Evaluation of the surface alterations of the different nikel-titanium files which used in retreatments for removing the root canal filling materials

The aim of this study was to evaluate the surface changes of nickel titanium rotary retreatment files after three and five times of use. Furthermore, effects of 2% sodium hypochlorite and chloroform solutions and sterilization procedures on the NiTi rotary retreatment surfaces were investigated.Protaper Retreatment files, R-endo files and Mtwo retreatment files were used for this study. The palatinal roots of maxillary first molar teeth were obturated with gutta percha and Ah26. After two months, retreatment procedures were performed with these retreatment file systems.Surface changes of NiTi rotary files which untreated, used for three and five times, embedded in NaOCl, chloroform and the files which were execuded sterilization procedures were investigated with atomic force microscopy and scanning electron microscopy. The RMS and Depth values, and three dimensional images were obtained. The surface of retreatment files were observed with SEM at various magnificaitons. EDX data was obtained to assess chemical composition of NiTi file surfaces.RMS and Depth values showed that all three NiTi rotary retreatment file systems showed significant deteriorations after three and five times of use. Cracks, damages and spiral construction deteriorations were detected on SEM images after three and five times of use. Furthermore, Mtwo 15 file was broken off after five times of use.AFM data indicated that 2% NaOCl caused significant surface deteriorations on NiTi rotary files. AFM and SEM evaluation showed that chloroform solution and sterilization procedures didn?t cause significant surface deteriorations.EDX data indicated that in all study groups; all changes occured physically, no chemical changes occured on NiTi rotary NiTi files.In conclusion, Protaper retreatment, R-endo and Mtwo retreatment files showed surface damages depending on retreatment procedures. Clinicians have to consider that retreatment files always have a tendency to break off when used for three times.Key words: Nickel titanium, Retreatment, Atomic force microscope, Scanning electron microscope, Sodium hypochlorite, Chloroform, Sterilization.