Enamel

Enamel
Presnted by
Dr Piyush

The anatomic crown of a tooth is covered by an
acellular, avascular, highly mineralised material
known as ENAMEL.

 It is the hardest calcified tissue in the human
body.
 It is the only calcified tissue arising from
ectoderm.
 It contains the largest crystals among the
mineralized tissues.

 It protects the less mineralised underlying
dentin of the tooth.
 It serves as a surface for chewing, grinding and
crushing of food.

1) Hardness
 Its high mineral content makes it the hardest
substance in the human body
 Surface enamel vs subsurface enamel
Hardness and density also decrease from the
cuspal/incisal tip towards the cervical margin
and from the surface towards the DEJ

2) Brittleness
The hardness which is comparable to mild steel
makes enamel brittle.
Compensated by the cushioning effect of
underlying resilient dentin.
Enamel is stiffer and more brittle than dentin.

3) Permeability
Enamel can act in a sense like a semipermeable
membrane, permitting complete or partial
passage of certain molecules.
4) Thickness
 It varies with shape of the tooth and location
Reaching a maximum of 2.5mm in the incisal or
occlusal areas and thinning down to almost a
knife-edge at the CEJ

5) Color
Enamel is naturally transparent.
 Ranges from yellowish white to grayish white.
Young enamel has a low translucency and whiter
in colour.
The translucency increases with age and the
yellow colour of underlying dentin becomes
darker and more apparent with age.

6) Specific gravity- 2.8
7) Compressive strength- 384 Mpa
8) Modulus of elasticity- 84 Gpa
9) Knoop hardness number- 350-430 KHN
10) Tensile strength- 10 MPa
10) Co-efficient of thermal expansion- 11.4

11) Density- 2.97
12) Refractive index-
Average refractive index of 1.62
13) Solubility-
 It dissolves in acid media.
 It is influenced by certain ions and molecules like
fluoride, carbonates, organic matrix etc.
 Surface enamel is less soluble than deeper enamel
14) Abrasion resistance-
 Is high, allowing it to wear down slowly

Calcium
hydroxyapatite
[Ca10(PO4)6(OH)2].
The mineral content
increases from the DEJ
to the surface.
Most crystallites are
regularly hexagonal in
cross-section.

A fine lacy network of organic material appears
between the crystal.
According to frank(1979), in the mature state,
the matrix constitutes of:-
 Enamel -only 0.3 %
 Proteins -58%
 Lipids -42%
 Lactates, ions, -trace
 sugars, citrates

 The proteins present in enamel are:-
1.Amelogenins
2.Ameloblastin
3.Amelin
4.Enamelin
5.Tuftelin
directs the growth of the crystals
Organic matrix
acts as a cementing medium

 90%.
 Important in crystal growth & organization.
 Nanospheres between which enamel crystals forms.
 Absence leads to hypoplastic.
 Also found in formation of acellular cementum.

 This is structureless layer of enamel.
30μm
Present in 70% permanent teeth & all
deciduous teeth.
More heavily mineralized than bulk
beneath it.
9/16/2014

Enamel rods near
dentin at the incisal
edge or cusps forms
more complicated,
this optical
arrangement of
enamel is called
Gnarled enamel.
9/16/2014

Basic structural unit is
the enamel prism or
rod.
 It consists of a tightly
packed mass of
millions of small,
elongated
hydroxyapatite
crystals in an
organised pattern.

 Many show fish scales
appearance in cross section.
Width is 4μm and length.
 Number of rods estimated as ranging from 5 million
in lower lateral incisor to 12 million in upper first
molars.
 Diameter of enamel increases from DEJ to outer
surface at a ratio about 1:2.

 The cross-sectional--
the keyhole
arrangement of enamel
prisms with the heads
pointing occlusally and
the tails pointing
cervically.
 Head of each rod is
made up of 1
ameloblast and tail is
made up of 3
ameloblasts.

Human enamel
contains rods
surrounded by rod
sheath and separated
by interrod substance.
Most common pattern
of enamel is keyhole
or paddle shaped
prism.

 In a longitudinal section, appearance of
rods separate by interrod substance.
Polarized light and roentgen-ray study
indicated that apatite crystals are
arranged approximately parallel to long
axis of prisms.
9/16/2014

 It confers strength to the enamel.
Their direction is an important consideration in
the cavity preparation for restorations
Enamel rods that are supported by hard
restorative material rather than more pliant
dentin are more likely to fracture

 Fracturing of unsupported rods in poorly
designed restorative preparations causes loss of
enamel around the margins of the filling
material resulting in marginal leakage and
makes the tooth more susceptible to carious
attack.
Additionally, it is also important to note that
the inclination of rods differs in permanent and
primary teeth and must be accounted for during
cavity preparation.

