Journal of Endodontics Research - http://endodonticsjournal.com
A scanning electron microscopic study of dentinal erosion by final irrigation with EDTA and NaOCl solutions
http://endodonticsjournal.com/articles/119/1/A-scanning-electron-microscopic-study-of-dentinal-erosion-by-final-irrigation-with-EDTA-and-NaOCl-solutions/Page1.html
By JofER editor
Published on 11/12/2008
 
W. Niu, T.Yoshioka, C. Kobayashi & H. Suda
Pulp Biology and Endodontics, Department of Restorative Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.

Aim.
The purpose of this in vitro study was to examine dentinal erosion caused by final irrigation with EDTA and NaOCl.

Conclusions.
Final irrigation with 6% NaOCl accelerates dentinal erosion following treatment with 15% EDTA.

Introduction - Materials and methods.
W. Niu, T.Yoshioka, C. Kobayashi & H. Suda
Pulp Biology and Endodontics, Department of Restorative Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.

Introduction.
The smear layer is produced by instrumentation of the root canal; it is not observed on uninstrumented surfaces. This thin amorphous structure is composed of both organic and inorganic components, and it occludes the orifices of dentinal tubules (McComb & Smith 1975, Goldman et al. 1982, Mader et al. 1984, Sen et al. 1995). Because the smear layer prevents the penetration of irrigants, medications and filling materials into dentinal tubules, and may even impede their contact with the canal wall, many researchers believe it to be detrimental (Kennedy et al. 1986, Cergneux et al. 1987, Karagozkucukay & Bayirli 1994). The use of a combination of EDTA and NaOCl solutions has been recommended for efficient  removal of the smear layer from the surface of the root canal wall (Yamada et al. 1983, Cengiz et al. 1990, Garberoglio & Becce 1994, Liolios et al. 1997). However, reports have also indicated that the use of EDTAand NaOCl may lead to dentinal erosion in the root canal wall (Baumgartner & Mader 1987, Calt & Serper 2000). Numerous reports indicate that the removal of the smear layer, as well as soft tissue and debris, is expedited by the alternate use of EDTA and NaOCl (Yamada et al.1983, Cengiz et al. 1990, Garberoglio & Becce 1994, Liolios et al.1997). However, less information is available about how final irrigation with EDTA and NaOCl results in the dentinal erosion.
The purpose of the present study was to morphologically evaluate dentinal erosion caused by final irrigation with EDTA and NaOCl.

Materials and methods.

Preparation of specimens.
Twenty-five intact single-rooted human mandibular anterior teeth stored in distilled water were used. Crowns were removed at the cemento-enamel junction level. After determining the working length (0.5 mm shorter than root canal length) by inserting a fine file (size 1 hand Profile, Dentsply Tulsa Dental, Tulsa, OK, USA), the root canal was prepared with rotary nickel- titanium Series 29 Profile instruments (0.04 taper, Dentsply Tulsa Dental, Tulsa, OK, USA) driven by a Tri Auto ZX (Morita Mfg Corp, Kyoto, Japan).The preparation sequence of instruments is showed in Table 1.After each step of instrumentation, 6% NaOCl solution (3 mL) (Purelox Oyalox, Tokyo, Japan) was applied to the root canal, with a size 27-gauge blunt-tip needle (Nissho, Osaka, Japan) using an up-down motion.

Table 1. The preparation sequence of instruments.

The preparation sequence of instruments

Grouping of specimens and scanning electron microscopic observation
Composition of the 15% EDTA solution was as follows: EDTA disodium salt (17 g), 5 N sodium hydroxide solution (9.25 mL) and distilled water (100 mL). Teeth were randomly divided into five groups according to the irrigation regimens (see Table 2).
Roots were split longitudinally, and one-half was dried and sputter-coated with platinum-palladium (Eiko Ion Coater IB-5, Ibaragi, Japan). Specimens were observed at 3000x magnification using a scanning electron microscope (Hitachi S-4500, Tokyo, Japan), and photomicrographs were taken at1, 3 and 6 mm from the apex.

Table 2. Grouping of the specimens and final irrigating solutions.

