Comparison of removal of endodontic smear layer using NaOCl, EDTA, and different concentrations of maleic acid A SEM study

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1 Endodontology, Vol. 15, 2003 Comparison of removal of endodontic smear layer using NaOCl, EDTA, and different concentrations of maleic acid A SEM study *Prabhu SG **Rahim N ***Bhat KS ***Mathew J ABSTRACT The purpose of this in vitro study on extracted teeth was to evaluate and compare the ability of maleic acid in different concentrations, NaOCl and EDTA in the removal of smear layer formed along the root canal walls after chemomechanical preparation. Sixty freshly extracted teeth human maxillary incisors were divided into six groups and root canals were prepared with step back technique, using different solutions; namely, 5%,7%, 10% and 15% maleic acid,5.25% NaOCl and 17%EDTA.The teeth were then split and the canal surfaces were viewed under SEM for removal of smear layer. The results showed that NaOCl failed to remove the smear layer. Smear removing ability of maleic acid was significantly better than EDTA. Key words Gutta percha removal, Xylene, Gates Glidden, Profiles, Hedstrom files. Introduction The complete obliteration of root canal space with an inert filling material and creation of a fluid tight seal are the goals for successful endodontic therapy 1. In order to create a fluid tight seal, it is imperative that the endodontic filling material closely adapts or bonds to the tooth structure. This however is impaired by the presence of endodontic smear layer, which invariably forms after instrumentation 2,3. The smear layer contains organic material, odontoblastic processes, bacteria and blood cells. Although there is some controversy * Assistant Professor ** Former PG student *** Professor Emeritus **** Associate Professor, Dept of Conservative Dentistry & Endodontics, College of Dental Surgery, Manipal Academy of Higher Education, Karnataka 20 regarding the desirability of retaining the smear layer in adhesive dentistry, in endodontics, its removal is considered to be advantageous and highly desirable. Various materials and techniques have been reported with wide variations in their efficacy regarding removal of the intra canal smear layer 2, 4. The most widely used chemical for the purpose is EDTA in different formulations 5. They have been reported to consistently produce canals with patent dentinal tubules 6. However, it has been found to be less efficient in narrow portions of the canal 7, requires a long application time for optimum results 8 and can seriously damage the dentin, if used in excess 9. Modern adhesive techniques utilize suitable treatment of smear layer by the application of a conditioner, which either

2 Prabhu SG et al. removes it or modifies it, depending upon the adhesive systems used. Some of the adhesive system use 10% maleic acid as a dentin conditioner to remove the smear layer 10, 11 while others reported that it modifies the smear layer 12. The review of literature shows that maleic acid has not been tested against the endodontic smear layer. The aim of this in vitro study was to use different concentration of maleic acid to remove the endodontic smear layer and to evaluate the outcome, using scanning electron microscopy and compare its ability with sodium hypochlorite and EDTA solutions. Materials and Methods Sixty freshly extracted human maxillary anterior teeth were selected. After access opening, a no 10 K-file was placed in the canal until it was just visible at the apical foramen. The working length was established by reducing 1 mm from this point. The apical portion of the root tip was then covered with sticky wax. Chemomechanical preparation was done according to the conventional step back preparation using K flex files. The apical portion was enlarged to a no 40 file and irrigated with NaOCl solution after each file. Following this, the samples were divided randomly into 6 groups as follows: Group I : 5.25% NaOCl Group II : 17% EDTA solution Group III : 5% Maleic acid Group IV : 7% Maleic acid Group V : 10% Maleic acid Group VI : 15% Maleic acid The root canals were then step backed to no 60 file and the coronal third was enlarged using gates glidden drills from sizes 2 to 5. Irrigation was done after each instrument with 1ml of the test solution using a syringe, the needle was placed as far as possible into the canal without binding. The root canals were finally irrigated with 3ml of distilled water to remove any precipitate that may have formed from the test irrigants. After the root canal preparation, the canals were dried with paper points. A cotton pellet was placed in the access cavity and the tooth was stored in a plastic bag placed in a humidor. A