Each enamel rod is built up of segments
separated by dark lines that give it a
striated appearance.
The striations are more pronounced in
enamel that is insufficiently calcified.
9/16/2014

 Generally they are
oriented at right angle to
dentin.
 Near the incisal edge or
cusp tip they change
gradually to an
increasingly oblique
direction until they are
almost vertical in the
region of edge or tip of
cusp.

 In cervical and central parts of deciduous tooth
they are approximately horizontal.

More or less changes
in the direction of
rods may be regarded
as functional
adaptation minimizing
the risk of cleavage
due to occlusal
loading forces. This
changes in direction of
rods is responsible for
appearance the
Hunter-Schreger bands.

Careful decalcification and staining gives
evidence that these are not solely optical
phenomenon.
These are composed of zones different
permeability and organic content.
Some books suggest that this is an optical
phenomenon produced merely by changes in
direction of lights.
9/16/2014

 They appears as brownish bands
in ground section of the enamel.
 They illustrate the incrimental
pattern of enamel, during
formation of crown.
 They reflect variation in
structure and mineralisation,
and are either hypomineralised
or hypermineralised.

Banding patterns formed during illness will
show up on contralateral teeth which are
developing at the same time.
Patterns of enamel hypoplasia on a single tooth
or on one side indicate trauma or a localised
rather than systemic infection.

A delicate membrane that covers entire portion
of newly erupted crown is enamel cuticle or
Nasmyth’s membrane.
 It soon get removed by mastication.
 This is secreted by ameloblast when enamel
formation is complete.
This is hypomineralised structure.

Thin, leaflike
structures.
Penetrate into dentin.
 Organic material.
 This is
hypomineralised
structure.

Lamellae may develop in planes of tension.
Where rods cross such a plane, a short segment
of the rod may not fully calcify.
 This leads to formation of three types of
lamellae:-
 type A:- poorly calcified rods
 type B:- degenerated cells
 type C:- arising in erupted teeth where the cracks are
filled organic matter, presumably originating from saliva.
9/16/2014

Represents a significant weakness in the
structure of enamel and is susceptible to
cracking and and form a road for the entry of
bacteria that initiate caries.

 Arise at the DEJ and
reach into enamel to
about one fifth to one
third of its thickness.
Tufts consists of
hypocalcified enamel
rods and interprismatic
substances.
Tufts are hypomineralised
structure.

No major clinical significance, but represent
areas of enamel weakness.

The surface of dentin
at DEJ is pitted which
fit rounded
projections of enamel.
 Scalloped appearance.
The DEJ is more
prominent in the
occlusal area.
 It is hypomineralised
structure.

Occasionally odontoblast
processes pass across the
DEJ into enamel, many
of them are thickened at
there end, they are
termed as enamel
spindles.
 This is hypomineralised
structure.

No major clinical significance but may confer
additional permeability to the deeper layers of
enamel.

 Striae of Retzius often
extends from DEJ to
outer surface, when
they end in shallow
furrows known as
Perikymata

1) Prismless enamel- Primary teeth are more
likely to have a prismless surface zone than
are permanent teeth. A difference in the
reaction to conditioning agents is suspected
because less etching occurs on primary tooth
than on permanent tooth enamel during acid
conditioning.
2) Thickness- enamel is twice as thick on
permanent teeth as in primary teeth.

 3) Neonatal line-it is the
most prominent
incremental line in
primary teeth.it is due
to the metabolic trauma
to the developing tooth
at or near the time of
birth. Prenatal enamel
is less pigmented and
more free of defects
than postnatal enamel.

4)Enamel of primary teeth is whiter than that of
permanent teeth. This is believed to be because
much of primary tooth enamel is formed
prenatally and is not subject to some
enviornmental factors.
5)Direction of enamel rods-in the cervical area
the enamel rods in primary teeth are oriented
horizontally while in permanent teeth they are
inclined apically.

As the development of tooth progresses through
various stages of tooth development, the actual
formation of starts once ameloblasts are formed.
Ameloblasts are formed when tooth
development progresses to formation of bell
stage.

Enamel organ
 Dental lamina
 Dental papilla

Outer Enamel Epithelium
 Stellate Reticulum
 Stratum Intermedium
 Inner Enamel Epithelium

 It consists of a single
layer of cuboidal cells.
Function-
Exchange of
substances between
the enamel organ and
the environment.

