Enamel significance in operative dentistry /certified fixed orthodontic courses by Indian dental academy

ENAMEL :CLINICAL
SIGNIFICANCE IN
OPERATIVE
DENTISTRY

INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
www.indiandentalacademy.com


INTRODUCTION
• Enamel provides a hard durable
shape for the functions of teeth and a
protective cap for the vital tissues of
dentin and pulp.Both colour and form
contribute to esthetic appearance of
enamel.
• Much of the art of restorative dentistry
comes from efforts to stimate the
color,texture,translucency and
contours of enamel with synthetic
dental materials such as resin
composite or porcelain.

• Nevertheless, the lifelong preservation of
the patient’s own enamel is one of the
defining goals of the dentist.
• Although enamel is capable of lifelong
service,its crystallised mineral makeup and
rigidity as well as stress from
occlusion,make it vulnerable to acid
demineralization(caries),attrition(wear) and
fracture.
• Compared to other tissue mature enamel is
unique in that except for alterations in the
dynamics of mineralization repair or
replacement is only possible through dental
therapy.


COMPOSITION
• ENAMEL I S HIGHLY MINERALISED
TISSUE WITH 96% INORGANIC AND 4%
ORGANIC MATERIAL AND WATER.
• INORGANIC CONTENT OF ENAMEL IS
CRYSTALLINE
CaPo4,HYDROXYAPATITE.
• ENTIRE VOLUME OF ENAMEL IS
OCCUPIED BY DENSELY PACKED
HYDROXYAPATITE CRYSTALS,AND A
FINE LACY NETWORK OF ORGANIC
MATERIAL APPEARS BETWEEN THE
CRYSTALS. www.indiandentalacademy.com

• Bulk of the organic material
consists of Tyrosine rich
amelogenin polypeptide tightly
bound to the hydroxyapatite
crystals as well as nonameloginin
proteins.
• Proteins in enamel contains high
percentages of serine,glutamic
acid and glycine.

• DEVELOPMENT (AMELOGENESIS)
• Enamel is a ectodermally derived
tissue
EPITHELIAL ENAMEL ORGAN
• Enamel organ originating from stratified
epithelium of the primitive oral cavity
consists of 4 distinct layers.
1.Outer enamel epithelium
2.Stellate reticulum
3.Stratum intermedium
4.Inner enamel epithelium(ameloblastic
layer) www.indiandentalacademy.com

• Inner enamel epithelium differentiates
into ameloblasts to produce enamel
matrix
• The borderline between the inner
enamel epithelium and connective
tissue of the dental papilla is the
subsequent DeninoEnamel
junction.Its outline determines the
pattern of the occlusal or incisal part
of the crown.


• Enamel formation occurs in three stages
1.Formative stage:deposition of enamel
matrix.
2.Calcification or Mineralization stage:
The laid matrix is mineralised along with
removal of organic material and water.
3.Maturation stage: crystallites enlarge and
gradual completion of mineralisation.


DEVELOPMENTAL DEFECTS
• AMELOGENESIS IMPERFECTA
It represents a group of hereditary defects
of enamel unassociated with any other
generralised defects.
• It is entirely an ectodermal disturbance
and the mesodermal components of the
tooth are normal.


• According to the 3 stages in the development of
normal enamel,three basic types of AI are
recognised.
• 1.Hypoplastic type-there is defective matrix
formation.
cl.f:Enamel has not formed to full normal
thickness on newly erupted teeth
2.Hypocalcification type-defective mineralisation
of formed matrix.
cl.f:enamel is so soft that it can be removed by a
prophylaxis instument.


3)Hypomaturation type:Enamel
crystallites remain immature
cl.f:defective enamel can be pierced by
an explorer point under firm pressure
and can be lost by chipping away from
the dentin.


Hypoplastic


Hypomaturative


Hypocalcified


• GENERAL FEATURES
*crowns of affected teeth may show
discoration ranging from yellow to
dark brown.
*chalky texture or cheesy consistency
*surface may be smooth or with numerous parallel
vertical wrinkles or grooves
*chipped or show depressions in the base of which
dentin may be exposed.


* Contact points between teeth are often
open and occlusal surfaces and incisal
edges are severely abraded.


ROENTGENOGRAPHIC
FEATURES
Enamel may be totally absent or
Appear as thin layer,chiefly over the tips of the
cusps and the interproximal surfaces.
When the calcification of enamel is so
affected,it appears to have same radiodensity as
the dentin,making diffentiation between the
two difficult


ENVIRONMENTAL ENAMEL
HYPOPLASIA
 Possible factors capable of producing injury
to the ameloblasts are
 Nutritional deficiency (vit A, C, D)
 Exanthematous diseases (measles, chicken
pox)
 Congenital syphilis
 Hypocalcemia
 Birth injury,Rh hemolytic disease
 Local infection/trauma
 Ingestion of fluoride

Effects of flouride on enamel
► Anti cariogenic property
1.Increased enamel resistance or reduction in
enamel solubility.
2.Increased rate of post eruptive maturation
3.Remineralisation of incipient lesion
4.Inhibition of demineralisation
5.Interference with microorganisms
6.Modification of tooth morphology


Flourosis
► Caused by excessive systemic flouride during
enamel matrix formation and calcification.
► Mild intermittent white spotting
► Chalky or opaque areas
► Surface pitting
► Marked wear of enamel surface
► Brown stains
► Severe cases-corroded appearance


STRUCTURE OF ENAMEL
ENAMEL RODS
 The basic structural unit of enamel,the rods
owes its existence to the highly organised
pattern of crystal orientation.
 The rods are cylindrical in shape and are made
of crystals with their long axes running for the
most part parallel to the longitudinal axis of
the rods.
 The rods vary in number from 5 million for a
mandibular incisor to about 12 million for a
maxillary molar. www.indiandentalacademy.com

 From the DEJ the rods run in a tortuous course to
the surface of the tooth
 Rods located in the cusps,the thickest part of the
enamel are longer than those at the cervical areas
off the tooth.
 Diameter of rods increases from DEJ towards the
surface of the enamel at the ratio of about 1:2
 Enamel contain rods surrounded by rod sheaths
and separated by the inter-rod substances.
 The inter rod region is an area surrounding each
rod,in which crystals are oriented in a different
direction from those making up the rod

The boundary where crystals of the rod
meet those of inter-rod region at sharp
angles is known as the rod sheath.
Rod sheath contain more enamel protein
than other regions.
The consistent arrangement of rod
sheaths with their greater protein content,
account for fish scale appearance of
enamel matrix.