longitudinal groove was cut on the buccal and lingual surface without penetrating the canal using a fine diamond bur. Each tooth was then split into two with cutting pliers and stored until analysis with SEM. The specimens were dehydrated and coated with gold using an ion sputter and immediately examined for SEM evaluation. Several photomicrographs were made at X1000 and X3000 magnifications, at the middle and apical third to observe the surface morphology. The representative areas were evaluated under the following criteria by two independent evaluators who did not know the groups to which the samples belonged. The scoring was made, as described by Rome 13. Score Findings 0 No smear layer, all dentinal tubules open 1 Minimum smear layer > 50% dentinal tubules visible 2 Moderate smear layer; < 50% of dentinal tubules open 3 Heavy smear layer; outline of dentinal tubules obliterated. The acquired data was then subjected to statistical analysis using SPSS/PC+4.0, the statistical package from IBM PC (Chicago, USA) Results Removal of endodontic smear layer... The Wilcoxon matched-pairs signed rank test was used to compare the scores between two raters. Results showed that there was no 21

3 Endodontology, Vol. 15, 2003 significant difference between the two evaluators in all the groups, except in the middle third of group VI. Therefore, any difference in smear layer removal efficacy would be due to procedural variable and not due to inter examiner disagreement except probably in Group VI. The mean scores for the different groups in both the middle and apical third are given in Table 1. Statistical analysis revealed a very highly significant difference in the smear layer removing ability between sodium hypochlorite and all the other groups in both the middle & apical third (p=0) A very highly significant difference was found between EDTA and the different concentration of maleic acid in the middle third (p=0). In the apical third, there was a significant difference between EDTA and 5%maleic acid (p=0.0271) and 7%maleic acid (p=0.0244) whereas it was highly significant with 10% maleic acid (p=0.0001) and 15% maleic acid (P= ) No significant difference was found between 5% and 7% maleic acid (p=0.5533) and between 5% and 10%maleic acid in the middle third (p=0.7684). However, a highly significant difference was found between 5% and 15%maleic acid in the middle third (p=0.006), with 5%maleic acid showing better removing ability. In the apical third, no significant difference was seen between 5% and 7%maleic acid (p=0.3940) whereas compared to 5% maleic acid, highly significant difference with 10% (p=0.0083) and a significant difference with 15%maleic acid was seen (p=0.0230) Statistical analysis showed highly significant difference between 10% and 15%maleic acid in the middle third (p=0.0034) and no significant difference in the apical third (p=0.0771). Discussion The endodontic smear layer has been described as one that is formed during instrumentation, consisting of not only dentin but also necrotic and viable tissue, including remnants of odontoblastic processes, pulp tissue and bacteria 3. The smear layer plays an important role in the lateral sealing of the root canal, by acting as an intermediate physical barrier that may interfere with adhesion and penetration of the root canal sealer into the dentinal tubules 3. Pashley et al 14 had described the smear layer as a porous structure which was permeable to even large molecules like albumin. Mader et al 15 had stated that the smear layer was a non homogenous and weakly adherent structure and may slowly disintegrate and dissolve around leaking filling margins, thus creating voids between root canal walls and filling material / sealer. Kennedy et al 16 found that with the smear layer intact, apical leakage was significantly increased. The smear layer's presence plays a significant role in an increase or decrease in apical leakage. Its absence makes the dentin Table 1. Mean score for smear layer at middle and apical third NaOCl EDTA Maleic acid Maleic acid Maleic acid Maleic acid 5% 7% 10% 15% Middle third Apical third 22

