INTERACTION BETWEEN EDTA AND NaOCL
The addition of chelators to NaOCl reduces its pH in a ratio and time-dependent manner. This affects the forms of free chlorine in the solution and causes an increase in hypochlorous acid and chlorine gas, which subsequently reduces the amount of the hypochlorite ion.[48] According to Zehnder et al.[49] when 1% NaOCl was mixed with 17% EDTA (pH = 8) in ratios of 1:1, 1:5 and 5:1, the pH of the solutions ranged between 8.0 and 8. Furthermore, they showed that the addition of 10% citric acid to 1% NaOCl in the same ratios resulted in pH values between 1.8 and 4.3.
Irala et al.[50] mixed 1-2% NaOCl with 17% EDTA in equal proportions, resulting in a final pH value of 8 from an initial value of 10 after an elapse of 48 h. However, when mixed in 1:3 ratio and although with a larger volume of EDTA, the pH value was stable during the 48 h experimental time, probably because of an immediate interaction between the solutions. According to Baumgartner and Ibay[51] the reduction of pH values in the NaOCl solution caused the release of chlorine gas, which has potentially hazardous effects on humans. When EDTA is added to NaOCl, chlorine gas can be detected at relatively low levels. When citric acid is used, significantly more chlorine is detectable and present at a further distance. This is according to a laboratory-based investigation that studied the reactions between NaOCl (5.25%, pH = 12.12) and citric acid (50%, pH = 1.28) or EDTA (15%, PH = 7.51). Portions of the chelator were added to the NaOCl at regular time intervals for a total time period of 2 h; the release of chlorine gas was measured at 6 inches and 6 feet from the container.[51]
The consequences of chemical interactions between chelating agents and NaOCl result in a loss in the free available chlorine of the mixtures. Zehnder et al.[49] indicated that when NaOCl was mixed with citric acid, free available chlorine decreased to 0 in less than a minute, whereas EDTA required between 1 and 60 min decreasing the free available chlorine to the same level. Clarkson et al.[52] confirmed the findings of Zehnderet al.[49] and found that the available chlorine loss was up to 80%.
Using the spectroscopy, Girard et al.[53] assessed the interactions of gel-type preparations of chelators containing 15% EDTA and 10% urea peroxide with 1% NaOCl. Findings revealed that both compounds depleted the solution from its chlorine content after 5 min.
The dramatic reduction of free available chlorine in NaOCl mixtures caused by chemical interactions appears to explain the inability of NaOCl and EDTA mixtures to dissolve soft-tissues.[48] Irala et al.[50] evaluated tissue dissolving ability of NaOCl (1-2.5%) alone and combined with 17% EDTA in different ratios (2:2 and 1:3). Findings indicated that after 48 h only unmixed NaOCl was able to completely dissolve the tissue. Grawehr et al.[54] confirmed the findings of Irala et al.[50] NaOCl does not reduce the calcium chelating or smear layer ability of EDTA and citric acid.[48] Using standardized dentin disks, Saquy et al.[55] assessed the calcium chelation ability of a combination of 17% EDTA and distilled water and a combination of 17% EDTA and 0.5% NaOCl and found that greater calcium chelation occurred in the solution containing NaOCl. Another study indicated that NaOCl had little effect on EDTA's calcium chelating ability.
Saquy et al.[55] revealed that the addition of NaOCl to EDTA did not alter EDTA's ability to decalcify human dentin. According to Grawehr et al.[54] as well as Zehnder et al.[49] if the original free available chlorine values were modest, chelators could eliminate the antimicrobial efficacy of NaOCl, whereas EDTA and CA performance did not seem to be affected because of interactions with NaOCl. Using agar diffusion test, Grawehr et al.[54] assessed the antimicrobial activity of EDTA, NaOCl and their combination against E. faecalis and C. albicans. According to their findings, NaOCl produced smaller zones of inhibition compared to EDTA or mixture of EDTA/NaOCl.
Go to: