smear layer /certified fixed orthodontic courses by Indian dental academy

SMEAR LAYER

INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education

www.indiandentalacademy.com

Contents
 Introduction
 History
 What is smear layer?
 Morphology of the smear layer
 Physiological considerations
 Pathological considerations
 Smear layer in Restorative dentistry
 Smear layer in Endodontics
 Role of Bonding
 Methods of removal
 Advantages and Disadvantages
 conclusion


Introduction
 The term Smear layer is used most often to describe the

grinding debris left on dentin by cavity preparation.

 Any debris produced iatrogenically by the cutting, not

only of coronal dentin, but also of enamel, cementum

and even the dentin of the root canal.


History
 Smear layer -17th century – Leeuwenhock.
 Boyde,Switsur and Stewart,1963 - Grinding debris –
referred to as the smear layer.
 Eick and others,1970-Smeared layer.
 Mc Comb and Smith,1975 - Presence of smear layer-
instrumented root canals.
 Goldman and others 1982 - Smear layer after the use of
endodontic instruments.


What is Smear layer ?
 When tooth structure is 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.

 At the strategic interface of restorative materials and the
dentin matrix, most of the debris is scattered –enamel
and dentin www.indiandentalacademy.com
surface.

Definition

 Any debris ,calcific in nature,
produced by the reduction
or instrumentation of dentin,
enamel or cementum or as
a contaminant which
precludes interaction with
the underlying pure tooth
structure.
- Eick


Morphology of the Smear Layer

Formation
 Exact mechanism- incompletely understood.
 Boyde et al (1963)- Frictional heat during cavity
preparation –important factor.
 Frictional heat may be 600ºC below the melting point of
apatite -1800ºC to 2500ºC.
 Physiochemical phenomenon.


 Gwinett A.J. (1984) –Dentin richer source of protein than

enamel, so the dentin matrix may contribute to the smear

layer formed on enamel.

 Smear layer-by cutting when energy was expended.


Structure of smear layer

 SEM - Amorphous, irregular and

granular appearance.

 Eick et al (1970) - tooth particles –

less than 0.5µm to 15 µm.

 Pashley et al (1988) - Globular

subunits ,0.05 -0.1 µm -originated

from mineralized fibers.


 Light microscope-Smear layer is absent.

 SEM - undemineralized –low magnification-amorphous

apperance & dentinal tubules are obscured.

 Higher magnification-granular substructure.


Composition

 SEM : Organic and inorganic
 Organic : heated coagulated proteins (gelatin formed by
the deterioration of collagen heated by cutting
temperatures )
 Necrotic or viable pulp tissue
 Odontoblastic processes
 Saliva
 Blood cells and microorganisms.
 Inorganic
 Minerals from the dentinal structures
 Some non specific inorganic contaminants


Layers of the smear layer
 Cameron (1983) & Mader et al
(1984)- 2 parts
Superficial smear layer
Smear plugs
 Extension of the packed
material into dentinal tubules-
40µm
 Tubular packing phenomena-
action of burs & endodontic
instruments (Brannstrom and
Johnson 1974)
 Penetration of smear material
in to dentinal tubules-caused
by capillary action – Cengiz et
al (1990) www.indiandentalacademy.com

Thickness –Smear layer

 Goldman et al & Mader et al – 1-5µm
 Thickness depends on
Type and sharpness of the cutting instruments
Dry or wet cutting of the dentin
Size and shape of the cavity or root canal
Amount & chemical make up of irrigant used
 Thickest smear layer-10-15µm –coarse diamond blade
(Pashley)


Attachment to the dentin

 Gwinnet- smear layer is variable.

 Pashley – smear layer lying over the dentin is analogous

to wood being covered by wet saw dust.

 It is very tenacious but it is still permeable.


Smear layer after use of steel and
tungsten burs
 It produce an undulating pattern ,the troughs of which
run perpendicular with the direction of movement of the
handpiece.

 Fine grooves can be seen running perpendicular to the
undulations and parallel with the direction of rotation of
the bur - “Galling”
 Frictional humps represent a “rebound effect” of the bur
against the tooth surface.
 Galling phenomena - more marked with tungsten
carbide burs.
 Fine grooves can be related to small facets found on
cutting flutes of the bur.