4 Prabhu SG et al. more conducive to a better and closer adaptation of the gutta-percha to the canal wall 17. Maleic acid has been in use as acid conditioner in some of the adhesive systems. It has been reported to remove the smear layer present in cavities prepared for adhesive dentistry 10,11. The smear layer present in adhesive dentistry can be quite different from the endodontic smear layer. In the former, the tooth may be vital and the dentinal tubules contain odontoblastic processes and dentinal fluid, whereas in the case of the endodontic smear layer, the tooth is nonvital and devoid of dentinal fluid or odontoblastic processes. Hence it was decided to subject different concentrations of maleic acid and compare it with EDTA and sodium hypochlorite in the middle and apical third of the root canal under Removal of endodontic smear layer... controlled conditions. The results of this study indicate that sodium hypochlorite did not remove the smear layer in the middle and apical third of the root canal (Fig 1 & Fig 2). This is in agreement with studies done by earlier researchers 3,15. The other findings of the study indicates that EDTA is efficient in removing the smear layer mainly from the middle third (Fig 3), its action in apical third is however, very much impaired (Fig 4). This is in agreement with Ciucchi et al 18 who stated that there was a definite decline in the efficiency of irrigating solution along the apical part of the canals. This can probably be explained to the fact that dentin in the apical third is much more sclerosed and the number of dentinal tubules present there is less. Also EDTA requires an application time Fig. 1. Effects of 5.25% NaOCl on middle third of the root canal. Note the typical appearance of amorphous smear layer. The dentinal tubule openings are obscured by the adherent smear layer. Fig. 2. Effects of 5.25% NaOCl on apicle third of the root canal: The canal wall appears covered by a heavy smear layer. Cracks can be seen on the smear layer. Pieces of inorganic debris are scattered on the surface. Fig. 3. Effects of 17% EDTA on middle third of the root canal: The smear layer has been removed. Little debris can be seen. Smooth and flat intertubular dentin. The tubules are open and widened. Fig. 4. Effects of 17% EDTA on apical third of the root canal: Smear layer not completely removed. Some debris can be seen. Dentinal tubules are partially open and can be seen to have smear plugs in them. Fig. 5. Effects of 5% Maleic acid on middle third of the root canal: smear layer and smear plugs are completely removed. Little or no debris can be seen on the surface. Intertubular dentin smooth and flat. 23 Fig. 6. Effects of 5% Maleic acid on apicle third of the root canal: Partially opened dentinal tubules can be seen. Little or no debris on the canal wall.

5 Endodontology, Vol. 15, 2003 of not less than 15 minutes for optimum results 8 and it may also not have such a pronounced action at the narrow apical portion as in the middle third. In the present study, 5% maleic acid showed a very highly significant result (p<0.001) compared to EDTA in the middle third (Fig 5) and a significant result (p<0.05) in the apical part of the canal (Fig 6). There was no smear layer nor plugs in the middle third although many of the tubules were plugged in the apical third. There was little or no debris observed. The results show that 5% maleic acid is a good replacement for EDTA, as it shows better removal of the smear layer. There was no significant difference in the smear layer removing ability between 5% and 7% maleic acid, both in the middle and in the apical third of the root canal. There was little or no debris and the intertubular dentin was not demineratized nor damaged (Fig 7 & Fig 8). However, use of 10%maleic acid resulted in damage and demineralization to the intertubular dentin, although the smear layer was completely removed (Fig 9 & Fig10). A similar result was also seen with 15% maleic acid. In these groups the dentinal tubules were widened and fully open especially in the middle third (Fig11). In the apical third, the tubules were open and widened. Some of these tubules had smear plugs in them (Fig12). Thus a concentration below 10% can be recommended for removal of intracanal smear layer. The smear layer removing ability of maleic acid in the present study is in agreement with Erickson 10 and Van Meerbeek et al 11 who reported that the smear layer was removed in Fig. 7. Effects of 7% Maleic acid on middle third of the root canal: Smear layer has been removed. Dentinal tubules are widened and little or no debris can be seen. Fig. 8. Effects of 7% Maleic acid on apicle third of the root canal: Smear layer has been removed. Dentinal tubules are widened and little or no debris can be seen. Fig. 9. Effects of 10% Maleic acid on middle third of the root canal: Demineralization of the intertubular dentin can be seen. Fig. 10. Effects of 10% Maleic acid on apical third of the root canal: Dentin tubules are open and widened. Fig. 11. Effects of 15% Maleic acid on middle third of the root canal: Smear layer completely removed. Demineralization has taken place and dentin chips can be seen on the surface. 24 Fig. 12. Effects of 15% Maleic acid on apicle third of the root canal: Partially opened dentinal tubules can be seen alongwith demineralization of intertubular dentin.

