dent 5315/dh 2215 february 8, 2008

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

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”