SMEAR LAYER :

Introduction :

Unknown and unrecognized for years, the smear layer has become a

force to be reckoned with during the last decade. Most dentists know now it

exists but are often puzzled as to whether or not they should cope with it.

Since the smear layer has been recognized, dentist have come to realize that

they must renew their acquaintance with the science of dental materials so

they can understand the relationships of the products they work with to the

smear layer.

History :

Boyde et al (1963) were the first to describe and demonstrate the

presence of a “smear layer” on surfaces of cut enamel such a layer was

readily removed with sodium hypochlorite, leading them to conclude that

an organic layer containing apatite particles was deposited or smeared on

the enamel surface, through functional heat generated during cutting.

They believed that the heterogenous nature of enamel was the source of

the smeared components.

Provenza and Sardana (1996) evaluated means of removing debris

from enamel and dentin after the use of steel burs, diamond stones and

hand instruments. They reported variations in the degree to which debris

was removed. Detergents were relatively ineffective, EDTA left behind a

film, 0.1N hydrochloric acid was considered too destructive in its action,

hydrogen peroxide appeared to be most effective.

Nelsen and Zisman (1966) described the dynamics of cutting dental

tissues and appeared to imply the existence of an altered surface layer

due to elastic and plastic deformation of the tissue.

Eick et al (1970) found that surfaces cut dry are rougher and more

smeared than those in which water is used as a coolant. In the absence of

coolant, 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. Water coolant does not prevent

smearing but significantly reduces the amount and distribution of it.

Boyde et al (1963) attributed smearing of enamel to melting of the

tissue by functional heat. Studies have shown that temperatures will rise

upto 6000C in dentin when it is cut without a coolant. This value is

significantly lower than the melting point of apatite (i.e. 1500 – 18000C)

and has led to the conclusion that smearing is a physiochemical

phenomenon rather than a thermal transformation of apatite involving

mechanical shearing and thermal degradation of the protein. Plastic flow

of hydroxyapatite is believed to occur at lower temperatures than its

melting point and may also be a contributing factor to smearing.

Eick et al (1970) found the smear layer to be composed of an organic

film less than 0.5 m thick, included within it were particles of apatite

ranging from 0.5 – 15 m. They also found that coarse diamond burs

produced more smearing than tungsten carbide bur.

Eirich and Koblitz (1976) accounted for the formation of smear

layers especially in dentin by a brittle and ductile transition and

alternating rupture and transfer of apatite and collagen matrix onto the

surface. Dentin, comprising approximately 35% collagen matrix and

water, is a more abundant source of protein than enamel, which contains

approximately 2% protein matrix and water.

Researchers become aware of the endodontic smear layer by about

1975. It was first reported by Baker.

Tidmarsh in 1978, treated instrumented teeth with 50% citric acid

and found the dentin clear of smear layer and the dentinal tubules wide

open.

Goldman in 1979, demonstrated that the smear layer was tenacious

regardless of flushing with both a conventional and a perforated needle.

Two years, later, he tested various solutions individually and in

combination and concluded that chelating agent EDTA and sodium

hypochlorite was the best to remove the debris when used as a final

flush.

Baumgartner showed similar results with citric acid and sodium

hypochlorite.

Kennedy used warmed solution of sodium hypochlorite.

Cameron, used ultrasonics to produce a smear layer, found that the

layer was composed of two separate layers, each having a different effect

on the tubules and dependent on the time the ultrasonic was used.

White et al found that plastic filling material could penetrate dentinal

tubule when smear layer was removed.

Goldman discovered that smear layer removal improved the tensile

strength of post retention when the posts were cemented with a BIS –

GMA resin.

Mader, by SEM investigation measured thickness of the smear layer

and the depth of its penetration into the dentinal tubules.

Evans, injected thermoplasticized gutta-percha into canals after smear

layer removal and concluded that the presence or absence of the smear

layer had no significant effect on the apical seal.