6 Prabhu SG et al. adhesive dentistry using a self-etching primer (Scotch bond 2-3M) and disagrees with Jordon 12 who reported that it only modifies the smear layer. One possible explanation why the smear layer removing ability of maleic acid was less in vital teeth, could be due to the presence of the dentinal fluid which can exert pressure and so affect its complete removal. However, in the present study, irrigants were used during step back preparation of the canal. But earlier investigators' studies mentioned above, had exposed the instrumented canal surface to the test irrigants, maintained for different time intervals 8. Hence a fair comparison of the results is difficult. Conclusions Following conclusions were made from this study; 1. Maleic acid removed the smear layer effectively at all concentration. 2. 5% and 7% maleic acid can be an alternative to routine use of 17% EDTA. 3. An increase in concentration of maleic acid to 10% or more can result in demineralization and damage to root canal wall. 4. Sodium hypochlorite did not remove the smear layer. 5. EDTA, which is conventionally used to remove the smear layer, was less efficient than the all concentrations of maleic acid. 6. The technique of use and biologic effects of maleic acid on periapical tissues needs evaluation, before it is routinely employed for clinical use. References 1. Ingle JI : Beveridge EE: Endodontics 2nd editition Philadelphia: Lea and Biger: 1976;216. Removal of endodontic smear layer Baumgartner JC, Brown CM, Mader CL, Peters DD, Shulman JD : A scanning electron microscopic evaluationof root canal debridement using saline,naocl and citric acid. J Endododon. 1984;10: McComb and Smith DC. A preliminary scanning electron microscopic study of root canals after endodontic procedures. J Endodon. 1975;1 : Cunningham WT, Martin HA. SEM evaluation of root canal debridement with the endosonic ultrasonic synergistic system, Oral Surg. 1982;53: Michael SO, Leslie A, William J Beeler, Baumgartner JC. A comparative study of smear layer removal using different salts of EDTA. J Endodon. 2000;26: Goldman LB, Goldman M, Kronman JH. Efficacy of several irrigating solutions for endodontics; a SEM study. Oral Surg. 1981;52: Patterson S. In vivo and In vitro studies of the effects of disodium salt of ethylene diamine tetra acetate on human dentin and its endodontic implications.oral Surg. 1963;16: Goldberg F, Spielberg C. The effects of EDTAC and the variation of its working time analyzed with scanning electron microscopy. Oral Surg. 1982;53: Calt S. and Serper A. Time dependent effects of EDTA on dentin structures. J.Endodon. 2002;28: Erickson R L. Surface interactions of dentin adhesive materials, Oper Dent, supple 1992;5: Van Meerbeek B et al. Factors affecting adhesion to mineralized tissues.oper Dent, supple 1992;5; Jordan RE. Adhesives in dentistry: clinical considerations, Oper Dent, supple 1992;5: Rome WJ, Doran JE, Walker WA. The effectiveness of Gly-Oxide and NaOCl in preventing smear layer formation. J Endodon. 1985;11: Pashley DH et al. Effects of molecular size on permeability coefficients in human dentin. Arch Oral Biol, 1978;23: Mader CL, Baumgartner JC, and Peters DD. Scanning electron microscopic investigation of the smear layer on root canal walls. J.Endodon. 1984;10: Kennedy WA, Walker WA and Gough RW. Smear layer removal effects on apical leakage.j Endodon. 1986,12: Baumgartner JC, Mader CL. A scanning electron microscopic evaluation of four root canal irrigation regimens. J Endodon. 1987;13: Ciucchi B, Khettabi M, Holz J. The effectiveness of different endodontic irrigation procedures on the removal of the smear layer : a SEM study. Int Endod J. 1989;22: