Smear layer is a controversial topic in the field of operative dentistry and endodontics. This presentation includes composition, concepts, structure, advantages, disadvantages, and removal methods of smear layer.

1. THE SMEAR LAYER IN
ENDODONTICS
Presented By : Dr. Arpit Viradiya
Guided By : Dr. Shubhprabhat Gupta
Dr. Sandeep Metgud

2. Introduction
• The term ‘Smear layer’ is used most
often to describe the grinding
debris left on dentin by cavity
preparation.
• However the term applies to any
debris produced iatrogenically by
the cutting, not only of dentin, but
also of enamel, cementum and
even the dentin of the root canal.

3. • The complete cleaning of the root canal
system has always been a problem in
endodontics.
• Although successful endodontics is based on
the fundamentals of diagnosis,
instrumentation and obturation, it is generally
recognized that debridement of the root canal
is the most important aspect of successful
endodontic treatment.

4. • Smear layer differ from dusty pattern of the
superficial debris in that it is the layer of
muddy material composed of an amorphous
layer of organic and inorganic debris and
sometimes bacteria and it is assumed that
debris and bacteria left inside the canal can
affect the prognosis of root canal treatment.

5. CONCEPTS of SMEAR LAYER:
• It is difficult to say when or by whom, the
concept of the smear layer was first
introduced.
• The earliest studies on the effects of various
instruments on dental tissues were those
reported by Lammie, Draycott in 1952.
• Their attempts were limited principally to light
microscope and it has consistently failed to
identify the smear layer

6. • Boyde et al (1963) were the first to describe
and demonstrate the presence of a “smear
layer”.
• They concluded that an organic layer
containing apatite particles was deposited or
smeared on the enamel surface, through
functional heat generated during cutting.

7. • 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, hydrochloric acid was
considered too destructive in its action,
hydrogen peroxide appeared to be most
effective.

8. • 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.

9. • Goldman in 1979, 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.
• 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.

10. Definition
• 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”.
• According to Cohen – “An amorphous, relatively
smooth layer of microcrystalline debris whose
featureless surface cannot be seen with the
naked eye.”

11. • The American Association of Endodontists
defined smear layer as a “surface film of debris
retained on dentin or other tooth surfaces like
enamel, cementum after instrumentation with
either rotary instruments or endodontic files”.
• According to DCNA (1990) “when tooth structure
is cut, instead of being uniformly sheared, the
mineralised matrix shatters. Existing on the
strategic interface of restorative materials and
the dentin matrix most of the debris is scattered
over the enamel and dentin surface to form what
is known as smear layer”.

12. • 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.

13. • 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:
– A superficial layer.
– Loosely attached layer to dentin.

14. • 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 40m.

15. • Several factors may cause the depth of the
smear layer to vary from tooth to tooth –
– Dry or wet cutting of the dentin.
– The size and shape of the cavity or root canal.
– The type and sharpness of instrument used.
– The amount and chemical make up of the
irrigating solution.

16. • 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.

17. • Dentin is composed of 2 different layers.
– Superficial dentin (near the enamel).
– 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.

18. • 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.

19. • 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.

20. • 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.

21. Factors affecting formation of smear
layer in endodontics
• Type of Instruments :
– Increased centrifugal forces resulting from the
movement and the proximity of the instrument to
the dentine wall forms a thicker and more
resistant smear layer (Jodakin and Austin, 1981)
and thus the amount produced during automatic
preparations, as with Gates-Glidden or post drills,
will be greater in volume than that produced by
hand filling.

22. • Dentin cut wet / dry :
– Filing a canal without irrigation (or cutting without
a water spray) will produce a thicker layer of
dentin debris and smear layer.
• Proximity of the instrument of dentin walls:
– More closely the instrument to dentinal walls
more is the centrifugal forces producing thicker
smear layer.

23. • Size and shape of root canals
– The authors explained that, on account of the
reduced dimension of the root canal, air bubbles
frequently remain trapped and prevent total filling
with the irrigant.
– Mechanical stirring with a lentulospiral removes
the air bubbles, favors improved contact of EDTA
with the canal walls, and takes the solution to
areas that are not reached by the irrigating
needle.

24. COMPONENTS OF THE SMEAR LAYER
• Though the exact proportion of the
composition is not certain.
• Is composed of
– Organic component.
– Inorganic component.
• Inorganic component is made up of tooth
structure and some non-specific inorganic
components.

25. • 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.

26. Advantages of smear layer in
endodontics
• Reduction of dentin permeability to toxins and
oral fluids.
• Reduction of diffusion (usually inwards by
convection and outwards by hydrostatic
pressure) of fluids and prevents wetness of
cut dentin surface.
• Bacterial penetration of dentinal tubules is
prevented.

27. Disadvantages of smear layer
• It may harbour bacteria, either from original
carious lesion or saliva, which may multiply taking
nourishment from smear layer or dentinal fluid.
• Smear layer is permeable to bacterial toxins.
• Smear layer itself is infected. (Presence of
bacteria)
• The smear layer may prevent the adhesion of
composite resin system, bonding agents, GIC and
polycarboxylate cements.

28. • It blocks the antimicrobial effects of intracanal
disinfectants and increases disinfecting tissue.
• Presence of smear layer would necessitate use
of higher concentration and / or amount of
anti bacterial agents.
• Acts as a intermediate physical barrier,
interfere with adhesive penetration of sealers
(Obturating materials) with dentinal tubules.

29. 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.

30. • 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.

31. • 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.

32. • 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.

33. • 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.

34. • 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:
– Traditional phenolic or fixative agents like
camphorated mono chlorophenol (CMCP),
formacresol.
– Non – phenolic compounds like iodine potassium
iodide & calcium hydroxide.

35. • 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.

36. 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.

37. • Smear layer on root
canal walls acts as an
intermediate physical
barrier and may
interfere with
adhesion and
penetration of
sealers into dentinal
tubules.

38. • 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 40-60m.
• They concluded that tubular penetration may
increase the interface between the filling and
the dentinal structures and thus may prevent
leakage.

39. 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.

40. 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.

41. • 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 tubules and create a
secure interface between sealer
and canal wall.

42. • 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.

43. • 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.

44. • Urethane dimethacrylate
(UDMA) based root canal
sealers have been introduced.
• Their aim is to provide a better
bond to allow less
microleakage and increase the
fracture resistance of root filled
teeth through the creation of
monoblocks, when a core
material such as Resilon
replaces gutta-percha.

45. • Some studies indicate that smear layer
removal leads to higher tubule penetration,
increased sealer to dentine bond strength and
enhanced fluid-tight seal.

46. 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.

47. • When the smear layer was removed by
flushing with EDTA and sodium hypochlorite
rinse, the unfilled BISGMA 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.

48. Functional implications
• 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.

49. • 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).

50. • To increase the tensile strength of a cement
dentin interface there are several approaches:
• 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.

51. • 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.

52. Methods to remove the smear layer
• Chemical removal:
– The quantity of smear layer removed by a material
is related to its pH and the time of exposure
(Morgan & Baumgartner 1997).
– A number of chemicals have been investigated as
irrigants to remove the smear layer.
– According to Kaufman & Greenberg (1986), a
working solution is the one which is used to clean
and irrigate the canal.

53. • Chlorhexidine, whilst
popular as an irrigant and
having a long lasting
antibacterial effect through
adherence to dentine, does
not dissolve organic material
or remove the smear layer.

54. • Sodium hypochlorite:
– The ability of NaOCl to dissolve organic tissues is
wellknown (Rubin et al. 1979) and increases with
rising temperature (Moorer & Wesselink 1982).
– However, its capacity to remove smear layer from
the instrumented root canal walls has been found
to be lacking.
– The conclusion reached by many authors is that
the use of NaOCl during or after instrumentation
produces superficially clean canal walls with the
smear layer present (Baker et al. 1975).