ROD INTERRELATIONSHIP
 Rods in each row run in a direction nearly
perpendicular to the surface of dentin,with a slight
inclination towards the cusps as they pass outward.
 In deciduous tooth the rods run horizontally at the
central and cervical part of the crown,becoming
increasingly oblique to almost vertical at the tip of
cusps and incisal edges
 In permanent tooth the rod arrangement is similar in
occlusal 2/3 of the crown,but deviating from horizontal
to a more apical direction in the cervical region.

Submicroscopic strcture of enamel rod
 In transverse section the rods are
shaped with a rounded head or body
section and a tail section.
 Generally the head position is
oriented in the incisal or occlusal
direction,the tail section is oriented
cervically.


ENAMEL PRISM
The structural components of the enamel prism
are millions of small, elongated apatite
crystallites
The crystallites are tightly packed in a distinct
pattern of orientation that gives strength and
structural identity to the enamel prisms.
The long axis of the apatite crystallites within the
central region of the head(body) is aligned
almost parallel to the rod long axis

The crystallites incline with increasing
angles (upto 65 degree)to the prism axis
in the tail region
The susceptibility of these crystallites to
acid, either from an etching procedure or
caries,appears to be correlated with their
orientation.whereas the dissolution
process occurs in the head regions of the
rod,the tail regions and the periphery of
the head regions are relatively resistant
to acid attack.

GNARLED ENAMEL
Enamel rods follow a way,spiraling
course,progresing from the dentin toward
the enamel surface where they end a few
micrometers short of the tooth surface.
There are groups of enamel rods that may
entwine with adjacent groups of rods and
they follow a curving irregular path toward
the tooth surface,comprising of gnarled
enamel.

Gnarled enamel occurs near the
cervical regions and the incisal
and occlusal areas. It is not
subject to cleavage as is the
regular enamel. This type of
enamel formation does not yield
readily to the pressure of bladed,
hand cutting instruments in tooth
preparation.


HUNTER SCHREGER BANDS
These are optical phenomenon produced by
change in enamel rod direction
They are most clearly seen in longitudinal
ground sections viewed by reflected light .
These bands appear as alternate dark and light
zones of varying width with different
permeability and organic content.,originating at
the dentine enamel border and pass outward
ending at some distance from the outer enamel
surface

They are regarded as functional
adaptation ,minimising the risk of cleavage
in the axial direction under the influence of
occlusal masticating forces.


ENAMEL TUFTS


ENAMEL TUFTS
 They are hypo-mineralised
structures of enamel rods and
inter-prismatc substance arising
at the DEJ and reach into the
enamel to about 1/5th to 1/3rd of
its thickness.
 They extend into the enamel in

the direction of the long axis of
the crown may be involved in
the spread of dental caries.

ENAMEL LAMELLAE
 They are thin,leaf life faults between
enamel rod groups that extend from the
enamel surface toward the DEJ.they
extend to and sometimes penetrate the
dentin.
 They consist mostly of organic material

which is a weak area predisposing a
tooth to entry of bacteria and dental
caries.


Enamel lamellae


ENAMEL SPINDLE
 Occasionally odontoblast processes pass
across the DEJ into the enamel.Their
ends are thickened and are termed as
enamel spindles.
 They seem to originate from processes of

odontoblasts that extended into the
enamel epithelium before hard
substances were firmed.
 They may serve as pain receptors,

thereby explaining the enamel sensitivity
experienced by some patients during
tooth preparation.

INCREMENTAL LINES OF
RETZIUS
 Enamel rods are formed linearly by successive
apposition of enamel in discrete increments.
The resulting variations in structure and mineralisation
are called the Incremental striae of Retzius.
In horizontal sections they appear as concentric circles
and in longitudinal sections.the lines traverse the
cuspal and incisal areas in symmetric arc pattern.
When these circles are incomplete at the enamel
surface, a series of alternaing grooves called,the
imbrication lines of pickerill are formed.


The elevations between the gooves are
called perikymata.
They are continuous around a tooth and
usually lie parallel to each other and to the
CEJ


STRUCTURELESS OUTER LAYER OF
ENAMEL
It is about 30µm thick structureless outer
layer of enamel,most commonly toward
the cervical area and less often on cusp
tips.
There are no prism outlines visible,and
apatite crystals are parallel to one another
and perpendicular to striae of retzius.
Layer is heavily mineralisd.


 Microscopically,the enamel surface initially
has circular depressions indicating where
the enamel rods end.
 These concavities vary in depth and
shape and they may contribute to the
adherence of plaque material, with a
resultant caries attack.


DENTINOENAMEL JUNCTION

 Theinterface of the enamel and dentin is
established as these 2 hard tissues begin to
form and is scalloped in outline.
The convexities of the scallops are directed
toward the dentin
Scanning electron microscope shows it to be
a series of ridges that increase the surface
area and probably enhance the adhesion
between enamel and dentin.

 Itis hyper mineralised and 30µm
thick and the interdigitation
contributes to a firm attachment
between dentin and enamel


CEMENTOENAMEL JUNCTION

 The relation between enamel and cementum
at the cervical region of the tooth is variable.
 In 30% of all teeth,cementum meets the
cervical end of enamel in a relatively sharp
line.
 In about 10% of teeth,enamel and cementum
do not meet.
 In 60% of the teeth,cementum overlaps the
cervical end of enamel for a short distance.

