review on common root canal irrigants - Dharmsinh Desai University

JOURNAL OF DENTAL SCIENCES
Abstract:
Reader
REVIEW ON COMMON ROOT CANAL IRRIGANTS
Dept. of Conservative Dentistry & Endodontics,
Faculty of Dental Science, Dharamsinh Desai University,
College Road, Nadiad - 387 001. Gujarat, India
Dr. Kunjal S. Mistry M.D.S.
Dr. Shashin Shah M.D.S.
Volume 2 Issue 2
The triad of biomechanical preparation, pulp space sterilization and three-dimensional obturation is the hallmark of
endodontic success. Complete disinfection of the pulp space cannot be achieved with most sophisticated instrumentation
techniques. The role of irrigants in obtaining this goal cannot be underestimated. There is no single irrigating solution that
alone sufficiently covers all of the functions required from an irrigant. Optimal irrigation is based on the combined use of 2 or
several irrigating solutions, in a specific sequence. This article highlights the mechanism of action, safety and
biocompatibility of currently used irrigation solutions.
Key Words : Root Canal Irrigation, Mechanism of Actions, Chelators, Cytotoxicity
Introduction
Successful endodontic treatment requires combination of
variety of factors such as an accurate diagnosis, thorough
cleaning and shaping of the pulp space, a predictable
disinfection protocol achieved with the help of various
intracanal medicaments and irrigation solutions. This is
followed by three dimensional obturation of the pulp space
and adequate final restoration. Mechanical preparation of the
root canal achieved with the use of either hand instruments or
rotary nickel-titanium instruments helps in removal of vital
and necrotic remnants of pulp tissue, microorganisms and
microbial toxins to a certain extent. However, with the use of
recent imaging techniques, it is certain that some part of the
1
pulp space remains uninstrumented. These areas might
harbor necrotic tissues, microorganisms and their byproducts
resulting in persistent periradicular inflammation. Therefore,
irrigation is an essential part of debridement because it allows
for cleaning beyond what might be achieved by root canal
instrumentation alone.
Endodontic microbiology:
The role of microorganisms in infection of dental pulp and
periapical lesion formation has been elegantly demonstrated
2
in the classic studies of Kakehashi et. Al. Primary
intraradicular infection is caused by microorganisms that
invade and colonize necrotic pulp tissue. The microflora of
untreated teeth with necrotic pulp is usually found to be
mixed, comprising of Gram-positive and Gram-Negative
3
organisms, dominated by anaerobic bacteria. The
microorganisms associated with endodontic treatment failure
mainly comprised one or two species, these are
predominantly Gram-positive bacteria with Enterococcus
4
faecalis as the most prevalent organism. Fungi, specifically
Candida albicans can also be found at a significantly higher
5
rate than in primary infection. . The choice of irrigant solution
and irrigation protocol should be aimed at removal of all forms
of microorganisms including their presence in biofilm.
Desirable properties of Root Canal Irrigant as suggested
6
by Zehnder :
1. Broad antimicrobial spectrum
2. High efficiency against anaerobic and facultative
microorganisms organized in biofilm
3. Ability to dissolve necrotic pulp tissue remnants
4. Ability to inactivate endotoxins
5. Prevent formation of smear layer during instrumentation
or to dissolve the latter once it has formed.
6. Should be non toxic when they come in contact with vital
tissues, non caustic to periodontal tissues, and with little
potential to cause anaphylactic reactions.
The irrigating solutions that are currently used during
cleaning and shaping can be broadly categorized into
antibacterial and decalcifying agents or their combinations.
They include Sodium Hypochlorite (Here after Known as
NaOCl), Chlorhexidine Gluconate (Here after Known as
CHX), ethylenediaminetetraacitic acid (Here after Known as
EDTA), and a mixture of tetracycline, an acid and a detergent
(Here after Known as MTAD).
Sodium Hypochlorite (NaOCl):
Sodium hypochlorite (house hold bleach) is the most
frequently and dominantly used agent for root canal irrigation.
th
It has been known in medical fields since the beginning of 20
century and was introduced as a part of endodontic treatment
in 1936 by Walker. During the world war I the chemist Henry
Drysdale Dakin and surgeon Alexis Carrel extended the use
of buffered 0.5% NaOCl solution to the irrigation of infected
7
wound.
