Efficacy of sodium hypochlorite, ethylenediaminetetraacetic acid,
citric acid and phosphoric acid in calcium hydroxide
removal from the root canal: a microscopic cleanliness
evaluation
Juliana Melo da Silva, MD, Amanda Silveira, Elizandra Santos, Laiìs Prado, and
Oscar F. Pessoa, DDS, Belém, Brazil
DEPARTMENT OF ENDODONTICS, FEDERAL UNIVERSITY OF PARÁ
Rooted molars were subjected to standardized canal instrumentation to a master apical file (MAF). The
samples were dressed with Ca(OH)2, and after 7 days, teeth were reopened and Ca(OH)2 medication was removed by
1 of 4 different experimental procedures: 2.5% sodium hypochlorite (NaOCl) (n ⫽ 10); 17% EDTA-T (n ⫽ 10); 10%
citric acid (n ⫽ 10); or 37% phosphoric acid (n ⫽ 10). This was followed by reinstrumentation with MAF plus 15 mL
saline solution. The roots were prepared for scanning electron microscopic analysis of the cervical, middle, and apical
thirds. Statistical analysis was performed with the Kruskal-Wallis test. EDTA-T and phosphoric acid gave the best
results in the apical third, with significant statistical differences compared with other groups. NaOCl gave the worst
results. Irrigation with 17% EDTA-T and 37% phosphoric acid is more effective than sodium hypochlorite and citric
acid in the removal of calcium hydroxide from the apical third. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod
2011;112:820-824)
To achieve the best adaptation of filling material, it is
necessary to clean the smear layer and debris from the
dentin wall as well as give intracanal medication.1
Calcium hydroxide medication is frequently used, because ⬍0.2% of the calcium hydroxide slurry dissociates at body temperature into calcium ions (Ca2⫹) and
hydroxide ions (OH⫺), leaving most of the particles
undissolved.2 The size and shape of the calcium hydroxide particles may allow direct penetration into the
open dentin tubules.3 If this medication is not completely removed, several studies have shown that the
presence of calcium hydroxide on the dentin walls can
affect the penetration of sealers into the dentinal tubules.4-7 The removal of calcium hydroxide has been
investigated using various products and techniques,
such as chelants to dissolve the inorganic particles in
the smear layer, and intracanal medications.8 EDTA-T
(EDTA plus sodium lauryl ether sulfate) is widely used
as the best irrigant to clean the smear layer, mainly
when it is associated with a cationic detergent, which
allows better diffusion and effectiveness.9,10 Another
efficient irrigant that is used for the same purpose is
citric acid, which is used at various concentrations.11,12
For removal of Ca(OH)2 the most frequently described
Received for publication Sep. 9, 2010; returned for revision Aug. 4,
2011; accepted for publication Aug. 6, 2011.
1079-2104/$ - see front matter
© 2011 Mosby, Inc. All rights reserved.
doi:10.1016/j.tripleo.2011.08.001
820
method is instrumentation of the root canal with the
master apical file (MAF) in combination with copious irrigation by sodium hypochlorite (NaOCl) and
EDTA.13 However, it has been reported that the removal of Ca(OH)2 from the root canal wall is difficult8,5,13 because instrumentation and irrigation alone
cannot completely clean the entire area.14 None of the
above techniques is efficient at removing all the material from the canal walls, leaving up to 45% of the root
canal surface covered with remnants.8 The aim of the
present study was to evaluate the efficacy of 2.5%
NaOCl, 17% EDTA-T, 10% citric acid, and 37% phosphoric acid in the removal of calcium hydroxide from
the coronal, middle, and apical thirds of the human root
canal system.
MATERIALS AND METHODS
Ethical clearance was obtained from the Ethical
Committee (CEP-ICS/UFPA 190/08) of the Federal
University of Belém, Pará, Brazil. Forty-eight distal
and palatal rooted human molar teeth were used in this
study. Preoperative mesiodistal and buccolingual radiographs were exposed for each root to confirm the canal
anatomy.
