Surface Stability of Titanium Nitride Coated Dental Ni-Ti Alloy Files

The clinical Ni-Ti file is required the longest fatigue fracture life and wear resistance with small metallic ion dissolution in root canal space.Objective: The purpose of this study was to investigate the surface stability of titanium nitride coated dental Ni-Ti files Methods: ProTaper®9415;(Maillfer, Dentsply, Ballaigues, Switzerland) were used, respectively, for experiment. The surfaces of specimens were observed by FE-SEM at the upper, middle and lower part of Ni-Ti file. In order to decrease the defects, TiN film coating was carried out on the Ni-Ti file surface using pure Ti target materials with nitrogen gas at 25^oC, 40^oC and 300^oC. The metallic ion dissolution of TiN coated Ni-Ti file surface was investigated by using potentiodynamic, cyclic potentiodynamic polarization test and AC impedance test in 0.9% NaCl solution at 36.5±1 ^oC.

Results: The surface of as-Ni-Ti file showed the mechanical defects like a scratch formed by manufacture machine, whereas TiN coated surface showed decrease of mechanical defects. The corrosion potential(-130mV) of coated specimen was increased and current density was decreased with TiN coating temperature. Also pitting corrosion resistance(1250mV) of TiN coated Ni-Ti file was higher than that(500mV) of non coated Ni-Ti file. Polarization resistance(Rp) values of non-coated and TiN coated Ni-Ta file at 300^oC showd 1.40 X 10⁶ Ωcm² and 6.44X 10⁶Ωcm², respectively. Rp of TiN coated Ni-Ti file was higher than that of non-coated Ni-Ti file. TiN coated Ni-Ti file showed morphology of non metallic dissolution, but non-coated file was severely attacked by Cl^- ion.

Conclusion: It is considered that the dissolution of metallic ion of Ni-Ti file depended on TiN coating or not, and confirmed that maximum condition of TiN coating such as substrate temperature can be improved the bio-stability, wear resistance and fatigue fracture resistance of Ni-Ti file.(Corresponding author:hcchoe@chosun.ac.kr)