DENT 5315/DH 2215 February 8, 2008
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Transcript of DENT 5315/DH 2215 February 8, 2008
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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 for the teeth
derived from ectoderm Fig. 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 matrix
96% mineral 4% organic material & water
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Enamel & Amelogenesis
A. Hard Tissue Formation
B. Amelogenesis
C. 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 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
Enamel Matrix: Note Tomes’ processes & picket-fence appearance.
Hallmarks: Intense synthetic & 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 sites sg = secretory granules, ppTP = proximal
dp = 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 with carbonate ions
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Enamel - Amelogenesis
(Note how trajectory of enamel rods changes)
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Amelogenesis - Life Cycle of Ameloblasts
1. Morphodifferentiation
2. Histodifferentiation
3. Secretory (initial)
4. Secretory (Tomes’ process)
5. Maturation (ruffle-ended)
6. Maturation (smooth-ended)
7. Protective
Functional stages in life cycle of ameloblasts:
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Amelogenesis - Maturation Stage
Maturation Process:
1. Removal of water & organic material
2. 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
Ameloblasts
Ruffle-ended Smooth-ended
Ameloblastsincorporation of inorganic material
exit of protein fragments & 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 mature enamel, most mineral removed
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 * Enamelin
2. 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 enamel complete, enamel mature
Ameloblast layer & papillary layer form “reduced enamel epithelium”
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Enamel - Structure
R = Rod & IR
= Interrod Areas
Scanning Electron Microscopy
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 by interrod enamel
Young Enamel Older Enamel
Enamel: hydroxyapatite crystals
Enamel - Structure
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Crystals
Enamel - Structure
hexagonal contour to older mature crystals
recently formed thin crystals
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hexagons with unequal-sided peaks (un) & equal-sided peaks (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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3 Faces of an Enamel Block
Enamel - Structure
cross-section of rod-interrod area appearance compared to “keyhole”