 It forms the middle
part of the enamel
organ
The cells are star
shaped
Function-
Permit only a limited
flow of nutritional
elements from the
outlying blood vessels
to the formative cells.

The cells of the
stratum intermedium
are situated between
the stellate reticulum
and the inner enamel
epithelium.
They are flat to
cuboid in shape
Function-
Play role in
enamel formation

Before enamel formation
begins these cells assume a
columnar form and
differentiate into
ameloblasts that produce
the enamel matrix.
The borderline between the
inner enamel epithelium
and the connective tissue
of the dental papilla is the
subsequent DEJ

Development of enamel is described in two
parts:-
A. Life cycle of ameloblasts
B. Amelogenesis

Morphogenic stage
 Organizing stage
Formative stage
Maturative stage
Protective stage
Desmolytic stage

Before ameloblast differentiate and produce
enamel, they interact with adjacent
mesenchymal cells, determining shape of DEJ &
crown.
 During this stage cells are short columnar with
oval nuclei that almost fill cell body.

• This is characterized by presence of cells in inner el
epithelium.

During this stage there is changes in
organization and number of cytoplasmic
organelles related to initiation of enamel matrix.

• Enamel maturation begins after most of thickness of
enamel matrix has been laid down.

Ameloblast after maturation of enamel matrix
forms a protective layer i.e. reduced enamel
epithelium which is protective to enamel until
tooth erupt in oral cavity.

By desmolysis the cells of reduced enamel
epithelium help in eruption of tooth.

There are two processes involved in
development of enamel
 Formation of enamel matrix
 Maturation

Secretory activity starts when a small amount of
dentin is laid down.
Ameloblasts lose their projections.
 Islands of enamel matrix are deposited.
A thin continuous layer of enamel is formed
along the dentin called dentinoenamel
membrane.

The surface of
ameloblasts facing
developing enamel are
not smooth
There are interdigitation
of cells and enamel rods
that they produce. These
projections into enamel
matrix have been named
Tomes’ processes

The head of each rod is formed by one
ameloblast where as 3 others contribute to
tail of each rod. That is each rod is formed
by four ameloblasts and each ameloblast
contributes to four different rods.

Ameloblasts are shorter.
They have a villous surface near the enamel and
ends of cells are packed with mitochondria-typical
of absorptive cells.
 Organic components and water are lost during
mineralization.
 Over 90% of initially secreted protein is lost.

 It takes place in two stages:-
First, an immediate partial mineralisation -25-
30% of the total mineral content
The second stage, or maturation is
characterised by gradual completion of
mineralisation
Each rod matures from the depth to the surface,
and sequence of maturing rods is from cusps or
incisal edge toward the cervical

DESTRUCTION OF ENAMEL-Bacterial
i.e. Dental caries
Non Bacterial
i.e.
attrition,abrasion,erosion,abfraction

Dental Caries
The high mineral content of enamel which
makes this tissue the hardest in the human
body , also makes it susceptible to a
demineralisation process which often occurs as
dental caries.

Enamel caries is of two types:-
1)Smooth surface caries
2)Pit and fissure caries

 The initial lesion is a white spot
 Eventual loss of continuity of
the enamel surface which feels
rough to the point of an
explorer
 It typically forms a triangular or
a cone shaped lesion with the
apex towards the DEJ and the
base towards the surface
 The carious process has
extended into dentin but there
is still no cavitation

Before complete disintegration of enamel
several zones can be distinguished,
beginning on the dentinal side of the
lesion:-
ZONE 1-the translucent zone
ZONE 2-the dark zone
ZONE 3-the body of the lesion
ZONE 4-the surface zone

Caries beginning in a
fissure with
decalcification extending
from its sides and bottom.
 It forms a cone shaped
lesion with the base at
the DEJ and apex at
towards the surface
 It reaches the dentin and
spreads laterally.
 There is separation of
enamel and dentin and
fracture of the enamel
roof.

 Attrition
 Abrasion
 Erosion
 Abfraction

The physiologic
wearing away of a
tooth as a result of
tooth-tooth contact.
 This phenomenon is
physiologic rather
than pathologic

Pathologic wearing
away of tooth
substance through
some abnormal
mechanical process.
Generally occurs on
exposed surfaces of
roots.

 Irreversible loss of
dental hard tissue by
a chemical process
that does not involve
bacteria.
 Erosion is also related
to GERD.

