The effect of argon and nitrogen ion implantation on nickel-titanium rotary instruments.
BACKGROUND
This qualitative study investigated the effect of N(2)(+) and Ar(+) ion implantation on morphologic alterations and fatigue resistance in Pro Taper S1 NiTi (Dentsply-Maillefer, Ballaigues, Switzerland) rotary instruments.


METHODS
Instruments were divided into three groups: N(2)(+) implanted, Ar(+) implanted, and unmodified control group. All instruments were used to prepare five curved canals in epoxy resin blocks with brushing motion. The instruments were examined in a scanning electron microscope (SEM) before use, after first use, and after the fifth use. A more demanding cyclic fatigue test was undertaken, submitting the instruments to 15-second periods of continuous rotation inside the curved canals without a brushing motion. Crack formation was analyzed with the SEM, and the number of 15-second periods required to fracture each instrument was recorded.


RESULTS
No significant morphologic alterations were observed in the instruments after the preparation of five canals. Crack density was similar in all groups. In the subsequent cyclic fatigue test, instruments implanted with nitrogen performed worse than those implanted with argon and the control group. Fracture faces show differences in the fracture modes.


CONCLUSIONS
Ar(+) implantation improved the performance of S1 files moderately, whereas nitrogen ion-implanted files performed worse in the fatigue test. A reduction in file performance seems to be caused by nitrogen diffusion in the grain boundaries, instead of the desired improvement caused by titanium nitride formation.
School of Dentistry, Universidade Luterana do Brasil (ULBRA), Canoas, RS, Brazil. carlosfbwolle@ibest.com.br
Carlos Frederico Brilhante
CF
Wolle
Marcos Antônio Zen
MA
Vasconcellos
Ruth
R
Hinrichs
Alex Niederauer
AN
Becker
Fernando Branco
FB
Barletta
D001128:Argon / Q000737:chemistry*; D003722:Dental Alloys / Q000737:chemistry*; D003786:Dental Pulp Cavity / Q000033:anatomy & histology; D004853:Epoxy Resins; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008953:Models, Anatomic; D009532:Nickel / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D018915:Root Canal Preparation / Q000295:instrumentation*; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*
D003722:Dental Alloys; D004853:Epoxy Resins; C040654:titanium nickelide; D001128:Argon; D009532:Nickel; D014025:Titanium; D009584:Nitrogen