The criteria for tooth selection included: a single root
canal, no visible root caries, fractures, or cracks, no
signs of internal or external resorption or calcification,
and a completely formed apex. Roots with ⱕ5° of
curvature were considered to be straight and were included in this study. The teeth were decoronated to
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da Silva et al. 821
Fig. 1. Photomicrographs of root canal walls of apical third: A, score 0: no visible remnants of calcium hydroxide and dentinal
tubules exposed, B, score 1: scattered remnants of calcium hydroxide; C, score 2: densely packed remnants of calcium hydroxide
and dentinal tubules closed.
standardize the root length to 15 mm, and the working
length was established by inserting a #10 K-file
(Maillefer Instrumentos/Dentsply, Petrópolis, Brasil)
into each root canal until it was just visible at the apical
foramen (observed under magnifying loupes) and by
subtracting 1 mm from this point. This same file was
used during preparation and was introduced into the
canal until it was visible at the apical foramen to ensure
patency at all times.
The roots were subjected to standardized root canal
instrumentation (step-back technique) using a #45
MAF and were irrigated with 2.5% NaOCl after each
instrument, followed by 10 mL 17% EDTA-T as a final
rinse. Irrigation was performed using 5-mL disposable
plastic syringes with 27-gauge needle tips (Endo EZ;
Ultradent Products, South Jordan, UT, USA) placed
passively into the canal, up to 3 mm from the apical
foramen without binding.
The samples were dried and filled with Ca(OH)2
mixed with saline solution (1:1.5 w/v). Pastes were
positioned with a size 35 lentulo paste carrier until the
medicament was visible at the apical foramen. The
access cavities were temporarily sealed with a cotton
pellet and a filling (Cavit; Espe, Seefeld, Germany) to
a depth of 3 mm. They were then stored at 37 ⫾ 1°C
and 100% relative humidity for 7 days.
After 7 days, the teeth were reopened and the
Ca(OH)2 medication was initially removed using 10
mL saline solution and reinstrumentation with MAF
(#45) using a circumferential filing action. The patency
of the apical foramen was obtained by introducing a
#10 K-file until it was visible at the apical foramen
several times during the procedure.
After this, the samples were divided into 4 different
experimental groups: group 1: 5 mL 2.5% NaOCl (n ⫽
10); group 2: 5 mL 17% EDTA-T for 3 minutes (n ⫽
10); group 3: 5 mL 10% citric acid for 30 seconds
(n ⫽ 10); and group 4: 5 mL 37% phosphoric acid for
30 seconds (n ⫽ 10). A final flush was performed using
5 mL saline solution. Irrigation was performed under
the same conditions as in the instrumentation phase.
The negative control teeth (n ⫽ 4) were not filled with
Ca(OH)2, whereas the Ca(OH)2 was not removed from
the positive control teeth (n ⫽ 4).
Longitudinal grooves were then prepared on the buccal and lingual surfaces of each root with the use of a
diamond disk at a slow speed without penetrating the
canal. The roots were then split into 2 halves with the
use of a chisel and stored in deionized water at 37°C
until scanning electron microscope (SEM) analysis.
The samples were then mounted on metallic stubs, gold
sputtered using an ion sputterer, and examined under a
scanning electron microscope.
The selected dentinal surfaces of the cervical, middle, and apical thirds (9, 6, and 3 mm from the apex,
respectively), equidistant from the lateral walls, were
observed by SEM at ⫻1,000 magnification. Three calibrated examiners analyzed, independently and in a
blind manner, the removal of calcium hydroxide and
the cleanliness of the dentinal walls with the use of a
graded scale. The scale used was: score 0, no visible
remnants of calcium hydroxide and dentinal tubules
exposed; score 1, scattered remnants of calcium hydroxide and few dentinal tubules exposed; and score 2,
densely packed remnants of calcium hydroxide and
dentinal tubules closed (Fig. 1).
The interexaminer reliability was verified using the
kappa test. Statistical analysis was performed using the
Kruskal-Wallis test at the 5% level of significance.
RESULTS
The kappa test results showed that there was no
statistically significant difference between the 3 examiners’ values for scoring the calcium hydroxide in the
coronal, middle, and apical thirds in each group. All
irrigation regimens left debris on the canal walls. The
822
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da Silva et al.
Table I. Removal of Ca(OH)2 medication scores and median value
Kruskal-Wallis statistical analysis (P ⬍ .05)*
Score
0
Group 1—NaOCl
Coronal
Middle
Apical
Group 2—EDTA-T
Coronal
Middle
Apical
Group 3—citric acid
Coronal
Middle
Apical
Group 4—phosphoric acid
Coronal
Middle
Apical
1
2
Median
_
_
_
1
1
_
9
9
10
2.0
2.0
2.0
5
6
3
5
3
6
_
1
1
0.5
0.0
1.0
2
_
_
5
5
2
3
5
8
1.0
1.5
2.0
5
3
2
3
2
3
2
5
5
0.5
1.5
1.5
vs. thirds
Coronal
Middle
Apical
n.s.
