Smear layer / dental courses

SMEAR LAYER
INDIAN DENTAL ACADEMY
Leader in continuing Dental
Education
www.indiandentalacademy.com

-INTRODUCTION
-WHAT IS THE SMEAR LAYER?
-STRUCTURE AND COMPONENTS OF THE SMEAR LAYER:
-THE SMEAR PHENOMENON
-MORPHOLOGY OF THE SMEAR LAYER
-BONDING AND THE SMEAR LAYER
SMEAR LAYER:
PHYSIOLOGICAL CONSIDERATIONS

-Remove the smear layer by etching with acid
-ENDODONTICS
FUNCTIONAL IMPLICATIONS:
-DENTAL MATERIALS
-PERIODONTICS
-INFLUENCE OF SENSITIVITY OF DENTIN
-ON DENTIN INFLUENCE OF PERMEABILITY

SMEAR LAYER:
REMOVAL AND BONDING CONSIDERATIONS
-SMEAR LAYER ON DENTIN
EXPOSED TO THE ORAL CAVITY
-REMOVAL OF THE SMEAR LAYER UNDER RESTORATIONS
-THE PROTECTIVE EFFECT OF SMEAR LAYER IN TUBULE
APERTURES AND THE CONSEQUENCE OF REMOVING
THE PLUGS
-PULPAL IRRITATION DUE TO SMEAR LAYER REMOVAL

SMEAR LAYER:
REMOVAL AGENTS
-Normal saline
-HYDROGEN PEROXIDE
-CHLORHEXIDINE
-CHELATING AGENTS
-SUCCIMER (Brand name Chemet)124 &
TRIENTENE HCI (Syprine)
-SODIUM HYPOCHLORITE
-ORGANIC ACIDS
-SODIUM HYPOCHLORITE AND EDTA
-EGTA
-ULTRASONICS

-LASERS:
ND: YAG LAYER
-APICAL LEAKAGE
-SEALERS
SUMMARY & CONCLUSION

INTRODUCTION
The success of root canal therapy depends on the method
and the quality of instrumentation, irrigation, disinfection and
three – dimensional obturation of the root canal. Different
types of hand or engine – driven instruments have been
employed for the instrumentation of root canals.
The aim of instrumentation and irrigation is to prepare a
clean, debris – free canal for obturation. However, current
techniques may not cleanse the entire root canal system,
especially in irregular and/ or curved canals. In addition to
superficial debris, it has been shown, using the scanning
electron microscope, that a layer of sludge material was
always formed over the surface of dentinal walls whenever
dentine was cuT. This layer of debris has been called the
smear layer. Boyde et al (1963), first described the
presence of smear layer on the surface of cut enamel, and
Mc Comb and Smith (1975) observed this layer on the wall
of instrumented root canals and reported that it was similar
in appearance to coronal smear layer.www.indiandentalacademy.com

WHAT IS THE SMEAR LAYER?
• When tooth structures are cut, instead of being uniformly
sheared, the mineralized matrix, shatters. Considerable
quantities of cutting debris, made up of very small particles of
mineralized collagen matrix, are produced. Existing at the
strategic interface of restorative materials and the dentin matrix,
most of the debris are scattered over the enamel and dentin
surfaces to form what is known as the smear layer. A much
used analogy compares the smear layer to a clump of wet saw
dust.
In Endodontics, the smear layer results directly from the
instrumentation used to prepare the canal wall and are found
only where the walls are prepared and not in uninstrumented
areas. The amount of smear layer produced by automatic
preparation will be greater in volume than produced by finger
filling.

Because it is a very thin layer and is soluble in acid, the smear
layer will not be apparent on routinely processed specimens
examined with the light microscope. This may be the reason
why the smear layer received so little attention by restorative
dentists. When examined by the scanning electron
microscope, the smear layer will rarely be discernible on
specimens of demineralized teeth because it will be dissolved
during the process of demineralization. Under mineralized
specimens will appear on electron microscope examination as
a uniform sludge, relatively smooth and featureless.

The presence or absence of the smear layer in endodontics
is important. When a canal is instrumented, the smear layer
produced will remain within the canal pulp chamber. The
bacteria and bacterial products found in the smear layer
chamber. The bacterial and bacterial products found in the
smear layer can provide a reservoir of potential irritants.
With this thought in mind, the complete removal of the layer
and its corps of inhabitants has been the subject of
numerous investigations.

Another source of indecisiveness about keeping or removing
the smear layer was its long – term stability. The smear layer
and its provisional tenacity is a separate structure from the
underlying dentin. It may crack open and pull away from the
underlying dentinal tubules. A situation such as this would be
deadly to the foundation of gutta percha obturated over the
smear layer. Thus, it was axiomatic that removal of the smear
layer permits a better adaptation of sealers and obturating
materials in the dentin

STRUCTURE AND COMPONENTS OF THE SMEAR
LAYER:
STRUCTURE:
The Smear Layer has an amorphous, irregular and granular
appearance when viewed under the scanning electron
microscope. This appearance may be formed by
translocating and burnishing the superficial components of
the dentin walls during endodontic instrumentation.
McComb and Smith suggested that the Smear Layer
associated with root canal treatment consisted not only of
dentin as in coronal Smear layer, but also remnants of
odontoblastic processes, pulp tissue and bacteria. Hence, it
may contain both organic and inorganic materials.

Cameron suggested that the Smear Layer on the wall of
the root canal could have a relatively high organic content
in the early stages of instrumentation because of necrotic
and/or viable pulp tissue in the root canal.
Eick et al (1970) showed that the smear layer was
made of tooth articles ranging from less than 0.5µ m to 15
µ m.
Pashley et al (1988)found that these particles were
also composed of globular subunits, approximately 0.05 –
0.1 µ m in diameter which originated from mineralized
fibers.
Goldman et al (1981) and Mader et al (1984),
reported the thickness of the Smear Layer to be 1-5µm in
diameter which originated from mineralized fibers.

Goldman et al (1981) and Mader et al (1984), reported the
thickness of the Smear Layer to be 1-5 µm. This thickness
depend on the type and sharpness of the cutting instruments
and whether the dentin was cut dry or wet.
Increased centrifugal forces resulting from the movement
and the proximity of the instrument to the dentin wall form a
thicker and more resistant Smear layer and thus the amount
produced during automatic preparation, as with Gates
Glidden post drills will be greater in volume than that
produce by hand – filling.

