Enamel

Enamel
 Definition.
Properties
A. Physical
B. Chemical.
 structure of enamel
A. Rod.
B. Inter rod
C. Rod sheath.
 incremental lines
I. Cross striations.
II. Brown striae of Retzius.
III. Neonatal line.

Enamel
 Hypo-calssified structures.
1. Incremental lines.
2. ADJ
3. Enamel spindle.
4. Enamel tufts.
5. Enamel lamellae.
 surface structure.
a. Outer structureless enamel.
b. perikymata.
c. Rod end.
d. Cracks
e. Afibrillar cementum .

Definition
A material like colored glass that is
heated until it is liquid and then
used to decorate the surface of
metal, glass, or pottery.

Definition
 Ectodermal non-collagenous tissue
covering the anatomical crown of
teeth forming a protective
converging against masticatory
forces. It is the most highly
mineralized tissue in the body.
 Acellular, inert, non vital and
insensitive tissue, when destroyed
by any means usually wear or caries
it can not be replaced or
regenerated.

Properties
Physical properties
1. Color
2. Thickness
3. Hardness
4. Brittleness
5. Permeability

Properties
Physical properties
1. Color
Depending on degree of translucency which depends on
a. Degree of calcification.
b. Homogenisity of enamel.
Yellowish white Grayish white
More translucent More opaque

2. Thickness
Varies from 2.5 mm over the working surfaces to a feather edge at the
cervical line.
Properties
Physical properties

3. Hardness
 The hardest calcified tissue due to
a. High mineral content.
b. Crystalline arrangement.
 Micro-hardness is grater at surface and cusp tip than ADJ and cervical
line.
 Enamel of permanent teeth is harder than that of deciduous.
Properties
Physical properties

4. Brittleness
Brittle therefore an underlying layer of resilient dentin is necessary to
maintain its integrity.
Properties
Physical properties

5. Permeability
 It acts as a semi permeable membrane for some ions and dyestuffs
of small molecular size through pores between the crystals.
 Permeability is mainly from saliva to the outer layer of enamel, but
less from the pulp to the inner enamel layer across the dentin.
Properties
Physical properties

Properties
chemical properties
By weight
96% inorganic
crystalline calcium phosphate “hydroxyapatite”
Ca10 (PO4)6 (OH)2
(OH) can be replaced by F
4% organic
1-2% non-collagenous proteins “ E Prs.”
and 2-3% water. Fine lacy network, forms
an envelop surrounding each crystal.
By volume both are equal

Enamel
 Definition.
 Properties
A. Physical
B. Chemical.
 Structure of enamel
A. Rod.
B. Inter rod
C. Rod sheath.
 Incremental lines
II. Brown striae of Retzius.
III. Neonatal line.

Structure of enamel
Decalcification
Staining
Ground sections

Structure of enamel
Unite structure of enamel is enamel
rod enveloped with rod sheath and
surrounded by inter rod substance.
Enamel
Rod
Rod
SheathInter rod
substance

When rod is cut transversely, different
patterns are revealed rounded, oval,
fish scales & key hole.
When rod is cut longitudinally it
appears cylindrical separated by less
calcified dark lines “cross striations”.
Structure of enamel
A. Enamel Rod

I. By light microscope (LM)
 Either TS or LS it appear clear and structure less because
of the tightly packed crystals to allow light to pass through.
 The use of electron microscope with thinner sections and
grater resolving power.
Structure of Enamel
A. Enamel Rod

II. By electron microscope (EM)
 LS.. Cylindrical separated by less calcified dark lines.
 TS .. Oval, fish scales, rounded, hexagonal or Key hole
with the head directed occlusally and the tail points
cervically.
Crystals.. at the central part parallel to the long axis of
the rod. “0-40 degrees” as they approach the rod
boundary, they flare laterally to an increasing degree.
The difference in the angulation causes difference in
the reflective index.
Structure of Enamel
A. Enamel Rod

III. Number
Varies 5 millions at lower central and up to 12 millions at the upper 1st
permanent molar.
IV. Diameter
Ratio between inner and outer E. surface is 1:2.
i.e. 3-4 microns at ADJ…. 8 microns at outer surface.
Structure of Enamel
A. Enamel Rod

