Danilo Mathias
Zanello Guerisoli
FAPESP Fellow, Ribeirão Preto Dental School, University of São
Paulo, Ribeirão Preto, SP, Brazil
Reginaldo Santana
da Silva
Chemical Technician, Ribeirão Preto Dental School, University
of São Paulo, Ribeirão Preto, SP, Brazil
Jesus Djalma Pécora
Chairman of the Department of Restorative Dentistry, Ribeirão
Preto Dental School, University of São Paulo, Ribeirão Preto,
SP, Brazil
Department of Restorative Dentistry, Ribeirão Preto Dental School,
University of São Paulo
Av. do Café s/n
Ribeirão Preto, SP
Brazil
14040-904
For maximum efficiency, the shelf-life of these solutions must be observed, since the chlorine loss is rapid (PÉCORA et al.8, PISKIN and TÜRKÜN10, JOHNSON and REMEIKIS6).
Undoubtedly, sodium hypochlorite is the most used irrigating solution in the instrumentation of root canals worldwide. Due to the lack of information about the properties of these solutions, some physico-chemical properties (density, surface tension, pH, viscosity, wetting capacity and conductivity) of sodium hypochlorite solutions, at concentrations of 0.5%, 1.0%, 2.5% and 5.0% were studied in this investigation.
The densities of the solutions were obtained by the relation between mass and weight, using an electronic analytical balance (CG-Libror model 3200 H) and a graduated measuring glass (100 ml, Pyrex).
To determine the surface tension of the solutions, a tensiometer (Fischer Scientific, Surface Tensiomat 21) was used.
pH was measured with a pH meter (Digimed, DMPH-2).
The viscosity values were obtained using an Ostwald viscometer, based on the flow time of a liquid from a bulb through a capillary when subjected to its own weight. The flow time of the solution was compared with the time of a known viscosity liquid (water), thus, the viscosity of the solutions were obtained. Ten repetitions were made for each experimental group.
The wetting capacity measurements were made by the Draves method modified by PÉCORA et al.9: a 250 ml student beaker was filled with 200 ml of the liquid to be tested, leaving a 2 cm space from the border of the beaker to the surface of the solution. A 2-cm piece of thread (Corrente, 100% cotton) was then dropped from the border of the beaker, touching the surface of the liquid. The time spent for the thread to become completely wet and hit the bottom of the beaker was measured. Twenty repetitions for each solution were made.
The conductivity values were obtained by using an ohmmeter (Analion C-701).
All the measurements were made at 25 ºC.
Table 1: Mean values of the physico-chemical properties of the NaClO
solutions.
| Property |
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| Density (g/cm3) |
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| Surface tension (dynes/cm) |
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| pH |
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| Viscosity (centipoise) |
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| Wetting capacity (time) |
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| Conductivity (miliSiemens) |
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The density of the solutions changed in direct proportion to their concentration. The linear regression and correlation tests showed a direct relation between the results and a correlation at the level of 1.0%.
The results found for the surface tension indicate similar values for the NaClO solutions.
The pH test showed a direct relation between the solutions and correlation at the level of 1.0%.
Variance analysis showed significant statistical difference at 1% for the viscosity of the studied solutions.
The Tukey test showed that the solutions can be divided into 2 groups, with different values of viscosity. Group 1, formed by the 0.5% and 1.0% sodium hypochlorite solutions had the lowest viscosity values and group 2, formed by the 2.5% and 5.0% NaClO solutions had the highest.
The values for the wetting capacity of the tested solutions revealed that 1.0% and 2.5% sodium hypochlorite solutions are statistically the same; 0.5% NaClO has a lower capacity to wet the thread, while 5.0% NaClO has the highest wetting capacity.
The conductivity test showed less resistance to the electrical current as the concentration of NaClO increased.
The NaClO solutions showed surface tension values similar between them. These surface tension values are close of the value found for water (72.73 dynes/cm, PÉCORA et al.9). This can be undesirable, since a high surface tension can avoid the contact between the liquid and the surface.
Sodium hypochlorite solutions are alkaline and the higher their concentration, the higher will be the pH, due to the quantity of NaOH molecules present. The high pH values of sodium hypochlorite does not represent a disadvantage, since its action is limited to the surface of the tissue (ROSENFELD et al.11, THÉ et al.13).
The viscosity of the NaClO solutions increased with the NaClO concentration.
The wetting capacity of the solutions was dependent on the NaClO concentration, in a directly proportional relation (the shorter the time, the higher wetting capacity).
The conductivity of the studied solutions showed to be directly proportional to their concentrations. This can be explained by the number of available ions present in the media, higher in the more concentrated solutions.