Introduction
The smear layer originated from endodontic instrumentation is a thin layer with average thickness of 1 micrometer which occludes the dentinal tubules of the prepared root canal walls.(1,2) Some investigators believe that it is beneficial to remove the smear layer for eliminating the microorganisms inside the root canal system and to improve the obturation seal while others believe preserving that occludes the orifices of dentinal tobuli and prevents the penetration of irrigants , medications and filling materials into the dentinal tubules so it is still controversial whether to remove or to  remain this layer . The irrigation of root canal  system with 10 mls of  17% Ethylene Diamine Tetraacetic Acid (EDTA) followed by 10 mls  of 5.25% Naocl is the most effective method for smear layer removal since EDTA  removes the inorganic portions of the smear layer while Naocl solution dissolves and  bubbles out the organic compartments of this layer(3,4,5). The purpose of this research was to compare the effects of 2 commerical types of EDTA with final irrigation of the root  canals with 5.25% Naocl for removing the smear layer.

Materials And Methods
28 straight single root teeth with mature apexes were collected from dental clinics. These teeth were extracted for full  denture purposes. The teeth were immersed within 10% formalin solution (Merck - Germany) first and were kept in Normal saline (Samen - Mashad) through performing the research. Access cavities were made by diamond bur (Diatech - Germany) on the teeth and all samples were instrumented up  to the # 60 by K files (mailferr Swiss). the samples were irrigated with 5.25% Naclo solution (Shimin - Iran) during the cleaning and shaping procedure.These teeth were divided into 2 experimental groups (Group A and GroupB) each group consisting of 12 teeth. The remaining  four teeth were assigned as a control group. After instrumentation, the root canal systems of the group A samples were irrigated with 10 mls of 17% EDTA (Ariadent_ Iran) followed by 10 mls  of 5.25%Naocl and the group B were irrigated with 10 mls of 17% EDTA (Merck - Germany)followed by 10 mls of 5.25% Naocl respectively.The time of application of the EDTA was 1 minute in both groups.

The control group were just irrigated with 10 mls of 5.25% Naocl .The crowns of the teeth  were removed by a diamond Disc # 4 (Diatech - Germany) at the cemento enamel junction .Finally the roots of all experimental groups were sectioned longitudinally and were processed for SEM (Oxford England) observation at 2000 X magnification .The smear layer removed in each  experimental group was scored in a blind manner according to Schafer,s grading criteria. (6,7,8,9,10,11)
Results
Both Iranian and foreign 17% EDTA + 5.25% NAOCL solution had successfully removed smear layer from all parts of the sectioned root

Canals. (Score 1). So there was significant statistical diference between both Group A and Group B samples with the control group in which the smear layer had completely covered all parts of the roots. (Score 5) (p<0.05).There was not significant  statistical difference between group A and group B. (P>0.05).

Discussion
In this study the  smear layer removing efficacy of 2 different commercial types of Ethylene diamine tetraacetic acid solutions with similar concentrations (17%)   was compared and evaluated. All extracted teeth had straight root canals and the amount of preparation was the same in all groups.The time of application of  the EDTA and  also the time of final irrigation the root canals with5.25% NAOCL solution was  the same in all experimental groups. So just the capacity of  these 2 commercial trends of this chemical composition (EDTA) was compared for the purpose of the smear layer removal.

In the past,several different studies have confirmed the smear layer removing efficacy of the chelating agent Ethylene Diamine Tetraacetic acid.(12) Results of the current  investigation corroborate with the findings of Crumpton  et al who reported complete removal of smear layer and lower erosiveness of this irrigation regimen in 2005.(13) On the other hand  Calt & Serper, Niu& Yoshioka and Gande & Plotino have reported that the application of 17% EDTA longer than 1 minute can cause adverse erosion of the root canal surfaces.(9,14,15).The PH Of the EDTA   is another important factor which affects the debris and smear layer removing capacity of this solution. In this study The PH Of applied EDTA in both group A and group B was between 6 and 10 which is a neutral PH that has previously been shown to be more effective than acidic and alkaline PH for removing the smear layer.(16)

Conclusion
Based on the results of this investigation it seems that the Iranian product of EDTA made by Ariadent company has similar capacity of removing the smear layer with the international type made by Merck company in Germany with less price.

This study is supported by the research center of Kerman university of medical sciences & health services.

References
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