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SHELF-LIFE OF 5% SODIUM HYPOCHLORITE SOLUTIONS
Jesus Djalma Pécora
Professor Titular da Faculdade de Odontologia de Ribeirão Preto
- USP |
Danilo M. Zanello Guerisoli
C.D., Estagiário do Laboratório de Endodontia da Faculdade
de Odontologia de Ribeirão Preto - USP e Bolsista CNPq |
Reginaldo Santana da Silva
Técnico em Química do Laboratório de Endodontia da
Faculdade de Odontologia de Ribeirão Preto - USP |
Luiz Pascoal Vansan
Professor Associado da Faculdade de Odontologia de Ribeirão Preto
- USP |
The effects of storage time and temperature on the stability of 5% sodium
hypochlorite solutions were studied for 18 months. The samples were stored
at ambient temperature, lower part of refrigerator (9 ºC) and receiving
direct sunlight. The available chlorine was determined quantitatively each
month by iodometric titration. All solutions showed degradation versus
time, and no significant difference in the chlorine loss was found among
the three groups.
Introduction
The use of sodium hypochlorite (NaOCl) as an anti-septic began by the end
of 18th century, with the water of JAVELLE (1792), a solution containing
sodium and potassium hypochlorite, according to PUCCI9. This author also
relates that Labaraque’s liquor, a solution containing 2.5% sodium hypochlorite,
appeared in 1820.
A solution containing 0.5% available chlorine with boric acid to reduce
its pH was proposed by DAKIN3, in order to disinfect wounds during World
War I.
The introduction of 5% sodium hypochlorite in dentistry was made by
WALKER13, reinforced by GROSSMAN and MAIMAN4.
The effects of sodium hypochlorite on the pulp tissue dissolution,
on the dentin permeability, on the cleaning of the root canal and its bactericide
action were studied by many authors, among them SHIH et al.10, PÉCORA6,
WAYMAN et al.14, BAUMGARTNER and CUENIN2, JOHNSON and REMEIKIS5, BARBOSA
et al.1 and PÉCORA7.
The purpose of this study was to investigate the effects of time and
storage temperature on the active chlorine loss of 5% sodium hypochlorite
solutions, for 18 months.
Material and Methods
The 5% sodium hypochlorite solution used in this study was dispensed
at the Endodontics Research Laboratory at FORP-USP, and its active chlorine
concentration was determined by iodometric titration. After this, the solution
was divided in three different groups, stored in amber glass bottles tightly
closed.
The different temperatures and ambient conditions used in this
research were determined by observing habits and situations found in dental
practices.
The bottles were kept in the following conditions for 18 months:
a) ambient temperature, away from sunlight; b) lower part of refrigerator
(9 ºC); c) receiving direct sunlight by the morning.
The quantitative iodometric titrations were made every 30 days,
three repetitions each in order to minimize the experimental error. The
amount of available chlorine of each experimental group was determined
after a arithmetic mean of the three results.
Results
Table 1 indicates the mean results of available chlorine found in
the 5% sodium hypochlorite solutions stored at different conditions and
their respective chlorine loss over the time.