Grouping of the specimens and final irrigating solutions

Qualitative SEM evaluation.
The amount of remaining debris on the root canal wall (representative areas: 37 mm _ 30 mm) was evaluated in each specimen at 1, 3 and 6 mm from the apex, and graded using the qualitative scale advocated by Gorman et al. (1995) (0 = none, 1 = minimal, 2 = moderate and 3 = heavy).

Quantitative evaluation of SEM microphotographs.
Dentinal tubule orifice diameters were measured in each of the photomicrographs. One-way anova and Fisher’s PLSD tests were used to evaluate differences amongst the groups in the amount of remaining debris, and amongst the groups in the open orifice diameters. Values were expressed as mean _ SD, and P-values less than 0.05 were considered significant.

Results.
  • GroupA: Typical amorphous smear layer was observed on the root canal wall of each specimen (Fig. 1, A1-3).
  • GroupB: Peritubular and intertubular surface dentine appeared smooth and flat. Individual dentinal tubule orifices were clearly observed. A small amount of debris was observed on the dentine wall at each distance from the apex (Fig.1, B1-3).
  • Group C: At 3 and 6 mm from the apex, peritubular and intertubular surface dentine was neither smooth nor flat. Dentinal tubule orifices were seen to be irregularly enlarged and rough in appearance. A small amount of debris also remained (Fig. 1, C1-3).
  • Group D: Similar to group B, the root canal walls appeared smooth and flat (Fig.1, D1-3).
  • Group E: Severe peritubular and intertubular dentinal erosion was observed. Surface dentine was neither smooth nor flat, and dentinal tubule orifices were irregularly enlarged. In some areas, excessive erosion led to the conjugation of two or more dentinal tubules (Fig.1, E1-3 and Fig. 2).
Figure 3 shows the grades given for remaining debris in groups B-E. At 6 mm from the apex, the remaining debris of group E was significantly less than that of groups B or D (one-way anova, Fisher’s PLSD test, P < 0.05).
Figure 4 depicts the diameter of dentinal tubules. For each group, at 3 and 6 mm from the apex, the diameters of dentinal tubules of group E were significantly larger than those of group D, and those of group C were larger than those of group B (one-way anova, Fisher’s PLSD test, P < 0.05).

Figure 1. Photomicrographs of root canal wall in each group after final irrigation (original magnification: 3000x; scale bar in A1 is 10 mm). A1-E1, A2-E2 and A3-E3 show canal walls at 6, 3 and 1 mm from apex, respectively. In group A, typical amorphous smear layer on root canal wall, and no dentinal tubule openings were observed. In groups B and D, peritubular and intertubular surface dentine appeared smooth and flat. Individual orifices of dentinal tubules were clearly observed. In groups C and E, erosion of peritubular and intertubular dentine was observed. The surface of dentine wall was neither smooth nor ?at, and dentinal tubule orifices were irregularly enlarged and were rough in appearance. In some areas, excessive erosion led to conjugation of two or more dentinal tubules.

Photomicrographs of root canal wall in each group after final irrigation

Figure 2. Peritubular and intertubular detinal erosion at 6 mm from apex in group E. Original magnifications of left and right photographs are 4000 and 15 000x, respectively. Dentine was neither smooth nor ?at, and dentinal tubule orifices were irregularly enlarged and were rough in appearance.

eritubular and intertubular detinal erosion

Figure 3. Score of remaining debris (*P < 0.05).

Score of remaining debris

Figure 4. Diameter of dentinal tubules (*P < 0.05).