Cameron (1983) and Mader et al (1984) described the
smear material into two parts. First, superficial Smear Layer
and Second, the smear material packed into the dentinal
tubules. The extension of this packed material into dentinal
tubules was calculated as extending up to 40µm. It was also
concluded that this tubular packing phenomenon of Smear
Layer was due to the action of burs and endodontic
instruments
Cengiz et al (1990) proposed that the penetration of the
Smear Layer into the dentinal tubules could be caused by
capillary action as a result of adhesive forces between the
dentinal tubules and the smear material.

COMPONENTS OF THE SMEAR LAYER:
The exact proportionate composition of the endodontic smear
layer has not been determined, but scanning electron
microscopic examinations have disclosed that its composition
was both organic and inorganic. The inorganic materials was
made up of tooth structure and some non specific inorganic
contaminants. The organic components may consists of
heated coagulated proteins (gelatin formed by the
deterioration of collagen heated by cutting temperatures),
necrotic or viable pulp tissue and odontoblastic processes
plus saliva, blood cells and micro organisms.

Once a root canal has been instrumented, the high
magnification of the scanning electron microscope will
disclose that the normal canal anatomy has been lost by the
instrumentation and that a thick smear layer has been found.
The dentin surface of the canal appears granular,
amorphous and irregular. Superficial debris and cracks may
be present in the dentin. Occasionally, the cracks can be
attributed to the process of preparing the specimens for
scanning electron microscopic examination

. The older methods of root canal preparation, especially
chelation and irrigation, did not produce a clean surface for
permanent sealing, but with the newer chelants (EGTA) the
canal surface was clean which aids in the sealing. It has a
superior action even in the very important apical third.
The flushing action of the irrigating solution was imperative
for the debris removal, but scanning electron microscopic
studies after instrumentation still showed the presence of a
Smear Layer.
In addition to restricting the fluid flow across dentin, the Smear
Layer is a further liability because it harbors bacterial
products. If the Smear Layer is not removed, the bacteria
within the layer may be detrimental if they survive flushing and
obturation. www.indiandentalacademy.com

SMEAR LAYER:
MORPHOLOGICAL CONSIDERATIONS
THE SMEAR PHENOMENON
Significant amounts of energy are expended at the
interface of a substrate and a tool during cutting and
abrading. The generation of frictional heat and plastic and
elastic deformation can all contribute potentially to alteration
and deterioration of the substrate. These consequences are
well understood in lapidary and machining contexts in which
grinding debris from the substrate or the tool itself may be
deposited or smeared upon the work surface unless steps are
taken to control the cutting process. Such smeared
contaminants lower the surface energy and therefore have a
profound effect upon the reactivity of the substrate surface.

Dentinal smearing occurs when “hydroxyappatite” within (the
tissue) is either plucked out or broken, or swept along and
results in the smeared out matrix. Hard dental tissues are
heterogeneous, comprising submicroscopic crystallites of
appatite enveloped in an organic matrix. Significant variations
in the proportions of these contributing to a wide range of
topographical anomalies, which can be related to the type of
instrumentation and the manner and conditions under which it is
used.

MORPHOLOGY OF THE SMEAR LAYER:
Extensive use of scanning electron microscopy is done
because it is well suited to identify and characterize the
changes produced during cutting and abrading dental
tissues.
The differences in topographical detail after dentin and
enamel with steel and tungsten carbide burs and
abrading it with diamond stones are clearly evident

Fig
Scanning electron micrograph showing the galling pattern on
a dentin surface cut with a water – cooled, tungsten carbide
bur. X 150

Fig
SEM showing grooves traversing a dentin surface abraded
with diamond X 300.

Steel and tungsten carbide burs produce an undulating
pattern, the troughs of which run perpendicular with the
direction of movement of the hand piece. Fine grooves can
be seen running perpendicular to the undulations and parallel
with the direction of rotation of the bur. Such a phenomenon
is referred to as galling and the frictional humps represent a
“rebound effect” of the bur against the tissue. The galling
phenomenon appears more marked with tungsten carbide
burs run at high speed. The appears more marked with
tungsten carbide burs run at high speed. The fine grooves
can be related to small facets found on the cutting flutes of
the bur. These scabrous facets arise because of wear of the
flutes and act as abrading points, scratching the plastically
and elastically deformed surface as the bur rotates.

Fig.
SEM of the cutting anomalies on dentin following the use of
cross – cut steel bur. Note the debris and evidence of
smearing.

Debris, irregular in shape and non – uniform in size and
distribution remains on the surface even after thorough
lavage with water.These relatively flat, sometimes finely
grooved, homogenous islands often appear to be oriented in
a direction parallel with the movement of the hand piece.
Discontinuities exit in the smear layer and some portions of
the smear layer adhere firmly to the tissue surfaces, while
others have lifted free by delamination.
The mechanism by which burs remove dental tissue
was significantly different from the abrading action of a
diamond. As the bur rotates, the flute undermines the
tissue, the amount being undermined by such factors as the
angle of the flute. There was no evidence of the tubular
structure of the dentin or the prismatic content of enamel
when relatively coarse diamonds are used.

Following the use of fine abrasives, such as diamond and
silicon carbide, the structure of both enamel and dentin were
partly disclosed though the tubules of the dentin were
frequently occluded.

Fig.
SEM of dentin abraded with 600 grit silicon carbide abrasive
paper. Note the occluded tubules and the prominent
peritubular dentin moulds. Surface cleaned with 3% H2O2
X 3800.

A significant difference exists between diamond burs used
with and without a coolant of waterspray. In the absence of
coolant, smeared debris can be found commonly on the
surface. The smeared debris does not form a continuous
layer, but exists rather as localized islands with discontinuities
exposing the underlying dentin. If the diamond is allowed to
clog with cutting debris, the smear layer appears to cover a
wider area .

Coolant of water spray does not prevent smearing but
appears to significantly reduce the amount and distribution
of it. If the tissue cleaved at right angles to the cut surface,
a qualitative estimate of the thickness of morphological
change can be made. The extent of tissue alteration was
usually quite superficial involving approximately 5 µm. of
the surface. The tubules were often occluded with cutting
debris.

BONDING AND THE SMEAR LAYER:
In general, diamonds through the introduction of
grooved anomalies, produce a greater surface area than
burs. This has implications in bondings where differences in
the bond strength of resin attached to enamel have already
been reported to be higher for diamonds compared to burs.
the increased surface area probably offered a larger number
of reaction or retentive sites. These sites in enamel are
primarily micromechanical and the retention mechanism for
this tissue lies in the multitude of superficial micro pores
enhanced following acid conditioning of the tissue.
the lumen of the dentinal tubules were significantly enlarged.
Brannsstrom and Nordenvall (1977) and Gwinnet
demonstrated that conditioning of dentin with phosphoric acid
facilitates penetration of resin into the dentinal tubules.