55. Chelating agents
• Smear layer components include very small
particles with a large surface, which makes
them soluble in acids.
• The most common chelating solutions are
based on EDTA which reacts with the calcium
ions in dentine and forms soluble calcium
chelates.
• It has been reported that EDTA decalcified
dentine to a depth of 20–30 um in 5 min

56. • Different formulations of EDTA have been
used as root canal irrigants.
• In a combination, urea peroxide is added to
encourage debris to float out of the root
canal.
• Many studies have shown that paste-type
chelating agents, whilst having a lubricating
effect, do not remove the smear layer
effectively when compared to liquid EDTA.

57. • A quaternary ammonium bromide (cetrimide)
has been added to EDTA solutions to reduce
surface tension and increase penetrability of
the solution.
• McComb & Smith (1975) reported that when
this combination (EDTAC) was used during
instrumentation, there was no smear layer
remaining except in the apical part of the
canal.
• This study also showed that EDTAC was the
most efficient irrigating solution for removing
smear layer.

58. • Bis-dequalinium-acetate (BDA), a dequalinium
compound and an oxine derivative has been
shown to remove the smear layer throughout
the canal, even in the apical third.
• Salvizol (Ravens Gmbh, Germany) is a
commercial brand of 0.5% BDA and possesses
the combined actions of chelation and organic
debridement.
• Kaufman et al. (1978) reported that Salvizol
had better cleaning properties than EDTA.

59. • When comparing Salvizol
with 5.25% NaOCl, both
were found comparable in
their ability to remove
organic debris, but only
Salvizol opened dentinal
tubules.

60. • Tetracylines are antibiotics effective against a
wide range of microorganisms.
• Tetracyclines have unique properties in
addition to their antimicrobial aspect.
• They have low pH in concentrated solution,
and because of this can act as a calcium
chelator and cause enamel and root surface
demineralization.

61. • The surface demineralization of dentine is
comparable with that of citric acid.
• Barkhordar et al. (1997) reported that
doxycycline hydrochloride (100 mg mL-1) was
effective in removing the smear layer from the
surface of instrumented canals and root-end
cavity preparations.
• Hazne (2001) showed that 1% tetracycline
hydrochloride or 50% citric acid can be used to
remove the smear layer from surfaces of root
canals.

62. • In an effort to produce an
irrigant capable of both
removing the smear layer
and disinfecting the root
canal system, Torabinejad et
al. (2003) developed a new
irrigating solution containing
a mixture of a tetracycline
isomer, an acid, and a
detergent (MTAD).

63. • Their work concluded MTAD to be an effective
solution for the removal of the smear layer.
• It does not significantly change the structure
of the dentinal tubules when the canals are
irrigated with sodium hypochlorite and
followed with a final rinse of MTAD.

64. • Components of MTAD-
– Acids – EDTA, acetic acid, citric acid, tannic acid,
polyacrylic acid, bi- dequalinium acetate. This
helps to remove smear layer
– Tetracycline— Bacteriostatic and prevents
production of endotoxin.
– Detergent- Decrease surface tension and
increase penetrability.

65. Organic acids
• The effectiveness of citric acid as a root canal
irrigant has been demonstrated (Loel 1975,
Tidmarsh 1978) and confirmed to be more
effective than NaOCl alone in removing the
smear layer.
• Citric acid removed smear layer better than
polyacrylic acid, lactic acid and phosphoric
acid but not EDTA.

66. • Citric acid, in addition to removing the smear
layer, is a powerful antimicrobial agent, but its
antimicrobial action is not as great as that of
5.25 percent sodium hypochlorite, which acts
as a broad spectrum antibiotic effectively
against bacteria, bacteriophages, spores,
yeasts, and viruses.
• Combining the two, sodium hypochlorite
followed by 6 per cent citric acid would give
an ideal endodontic irrigant.

67. • Wayman et al. (1979) showed that canal walls
treated with 10%, 25% and 50% citric acid
solution were generally free of the smeared
appearance, but they had the best results in
removing smear layer with sequential use of
10% citric acid solution and 2.5% NaOCl
solution, then again followed by a 10%
solution of citric acid.