Smear Layer– Carbide bur


Diamond burs

 Diamond points unlike carbide burs remove the dentinal

structure by abrading action.

 Fine diamond burs- thin & dense smear layer

 Coarse diamond burs-thicker &looser smear layer


 Absence of coolant- smeared debris can be found
commonly on the surface.
 It does not form a continuous layer but exists rather as
localized islands with discontinuities exposing the
underlying dentin.
 Coolant of water spray- reduce the amount and
distribution of smeared debris.


Smear layer after the use of rotary
instruments
Hero 642-Snowy appearence
ProFile-Shiny & burnished

Engine Reamers –thinner & Profile -Muddy Appearance
less compressed


PHYSIOLOGICAL CONSIDERATIONS

INFLUENCE ON PERMEABILITY OF DENTIN

Substances diffuse across dentin at a rate that is proportional
Concentration gradient
Surface area available for diffusion.

The area available for diffusion in dentin is determined by
Density of the tubules
Diameter of the tubules.

Theoretical area of diffusional surface varies from about 1% at DEJ
to 22% at the pulp.

Pashley distinguished between fluid movement inwards
from the dentin surface and outwards from the dentinal tubules.

‘Diffusion ’ as the movement of fluid from a high to low
concentration. The rate of such movements varies with square
of radius (r 2 ).

‘ Convection’ as the pressure gradient in the tubules which
results in a tendency for fluid outflow from the tubules ends.
This varies with fourth power of radius (r 4 ).


(d4) (2π) (∆P)
Fluid flow = ----------------- = 16 x
(n) (L)

The presence of smear layer - effect on the resistance
to movement of fluid across dentin by modifying tubule
radius.

Pashley & Others in 1978 - 86% of the total
resistance to flow of fluid.

After etching with acid, the rate of flow of fluid increased
-15 fold and (Reeder and Others 1978) 32 fold.

Pashley - smear layer is removed

Diffusion - ↑ 5 – 6 times.
Convection - ↑ 25 – 26 times


INFLUENCE ON SENSITIVITY OF DENTIN

 Dentin sensitivity-open tubules in exposed
dentin (Brannstrom 1982 ).
 Pashley et al- Movement of fluid in dentinal tubules –
Dentin sensitivity.
 Etching dentin greatly increases the ease with which fluid
can move across dentin.
 ↑ sensitivity of dentin to osmotic, thermal and tactile
stimuli.


 If dentin is sensitive, then according to hydrodynamic

theory of dentin sensitivity, the dentinal tubules must be

patent and must allow movement of fluid across dentin.

 The presence of smear layer will prevent bacterial

penetration of the tubules but will permit bacterial

products to diffuse slowly into pulp.


PATHOLOGICAL CONSIDERATIONS

a) Bacteria in the smear layer under restorations:

 Brannstrom and Nyborg, 1971- growth of bacteria under
silicate restorations.17 of the water cleaned cavities, with
smear layer remaining, numerous bacteria were present.
Antiseptically cleaned & restored cavities-bacteria present.

 Bacteria may multiply on cavity walls even if there is no
appreciable communication to the oral cavity seems to indicate
that certain microorganisms get sufficient nourishment from
the smear layer and dentinal fluid.

b) Smear layer on dentin exposed to oral cavity

When a smear layer is produced experimentally on human dentin,

and left exposed, it disappears after a couple of days and is

replaced by bacteria and after a week all most all tubules are

opened and some even widened.

The consequence is the invasion of bacteria.


c)The protective effect of smear plug in tubule
apertures and the consequences of removing the
plugs
 Vojinovic, Nyborg and Brannstrom, 1973 - Etching the
cavity prior to the placement of composite resin -massive invasion of
bacteria into 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 dentinal tubules.

Smear plugs in the aperture of the tubules -prevented bacterial
invasion.


 Pashley (1984) - smear plugs reduced the permeability
of dentin.

 Etching and removal of smear plugs and peritubular
dentin - area of wet tubules may increase from about
10% to 25% - Garberoglio and Brannstrom, 1976

 Difficult to dry the dentin.


d) Pulpal irritation due to removal of smear layer

Cut dentin should not be treated with acid or EDTA -tubules become
open and widened.

e) Smear layer in root canals after reaming

Carlson. L. Mader, J. Craig Baumgartner . Root canals
- instrumented with k-type files and irrigated with 5.25% NaOCl
solution.