Fig 8
SEM of resin which had penetrated deep into the dentinal
tubules after conditioning with phosphoric acid and sodium
hypochlorite. Resing was disclosed by tissue dissolution X
150.

Such penetration probably contributes to the increased bond
strengths of resins employing acid conditioning of dentin.
There was equivocation as to whether the values decline or
are stable with time in the presence of water. It was clear from
many studies that while phosphoric acid removes the Smear
Layer and enlarges the dentinal tubules, it also appears to
degrade the collagen matrix. Some of the degradation
products may be removed with water but the surface of the
acid – conditioned dentin appears relatively smooth with a
gelatinous quality even after a through lavage. Subsequent
treatment of the same surface with a solution of sodium
hypochlorite brings about significant morphological changes.

Fig.
Scanning electron micrograph show dentin etched for 10
seconds with 50% phosphoric acid. A significant
morphological difference exists following additional treatment
for 60 seconds with 5 – 25% sodium hypochlorite X 1520.

The sodium hypochlorite dissolves the organic material to
produce a rougher texture to the surface, which is
dependent upon the time of application of this agent. When
tubules are exposed in longitudinal section, lateral canals
increase in number with time of application of sodium
hypochlorite .

Smear Layer comprising organic and inorganic
components are formed during cutting and abrading of dental
tissues. Such layers exist irrespective of the type of
instrumentation or the manner in which it was used. The
quality or quantity of such layering are influenced by the
operating conditions in which coarse diamond abrasives,
used dry, produce the thickest deposits. Most coarse
diamond abrasives, used dry, produce the thickest deposits.
Most rotary instruments create surface anomalies such as
grooves which, together with cutting debris, obliterate the
normal structural features of the dental tissues. The Smear
Layers are not always firmly attached to continuous over the
substrate. The surfaces are not conducive to the
development and retention of optimum bond strengths with
restorative materials and of necessity must be modified with
biocompatible agents.www.indiandentalacademy.com

SMEAR LAYER:
PHYSIOLOGICAL CONSIDERATIONS
Whenever dentin is cut with either a hand instrument or a
rotary instrument, the mineralized matrix shatters rather than
being uniformly sheared or cleaved, producing considerable
quantities of cutting debris. Much of the debris, made up of
very small particles of mineralized collagen mineralized
collagen matrix, was spread over the surface of the dentin to
form what is called a “Smear Layer” (Eick et al 1970). This by
light microscopy because the Smear Layer was dissolved
during demineralization.
When examined in undermineralized specimens by
scanning electron microscopy, the Smear Layer looks like an
amorphous, relatively smooth, featureless surface.

Its constituents are below resolution of the Scanning
electron microscope (SEM). Transmission electron
microscopy provided important new information about the
size of the particles constituting the Smear Layer as well as
their packing density and the dimensions of the diffusion
channels between the Particles.
The depth of the Smear layer varies widely upon
whether the dentin was cut dry or wet, the amount and
composition of the irrigating solution used, the size and
shape of the cavity (or root canal), and the type of
instrument employed. (Gilboe et al, 1980). Generally
speaking, cutting without water spray generates a thicker
layer of Smear Layer (debris) than cutting with a copious
spray of air and water.

Further, coarse diamond burs tend to produce thicker Smear
Layers than carbide fissure burs (Brannastrom, Glantz &
Nordenvall), 1979, Shortall 1981). Perhaps the thickest
Smear Layers that have been produced (∼10-15µm thick)
were produced in vitro with a coarse diamond blade mounted
on a metallurgical saw. This device tends to pack and
burnish the debris into a smooth, highly glossy finish
(Pashley, Michelich & Kehl, 1981).
The Smear Layer increases the resistance to movement of
fluid across dentin discs, both in vivo in vitro. As the rates of
filtration provide a convenient, quantitative method of
assessing the presence of a smear layer, they were used to
compare a variety of different methods of producing a smear
layer on dentin etched with acid in vitro

FUNCTIONAL IMPLICATIONS:
DENTAL MATERIALS
Dental material scientists have been concerned about the
smear layer in so far as it masks the underlying dentin matrix
and may interfere with the bonding of adhesive dental
cements such as the polycarboxylates and glass ionomers,
which may react chemically with the dentin matrix. Dahl
1978) demonstrated that simply pumicing the dentin surface
produced a three – fold increase in the tensile strength of the
bond between dentin and polycarboxylate cement (Durelon,
Premier Dental Products Col, USA) over that seen with Zinc
Phosphate cement (Mizzy Inc, USA), which relies strictly
upon mechanical roughness for retention.

Presumably allowing cements to react chemically with the
Smear Layer, rather than the matrix of sound intertubular
dentin, produced a weaker bond due to the fact that the
Smear Layer can be torn away form the underlying matrix.
When cements were applied to dentin covered with a
Smear Layer and then tested for tensile strength, the failure
was either adhesive (Between cement and smear layer) or
cohesive (between constituents of the smear layer). If one
wanted to increase the tensile strength of a cement – dentin
interface there are several approaches to the problem.

Remove the smear layer by etching with acid:
(Lee et al, 1971,1973, Bowen1983, Brannstrom et al 1979,
1980, Pashley et al 1981). This seemingly extreme
procedure does not injure the pulp (Brannstrom, 1982),
especially if dilute acids (Bowen, 1978) are used for short
periods of time.
Etching dentin with 6% citric acid for 60 seconds, removed all
of the Smear Layer (and smear plugs) as does 15 seconds of
etching with 37% phosphoric acid.. The advantages were
that the Smear Layer was entirely removed, the tubules were
open and available for increased retention, and the surface
collagen was exposed for possible covalent linkages with
new experiment as primer for cavities. Further, with the
Smear Layer gone, one doesn’t have to worry about it slowly
dissolving under a leaking restoration or being removed by
acid produced by bacteria, leaving a void between the cavity
wall and the restoration, which might permit bacterial
colonization. www.indiandentalacademy.com

The disadvantage of removing the Smear Layer was that, in
its absence, there was no physical barrier to bacterial
penetration of the dentinal tubules. Further, with nothing
occluding the orifices of the tubules, the permeability of the
dentin increased 4 to 9 fold depending upon the size of the
molecule.
Another entirely different approach would be – to use a resin
that would
infiltrate through the entire thickness of the Smear Layer and
either bond to the underlying matrix or penetrate into the
tubules. The impressive tensile strength for Scotchbond (3
M Dental Products division, USA) may be due to such a
process. Results indicate stronger bonds between the resin
and pumiced dentin than between the resin and etched
dentin.