A
a
a
n.s.
B
b
b
B
b
a
B
b
b
b
b
a
n.s.
n.s., Not significant.
*Statistical comparison between thirds of the same group and between groups. Different letters denote significant differences.
Fig. 2. Comparison of score distribution of calcium hydroxide removal among the test irrigants in the coronal, middle, and apical
thirds of the root canal system.
NaOCl group gave the worst results, with significant
differences in the cervical and middle thirds compared
with the other groups. EDTA-T and phosphoric acid
gave the best results in the apical third, with significant
differences compared with the other groups (Table I).
Figure 2 presents the comparative score distribution of
calcium hydroxide removal among the test irrigants in
the coronal, middle, and apical thirds of the root canal
system. In the apical third, NaOCl and citric acid gave
the worst results, with no significant differences compared with the positive control (P ⬎ .05). The positive
control teeth in all groups showed more densely packed
remnants in all thirds compared with the negative control.
DISCUSSION
Given that remnants of calcium hydroxide may interfere with the sealing ability of endodontic cement,4-7
several studies have tried to determine the best protocol
to remove all calcium hydroxide medication before root
canal filling. Besides antimicrobial and tissue-dissolving properties, the chemical substances used as irrigants
during biomechanical preparation should also have the
ability to lubricate and clean the root canal walls,
allowing better action of the intracanal medication and
proper adherence of the obturation material to the dentinal walls.15
The most common irrigant used to dissolve organic
tissues is NaOCl, in concentrations ranging from 0.5%-
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5.25.16-19 However, its capacity to remove the 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 remaining.20 In routine root canal treatment, the Ca(OH)2 is removed by instrumentation and
irrigating the canal with NaOCl solution before obturation.4 The present study showed the worst results for
calcium hydroxide removal in the NaOCl group, with
significant differences compared with all of the other
groups. Similar results were found by other authors.1,21,22
The most common chelating solutions are based
on EDTA, which reacts with the calcium ions in dentine and forms soluble calcium chelates.20 It is worth
mentioning that the use of 10% citric acid and 17%
EDTA-T for final irrigation has shown good results in
terms of smear layer removal, owing to its efficacy
against calcium ions, compared with other substances,
such as sodium hypochlorite.23 In the present study, the
efficacy of the chelating agents 10% citric acid and
17% EDTA-T did not differ significantly in the coronal
and middle thirds except for the apical third where 10%
citric acid was statistically less efficient, according to
other studies.1,24,25
To remove the inorganic component of root dentin,
phosphoric acid can be used at different concentrations
and applied in different ways.26-29 No earlier studies
have used phosphoric acid as a chemical substance to
remove the calcium hydroxide from the root canal.
Irrigation with 17% EDTA-T and 37% phosphoric acid
is more efficient than sodium hypochlorite and citric
acid in the removal of calcium hydroxide.
In the apical third, which is a crucial area for disinfection, 17% EDTA-T and 37% phosphoric acid
showed significantly better Ca(OH)2-removing ability
than 2.5% NAOCl and 10% citric acid.
The complete removal of calcium hydroxide can
improve the adaptation of filling materials to the root
canal. Further studies should be conducted to evaluate
the effects of remnants of calcium hydroxide on the
bond strength of endodontic sealers to root dentin and
on the apical and coronal microleakage that occurs with
most sealers currently used for canal filling.
CONCLUSION
According to this methodology and the limitations of
this study, NaOCl gave the worst results for calcium
hydroxide removal, with statistical differences in the
cervical and middle thirds compared with the other
groups. Irrigation with 17% EDTA-T and 37% phosphoric acid was more efficient than 2.5% sodium
hypochlorite and 10% citric acid in the removal of
da Silva et al. 823
calcium hydroxide from the apical root canal. Independently of the irrigator solution used, all experimental groups left remnants of Ca(OH)2.
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Reprint requests:
Juliana Melo da Silva
Rua Cônego Jerônimo Pimentel n° 900, apt° 1202
Umarizal, Belém, PA
Brazil
CEP: 66055-000
[email protected]