Definition of smear layer :

According to Shwartz – “Any debris, calcific in nature, produced by

reduction or instrumentation of dentin, enamel or cementum or as a

contaminant that precludes interaction with the underlying pure tooth

tissue”.

What is smear layer ?

When tooth structure is cut, instead of being uniformly sheared, the

mineralized matrix shatters and considerable quantities of cutting debris

made of small particles of mineralized collagen matrix are produced that is

scattered over the enamel and dentin surfaces at the interface of restorative

materials and dentin matrix and is known as the “Smear layer”.

In endodontics, the smear layer results directly from the

instrumentation used to prepare the canal wall and is found only where the

wall is instrumented and not in uninstrumented areas.

Because it is a very thin layer and is soluble in acid it is not very

apparent. It cannot be seen in demineralized teeth as it dissolves in the

process of demineralization. It is only visible under SEM or TEM.

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.

The smear layer consists of two separate layers:

1) A superficial layer.

2) Loosely attached layer to dentin.

Dentin debris enters the orifices of the dentinal tubules and acts as a

plug (smear plug) to occlude the ends of the tubules.

The smear layer is made up of tooth particles ranging from less than

0.5 m to 15 m. The particles are composed of globular subunits

approximately 0.05 – 0.1 m in diameter which originated from mineralized

fibers. The thickness of this layer is 1-5 m. The depth entering the tubules

may be from a few m upto 40m. This tubular packing phenomenon is due

to action of burs and endodontic instruments. However Cengiz et al

proposed that the penetration of smear material into dentinal tubules could

be caused by capillary action as a result of adhesive forces between the

dentinal tubules and the smear layer. This hypothesis of capillary action

may explain the packing phenomenon observed by Aktener et al who

showed that this penetration was increased upto 110m.by the use of

surface achieve reagents as a working solution during endodontic

instrumentation.

One can conclude that a smear layer is present on all restoratively or

endodontically prepared teeth unless the dentin surface was treated with an

acid or a chelating agent.

Several factors may cause the depth of the smear layer to vary from

tooth to tooth – i.e. :

1) Dry or wet cutting of the dentin.

2) The size is shape of the cavity or root canal.

3) The type and sharpness of instrument used.

4) The amount and chemical make up of the irrigating solution.

5) 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.

6) The amount produced during automatic preparation as with gates –

glidden or post drills will be greater in volume than that produced by

hand filing. Instrumentation with K files and reamers and giromatic

files created similar surfaces.

If there is a difference in the rate of flow of fluid across dentin before

and after removal of the smear layer, the magnitude of rate change is an

indication of the thickness or density of the smear layer.

Filing a canal without irrigation or cutting without water spray will

produce thicker debris than otherwise similarly coarse diamond burs

produce thicker debris than carbide burs.

Dentin is composed of 2 different layers:

1) Superficial dentin (near the enamel).

2) Deep dentin (near pulp).

Smear layer on deep dentin contains more organic material than

superficial dentin. This is because of greater number of proteoglycans lining

the tubules or the greater number of odontoblastic processes near the pulp.

The adhesive strength of all cements is always 50% greater in

superficial dentin. This may indicate that the quality or quantity of the smear

layer found on superficial dentin may be greater than that produced in deep

dentin.

The movement of fluid across dentin meets a resistance directly

proportional to the quantity and quality of smear layer present. In vital teeth

the smear layer restricts the dentinal fluid from flushing the dentin surface.

It also hinders the chemical process that produces marginal seal. The

presence of smear layer, however, does not appear to restrict the adaptation

of freshly condensed amalgam to cavity surface.

In non-vital teeth, marginal seals are improved because of the lack of

moisture within the dentinal tubules. When the acid etch technique is used

the retention of the smear layer is not an important factor in the

development of a marginal seal around composite resin restorations. The

initial sealing process occurring under amalgam restorations may be

compromised because of the instability of the smear layer and its penchant

for leaching under the amalgam. This leaching process will produce a

widening of the amalgam – tooth micro crevice and ultimately weaken the

sealing mechanism.