Pathologic loss of
both enamel and
dentin caused by
biomechanical loading
forces.

Amelogenesis Imperfecta
Enamel Hypoplasia
Mottled Enamel
Enamel Pearls
Tetracycline Stains

A structural defect of
tooth enamel.
There is disturbance in
the differentiation or
viability of ameloblast.
Both deciduous as well
as permanent dentitions
usually are involved.

Three main groups: hypoplastic(60-73%),
hypocalcified(7%), and hypomature(20-40%).
 Classification of amelogenesis imperfecta
according to Witcop :-
Type Ι Hypoplastic
Type ΙΙ Hypomaturation
Type ΙΙΙ Hypocalcified
Type ΙV Hypomaturation-hypoplastic with
taurodontism

 No specific treatment, except for
improvement of cosmetic appearance.

 Incomplete or defective formation of organic
enamel matrix.
 Rickets during formation of enamel is most
common cause of Enamel hypoplasia.
As rickets is not a prevelant disease, vitamin A
& C have been named as cause.

Considerable contraversy are there about any
relation between caries & enamel hypoplasia. It
is most reasonable to assume that the two are
not related, although hypoplastic teeth appear
to decay at somewhat more rapid rate once
caries has been initiated.

Term mottled enamel is described by GV Black
and Frederick S McKay in 1916.
 Ingestion of fluoride containing water during
time tooth formation is most important.
More than 1 ppm of fluoride causes significant
mottling.
0

 There is wide range of
severity in the
appearance of mottled
teeth, varying from
I. Mild changes (white
opaque areas)
II. Moderate and severe
(pitting and brownish
staining)
III. A corroded appearance of
the teeth.

 Discoloration occurs due
to prophylactic
administration of
tetracycline to pregnant
female or postpartum in
the infants.
Yellowish or brownish-gray
discoloration.
 Crucial period is 4 months
in utero to about 7 years
of age.

The direction of enamel rods is of
importance in cavity preparation:

 One of the most important principles in tooth
preparation is the concept of the strongest
enamel margin
 It is formed by full length enamel rods whose
inner ends are on sound dentin.

The American Society for Testing and Materials
defines adhesion as “the state in which two
surfaces are held together by interfacial forces
which may consist of valence forces or
interlocking forces of both”.
Advantages
1) Cusp reinforcement after tooth preparation.
2) Reinforce remaining enamel and dentin.

 It is important technique in
clinical practice.
 It involves use of etchant to
produce change in surface
texture of enamel.

 There are three types of Enamel etching seen
Type A- Dissolve enamel rod
Type B- Dissolve interrod enamel
Type C- Irregular and indiscriminate
9/16/2014

 It achieves desired effects in two stages:-
1) Removes plaque and other debris
2) Increases the porosity of exposed surfaces
 Increases the free surface energy of enamel.
Micromechanical bonding.
9/16/2014

Bleaching may be defined as the lightening
of color of tooth through application of
chemical agent to oxidize organic
pigmentation of tooth.
H₂O₂ has low molecular weight that enables it to
fuse through enamel.

 Oxidation reaction
 Low pH can cause destruction of enamel by
demineralisation

i) Microabrasion-
Microabrasion techniques improve appearance
of fluorotic teeth.
 McCloskey reported that Kane succesfully removed
fluorosis stains by applying acid and heat in 1916.
 In 1960s, McInnes used five parts of 36% HCL, five
parts of 30% H₂O₂ and one part of Ether.

Ether – Removes surface debris
HCL – Etches Enamel
H₂O₂- Bleaches Enamel
Fluoride-stained teeth are difficult to bleach
and require longer and repeated sessions to
decolorize them.
9/16/2014

ii) Macroabrasion –
an alternative method to removal of
superficial white spots.
Uses a 12-fluted composite finishing bur or
a fine grit finishing diamond at high speed.
Next, a 30-fluted composite finishing bur is
used.
Final polishing is achieved with an abrasive
rubber point.

Increases resistance to caries.
Melting and fusing of enamel-70-85%resistant to
acids.
When laser technique is used with fluoride -
cavities were completely stopped.

 absorption of fluoride ions on enamel
 This increases resistance to acid dissolution
of enamel
9/16/2014

 Orban’s oral histology and embryology .
 Oral histology- Tencate .
 Dental embryology, histology and anatomy-
Mary Bath-Balogh And Margaret J. Fehrenbach.
 Textbook of operative dentistry- Sturdevant.
 Grossman’s Endodontic Practice.
 Philips’- Science of Dental Material.

Enamel

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