JADA Continuing Education
Dissolution of root canal sealers in EDTA and NaOCl solutions
Ali Keles, DDS and
Mustafa Köseoglu, DDS, PhD
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ABSTRACT
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Background. Solutions of ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) have been used as canal irrigants in endodontic treatment. The authors conducted a study to compare the ability of these solutions to dissolve sealers.
Methods. The authors assessed the solubility of six sealers—calcium hydroxide, polyketone, zinc oxide–eugenol, silicone and two epoxy resins—in EDTA and two concentrations of NaOCl (2.5 percent and 5.0 percent). They immersed standardized samples (n = 5) of each sealer for two minutes and 10 minutes. They obtained the mean values of sealer dissolution in solutions by calculating the difference between the original preimmersion and postimmersion weights to determine the amount of sealer removed. They compared the values via factorial analysis of variance. They analyzed differences between the six sealers with respect to their solubility in EDTA or NaOCl solutions at two minutes and 10 minutes by using a one-way analysis of variance (P < .05).
Results. In comparison with NaOCl solutions, EDTA was markedly superior in dissolving root canal sealers (P < .05). There were no significant differences between the two concentrations of NaOCl. The two epoxy resins and the silicone-based sealer were of low solubility. The zinc oxide–eugenol—based sealer was significantly more soluble than were the epoxy resins and the silicone-based sealers. Polyketone and calcium hydroxide–based sealers were the most soluble sealers (P < .05).
Conclusions and Clinical Implications. The results of this study indicate that during nonsurgical endodontic re-treatment, EDTA and NaOCl solutions used for removing smear layer aided in the retreatment by dissolving some root canal sealers.
Key Words: Sodium hypochlorite; ethylenediaminetetraacetic acid; solubility, sealersAbbreviations: EDTA: Ethylenediaminetetraacetic acid. • NaOCl: Sodium hypochlorite.
Despite being highly successful in general, some endodontic treatments do not respond to initial therapy for different reasons and, hence, necessitate retreatment. Removal of endodontic filling material from the root canal is a requirement for re-treatment.1
The most commonly used root canal filling material is gutta-percha in combination with a root canal sealer, because the use of gutta-percha without a sealer fails to seal the root canal system completely. Therefore, re-treatment of previously filled canals demands that both the gutta-percha and the sealer must be removed from the canal walls and anatomical ramifications to ensure complete cleaning of the root canal system during the chemomechanical preparation and application of antimicrobial dressings.2 Various removal methods are available, including the use of solvents, heat and mechanical instrumentation, alone or in combination.3 Usually, mechanical removal is accomplished by means of various chemical solvents.4
Different solvents for dissolving root canal filling material have been studied. Many solvents that would be effective for dissolving root canal–filling materials are considered too toxic.5 Some of these solvents have been reported to be cytotoxic6,7 and some to be potential carcinogens.8–10 The choice of an ideal solvent for endodontic re-treatment requires a balance between clinical safety in usage (substances with low toxicity and aggressivity toward tissues) and great chemical capacity for dissolution.11
Irrigation solutions are used in endodontic therapy to remove debris from the root canal, eliminate microorganisms and serve as a lubricant during instrumentation.12 The tissue-dissolving and disinfecting properties of sodium hypochlorite (NaOCl) make it the irrigant of choice. In endodontics, ethylenediaminetetraacetic acid (EDTA) is used to open calcified canals and eliminate potentially infected smear layers13,14 and is used as a lubricant during treatment of root canals.
Irrigating solutions have been analyzed from different points of view by several authors. Some of them looked for solutions capable of removing the smear layer15,16 or disinfecting the dentin and root canal system,17,18 and others compared the solutions’ cytotoxic effects.12,19,20 To our knowledge, no investigators have performed a study of the relative solubilities of root canal sealers in EDTA and NaOCl solutions. Therefore, the aim of our in vitro study was to compare the ability of EDTA and NaOCl solutions to dissolve six different root canal sealers.
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MATERIALS AND METHODS
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In this study, we examined 15 percent EDTA (Wizard, Rehber Chemistry, Istanbul, Turkey) and two concentrations (2.5 percent and 5.0 percent) of NaOCl (Wizard, Rehber Chemistry). We used six sealers (Table 1
): two epoxy resins (AH 26 and AH Plus, both manufactured by Dentsply DeTrey GmbH, Konstanz, Germany), a silicone (RSA, Roeko, Langenau, Germany), calcium hydroxide (Sealapex, Kerr, Salerno, Italy), polyketone (Diaket, 3M ESPE AG, Seefeld, Germany) and zinc oxide–eugenol (Endométhasone N Powder, Septodont, Paris). We used 180 standardized stainless steel molds 8 millimeters in diameter and 2 mm in height, and we drilled a 4 mm–diameter hole centrally in each mold for specimen placement (4 mm in diameter x 2 mm thick). We cleaned all molds with acetone for 15 minutes and weighed each three times before use. All weight measurements throughout the study were in grams recorded to four decimal places.
