Studies have shown that
current methods of cleaning and shaping root canals produce a smear layer that covers
the instrumented walls. This layer contains inorganic and organic substances
that include fragments of odontoblastic processes,
microorganisms, and necrotic materials.
The advantages and
disadvantages of the presence of the smear layer created by root canal
instrumentation, and if it should be removed from instrumented root canals are
still controversial issues. Nowadays, the consensus is toward smear layer
removal. Various techniques and chemicals were used for smear layer removal
including the use of chelating agents, acids, ultrasonic agitation and laser…
Root canal treatment
can be summarized as a series of procedures access, cleaning, shaping and three
dimensional filling of the root canal system to prevent reinfection.
One of the principal
goals of root canal treatment is the cleaning of the entire root canal system
through the removal of pulpal debris, smear layer,
and smear plugs …
Structure of Smear Layer:
It has been recognized that root canal
instrumentation produces a smear layer that cover the surfaces of the prepared
canal walls. It is composed of debris compacted into the surface of dentinal
tubules by the action of instruments. It is burnished into the surfaces as the
edges of instruments slide by.
This layer contains inorganic and organic
substances that include fragments of odontoblastic
processes, microorganisms and necrotic materials.
Advantages and Disadvantages of Smear Layer:
Despite the controversy regarding the
effect of the smear layer on the quality of instrumentation and obturation, several investigators have found that the smear
layer itself may be infected and may protect the bacteria already present in
the dentinal tubules. Presence of this smear layer prevents
or delays penetration of intracanal medication, intracanalirrigants and
antimicrobial agents into the irregularities of the root canal system and the
dentinal tubules and also prevents complete adaptation of obturation
materials to the prepared root canal surfaces. Because of these concerns,
one may deem it prudent to remove the initially created smear layer in infected
root canals and to allow the penetration of intra canal medication into
Clinicians in favor of leaving the smear
layer intact argue that it may be a clinical factor that actually enhances endodontic success. It appears to plug the dentinal tubules,
microbes and tissue included preventing bacterial egress from the tubules after
the consensus is toward smear layer removal in order to reduce the microflora and associated endotoxins,
enhance the sealing capability of obturating
materials and decrease the potential of the bacteria to survive and reproduce.
Methods of Smear Layer Removal:
ultrasonic instruments, and lasers have been used to remove the smear layer.
vCombination of Sodium Hypochlorite and EDTA:
The components of the
smear layer are very small particles with a large surface-mass ratio, which
make them very soluble in acids. Because of this characteristic, acids have
been used to remove the smear layer. At present, chemical conditioning is the
only way to obtain complete cleaning of dentinal walls. Smear layer removal
requires a combination of sodium hypochlorite (an organic solvent) and
substances active on inorganic compounds, including chelating agents (EDTA or REDTA)
or acids (orthophosphoric, polyacrylic,
tannic, maleic or citric acid) to remove both organic
and inorganic components.
Sodium hypochlorite (NaOCl) is the most commonly used irrigant
in root canal treatment, and has proven to be an excellent irrigating solution,
due to its tissue dissolving capability and microbicidal
activity. However, its action does not affect inorganic material. EDTA
complements the action of sodium hypochlorite, by chelating calcium ions in
dentine and making instrumentation of the root canal easier, and is effective
at neutral pH.
O’Connell et al (1) evaluated three solutions of EDTA
for their ability to remove the smear layer. All solutions
were adjusted to pH 7.1 using either sodium hypochlorite or HCl.
When the EDTA solutions were alternately used for root canal irrigation with
5.25% sodium hypochlorite, they completely removed the smear layer in the
middle and coronal thirds of canal preparations, but were less effective in the
of the EDTA solutions by themselves were effective in completely removing the
smear layer at any level. A final irrigation of the root canal system with
sodium hypochlorite after EDTA irrigation seems to produce the cleanest walls. The
alkaline tetra sodium salt, pH adjusted with HCl, is
more effective and performed equally as well as the more commonly used disodium salt (1).
