Antimicrobial activity

According to Patterson,[²⁸] EDTA had limited antibacterial activity. It seems that the antibacterial activity of EDTA is due to the chelation of cations from the outer membrane of bacteria. Russell[²⁹] revealed that 10% EDTA produced a zone of bacterial growth inhibition similar to Creosote. However, lower concentrations of EDTA produced little to non-inhibition zone. Kotula and Bordácová[³⁰] indicated that the antimicrobial effect of Na-EDTA was maintained as long as the chelators have not formed bonds with metal ions. Yoshidaet al.[³¹] assessed the antibacterial activity of EDTA combined with ultrasonic activation clinically. After 7 days, without placing any intracanal medicament, most cases were bacteria-free. According to Heling and Chandler,[³²] RC-Prep was more effective against gram-negative bacteria than Gram-positive ones. According to Heling et al.[³³] increasing the temperature of RC-Prep from 10°C to 45°C increased its efficacy against Staphylococcus aureus. A study investigated the effect of components of RC-Prep onStreptococcus sobrinus. Findings revealed that minimum concentration for a bactericidal effect was 0.25% for EDTA and 50% for glycol.[³⁴] On the other hand, Orstavik and Haapasalo[³⁵] putted the antibacterial activity of 17% EDTA under question. Ordinola-Zapata et al.[³⁶] revealed that EDTA had no significant effect on the biofilm viability and architecture. Ballal et al.[³⁷] indicated that efficacy of EDTA againstEnterococcus faecalis was equivalent to maleic acid. Arias-Moliz et al.[³⁸] showed that EDTA had no efficacy against E. faecalis even after 60 min contact. Bystrom and Sundqvist[³⁹] demonstrated that combination of EDTA and 5% NaOCl had better antibacterial activity of NaOCl alone. Using the agar diffusion technique, Sen et al.[⁴⁰] revealed that EDTA was effective against Candida albicans.

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Effects on dentine microhardness

Pawlicka[⁴¹] reported that chelators can reduce the root dentine microhardness, whereby the greatest differences are to be found in dentine immediately adjacent to the root canal lumen. The effect of the chelator is already apparent after 5 min and cannot be significantly increased by extending the working time to 24 h.

Cruz-Filho et al.[⁴²] evaluated the effect of different chelating solutions on the microhardness of the most superficial dentin layer from the root canal lumen. Findings revealed that EDTA and citric acid had the greatest overall effect, causing a sharp decrease in dentin microhardness without a significant difference from each other. In another study, Ballal et al.[⁴³] found that there was no significant difference between EDTA and maleic acid in the reduction of microhardness of dentine.

Eldeniz et al.[⁴⁴] assessed the effect of citric acid and EDTA solutions on the microhardness and the roughness of dentine. Findings revealed that there was a significant difference in microhardness among the test groups, citric acid group being the least hard. In another study, Ari et al.[⁴⁵] as well as Cruz-Filho et al.[⁴⁶] confirmed decreasing dentine microhardness after using EDTA. De-Deus et al.[⁴⁷] assessed the effect of EDTA, EDTAC and citric acid on dentine microhardness and found that microhardness decreased with increasing time of application of chelating solutions. There were no significant differences between initial microhardness and after 1 min. After 3 min, EDTA produced a greater reduction in microhardness. However, there was no difference between EDTA and EDTAC after 5 min.

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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.

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