8
Mechanism of Action:
Two unique properties of NaOCl- antimicrobial activity and
organic tissue dissolution can be explained by following
reactions that takes place when it comes in contact with the
organic tissues or microorganisms.
Address for Correspondence :
Dr. Kunjal S. Mistry M.D.S.
Reader, Dept. of Conservative Dentistry & Endodontics,
Faculty of Dental Science, Dharamsinh Desai University,
College Road, Nadiad - 387 001. Gujarat, India
Ph: 9825334526 E-mail : Sharnam2005@yahoo.co.in
27

JOURNAL OF DENTAL SCIENCES
NaOCl acts as an organic and fat solvent, degrading fatty
acids and transforming them into fatty acid salts (soap) and
glycerol (alcohol) which reduces the surface tension of the
remaining solution.
NaOCl neutralizes amino acids forming water and salt. With
the exit of hydroxyl ions, there is reduction of pH.
Hypochlorus acid, a substance present in sodium
hypochlorite solution, when in contact with organic tissue acts
as a solvent and releases chlorine, which combines with
protein amino groups to form chloramines. The
chloramination reaction between chlorine and the amino
group (NH) forms chloramines that interfere in cell
metabolism. Chlorine has an antimicrobial action, inhibiting
bacterial enzymes and leading to an irreversible oxidation of
SH groups (sulphydryl groups) of essential bacterial
enzymes.
Concentration of NaOCl:
Various concentrations of NaOCl from 0.5% to 5.25% have
9,10
been tried out. Higher the concentration better will be
antimicrobial effect and tissue dissolving capacity. At the
same time higher concentration also carries the risk of toxicity
and tissue reaction. Literature is full of studies showing
severe irritations when concentrated solution were
inadvertently forced into the periapical tissues beyond apex
11,12
of the tooth under endodontic treatment. 5.25% NaOCl
has an unpleasant odour and this odour decreases as the
concentration decreases. From in vitro observations, it has
been shown that 1% NaOCl is sufficient to dissolve the pulp
13
tissue. Although less concentrated solutions have shown
14
antimicrobial efficacy higher concentrations of NaOCl
present faster and greater bactericidal effect. However, the
Volume 2 Issue 2
higher the concentration of this substance the greater is its
9
cytotoxic effects . Hence based on these studies, there is no
rationale for using hypochlorite solutions at concentrations
higher than 1%.
Increasing the efficacy of NaOCl:
1. Heating
An increase in temperature of low concentration NaOCL
solution increases its tissue dissolution and antimicrobial
properties. This is supported by a recent study where a
temperature rise of 25ºc. increased NaOCl efficacy by a
factor of 100. The capacity of 1% NaOCl at 45ºc. to dissolve
human dental pulp is found to be equal to that of a 5.25%
15
solution at 20ºc.
Ultrasonics:
Ultrasonic activation of sodium hypochlorite has also been
suggested to accelerate the chemical reaction, create
cavitational effects and achieve superior cleansing action.
When a small file (mostly ISO no. 15) is held free in an
enlarged canal filled with NaOCl and ultrasonically activated,
the ultrasonic energy warms the solution in the canal and the
resonant vibrations cause movement of aqueous NaOCl into
the difficult to reach ramifications in the canal, an effect called
16
“Acoustic streaming”. However, it appears important to
apply the instrument after the canal preparation has been
completed. An instrument that oscillates freely in the canal
gives more ultrasound effects in the irrigating solution than
the instrument that binds to canal wall. Therefore, to use a No.
15 file in an ultrasonic hand piece 1 mm. short of working
length, the canal should be enlarged apically at least to a size
25.
Chlorhexidine:
Chlorhexidine was developed in the late 1940s in the
6
research laboratories of Imperial Chemical Industries Ltd.
CHX is a cationic biguanide that possesses broad
antibacterial activity in combination with relatively low
toxicity and the ability to bind to skin and mucous
membranes.
Mechanism of Action:
The CHX molecule reacts with negatively charged groups on
the cell surface, causing an irreversible loss of cytoplasmic
constituents, membrane damage, and enzyme inhibition. At
high concentrations, CHX results in extensive cell damage,
coagulation of cytoplasm, and precipitation of proteins and
17
nucleic acids. CHX is a positively charged hydrophobic and
lipophilic molecule that interacts with phospholipids on the
cell membrane of bacteria and then enters the cell through
some type of active or passive transport mechanism. Its
efficacy is based on interaction between positive charge of
the molecule and negatively charged phosphate groups on
the bacterial cell wall that increases the permeability of cell
wall and allows it to penetrate into bacteria with intracellular
toxic effects. CHX at low concentration will result in
bacteriostatic effect but at higher concentrations, it is
bactericidal due to precipitation and/or coagulation of the
cytoplasm which is probably caused by protein cross-
18
linking.