Jodaikin proposed a conflicting theory about the smear layer in the

sealing mechanism of a restoration. He believed that a chemical effect was

in force that provided a substrate that interacted with the restoration

substrates or other substances that might find their may into the micro

crevices at the restoration – tooth interface. He theorized that the smear

layers presence provided an environment that was conducive to the

initiation and progression of the sealing mechanism. By restricting the

dentinal fluid from flushing the molecules that affected the seal from the

restoration – tooth interface, the smear layer may also play a physical as

well as chemical role in margin sealing.

According to some investigators, after a canal is instrumented the

smear layer produced can harbour bacteria and bacterial products that can be

a reservoir of potential irritants. The smear layer is a separate structure from

the underlying dentin and may crack open and pull away from the

underlying dentinal tubules. A situation like this could be harmful to the

foundation of gutta-percha obturated over the smear layer. Hence they

thought it best to remove the smear layer, though controversy still remains.

COMPONENTS OF THE SMEAR LAYER :

Though the exact proportion of the composition is not certain.

Is composed of

i) Organic component.

ii) Inorganic component.

Inorganic component is made up of tooth structure and some non-

specific inorganic components.

Organic component consists of 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 micro-organisms.

Advantages of smear layer :

1) Reduction of dentin permeability to toxins and oral fluids.

2) Reduction of diffusion (usually inwards by convection and outwards

by hydrostatic pressure) of fluids and prevents wetness of cut dentin

surface.

3) Bacterial penetration of dentinal tubules is prevented.

Disadvantages of smear layer :

1) It may harbour bacteria, either from original carious lesion or saliva,

which may multiply taking nourishment from smear layer or dentinal

fluid.

2) Smear layer is permeable to bacterial toxins.

3) The smear layer may prevent the adhesion of composite resin system,

bonding agents, GIC and polycarboxylate cements.

PHYSICAL BARRIER FOR BACTERIA AND DISINFECTANTS :

When pathologic changes occur in the dental pulp, the root canal

system can harbour several species of bacteria, their toxins and by products.

These bacteria are predominantly gram-negative anaerobes. The

morphology of the root canals is very complex therefore the mechanically

prepared canals contain areas not accessible by endodontic instruments and

bacteria will be found more in number in these areas.

Available evidence shows that bacteria and its by products present in

infected root canals may invade the dentinal tubules. Investigators have

reported the presence of bacteria in the dentinal tubules of infected teeth at

approximately half the distance between the root canal walls and the

cemento-dentinal junction. Bacterial penetration into the dentinal tubules is

seen upto 150 m. in the apical 2/3rd of the root. Thus even after

chemomechanical instrumentation of the root canal, some bacteria still

remain in the canal and dentinal tubules, for this reason, chemomechanical

cleansing is often supported by the use of disinfectants.

Drake et al showed that removal of the smear layer opened the

tubules, allowing bacteria to colonize in the tubules to a much higher degree

(10 fold) compared with roots with an intact smear layer, removal of smear

layer facilitates passive penetration of bacteria. It was shown that smear

layer delayed the penetration of proteus vulgaris but it was also found that

pseudomonas aeruginosa penetrated even thicker dentin slices by removing

the smear layer it self and by opening the orifices of dentinal tubules after

possible collagenase production. A. Viscosus, corynebacterium spp. and S.

sanguis also digested the smear layer and facilitated their penetration. Smear

layer is permeable even to large molecules such as albumin. Therefore this

layer is not a strict barrier to bacteria.

According to some authors the presence of smear layer may block the

antimicrobial effects of intracanal disinfectants into the tubules, various

medicaments have been proposed for disinfection of root canals, they are:

1) Traditional phenolic or fixative agents like camphorated mono

chlorophenol (CMCP), formacresol and cresatin.