68. • However, Yamada et al. (1983) observed that
the 25% citric acid–NaOCl group was not as
effective as a 17% EDTA–NaOCl combination.
• Berry et al reported Polyacrylic acid at 40% to
be very effective for removal of the smear
layer.
• They have been used to demineralize dentin
surfaces, uncover and widen the orifices of
dentinal tubules and expose the dentin
collagen matrix.

69. Sodium hypochlorite and EDTA
• When irrigating a root canal the purpose is
twofold:
– To remove the organic component, the debris
originating from pulp tissue and microorganisms,
– And the mostly inorganic component, the smear layer.
• As there is no single solution which has the ability
to dissolve organic tissues and to demineralize
the smear layer, the sequential use of organic and
inorganic solvents has been recommended.

70. • Numerous authors have agreed that the
removal of smear layer as well as soft tissue
and debris can be achieved by the alternate
use of EDTA and NaOCl.
• Goldman et al. (1982) examined the effect of
various combinations of EDTA and NaOCl, and
the most effective final rinse was 10 mL of
17% EDTA followed by 10 mL of 5.25% NaOCl,
a finding confirmed by Yamada et al. (1983).

71. Ultrasonic smear removal
• Following the
introduction of dental
ultrasonic devices in
the 1950s, ultrasound
was investigated in
endodontics.

72. • NaOCl activated by an ultrasonic delivery
system was used for the preparation and
irrigation of canals and smear-free canal
surfaces were observed using this method.
• Researchers who found the cleaning effects of
ultrasonics beneficial used the technique only
for the final irrigation of root canal after
completion of hand instrumentation.

73. • This has given the term passive ultrasonic
irrigation.
• Ahmad et al. (1987) claimed that direct
physical contact of the file with the canal walls
throughout instrumentation reduced acoustic
streaming.
• Acoustic streaming is maximized when the tips
of the smaller instruments vibrate freely in a
solution.

74. • Baumgartner & Cuenin (1992) also observed
that ultrasonically energized NaOCl, even at
full strength, did not remove the smear layer
from root canal walls.
• Guerisoli et al. (2002) evaluated the use of
ultrasonics to remove the smear layer and
found it necessary to use 15% EDTA with
either distilled water or 1% sodium
hypochlorite to achieve the desired result.

75. Laser removal
• Lasers can be used to
vaporize tissues in the
main canal, remove the
smear layer and eliminate
residual tissue in the
apical portion of root
canals.

76. • The 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-to-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.

77. • The main difficulty with laser removal of the
smear layer is access to the small canal spaces
with the relatively large probes that are
available.

78. Conclusion
• The problem of smear layer is yet a controversy.
To keep it or remove it is still a problem.
• However, if the smear layer is to be removed the
method of choice seems to be the alternate use
of EDTA and sodium hypochlorite solutions.
• It is upto the dentists judgement , knowledge and
understanding to treat the smear layer or not.
• Clinical investigations are needed to determine
the role of smear layer in the outcome of root
canal therapy.

79. References
• Ingle’s Endodontics 6th Edition.
• Violich DR, Chandler NP. The smear layer in endodontics–a
review. International Endodontic Journal. 2010 Jan
1;43(1):2-15.
• Torabinejad M, Handysides R, Khademi AA, Bakland LK.
Clinical implications of the smear layer in endodontics: a
review. Oral Surgery, Oral Medicine, Oral Pathology, Oral
Radiology, and Endodontology. 2002 Dec 31;94(6):658-66.
• Czonstkowsky M, Wilson EG, Holstein FA. The smear layer in
endodontics. Dental Clinics of North America. 1990
Jan;34(1):13-25.
• Şen BH, Wesselink PR, Türkün M. The smear layer: a
phenomenon in root canal therapy. International
Endodontic Journal. 1995 May 1;28(3):141-8.

80. •Thank you