Etching with acid, in addition to removing the Smear Layer
and exposing the surface collagen, also removed the
peritubular dentin from the top 5 –10 µm of the tubules,
yielding a tubule with a funnel shaped orifice. Additionally,
etching with acid demineralized the surface, which would
lower the adhesive bond between cements and the
mineralized dentin.
Smear layers on deep dentin may have more organic
material in them than those on superficial dentin. This may
be due to the number of odontoblastic process or to the
greater amount of proteoglycans lining the tubules.

Etching with acid, i.e.., removal of the Smear Layer, increased
the adhesive strength of composite resins (Adaptic, Clearfil) to
superficial dentin by 800-1000% over that to deep dentin even
though far more tubules were available for penetration of resin in
deep dentin than in the superficial dentin. This indicates that
composite resins probably do not derive their adhesiveness from
penetration of resin into the tubules, but rather by interacting
with mineralized intertubular dentin.
Another variable interfering with the adhesive of
substances to dentin was the presence of dentinal fluid, a fluid
much like other interstitial fluids, both within the dentinal tubules
and within the Smear Layer. Brannstrom et al indicated that, in
dentin etched with acid, dentinal fluid could be removed by
blasts of air and replaced by tags or resin extending deep into
the tubules. Bowen’s approach was to treat the dentin with
solutions of resin in acetone which was miscible with dentinal
fluid yet compatible with hydrophobic polymers.

Another approach was to try to fix the Smear Layer with
Gluteraldehyde (Hoppenbrouwers, Driessens
&Stadhouders, 1974) or tanning agents such as tannic acid
or ferric chloride (Powis et al, 1982). The idea was to
increase the cross linking of exposed collagen fibers within
the Smear Layer and between it and the matrix of the
underlying dentin to improve its cohesion.

The most convenient approach to the problem was to
remove the Smear Layer by etching with acid and replace
it with an artificial Smear Layer composed of a crystalline
precipitate (Causton and Johnson, 1982). Bowen used
this approach by treating dentin with 5% ferric oxalate,
which replaced the original Smear Layer with a new
complex permitting extremely high bond strengths to be
produced between resin and dentin. Greenhill and
Pashley have produced similar artificial Smear Layer with
a variety of chemicals as a method of desensitizing
hypersensitive radicular dentin.

ENDODONTICS:
The presence or absence of the Smear Layer is of interest not
only to restorative dentists, but to endodontists as well.
Whenever dentin is filed, a smear is produced on its surface. If a
Smear Layer containing bacteria or bacterial products were
allowed to remain with the pulp chamber or root canals, it might
provide a reservoir of potential irrigants. The removal of the
Smear Layer from the dentin lining the pulp chamber and root
canals has been the subject of numerous investigations.

PERIODONTICS:
Periodontists produce a Smear Layer on root dentin
during deep scaling or root planning. Register1973
found, empirically, that etching radicular dentin with
saturated citric acid facilitated reattachment following
periodontal flap surgery. Register (1973), register and
Burdick (1975, 1976), Ririe, Crigger and Selvig (1980)
and Nalbandian and Cote (1982) have shown that
etching with citric acid stimulates cementogenesis and
the subsequent intertwining of collagenous fibres of the
matrix of dentin or cementum. They also demonstrated
that cementum did not form as readily on dentin covered
with a Smear Layer. Apparently, cementoblasts do not
find the Smear Layer a very hospitable environment.
Further, epithelial cells migrate rapidly across planed
(Smeared) radicular dentin etched with acid.

Careful examination of published Transmission electron
micrographs taken of mineralized sections of roots that were
planed but not etched with acid reveals the presence of a
finely granular organic layer interposed between root dentin
and developing cementum. This has been demonstrated in
monkeys (Listgarten, 1972), cats (Nalbandian & Frank 1980)
and humans (Frank, Fiore Donno & Cimasoni, 1983). These
authors have called it zone 3’ or granular junctional
epithelium’ it probably represents simply a fine, thin, Smear
Layer created on the surface of radicular dentin during root
planning (Jones, Lozdan & Boyde, 1972; Polson et al, 1984).
Its presence clearly modified local reactions of tissue in that
it apparently inhibited attachment of firm new connective
tissue while permitting migration of the epithelium over its
surface.

Etching effectively removes the Smear Layer in addition to
exposing collagen fibers in the matrix of radicualr dentin.
Even after removal of the mineral phase of the Smear
Layer, which may interfere with subsequent interdigitation
of collagen fibers of periodontal ligament and dentin matrix.
The organic Smear Layer was easily rubbed off with a
cotton pellet and this indicates how important it may be to
standardize technique of etching, namely, specifying
concentration of acid, time of exposure, time or rinsing,
dabbing or rubbing and so forth.

INFLUENCE OF SENSITIVITY OF DENTIN:
Etching the dentin of roots, whether done therapeutically or
by the action of microorganisms of plaque, can remove the
thin layer of covering cementum or Smear Layer, or both,
thereby exposing the patent dentinal tubules to the oral
cavity. This can lead to sensitivity of dentin to the point
where it interfered with the patient’s oral hygiene. As
movement of fluid was central to the hypothesis, several
studies have been made of the most important variables
influencing movement of fluid through dentin (Reeder et al,
1978, Pashley, Livington and greenhill, 1978, Bayer & Svare,
1981; Pashley, Thompson & Stewart, 1983,) These studies
indicated that most of the resistance to the flow of the fluid
across dentin was due to the presence of the Smear Layer.

Etching dentin greatly increased the ease with which fluid can
move across dentin. This was accompanied clinically by
increased sensitivity of dentin to osmotic, thermal and tactile
stimuli.
If dentin was sensitive then according to the hydrodynamic theory
of dentin sensitivity, the dentinal tubules must be patent and must
allow movement of fluid across dentin. If fluid can move, it seems
reasonable to assume that bacterial products from plaque
covering those surfaces of sensitive dentin may also permeate
dentin into the pulp. The presence of a Smear Layer will prevent
bacterial penetration of the tubules but will permit bacterial
products to diffuse slowly into the pulp. This may produce a mild,
low – grade inflammatory response that lower the pain threshold
in the affected teeth, making them more sensitive than they would
be in the absence of plaque.

