|Year : 2015 | Volume
| Issue : 1 | Page : 26-32
Evaluation of the effect of duration of application of Smear Clear in removing intracanal smear layer: SEM study
Ankur Dua1, Deepti Dua1, Veerendra M Uppin2
1 Department of Restorative Dentistry and Endodontics, IBN Sina National College for Medical Studies, Jeddah, Saudi Arabia
2 Department of Restorative Dentistry and Endodontics, 1Karnataka Lingayat Education Viswanath Katti Institute of Dental Sciences, Belgaum, Karnataka, India
|Date of Web Publication||12-Jan-2015|
Department of Restorative Dentistry and Endodontics, IBN Sina National College for Medical Studies, P.O. Box 31906, Jeddah 21418
Source of Support: None, Conflict of Interest: None
Aim: To evaluate the effect of duration of application of 17% ethylene diamine tetraacetic acid (EDTA) and SmearClear on the removal of intracanal smear layer by SEM. Materials and Methods: Seventy-two extracted maxillary incisors were root canal instrumented and randomly distributed into three groups of 24 teeth each according to different final irrigation regimens, Group A-17% EDTA + 1% sodium hypochlorite (NaOCl), Group B-SmearClear + 1% NaOCl, Group C (Control group)-Distilled water + 1% NaOCl. Further each group was subdivided into 3 subgroups according to the duration of application of the irrigating solutions for 1, 3 and 5 minutes. Following de-coronation and splitting of roots, one-half of each root was examined under scanning electron microscope (SEM) at 1000Χ magnification for smear layer at 6 mm and 2 mm levels. Data were subjected to statistical analysis using Kruskal-Wallis and Mann-Whitney U test (P < 0.05) Results: At 6 mm level, the mean smear scores were similar with both 17% EDTA solution and Smear Clear, however, at 2 mm level, they were significantly lower with Smear Clear (P < 0.05). The smear scores decreased as the duration of application of either 17% EDTA or Smear Clear increased from 1 to 5 minutes. Conclusion: Final irrigation with either 17% EDTA solution or Smear Clear followed by 1% NaOCl was effective in removing the smear layer for all three durations of applications. But, in the apical third, Smear Clear was more effective when compared with 17% EDTA solution.
Keywords: 17% ethylene diamine tetraacetic acid, irrigating solution, scanning electron microscope smear layer, surfactants
|How to cite this article:|
Dua A, Dua D, Uppin VM. Evaluation of the effect of duration of application of Smear Clear in removing intracanal smear layer: SEM study. Saudi Endod J 2015;5:26-32
|How to cite this URL:|
Dua A, Dua D, Uppin VM. Evaluation of the effect of duration of application of Smear Clear in removing intracanal smear layer: SEM study. Saudi Endod J [serial online] 2015 [cited 2020 Aug 9];5:26-32. Available from: http://www.saudiendodj.com/text.asp?2015/5/1/26/149083
| Introduction|| |
Successful endodontic treatment depends amongst other factors on the removal of microorganisms through chemo-mechanical instrumentation of the root canal system. After mechanical instrumentation, an amorphous, irregular layer composed of inorganic and organic material is formed on root canal walls known as the smear layer. This layer contains remnants of ground dentin, pulpal tissue, odontoblastic processes; and in infected teeth, bacteria.  It is typically 1-2 μm in thickness but smear plugs may be packed into the dentinal tubules as far as 40 μm. 
It is known that the smear layer may harbor bacteria, preventing the canal from being disinfected. , The smear layer has also been shown to hinder the penetration of intracanal medicaments  and sealers ,, into dentinal tubules and has the potential of compromising the seal of the root canal filling. ,, Although, it has been suggested that an intact smear layer may prevent initial bacterial penetration of dentinal tubules,  degradation of the smear layer after treatment may contribute to leakage and re-infection of the root canal space. Studies have shown that elimination of the smear layer reduced the leakage of bacteria through the root canal system after root filling.  So, it would appear prudent to remove the smear layer before obturating the root canal. 
Many authors have recommended the use of a chelating agent such as 17% ethylene diamine tetraacetic acid (EDTA) solution to ensure the removal of the inorganic component, followed by a final irrigation with 1% sodium hypochlorite (NaOCl) solution to dissolve any remaining organic component  of the smear layer. One possible method to increase the penetration of irrigating solutions into the dentinal tubules is the addition of surfactants. This reduces the surface tension and fluid viscosity, thus enabling the chelating solution to be carried more easily to the full-depth of the canal.  Another method to improve the ability of the irrigating solution to remove the smear layer may be by increasing its contact time. But, the literature demonstrates a great variation in the duration of final irrigation. In one study, EDTA has been reported to remove the smear layer in less than a minute,  whereas another study suggested that the solution should be kept in the root canal for 15 minutes to obtain optimum results. 