The smeared material -2 components

Smeared layer on canal walls (1-2 µ m )
Depth of tubule packing -few µ m to 40 µ m


Smear layer in restorative dentistry

 Operative cutting process-smear layer.
 Before restoration the layer

Left in place
Dissolved
Can be replaced
Modified or impregnated.

 Various studies-bacteria entrapped in the smear layer may
survive and multiply under restorations.


Composite resin restorations

 Early bonding agents utilizing the smear layer. Bond
strength-un satisfactory.
 Newer bonding system –partially or totally removed or
impregnate the smear layer.
Cements
 Glass ionomer and polycarboxylate-removal of smear
layer.
 10 % polyacrylic acid,30 %citric acid or hydrogen
peroxide and distilled water.


Dahl (1978) - pumicing the dentin - three fold
increase in the tensile strength of the bond .

When cements are applied to dentin covered with a
smear layer and then tested for tensile strength

The failure - either adhesive (between cement & smear layer)
or cohesive (between constituents of smear layer)


Tensile strength of a cement-dentin interface,

 Remove the smear layer by etching with acid.
 Use a resin that would infiltrate through the entire
thickness of the smear layer.
 To fix smear layer with glutaraldehyde (Hoppenbrouwers ,
Driessens & stadhouders, 1974) or tanning agents such as
tannic acid or Ferric chloride (Powis & other ,1982).
 To remove the smear layer by etching with acid and replace
it with an artificial smear layer composed of crystalline
precipitate(causton & Johnson,1982).

Bowen used 5% ferric oxalate….

Cast restorations
 While cementing cast restorations- pressure generated on
and inside the casting .
Since the cement is an incompressible liquid, it will transfer this
pressure of fluid on and in dentin.
Displacement of fluid in dentinal tubules.
Thus it may be movements of fluid rather than the acidity of the
cement, produces pain and pulpal irritation.

 The ease with which fluid can be forced across dentin is
formalized by a term called “Hydraulic conductance ”.

 Volume of fluid transported across a known area of surface
per unit time under a gradient of unit pressure (Reeder &
Others, 1978).

SMEAR LAYER IN ENDODONTICS

If a smear layer containing bacteria or bacterial products
-allowed to remain within pulp chamber or root canals,it might
provide a reservoir of potential irritants.

Apical Leakage

 Kennedy-absence of smear layer-less apical leakage.
 Removal of smear layer would improve gutta percha seals if
master cones are softened with chloroform and used with
sealer and lateral condensation.
 Plasticized gutta percha –dentinal tubules-smear layer is
absent –mechanical lock between the guttapercha and the
canal wall.

B.Sealers

Endodontic sealers acts as a glue to -good adaptation of
gutta percha to the canal walls.

If the smear layer is not removed, the gutta percha may partly
be glued to dentin in the smear layer as well as to the exposed
parts of the canal wall.

Removing the smear layer from the root canals permits
increased tensile strength of plastic posts(Goldman &
others,1984).


ROLE OF SMEAR LAYER IN
BONDING
 Smear layer-removed or
altered-strong adhesive
bond.
 Acid etching of the dentin
Pka of the acid
PH
Chemical concentration&
Viscosity.


Adhesive Strategies-A Scientific
Classification of Modern Adhesives.
 3 Adhesion strategies-interact with the smear layer.

1.modify the smear layer &incorporate it in the bonding
processes.

One and two step

2. removes the smear layer .

Two-step and three-step

3. Dissolves the smear layer.

One and two step

Smear layer –Modifying Adhesive
 Smear layer –natural barrier to
the pulp.
 Protecting it against bacterial
invasion.
 Limiting the outflow of pulpal
fluid.
 Effective wetting and in situ
polymerization of monomers-
micromechanical +chemical
bond. www.indiandentalacademy.com

Smear layer –Removing Adhesives
 Removal of smear layer-total-etch
concept.
 Three-step smear layer –removing
adhesives.
 With the newest generationof one-
bottle or single-bottle adhesives -3
step smear layer removing
systems-reduced to two steps.


Smear Layer-Dissolving Adhesives
 Self-etching adhesives.

 Self-etching primers partially
demineralize the smear
layer & the underlying dentin
–with out removing
dissolved smear layer
remnants or unplugging the
tubule orifices.

