dent 5315/dh 2215 february 8, 2008
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DENT 5315/DH 2215 February 8, 2008. Dr. Sandra Myers [email protected]. 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. - PowerPoint PPT PresentationTRANSCRIPT
DENT 5315/DH 2215 February 8, 2008Dr. Sandra Myers [email protected]
What are elephant tusks made of?
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A. Enamel
B. Dentin
C. Enamel & Dentin
D. Chalk
E. Marble
Ectoderm & Enamel
Enamel: an epithelially derived protective covering for the teeth
derived from ectoderm Fig. 2-12 p. 26
Ectoderm & Enamel
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What happens when ectoderm fails to form or form properly?
Enamel & Amelogenesis
Enamel: most highly mineralized extracellular matrix
96% mineral 4% organic material & water
Enamel & Amelogenesis
A. Hard Tissue Formation
B. Amelogenesis
C. Structure of Enamel
D. Clinical Correlations
Hard Tissue Formation “Bell Stage”
A. Hard Tissue Formation
B. Amelogenesis
C. Structure of Enamel
D. Clinical Correlations
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)
Amelogenesis
Begins first at cusp tips
Then sweeps down crown slopes
Stops at CEJ
Amelogenesis - Secretory Stage
pcw = proximal cell web
dcw= distal cell web
cell webs hold cells in formation
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
Amelogenesis - Secretory Stage
IGS = interrod, RGS = rod growth sites sg = secretory granules, ppTP = proximal
dp = distal portion of Tomes process
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
Enamel - Amelogenesis
(Note how trajectory of enamel rods changes)
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:
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
Amelogenesis - Maturation Stage
Ameloblasts
Ruffle-ended Smooth-ended
Ameloblastsincorporation of inorganic material
exit of protein fragments & water
Amelogenesis - Maturation Stage
Ameloblast Modulation
regional pH variations maturing enamel (rat incisors)Large bands = ruffle-ended cells
Smaller bands = smooth-ended cells
(a visually dramatic activity)
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
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
http://dentistry.uic.edu/CraniofacialGenetics/ResearchTED.htm
Ameloblasts
Amelogenesis - Enamel Proteins
Amelogenin protein (stained red)
Amelogenin vs Ameloblastin
Amelogenesis - Enamel Proteins
Protective Stage
What is the enamel space?
Full thickness of enamel complete, enamel mature
Ameloblast layer & papillary layer form “reduced enamel epithelium”
Enamel - Structure
R = Rod & IR
= Interrod Areas
Scanning Electron Microscopy
A. Hard Tissue Formation
B. Amelogenesis
C. Structure of Enamel
D. Clinical Correlations
Aapd.org/publications/peddent/
Enamel - Structure
Note: rod, interrod crystals same, but divergent orientation
Transmission EM:
rod surrounded by interrod enamel
Young Enamel Older Enamel
Enamel: hydroxyapatite crystals
Enamel - Structure
Crystals
Enamel - Structure
hexagonal contour to older mature crystals
recently formed thin crystals
hexagons with unequal-sided peaks (un) & equal-sided peaks (eq) x 300,000 (rat incisor)
Crystal Profiles
Enamel - Structure
A: alternating orientations
B: row arrangement
C: note thin, long apatite crystals
Enamel - Structure
enamel rod orientation
Cat Secretory Stage Enamel Mature Cat Enamel
Enamel - Structure
rod sheath
rod sheath = boundary between rod & interrod enamel, contains organic material
3 Faces of an Enamel Block
Enamel - Structure
cross-section of rod-interrod area appearance compared to “keyhole”