 Thisoccurs when the enamel epithelium
degenerates at its cervical termination,
permitting connective tissue to come in
direct contact with the enamel surface.
Electron microscopic evidence indicates that
when connective tissue cells, cementoblasts
come in contact with enamel the produce a
laminated, electron dense ,reticular material
termed afibrillar cementum.

FISSURES AND GROOVES
 They are formed at the junction of the developmental
lobes of the enamel.Sound coaleacence of the lobes
results in grooves,faulty coalescence results in
fissures.
 Fissures act as food and bacterial traps that may
predispose tooth to dental caries.
 Occlusal grooves,which are sound,sserve an
important function as an escape path for the
movement of food to the facial and lingual surfaces
during mastication.
 The resulting narrow clefts provide a protected niche
for acidogenic bacteria and the organic nutrients they
require.

PRIMARY ENAMEL CUTICLE OR
NASMYTH MEMBRANE
 Ameloblast cell degenerates following
formation of enamel rod. The final act of
ameloblast cell is the secretion of a
membrane covering the end of the enamel
rod. This membrane covers the entire
crown of newly erupted tooth but is
probably soon removed by mastication
and cleaning


PELLICLE
 An organic deposit called pellicle covers
the erupted enamel.
 It is a precipitate of salivary proteins.
 The pellicle reforms within hours after an
enamel surface is mechanically cleaned.
 Microorganisms may invade the pellicle to
form bacterial plaque,a potential precursor
of dental caries

PROPERTIES OF ENAMEL
 HARDNESS:
The haardest substance of the human
body is enamel.
Its Knoop Hardness number is 343 (68
for dentin)
Hardness vary over the external tooth
surface according to the location. It
decreases inward with hardness lowest at
the DEJ

 Density of enamel also decreases from
the surface to DEJ.
 Enamel is very brittle structure with a high
elastic modulus and low tensile strength,
which indicates a rigid structure
 Enamel will wear because of attrition or
frictional contact opposing enamel or
harder restorative materials, such as
porcelain,
 Normal physiological wear of enamel is
29µm/year.

 However dentin is a highly compressive
tissue that acts as a cushion for the
enamel.Enamel requires a base of dentin
to withstand masticatory forces.
 Enamel rods that fail to possess a dentin
base because of caries or improper cavity
preparation design are easily fractured
away from neighbouring rods.For
maximum strength in tooth preparation,all
enamel rods should be supported by
dentin

PERMEABILITY
 The organic matrix and water contained in the enamel
is in a network of micropores opening to the external
surface.
 The micropores form a dynamic connection between
the oral cavity and the systemic, pulpal and dentinal
tubules fluids.
 Various fluids,ions and low molecular weight
substances,whether deleterious,physiologic or
therapeutic can difusse through the semipermeable
enamel.
 The dynamics of acid demineralisation,caries
reprcipitation or remineralisation,flouride uptake are
therefore not limited to the surfac but are active in 3
dimensions www.indiandentalacademy.com

COLOUR AND
TRANSLUCENCY
 Enamel is mostly gray and semitranslucent.
 Its colour is primarily a function of its thickness
and the colour of the underlying dentin.
 From approximately 2.5mm at the cusp tips
and 2mm at the incisal edges, enamel
thickness decreases significantly below deep
occlusal fissures and tapers to a negligible
thickness cervically at the junction with the
cementum or dentin of the root.

 The young anterior tooth has a translucent
gray or slightly bluish enamel tint at the
thick incisal edge.
 A more chromatic yellow orange shade
predominates cervically where dentin
shows through thinner enamel.
 Caries and demineralisation, anomalies of
development, extrinsic stains,antibiotic
therapy and excessive fluorides can alter
the natural colour of the teeth

 Enamel becomes temporarily whiter within
minutes when a tooth is isolated from the
moist oral environment.
(temporary loss of loosely bound water)
 Shade must be determined before
isolation and the preparation of a tooth for
a tooth colored restoration.


RESILIENCE
 Although enamel is vulnerable and incapable of
self repair,its protective and functional
adaptation is noteworthy.Carious
demineralisation to the point of cavitation
generally takes 3-4 years.Demineralisation of
enamel is impeded because the apatite crystals
10 times larger than those in dentin.
 Enamel apatite crystals offer les surface to
volume exposure and little space for acid
penetration between the crystals

 With preventive measures and exogenous or
salivary renewal of calcium,phosphate and
especially fluoride,the dynamics of
demineralisation can be stopped or
therapeutically reversed
 Enamel thickness and degree of mineralisation
are greatest at the occlusal and incisal surfaces
where masticatory contacts occurs.If enamel
were uniformly crystalline,it would shatter with
occlusal forces.


 A substructure, organised into discrete parallel rods
with the scalloped DEJ, minimises the transfer of
occlusal stress laterally and directs it anisotropically or
unidirectionally to the resilient dentinal foundation.
 The interwoven paths and interlocked key-hole
morphology of the enamel rods help control lateral
cleavage.As a functional adaptation to occlusal stress,
spiraling weave of rod direction is so pronounced at
the cusp tips of posterior teeth i.e. refered to as
Gnarled Enamel.
 Further subdivision of enamel rods into distinct
crystals separated by a thin organic matrix provides
additional relief to help prevent fracture.

ACID ETCHING
 Because there are 30,000 to 40,000
enamel rods/sq mm and the etch
penetration increases the bondable
surface area 10 to 20 fold,
micromechanical bonding of resin
restorative materials to enamel is
significant.Acid etch modification of
enamel for restoration retention provides a
conservative, reliable alternative to
traditional surgical methods of tooth
preparation and restoration.

 The enamel rod boundaries form natural
cleavage lines through which longitudinal
fracture may occur. The fracture resistance
between enamel rods is especially imperiled if
the underlying dentinal support is pathologically
destroyed or mechanically removed by dental
instrument.
 Loss of enamel rods that form the cavity walls or
cavo margin of a dental restoration creates a
gap defect similar to an occlusal fissure.
Leakage or ingress of bacteria or their products
may lead to secondary caries. Therefore, a basic
tenet of cavity wall preparation is to bevel or
parallel the direction of enamel rods and to avoid
undercutting them.