Smear Layer Treatment and Dentin
Bonding Agents

 To chemically attach a restorative system to tooth

structure one of several options must be considered for

the smear layer.

 Smear layer is managed- 5 ways (John et al).

 1. No treatment at all. Smear layer is left intact.

Eg. Scotch Bond 2 and prisma.


 Dissolution : Dissolved smear layer plays a part in the
chemical attachment of dentin bonding
agent.
Eg: Scotch bond 2 and Mirage bond.

Treatment agent :SB-2 -Maleic acid.
Mirage Bond-HEMA
 Removal: Gluma
Treatment agent-EDTA.


Modification

Eg: XR Bond, All bond

 Treatment agent: XR Bond-ethyl alcohol,po4 ester.

All bond- Succinic acid &HEMA

Removal & Replacement Eg-Tenure –replaces the smear

Layer with oxalate crystals which are deposited in the

dentinal tubules.

 Treatment agent –Nitric acid, Aluminium oxalate.


Advantages
Smear layer-Acts as a Biological Bandaid.
It affords a drier surface for adhesion.
Dentinal fluid flow rate –reduced in the presence of smear
layer.
Bacterial penetration –dentinal tubules is prevented.

Disadvantages
It do not afford adequate bonding of material to dentin through
them.

It affect the physiologic status of the odontoblastic process in
the underlying dentin.


 25-30 % porous –cant produce totally effective sealing.

 Failure of retrograde filling following apical surgery.

 Avenue for leakage of microorganisms & a source of

substrate for bacterial growth.

 Viable bacteria-remain in dentinal tubules use the smear

layer –sustained growth &activity.


Methods of removal-smear layer

Smear layer removal is a controversy –fluctuates
with the various modalities of restorative dentistry.

Pashley-removing most of the smear layer over the
tubules is difficult to achieve clinically - complex geometry of
many cavities .

Irrigating solutions - used during and after instrumentation to
increase cutting efficacy of root canal instruments and to
flush away debris.


The efficacy of the irrigating solution is dependent on :

Chemical nature of solution

Quantity and temperature

Contact time

Depth of penetration of irrigation needle

Type and gauge of needle

Surface tension of irrigating solution

Age of solution (Ingle 1985).


SODIUM HYPOCHLORITE

NaOCl -organic tissue dissolving capacity.

Use of NaOCl during or after instrumentation - superficially
clean canal walls with smear layer present (Baken et al
1975, Goldman et al 1981).

Alternating use of hydrogen peroxide and NaOCl
Mc Combe and Smith (1975) - combination was not more
effective in removing smear layer than NaOCl alone
produced.


CHELATING AGENTS

Ethylene – Diamine tetra acetic acid
(EDTA) which reacts with calcium ions
in dentin -soluble calcium chelates
(Grossman et al 1988).

Fehr and Nygaard-Ostby (1963) -
Decalcified dentin to a depth of 20 – 30
µm in 5 mins.

Fraser (1974) - chelating effect
-negligible in apical third of root canals.
EDTA for 5 mins
In a combination, urea peroxide was
added (Rc-Prep) to float the dentinal
debris -root canal (Stevard et al 1969).

A quarternary ammonium bromide (Cetrimide) -added to
EDTA (Fehr and Nygaard – Ostby 1983).

Mc Combe and Smith,1975 -when this combination (REDTA)
was used -no smear layer except in apical part of canal.

EDTAC – Circumpulpal surface had a smooth structure;Dentinal
tubules-regular circular appearence. 15 mins-working time
(Goldberg and Spielbers, 1982).

-Salvisol - based on Aminoquinaldinum diacetate .
combined action of chelation and organic debridement .
Better cleansing properties than EDTA-C (Frenstiller et al 1988).


ORGANIC ACIDS

Citric acid -effective root canal
irrigant (coel 1975) and even more
effective than Naocl alone in
removing the smear layers
(Baumgartner et al 1984).
50% Citric acid
Citric acid removed smear
layer better -polyacrylic acid , lactic
acid and phosphoric acid except
EDTA .

