2. PHYSICAL CHARACTERISTICS
Hard, brittle, totally acellular , highly mineralized
Secretory product of stratified squamous epithelium
Calcified tissue
Hydroxyapatite crystal arrange in prism or rods
Density:Decreases from the surface of enamel to the
dentino-enamel junction.
Thickness:Thickness over the cusps of the molars where it
measures 2.5 mm & incisal edges of incisors where it is
2.0 mm.
3. ENAMEL
1.
2.
3.
4.
5.
6.
Forms a protective covering (2 mm – knife
edge).
Forms a resistant covering (suitable for
mastication).
The hardest calcified tissue in human body.
enamel is very brittle but the underlying dentin
provides some resilience
Acts as semipermeable membrane (selectively
permeable).
Color: yellowish white to grayish white
depends on translucency.
4.
Enamel gains mechanical
strength by interweaving HAP
crystals
Enamel rod – 5-12 million/tooth
Appatite crystal is hexagonal
Enamel initially starts with a high
protein content, but these are
removed and the voids backfilled
with HAP as the tooth matures
5. CHEMICAL PROPERTIES
96% inorganic - by weight
inorganic crystalline calcium phosphate –
hydroxyapatite
various ions like strontium, magnesium, lead
and fluoride are present at some point during
enamel formation
7. CROSS SECTION
Cross section of enamel rod shows the key
hole pattern
Head represents the rod and key shows the
inter rod region
Head is directed towards the occlusal aspect
and tail towards the cervical region of the
tooth
10. CHARACTERISTICS - ENAMEL ROD/PRISM
Number: 5 – 12 millions.
Direction: Run in oblique direction and wavy
course.
Length: greater than the thickness.
Diameter average: 4 µm.
Appearance: Have a clear crystalline appearance.
Cross-section: hexagonal, round, oval, or fish
scales.
12. Head of enamel rod is formed by one
ameloblast and tail is formed by three
ameloblasts
Thus each rod is formed by four ameloblasts
13. SUBMICROSCOPIC STRUCTURE
OF ENAMEL RODS
Keyhole or paddle-shaped.
Separated by interrod substance.
About 5 µm in breadth and 9 µm in length.
The bodies are near the occlusal or incisal surface.
The tails point cervically.
The crystals; parallel to the long axis of the prism
heads.
Deviate about 65° from the tails.
14. ROD SHEATH
the boundary between rod
and interrod is delimited by
a narrow space containing
organic material – rod
sheath
A thin peripheral layer.
Darker than the rod.
Relatively acid-resistant.
Less calcified and contains
more organic matter than
the rod itself.
Electron Microscope : often
incomplete.
15. ALTERNATING ROD DIRECTIONALITY
Hunter Schreger bands are
alternating light and dark
bands seen in a section of
enamel
when
cut
longitudinally and illuminated
in a special way.
•The bands are produced by
the orientation of groups of
rods.
•If the light passes through
rods cut in cross-section, the
band appears light.
•If the light passes through
rods cut in longitudinally, the
band appears dark.
16. STRIATIONS
E. rod is built-up of segments (dark lines).
Best seen in insufficient calcified E.
In a longitudinal section dark lines are seen
that shows the daily deposition of enamel
(rhythmic manner of E. matrix formation).
These lines are known as cross striation
Segment length: about 4 µm.
18. DIRECTION OF RODS
Near the edge or cusp tip they are oblique
At the cusp tip they are almost vertical
Run from DEJ to surface of enamel
Usually at right angles to the Dentin surface.
Follow a wavy course in clockwise and
anticlockwise deviation full thickness of enamel
At the cusps or incisal edges: gnarled enamel.
At pits and fissures: rods converge in their
outward course.
19. STRAIGHT ENAMEL RODS -LONGITUDINAL
LABIOLINGUALSECTION
The enamel rods
project in the direction
of the arrow.
Can you see the striaof
Retzius?
20. Wavy course of enamel rod
• A more spiral course is noted at cusps & incisal areas Gnarled enamel
21. GNARLED ENAMEL
Enamel rods are general not
straight throughout their length.
In the cuspal region, the rods
are very wavy.
This is referred to as gnarled
enamel.
In this section, you can see the
end of an odontoblasticprocess
penetrating the enamel just past
the DEJ.
This structure is called an
enamel spindle.
Legend
Legend: A, Gnarled enamel; B,
Enamel spindle
23. HUNTERSCHRAGER BANDS
Optical phenomenon seen in reflected light
Alternate light and dark bands
Seen in ground longitudinal section
Due to abrupt change in the direction of
enamel rod
Originate from the DEJ.
26. ENAMEL -TRANSVERSE GROUND SECTION
In a transverse section of tooth, the stria of
Retzius appear as concentric bands parallel
to the dentino-enamel junction (DEJ). In
addition to the "hypo-mineralized" dark striaof
Retzius, there also exist hypo-mineralized
areas perpendicular to the DEJ. These are
enamel lamellae(that traverse the entire
thickness of enamel) and enamel
tufts(that traverse the inner third of
enamel adjacent to the DEJ
28. STRAE OF RETZIUS
Incremental lines of growth
Eccentric growth rings
DEJ to outer surface of enamel
Where they end as shallow furrows known as
perikymata
30. NEONATAL LINE
The E. of the deciduous teeth and the 1st permanent
molar (It is incremental line that is the boundary
between the enamel forms before and after the birth)
The neonatal line is usually the darkest and thickest
striaof Retzius.