 A common precept, that cavity preparation
should always be cut perpendicular to the
external coronal surface, is not supported
histologically. Each successive row of
enamel rods runs slightly different course
in a wave pattern, both horizontally and
vertically, through the inner half of the
thickness. And then continues in a relative
straight parallel course to the surface.
 However ,on axial surfaces and cuspal
slopes,the path of each row terminates a
an oblique angle to the surface rather than
at a perpendicular tangentt of 90 degrees.

 Starting at 1 mm from the CEJ,the rods on the vertical
surfaces run occlusally or incisally at approximately a
60 degree inclination and progressively incline
approaching the marginal ridges and cusp tips,where
the rods are essentially parallel to the long axis of the
crown.
 The rods beneath the occlusal fissures are also
parallel to the long axis,but rods on each side of the
fissure vary upto 20 degrees from the long axis.
 Therefore if cut perpendicular to the external surface,
occlusal walls of preparations on axial surfaces might
incorporate compromised enamel.An obtuse enamel
cavosurface angle would more parallel the rod
direction and preserve the integrity of the enamel
margin.

ADHESION TO ENAMEL
 Adhesion to enamel is achievd through acid
etching of this highly mineralised substrate,which
substantially enlarges its surface area for
bonding.
 This enamel bonding technique known as the acid
etching technique,was the invention of Buonocore
in 1955.
 Research into the underlying mechanism of the
bond suggested that tag like resin extensions
were formed and micromechanically interlocked
with the enamel micro porosities created by
etching www.indiandentalacademy.com

 Enamel etching transforms the smooth
enamel surface into an irregular surface with
a high surface –free energy (about 72
dynescm).
 Acid etching removes about 10µm of the
enamel surface and creates a micro porous
layer from 5 to 50 µm deep.


 3 enamel etching patterns have been
described.
 Type 1:there is predominant dissolution of the
prism cores.
 Type 2:there is predominant dissolution of the
prism peripheries.
 Type 3:no prism structures are evident.
Microtags are formed circularly between
enamel prism peripheries;microtags are formed
at the cores of enamel prisms.Microtags
probably contribute most to the bond sterngth
because of their greater quantity and large
surface area www.indiandentalacademy.com

 PHOSPHORIC ACID ETCHANTS
Generally use of a phosphoric acid
concentration between 30% and 40%,an
etching time of not less than 15seconds and
washing times of 5-10 seconds are
recommended to achieve the most
receptive enamel surface with bonding.


 UNIVERSAL ENAMEL DENTIN CONDITIONING
The selective enamel etchings technique is
replaced by a total etch concept in which the
conditioner or acid etchant is applied
simultaneously to enamel and dentin.
As a result 2 different micro retentive surfaces are
exposed in which the adhesive resin will become
micro mechanically inter-locked.
Less concentrated phosphoric acids or weaker
acids in variant concentrations such as
citric,maleic,nitric and oxalic acid are used.


 The objective of such universal enamel
dentin conditioning agents is to find the best
compromisd between etching enamel
sufficiently to create a micro-retentive
etched pattern and etching dentin
mildly,avoiding exposure of collagen to a
depth that is inaccessible for complete
infiltration by resin.


CONFIGURATION
AND CORRELATION
OF ENAMEL WALLS

• The configuration of enamel walls is
the shape, dimension, location, and
angulation of enamel components in
final tooth preparation.
• The correlation is the relationship of
the enamel configuration to
surrounding tooth preparation and
restoration details.


• Whenever enamel is stressed, it
tends to split along the length of the
rods. This splitting is easier when the
enamel rods is parallel to each other
and will be somewhat difficult if the
rods are interlaced and twisted
together.
• For an ideal enamel wall,Noy devised
certain structural requirements.
These requirements tend to take full
advantage of the enamel’s hardness
and strength and avoid the
disadvantages of the enamel’s
splitting characteristics.

• STRUCTURAL REQUIREMENTS
The enamel wall must rest upon some
dentin.
All carious dentin must be removed
and the enamel cut back until it is
supported by sound tooth structure.
Otherwise there would be some
portion of the enamel left standing
that has been weakened by the
dissolution of its minerals in
backward caries. This enamel would
most likely break down under the
stress of mastication.

 The enamel rods which form the
cavosurface angle must have the
inner ends resting on sound dentin.
When this condition is
established the dentin which is
elastic gives the enamel which is
brittle a certain degree of elasticity
which is very important at the
margins of restoration


The cavosurface angle must be
so trimmed or bevelled that the
margins will not be exposed to
injury in condensing the
restorative material against it.


 GENERAL PRINCIPLES FOR
FORMULATION OF ENAMEL
WALLS
 The enamel portion of a wall should
be the smoothest portion of the
preparation anatomy. Any roughness
besides interfering with the
proximity of tooth with the
restorative material, will increase
possibility of frail, loosely attached
enamel rods, which will be detached
during function increasing the
leakage space in the critical marginal
area. www.indiandentalacademy.com

 Junction between different enamel
walls should be rounded.This will
improve adaptability of the
restorative material at the
preparation corners,in addition to
decreasing sress concentration
there.
 If inclining a preparation wall to
follow the direction of enamel rods
will nullify its resistance and
retention capabilities,different
planes for that walls should be
established.

• When the enamel preparation
margins come to an area of abrupt
directional changes of enamel
walls,this area should be included in
the preparation and the margins
placed in areas of a more predictable
rod pattern.


ENAMEL CARIES
HISTOLOGY :
The striae of Retzius are regions
characterised by reltively higher organic
contents.Both the striae and the inherent
spaces in prism boundaries provide
sufficient porosity to allow movement of
water and ions.
Movement of ions though carious enamel
can result in acid solution of the
underlying dentin before actual cavitation
of enamel surface.

