Smear Layer Removal by EGTA

Printed in U.S.A. VOL. 26, No. 8, AUGUST 2000

JOURNAL OF ENDOCONTICS Copyright 0 2000 by The American Association of Endodontists

Smear Layer Removal by EGTA Semra Galt, DDS, PhD, and Ahmet Serper, DDS, PhD

ethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) is reported to bind Ca2+ more specifically (7). The purpose of this study was to evaluate the effects of EGTA on removal of the smear layer on the canal wall as an alternative to EDTA by using scanning electron microscopy (SEM). Smear layer was removed from the instrumented root canals by irrigation with 17% EGTA or 17% EDTA, followed by 5% NaOCl. The effects of these two processes were compared.

The purpose of this study was to compare the effects of ethylene glycol-bis (P-aminoethylether)N,N,Nr, W-tetraacetic acid (EGTA) and EDTA on removal of the smear layer by using scanning electron microscopy. Fifteen single-rooted teeth were instrumented to size 60. Three teeth served as the control group, and the remaining teeth were assigned into two groups. After instrumentation,root canals of the first group were irrigatedwith 10 ml of 17% EDTA, and the second group was irrigated with 10 ml of 17% EGTA for 2 min. Both were then irrigated with 10 ml of 5% NaOCI. The teeth in the control group were irrigated with only 10 ml of 5% NaOCI. Then the specimens were sectioned longitudinally and processed for scanning electron microscopy. The results showed that the smear layer was completely removed by EDTA, but it caused erosion of the tubuli. EGTA was somewhat effective in removing the smear layer without inducing erosion. Our results suggest that EGTA is an alternative chelator for removing the smear layer.

MATERIALS AND METHODS Fifteen extracted human permanent teeth with single canals were selected. The root canals were enlarged to the apical foramen with K-files to size 60. A standard flare was produced by the insertion of #2 to #5 Gates-Glidden drills. Irrigation during cleaning and shaping was accomplished using a 5% NaOCl solution. Three teeth served as the control group, and the remaining teeth were randomly assigned into two experimental groups. After instrumentation, root canals of the fiist group were irrigated with 10 ml of 17% EDTA (Sigma, St. Louis, MO), followed by 10 ml of 5% NaOCl. The second group was imgated with 10 ml of 17% EGTA (Sigma), followed by 10 ml of 5% NaOCl. The pH of the EDTA and EGTA solutions was adjusted to 7.5 by addition of NaOH. The teeth in the control group were irrigated with only 10 ml of 5% NaOCl. The irrigation process in all groups was continued for 2 min. Then the crowns of the teeth were removed by a high-speed handpiece with a water spray at the cementoenamel junction, and all the roots were sectioned longitudinally and processed for SEM (JEOL-SEM 6400) evaluation.

The smear layer associated with endodontic instrumentation is currently thought to be a thin layer that occludes the orifices of the dentinal tubules and covers the intertubular dentin of the prepared canal wall (1). Whether it is beneficial or detrimental to a successful root canal therapy is still controversial. The smear layer may be beneficial because it reduces the permeability of dentin and prevents or attenuates the penetration of bacteria into the dentinal tubules. However the smear layer may also be considered deleterious, because it prevents the penetration of imgants, medications, and filling materials into the dentinal tubules or it may even impede their contact with the canal wall (1-3). To date, no single irrigant has been demonstrated to be capable of dissolving organic pulpal material and predentin as well as demineralizing the organic calcified portion of the canal wall. Thus combination of various irrigants have been recommended to accomplish these goals (4).It is widely accepted that the most effective method to remove the smear layer is to irrigate the root canals with 10 ml of 17% EDTA followed by 10 ml of 5% NaOCl (5, 6). EDTA chelates with Ca2+ and other divalent cations, demineralizes dentin, and removes the inorganic components of the smear layer. Another chelator, ethylene glycol-bis (p-amino-

RESULTS SEM examination of the control teeth showed an accumulation of a typical amorphous smear layer in all instrumented areas of the root canal. In preparations in which root canals were irrigated with EDTA followed by NaOCl, it was observed that the smear layer was completely removed from the instrumented root surfaces obtained from the middle and the apical third. However in these specimens intertubular and peritubular dentinal erosion was observed in the middle third of the root canals. In some areas, this excessive erosion lead to conjugation of two or more tubules that indicated the destructive effect of EDTA (Fig. 1). The combination of EGTA and NaOCl irrigation was effective in removing the smear layer from the dentin walls. In these specimens, dentinal tubules seemed to be completely open to the canal surface, and they were not obscured by the smear layer in the 459

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FIG 1. Peritubular and intertubular dentinal erosion is seen after EDTA and NaOCl administration on the middle third of the root canal. Conjugation of two or more tubules is seen with reduction of intertubular distance ( ~ 3 0 0 0 ) .

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FIG 3. Effects of EDTA and NaOCl administration on the middle third of the root canal on the longitudinal section. The superficial smear layer is completely removed, and dentinal tubule orifices are open and enlarged (x2000).

