Hard, brittle, totally acellular , highly mineralized
Secretory product of stratified squamous epithelium
Hydroxyapatite crystal arrange in prism or rods
Density:Decreases from the surface of enamel to the
Thickness:Thickness over the cusps of the molars where it
measures 2.5 mm & incisal edges of incisors where it is
Forms a protective covering (2 mm – knife
Forms a resistant covering (suitable for
The hardest calcified tissue in human body.
enamel is very brittle but the underlying dentin
provides some resilience
Acts as semipermeable membrane (selectively
Color: yellowish white to grayish white
depends on translucency.
Enamel gains mechanical
strength by interweaving HAP
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
96% inorganic - by weight
inorganic crystalline calcium phosphate –
various ions like strontium, magnesium, lead
and fluoride are present at some point during
Cross section of enamel rod shows the key
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
CHARACTERISTICS - ENAMEL ROD/PRISM
Number: 5 – 12 millions.
Direction: Run in oblique direction and wavy
Length: greater than the thickness.
Diameter average: 4 µm.
Appearance: Have a clear crystalline appearance.
Cross-section: hexagonal, round, oval, or fish
• Enamel Rod: Basic Structural
Head of enamel rod is formed by one
ameloblast and tail is formed by three
Thus each rod is formed by four ameloblasts
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
Deviate about 65° from the tails.
the boundary between rod
and interrod is delimited by
a narrow space containing
organic material – rod
A thin peripheral layer.
Darker than the rod.
Less calcified and contains
more organic matter than
the rod itself.
Electron Microscope : often
ALTERNATING ROD DIRECTIONALITY
Hunter Schreger bands are
alternating light and dark
bands seen in a section of
longitudinally and illuminated
in a special way.
•The bands are produced by
the orientation of groups of
•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.
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.
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
STRAIGHT ENAMEL RODS -LONGITUDINAL
The enamel rods
project in the direction
of the arrow.
Can you see the striaof
Wavy course of enamel rod
• A more spiral course is noted at cusps & incisal areas 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
In this section, you can see the
end of an odontoblasticprocess
penetrating the enamel just past
This structure is called an
Legend: A, Gnarled enamel; B,
Optical phenomenon seen in reflected light
Alternate light and dark bands
Seen in ground longitudinal section
Due to abrupt change in the direction of
Originate from the DEJ.
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
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
Due to sudden change in the environment and nutrition.
The antenatal E. is better calcified than the postnatal E.
Are thin, leaf like structures,
Develop in planes of tension.
Extends from E. surface towards the DEJ.
Confused with cracks caused by grinding
Extend in longitudinal and radial direction.
Represent site of weakness in the tooth and three
types; A, B, and C.
In this ground crosssection of tooth, you can
see enamel lamellae
and enamel tufts You
can also see the
•What do all three of
these structures have in
Answer: They are all
Legend: A, Enamel
lamella; B, Enamel tuft;
C, Neonatal line
Enamel tufts are less
mineralized areas of
enamel in the inner third of
enamel adjacent to the
DEJ. They resemble tufts
•They are wavy due to the
waviness of the adjacent
•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
ENAMEL TUFTS -TWO PLANES OF FOCUS
Enamel tufts consist of
"leaves" of hypocalcified enamel.
•They display a wavy
•Enamel spindles are the
into the enamel.
Legend: A, Enamel
spindle; B, Enamel tuft
Scalloped junction – the convexities towards
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
usually end at the DEJ.
However, sometimes the
ends of the process become
embedded in the enamel as it
•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
Legend: A, Enamel
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.
LIFE CYCLES OF THE AMELOBLASTS
According to their function, can be
divided into six stages:
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
Inner enamel epithelium interact with the
cells of dental papilla which differentiate into
Cells become elongated
Proximal part contain nuclei
Distal end is nucleus free zone
Dentin formation begins
Cell free zone disappear
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
Formatve stage starts After the dentine
Enamel matrix formation starts
Development of blunt cell process on the
ameloblast surface which penetrate the basal
lamina and enter the predentin
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
After enamel calcification cells on ameloblast
can no longer be differentiated from stratum
intermedium and outer enamel epithelium
These layer forms reduced enamel
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
Reduced enamel epithelium induces atrophy
of connective tissue separating it with oral
epithelium thus fusion of the two epithelia
Premature degeneration of the reduced
enamel epithelium may prevent the eruption
of he tooth
Organic matrix formation (follows
incremental pattern – brown striae of
ORGANIC MATRIX FORMATION
dpTP=distal portion of Tome’s process
ppTP=proximal portion of Tome’s process
Sg=secretory granules(E. protein)
Schematic representation of
the various functional stages
in the life cycle of ameloblasts
as would occur in a human
1, Morphogenetic stage;
2, histodifferentiation stage;
3, initial secretory stage (no
4, secretory stage (Tomes’
5, ruffle-ended ameloblast of the
6, smooth-ended ameloblast of
the maturative stage;
7, protective stage.