-ended cells

  20. Amelogenesis - Maturation Stage Enamel hardens before tooth erupts Results from growth in width, thickness of crystals Amelogenesis slow process almost mature enamel, most mineral removed

  21. Amelogenesis - Enamel Proteins Enamel Proteins: (Table 7-2 text) 1. Contributing to appositional growth, thickness enamel * Amelogenin (main protein in forming enamel) * Ameloblastin * Enamelin 2. Postsecretory processing & protein degradation 3. Related to basal lamina covering maturing, preeruptive enamel 4. Legacy proteins

  22. Amelogenesis - Enamel Proteins Amelogenin protein (stained red) Ameloblasts http://dentistry.uic.edu/CraniofacialGenetics/ResearchTED.htm

  23. Amelogenesis - Enamel Proteins Amelogenin vs Ameloblastin

  24. Protective Stage Full thickness of enamel complete, enamel mature Ameloblast layer & papillary layer form “reduced enamel epithelium” What is the enamel space?

  25. Enamel - Structure Hard Tissue Formation Amelogenesis Structure of Enamel Clinical Correlations Scanning Electron Microscopy R = Rod & IR = Interrod Areas

  26. Enamel - Structure Aapd.org/publications/peddent/ Note: rod, interrod crystals same, but divergent orientation

  27. Enamel - Structure Enamel: hydroxyapatite crystals Young Enamel Older Enamel Transmission EM: rod surrounded by interrod enamel

  28. hexagonal contour to older mature crystals recently formed thin crystals Enamel - Structure Crystals

  29. Enamel - Structure Crystal Profiles hexagons with unequal-sided peaks (un) & equal-sided peaks (eq) x 300,000 (rat incisor)

  30. Enamel - Structure enamel rod orientation A: alternating orientations B: row arrangement C: note thin, long apatite crystals

  31. Enamel - Structure rod sheath rod sheath = boundary between rod & interrod enamel, contains organic material Cat Secretory Stage Enamel Mature Cat Enamel

  32. Enamel - Structure 3 Faces of an Enamel Block cross-section of rod-interrod area appearance compared to “keyhole”

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