MONICA MONEA, CARMEN BIRIS, EDWIN SEVER BECHIR, NICOLETA SUCIU, ANCA MARIA POP, PETER OLAH EFFECTIVENESS OF NICKEL-TITANIUM ENDODONTIC INSTRUMENTS ON SMEAR LAYER REMOVAL FROM RADICULAR DENTIN A SCANNING ELECTRON MICROSCOPY STUDY The aim of our study was to evaluate the cleaning effect of nickel-titanium (Ni-Ti) rotary files on the smear layer formed on the radicular dentine walls during endodontic procedures. We used 50 freshly extracted maxillary permanent teeth divided in two study groups according to the instruments used for cleaning: Group 1 with ProTaper Ni-Ti rotary files, Group 2 with manual Ni-Ti files. Longitudinal sections of root canals from each group were evaluated by scanning electron microscopy (SEM) in the apical, middle and coronal sections. Representative microphotographs were taken and double blind scoring was performed by calibrated examiners. The amount of smear layer was measured according to Hulsmann scoring system and the data were statistically analyzed. There were statistically significant differences between instruments in the apical root canal sections (p<0.05), where the manual Ni-Ti files gave the best cleaning scores. There were no differences between groups for the middle and coronal thirds. In conclusion, the best approach for an effective removal of smear layer is to combine manual files with rotary Ni-Ti instruments during the endodontic treatment.