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JOURNAL OF DENTAL SCIENCES
Antibacterial activity:
CHX is active against a wide range of microorganisms, such
as Gram-positive and Gram-negative bacteria, bacterial
spores, lipophilic virus, yeast, and dermatophytes, being
bacteriostatic at low concentrations and bactericidal at high
19
concentrations. CHX shows a substantial antimicrobial
activity against common endodontic pathogens like
staphylococcus aureus, Porphyromonas endodontalis,
foreign body granuloma formation at 2 weeks, which resolved
24
over time. To help evaluate the inflammatory response of 2%
Chlorhexidine, Tanamaru Filho et al. separately injected
0.5% NaOCl, 2% Chlorhexidine digluconate, and phosphatebuffered
saline into the peritoneal cavity of mice. This study
found the number of inflammatory cells resulting from 2%
CHX injection was similar to the phosphate-buffered saline
control at all times tested, while the 0.5% NaOCl injection
25
resulted in significantly larger number of inflammatory cells.
Ribeiro et al. evaluated the genotoxiciy of formocresol,
paramonochlorophenol, calcium hydroxide, and CHX against
Chinese hamster Ovary cells. Results showed that none of
26
the mentioned agents contributed to DNA damage. Thus, in
the clinically used concentrations, the biocompatibility of
CHX is acceptable.
While CHX has so many positive qualities, it lacks tissue
dissolution property. Naenni et al. used full thickness palatal
mucosa from pigs incubated in 10ml of 10% Chlorhexidine for
2 hours. At the end of 2 hours, the pig mucosa retained 90% of
its initial weight while 1% NaOCl caused the pig mucosa to
27
retain only 7% of the initial weight. Khademi et al. treated
fifty pieces of bovine pulp tissue with normal saline, MTAD,
2% Chlorhexidine digluconate and 2.5% NaOCl and
concluded that Chlorhexidine has the weakest tissue
28
dissolution capacity.
Chelator solutions:
Volume 2 Issue 2
Chelating agents were introduced into endodontics as an aid
in preparation of narrow and decalcified canals by Nygaard
–Ostby in 1957 who recommended the use of 15% EDTA at
pH 7.3.
EDTA and citric acid
Sodium Hypochlorite has a limited action of removing only the
Porphyromonas gingivalis, Prevotella intermedia,
organic contents from the smear layer, therefore
1 0 demineralizing agents such as ehylenediamine tetra acetic
Enterococcus faecalis, candida albicans. and
20
acid (EDTA) and citric acid have been recommended for
Streptococcus mutans. The antimicrobial action is related to
complete elimination of smear layer during root canal
type, concentration, and presentation form of the irrigants as
therapy. Chelating agents are available in both liquid and
well as the microbial susceptibility. The concentration often
paste forms. EDTA is used in 17% concentration and citric
used in endodontic therapy is 2% Chlorhexidine. This has
acid is used in the concentration of 10 to 20%. In vitro studies
been found to be more effective in the least time when
have shown their cytotoxicity, and 10% citric acid has proven
compared with other concentrations of Chlorhexidine ranging
20
to be more biocompatible than 17% EDTA-T and 17%
from 0.002% to 2%. CHX can be used in liquid or gel
29
EDTA.
formulations. The CHX gel makes instrumentation easier,
21
thus increasing the mechanical removal of tissues. MTAD
Furthermore it also decreases the smear layer formation It was introduced as an alternative to EDTA to remove the
22
which does not happen with liquid formulation.