ON DENTIN INFLUENCE OF PERMEABILITY
The presence of smear layer has a large influence on
dentinal permeability. Substances diffuse across dentin at
a rate that is proportional to their concentration gradient
and the surface area available for diffusion. The area
available for diffusion in dentin was determined by the
density of dentinal tubules i.e., the number of tubules per
square millimeter, and by the diameter of these tubules.
Both of these values vary as a function of distance from
the pulp chamber. (Forsell – Ahlberg, Brannstrom
&Edwall, 1975; Garberoglio & Brannstrom, 1976,80).

If one looks at the surface of a Smear Layer in scanning electron
micrograph, one would predict that it might be impermeable.
However, experiments both in vitro and in vivo have demonstrated
that isotopic ally labeled solutes of various molecular sizes easily
penetrate the Smear Layer. By measuring the fluxes of
radioactive water and albumin across known areas of surface and
by knowing the rates of diffusion of these substances in free
solution, one can calculate the effective area of diffusional surface
available for the diffusion of these tracers, even through a smear
layer. In dentin discs prepared by sawing from midcoronal dentin,
would have an area of diffusional surface of approximately 7-8%,
which was determined by the use of triurated water as a tracer to
have an effective or functional area of diffusional surface of the
smear layer of 1.7%

The total resistance to flow of fluid was measured, followed
by etching the Smear Layer with acid and repetition, of the
measurement of resistance to flow of fluid. Following this,
the pulpal tissue was removed and rates of fluid flow
remeasured. Using this approach, the authors concluded
that the Smear Layer accounted for 86% of the total
resistance to flow of fluid (Pashley et al, 1978). Thus after
etching with acid, the rate of fluid flow increased 15 fold.
Reeder et al (1978) reported a 32 fold increase; and Pashley
et al (1983) reported a 42 fold increase. Contrast to this,
Boyer and Scare (1981) reported only a 7 fold increase

It should be clear that removing the Smear Layer increases
dentin permeation by diffusion about 5-6 times in vitro but
increase dentin permeation by convection (i.e., filtration) about
25-36 times. If the smear Layer was thick, the initial
permeability of dentin will be low but should increase more after
etching. Teeth that have little or no Smear Layer will have high
initial permeability's, which will not change much following
etching since there is little debris occluding the tubules. Thus,
the magnitude of the change in the rate of flow of fluid across
dentin before and after etching indicates the thickness or
density of the Smear Layer.

The Smear Layer occupies a strategic position in
restorative Density. It exists at the interface of most restorative
materials and the dentin matrix. Because it is a very thin layer
and is soluble in acid, it is not apparent on examination with the
light microscope of routinely processed specimens. This was
probably why the Smear Layer has received to little attention by
restorative Dentists.

There are two extreme points of view regarding the Smear
Layer.
One is that it was beneficial, iatrogenically produced cavity
liner that reduced dentin permeability far more effectively than
any of the marketed cavity vanishes.
At the other extreme was the view that it interfered with the
apposition or adhesion of dental materials to dentin and that it
may serve as a depot of microorganisms or their products, both
of which are injurious to the pulp.
Both points of view are correct. The former perspective was
the most appropriate for clinicians using the most commonly
available restorative materials, which exhibit micro leakage and
a lack of adhesion to tooth structure. The latter perspective
may be more appropriate in the future when truly adhesive
materials are in routine use.www.indiandentalacademy.com

SMEAR LAYER:
REMOVAL AND BONDING CONSIDERATIONS
Disturbed surface layers of dentin and enamel that are
formed by cutting or abrading instruments must be removed
or altered to obtain strong adhesive. These layers can be
removed by acids, including formic and ascorbic acids or
chelating compounds both of which form soluble or insoluble
reaction compounds (Bowen, 1978).

Solutions of ferric oxalate also dissolve the smeared surface
layer yet form insoluble reaction products that apparently
occlude the openings of the dentinal tubules (Bowen, Cobb &
Rapson, 1982). These solutions also remove the smeared
layer on cut enamel, revealing typical patterns of enamel
prisms. When the ferric oxalate was followed by treatment
with solutions of a specific surface active compound and then
a polymerizable coupling agent, strong adhesive bonds with
composites are possible on dentin and enamel in vitro
(Bowen et al, 1982). Removal of the smeared layer, however
may be inappropriate if there was to be no bonding or
improved adaptation,.

SMEAR LAYER ON DENTIN
EXPOSED TO THE ORAL CAVITY:
Another question concerns what may happen to the
Smear Layer on surfaces exposed to the oral cavity and left un
restored, for example in root planning after superficial grinding,
or under poorly fitting temporary crowns. It was found that
when a Smear Layer is produced experimentally on the human
dentin and left exposed it disappears after a couple of days and
was replaced by bacteria and after a week almost all the
tubules are opened and some widened (Brannstrom, 1982).
There may be 10,000 – 20,000 tubules per square millimeter
exposed on a superficial hypersensitive exposure. The
consequence is the invasion of bacteria. In single tubules, they
can be found to have penetrated rather deeply (Lundy &
Henley, 1969, Olgart et al 1974). Bacteria may plug the tubular
apertures. However after weeks, occasionally a mineralized
pellicle was seen blocking the aperture of the tubules
(Brannstrom 1982). www.indiandentalacademy.com

REMOVAL OF THE SMEAR LAYER UNDER RESTORATIONS:
We cannot expect a mineralized pellicle to develop under a
restoration where saliva does not does not circulate. However, we
know that the outward flow of fluid in dentinal tubules and around
the fillings may be reduced with time. The pulpal ends of the
tubules may be partly blocked by irregular dentin. As reported by
Pashley (1984), accumulation of solids in tubules and at their
outer apertures may contribute to a reduce flow of fluid. Under
favorable conditions, a mineralized pellicle may develop at the
outer aperture of the contraction gap. The same has been
observed in the aperture of tubules of cut dentin left unprotected.

