oral histology enamel prof gobran_.pptx

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.

 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

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.

• Thickness
• Color
• Hardness
• Brittleness
• Permeability
• Solubility
Physical characteristics

1. Thickness
Thickness of enamel decrease gradually from cusps or incisal
edges to CEJ.
Varies from 2.5 mm over the working surfaces to a feather edge at the
cervical line about 0.5mm.

2. Color
-Depends on
1- thicknes
2- Degree of calcification.
3-Homogenisity of enamel.
Yellowish white
Grayish white
More translucent More opaque
The color of enamel is usually translucent in nature.

3. Hardness
Enamel is the hardest calcified tissue in the body Because
of its high content of minerals.( 96% )
Enamel can withstand load of mastication and resist wear process.
 Micro-hardness is grater at surface and cusp tip than ADJ and cervical
line.
 Enamel of permanent teeth is harder than that of deciduous.

4. Brittleness
Although it is hard , enamel is extremely brittle thus it has low tensile strength
and depends on the strength of the underlying dentin. the dentin acts as a
cushion for enamel when masticatory forces are applied on it. For this reason,
during tooth preparation, for maximal strength of underlying remaining tooth
structure all enamel rods should be supported by healthy dentin base.

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.

Solubility
Enamel dissolves in acid media. Its surface is less soluble
than deep enamel.
Significance
Acid etching of enamel which is very important
technique for conditioning enamel for many clinical
procedures such as fissure sealants, restoration,
cementing or orthodontic bands..etc.

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
Chemical properties

ASG
INORGANIC MATERIAL 96 %
CALISIUM PHOSPHATE CRYSTALLINE
(
HYDROXY APATITE
)
3
Ca3 (PO4)2 . Ca (OH)2
The apatite crystals of enamel are the largest of all
those of the other calcified structures
(thickness 300 angstrom; width 900 angstrom,
length 0.05-1.0 micron.).
The susceptibility of these crystals to dissolution
by acids provides the chemical basis for the carious
lesion to attack the enamel.

• Most crystallites are regularly
hexagonal in cross-section

Enamel proteins
The organic matrix of enamel is made from non
collagenous proteins only and contains several
enamel proteins and enzymes.
90% of the enamel proteins are amelogenins;
the remaining 10% consists of nonamelogenins,
such as enamelin and ameloblastin.

 The proteins present in enamel are:-
1.Amelogenins
2.Ameloblastin
3.Amelin
4.Enamelin
5.Tuftelin

 90%.
 Important in crystal growth & organization.
 Nanospheres between which enamel crystals forms.
 Absence leads to hypoplastic.

• Water
• By weight: 2-3%
• Location
• Between crystals & organic material
• Clinical importance-
• fluoride travel through the water component

Ground sections Demineralized sections

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

Dentin
Rodless
enamel
Rodless
enamel
Rod
( Prismati
c
)
Enamel
Ameloblast
without
Tomes
process
amelo
with
Tom
proc
blast
out
es
es
s
Amelob
wit
Tom
proce
las
t
h
es
s
s

Tomes' processes
determine the orientation
of the newly formed
enamel hydroxyapatite
crystals.

Crystals in rod and interrod enamel are similar in structure but diverge in orientation

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

Direction:
generally perpendicular to the dentin surface.
A) in deciduous teeth:roughly vertical in the cusp tip or incisal ridge. They
become oblique towards the occlusal surface in the middle third. In the cervical region they became
horizontal.
B) in permanent teeth :similar except cervically the rods are directed root
wise( obliquely).

Vertical
Oblique
Vertical
Oblique
Horizontal
Knife edge
Direction

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.

D
Twisted
course of
enamel rods
Gnarled
enamel
GNARLED ENAMEL :
Resulted from twisting of enamel rods at the incisal
ridges and under the cusp tip .This pattern give maximum
strength to these areas subjected to masticatory forces.

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.

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.

:Cross Section ,Hexagonal, fish
scales
keyhole pattern

Bands of Hunter and
Schreger
An optical phenomenon
produced 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.

These bands appear as
alternating dark
(diazones) light
(parazones).

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.

B. Inter rod Substance
It separates enamel rods from each
other.
It is as highly calcified as the enamel
rods.
 It has a different refractive index.

C. Rod Sheath
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.

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.

Incremental lines
Incremental lines of enamel means growth lines or bands
seen in tooth enamel.
 It includes :
II. Brown striae of Ratzius.
III. Neonatal line.

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
appears to be divided horizontally into
equal segments by less calcified dark
lines.
 Also known as short increments.

II. Brown striation of Retzius
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.

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).

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

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).
Neonatal line

PRENATAL
ENAMEL
POSTNATAL
ENAMEL
POSTNATAL
ENAMEL
PRENATAL
ENAMEL
ASG

Enamel
I. Incremental lines.
II. ADJ
III. Enamel spindle.
IV. Enamel tufts.
V. Enamel lamellae.
a) Outer structureless enamel.
b) perikymata.
c) Rod end.
d) Cracks

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 firm attachment
between enamel and de

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.

3. Enamel spindle.
It is a short, straight, thin, dark
structures which extend for only short
distances into enamel.

* Before enamel forms, some developing odontoblasts
process extend into the ameloblast layer, and when
enamel formation begins become trapped to form
enamel spindles.
Significance: Spindles serve as pain receptors, that is
why, when we cut in the enamel patient complains of
pain.

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

4. Enamel Tufts.
 grass 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.
 Significance: Enamel tufts are
hypomineralized structure in the enamel,
thus play role in spread of dental infection.

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.

Several enamel tufts, which appear as
wavy groups of enamel rods, extend from
the dentinoenamel junction into enamel to
about one quarter of its thickness.

5. Enamel Lamellae.
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

Enamel lamellae
In enamel
only
Extending in enamel and
dentin

The enamel lamellae appear as longitudinal
cracks in the enamel that sometimes extend
into the dentin.

Enamel
1. Incremental lines.
2. ADJ
3. Enamel spindle.
4. Enamel tufts.
5. Enamel lamellae.
a. Outer structureless enamel.
b. perikymata.
c. Rod end.
d. Cracks

surface structure
a. Outer structure less enamel
The outer most 30 microns of enamel.
Found in all deciduous teeth an 70% of
permanent teeth.
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 responsible for rod and inter
rod substance and rod sheath 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.
Outer structure less
Inner structure less
ADJ

Denti
n
Rodless
enamel
Rodless
enamel
Rod
( Prismati
c
)
Enamel
Ameloblast
without
Tomes
process
amelo
with
Tom
proc
blast
out
es
es
s
Amelob
wit
Tom
proce
las
t
h
es
s
s
Beginnin
g
secretor
y
Secretory
stage
End of
secretory
stag
e

b. perikymata
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.

Perikymata
grooves
Perikymata
ridges

PARALLEL TO EACH OTHER AND
TO C.E.J.
CONTINUOUS AROUND THE
TOOTH.
30/ mm – AT THE REGION OF
C.E.J.
10/ mm – NEAR TO THE
OCCLUSAL OR INCISAL EDGES
ASG

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

SHALLOWER
CERVICALLY
DEEPER
OCCLUSALLY
ASG

d. Cracks.
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.

ASG
- 0.2 um thick.
- Its structure is
similar to the basal
lamina of the
epithelium.
- It is the last
product of the
ameloblasts.
PRIMARY ENAMEL CUTICLE
(Nasmyth’s membrane)

Enamel Pellicle
Enamel pellicle (arrow) is the uniform thick deposition of
salivary protein between a thin layer of immature bacterial
plaques and enamel

oral histology enamel prof gobran_.pptx

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