Etiology
Due to sudden change in the environment and nutrition.
The antenatal E. is better calcified than the postnatal E.
32. ENAMEL LAMELLAE
Are thin, leaf like structures,
Develop in planes of tension.
Extends from E. surface towards the DEJ.
Confused with cracks caused by grinding
(decalcification).
Extend in longitudinal and radial direction.
Represent site of weakness in the tooth and three
types; A, B, and C.
33. ENAMEL LAMELLAE
In this ground crosssection of tooth, you can
see enamel lamellae
and enamel tufts You
can also see the
neonatal line.
•What do all three of
these structures have in
common?
Answer: They are all
hypocalcified.
Legend: A, Enamel
lamella; B, Enamel tuft;
C, Neonatal line
36.
Enamel tufts are less
mineralized areas of
enamel in the inner third of
enamel adjacent to the
DEJ. They resemble tufts
of grass.
•They are wavy due to the
waviness of the adjacent
rods.
•Structures rich in organic
matter (i.e. less
mineralized) that project to
the surface of the enamel
are enamel lamellae.
Legend: A, Enamel tufts;
B, Enamel lamella
37. ENAMEL TUFTS -TWO PLANES OF FOCUS
Enamel tufts consist of
several unconnected
"leaves" of hypocalcified enamel.
•They display a wavy
twisted appearance.
•Enamel spindles are the
processes of
odontoblastsprojecting
into the enamel.
Legend: A, Enamel
spindle; B, Enamel tuft
40. DENTINO-ENAMEL JUNCTION
Scalloped junction – the convexities towards
D.
At this junction, the pitted D. surface fit
rounded projections of the enamel.
The outline of the junction is performed by
the arrangement of the ameloblasts and the
B. M.
42. ENAMEL SPINDLES
Odontoblast
processes
usually end at the DEJ.
However, sometimes the
ends of the process become
embedded in the enamel as it
forms.
•These very small, usually
straight structures that you
can see adjacent to the DEJ
are enamel spindles.
•They are only about one
tenth the length of an enamel
tuft. Legend: A, Enamel
spindle;
B,
Odontoblastprocesses in
dentin
49. D. CRACKS
Narrow fissure like structure.
Seen on almost all surfaces.
They are the outer edges of lamellae.
Extend for varying distance along the surface.
At right angles to CEJ.
Long cracks are thicker than the short one.
May reach the occlusal or incisal edge.
51. LIFE CYCLES OF THE AMELOBLASTS
According to their function, can be
divided into six stages:
1.
Morphogenic stage.
2.
Organizing stage.
3.
Formative stage.
4.
Maturative stage.
5.
Protective stage.
6.
Desmolytic stage.
52. Morphogenic stage.
React by differential growth
Produce shape of the crown
Terminal bar appears
Basal lamina separates the inner enamel
epithelium and cells of the dental papilla
Pulpal layer adjacent to the basal lamina is a
cell free zone
At cervical region – cell is relatively
undifferentiated
53. Organizing stage.
Inner enamel epithelium interact with the
cells of dental papilla which differentiate into
odontoblast
Cells become elongated
Proximal part contain nuclei
Distal end is nucleus free zone
Dentin formation begins
Cell free zone disappear
54. As dentine is formed nutrition supply of the
inner enamel epithelium changes from dental
papilla to the capillaries that surround the
outer enamel epithelium
Reduction and gradual disappearance of the
stellate reticulum
55. Formative stage.
Formatve stage starts After the dentine
formation
Enamel matrix formation starts
Development of blunt cell process on the
ameloblast surface which penetrate the basal
lamina and enter the predentin
56. Maturative stage.
Maturation starts after most thickness of
enamel matrix formation in occlusal and
incisal area. In cervical area matrix formation
is still in progress
Ameloblast reduce in length
Cells of stratum intermedium takes spindle
shape
57. Protective stage.
After enamel calcification cells on ameloblast
can no longer be differentiated from stratum
intermedium and outer enamel epithelium
These layer forms reduced enamel
epithelium
Protect the enamel from connective
tissue until the tooth erupts, if it contacts
then anomalies develop enamel may be
resorbed or cementum cover may form
(afibrillar cementum)
58. Desmolytic stage.
Reduced enamel epithelium induces atrophy
of connective tissue separating it with oral
epithelium thus fusion of the two epithelia
can occur
Premature degeneration of the reduced
enamel epithelium may prevent the eruption
of he tooth
61. AMELOGENESIS
Schematic representation of
the various functional stages
in the life cycle of ameloblasts
as would occur in a human
tooth.
1, Morphogenetic stage;
2, histodifferentiation stage;
3, initial secretory stage (no
Tomes’ process);
4, secretory stage (Tomes’
process);
5, ruffle-ended ameloblast of the
maturative stage;
6, smooth-ended ameloblast of
the maturative stage;
7, protective stage.