|
Storage conditions
|
Time (in days)
|
Refrigerator
|
Ambient
|
Direct sunlight
|
Concentration
|
% loss
|
Concentration
|
% loss
|
Concentration
|
% loss
|
0
|
5,00
|
0,0
|
5,00
|
0,0
|
5,00
|
0,0
|
30
|
4,94
|
1,2
|
4,96
|
0,8
|
4,83
|
3,4
|
60
|
4,90
|
2,0
|
4,77
|
4,6
|
4,72
|
5,6
|
90
|
4,78
|
4,4
|
4,43
|
11,4
|
4,62
|
7,6
|
120
|
4,59
|
8,2
|
4,32
|
13,6
|
4,45
|
11,0
|
150
|
4,22
|
15,6
|
4,26
|
14,8
|
4,19
|
16,2
|
180
|
3,93
|
21,4
|
4,07
|
18,6
|
3,83
|
23,4
|
210
|
3,71
|
25,8
|
3,67
|
26,6
|
3,52
|
29,6
|
240
|
3,63
|
27,4
|
3,51
|
29,8
|
3,30
|
34,0
|
270
|
3,38
|
32,4
|
3,23
|
35,4
|
2,97
|
40,6
|
300
|
3,19
|
36,2
|
3,16
|
36,8
|
2,62
|
47,6
|
330
|
2,86
|
42,8
|
2,70
|
46,0
|
2,38
|
52,4
|
360
|
2,64
|
47,2
|
2,36
|
52,8
|
1,92
|
61,6
|
390
|
2,55
|
49,0
|
2,19
|
56,2
|
1,77
|
64,6
|
420
|
2,26
|
54,8
|
1,84
|
63,2
|
1,53
|
69,4
|
450
|
1,93
|
61,4
|
1,58
|
68,4
|
1,46
|
70,8
|
480
|
1,66
|
66,8
|
1,32
|
73,6
|
1,29
|
74,2
|
510
|
1,40
|
72,0
|
1,14
|
77,2
|
1,01
|
79,8
|
The Kruskal-Wallis test indicated that there were no statistic differences
between the results (p>0.05). The linear regression analysis showed correlation
by the level of 1%, indicating an inversely proportional relation between
the storage time and available chlorine of the solutions.
Figure 1 shows the degradation curves of the different experimental
groups.
Discussion
An essential factor in the success of an endodontic treatment is the correct
cleaning and disinfection of the root canal system. Its correct chemo-mechanical
preparation depends not only on the ability of the dentist, but also on
the quality of the products used.
Sodium hypochlorite solutions are of an unstable nature, due to the
high rates of available chlorine loss. Knowing this, the professional must
give preference to fresh prepared solutions, stored in amber glass bottles
tightly closed; by doing so there will be no risk of using a NaOCl solution
with available chlorine rates below nominal.
The statistical analysis showed that there is no influence of temperature
on the degradation of sodium hypochlorite solutions, when stored in amber
glass bottles tightly closed; the loss of active chlorine over time was
similar in the three different experimental groups.
The results found in this study allow to state that storage time exercise
great effect on the degradation of sodium hypochlorite solutions.
As can be observed in table 1, after approximately 300 days a 5% sodium
hypochlorite solution has its available chlorine reduced by half, no matter
where the solutions were stored. PISKIN and TÜRKÜN8, in a similar
experiment, found the same available chlorine loss in 5% NaOCl solutions
stored at 24 ºC, although state that this loss is reduced when the
solutions are kept in low temperatures.
The dentist doesn’t necessarily need to discard this solution; it can
be used in procedures where there is no need of high chlorine concentrations.
But, on the other hand, if the professional wants to use a 5% sodium
hypochlorite solution, he must do it in the 30 first days from the production
date (table 1). As many professionals prefer to use a sodium hypochlorite
solution with available chlorine concentrations of 4 to 5%, the product
can be used for 150 days from the production date.
After 510 days, it was observed that the solutions had only 1% of available
chlorine; this concentration is also very utilized in endodontics.
According to the methods used and results found in this study, we can
conclude that when the 5% sodium hypochlorite solution is kept in amber
glass bottle tightly closed, the available chlorine loss is directly proportional
to the storage time, independent of temperature conditions.
References
1. BARBOSA, S.V. et al - Influence of sodium hypochlorite on the permeability
and structure of cervical human dentine. Int. Endod. J. 1994, Nov, 27:06,
309-12.
2. BAUMGARTNER, J.C. CUENIN, P.R. - Efficacy of several concentrations
of sodium hypochlorite for root canal irrigation. J. Endod 1992, Dez, 18:12,
605-12.
3. DAKIN, H. D. - In the use of certain antiseptic substance in the
treatment of infected wound. Brit. Med. J.; (2):318-20, Aug. 1915.
4. GROSSMAN, L.I. & MEIMAN, B.W. - Solution of pulp tissue by chemical
agents. J. Amer. Dent. Ass., 28(2):223-5, Feb. 1941.
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