The main disadvantages of the use of EDTA include its destructive
effects on coronal and middle thirds of root dentin and its limited antibacterial
are broad spectrum antibiotics that are effective against a wide range of
microorganisms. Tetracyclines have many unique
properties in addition to their antimicrobial effect .They have low pH in concentrated
solution and thus can act as a calcium chelator, and
they can cause enamel and root surface demineralization. The ability of the
tetracycline family of antibiotics to remove the smear layers has also been
studied. They have been used to demineralize dentin
surfaces, uncover and widen the orifices of dentinal tubules, and expose the
dentinal collagen matrix.
et al (2)investigated the
effect of a mixture of a tetracycline isomer, an acid, and a detergent (MTAD)
as a final rinse on the surface of instrumented root canals. Forty-eight
extracted maxillary and mandibular single-rooted
human teeth were prepared by using a combination of passive step-back and
rotary 0.04 ProFile taper nickel-titanium files.
Sterile distilled water or 5.25% sodium hypochlorite was used as intracanalirrigant. The canals
were then treated with 5 ml of one of the following solutions as a final rinse:
sterile distilled water, 5.25% sodium hypochlorite, 17% EDTA, or a new
solution, MTAD. The presence or absence of smear layer and the amount of
erosion on the surface of the root canal walls at the coronal, middle, and
apical portion of each canal were examined under a scanning electron
microscope. The results showed that MTAD is an effective solution for the removal
of the smear layer and does not significantly change the structure of the
dentinal tubules when canals are irrigated with sodium hypochlorite and
followed with a final rinse of MTAD(2).
In contrast to the destructive effects of 5-minute EDTA exposure, they
observed no significant dentinal erosion in a pilot project when the surfaces
of the root canals were in contact with MTAD for periods ranging from to 20 minute (2).
Citric acid (a week organic acid) has been
applied previously on the root surfaces altered by periodontal disease and
instrumentation in order to increase cementogenesis
and to accelerate healing and regeneration of a normal periodontal attachment
after flap surgery. In operative dentistry citric acid has been proposed as a
mild etchant for dental hard tissue. In endodontic research, substitution of EDTA with an aqueous
citric acid solution as an endodonticirrigant has recently been proposed (3).
DiLenarda et al (3)evaluated in
vitro the cleansing and smear layer removal capability of alternate canal irrigation
with citric acid and Sodium Hypochlorite. Eighty one teeth were divided into
three groups on the basis of the type of instrumentation then they were divided
on the basis of irrigation protocol: 5% sodium hypochlorite alone, sodium
hypochlorite alternated with 1 mol/L citric acid solution or a combination of
15% EDTA and Cetrimide solution. Results showed that
1 mol/L citric acid solution was as effective in removing smear layer as10% EDTA,
but was superior in specimens treated with ProFile 0.04
taper instruments. 10% EDTA and 1mol/L citric acid, both alternated with sodium
hypochlorite had an efficacy that varied with the duration of application. The
simple preparation, low cost, good chemical stability if correctly used and
their effectiveness even with short application times suggests citric acid irrigant suitable for clinical use (3).
with citric acid use:
One of the main problems associated with
using citric acid is its very low pH, whilst an EDTA solution is almost
neutral. Irrigation of the canal with both citric acid and sodium hypochlorite
ensures neutralization of the previous irrigant, with
a drastic modification of the pH inside the canal and the liberation of gaseous
Sodium hypochlorite and EDTA must be in
direct contact with the surface for effective action. Due to the small diameter
of root canals, it is often difficult for the irrigating solutions to reach the
apex of the tooth. Ultrasonically activated files may be a means of reaching
the entire length of the root canal with irrigating solutions. The cleaning
ability of such files is assisted by acoustic microstreaming.
et al (4) evaluated smear
layer removal by different irrigating solutions under ultrasonic agitation.