2) Non – phenolic compounds like iodine potassium iodide & calcium

hydroxide.

Researchers found that in absence of smear layer, liquid camphorated

monochlorophenol disinfected the dentinal tubules rapidly and completely

but calcium hydroxide failed to eliminate enterococcus faccalis even after 7

days of incubation and hence concluded that smear layer did delay but not

abolish the action of the disinfectants. However following removal of smear

layer, bacteria in dentinal tubules can be easily destroyed and in this way, it

may be beneficial to use lower concentrations of antibacterial agents since

all these agents show some degree of toxicity to viable host cells.

Smear layer and microleakage :

An important consideration in endodontics is the ultimate seal of root

canals in order to prevent possible microleakage which may be the cause of

future failure of the root filling. Prepared dentin surfaces should be very

clean to increase the sealing efficiency of obturation. Smear layer on root

canal walls acts as an intermediate physical barrier and may interfere with

adhesion and penetration of sealers into dentinal tubules.

Investigators observed that plastic filling materials and sealers

penetrated into the dentinal tubules after removal of smear layer, and its

presence obstructed their penetration. The penetration in smear free groups

ranged from 40-60m.They concluded that tubular penetration may increase

the interface between the filling and the dentinal structures and thus may

prevent leakage. However there is no strong evidence to this statement.

Pashley et al observed extensive reticular network of micro-channels

with thickness of 1-20m around restorations that had been placed in

cavities with intact smear layer and this provided a passage for

microleakage to occur. They concluded that removal of smear layer

decreased microleakage but increased dentin permeability.

In a recent study it was definitely shown that coronal leakage of root

canal filling was less in smear free groups than those with smear layer.

Microleakage in root canal is very complicated and many variables

may contribute to it like anatomy and instrumented size of the root canal,

irrigating solutions, root filling techniques, physical and chemical properties

of the sealers and the infectious state of the canal etc.

Apical leakage :

According to Evan et al, the use of injected thermoplasticized gutta-

percha should be accompanied by the use of sealer regardless of whether or

not the smear layer has been removed. But Kennedy stated that an absence

of the smear layer causes less apical leakage than gutta-percha filled canal

with the smear layer intact. He also stated that the use of chelating agents on

the smear layer would increase apical leakage. He concluded that removal

of smear layer would improve gutta-percha seals if the master cones are

softened with chloroform and used with a sealer and lateral condensation,

technique.

The greater the degree of canal preparation, the smaller the amount of

apical leakage.

It is still inconclusive whether the presence of dentinal fillings or

plugs will enhance the seal of root canal filling as the dentinal plugs were

porous and permeable and apical leakage existed in some situations.

Sealers :

Endodontic sealers act as a glue to ensure good adaptation of gutta-

percha to the canal walls. If the smear layer is not removed then the gutta-

percha is not firmly attached to the dentin and the smear layer may laminate

off the canal wall and create a false seal, voids in the fill and an

environment for microleakage.

The type of sealer used has different implications once the smear

layer has been removed. For example Grossman sealer which is a powder

liquid combination, contains small particles in the powder that enter the

dentinal tubule orifices and create a secure interface between sealer and

canal wall, after the removal of smear layer, calcium hydroxide based

sealers promote the apposition of the cementum at the canal apex and seal it

off against microleakage by the formation of osteoid or dentoid type

material. Circulation of blood is needed for the calcium ion to promote new

tissue thus the calcium hydroxide sealers are effective for sealing only at the

root apex. If more cementum is going to form to create a better apical seal,

dentin chips at the apex of a root canal acts as a nidus for formation of hard

tissue. Bacterial contamination by the presence of a smear layer can prevent

this.

There is no practical advantage to the use of auto cure unfilled resin

as a seal over the tubules before gutta-percha oburation, as the resin would

be susceptible to moisture though lateral canals and the apex and upon

polymerization the resin would shrink creating a gap between the fill and

the canal wall.

