1. Structural Components of Teeth
Enamel, Dentin, Cementum
Dermal denticles of sharks

2. Enamel

3. Enamel
Hard, vitreous-like substance that covers, protects the anatomic crown
Highly mineralized - 96% inorganic
Fundamental unit is the enamel rod or enamel prism
Formed by ameloblast cells (amelogenesis)

4. Physical Properties

5. Hardness: Moh’s hardness 5 - 8 (diamond is 10)
Knoop hardness number (KHN) of 300:
Dentin 65
Pure gold 32
Amalgam 90
Composite 60
Peripheral enamel harder than deeper enamel

6. Density: Increases from DEJ to surface Enamel thickness varies:
Thicker in cusp and incisal areas
Thins out towards cervical areas

7. Color:
Semi-translucent, partly dependent on enamel thickness and underlying dentin
Polychromatic (different colors)
Thinner - yellow white (underlying yellow dentin)
Thicker layer blue-grayish white

8. Tensile strength and compressibility:
Hard but brittle - prone to splitting and chipping (high compressibility but very low tensile/shear strength)
Cushioned and supported by underlying dentin

9. Solubility: Dissolved by acid (demineralization)
Certain minerals (fluoride) reduce solubility and increase hardness
Surface enamel less soluble than deep enamel

10. Permeability: Selectively permeable (shown by organic dyes)
Submicroscopic pores act like a molecular sieve
Water and ions pass via osmosis

11. Chemical Composition:
Inorganic: 96%
Organic: 1%
Water: %

12. Inorganic Content 96% inorganic by weight
Calcium + phosphate + hydroxyl ions = hydroxylapatite
Hydroxylapatite crystal: Ca10(PO4)6 (OH)2
Fl combines with Ca ion to form the harder fluoroapatite crystal

13. Organic Content 1% organic matter
Various amino acids, carbohydrates and lipids

14. Water Content 3 - 4% by weight
Hydrated shell or covering around the apatite crystal

15. Enamel Prisms (Rods) Fundamental unit of enamel
Cross-section described as “key-hole” shape, interlocking

16. Enamel prisms... Run from DEJ to surface
Essentially perpendicular to surface (fig. A & B)
Primary rods perpendicular to DEJ* (fig. C)

17. Lines of Retzius Incremental growth lines in enamel
Concentric series of brown lines (“tree-rings”)
Formed by hypomineralized bands
Arc-like pattern
Wave-like surface characterization called “perikymata”

18. Hunter-Schreger Bands
Alternating light and dark bands of enamel rods (artifact of specimen sectioning)
Dark bands: diazones
Light bands: parazones

19. Dentin

20. Dentin Main component of tooth structure
Covered by enamel (crown portion) and cementum (root portion)
Formed by odontoblast cells (dentinogenesis)
Dentinal tubules: microscopic tubes that radiate outward from the pulp

21. Dentin…
Odontoblast processes: extensions of odontoblast cells within dentinal tubules

22. Physical Properties Color is yellowish-white Knoop hardness of 65:
Less than enamel
Greater than bone or cementum
Elastic property: supports brittle enamel
Highly permeable - decreases with age

23. Chemical Composition
75% inorganic
20% organic
5% water, etc

24. Inorganic composition:
Calcium phosphate as hydroxylapatite
Fluoride presence is 2-3X that found in enamel
Higher in permanent than primary teeth
More concentrated closer to pulp
Concentration increases with age

25. Organic composition: Mainly collagen (protein)
Glycine, alanine, proline, hydroxyproline
Thought to be a seeding agent in apatite crystal formation
Some lipids (cholesterol)

26. Structural Components
Odontoblasts and their processes located within dentinal tubules
Tubules bigger towards pulp and narrow towards DEJ

27. Dentinal matrix…
Dentinal matrix: intertubular dentin and peritubular dentin
Peritubular dentin more mineralized than intertubular dentin

28. Dentinal matrix...
Intertubular dentin mainly collagenous fibers criss-crossing between tubules

29. Structural morphology:
Imbrication lines (Lines of Owen): incremental lines of growth similar to Lines of Retzius (e.g. tree rings)
Roman imbrice

30. Structural morphology...
Neonatal line: demarcation between prenatal and postnatal dentin (in primary teeth and permanent first molars)

31. Types of Dentin Primary dentin (initial formation of tooth)
Secondary dentin (next to pulp,lifelong)
aka Physiologic secondary dentin
Tertiary dentin (reaction to caries)
aka Reparative secondary dentin
PSD
RSD

32. More types of dentin…
Sclerotic dentin: tubules obliterated by minerals
Dead tracts: tubules with dead odontoblast processes

33. Cementum

34. Characteristics Protects root dentin
Provides for attachment to alveolus via Sharpey’s fibers
Formed by cementoblast cells (cementogenesis)

35. Physical characteristics:
Light yellow color
Chemical composition
50% inorganic (hydroxylapatite)
50% organic material and water

36. Types of Cementum Acellular cementum Cellular cementum
Cervical 2/3 of root
Mainly calcified substance
Cellular cementum
Apical 1/3 of root
Mainly cementocytes
Secondary cementum
Forms as a result of trauma or pathology

37. Adhesive bonding to tooth

38. Bonding to enamel:
Acid etching to remove microscopic amounts of enamel hydroxylapatite
Resin flows into roughened crevices and bonds mechanically

39. Bonding to dentin: More complex than bonding to enamel
Etch removes mineral components leaving collagen matrix
Resin primer infuses between collagen matrix and into dentinal tubules: collagen/resin hybrid layer

40. Video of Premolar Wax-up
Lab Project
Video of Premolar Wax-up

41. Questions???