Efficacy Of Different Final Irrigation Techniques On The Removal Of Smear Layer From The Root Canal – A Scanning Electron Microscopic Analysis

INTRODUCTION

Instrumentation of root canal has been shown to produce an agglomeration of debris called the smear layer on its walls. Under scanning electron microscope smear layer shows an amorphous, irregular and granular appearance¹. It blocks the antimicrobial effect of intra-canal disinfectants from reaching into the tubules.^2,3 Furthermore, smear layer on the canal walls may act as an intermediate physical barrier, removal of which has been shown to promote dentine permeability enhancing diffusion and action of intracanal medication , greater penetration of filling material into lateral canals and dentinal tubules.⁴ A systematic and Meta analysis report observed that majority of the studies conducted agree with the removal of the smear layer than its retention.⁵

Various methods that advocated for the removal of the smear layer include syringe needle irrigation with NaOCl and chelating solutions, acids, MTAD, mechanical agitation of irrigants using sonics, ultrasonics, brushes, and other devices like Endo Vac system, Rinsendo etc.⁶

Canal irrigation is an integral part of root canal debridement because it allows for cleaning beyond what might be achieved by root canal instrumentation alone. Because no single irrigating solution is capable of dissolving organic tissues and dimineralize the smear layer, a sequential use of organic and inorganic solvents such as sodium hypochlorite (NaOCl) and Ethylene- diamine-tetracetic acid (EDTA) is often recommended as the final rinse.² Ultrasonic agitation of irrigants such as NaOCl has also been found to be effective in debriding the canal and studies on these systems have shown that teeth thus prepared have significantly cleaner canals.⁷ Other studies fail to demonstrate the superior cleaning efficacy of the ultrasonics.⁸ Endodontic literature supports the use of ultrasonics after the completion of root canal instrumentation known as passive ultrasonic irrigation.⁹ However Ultrasonic irrigation takes additional minutes per canal for adequate debridement, and there is increased rate of file breakage at high level of ultrasound activation. Further during passive ultrasonic irrigation, accidental canal contact with ultrasonic and sonic instruments can potentially damage the canal wall or finished canal preparation, forming longitudinal parallel grooves on the canal walls.¹⁰ To overcome the disadvantages F- File a polymer based plastic rotary finishing file (Plastic Endo, LLC, Buffalo Grove, IL, USA) was introduced. It claims to be effective in removing the canal debris and smear layer without further enlarging the canal when used prior to obturation.¹⁰ Very few studies are available on F-File and there are conflicting results on the effectiveness of F-File.¹¹ Hence, this SEM study was undertaken to evaluate the efficacy of F-file to remove smear layer and compare it to two other final irrigation methods namely , needle syringe irrigation using 17% EDTA followed by 5.25% NaOCl and passive ultrasonic agitation of 5.25% NaOCl.

MATERIALS AND METHOD

60 freshly extracted intact caries free human teeth with straight single canal and mature apices were selected. The teeth were cleaned to remove the superficial debris and stored in physiologic saline until use.Conventional endodontic access cavities were prepared using Endo Access Bur (Dentsply). The root canals were scouted with no#10 K file and checked for patency. Following working length determination, Glydepath was established up to the working length. This was followed by instrumentation with rotary ProTaper system (Dentsply). Shaping of the canals with S1 and S2 was done, followed by the finishing files F1, F2 up to the working length. Canals were irrigated with 5.25% NaOCl in between instrumentation. Following instrumentation the apices of all the teeth were sealed with modeling wax. The teeth were then divided in to three groups consisting of twenty teeth each based on the final irrigation regimen used.

Group A – Needle irrigation with 3ml of 17% EDTA followed by 3ml of 5.25%NaOCl. Depth of the needle penetration was standardized up to 2-3mm short of apex.

Group B – Ultrasonic agitation of 5.25% of NaOCl with irrigation tips (Pro ultra-Dentsply) for 1minute.

Group C – F-file + 5.25% of NaOCl. The plastic finishing file with a rubber stop set at working length was attached to a slow speed torque controlled hand piece set at 600rpm. The file was passively placed into the canal filled with NaOCl and circumferentially worked with cyclic axial motion (up and down) for 30 seconds. Care was taken to see that the F-file did not bind the canal walls during the procedure. A new F-file was used for every canal.The canals were then given a final flush of 3ml of 5.25% NaOCl.

Following final irrigation, all the teeth were decoronated at the CEJ. Vertical grooves were made on the buccal and lingual surfaces and the roots were split in to two halves with the help of chisel and mallet and the best half was selected for SEM analysis. The root sections of all groups were splutter coated with gold (JFC 1100E JEOL, Japan) for viewing under SEM. Photomicrographs of the coronal, middle and apical areas of section were obtained at 1000 X magnification(figure 1).

SCORING OFTHE SMEAR LAYER

The photomicrographs were projected on a screen in a dark room. The scoring of smear layer was done by three independent observers according to the criteria set by Hulsmann.¹

Score 1: No smear layer, dentinal tubuli open.

