Comparison of the remaining smear layer following use of manual and rotary instruments with various speeds

Comparison of the remaining smear layer following use of manual and rotary instruments with various speeds Dr. M. Bidar* - Dr. M. Zarei** - Dr. A.A Madani***, Dr. MDJ. Kharazifard**** * Associate Professor of Endodontics Dept., Faculty of Dentistry, Mashhad University of Medical Sciences. ** Assistant Professor of Endodontics Dept., Faculty of Dentistry, Mashhad University of Medical Sciences. *** Assistant Professor of Prosthodontics Dept., Faculty of Dentistry, Mashhad University of Medical Sciences.**** Statistical editor of research & statistic center, Faculty of Dentistry, Tehran University of Medical Sciences Background and Aim: Endodontic smear layer (SL) can reduce the apical seal and adaptation of gutta-percha to root canals (RCs). Instruments with adequate flexibility and proper speed create less smear during RC preparation. The purpose of this in vitro study was to compare the amount of SL following canal preparation by hand and rotary instrumentation. Materials and Methods: Sixty freshly extracted single-rooted teeth with minimum curvatures were divided into two groups. All canals in group 1 were instrumented with SS-type K-files using a step-back technique. The remaining teeth constituting group 2 were divided into 3 subgroups and prepared by employing the GT profile system at rotational speeds of 1000, 8000, and 24000 rpm. In both groups, 2 teeth were selected as controls, which were placed in 17% EDTA for 15 minutes and then washed with 5.25% Naocl. All specimens were cut bucco-lingually, and evaluated under an electron microscope. Kruskal-Wallis and Man-Whitney U tests were used to compare the groups. Results: A significant difference in the amount of SL was not observed between the three rotational speeds at the coronal portions of the RCs. These sections were cleaner in the 1000 and 24000 rpm groups. No significant difference was found between the two instrumentation techniques in the apical portions. The mean size of the smear plug was larger and showed a greater amount of attachment in group 1 as compared to group 2. Conclusion: Ni-Ti rotary instruments produced a thinner SL with less attachment to the root canal walls making it easy to remove with sufficient irrigation. Key words: Electron microscope – Smear layer - Rotary instruments