RESUMO
Recently, the Nickel-Titanium rotary instruments have been noticed because of their desired properties such as high flexibility, less transportation and perforation and less time consumption. Therefore, the aim of this study was to compare the cleaning efficiency of these instruments with hand stainless steel [SS] and Nickel-Titanium [NiTi] files. In this invitro experimental study 46 freshly extracted human molars with the curvature of 15-25 degree in mesial root were used. The teeth were randomly divided into 4 experimental groups, each containing 11 teeth and two control teeth. Then mesial canals were instrumented as follows: group 1: step back instrumentation with stainless steel hand files. group 2: passive step back instrumentation with stainless steel hand files group 3: step back instrumentation with Nickel- Titanium hand files group 4: crown down instrumentation with rotary Profile system No instrumentation was done on two control teeth. After crown amputation of teeth, the mesial roots were split in half and one half was randomly selected for SEM investigation. After SEM preparation, the photomicrographs were prepared from apical, middle and cervical part of canal with magnification of 2000 under SEM. These graphs were scored by an endodontist in a blind manner, according to the amount of residual debris and smear layer on canal surface. Then, the data was analyzed by Kruskal-Wallis and Mann-Whitney tests. The difference between 4 groups was not statistically significant according to the amount of residual debris [P>0.05]. But, rotary Profile system had produced more smear layer than other three groups [P<0.01]. This study showed that the amount of residual debris and smear layer after canal preparation in apical third is more than middle third and in middle third is more than cervical third [P<0.01]. After using the rotary instrumentation, it is better that canals were finally irrigated with combination of 17% EDTA and 5.25% NaOCl to remove the smear layer