Diameter of dentinal tubules


Discussion - References.
Discussion.
A combination of EDTA and NaOCl solutions is recommended for the efficient removal of the smear layer from the surface of the root canal wall. Numerous reports have suggested that dentinal erosion on the canal wall is the result of hyper-decalcification induced by EDTA. However, few studies have been conducted on the relationship of erosion to irrigation with alternate use of EDTA and NaOCl solutions. In the present study, the effects of final irrigation with EDTA or NaOCl were examined; dentine erosion occurred when EDTA irrigation was followed by final irrigation with NaOCl.
Baumgartner & Mader (1987) reported that when EDTA and NaOCl solutions were alternately applied to uninstrumented root canal wall, dentine showed an eroded appearance, and tubular orifice diameters were enlarged. Cergneux et al. (1987) applied 15% EDTA to the root canal for 4 min, and observed that dentinal tubule orifices were enlarged, and that the thickness of intertubular dentine was reduced. Calt  & Serper (2000) reported that dentinal erosion was observed in the central portion of instrumented root canals when irrigated with 10 mL of 17% EDTA solution followed by 10 mL of 5% NaOCl. However, it is not known how NaOCl affected dentinal erosion during this process.
In the present study, the morphological changes in instrumented root canal wall at 1, 3 and 6 mm levels from the apex were evaluated, using different irrigation methods. When final irrigation was conducted with 15% EDTA (in groups B and D), the surface dentine appeared smooth but not eroded, and dentinal tubule orifices were regular and separated. However, when15% EDTA irrigation was followed by 6% NaOCl (in groups C and E), peritubular and intertubular dentinal erosion was observed. Dentine in the root canal wall surface was rough in appearance and dentinal tubule orifices were irregularly enlarged due to decalcification of the inorganic component by EDTA and the dissolution of the organic matrix by NaOCl (Fig.1, E1-3 and Fig. 2).
Yamada et al. (1983) demonstrated that 10 mL of the EDTAand10 mL NaOCl combination is the most efficient volume for smear layer removal. Liolios et al. (1997) reported that erosion of dentinal wall was observed after irrigation with only 2 mL of these irrigants. Calt&Serper (2000) suggested that dentinal erosion can be minimized by applying EDTA solution for a shorter time or in a smaller volume. In the present study, despite limiting both the volume of EDTA (3 mL) and irrigation time (1 or 3 min), erosion of dentine surfaces was observed in both groups C and E. Dentinal tubule diameter was 3.43 _0.23 mm in group C and 3.93 _0.44 mm in group E, which is larger than usually seen (2.90 _ 0.22 mm) in human permanent teeth (Schilke et al.2000).This erosion was produced even though a limited volume of EDTA was applied for a short time to remove the smear layer. These results suggested that final irrigation with NaOCl accelerates dentinal erosion following irrigation with EDTA.
Kennedy et al. (1986) reported that creating open dentinal tubules in teeth from physiologically young individuals was easier than in teeth from the aged. This observation was particularly clear in the more sclerotic middle and apical thirds when the smear layer removal technique was used. In our study, although the teeth used were most probably extracted from old patients, predominantly because of periodontal disease, and the dentine walls were considered to be highly mineralized, dentinal erosion was easily produced by irrigation with EDTA followed by NaOCl. Therefore, erosion of the instrumented root canal wall cannot be explained solely by the degree of tooth mineralization associated with ageing.
EDTA is believed to demineralize the inorganic component of dentine and NaOCl is thought to subsequently dissolve the organic matrix. Baumgartner & Mader (1987) suggested that organic material accumulated on the canal surface and prevented further dentine dissolution when EDTA alone was used to irrigate the canal. Conversely, when NaOCl alone was used as an irrigant, the exposed in organic material prevented further dissolution of dentine. In this study, NaOCl solution was used as an irrigant at every stage of root canal preparation and EDTA plus NaOCl were used at the end. Morphological findings suggest that EDTA may decalcify peritubular dentine during the early stages of root canal irrigation and that the subsequent use of NaOCl dissolves the exposed organic matrix. These complementary effects may result in the erosion of the dentinal wall. Enlargement of the superficial part of dentinal tubules has also been described after use of 19% citric acid or EDTAC on instrumented dentine surfaces (Goldberg & Abramovich 1977, Di Lenarda et al. 2000).Detailed observation of the dentinal tubules revealed the erosion of dentine not only on the surface of the canal wall but also inside the dentinal tubules after irrigation with EDTA followed by NaOCl (Fig. 2). Several unresolved issues on the enlargement of dentinal tubules by irrigation with EDTA and NaOCl remain. These include how deep the enlargement penetrates into the root canal lumen surface, and whether there is a change in the sealing ability of the root canal filling material. The influence of erosion on endodontic prognosis needs to be studied further, particularly testing the effects of tubule enlargement on root canal filling and sealing ability.
Yamada et al. (1983) showed that the most efficient final irrigation for removing superficial debris was with 5.25% NaOCl solution. The present study demonstrated that debris was removed at each level of the root canal wall by irrigation with EDTA followed by NaOCl but not with EDTA alone (Fig. 1, C1-3 and E1-3).

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