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FIG 2. Effects of EGTA and NaOCl administration on the middle third of the root canal. The instrumented root canal is clean, the smear layer is completely removed, and sharply defined orifices of the dentinal tubules are observed (~3000).

FIG 4. Effects of EGTA and NaOCl administration on the middle third of the root canal on the longitudinal section. The Superficial smear layer is completely removed, and dentinal tubule orifices are open (x2000).

middle third (Fig. 2). We observed that an EGTA and NaOCl combination did not cause erosion of the intertubular and peritubular dentin. However the EGTA and NaOCl combination did not completely remove the superficial smear layer in the apical third, and some of the dentinal tubular orifices were clogged. The effects of EDTA and EGTA were also compared in longitudinal sections (Figs. 3 and 4). In both specimens, tubule openings seemed to be unplugged; however the EDTA specimens displayed widening of the tubules and erosion at the site of openings when compared with EGTA-treated specimens.

chelate. Removal of calcium ions from the dentin softens the dentinal tissue, especially the hydroxyapatite-rich peritubular dentin and increases the diameter of exposed dentinal tubules (8). Baumgartner and Mader (4) reported that the combination of NaOCl and EDTA caused a progressive dissolution of the dentin at the expense of peritubular and intertubular areas, so that the diameters of tubular orifices on the instrumented canal walls were enlarged to 2.5 to 4 pm. Kennedy et al. (9) reported that, when the smear layer removal technique was used, it was much easier to create open dentinal tubules in young teeth than in physiologically older teeth, especially in the more sclerotic middle and apical thirds. The erosion of the exposed globular surface of the calcospherites and the enlargement of the orifices of the dentinal tubules probably resulted from the alternating action of NaOCl, which dissolved the organic component of the dentin, and EDTA that demineralized the inorganic component (4). We also observed that dentinal tubules are conjugated in some areas upon application of EDTA; however, this effect was not observed during EGTA administration. It has been shown that demineralization of the hard

DISCUSSION In this study we compared the effects of EGTA and EDTA on the removal of smear layer and demonstrated that EGTA was somewhat effective in removal of the smear layer on the canal wall. These agents are well-known chelators. A chelator reacts with calcium ions in the hydroxyapatite crystals to produce a metallic

Vol. 26, No. 8, August 2000

Effect of EGTA on Smear Layer

tissue is more effective at a neutral pH than acidic or alkaline pH (10). We prepared the solutions of both chelators at pH 7.5, and therefore the difference in their erosive effectiveness cannot be explained by the effects of pH. Yamada et al. (5) suggested that the combination of NaOCl and EDTA should be applied in 10 ml volume. Liolios et al. ( 1 1 ) reported that the same result can be obtained by 2 ml of the irrigant. Meryon et al. (12) reported that the smear layer was completely removed in vivo with 10% EDTA for 60 s. However peritubular dentin is removed around most tubules, resulting in increased tubular orifice sizes. Similar to other studies, Cergneux et al. (13) applied 15% EDTA in the root canals for 4 min and reported that the tubule foramina are enlarged, and the thickness of intertubular dentin is reduced. Goldberg and Spielberg (14) showed that cleansing properties of EDTAC are observed after 5 min of application, and they suggested that the optimum working time is 15 minutes. They reported that a longer period of administration does not increase the cleansing effect, so renewal of EDTAC solution every 15 min is recommended. Contrary to this study, Yamada et al. (5) suggested that a few seconds of EDTA administration are sufficient. According to our findings, to inhibit the erosion of dentin by 17% EDTA solution, it has to be applied for a shorter period of time or in a lower volume. To remove the smear layer on the canal wall, as an alternative to EDTA, we investigated the effects of EGTA on the same conditions. We observed that EGTA was somewhat effective in removing the smear layer without inducing erosive action. Segura et al. (15) demonstrated that EDTA concentrations lower than those used in root canal preparation inhibited vasoactive intestinal peptide binding to macrophage membranes. This result suggests that EDTA leakage during root canal preparations could modify inflammatory reactions in periapical tissues. They reported that EGTA was able to inhibit tracer binding, but with a 4-fold lower potency than EDTA. This result suggests that the inhibitory effect of EDTA on vasoactive intestinal peptide binding is caused not only by chelation of calcium ions, but also by chelation of other divalent cations, such as MgZf. EGTA was not as effective as EDTA in the important apical third. Further it is not clear that the erosion and joining of orifices

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from EDTA action is deleterious. These results seem to indicate that EDTA action is simply stronger than that of EGTA. Drs. Calt and Serper are affiliated with the Department of Endodontics, Hacettepe University, Faculty of Dentistry, Ankara, Turkey. Address requests for reprints to Dr. Semra Can, Department of Endodontics, Hacettepe University, Faculty of Dentistry, Sihhiye (06100)Ankara, Turkey.

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