Enamel amelogeneis, physical properties and histology

Enamel amelogenesis, physical properties and histology

1. Enamel
Mineralised tissue of ectodermal origin
covering anatomic crowns of human teeth

2. Enamel: A Special Tissue
•Ameloblasts, the enamel forming cells are ectodermal.
•Enamel formation takes place only for a short period of
time.
•Enamel is not lined by its formative cells.
•Does not have the capacity to repair or regenerate.
•Is a nonliving tissue. Does not contain cells or cellular
components.
•Is avascular and insensitive.
•Organic matrix of enamel is unique composed of enamel
proteins and is non-collagenous.

3. •Physical Characteristics
•Chemical Characteristics
•Structure
•Age Changes
•Clinical Considerations
•Development of Enamel
▫Epithelial Enamel Organ
▫Life cycle of Ameloblasts
▫Amelogenesis
▫Clinical Considerations

5. •Thickness:
▫Variable thickness. Maximum thickness of 2-2.5mm
over cusps of molars & PM. Knife edge thin at cervical
margins.
•Strength & Hardness:
▫Hardest calcified tissue in body: 343 KHN. Sp gravity
of 2.8.
▫Hardness decreases from surface to deeper regions
and from cuspal to cervical region.
▫Brittle in nature and therefore resilient dentin support
is very essential

6. •Permeability:
▫Will allow complete or partial passage of certain
molecules.
▫Acts like a semi-permeable membrane.
•Color & Translucency:
▫Color of enamel covered crown ranges from Yellowish
white to Grayish white.
▫Color determined by translucency of enamel.
▫Yellowish teeth- thin, translucent enamel allowing
yellow color of dentin to show through.
▫Grayish teeth- more thick and opaque enamel.

7. •Refractive Index:
▫Birefrengent
▫RI - 1.62
•Solubility:
▫Enamel is soluble in acids.
▫Surface enamel is less soluble.

9. •Constitution:
▫Inorganic matter- 96%
▫Organic matter and Water- 4%
•Organic Matter:
▫Enamel proteins and Lipids
▫Amelogenins (90%); Non amelogenins (10%)

10. •Inorganic Matter:
▫Calcium and phosphate [2:1] in the form of
hydroxyapatite crystals.
▫Other components include strontium, magnesium,
lead and fluoride.
•Hydroxyapatite crystal:
▫Rod shaped with equilateral hexagonal base.
▫HA crystals are arranged to form ENAMEL
RODS- Primary structural component of Enamel.
▫Length -160 nm -1000nm
▫Breadth - 40nm
▫Thickness - 25 -60 nm
▫Largest Hydroxyapatite crystals in the body

11. •Enamel Rods and Ultrastructure
•Structural Lines
•Hypocalcified structures
•Surface structures
•DEJ

12. Methods used to study enamel
•Ground section: Unlike other hard tissues
decalcified sections cannot be used to study
enamel
•Light microscope or polarized microscope can be
used.
•Electron microscope may also be used to study
the ultra structure.

14. Enamel Rods

15. •Are the fundamental structural unit of enamel.
•Each rod extends from its site of origin at the
dentino-enamel junction (DEJ) to the outer surface
of enamel.
•The rods are roughly cylindrical in the longitudinal
section.
•Average diameter of 3-4 microns near DEJ;
diameter increases gradually to the surface at a ratio
of 1:2.
•Number of rods varies from 5 million in lower
incisors to 12 million in upper 1
st
molars

16. Direction of Rods
•From DEJ - wavy tortuous course towards outer surface
of tooth.
•Cuspal & incisal edges - rods run perpendicular from
DEJ to outer surface.
•On lateral surfaces - rods run obliquely from DEJ to
outer surface.
•In dev pits & fissure on occlusal aspect - rods converge in
their outward course.
•Rods are never straight because of oblique direction and
wavy course.
•Rods in cuspal region longer than those in cervical.

19. Structure of Rods
•Clear crystalline appearance permitting light to
pass.
•Rod proper (Core), Rod sheath, Interrod enamel.
•Shape:
▫Under light microscope – hexagonal sometimes
round or oval – fish scale appearance
▫In electron microscope – key whole pattern or
paddle shape

22. •In transverse section, the enamel rods have a
keyhole shape with a head formed by the rod and
a tail formed by interrod enamel immediately
cervical to it.
•Rod - head
tail

•Tail fits into area created by convexities of
adjacent rounded head.
•Head directed towards incisal edge or cusp tip

25. •Dimensions:
▫Total length – 9 µ
▫Diameter at DEJ - 4 µ; Outer surface - 6-8 µ
▫From DEJ - outer surface – diameter of enamel
rods increase in the ratio 1:2

26. •Orientation of Apatite crystals in Rods:
•Apatite crystals in Head region - parallel to long
axis of rod

•In Tail region - 65° deviation as they fan out into
tails of prism.

28. •Rodless Enamel: (Structureless Surface
Enamel)
•Outermost 30 µ or 50 µ of all primary teeth
•Gingival 3
rd
of enamel of permanent teeth
•No rod outlines are visible.
•Apatite crystals are perpendicular to surface of
enamel.
•More heavily mineralized than rest of the
enamel.

30. Structural Lines
•Cross striations
•Incremental Lines
•Neonatal Line

31. Cross Striations
•Rods are built up of segments separated by dark
lines. These dark lines are called cross striations.
•Cross striations indicate diurnal or circadian
variation in secretory activity of ameloblasts.
•In humans, enamel forms at a rate of 4 µm/day.
So cross striations are also seen at uniform
length of 4µm.

32. DEJ
Outer
Surface
4µm
Cross Striation