We mixed sealers in accordance with the manufacturers’ instructions and carefully introduced freshly mixed materials into sample molds. Because calcium hydroxide–based sealer requires moisture for setting,21 we mixed Sealapex with a spatula moistened with tap water. We left all samples to set at room temperature for 48 hours. We then trimmed excess material level to the surface of the mold with a scalpel. For each sealer, we prepared 30 samples, which we divided into three groups; we further divided each of those groups into two subgroups of five each according to immersion period (two minutes and 10 minutes). Thus, we prepared a total of 180 samples for this study. Before immersing the samples, we weighed all sealers in their molds three times and recorded the average reading.
At room temperature, we immersed sealer samples in 20 milliliters of solvent. The immersion was such that both surfaces of each sample were readily accessible to the solvent. We did not agitate the samples in the solutions.
We removed the sealer samples from the solvents after the specified immersion period (either two or 10 minutes) by using a pair of tweezers, touching only the metal mold. We then washed samples with 100 mL of double-distilled water. We placed the specimens on a grating in such a way that only the metal molds touched the grating and allowed them to dry for 24 hours. Thereafter, we weighed the samples three times and determined the amount of sealer removed from the specimen as the difference between the original weight of the sealer and its final weight.
Eighteen empty sample molds acted as controls in terms of solvent action on metal molds. We immersed three molds for two minutes and three others for 10 minutes in each of the three solvents and recorded any changes in weight.
We calculated the mean and SD values of weight loss at each time interval for each group of specimens. We compared the values by means of factorial analysis of variance by using commercially available software (SPSS 10.0, SPSS, Chicago). We analyzed differences between the six sealers with respect to their solubility in EDTA or NaOCl solutions at two or 10 minutes by using a one-way analysis of variance (P < .05). We further analyzed multiple comparison intervals to identify statistically homogeneous subsets (P = .05) by using the post hoc Duncan multiple range test (P < .05). We analyzed differences between the six sealers within each solution separately by means of the Duncan multiple range test (P < .01).
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RESULTS
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The weight of the empty molds did not change after immersion in either solution after any of the immersion periods. Table 2 presents a summary of mean values and SDs of dissolution recorded for the solvents. In comparison with NaOCl solutions, EDTA had a markedly superior ability to dissolve root canal sealers (P < .05). There were no significant differences between NaOCl solutions. The epoxy resin–based materials and silicone-based material were of low solubility. There were no significant differences between the weight loss of the two epoxy resin–based sealers and the silicone sealer after immersion in any of the three solvents at all exposure times (P > .05). The zinc oxide–eugenol—based sealer was significantly more soluble than were either the epoxy resin–based sealers or the silicone-based sealers (P < .05). Polyketone and calcium hydroxide–based sealers were the most soluble (P < .05). For some sealers, some solutions were more effective after 10 minutes than after two minutes. Both EDTA and 5 percent NaOCl effectively dissolved polyketone-based sealers in proportion to the contact time.
We found highly significant differences between sealer and immersion-period interactions with each solution (P < .01). In EDTA, the polyketone-based sealer exhibited the most solubility (0.0282 ± 0.0033) at 10 minutes (P < .01). The calcium hydroxide–based sealer was significantly more soluble than others (P < .01) at two minutes (0.0120 ± 0.0024) (Figure 1).
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Figure 1. Dissolution of sealers in ethylenediaminetetraacetic acid across time, shown as means and SDs (cross bars). Different letters between samples represent statistically significant differences (P < .01). AH Plus and AH 26 are manufactured by Dentsply DeTrey, Konstanz, Germany.
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In 5.0 percent NaOCl, the zinc oxide–eugenol—based sealer was significantly more soluble than other sealers (P < .01) at two minutes (0.0050 ± 0.0016). Zinc oxide–eugenol—based and polyketone-based sealers were the most soluble sealers (0.0048 ± 0.0008 and 0.0036 ± 0.0011) at 10 minutes (P < .01) (Figure 2).
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Figure 2. Dissolution of sealers in 5.0 percent sodium hypochlorite solution across time, shown as means and SDs (cross bars). Different letters between samples represent statistically significant differences (P < .01). AH Plus and AH 26 are manufactured by Dentsply DeTrey, Konstanz, Germany.
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In 2.5 percent NaOCl, zinc oxide–eugenol—based sealer exhibited the most solubility (0.0052 ± 0.0015 and 0.0062 ± 0.0015) at both time intervals (P < .01) (Figure 3).
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Figure 3. Dissolution of sealers in 2.5 percent sodium hypochlorite solution across time, shown as means and SDs (cross bars). Different letters between samples represent statistically significant differences (P < .01). AH Plus and AH 26 are manufactured by Dentsply DeTrey, Konstanz, Germany.