V. Direction
Structure of Enamel
A. Enamel Rod
Vertical
Oblique
Vertical
Oblique
Horizontal
Knife edge

VI. Course
 From ADJ outward … wavy course.
 BUT just before they reach the outer surface
they become straight.
 Under cusp tip or incisal edge; rods become
twisted to give maximum strength.. This is
known as Gnarled Enamel.
Structure of Enamel
A. Enamel Rod

Structure of Enamel
A. Enamel Rod

Bands of Hunter and
Schreger
 An optical phenomenon produced
solely by changes in rod direction.
They are seen most clearly in
longitudinal ground sections
by reflected light.
 Found in the inner two thirds of
enamel.
Structure of Enamel
A. Enamel Rod

Bands of Hunter and
Schreger
These bands appear as
alternating dark (diazones)
light (parazones).
Scanning electron microscopy
clearly reveals the difference
orientation of groups of rods
within these zones.
Structure of Enamel
A. Enamel Rod

Bands of Hunter and
Schreger
It may be due to:
1. Change in the direction of enamel
rods.
2. Variation in calcification of the
enamel.
3. Alternate zones having different
permeability and organic material.
Structure of Enamel
A. Enamel Rod

Structure of enamel
Enamel
Rod
Rod
SheathInter rod
substance
 LM
 EM
 Number
 Diameter
 Direction. “P&D”
 Course. “G E & H-S B”

 It separates enamel rods from each
other.
 It is as highly calcified as the enamel
rods.
 It has a different refractive index.
 In human teeth it appears to be
minimum or even absent in certain
areas.
Structure of Enamel
B. Inter rod Substance

Structure of Enamel
B. Inter rod Substance

The peripheral part of the enamel
rod is called rod sheath.
 It forms an incomplete envelope
around the rod.
It is less calcified than the rod
itself i.e. it has a higher organic
content, thus it resists
decalcification more than the rod.
Structure of Enamel
C. Rod Sheath

It is formed along the interface
between groups of crystals with
different angulation in the rods and
inter rod regions, due to the abrupt
change in crystal orientation.
 For this reason the crystals in the rod
sheath are not so tightly packed,
allowing more spaces between them for
more organic material to be present.
Structure of Enamel
C. Rod Sheath

Incremental lines
 Incremental means increasing or adding on, especially in a
regular series.
Incremental lines of enamel means growth lines or bands
seen in tooth enamel.
 It includes :
II. Brown striae of Ratzius.
III. Neonatal line.

Incremental lines
I. cross striations

 Periodic bands of 3-4 µm intervals across
the rod.
These represent daily rhythm of the
enamel deposition.
More visible when GLS of enamel is
treated with mild etching solution, the
cylindrical clear crystalline enamel rod
appears to be divided horizontally into
equal segments by less calcified dark
lines.
 Also known as short increments.
Incremental lines
I. cross striations

Scanning EM reveals alternating
constrictions and expansions.
Close examination reveled that
constrictions are concavities in the
rod structure.
Incremental lines
I. cross striations

 Brownish bands appear in the GS of
enamel.
 It represents the weekly rhythm of enamel
formation “periods of activity alternating
with periods of rest”.
 Metabolic disturbance leads to prolonged
periods of rest and broadening of the
incremental lines.
Incremental lines
II. Brown striae of Retzius

In L/S:
 At the middle and cervical parts: they
run obliquely and deviate occlusally
reach the enamel surface and become
represented as a series of transverse
depressions (perikymata).
 At cusp tips and incisal ridges: these
bands form semicircle as they do not
reach the surface (surround the tip of
dentin).
Incremental lines

In C/S:
 Seen as concentric rings
resembling that of the growth
rings of a tree.
Incremental lines

The darkest stria of Retzius that occurs at the
time of birth. It is due to the stress of birth.
Present only in deciduous teeth and first
permanent molars (enamel develops partly
before and partly after birth).
Separates prenatal enamel from postnatal
enamel.
The quality of prenatal enamel is better than
the postnatal enamel (more protected
condition and constant nutrition of the fetus).
Incremental lines
III.Neonatal Line

Enamel
 Hypo-calssified structures.
I. Incremental lines.
II. ADJ
III. Enamel spindle.
IV. Enamel tufts.
V. Enamel lamellae.
 surface structure.
a) Outer structureless enamel.
b) perikymata.
c) Rod end.
d) Cracks
e) Afibrillar cementum .

Hypo-calssified structures.
2. Amelo-Dentinal Junction “ADJ”
The junction between enamel and dentin is
seen as a scalloped profile in ground section
with the convexities directed towards the
dentin.
 These scallops provide undercuts that was
thought at one time to be the cause of the firm
attachment between enamel and dentin.
 However these scallops occasionally seem to
be absent and in this case the ADJ appears
smooth and still enamel and dentin are firmly
attached!!!!

The cause of the firm attachment is due to
the interdigitating at the ADJ between the
fibrils of the first formed layer of dentin and
the fibrils of the organic matrix of the first
formed layer of enamel.
 Consequently the interdigitating between
the hydroxyapatite crystals that are
deposited during the mineralization of both
structures.
2. Amelo-Dentinal Junction “ADJ”

It is a short, straight, thin, dark
structures which extend for only short
distances into enamel.
They are residual tubules formed when
odontoblastic processes extend across
ADJ during odontogenesis before
enamel forms.
3. Enamel spindle.

In GS; the odontoblastic
processes disintegrate and are
replaced by air which appears
dark in transmitted light.
3. Enamel spindle.

 Ribbon like structure; project from ADJ for a
short distance into enamel (1/5-1/3).
 Occur developmentally because of abrupt
changes in the direction of groups of rods that
arise from different regions of the scalloped
ADJ.
 They appear to be branched and contain
greater concentration of enamel proteins.
They resemble tufts of grass.
4. Enamel Tufts.

Best seen in transverse thick sections of
enamel with low magnification.
Usually best demonstrated in G.S but
can also seen in carefully demineralized
sections of enamel.
4. Enamel Tufts.

 Fissure or leaf like defects and extend from
enamel surface for varying depth in enamel.
This defect is filled with organic material.
Could help in spread of caries.
Types
I. Type A “ true lamella”
II. Type B
III. Type C
5. Enamel Lamellae.

5. Enamel Lamellae.

5. Enamel Lamellae.
Type A Type CType B

surface structure
a. Outer structure less enamel
The outer most 30 microns of enamel.
Found in all deciduous teeth an 70% of
permanent teeth.
Most common in cervical area and least often
in cusp tip or incisal edge.
No rod outline is visible; crystals are arranged
parallel to each other and perpendicular to the
surface.
it is highly mineralized “hyper-mineralized”

 Tome’s process is absent during formation of
this layer; which insure its role in rod and inter
rod substance and rod sheath. “responsible for
crystal arrangement”
 Similar to it; there is inner structure less
enamel, which is formed before Tome’s process
formation.
 In inner structure less enamel, crystals are
arranged parallel to each other and
perpendicular to dentine surface.
surface structure
a. Outer structure less enamel
Outer structure less
Inner structure less
ADJ

 Transverse wave like groves believed
to be the external manifestation of
striae of Retzius.
Continuous around the tooth and
parallel to the CEJ.
There are 30mm in cervical area and
decrease toward the occlusal surface to
about 10mm.
surface structure
b. perikymata

They are concave depression vary in
depth and shape.
They are shallow at the cervical region
and deepen near the incisal or occlusal
surface.
surface structure
c. Rod End.

They are narrow fissure like structure
found on almost all enamel surfaces and
extend for varying distance.
They are actually the outer edge of enamel
lamellae. Completely disappear by careful
decalcification.
surface structure
d. Cracks.

It is coronal cementum is formed on the cervical
portion of the crown; it serves no anchoring
function.
 Its presence is restricted to localized areas of REE
degeneration.
The exposed enamel provides a surface on which
cementoblasts from the dental follicle are able to
deposit cementum.
surface structure
e. Afibrillar cementum.

In histological sections it may appear as
an "island or a "spur" of cementum
continuous with radicular cementum
and overlapping the cervical enamel.
Generally, coronal cementum in
humans is acellular and afibrillar.
surface structure
e. Afibrillar cementum.

Enamel

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