THE PROTECTIVE EFFECT OF SMEAR LAYER IN TUBULE
APERTURES AND THE CONSEQUENCE OF REMOVING
THE PLUGS.
Vojinovice et al, 1973 reported that etching the cavity
prior to the placement of composite resin resulted in a massive
invasion of bacteria in the dentinal tubules. The corresponding
cavities, cleaned by water and with the smear layer left, had a
bacterial layer on cavity walls but practically no invasion into the
dentinal tubules. Obviously, smear plugs in the apertures of the
tubules had prevented bacterial invasion. Inflammation was
present under all infected cavities, but the difference was not
great. The conclusion from Vojinovic’s study was that smear
plugs did not prevent bacterial toxins from diffusing into the
pulp. This was confirmed by Bergenhottz 1977). The degree of
inflammation in the pulp seems to depend on the amount and
type of toxin, from both live and dead bacteria, reaching the
pulp, rather than the presence of bacteria within the tubules.

However, toxins, sometimes in combination with an unduly
intense reaction, may lead to a local necrosis. From opened
tubules, the bacteria may easily reach the pulp and multiply
(Brannstrom, 1982). therefore, demonstrated that the smear
plugs reduces the dentinal permeability.
Another important consequence of etching and the
removal of smear plugs and peritubular dentin at the surface is
that the area of wet tubules may increase from 10-25% of the
total (Garberoglio and Brannstrom, 1976, Johnson &
Brannstrom 1974). Subsequently, it is difficult to get the dentin
dry because fluid continues to be supplied from below through
the tubules. This moisture does not favor adhesive or
mechanical bonding to dentin.

PULPAL IRRITATION DUE TO SMEAR LAYER REMOVAL:
An application of 50% citric acid or 37% phosphoric acid
for even 5 seconds is sufficient to remove the smear plugs and
the peritubular dentin at the surface (Brannstrom & Johnson,
1974, Nordenvall and Brannstrom, 1980).
It was found that, 37% phosphoric acid or 50% citric
acid applied for 15 seconds, or one minute does not result in
any appreciable pulpal reaction, inflammation or necrosis. This
is true, even if we are very near the pulp or apply the acid to an
exposed pulp for 15 seconds.
Acid etchants, detergents, a thin mix of phosphate
cement, silicates, glass – ionomer cement and resins do not
produce any appreciable damage and inflammation to the pulp,
not even when applied to exposed pulps (Brannstrom, 1982,
1984). The cut dentin should not be treated with acid or EDTA
in such a way that the tubules become open and widened.

In cavities and on surfaces of dentin prepared for
restorations and abutments, the superficial Smear Layer should
be removed and the remaining smear plugs treated
antiseptically. The advantage of this is that
The surface is easier to dry with a blast of air as a outward flow
of fluid is avoided
Improved adaptation is obtained for lining material and luting
cements
There is a reduced risk of bacteria multiplying in the Smear
Layer and in a fluid gap between the lining and the surface of
cut dentin.
Demineralizing cleansers that remove the smear plugs and
widen the tubular apertures should be avoided. The dentin will
be wetter and in the case of bacterial contamination, there will
be an invasion of bacteria into dentinal tubules. Further more,
the surface will become several times more permeable to toxins
diffusing to the pulp. www.indiandentalacademy.com

The problem is similar smear produced by remaining root canals,
though the removal of smear plugs with demineralizing solutions
may have both positive and negative effects, it depends on the
infectious situation in the root, the morphology of the dentin of the
root and the way, the treatment is performed.

SMEAR LAYER:
REMOVAL AGENTS
Irrigating solutions have been used during and after
instrumentation to increase cutting efficiency of root canal
instruments and to flush away debris. The efficiency of the
irrigating solution is dependent not only on the chemical nature
of the solution, but also on the quality and temperature. The
contact time, the depth of penetration of the irrigation needle,
the type and gauge of the needle, the surface tension of the
irrigating solution and the age of the solution (ingle, 1985).

Irrigants are used for the following reasons:
To lubricate the canal walls during instrumentation
To remove debris by flushing the canals
To dissolve organic matter
To dissolve inorganic matter
To destroy micro-organisms
To aid cleaning in areas that are inaccessible to mechanical
cleansing methods

Normal saline:
Normal (physiological) saline solution does not have any
effect on the removal of dentinal debris and smear layer.
The saline solution produce a sludge layer made up of
residual debris that occluded the dentinal tubules.
Brianstrom and Sundqvist, 1981 reported significant
reduction in the number of bacteria present in the canals,
but not such that negative cultures are achieved during one
appointment.

HYDROGEN PEROXIDE:
Another irrigating solution that has had extensive use in
root canal irrigation is Hydrogen peroxide (H2O2). The
mechanism of action of this oxidizing solution involves the
reaction of super oxide ions to produce hydroxyl radicals
which are the strongest radicals known. This radical can
attack membrane lipids, DNA and other essential cell
components.
The antimicrobial action suggested is the result of
oxidation of sulphydryl groups and double bonds in
proteins, lipids and surface membranes. In the presence of
Mucoperoxidase enzyme, chloride in the bacteria may be
oxidized to hypochlorite (Block, 1991).

CHLORHEXIDINE:
Chlorhexidine (CHX) is a common irrigant in periodontal
treatment, and has been suggested for use in Endodontics
(Delaney et al, 1982). The antimicrobial effect of CHX is
mediated by several mechanisms. It binds electrostatic ally
to negatively charged sites on bacteria. By attaching to the
bacterial cytoplasmic membranes. CHX causes the osmotic
balance to be lost, resulting in leakage of intracellular
material. It also binds to hydroxyaptite and soft tissues,
changing their electrical field to compete with bacterial
binding.

CHELATING AGENTS:
The most common chelating solutions are based on ethylene
diamine tetracetic acid (EDTA) which reacts with calcium
ions in dentin and forms soluble calcium chelates (Grossman
et al 1988). Fehr and Nygaard – Ostby (1963)found that
EDTA decalcified dentin to a depth of 20-30 µ in 5 min,
Fraser (1974) stated that the chelating effect was almost
negligible in the apical thirds of root canals.
Different preparations of EDTA have been used as a
root canal irrigant. In a combination, Urea Peroxide was
added to float the dentinal debris from the root canal
(Steward et al, 1969). However it appeared that despite
further instrumentation and irrigation, a residue of this
mixture (RC – Prep, medical products laboratories,
Philadelphia, PA, USA) was left on the canal walls
(Zurbrigger et al, 1975). This may be a disadvantage in
hermetic sealing of root canals.www.indiandentalacademy.com

A quaternary ammonium bromide (cetrimide) has been
added to EDTA solutions to reduce surface tension and
increase permeability of the solution. Mc Comb and Smith
(1975)reported that even this combination (REDTA, Roth
International Ltd, Chicago IL, USA) was used during
instrumentation, there was no smear layer except in the
apical part of the canal. After in vivo use of REDTA, it was
shown that the root canal surfaces were uniformly occupied
by patent dentinal tubules with very little superficial debris
(Mc Comb et al, 1976) when used during and after
instrumentation, remnants of odontoblastic processes could
still be seen within the tubules even though there was no
smear layer present (Gold man et al 1981). Goldman and
Abramovich (1977) observed that circumpulapal surface had
a smooth structure and that the dentinal tubules had a
regular circular appearance with the use of EDTAC (Farma
– dental Labs, Buenons Aires, Argentina).