smear layer by Torabinejad et al. It is a mixture of 3%
Cytotoxicity:
doxycycline, 4.25% citric acid and detergent-Tween 80. It has
30
a combined chelating and antibacterial properties. In the
Results from a laboratory study on the toxicity of CHX to
MTAD preparation, citric acid may serve to remove the smear
human gingival cells showed that the toxic potency of CHX is
layer allowing the doxycycline to enter the dentinal tubules
dependent on the length of exposure and the composition of
23
and exert an antibacterial effect. The effectiveness of the
the exposure medium. While Chlorhexidine does not appear
MTAD to completely remove the smear layer is enhanced
to cause any long-term damage to host tissues, it may still
when a low concentration of NaOCl (1.3%) is used as an
cause an inflammatory response in these tissues if
intracanal irrigant before placing 1 ml of MTAD in a canal for
expressed beyond root canal. Yesilsoy et al. injected 0.12%
five minutes and rinsing it with an additional 4 ml of MTAD as
Chlorhexidine into the subcutaneous tissues of the backs of
31
the final rinse. However, a final rinse with MTAD might have
pigs to help asses short term toxic effects. After histological
a negative effect on the bonding ability of both resin based
examination, they found a mild inflammatory response after 2
and calcium hydroxide based sealers due to the precipitate
hours, moderate inflammatory response after 2 days, and a
32
formation. MTAD also has been shown to adversely affect
the bond strength of Gutta-perch and AH plus filling material
33
to root dentin when used as final rinse.
Maleic Acid:
Maleic acid is a mild organic acid used as an acid conditioner
in adhesive dentistry. It efficiently removes the smear layer at
5% and 7% concentration. However, at 10% or more
concentration it can result in demineralization and damage to
34
root canal wall. Final irrigation with 7% Maleic acid is more
efficient than 17% EDTA in removal of smear layer from apical
third of the root canal system, which is a crucial area for
35
disinfection. Also 7% Maleic acid produces maximum
surface roughness on root canal walls as compared to 17%
EDTA. This surface roughness produces an important role in
36
micromechanical bonding of resin sealers. However, the
technique of use and biologic effects of Maleic acid on
periapical tissues needs evaluation, before it is routinely
employed for clinical use.
Tetraclean:
Tetraclean (Ogna Laboratori Farmaceutici, Muggiò (Mi),
Italy), like MTAD, is mixture of an antibiotic, an acid and a
detergent. However, the concentration of the antibiotic
(doxycycline-50 mg/ml), and the type of detergent
37
(polypropylene glycol) differ from those of MTAD. It shows
a high action against both, strictly anaerobic and facultative
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JOURNAL OF DENTAL SCIENCES
38
anaerobic bacteria. It removes the smear layer and opens
up the dentinal tubule orifices. It has low surface tension
which enables a better adaptation of the mixtures to the
37
dentinal walls. It is also more effective than MTAD against E.
faecalis in planktonic culture and in mixed species in vitro
39
biofilm. In another study, they compared the antimicrobial
efficacy of 5.25% NaOCl, MTAD, and Tetraclean against an
E. faecalis biofilm generated on cellulose nitrate membrane
filters. Only the NaOCl could disaggregate and remove the
biofilm at every time interval tested although treatment with
Tetraclean caused a high degree of biofilm disaggregation at
40
each time interval when compared with MTAD.
Interaction between commonly used irrigants
It is important to note here that both EDTA and citric acid
41
strongly interact with NaOCl. They immediately reduce the
available chlorine in the solution, rendering the sodium
hypochlorite irrigant ineffective on bacteria and necrotic
42
tissues. Hence, it has been suggested that citric acid or
EDTA should never be mixed with sodium hypochlorite. Once
irrigation has been completed with NaOCl, the remaining
NaOCl should be removed and only then should the irrigation
with EDTA begin.
CHX has no tissue-dissolving activity and there have been
efforts to combine CHX with hypochlorite for added benefits
from the two solutions. However, CHX and NaOCl are not
soluble in each other; a brownish-orange precipitate is
formed when they are mixed. Atomic absorption
spectrophotometry has indicated that the precipitate contains
43
iron, which may be the reason for the orange development.
Presence of parachloroaniline, which may have mutagenic
potential, has also been demonstrated in the precipitate. Until
this precipitate is studied further, its formation should be
avoided by removing the NaOCl before placing CHX into the
44
canal.
Conclusion
Irrigation has a key role in successful endodontic treatment.
Although NaOCl is the most important irrigating solution, no
single irrigant can accomplish all the tasks required by
irrigation. Detailed understanding of the mode of action of
various available and commonly used solutions is important
for optimal irrigation. New developments in the composition
of the irrigating solutions and mechanical devices used for
effective delivery of the solution in intricate areas of the root
canal system willhelp to advance safe and effective irrigation.
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