• Because the striae form horizontal
lines of greater permeability in the
enamel,they probably contribute to
the lateral spread of the smooth
surface lesions.


• THE CLINICAL CHARACTERISTICS :
On clean dry tooth earliest evidence of
caries is a white spot which are chalky
white and opaque and they are revealed
only when the tooth surface is dry.This
is incipient caries where the surface
texture is unaltered and these areas of
enamel loose their translucency because
of the extensive surface porosity
caused by demineralisation.
Care must be taken to distinguish white
spots of incipient caries from
developmental white spot
hypocalcification of enamel.

• Incipient caries will partially or totally
disappear visually when the enamel is
hydrated(wet),while hypocalcified enamel is
unaffected by drying and wetting.
A more advanced lesion develops a rough
surface i.e. softer than the unaffected
normal enamel.Softened chalky enamel
that can be chipped away with an explorer
is a sign of active caries.
Incipient caries of enamel can reminieralise.
Non cavitated lesions retain most of the
original crystalline framework of the
enamel rods and the etched crystallites
serve as nucleating agents for
remineralisation.

• Calcium and phosphate ions from the
saliva can then penetrate the enamel
surface and precipitate on the highly
reactive crystalline surface.The
supersaturationof saliva with calcium and
phosphate ions serves as the driving force
for the mineralisation process. Pesence of
trace amounts of flouride ions during this
process greatly enhances precipitation of
calcium and phosphate ions resulting in
the enamel becoming more resistant to
subsequent caries attacks, because of the
incorporation of more acid resistant
flurophosphate.

• Remineralised[arrested]lesions is
observed clinically as intact,
discolored, usually brown or black
spots. The change in color is due to
trapped organic debris and metallic
ions within the enamel.These
remineralised caries are more
resistant to caries attack. They are
not restored unless they are
esthetically objectionable..


ZONES OF INCIPIENT
LESION
• The four regularly observed zones in
a sectioned incipient lesion are
• The translucent zone
• The dark zone
• The body of lesion
• The surface zone


• TRANSLUCENT ZONE
• Deepest zone
• The pores or voids form along the
enamel prism boundaries due to
hydrogen ion penetration.
• Pore volume is 1%, 10 times greater
than normal enamel.
• DARK ZONE
• Does not transmit polarised light.
• Pore volume is 2-4%.
• Loss of crystalline structure
suggestive of demineralisation

• BODY OF LESION
• Largest portion in demineralising
phase.
• Largest pore volume from 5% at the
periphery to 25% at the centre.
• Striae of retzius are well marked
indicating preferential dissolution along
the areas of relatively higher porosity.
• SURFACE ZONE
• Relatively unaffected by caries attack.
• Lower pore volume than the body of
lesion.

Minimal intervention
dentistry
• ART
It is a procedure based on excavating
carious cavities in teeth using hand
instrument only and restoring with
adhesive filling material like GIC.


Chemo mechanical system
• Carisolv
A gel that selectively attacks
denatured collagen in carious
dentin.thus making the carious
dentin softer.A set of specially
designed instrument used for
removal of softened material.


Air Abrasion (Kinetic
System)
• It uses a concentrated stream of air
and fine powder to remove decay
without drilling.
• Uses finely graded 27.5µm
aluminium oxide powder aministerd
under compressed air through a fine
tip.


Ozone treatment
• Powerful biocide
• Rapidly penetrate the bacteria and
kill them in their niche.
• Alters metabolic products of bacteria
that inhibits mineralization


• INTRODUCTION
• PHYSICAL CHARACTERISTICS
• CHEMICAL CHARACTERISTICS
• STRUCTURE OF ENAMEL
• DEVELOPMENT
• AMELOGENESIS
• MINERALIZATION OF ENAMEL
• ELECTRON MICROSCOPIC STUDY OF AMELOGENESIS
• DEVELOPMENT OF CARIES IN ENAMEL
• CAVITY PREPARATION
• ENAMELOPLASTY
• ENAMEL FISSURES
• ACID ETCHING (OR ACID CONDITIONING)
• FLUORIDATION


• FLUOROSIS
• ENAMEL MACROABRASION
• BLEACHING
• TYPES OF BLEACHING
• LASER TOOTH WHITENING
• DEFECTS IN AMELOGENESIS
• AMELOGENISIS IMPERFECTA
• RECENT ADVANCES
• REFERENCE


PHYSICAL CHARACTERISTICS
• Because of high mineral content, enamel is extremely hard,
a property that enables it to withstand the mechanical
forces during mastication
• Enamel forms a protective covering of variable
thickness over the entire surface of the crown.
• It is approx.2-2.5 mm near the cusps thinning to
knife edge at the neck of the tooth. This variation
in thickness influences the color of enamel, since
the underlying dentin is seen through the thinner
regions.
• It is translucent and varies in colour from light
yellow to grayish white


• Translucency can be attributed to variation in
degree of calcification and homogenicity.
• Yellowish teeth has a thin, translucent enamel
through which the yellow colour of the dentin is
visible, and grayish teeth has a more opaque
enamel. Grayish teeth frequently show a slighty
yellow colour at the cervical area, presumably
because the thinness of the enamel permits the
light to strike the underlying yellow dentin and be
reflected. Incisal areas has bluish tinge where the
thin edge consists only of a double layer of
enamel.


CHEMICAL CHARACTERSITICS
• It is highly mineralized tissue with 96% mineral
and 4% organic material and water.
• Inorganic content of enamel is crystalline calcium
phosphate.
• Various ions such as Sr, Mg, Pb a F, if present
during enamel formation may be adsorbed or
incorporated by the hydroxapatite crystals.
• The entire volume of enamel is occupied by the
densely packed hydroxyapatite crystals.
• The organic material consists of tyrosine rich
amelogin polypeptide.
• Proteins in enamel contains high percentages of
Serine, Glutamic acid and Glycine.


