Effect of Plasma immersion ion-implantation on NiTi instrument surfaces

Nickel-titanium (Ni-Ti) rotary instruments have been widely used in modern root canal therapy. Surface treatment was a promising way to change the properties of Ni-Ti instruments. Objectives: The objective of this study was to investigate the morphologic change on NiTi rotary instruments with two type surface characteristics after Plasma Immersion Ion Implantation. Methods: A total 34 ProTaper® F2 NiTi rotary instruments (Dentsply/Maillefer) was used in this study. Group I: seventeen instruments were old-type ProTaper® without electro-ploish surface treatment, Group II: the other seventeen files were new type ProTper® with electro-polish surface treated. PIII procedures were carried out at a target Voltage of -25 KV, with an incident Nitrogen dose of 5×1017 ions/cm2. All instruments were observed and investigated before and after PIII treatment, by scanning electric microscope (TOPCON, Tokyo, Japan). Results: In Group I, compared to pre-treatment images, surface destruction was observed in 9 of 17 (53%) instruments. The other 8 (47%) instruments were intact without destructive surface observed. In Group II, none of any evidence of surface destructive findings in all 17 instruments (0%). There was significant difference between these two groups (P<0.01, t-tests).In surface analysis with SEM, the destructive characteristics of the surface including material sputtering, ion bombing, and heat melts. Conclusion: PIII was a promising surface treatment technique. NiTi instruments with electro-polish surface treatment were most suitable to accept the new PIII surface treatment technique.