Electrochemical corrosion assessment of nickel titanium rotary endodontic instruments during root canal preparation

Abstract

Materials and Methods: total of 450 nickel-titanium (NiTi) endodontic rotary files were used in this experiment. 72 files randomly distributed in 4 groups, were made for each file type producing a total of 288 file in working groups. RaCe files and same sizes of Mtwo files were used to preparation 1 root canal of first mandibular human molars and another series of these files used for preparation 2 root canals and this procedure continued to preparation of 8 root canals. Group A consist of RaCe files were used with this manner with 2. 5% NaOCl as irrigant and standard autoclave procedure for NiTi files between each use. Group B was as like as group a differing only in type of irrigant (Normal saline). Group C consist of Mtwo files were used with this manner with 2. 5% NaOCl as irrigant and standard autoclave procedure for NiTi files between each use and Group D is as like as group C differing only in type of irrigant ( Normal saline ). In second part of experiment 72 files randomly distributed in 2 groups were made for each file type producing a total of 144 file in autoclave groups. This procedure continued to 8 cycles of sterilization on a series of RaCe and Mtwo files. Then instruments were sent for corrosion assessment. Nine as received files for each file type used in this study for corrosion resistance assessment as control groups. .normal distribution of data were tested by Shapiro-Wilk test and assumptions for parametric tests were violated solely used non parametric tests .Mann-Whitney U test was used for independent groups and wilcoxon was used for dependent groups. Level of statistical significance was set at (p 0.05). Results & Conclusions: Cyclic polarization curves demonstrated that the corrosion resistance of NiTi rotary files after 4 clinical uses with NaOCl corrosion resistance significantly decreased and caution should be used after 4 cycle of preparation in conjugation with sterilization in clinical situations for both file type. Amount of the corrosion resistance in Mtwo files significantly higher than RaCe files and these properties may affect on clinical efficiency of this instrument and need further investigations. Mtwo Files more resisted to corrosion in NaOCl than RaCe files and the number of autoclave procedures enhanced corrosion resistance of Mtwo files this finding need to further studies to find possible mechanisms.