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
Time (in days)	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

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