It was indicated that the optimal working time of EDTAC in
the root canal was 15 min. and no more chelating action
could be expected after this period. (Goldberg &Spielburg,
1982). It was also found that REDTA was the most efficient
irrigating solution in this study in the removal of the smear
layer.
Another root canal chelating agent is Salvizol (Ravens
gmbH, Konstanz, Germany) which is based on amino
quinaldinum diacetate. It has surface acting properties
similar to materials of the quarternary ammonium group and
possesses the combined actions of chelation and organic
debridement. While Kaufman et al (1978) reported that
Salvizol had better cleansing properties than EDTA
containing cetavlon (EDTA – C, Frenstiller or Wyegaard &
Co., Norway), Berg et al 1986)found that REDTA surpassed
Salvizol and other solutions in its cleansing action.www.indiandentalacademy.com

SUCCIMER (Brand name Chemet)124 &
TRIENTENE HCI (Syprine)
Succimer is taken orally to remove excess lead from the
body (acute lead poisoning) specially in small children.
Trientene HCI is taken orally to treat Wilson’s Disease a
condition manifested by the accumulation of too much copper
in the body.
Both materials are available in capsules, which can be
transformed into solution by mixing with deiodized water.

Both these agents are effective in the removal of the smear layer
and widening of the dentinal tubules. In fact, they even provide a
greater overall widening when compared with EDTA. These two
(products) irrigants can be effectively used to remove both smear
layer and also widen the dentinal tubules of the root canal system
of the human teeth.

SODIUM HYPOCHLORITE:
The organic tissue dissolving capacity of NaOCI is well
known and increases with rising temperatures. However, the
capacity to remove smear layer from the instrumented root
canal walls has been found to be insufficient. Many authors
have concluded that the use of Na OCI during or after
instrumentation produces superficially clean canal walls with
the smear layer present.
The alternating use of Hydrogen peroxide and NaOCI
solution was often advocated in the past. Mc Comb and
Smith (1975) and Bitter (1989) showed that this combination
was not more effective in the removal of the smear layer than
NaOCI alone and produced canal surfaces similar to that
formed with water. Adding surface active reagents to NaOCI
to increase its action proved also ineffective (Cameron,
1986). www.indiandentalacademy.com

ORGANIC ACIDS:
Citric acid appeared to be an effective root canal
irrigant (Loel, 1975)and was more effective than NaOCI
alone in the removal of the smear layer (Baumgartner et al,
1984). This acid removed smear layer better than many
acids such a polyacrilic acid, lactic acid and phosphoric acid
except EDTA (Meryon et al 1987).
Wayman et al (1979)showed that the canal walls treated with
10%, 25% and 50% citric acid solution were generally free of
the smear layer, but they had the best results is removing the
smear layer with sequential use of 10% citric acid solution
and 2.5% NaOCI solution, then again followed by 10%
solution then again followed by 10% solution of citric acid.

The 25% citric acid NaOCI group was not effective as the
17% EDTA – NaOCI combination (Yamada et al, 1983).
besides citric acid precipated crystals in the root canal which
might be disadvantageous in the root canal obturation
With 50% Lactic acid, the canal walls were generally
clean, but the openings of the dentinal tubules did not appear
to be , completely patent (Wayman et al, 1979).
Bitter (1989)introduced the use of 25% tannic acid solution as
a root canal irrigant cleanser. It was demonstrated that the
canal walls irrigated with this solution appeared significantly
cleaner and smoother than the walls treated with a
combination of H2O2 and NaOCI, and that the smear layer
was removed.

SODIUM HYPOCHLORITE AND EDTA
The purpose of irrigation is two fold: to remove gross
debris originating form pulp tissue Mc Comb and Smith (1975)
compared the efficacy of 20% polyacrylic acid with REDTA and
found that it was no better than REDTA, in removing or
preventing the build up of smear layer, probably owing to its
higher viscosity, Mc Comb et al (1976) also used 5% and 10%
polyacrylic acid as an irrigant and observed that it could remove
the smear layer only in accessible regions.
and possible bacteria, the organic component, and to remove
the smear layer, the mostly inorganic component. Because
there is not a single solution which has the ability to dissolve
organic tissue and to demineralize the smeared layer, a
sequential use of organic and inorganic solvents have been
recommended.

Numerous authors have agreed that the removal of smear layer
as well as soft tissue and debris can be expedited by the
alternate use of EDTA and NaOCI. In this respect, validity of
the term irrigation solution should be reevaluated as these
solutions may be used during and after instrumentation.
According to Kaufman and Greenberg (1986), a working
solution is the solution which is used to clean and shape the
canal, and an irrigation solution is the one which is essential to
remove the debris and smear layer created by the
instrumentation process.

Goldman et al (1982)examined the effect of various
combinations of EDTA and NaOCI as working and/ or irrigation
solution during and after instrumentation. According to their
results, the most effective final flush was 10ml of 5.25% NaOCI,
which was also confirmed by Yamada et L (1983).

EGTA
(Ethylene glycol – bis (β - amino ethyl ether) – N, N,
N1,N1 – tetra acetic acid). S
EGTA is a chelant which has been introduced recently
for root canal irrigation. EGTA is reported to bind Ca2+ more
specifically.
To remove the smear layer on the canal wall. EGTA
was used as an alternative to EDTA. EGTA was effective in
removing the smear layer without inducing any erosion. The
results of their study showed that EGTA was not as effective as
EDTA in the important apical third. Further it was still not clear
that the erosion and joining of orifices from EDTA action is
deleterious.

ULTRASONICS:
After the introduction of ultrasonics, the use of ultrasound
was investigated in endodontics (Martin et al, 1980, Cunningham
et al 1982, Cunningham & martin, 1982). A continuous flow of
sodium hypochlorite solution activated by a ultrasound delivery
system was used for the preparation and irrigation of the root
canal. It was observed that this method produced smear free root
canal surfaces (Cameron 1983, 1987, Griffiths & Stock 1986,
Alcam 1987).

