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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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