Smear Clear (SybronEndo, Orange, CA, USA) is a recently introduced chelating agent that contains 17% EDTA solution with two additional proprietary surfactants. In regards to SmearClear, all the studies that have evaluated this product have used it for 1 minute as per according to the manufacturer's instructions. There has not been much research to evaluate the effect of increasing the duration of application on its ability to remove the intracanal smear layer.
The present in-vitro study is an attempt to compare the efficacy of SmearClear, 17% EDTA solution and to evaluate the influence of their duration of application on the removal of intracanal smear layer.
| Materials and Methods|| |
Seventy-two extracted non-carious human permanent maxillary incisors were selected for this study. These teeth were collected from different dental clinics in Belgaum, Karnataka, India. All teeth were extracted for periodontal reasons and were grouped irrespective of patient's gender, age or race, whether they were from the right or left side. Central incisors and lateral incisors were included in the study. Teeth with straight and single patent root canal and without any anatomical variations, no visible root caries and no signs of external or internal resorption and with completely formed apices were used in the study. Following extraction, teeth were cleaned by removing the remaining soft tissue and then stored in 0.1% thymol solution (Loba Chemicals, India) at room temperature. Before utilization, teeth were taken out and washed under tap water to remove the traces of thymol solution. Each tooth was numbered on the buccal and palatal surfaces of the root.
Endodontic access was obtained and a size 15 K-file (Kendo, VDW, Germany) was introduced into the root canal until the tip was just visible at the apical foramen. The working length (WL) for preparation of the canal was determined by deducting 1mm from the length recorded when the file was visible at the apex. Root apices were covered with sticky wax to create closed end canal model that more accurately simulates in-vivo situations by creating vapor-lock effect. All teeth were prepared with ProTaper Nickel-Titanium rotary instruments (Dentsply Maillefer, Switzerland) up to apical size F5 (ISO size 50). During instrumentation, canals were irrigated with 1 ml of 1% sodium hypochlorite (Vishal Dentocare, Ahmedabad, India), between every instrument change using a 27-gauge needle. All the teeth were instrumented by a single operator to avoid the inter-operator bias.
After completion of preparation, samples were randomly distributed into three groups of 24 teeth each, Group A-Final irrigation with 5 ml of 17% ethylene diamine tetraacetic acid (EDTA) (Canalarge, Ammdent, India) solution followed by 5 ml of 1% NaOCl solution; Group B-Final irrigation with 5 ml of SmearClear (SybronEndo, Orange, CA, USA) solution followed by 5 ml of 1% NaOCl solution; Group C (Control group)-Final irrigation with 5 ml of distilled water followed by 5 ml of 1% NaOCl solution. Further, each group was divided into 3 subgroups of 8 teeth each according to duration of application of the irrigant:-
- A1-Final irrigation with 5 ml of 17% EDTA solution followed by 5 ml of 1% NaOCl solution for 1 min. n = 8
- A2- Final irrigation with 5 ml of 17% EDTA solution followed by 5 ml of 1% NaOCl solution for 3 mins. n = 8
- A3- Final irrigation with 5 ml of 17% EDTA solution followed by 5 ml of 1% NaOCl solution for 5 mins. n = 8
- B1- Final irrigation with 5 ml of Smear Clear solution followed by 5ml of 1% NaOCl solution for 1 min. n = 8
- B2- Final irrigation with 5 ml of Smear Clear solution followed by 5ml of 1% NaOCl solution for 3 mins. n = 8
- B3- Final irrigation with 5 ml of Smear Clear solution followed by 5ml of 1% NaOCl solution for 5 mins. n = 8
- C1- Final irrigation with 5 ml of distilled water followed by 5ml of 1% NaOCl solution for 1 min. n = 8
- C2- Final irrigation with 5 ml of distilled water followed by 5ml of 1% NaOCl solution for 3 mins. n = 8
- C3- Final irrigation with 5 ml of distilled water followed by 5ml of 1% NaOCl solution for 5 mins. n = 8
Following irrigation, the canals were dried with sterile absorbent paper points (Dentsply Maillefer, Ballaigues, Switzerland) and the entrance to each of the canals were protected with a cotton pellet to prevent penetration of the dentinal debris into the canals during de-coronation. Using diamond discs with water, the crown was removed at Cemento-enamel junction (CEJ) and deep grooves were made on the buccal and palatal surfaces of the roots without perforating the canal. The roots were then split longitudinally using a chisel. One-half of each root was selected for examination under scanning electron microscope (Cambridge, Sterioscan 360, Cambridge, UK).