Cameron (1988) showed that while concentrations of 2% -
4% NaOCI in combination with ultrasonic energy, were able
to remove the smear layer, lower concentration of the
solution were unsatisfactory. However, Ahmed et al (1987)
claimed that their technique of modified ultrasonic
instrumentation using 1% NaOCI removed the debris and
smear layer more effectively than the technique
recommended by Martin and Cunningham (1983). It was
observed that the apical region of the canals showed less
debris and smear layer than the coronal aspects depending
on the acoustic steaming, which was more intense in
magnitude and velocity at the apical regions of the file.

Researchers who found beneficial cleaning effects of
ultrasonic used the technique only for final irrigation of root
canal after completion of instrumentation by hand (Alacam
1987, Ahmed et al 1987, Cameron 1988). They exercised
extreme care not to touch the ultrasonic file to the canal wall
so as to allow free oscillation. Ahmad et al (1987) claimed
that direct physical contact of the file with the canal walls
throughout the ultrasonic instrumentation reduced acoustic
steaming. This may be the reason for the contradictory
results of the studies which showed that the use of
ultrasonics did not remove the smear layer.

LASERS:
ND: YAG LAYER
Gelskey et al used Nd: YAG laser to reduce dentin
hypersensitivity to air by 58% and to mechanical stimulation by
61% Nd: YAG lasers causes melting of dentin and closure of
exposed dentinal tubules without dentin surface cracking. But,
the depth to which Nd: YAG laser could work into the dentinal
tubule orifices. Such a dentin surface modification may be
accepted in the future as a treatment modality, because
melting and resolidification of the dentin and closure of the
tubules without dentin surface cracking may be permanent and
short lived.

APICAL LEAKAGE:
Plasticized gutta percha can enter the dental tubules when the
smear layer is absent. This can establish a mechanical lock
between the gutta percha and the canal wall coupled with the
increased surface area the interface between filling and canal
wall, this lock should create an impermeable seal. Dye tests,
however failed to substantiate this theory when tested after the
removal of the smear layer. The dye penetrated accessory canals
and spread laterally along the filling canal interface.
Thus the injection of thermplasticized gutta percha should
be accompanied by the use of a sealer regardless of whether or
not the smear layer has been removed. Follow – up dye tests,
with the smear layer intact and the use of sealer and lateral
condensation, showed no dye penetration.

Kennedy stated that an absence of the smear layer causes less
apical leakage than gutta percha filled canals with the smear
layer intact. He also stated that the use of a chelating agent on
the smear layer would increase apical microleakage.
Furthermore, he stated that a 7 – day duration between
instrumentation and obturation allows for an increased amount
of apical leakage. He concluded that removal of the smear
layer would improve gutta percha seals if the master ones are
softened with chlorform and used with a sealer and lateral
condensation.

The greater the degree of canal preparation, the smaller the
amount of apical leakage. It is still inclusive whether or not the
presence of dentinal fillings will enhance the seal of a root canal
filling. When it was noted that stoppage of leakage occurred, it
was related to smaller file sizes. With situations in which apical
leakage existed in the presence of dentin plugs, it must be
concluded that the plugs were permeable. Their porosity allowed
them to fall short of the goal of creating a hermetic apical seal.
In addition to being porous, dentin plugs allowing micro
leakage exhibited large amounts of shrinkage. Scanning electron
microscopic examination of unsatisfactory apical plugs always
showed marginal and structural defects. Further considerations for
advocating smear layer removal in Endodontics are the
importance of creating a good apical plug and the effects the two
main types of sealer have on the canal walls.

SEALERS:
Because of the bacterial content of the smear layer, any apical
extrusion of the smear layer during instrumentation or
obturation can defeat one of the goals of Endodontic therapy:
the return to and maintenance of an inflammation – free state
in the periapical area. To be considered an ideal sealer, a
material should not of itself cause of further irritation in this
tissue. Some root canal filling materials, especially N2 paste
and silver points, are not biocompatible. To risk further tissue
trauma with a technique that may induce or potntiate periapical
inflammation is unthinkable.

Endodontic sealers act as a glue to ensure a good
adaptation of gutta percha to the canal walls. If the smear
layer is not removed, the gutta percha may occasionally be
glued to the dentin in the smear layer as well as to exposed
parts of the canal wall. Not being firmly attached to the
dentin, the smear layer may laminate of the canal wall and
create a false seal, voids in the filling and an expected
environment for micro leakage.
Smear layer induced inflammation of the periapical
area can be caused by over instrumentation or by the
careless measurement and filling of a master cone. It has
long been recommended that master cones be fore-
shortened to fit 1m short of the apex as an effective
countermeasure to creating pre and post obturation
periodicals inflammation.

SUMMARY & CONCLUSION
With the cascade of new restorative products being unveiled
almost monthly, Endodontics must be able to evaluate the
potential of these products for successful integration into their
procedures. This evaluation should be based on a knowledge
of how the new products relate to the smear layer formed along
the root canal walls. Rather than relying information supplied by
the Dental manufactures, the watchful dentist should regularly
resort to the most current research reports available in Journal
or Abstract form.
With the use of certain products in some clinical
situations, other branches of Restorative Dentistry may suggest
retention of the smear layer. Although pulpally infected teeth
have been successfully treated for generations in the presence
of smear layer, it has become accepted practice now in
Endodontics to remove the smear layer.www.indiandentalacademy.com

Different quantities and qualities of smear layer can be produced
by various techniques of instrumentation. However, they all
present a barrier to intimate contact between obturating materials
and the canal wall. Various types of solvents will produce different
results in the removal of the smear layer. One ideal endodontic
irrigant follows the use of antimicrobial 5.25% NaOCI solution
with the equally antimicrobial 17% EDTA.
Chelating agents are effective in that they remove the
smear layer open the dentinal tubules, and produce a clean
surface for closer obtruation. Removal of the smear layer
encourages the creation of a good apical plug to prevent over
filling, post filling sensitivity, and possible micro leakage.
The use of glass ionomer cements and unfilled resin as a
cementing medium following smear layer removal shows
promising results in both strength of cementation and possibility of
reducing post lengths.

Controversies will always arise in Dentistry with the advent of
new information and the discovery of new clinical techniques.
But a total awareness of both sides of a controversy will enable
the practitioner to find a way through the confusion.

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