1. DENT 5315/DH February 8, 2008
Dr. Sandra Myers

2. What are elephant tusks made of?
Enamel
Dentin
Enamel & Dentin
Chalk
Marble

3. Ectoderm & Enamel
Enamel: an epithelially derived protective covering for the teeth
derived from ectoderm Fig p. 26

4. What happens when ectoderm fails to form or form properly?
Ectoderm & Enamel
What happens when ectoderm fails to form or form properly?

5. Enamel & Amelogenesis
Enamel: most highly mineralized extracellular matrix
96% mineral % organic material & water

6. Enamel & Amelogenesis
Hard Tissue Formation
Amelogenesis
Structure of Enamel
Clinical Correlations

7. Hard Tissue Formation “Bell Stage”
Amelogenesis
Structure of Enamel
Clinical Correlations

8. 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)

9. Amelogenesis Begins first at cusp tips Then sweeps down crown slopes
Stops at CEJ

10. Amelogenesis - Secretory Stage
pcw = proximal cell web
dcw= distal cell web
cell webs hold cells in formation

11. Amelogenesis - Secretory Stage
Hallmarks: Intense synthetic & secretory activity
Secretion is continuous
Secretory granules not stored
Almost immediate mineralization
Initial layer does not contain rods
Enamel Matrix: Note Tomes’ processes & picket-fence appearance.

12. Amelogenesis - Secretory Stage
IGS = interrod, RGS = rod growth sites sg = secretory granules, ppTP = proximal dp = distal portion of Tomes process

13. Amelogenesis - Secretory Stage
Enamel crystals:
What are these composed of?
Initial enamel: “no rods”
crystalline calcium phosphate (hydroxyapatite) substituted with carbonate ions
“pits filling with enamel”

14. Enamel - Amelogenesis
(Note how trajectory of enamel rods changes)

15. Amelogenesis - Life Cycle of Ameloblasts
Functional stages in life cycle of ameloblasts:
Morphodifferentiation
Histodifferentiation
3. Secretory (initial)
4. Secretory (Tomes’ process)
Maturation (ruffle-ended)
Maturation (smooth-ended)
Protective

16. Amelogenesis - Maturation Stage
Maturation Process:
Removal of water & organic material
Introduction of additional inorganic material
Process = “Modulation”
cyclic creation, loss, and recreation of highly invaginated ruffle-ended apical surface on ameloblasts

17. Amelogenesis - Maturation Stage
Ruffle-ended
Smooth-ended
Ameloblasts
incorporation of inorganic material
exit of protein fragments & water
Ameloblasts

18. Amelogenesis - Maturation Stage

19. Ameloblast Modulation
(a visually dramatic activity)
regional pH variations maturing enamel (rat incisors)
Large bands = ruffle-ended cells
Smaller bands = smooth-ended cells

20. Amelogenesis - Maturation Stage
Enamel hardens before tooth erupts
Results from growth in width, thickness of crystals
Amelogenesis slow process
almost mature enamel, most mineral removed

21. Amelogenesis - Enamel Proteins
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

22. Amelogenesis - Enamel Proteins
Amelogenin protein (stained red)
Ameloblasts

23. Amelogenesis - Enamel Proteins
Amelogenin vs Ameloblastin

24. What is the enamel space?
Protective Stage
Full thickness of enamel complete, enamel mature
Ameloblast layer & papillary layer form “reduced enamel epithelium”
What is the enamel space?

25. Scanning Electron Microscopy
Enamel - Structure
Hard Tissue Formation
Amelogenesis
Structure of Enamel
Clinical Correlations
Scanning Electron Microscopy
R = Rod & IR = Interrod Areas

26. Note: rod, interrod crystals same, but divergent orientation
Enamel - Structure
Aapd.org/publications/peddent/
Note: rod, interrod crystals same, but divergent orientation

27. Enamel: hydroxyapatite crystals
Enamel - Structure
Enamel: hydroxyapatite crystals
Young Enamel
Older Enamel
Transmission EM:
rod surrounded by interrod enamel

28. Enamel - Structure
Crystals
hexagonal contour to older mature crystals
recently formed thin crystals

29. Enamel - Structure
Crystal Profiles
hexagons with unequal-sided peaks (un) & equal-sided peaks (eq) x 300,000 (rat incisor)

30. Enamel - Structure
enamel rod orientation
A: alternating orientations
B: row arrangement
C: note thin, long apatite crystals

31. Enamel - Structure rod sheath
rod sheath = boundary between rod & interrod enamel, contains organic material
Cat Secretory Stage Enamel
Mature Cat Enamel

32. Enamel - Structure
3 Faces of an Enamel Block
cross-section of rod-interrod area appearance compared to “keyhole”