After assembly on coded stubs, the specimens were gold sputtered and examined under a scanning electron microscope at 1000× magnification. The dentinal wall of the middle and apical third was observed for the presence/absence of smear layer and visualization of the entrance to the dentinal tubules. Photomicrographs were taken of the canal walls at 6 and 2 mm from the apical foramen of each specimen representing middle and apical thirds, respectively [Figure 1] and [Figure 2]. These photomicrographs were evaluated individually by two previously calibrated examiners, who were blind to the irrigation regimens and attributed scores according to the rating system developed by Rome et al.,  in 1985:-
|Figure 1: Representative SEM photographs of all the groupsat 6 mm level (middle third). A1-17% EDTA solution followed by1% NaOCl solution for 1 min.A2-17% EDTA solution followed by|
1% NaOCl solution for 3 mins, A3-17% EDTA solution followed by1% NaOCl solution for 5 mins, B1-Smear Clear solution followedby 1% NaOCl solution for 1 min, B2-Smear Clear solution followed
by 1% NaOCl solution for 3 mins, B3-Smear Clear solution followedby 1%NaOCl solution for 5 mins, C1-Distilled water followed by 1%NaOCl solution for 1 min, C2-Distilled water followed by 1% NaOCl solution for 3 mins, C3-Distilled water followed by 1% NaOCl solution for 5 mins
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|Figure 2: Representative SEM photographs of all the groups at 2 mm level (apical third). A1-17% EDTA solution followed by 1% NaOCl solution for 1 min, A2-17% EDTA solution followed by 1% NaOCl solution for 3 mins, A3-17% EDTA solution followed by 1% NaOCl solution for 5 mins, B1-Smear Clear solution followed by 1% NaOCl solution for 1 min, B2-Smear Clear solution followed by 1% NaOCl solution for 3 mins, B3-Smear Clear solution followed by 1% NaOCl solution for 5 mins, C1-Distilled water followed by 1% NaOCl solution for 1 min, C2-Distilled water followed by 1% NaOCl solution for 3 mins, C3-Distilled water followed by 1% NaOCl solution for 5 mins|
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- 0 = No smear layer, dentinal tubules open, free of debris
- 1 = Moderate smear layer, outlines of dentinal tubules visible or partially filled with debris
- 2 = Heavy smear layer, outlines of dentinal tubules obliterated
Attributed scores were tabulated and submitted to statistical analysis. The data obtained were analyzed with the kappa test to determine concordance among the examiners. Mann-Whitney U test and Kruskal-Wallis were used to compare the groups at 5% level of signiﬁcance.
| Results|| |
Intra-examiner and inter-examiner reliabilities were verified using the kappa test, significance set at 0.5, which showed satisfactory value of 0.87 [Table 1]. Since the kappa test showed satisfactory inter-examiner reliability, only the values of the first examiner were considered for the statistical analysis. The mean with standard deviation of smear scores of the three groups at 6 mm and 2 mm is shown in [Table 2] and [Table 3], respectively.
|Table 2: Mean with standard deviation of smear scores of the three groups at 6 mm|
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|Table 3: Mean with standard deviation of smear scores of the three groups at 2 mm|
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At 6 mm level, significant difference was found between Groups A1 with both A2 and A3, using the post-hoc analysis. But no significant difference found between groups A2 and A3. Also, significant difference was found between Groups B1 with both B2 and B3, whereas no significant difference between groups B2 and B3.
At 2 mm level, significant difference was found between Groups A1 and A3, using the post-hoc analysis. But no significant difference was found between groups A1 and A2 or A2 and A3. Further, significant difference was found between Groups B1 and B3, whereas no significant difference was found between groups B1 and B2 or B2 and B3.
| Discussion|| |
The present in-vitro study was designed to evaluate the effect of addition of surfactants and the effect of duration of application of final irrigating solution in removing the intracanal smear layer.