• Roentgen-ray diffraction studies reveal that the
molecular structure in typical of the group of
proteins called cross-beta-proteins.
• In addition, histochemcial reactions have
suggested that the enamel forming cells of
developing teeth also contain a polysaccharide-
protein complex and that an acid
mucopolysaccharide enters the enamel itself at
the time when calcification becomes a prominent
feature.


AGE CHANGES
• Enamel is a non-vital tissue that is incapable of
regeneration.
• With age, it becomes progressively worn away in
the regions of masticatory area.
• Wear facets are increasingly pronounced in older
people
• Other age changes seen are discoloration and
reduced permeability
• Linked to these changes there is an apparent
reduction in incidence if caries.
• Water content of enamel also decreases.
• Teeth darken with age. It may be due to addition
of organic material to enamel from the
environment or may be due to the deepening of
dentin colour seen through the progressively
thinning layer of transclucent enamel.

OUTER ENAMEL EPITHELIUM
• In early stages of development the outer enamel
epithelium consists of single layer of cuboidal
cells separated from the surrounding connective
issue of denial sac by a delicate basement
membrane.
• During enamel formation the cells of outer
enamel epithelium develop villi, cytoplasmic
vesicles and increase in number of mitochondria
all indicating cell specialization for active
transport of materials.


STELLATE RETICULUM
• it forms the middle part of the enamel organ, the
neighboring cells are separated by the wide
intercellular spaces filled by a large amount of
intercellular substances.
• They are flat to cuboidal in shape and are
arranged in one to three layers.
• They are connected with each other with the
neighboring cells of stellate reticulum and the
inner enamel epithelium by desmosomes.
• It is believed that stratum intermedium is
involved in production of enamel itself.


INNER ENAMEL EPITHELIUM
• The cells of the inner enamel epithelium are
derived from the basal cell layer of oral
epithelium.
• Before enamel formation begins, these cells
assume a columnar form and differentiate into
ameloblast that produce the enamel matrix.
• The cell differentiation occurs earlier in the region
of the incisal edge or cusps than in the area of
cervical loop.


AMELOGENESIS
• Enamel formation occurs in 2 steps
• First step produces a partially mineralized (30%)
of enamel once the full width of the enamel has
been depicted.
• The second step involves significant influx of
mineral along with removal of organic materials
and water.
• Enamel formation begins at the early crown stage
of tooth development and involves the
differentiation of cells of the tips of the cusps.
• Secretory phase of amelogenesis
• This phase involves secretion and synthesis of the
organic matrix of the enamel.


• The organic matrix consists of enamel protein, a
number of enzymes including serine proteases,
metallo proteases, phosphates and traces of
other protein analogous to glycerolated
phosphorylated and sulphated non-collagenous
proteins.
• 90% of enamel proteins are amelogenin
• 10% are tuftelin and amelin


MINERALIZATION OF ENAMEL
• It takes places in IV stages
• I stage involves immediate partial mineralization
in the matrix segments and the interprismatic
substances as they are laid down.
• 30% of mineralization is achieved during I stage.
• In the II stage (maturation) there is greater
completion of mineralization.
• The II stage begins with a secondary increase in
mineralization that starts at the surface of the
enamel and sweeps rapidly into the deeper layer
until reaches the innermost 8 micron layer.
• A tertiary increase in mineral rebounding from
the innermost layer outward the enamel surface
forms the III stage.
• A surface layer of 15 microns wide can be
distinguished during this phase and it mineralizes
slowly. www.indiandentalacademy.com

• As the IV stage commences the outer layer
mineralizes rapidly and heavily and becomes the
most mineralized part of the enamel.
• Enamel is most highly mineralized at its surface
with the degree of mineralization decreasing
toward the DEJ until the inner most layer is
reached where there is increased mineralization.
• Throughout amelogenesis this complicated
process in under cellular control and associated
cells undergo significant morphologic changes.


CLINICAL CONSIDERATION
Development of caries in enamel
• Dental caries is a microbial disease of the calcified
tissue of the teeth, characterized by
demineralization of inorganic portion and
destruction of organic substance of tooth.
• Clinical characteristics
• Patients with dental caries usually have extensive
deposits of plaque on the tooth which must be
removed before clinical examination.
• On clean dry tooth the earliest evidence of caries
is a white spot which are chalky white and
opaque and they are revealed only when the
tooth surface is dry. This is incipient caries where
the surface texture is unaltered and these areas
of enamel lose their translucency because of the
extensive subsurface porosity caused by
demineralization.

• Care must be exercised to distinguish white spots
of incipient caries from developmental white spot
hypocalcification of enamel. Incipient caries will
partially or totally disappear visually when the
enamel is hydrated (wet), while hypocalcified
enamel is unaffected by drying and wetting.
• A more advanced lesion develops a rough surface
that is softer than the unaffected normal enamel.
Softened chalky enamel that can be chipped
away with an explorer is a sign of active caries.
• Incipient caries of enamel can remineralize. Non-
Cavitated lesions retain most of the original
crystalline framework of the enamel rods and the
etched crystallites serve as nucleating agents for
remineralization, Calcium and phosphate ions
from the saliva can then penetrate the enamel
surface and precipitate on the highly reactive
crystalline surfaces in the enamel lesion. The
super saturation of saliva with the Calcium and
Phosphate ions serves as the driving force for the
remineralization process.

• Presence of trace amounts of Fluoride ions during
this remineralization process greatly enhances
the precipitation of Calcium and Phosphate ions,
resulting in the remineralized enamel becoming
more resistant to subsequent caries attacks,
because of the incorporation of more acid-
resistant Flouorophosphate.
• Remineralized (arrested) lesions is observed
clinically as intact, discolored, usually brown or
black spots. The change in colour is due to
trapped organic debris and metallic ions within
the enamel. These remineralized caries are more
resistant to caries attack than the adjacent
unaffected enamel. They shouldn't be restored
unless they are esthetically objectionable.


