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DENT 5315/DH February 8, 2008 Dr. Sandra Myers
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What are elephant tusks made of?
Enamel Dentin Enamel & Dentin Chalk Marble
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Ectoderm & Enamel Enamel: an epithelially derived protective covering for the teeth derived from ectoderm Fig p. 26
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What happens when ectoderm fails to form or form properly?
Ectoderm & Enamel What happens when ectoderm fails to form or form properly?
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Enamel & Amelogenesis Enamel: most highly mineralized extracellular matrix 96% mineral % organic material & water
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Enamel & Amelogenesis Hard Tissue Formation Amelogenesis Structure of Enamel Clinical Correlations
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Hard Tissue Formation “Bell Stage”
Amelogenesis Structure of Enamel 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 tips Then 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
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.
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Amelogenesis - Secretory Stage
IGS = interrod, RGS = rod growth sites sg = secretory granules, ppTP = proximal dp = distal portion of Tomes process
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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”
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Enamel - Amelogenesis (Note how trajectory of enamel rods changes)
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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
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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
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Amelogenesis - Maturation Stage
Ruffle-ended Smooth-ended Ameloblasts incorporation of inorganic material exit of protein fragments & water Ameloblasts
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Amelogenesis - Maturation Stage
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Ameloblast Modulation
(a visually dramatic activity) regional pH variations maturing enamel (rat incisors) Large bands = ruffle-ended cells Smaller bands = smooth-ended cells
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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
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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
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Amelogenesis - Enamel Proteins
Amelogenin protein (stained red) Ameloblasts
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Amelogenesis - Enamel Proteins
Amelogenin vs Ameloblastin
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What is the enamel space?
Protective Stage Full thickness of enamel complete, enamel mature Ameloblast layer & papillary layer form “reduced enamel epithelium” What is the enamel space?
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Scanning Electron Microscopy
Enamel - Structure Hard Tissue Formation Amelogenesis Structure of Enamel Clinical Correlations Scanning Electron Microscopy R = Rod & IR = Interrod Areas
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Note: rod, interrod crystals same, but divergent orientation
Enamel - Structure Aapd.org/publications/peddent/ Note: rod, interrod crystals same, but divergent orientation
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Enamel: hydroxyapatite crystals
Enamel - Structure Enamel: hydroxyapatite crystals Young Enamel Older Enamel Transmission EM: rod surrounded by interrod enamel
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Enamel - Structure Crystals hexagonal contour to older mature crystals recently formed thin crystals
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Enamel - Structure Crystal Profiles hexagons with unequal-sided peaks (un) & equal-sided peaks (eq) x 300,000 (rat incisor)
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Enamel - Structure enamel rod orientation A: alternating orientations B: row arrangement C: note thin, long apatite crystals
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Enamel - Structure rod sheath
rod sheath = boundary between rod & interrod enamel, contains organic material Cat Secretory Stage Enamel Mature Cat Enamel
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Enamel - Structure 3 Faces of an Enamel Block cross-section of rod-interrod area appearance compared to “keyhole”
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