Sodium hypochlorite is the most widely used chemical solution in the biomechanical preparation of root canal system.  However, despite its excellent antimicrobial activity and capacity of dissolving organic materials, this solution alone does not effectively remove the smear layer. , The association of EDTA and NaOCl solutions has proved effective in removing smear layer.  EDTA acts upon the inorganic components of the smear layer, causes the decalcification of peri-tubular and inter-tubular dentine, and leaves the collagen exposed. Subsequently, the use of NaOCl dissolves the collagen, leaving the entrances to the dentinal tubules more open and exposed. Goldman et al.,  and Yamada et al.,  found that the use of a high volume final flush with 17% EDTA followed by NaOCl effectively removed the smear layer.
New irrigating solutions for the removal of smear layer are being constantly introduced into the market, and it is thus necessary to investigate the efficacy of these products to evaluate their effect on the clinical success rate of endodontic treatment. Smear Clear has been recently introduced to the market as a 17% EDTA-based endodontic irrigant containing cetrimide and two additional surfactants namely, polyoxyethylene and iso-octylcyclohexyl ether. 
The results of the present study showed a significant difference between the use of NaOCl alone and the other two experimental groups with respect to smear layer removal as in accordance with other studies that have shown that NaOCl alone is not effective in removing the smear layer. ,, In general, better results were achieved in smear removal at the 6 mm level compared with the 2 mm level in all samples regardless of the type of chelating agent or the duration of application of the irrigating solution. This finding is coinciding with the results of various studies ,, that have shown an effective cleaning action in the coronal and middle thirds of the canals even when different irrigation times and volumes of the solutions were investigated. A larger canal diameter in the coronal and middle third expose the dentin to a higher volume of irrigants, allowing a better flow of the solution and hence further improving the efficiency of smear layer removal. ,, It is possible that a deeper introduction of the needle would permit better cleaning. However, such implementation in clinical practice would bring greater risk of injuring the periapical tissues on account of the possible extrusion of the irrigants. 
The findings of the present study showed that Smear Clear and EDTA had similar performance in smear layer removal from the middle third of the root canal. But, in the apical third Smear Clear showed significantly better smear layer removal compared to 17% EDTA solution. Surface tension may be defined as the force between molecules that produces a tendency for the surface area of the liquid to decrease. This force tends to inhibit the spread of a liquid over a surface or limit its ability to penetrate a capillary tube. Reducing surface tension of endodontic solutions improves their dentin-wetting ability  and improves their flow into narrow root canals,  which might be the probable reason for the better smear layer removal from the apical area in the Smear Clear group in our study.
Variation in the duration of application of the final irrigating solutions may also have an effect on its ability to remove the smear layer. Numerous studies have been conducted in regards to this, showing conflicting results. An in-vitro study,  evaluated the effect of ethylenediamine tetra-acetic acid plus Cetavion (EDTAC) after 5, 15 and 30 minutes and concluded that the effect of EDTAC could be seen after 5 minutes but the strongest effect was detected at 15 min with no variations after 30 minutes. In contrast, Yamada et al.,  reported a few seconds of EDTA administration is sufficient. Meryon et al.,  reported that the smear layer was completely removed with 10% EDTA for 1 min, resulting in increased orifice size. Cergneux et al.,  also reported similar findings when 15% EDTA that was applied in root canal for 4 minutes. Calt and Serper  compared the effects of 17% EDTA on smear layer removal and on the structure of dentin, after 1 and 10 minutes of application. Their results showed that 1 minute EDTA irrigation is effective in removing the smear layer whereas a 10 minute application caused excessive peritubular and intertubular dentinal erosion. Another in-vitro study,  evaluated the influence of irrigation time of 1, 3 and 5 minutes with 15% EDTA and 1% NaOCl on intracanal smear layer removal. Their results showed that although no significant difference existed but the time of 1 minute proved insufficient in cleaning the apical third. The longer application time of EDTA and NaOCl produced the best results in the apical third.
In respect to the application time of Smear Clear, all the studies ,,, that have evaluated this product have used it for 1 minute as per according the manufacturer's instructions. There has not been much research to evaluate the effect of increasing the application time of Smear Clear on its smear removal efficacy.
In the present study, in general, the ability of EDTA and Smear Clear to remove the smear layer was enhanced as the duration of application of the irrigating solution increased. In both the experimental groups, (17% EDTA and Smear Clear) the variation with time was different according to the different levels of root canal. At 6 mm level (middle third), the amount of smear layer on the dentinal walls decreased significantly as the time was increased from 1 minute to 3 minutes, but no statistically significant difference was seen between 3 and 5 minutes duration.