The use of some dentin bonding agents to harden the smear layer to

the canal wall and to harden the apical plug is a subject of research and is

doubtful that the bonding agent would be antimicrobial to the bacteria in the

smear layer.

Post cementation :

Removal of smear layer increases the cementation bond and the

tensile strength of the cementing medium for post cementation.

Glass ionomer cements are effective in post cementation after smear

layer removal because the glass ionomer has better union with tooth

structure.

When the smear layer was removed by flushing with EDTA and

sodium hypochlorite rinse, the unfilled BIS. GMA resin (cementing media)

flowed into the exposed dentinal tubules and into serrations on the post,

improving retention vastly, and with the removal of smear layer and an

unfilled resin bonding agent, shorter posts can be used.

Functional implications :

1) Dental materials :

The presence of smear layer masks the underlying dentin matrix and

may interfere with the bonding of adhesive dental cements such as

polycarboxylates and glass ionomer that reacts chemically with the dentin

matrix. Zinc phosphate require dentin matrix for mechanical roughness to

aid in retention.

The cements that react chemically to smear layer rather than the

matrix of sound intertubular dentin produce a weaker bond as the smear

layer can be torn away from the underlying matrix, and when these cements

are tested for tensile strength, the failure can be either adhesive (between

cement and smear layer) or cohesive (between constituents of smear layer).

To increase the tensile strength of a cement dentin interface there are several

approaches:

1) Remove the smear layer by etching with acids. This procedure does

not injure the pulp if dilute acids are used for shorter periods of time ex:

etching dentin with 6% citric acid for 60secs removes all the smear layer

as does 15secs of etching with 37% phosphoric acid. The advantages are

that the smear layer is entirely removed, the tubules are open and

available for increased retention and the surface collagen is exposed for

covalent linkage with new experimental primers for cavities.

The disadvantage is that there is a physical barrier for bacterial

penetration and the permeability of dentin increases.

2) Another 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 of Scotch bond is due to this process. The bond is stronger

between resin and pumiced dentin that between resin and etched dentin.

Removing smear layer with acid etching exposes surface collagen and

removes peritubular dentin from the top 5-10 m. of the tubules, yielding

a tubule with a funnel shaped orifice. If the resin penetrates only into the

funneled portion of tubule rather than where the tubules are normal and

of uniform diameter then retention would be less due to diverging tubule

walls rather than normal parallel walls of unetched tubules. Additionally,

acid etching demineralizes the surface which lowers the adhesive bond

between cement and minieralized dentin.

The adhesive strength of clearfil resin to dentin with a smear layer

present was as high as polycarboxylate and glass – ionomer cement. Etching

dentin doubled the adhesion of clearfil resin to etched superficial dentin.

Acid etching and removal of smear layer increases the adhesive

strength of composite resin to superficial dentin by 800 – 1000% over that

of deep dentin even though far more tubules are available for penetration of

resin. 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.

3) Another approach is to fix the smear layer with gluteraldehyde or

tanning agents such as tannic acid or ferric chloride. This increases 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.

4) A fourth and most convenient approach is to remove the smear layer

by etching with acid and replace it with an artificial smear layer

composed of a crystalline precipitate. Bowen used this approach by

treating dentin with 5% ferric oxalate which replaces the original smear

layer with a new complex permitting extremely high bond strength to be

produced between resin and dentin.

ENDODONTICS :

Smear layer might provide a reservoir of potential irritants. Alternate

use of sodium hypochlorite and EDTA is employed to remove smear layer.

The sodium hypochlorite removes organic material and collagenous matrix

of dentin and EDTA removes mineralized dentin thereby exposing more

collagen.

Removal of smear layer results in better adaptation of obturating

materials and sealers to dentin. Goldman also demonstrated increased

tensile strength of plastic posts after smear layer removal as these is more

penetration of resin into the open dentinal tubules.

Restorative dentistry :

When cementing a casting or condensing amalgam and during normal

mastication there is considerable force or pressure applied to the tooth. This

pressure is transferred to dentin which causes movement of dentinal fluid

and displacement of fluid into the pulp that might cause pain. The presence

of smear layer can prevent this phenomenon to a certain extent.

Influence on sensitivity and permeability of dentin :

Sensitivity of dentin is due to movement of fluid (hydrodynamic

theory of pain) most of the resistance to the flow of fluid across dentin (86%

of total resistance) is due to the presence of smear layer. Etching dentin to

remove the smear layer greatly increases the ease with which fluid can

move across dentin. This is accompanied by increased sensitivity of dentin

to osmotic, thermal and tactile stimuli.

Though the smear layer is permeable to bacterial toxins and its by

products to a certain extent but it still reduces the permeability of bacteria as

compared to smear layer free area. Transport of material across dentin can

be by 2 ways :

1) Diffusion.

2) Convection.

In diffusion, there is movement of substance from higher to lower

concentration and the concentration of the substance is dissipated over a

distance.

In convection, movement of substance is due to a pressure gradient

but no dissipation of concentration occurs.

It is shown that removal of smear layer increases dentin permeability

by diffusion by about 5-6 times and convection by 25-36 times.

Different treatment modalities on smear layer :

1) No treatment of the smear layer at all eg- PRISMA.

2) No removal of smear layer, just partial demineralization.

3) Complete removal of smear layer.

4) Modification of smear layer by keeping smear plugs intact.

5) Removal of natural smear layer and replacement by artificial smear

layer. eg – ferric oxalate.

Removal of smear layer :

Irrigating solutions have been used during and after instrumentation

to increase cutting efficiency and flush away debris. The efficacy of the

irrigating solution is not only dependent on the chemical nature of the

solution but also on the quantity and temperature, the contact time, depth of

penetration of the irrigating needle, type and gauge of the needle, surface

tension of the irrigating solution and age of the solution.

Sodium hypochlorite :

The organic tissue dissolving activity of Naocl is well known and its

increases with rising temperatures. However, the capacity to remove smear

layer from instrumented canal has been found to be insufficient. It produces

a superficially Clean canal wall with smear layer present.

Alternating use of hydrogen peroxide and Naocl solutions that was

advocated in the past was no more effective than Naocl used alone. It was

seen that the effect produced by Naocl was similar to that produced by

water. Adding surface active reagents also did not improve the situation.

Chelating agents :

The most common chelating solutions are based on ethylene diamine

tetra acetic acid (EDTA) which reacts with calcium ions in dentin and forms

soluble calcium chelates.

It was shown that EDTA decalcified dentin to a depth of 20 – 30 m.

in 5 min, but its chelating effect was almost negligible in the apical third of

root canals.

Another preparation i.e. EDTA in combination with urea peroxide

(RC-prep) was used to float the dentinal debris from the root canal but

despite further instrumentation and irrigation a residue of this mixture was

left on the canal walls which was a disadvantage in hermetic sealing of the

root canal.

A quarternary ammonium bromide (utrimide) has been added to

EDTA (REDTA) solutions to reduce surface tension and increase

penetrability of the solution. When this combination was used during

instrumentation, there was no smear layer left except in the apical third of

the canal.

Another combination used was EDTAC i.e. EDTA with cetavlon. It

was seen that optimal working time of EDTAC is 15mins after which no

more chelating action takes place.

Another root canal chelating agent is Salvizol – based on amino

quinaldinum diacetate. It has surface acting properties similar to materials of

the quaternary ammonium group and possess the combined action of

chelation and organic debridement.

It was shown that REDTA was the most efficient irrigating solution

in removing smear layer.

Organic acids :

Citric acid appeared to be an effective root canal irrigant and was

more effective than Naocl alone in removing the smear layer, it was also

better than polyacrylic acid, lactic acid and phosphoric acid but not EDTA.

It was shown that canal walls treated with 10%, 25% and 50% citric

acid solutions were free of smear layer, but the best results were with

sequential use of 10% citric acid and 2.5% Naocl solution then again

followed by 10% citric acid. It was however observed that 25% citric acid –

Naocl group was not as effective as 17% EDTA – Naocl combination,

besides citric acid left precipitated crystals in the root canals which was a

hinderence during root canal obturation, with 50% lactic acid, the canal

walls were generally clean but the dentinal tubules openings were not

completely patent.

Another root canal irrigant cleanser used was 25% tannic acid. It was

demonstrated that the canal walls irrigated with this solution appeared

significantly cleaner and smoother than the wall treated with a combination

of Naocl and hydrogen peroxide and that the smear layer was removed.

The use of 20% polyacrylic acid was found as better than REDTA.

5% and 10% polyacrylic acids also removed smear layer but only in

accessible regions.

Sodium hypochlorite and EDTA : (method of choice)

The purpose of irrigation is two folds:

a) To remove gross debris originating from pulp tissue and

bacteria -organic component.

b) To remove smear layer – inorganic component.

Because there is no single solution which has the ability to dissolve

organic tissues and to demineralize the smear layer, a sequential use of

organic and inorganic solvents have been recommended. For example the

alternate use of EDTA and Naocl for removal of smear layer and soft tissue

debris.

According to a study it was found that the most effective working

solution was 5.25% Naocl and the most effective final flush was 10 ml of

17% EDTA followed by 10 ml of 5.25% Naocl.

Ultrasonics :

According to Matrin and Cunningham, a continuous flow of sodium

hypochlorite solution (2.4%) activated by ultrasound delivery system that

was used for preparation and irrigation of the root canal also produced

smear free root canal surfaces.

Ahmad et al showed that with modified ultrasonic instrumentation

and 1% Naocl, smear layer could be removed.

It was observed that the apical region of the canals showed less debris

and smear layer than the coronal aspects, depending on the acoustic

streaming, which was more intense in magnitude and velocity at the apical

region of the file. It was seen that a 3-5min. Irrigation produced smear free

canal walls.

In contrast to these results. It has been found by other investigators,

that ultrasonic preparation was not able to remove the smear layer. This

contradiction may be due to physical contact of the file with the canal wall

that reduced the acoustic streaming.

Lasers :

Takeda et al found that lasers can be used to vapourize tissues in the

main canal, remove the smear layer and eliminate residual tissue in the

apical portion of the root canals. Effectiveness of lasers depends on many

factors including the power level, the duration of exposure, the absorption of

light in the tissues, the geometry of the root canal and the tip target distance.

Takeda et al using the erbium – yttrium – aluminium – garnet (Er:

YAG) laser demonstrated optimal removal of smear layer without the

melting, charring and recrystallization associated with other laser types like

neodymium – yttrium – aluminium garnet (Nd:YAG) laser, carbon dioxide

laser, organ fluoride excimer laser and organ laser. Although there was

removal of smear layer it showed destruction of peritubular dentin. The

main difficulties with lasers is the access to small canals as only large

probes are available for delivery of laser beam.

CONCLUSION :

The problem of smear layer is yet a controversy. To keep it or

remove it is still a problem , the solution of which still eludes us. It is upto

the dentists judgement , knowledge and understanding to treat the smear

layer or not.

Introduction :

History Definition of smear layer :

What is smear layer ?COMPONENTS OF THE SMEAR LAYER :Advantages of smear layer :

Disadvantages of smear layer : PHYSICAL BARRIER FOR BACTERIA AND DISINFECTANTS Smear layer and microleakage Apical leakage Sealers :Post cementation Functional implications :

1) Dental materials

ENDODONTICS :

Restorative dentistry :Influence on sensitivity and permeability of dentin :Different treatment modalities on smear layer Removal of smear layer

CONCLUSION :