Resistance to corrosion of NiTi rotary files and surface treatments

Aim:

This study evaluated the pitting corrosion resistance of Ni-Ti rotary instruments with different surface treatments in 17% EDTA and NaCl solutions.

Methods:

A total of 30 instruments (.06 taper size 25) were used. All files were examined in the state as received from the manufacturers and after the experiments. The following groups were established:

µ Group A: Electropolished RaCe instruments as received from the manufacturer.

µ Group B: Non-electropolished RaCe instruments.

µ Group C: Alpha files with a TiN layer obtained by PVD-coating.

All experiments were conducted at 37°C in 17% EDTA solution and in an isotonic sodium chloride solution, using a potentiostat and the observations were performed using a SEM device.

Results:

17% EDTA has not effects in all the groups. In 0.9% NaCl solution the behaviour of the different NiTi rotary instruments was quite different. For group A, and C the potentiostat indicated an increased corrosion resistance. The SEM examination of the instruments allocated to group B revealed the presence of several fabrication marks on the surface of the instruments, while the surface of the electropolished instruments appeared to be smoother, nearly without any signs of surface defects. According to the present results, electropolishing procedures produce a surface free of structural defects

Conclusions:

In conclusion, on the basis of results obtained in this study, there is a risk of corrosion for NiTi instruments without surface treatments in contact with NaCl. Nickel-titanium rotary files with PVD and electropolishing surface treatments showed an increase corrosion resistance.