Score2: Small amount of smear layer, some dentinal tubuli open.

Score 3: Homogenous smear layer covering the root canal wall, only few dentinal tubuli open.

Score 4: Complete root canal wall covered by a homogenous smear layer, no open dentinal tubuli.

Score 5: Heavy, nonhomogenous smear layer covering the complete root canal wall.

The observers were blinded about the groups and all the examiners scored independently.

Method of statistical analysis

The data was entered in Microsoft Excel and statistical analysis was done using SPSS (Version 10.5) package. Statistical analysis was done using Kruskal Wallis test, Kappa Analysis and Mann Whitney U test to find out the significant difference between the study groups. p value <0.05was set as significant.

RESULT

The mean scores for the amount of smear layer were recorded. Group Ascored the highest for smear layer followed by group B and the least for group C. And the difference among the three groups were statistically significant (Tables 1,2). Coronal third of all the groups scored the least for smear layer followed by the middle third and maximum score was recorded for the apical third (Graph1). Statistical analysis revealed significant difference with in the study groups at all the three levels (Table3). Comparison between the study groups at the coronal, middle and apical third revealed significant difference between Groups B and C and Group A(Table 4).

DISCUSSION

This invitro study evaluated the effect of three different final irrigation regimens on the removal of smear layer. Significant differences were observed between the study groups. The syringe irrigation (Group1) was found to be least effective among the study groups in removing the smear layer.

In the conventional syringe needle irrigation, it has been shown that the irrigant is delivered only 1mm beyond the tip of the needle. The penetration depth of the irrigating solution and its ability to remove the smear layer in the apical third is thus limited. There is also no mechanical agitation of the irrigant ^13,14. This probably explains the poor performance of the needle syringe irrigation group. Various recommendations have been made to improve the efficacy of syringe needle irrigation. They are bringing the needle in close proximity to the apex, larger irrigation volume and smaller irrigation needles/cannulas .^15,16 However it may be difficult to standardize and control the fluid flow rate and greater care need to be taken to avoid apical extrusion .¹⁷

The ultrasonic activation of 5.25%NaOCl was found to be effective in removing the smear layer. It was reported in a study that when passive ultrasonic irrigation was used to agitate 3% NaOCl, complete removal of smear layer was obtained.⁷ Passive ultrasonic irrigation with EDTA and a combination of EDTAand sodium hypochlorite did not remove the smear layer from the apical third of the canal walls in another study.¹⁸ Observations of the present study also confirmed the presence of smear layer in the apical third of the canals irrigated with ultrasonics but, was less compared to conventional needle delivery group. There significant increase in dissolving capacity of organic material by NaOCl, when NaOCl is agitated by ultrasonic activation and during ultrasonic irrigation a much higher velocity of irrigant, due to acoustic micro streaming, is created in the canal which can be attributed for the enhanced performance of Group B.¹¹

The smear score recorded for the F-File was the least among the three groups. This could be attributed to its unique file design enabling agitation of the sodium hypochlorite into the areas of the canal that prior instrument did not reach. This facilitated the removal of dentinal wall debris and smear layer while not further enlarging the canal simulating the same effects as seen in the sonic and ultrasonic usage. It was also worked up to the working length. The plastic files tip size of 0.20mm with the taper of 0.04, provides a better clinical relationship to the rotary nickel titanium files currently available than sonic and ultrasonic instruments do¹⁰ .

The coronal third of all the root canals recorded the least mean score for smear layer. This was in accordance with the observations made by Yamashita et al. The apical third of all the canals scored poorly probably due to the narrow diameter that impaired the flow of the irrigants which in turn reduced the mechanical and chemical action of the irrigants to take place at this region.¹⁹  When the study groups were compared at the coronal, middle and apical thirds, Group C performed better than group A and the difference was statistically significant. Though the mean score for smear layer recorded at the middle and apical thirds was least for Group C, the difference was not statistically significant compared to Group B.

There are conflicting results regarding cleaning efficiency of F-File and various studies indicate that none of the systems and agitation protocols was effective in completely removing the debris from the apical third of the canal.^20,21,22,23 Further research is required due to inability of the different irrigation regimens to completely clear the smear layer especially from the apical third of the canal

CONCLUSION

In the present study we observed that the sterile, single use plastic finishing file was an efficient tool in removing the smear layer. Its efficacy was observed to be better than both ultrasonic as well as syringe needle irrigation and hence could be a useful alternative to ultrasonic irrigation. It can be used as the last file along with sodium hypochlorite in conventional endodontic treatment prior to obturation. It was easy to handle and use and had a time and cost saving advantage over the ultrasonic irrigation systems. Only straight canals were used in the present study. This is not the case in a clinical situation where variations in canal anatomy and configuration are a common entity. Clinical studies using F-File would give us better picture about the true efficacy of this file system.

Acknowledgement

The authors wish to acknowledge the cooperation extended by the management of M.S.Ramaiah Dental College and Hospital and the Indian Institute of Science, Bengaluru ,Karnataka for the SEM analysis.