• Hicks reported the effect of caries-like lesions and
progression in sound enamel after argon laser
irradiation. Surface melting and sealing (fusing)
of enamel and dentinal surfaces occurred. The
resulting surfaces lost a significant amount of
organic, water and carbonate content, resulting in
a marked resistance to demineralization. The
threshold pH for enamel dissolution was lowered
from 5.5 to 4.78. The hard tooth structure was
four times more resistant to acid dissolution.
This increased resistance resulted in a significant
reduction in carious lesions depth. The
mircropores of lased enamel may trap the
released ions (calcium, phosphate, fluoride) that
become dissolved during caries formation. Lased
enamel has a greater affinity for calcium,
phosphate and fluoride ions, with resulting
reprecipitation of the mineral phase. Laser
treatment is an important treatment in the
prevention of caries sound enamel.

• Irradiation of dental enamel by specific
wavelengths and fluences of CO2 laser light
beneficially alters the chemical composition of the
crystals, decomposing the carbonate component,
markedly reducing the acid relativity of the
mineral. Efficient conversion of light to heat in
the outer few micrometers of enamel increases
the resistance of the mineral to acid if a critical
threshold temperature is reached. This surface
alteration has a marked effect on inhibition of
subsurface caries progression.


Cavity Preparation
• Although enamel is the hardest tissue in human
body, it comprises one of the weakest points in a
preparation wall especially when it looses its
dentinal support.
• Enamel rods are stronger than interprismatic
enamel. So whenever enamel is stressed it tends
to split along the length of rods.
• This splitting is easier when the rods are parallel
to each other. If rods are interlaced and twisted
together then spitting will be difficult.
• Enamel must rest on sound dentine
• Enamel rod which forms the cavosurface angle
must be supported or be resting on sound
dentine and their outer end must be covered by
the restorative material.

• The Enamel rod which forms the cavorsurface
angle must have their inner end resting on sound
dentine.
• The vcavosurface angle must be so beveled that
the margins will not be exposed to injury in
condensing the restorative material.


Enameloplasty
• It is grinding away a shallow developmental
enamel fissure or pit to create a smooth saucer
shaped surface which is self cleansing or easily
cleaned.
• This procedure does not require external
outline form nor does it equire any restorative
material.


Prepartions of enamel wall
before acid conditioning
• Partial bevel: This should involve 1/3 to 1/2 of
the enamel wall at 45-70 degrees to the cavity
walls. It is always used when the cavity
preparation's internal anatomy and walls can
adequately retain the restoration, and acid-
conditioning is used only to reduce marginal
leakage. It is also to be used with restorative
resins exhibiting minimal setting shrinkage.
• Long bevel: In this design feature, the entire
enamel wall is beveled at 45-70 degrees to the
cavity wall. It is used when the cavity
preparations details are not retaining enough for
the resinous restoration, or when the resinous
material used exhibits considerable shrinkage
during polymerization. This design will also
decrease microleakage.

• Hollow ground bevel:In this design feature,
about two-thirds of the enamel wall thickness is
ground in a concave manner so the cavity margin
will have a right-angled cavo-surface angle, with
butt joint between the restorative material and
the marginal enamel. This combines the
advantage of the retaining, sealing and acid-
conditioning of the enamel with the strong butt-
joint and definite junction of tooth structure and
restorative material.
The hollow ground bevel is used for inaccessible
areas, e.g., gingival walls to avoid possible
overhangs which could occur with either partial
bevel or long bevel finish lines. It is also
indicated for areas of direct loading, to
accommodate the maximum bulk of restorative
material.


• Scalloping the margins:This feature is used in
conjunction with a partial or long bevel, in order
to further increase the surface area and
irregularities of the enamel that is to be
conditioned. It is used when conditioned enamel
will play a major role in the retention of the
restoration. Scalloping has the disadvantage of
greater possibilities of flash and overhangs.
Under no circumstances should scalloping be
used for gingival walls or inaccessible portions of
any wall margin.


• Skirting:This feature is used if conditioned
enamel will be the main retentive mode for
resinous material. In restoring a wide and
shallow defect, it is essential to involve enamel
from the surrounding surfaces of the tooth. The
involved enamel surface should be atleast double
the surface area of the defect to be restored or
minimally 1mm in width. Also, the involved
enamel surface should be distributed around the
defect so that principal, auxillary and
reciprocating retaining areas are in accordance
with the magnitude, location and direction of
loading forces, both in static and dynamic
occlusal contacts. Such surface involvement is
called a Skirt.


Etching Time
• An etching time of 60 secs was originally
recommended for permanent enamel using 37%
phosphoric acid. But studies using scanning
electron microscopy (SEM) showed that a 15 sec
etch enamel resulted in a similar surface
roughness as that provided by a 60 sec etch.
Clinically, reduced etching time do not appear to
diminish the retention of pit & fissure sealants.
Acids should be applied on enamel with a soft
sponge or cotton Pellet, using light patting
touches with no rubbing at all. Acid conditioned
enamel should be washed for one minute using a
copious stream of water. It should then be air-
dried before applying the components of the
restoration. After drying a characteristic whitish
or chalkish appearance is the sign for proper
enamel conditioning.

• Co2 laser can cause changes in enamel
comparable to acid etching. laser will not cause
any damage to dentin or pulp as the intensity is
controlled. The surface treated by laser is
resistant to caries attack and harder. This may
be considered comparable to acid etching
procedure and may be used as an adjuvant.
• Nd: YAG Laser absorption enamel can be
enhanced by placement of an initiator (a dark
organic substance) on the area of the enamelin
which etching is desired. By this technique, the
procedure time is saved by 50% and the need to
protect gingiva and dentinal tissue is eliminated.


