Discussion - References.
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).
Baumgartner JC, Mader CL (1987) A scanning electron microscopic evaluation of four root canal irrigation regimens. Journal of Endodontics 13, 147-57.
Calt S, SerperA (2000) Smear layer removal by EGTA. Journal of Endodontics 26, 459-61.
Cengiz T, Aktener BO, Piskin B (1990) The effect of dentinal tubule orientation on the removal of smear layer by root canal irrigants. A scanning electron microscopic study. International Endodontic Journal 23, 163-71.
Cergneux M, Ciucchi B, DietschiJM, Holz J (1987) The influence of the smear layer on the sealing ability of canal obturation. International Endodontic Journal 20, 228-32.
Di Lenarda R, CadenaroM, Sbaizero O (2000) Effectiveness of1 mol L_1 citric acid and 15% EDTA irrigation on smear layer removal. International Endodontic Journal 33, 46-52.
GarberoglioR, Becce C (1994) Smear layer removal by root canal irrigants. A comparative scanning electron microscopic study. Oral Surgery, Oral Medicine and Oral Pathology 78, 359-67.
Goldberg F, Abramovich A (1977) Analysis of the effect of EDTAC on the dentinal walls of the root canal. Journal of Endodontics 3, 101-5.
Goldman M, Goldman LB, Cavaleri R, Bogis J, Lin PS (1982) The efficacy of several endodontic irrigating solutions: a scanning electron microscopic study. Part 2. Journal of Endodontics 8, 487-92.
Gorman MC, Steiman HR, Gartner AH (1995) Scanning electron microscopic evaluation of root-end preparations. Journal of Endodontics 21, 113-7.
Karagoz-kucukay I, Bayirli G (1994) An apical leakage study in the presence and absence of the smear layer. International Endodontic Journal 27, 87-93.
Kennedy WA, Walker WA III, Gough RW (1986) Smear layer removal effects on apical leakage. Journal of Endodontics 12, 21-7.
Liolios E, Economides N, Parissis-Messimeris S, Boutsioukis A (1997) The effectiveness of three irrigating solutions on root canal cleaning after hand and mechanical preparation. International Endodontic Journal 30, 51-7.
Mader CL, Baumgartner JC, Peters DD (1984) Scanning electron microscopic investigation of the smeared layer on root canal walls. Journal of Endodontics10, 477-83.
McComb D, Smith DC (1975) A preliminary scanning electron microscopic study of root canals after endodontic procedures. Journal of Endodontics 10, 238-42.
Schilke R, Lisson JA, BauO O, Geurtsen W (2000) Comparison of the number and diameter of dentinal tubules in human and bovine dentine by scanning electron microscopic investigation. Archives of Oral Biology 45, 355-61.
Sen BH, Wesselink PR, Turkun M (1995) The smear layer: a phenomenon in root canal therapy. International Endodontic Journal 28, 141-8.
Yamada RS, Armas A, Goldman M, Lin PS (1983) A scanning electron microscopic comparison of a high volume final flush with several irrigating solutions. Part 3. Journal of Endodontics 9, 137-42.