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DENT 5315/DH 2215 February 8, 2008Dr. Sandra Myers myers025@umn.edu

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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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