On the other hand, at 2 mm level (apical third), the amount of smear layer on the dentinal walls decreased significantly as the time duration increased from 1 minute to 5 minutes. But no statistically significant difference was seen between 1 and 3 minutes or 3 and 5 minutes.
As far as it could be ascertained in the literature, Smear Clear has been evaluated in four in-vitro studies ,,, with permanent teeth. The first study,  compared the efficacy of different root canal irrigants (NaOCl, Smear Clear, 2% chlorhexidine, REDTA and BioPure MTAD) against Enterococcus fecalis biofilm. The authors found that Smear Clear had greater efficacy than chlorhexidine, REDTA and MTAD. These results may be attributed to the fact that Smear Clear has cetrimide in its composition, which is a quaternary ammonium compound and a cationic detergent that is effective against Gram-positive and Gram-negative microorganisms. However, the other three studies, ,, concluded that Smear Clear was effective in removing the smear layer, but no significant difference was found between Smear Clear and EDTA.
In our study, anterior teeth with straight canals were used. Teeth with curved and narrow canals could have been used for the study; with however, little effect on the consequences of the study since it is the volume of the irrigant and the duration for which when it is exposed to the smear layer determines its efficacy. This depends on the final apical size of the canal and the method of delivery of the irrigant. A. Khademi and M. Feizianfard found that use of both 17% EDTA and 7% citric acid can remove smear layer from narrow and curved canals, especially from apical region. 
Although, the scoring method involved qualitative analysis, the use of a simple and direct scoring system, as proposed by Rome et al.,  by multiple calibrated examiners with concordance between them (kappa test), as well as the large number of observations made in the present study, clearly increase the reliability of the results.
There are other scoring systems for smear layer as proposed by Torabinejad et al.,  Hulsmann et al.,  and Mayer et al.,  but the elaborate criteria could have compromised the quantitative analysis of the smear layer.
Torabinejad et al. described the following smear layer scoring criteria: 0, no smear layer, no smear layer on the root canal surface, with all the tubules clean and open; 1, moderate smear layer; 2, heavy smear layer, smear layer covers the root canal surface and the tubules.
Hulsmann et al., gave a ﬁve-score smear layer scoring criteria: (1) score 1: No smear layer, and all dentinal tubules were open; (2) score 2: A small amount of smear layer, and some dentinal tubules were open; (3) score 3: Homogenous smear layer covering the root canal wall, and only a few dentinal tubules open; (4) score 4: Complete root canal wall covered by a homogeneous smear layer, and no open dentinal tubules were observed; and (5) score 5: Heavy, homogeneous smear layer covering the complete root canal wall.
The results of the present study showed that Smear Clear is an effective root canal irrigant for the removal of intracanal smear layer. S. Anitha Rao and N Manasa  observed similar findings and suggested that Smear Clear and citric acid performed better than EDTA and NaOCl in calcium hydroxide removal in both coronal and apical grooves. The results of our study are in contradiction to the study done by Nelson-Filho P, Leite Gde A et al.,  da Silva LA, Sanguino AC  et al., who suggested that Smear Clear was able to remove the smear layer from the root canals of primary and permanent teeth, similarly as 14.3% EDTA. Andrabi SM, Kumar AN et al.,  have demonstrated enhanced activity of Smear Clear when manual dynamic activation was done. Nevertheless, these in-vitro results cannot be extrapolated completely to in-vivo situations. Hence, further research is required and more in-vivo studies need to be done to evaluate this product.
| Conclusion|| |
Within the limitations of the present study, it could be concluded that,
- NaOCl alone was not effective in the removal of intracanal smear layer
- Final irrigation with either 17% EDTA solution or Smear Clear followed by 1% NaOCl was effective in removing the smear layer. But in the apical third of the root canal, Smear Clear was more effective when compared to 17% EDTA solution. The addition of surfactants to EDTA in Smear Clear would have resulted in better smear layer removal compared with EDTA alone
- The final irrigation protocol of 17% EDTA solution or Smear Clear followed by 1% NaOCl proved to be effective in removing the smear layer for all durations of applications (1, 3 and 5 minutes). However, as the duration of application of the irrigating solution increased from 1 to 5 minutes, its efficacy to remove the smear layer was also enhanced.
| Acknowledgments|| |
The authors deny any conflicts of interest. The authors would like to thank Mr. Gurulingam, Indian Institute of Science, Bangalore for technical assistance and Mr. Dhareshwar for assistance in statistical analysis.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]