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Results of the Duncan multiple range test showed that the lowest solubility and disintegration in each solution occurred in the silicone and two epoxy resin–based sealers.
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DISCUSSION
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Considering the great success of most endodontic interventions, re-treatment is a conservative clinical approach in comparison with periapical surgery.22 A primary goal of re-treating previously filled root canals must be to remove all material and thereby disinfect the root canal system.
We used the method of evaluating root canal sealer solubility described by Whitworth and Boursin23 because it is simple, reproducible and cost-effective. In using this method, we could not consider several clinically relevant parameters—such as contact area, length of time of contact between root canal filling and solvents, temperature of solvents and dilution of solvent by biological fluids or irrigants—because of in vitro conditions.
Laboratory-based studies of the re-treatment of canals filled with laterally condensed gutta-percha and sealer revealed that the time required for removing material is approximately two to 10 minutes.24,25 Researchers in previous studies used the same immersion periods.22,23
We found that the silicone sealer and the two epoxy resin–based sealers demonstrated no statistically significant solvency in any of the three solvents (P > .05). It is possible that the plastic characteristic of silicone resulted in lower values of material loss through solvency.22 Results of previous studies have shown that AH Plus, one of the epoxy resins, was highly soluble in some solvents.23,25 Results of our study indicated that EDTA, 5.0 percent NaOCl and 2.5 percent NaOCl solutions are insufficient to dissolve AH Plus.
Martos and colleagues22 and Whitworth and Boursin23 reported that calcium hydroxide cements had a low solubility in solvents. In our study, calcium hydroxide–based sealer was significantly more soluble in EDTA than were sealers based on zinc oxide–eugenol, epoxy resins and silicone (P < .05).
Zinc oxide–eugenol exhibited greater solubility in both NaOCl solutions than did any other sealer material (P < .01). This sealer demonstrated similar solubility after two and 10 minutes for all solvents.
Several solvents have been recommended for dissolving root canal filling materials. All these solvents have some level of toxicity,6,7 so their use should be avoided if possible.26 Chloroform has been the most popular solvent in endodontics and is effective for gutta-percha removal.27 In 1976, the U.S. Food and Drug Administration banned the use of chloroform in drugs and cosmetics because of a report of suspected carcinogenicity.28 There was no associated ban on its use in dentistry.29 Benzene and xylene, which are effective solvents, may be potential carcinogens.10 Halothane, another solvent, is highly volatile.30 The high cost and volatility of halothane and its potential for inducing idiosyncratic hepatic necrosis make it a less desirable solvent.31 There are only a few published in vitro studies of the cytotoxic effects of NaOCl and EDTA solutions.12,19,20 These studies revealed that both EDTA and NaOCl are highly cytotoxic. To our knowledge, there have been no data in the literature regarding these materials’ carcinogenicity.
Mutagenicity and carcinogenicity are gaining increasing public interest. It easily can be argued that amounts of these materials absorbed by teeth and amounts absorbed in the course of dental treatment are negligible, but it must be emphasized strongly that a person is exposed to other mutagenetic substances—in the air, in clothing and textiles, in cosmetics—that always are present in the environment.32 Nowadays, solvents commonly used in endodontic practices, although criticized for their toxicity, have more capacity for dissolving sealers than do EDTA and NaOCl—and if they are used in a controlled manner at appropriate dose levels, they pose no health risk to the patient.31 All of the evidence published thus far, to our knowledge, has illustrated that it is difficult to eliminate filling materials from the walls of major canals completely during retreatment, and it presumably is more difficult to clean canals’ microscopic ramifications.23,33 Our findings indicate that during nonsurgical re-treatment, EDTA and NaOCl solutions used for removing smear layer helped by dissolving some root canal sealers.
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CONCLUSIONS
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In this study, we examined the ability of EDTA and NaOCl solutions, which commonly are used in endodontics, to dissolve some root canal sealers. Although they do not have as much dissolution effect as do other solvents commonly used in retreatment, the information that EDTA and NaOCl solutions used in the removal of smear layer can dissolve some sealers that can be left in root canals is going to be an advantage for EDTA and NaOCl solutions. These solutions may be of different concentrations in different countries. For further studies, therefore, investigators may want to compare the dissolution effect on sealers of various concentrations of these solutions or other irrigants, sealers’ dissolving capability when exposed to solvents other than those tested in our study and solvents’ cytotoxicity.
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FOOTNOTES
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Dr. Kele
is a research assistant, Department of Endodontics, Faculty of Dentistry, Atatürk University, Erzurum 25240/Turkey, e-mail "alikeles29{at}hotmail.com". Address reprint requests to Dr. Kele.
Dr. Köseo
lu is a professor, Department of Endodontics, Faculty of Dentistry, Atatürk University, Erzurum, Turkey.
Disclosure. Neither author reported any disclosures.
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ABSTRACT
MATERIALS AND METHODS