Enamel Microabrasion
• Enamel microabrasion is not a bleaching
technique but a selective erosion process that
removes stained enamel. Currently
microabrassion is recommended for the removal
of stains that are superficial and localized in
enamel. It is the primary treatment of choice for
superficial fluorosis stain, removal, small white
stains and some multicolored stains, but not deep
internal stains.
• The generic use of 18% hydrochloric acid and
pumice can be used for enamel microabrasion.
Only one commercially developed system
currently exists for enamel microabrasion. The
PREMA system (Premier enamel micro abrasion)
compound contains an abrasive mixed with
hydrochloric acid of approximately 10%. This
system offers a unique, easy and safe approach
to enamel microabrassion.

Macroabrasion
• An alternative technique for the removal of
localized superficial white spots (not subject to
conservative, remineralization therapy) and other
surface stains or defects is called macroabrasion.
macroabrasion simply utilizes a 12-fluted
composite finishing bur or a micron finishing
diamond in a high speed handpiece to remove the
defect. Care must be taken to use light
intermittent pressure and to carefully monitor
removal of tooth structure in order to avoid
irreversible damage to the tooth.


• Air-water spray is recommended not only as a
coolant, but also to maintain the tooth in a
hydrated state to facilitate assessment of defect
removal. Teeth that possess white spot defects
are particularly susceptible to dehydration
resulting in other apparent white spots that are
normally seen when the tooth is hydrated.
Dehydration exaggerates the appearance of white
spots and make defect removal difficult to assess.


• Microabrasion is recommended over
macroabrasion for the treatment of superficial
defects in children because of better operator
control and superior patient acceptance.To
accelerate the process, a combination of
macroabrasion and microabrasion also may be
considered. Gross removal of the defects
accomplished with macroabrasion followed by
finer treatment with microabrasion.


Bleaching
• The lightening of the color of a tooth through the
application of a chemical agent to oxidize the
organic pigmentation of the tooth is referred to as
bleaching. Most bleaching techniques use some
form or derivative of hydrogen peroxide in
different concentrations and application
techniques. The mechanism of action of bleaching
teeth with hydrogen peroxide is considered to be
oxidation of organic pigments. With all bleaching
techniques, there is a transtitory decrease in the
potential bond strength of composite when it is
applied to bleached, etched enamel. This
reduction in bond strength results in bond
strength results from residual oxygen or peroxide
residue in the tooth which inhibits set of the
bonding resin, Precluding enamel tag formation in
the tched enamel. However no loss of bond
strength is noted if the composite restorative
treatment is delayed at least 1 week after
cessation of any bleaching.

Types of Bleaching
1. Non-Vital bleaching
1. in-Office Thermocatalytic technique
2.Out of the office technique-Walking Bleach
2. Vital Bleaching
1.In Office technique-Power bleaching.
2.Dentist Prescribed home applied
technique (Nightguard vital bleaching)


Laser tooth whitening
• The whitening effect of the laser is achieved by a
chemical oxidation process. Once the laser energy
is applied, the hydrogen peroxide breaks down to
water and a free oxygen radical, which combines
with and thus removes the stain molecule.

• Laser tooth whitening was officially started in
Feb 1996 with the approval of ion laser
technology (ILT) argon and Co2 lasers to be used
wit a patented system of chemicals. Argon laser
energy, in the form of a blue light, with the
wavelength of about 480 nm in the visible part of
the spectrum, is absorbed by dark colour. It
seems to be the ideal instrument to be used in
tooth whitening when used together with
hydrogen peroxide and a patented catalyst. This
affinity to dark stains ensures that the yellow
brown colors can be easily removed.

Recent Advances
• As with other structured of the head and face, the
teeth are formed under the control of many
genes. Scientists at NIDCR and NIDCR supported
institutions have identified several of the genes
that go into making a tooth - from the dentin that
the lines the pulp cavity and root canals, to the
exterior enamel, the hardest substance in the
human body. Mature enamel is unique in that it is
practically pure mineral, a mix of calcium and
phosphate, with little of the protein component
that is present in bone. During enamel formation,
however, proteins are essential in laying down a
structural framework and serving as catalytic
sites for building enamel crystals. Recently,
researchers have made great strides in testing
out the roles of the various enamel proteins in
normal and abnormal tooth development

• Tuftelin is an important enamel protein whose
gene was recently located on chromosome 1.
Tuftelin is thought to bind mineral and acts as a
focal point for initial crystal formation. This gene
is a candidate for autosomal amelogenesis
imperfecta.Amelogenin, the most abundant
enamel protein, was found to have genes on both
the X and Y chromosomes. The genes produce
slightly different proteins, a fortuitous event that
now allows forensic scientists of determine the
sex of an individual from a mere tooth fragment.
Amelogenin is also thought to regulate the size
and orientation of the calcium hydroxyapatite
crystals during enamel formation.


• Not long ago, a deletion in the amelogenin gene
was found to be the cause of X-linked
amelogenesis imperfecta. This condition, which
occurs in about 1:14,000 individuals in the U.S.,
produces a weakened tooth enamel.Scientists at
NIDCR's laboratories in Bethesda, Marryland have
identifies a new protein that looks like another
key player in enamel formation. The protein,
named ameloblastin, was discovered through the
NIDCR's cranio facial, oral, dental genome
project. This ambitious undertaking has identified
over 400 genes that are active in rodent tooth
development 60 ler cent of them previously
unknown genes. The gene for ameloblastin is
particularly intriguing because it is active in
enamel forming cells. The human equivalent of
this gene is located on a region of
choromosome 4 that is linked to several tooth
disorders.

Reference
1. Oral history - Ten Cate.
2. Orban's histology and embryology
3. Operative dentistry - Clifford M. Sturdevant
4. Operative dentistry - Marzouk.
5. Contemporary Esthetic dentistry; Practice
fundamentals
-Bruce J.Crispin.
6. Dental Clinics of North America - Esthetic
Dentistry-October 1998.
7. Dental Clinics of North America -Laser Dentistry
-October 2000
8. Federation of Operative Dentistry -Volume I -
December, 1990.


Enamel significance in operative dentistry /certified fixed orthodontic courses by Indian dental academy

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