They used twenty recently extracted mandibular
incisors with a single root canal and divided them into four equal groups. Each
group was irrigated with either distilled water, 1% sodium hypochlorite alone
or associated with 15% EDTAC between each file size. The final group was not
instrumented but irrigated with 1.0% sodium hypochlorite and 15% EDTAC. A size
15 file energized by ultrasound was used with small amplitude filing movement
against the canal walls in all groups. Results
showed that groups irrigated with 1% sodium hypochlorite alone and that
irrigated with distilled water had canal walls covered with smear layer. Canals
irrigated with 1.0% sodium hypochlorite and 15% EDTA had less smear layer
throughout the canal, indicating that under ultrasonic agitation, sodium
hypochlorite associated with EDTAC removed the smear layer from root canal
walls, whereas irrigation with distilled water or 1.0% sodium hypochlorite alone
did not remove the smear layer. No statistical differences between root thirds
when groups were examined separately. The lack of differences between root
thirds may be explained by the low surface tension of the solution provided by
the cationic surfactant and the use of ultrasound.
The use of the laser beam, especially Nd:YAG laser, in the dental field
is well known and has been investigated by numerous researchers. In endodontic applications, Nd:YAG
laser can stop bleeding after pulpectomy or apicectomy, promote disinfection and sterilization, prevent
pain after treatment, seal dentinal tubules and remove debris and smear layer
from instrumented root canals.
Goya et al (5)evaluated the removal of smear layer at the apical stop by pulsed Nd:YAG laser irradiation with or
without black ink, and the degree of apical leakage after obturation
in vitro. Sixty extracted human single rooted teeth were used, instrumented up
to a size 40 K-file and then divided into three groups: group one was unlased, group 2 was treated with laser and the third group
was treated with laser and black ink. The laser was operated at 2 W and 20 pp
for 2 seconds, which is suitable for infected root canals without any injury to
periapical tissues. Results showed that all root
canal surfaces became melted, fused, and recrystallized
and in most cases the smear layer was also melted and fused to the dentinal
walls. 60% leakage was found in group1, 20% in group2 and no leakage in group 3.
Furthermore, the results demonstrated that the use of black ink enhanced the
effects of the Nd:YAG laser.
Therefore, after obturation, intimate contact between
obturating materials and root canal wall dentine was
achieved and a considerable reduction of apical dye penetration was observed.
It can be concluded that current methods
of root canal instrumentation produce a layer of organic and inorganic material
(smear layer) that may also contain bacteria and their byproducts. This layer
covers the instrumented walls and may prevent the penetration of intracanal medications into the dentinal tubules and may
affect close adaptation between root canal filling materials and the root canal
walls. This layer is removed by lasers as Nd:YAG laser which its effect is enhanced by the use of
black (Indian) ink, by ultrasonic agitation with 1% sodium hypochlorite combined
with 15% EDTAC, by organic acids as citric acid combined with sodium
hypochlorite, by chelating agents as the different salts of EDTA combined with
sodium hypochlorite and by the newest of all the MTAD which is effective when used as a
final rinse and cause no harm to the tissues…
1.O’Connell MS, Morgan LA, Beeler WJ,
Baumgartner JC.: A comparative study of smear layer
removal using different salts of EDTA.
J Endodon 2000; 26: 739-743.
2.Torabinejad M, Khademi A, Babagoli J, Cho Y, Johnson W, Boshilov K, Kim
J, Shabahang S.: A new solution to remove the smear
J Endodon 2003; 29: 170-175
3.R.DiLenarda, M. Cadenaro, O. Sbaizero.: Effectiveness of 1
mol/L citric acid and 15% EDTA irrigation smear layer removal.
IntEndod J 2000; 33: 46-52
4.Guerisoli DMZ, Marchesan MA, Walmsley AD, Lumley
PJ, Pecora JD.: Evaluation of smear layer removal by
EDTAC and sodium hypochlorite with ultrasonic agitation. IntEndod J 2002; 35: 418-421.