Disadvantage -leaves precipitated
crystals.
www.indiandentalacademy.com Crystals of Ca & P

50% lactic acid ,
Canal walls -clean, but the
openings of dentinal tubules did
not appear to be completely
patent .
Bitter (1989)- 25 % tannic
acid-canals were cleaner & lactic acid
smoother than the walls treated –
H2O2 and NaOCl.
McComb et al (1976) - 5
% and 10 % polyacrylic acid-
remove the smear layer –
accessible regions. polyacrylic acid

SODIUM HYPOCHLORITE AND EDTA

 Smear layer - organic and inorganic components .

 Combination - NaOCl and acids such as citric ,tannic,

polyacrylic or chelating agents such as EDTA.
 Most effective working solution -5.25% NaOCl and the

most effective final flush was 10ml. of 17% EDTA followed by

10ml. of 5.25% NaOCl (Goldman et al.1982).


1% NaoCl & EDTA
5 mins


MTAD and NaOCl
 MTAD-mixture of tetracycline isomer
Acid (citric acid )
detergent (Tween -80)
PH-2.15- removing inorganic substances.
NaOCl- removes organic portion.

EGTA and NaOCl
Ethylene glycol-bis (B-amino-ethyl ether)-N,N,N,N-Tetra
acetic acid.
No erosion –intertubular and peritubular dentin.


SUGGESTED METHODS FOR REMOVING SMEAR LAYER
Author Amount Solution

Goldman etal. (1981) REDTA 17% 20ml

Goldman etal. (1982) REDTA 17% 10ml
Naocl 5.25% 10ml

Yamada etal (1983) REDTA 17% 10ml
Naocl 5.25% 10ml

White etal (1984) REDTA 17% 10ml
Naocl 5.25 10ml

Ciucchi etal (1989) Naocl 3% 1ml
EDTA 15% 2ml

Gettleman etal (1991) EDTA 17% -

Ultrasonic removal

 A small file activated ultrasonically-fluid movement called
Acoustic streaming .

 Cameron (1988) - 2 % to 4 % NaOCl +ultrasonic energy-
removal of smear layer.

 Cameron (1983) -3-5 min irrigation-effective.

 Guerisoli et al- 15 % EDTAC +Distilled water or 1 %
Naocl.


Acoustic streaming

LASERS
Weichman & Johnson (1971) first

applied a laser to the root canals -to
seal the apical foramen in vitro -high

power CO2 laser.
Middle third

pashley et al (1992)- Co2 laser- dentin
permeability; melting smear layer.

Apical third

Nd:YAG laser- debris & smear layer
being removed or melted,fused and
recrystallized .(Harashima et al
1997).
Argon laser - efficient cleaning
activity on instrumented root canals
Middle third
(Harashima et al 1997)

Er : YAG laser -more effective - Ar
or Nd:YAG laser (Takalashi et. al.
1996)
Apical third

Potassium Titanyl phosphate (KTP) laser -wave

length of 532µm - remove smear layer and debris from root

canal. (Tenfik et. al 1998 )

Nano second-pulsed, frequency-doubled Nd:YAG

laser - smear layer removal (Arrastia-Jitosho et. al. 1998)


xenon chlorine (xecl) laser - 308 µm can melt dentine and
seal exposed dentinal tubules. (pini et. al. 1989, stabholz et.
Al)

Ar-fluoride (F) excimer laser–removal of peritubular dentine
at relatively high fluency (10 ~13 J/cm2) with melting and
resolidification of the dentinal smear layer (stabholz et. Al).


MICRO BRUSHES
Rotary and ultrasonic endobrushes - ISO length
contain 16mm. of bristles, - bristle diameters of 0.40, 0.50 ,
0.60 and 0.80mm.

Rotary activated micro brushes -300 RPM, helical
bristle pattern effectively -residual debris out of the canal in a
coronal direction.

Micro brushes designed for ultrasonic use- activate
NaOCl and 17% EDTA -produced cleaned canals.

Regardless of rotary versus ultrasonic activation,
microbrush can finish the preparation -17% EDTA for 1 min. to
clean the root canal system.


Conclusion

 Smear layer is seen as a part of our daily clinical
practice. Though its dimensions are in micrometers, it is
of strategic importance in restorative dentistry and
endodontics.

 To prevent the infection into the dentinal tubules,
microleakage, and for proper adhesion , it is advised to
remove the smear layer and smear plugs.


Thank you

smear layer /certified fixed orthodontic courses by Indian dental academy

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