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    DENT 5315/DH 2215 February 8, 2008Dr. Sandra Myers [email protected]

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    What are elephant tusks made of?

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    A. Enamel

    B. Dentin

    C. Enamel & Dentin

    D. Chalk

    E. Marble

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    Ectoderm & Enamel

    Enamel: an epithelially derived

    protective covering forthe teeth

    derived from ectodermFig. 2-12 p. 26

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    Ectoderm & Enamel

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    What happens when ectoderm fails to form or form properly?

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    Enamel & Amelogenesis

    Enamel: most highly mineralized

    extracellular matrix96% mineral4% organic material & water

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    Enamel & Amelogenesis

    A. Hard Tissue Formation

    B. AmelogenesisC. Structure of Enamel

    D. Clinical Correlations

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    Hard Tissue Formation Bell Stage A. Hard Tissue Formation

    B. Amelogenesis

    C. Structure of Enamel

    D. Clinical Correlations

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    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)

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    Amelogenesis

    Begins first at cusp tipsThen sweeps down crown slopes

    Stops at CEJ

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    Amelogenesis - Secretory Stage

    pcw = proximal cell web

    dcw= distal cell web

    cell webs hold cells in formation

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    Amelogenesis - Secretory Stage

    Enamel Matrix: Note Tomes processes& picket-fence appearance.

    Hallmarks: Intensesynthetic & secretory activity

    Secretion is continuous

    Secretory granules not stored

    Almost immediate mineralization

    Initial layer does not contain rods

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    Amelogenesis - Secretory Stage

    IGS = interrod, RGS = rod growth sitessg = secretory granules,ppTP = proximaldp = distal portion of Tomes process

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    Amelogenesis - Secretory Stage

    Initial enamel:no rods

    pits filling with enamel

    Enamel crystals: What are these composed of?

    crystalline calcium phosphate(hydroxyapatite) substituted withcarbonate ions

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    Enamel - Amelogenesis

    (Note how trajectory ofenamel rods changes)

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    Amelogenesis - Life Cycle of Ameloblasts

    1. Morphodifferentiation2. Histodifferentiation

    3. Secretory (initial)

    4. Secretory (Tomes process)

    5. Maturation (ruffle-ended)

    6. Maturation (smooth-ended)

    7. Protective

    Functional stages in life cycle ofameloblasts:

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    Amelogenesis - Maturation Stage

    Ameloblasts

    Ruffle-ended Smooth-ended

    Ameloblastsincorporationof inorganicmaterial

    exit of proteinfragments &water

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    Amelogenesis - Maturation Stage

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    Ameloblast Modulation

    regional pH variations

    maturing enamel(rat incisors)Large bands = ruffle-ended cells

    Smaller bands = smooth-ended cells

    (a visually dramatic activity)

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    almost matureenamel,most mineralremoved

    Amelogenesis - Maturation Stage

    Enamel hardens before tooth erupts

    Results from growth in width,thickness of crystals

    Amelogenesis slow process

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    Enamel Proteins: (Table 7-2 text)

    1. Contributing to appositional growth, thickness enamel* Amelogenin (main protein in forming enamel)* Ameloblastin

    * Enamelin2. Postsecretory processing & protein degradation

    3. Related to basal lamina covering maturing, preeruptive enamel

    4. Legacy proteins

    Amelogenesis - Enamel Proteins

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    http://dentistry.uic.edu/CraniofacialGenetics/ResearchTED.htm

    Ameloblasts

    Amelogenesis - Enamel Proteins

    Amelogenin protein (stained red)

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    Amelogenin vs Ameloblastin

    Amelogenesis - Enamel Proteins

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    Protective Stage

    What is the enamel space?

    Full thickness of enamelcomplete, enamel mature

    Ameloblast layer & papillary layerform reduced enamel epithelium

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    Enamel - Structure

    R = Rod & IR

    = Interrod Areas

    Scanning ElectronMicroscopy

    A. Hard Tissue Formation

    B. Amelogenesis

    C. Structure of Enamel

    D. Clinical Correlations

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    Aapd.org/publications/peddent/

    Enamel - Structure

    Note: rod, interrod crystals same, but divergent orientation

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    Transmission EM:

    rod surrounded byinterrod enamel

    Young Enamel Older Enamel

    Enamel:hydroxyapatite crystals

    Enamel - Structure

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    Crysta ls

    Enamel - Structure

    hexagonalcontour toolder maturecrystals

    recentlyformed thincrystals

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    hexagons withunequal-sided peaks

    (un) & equal-sidedpeaks (eq) x 300,000(rat incisor)

    Crystal Profiles

    Enamel - Structure

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    A: alternating orientations

    B: row arrangement

    C: note thin, long apatite crystals

    Enamel - Structure

    enamel rod orientation

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    Cat Secretory Stage Enamel Mature Cat Enamel

    Enamel - Structure

    rod sheath

    rod sheath = boundary between rod & interrod enamel,contains organic material

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