The effect of cleaning procedures on fracture properties and corrosion of NiTi files.
OBJECTIVE
To evaluate the effect of repeated cleaning procedures on fracture properties and corrosion of nickel-titanium (NiTi) files.


METHODS
New NiTi instruments were subjected to 2, 5 and 10 cleaning cycles with the use of either diluted bleach (1% NaOCl) or Milton's solution (1% NaOCl plus 19% NaCl) as disinfectant. Each cleaning cycle consisted of scrubbing, rinsing and immersing in NaOCl for 10 min followed by 5 min of ultrasonication. Files were then tested for torsional failure and flexural fatigue, and observed for evidence of corrosion using scanning electron microscope (SEM). Four brands of NiTi files were immersed in either Milton's solution or diluted bleach overnight and evaluated for corrosion.


RESULTS
Up to 10 cleaning cycles did not significantly reduce the torque at fracture or number of revolutions to flexural fatigue (P > 0.05, two-way anova), although decreasing values were noted with increasing number of cleaning cycles using Milton's solution. No corrosion was detected on the surface of these files. Files immersed in 1% NaOCl overnight displayed a variety of corrosion patterns. The extent of corrosion was variable amongst different brands of files and amongst files in each brand. Overall, Milton's solution was much more corrosive than diluted bleach. Corrosion of file handles was often extreme.


CONCLUSIONS
Files can be cleaned up to 10 times without affecting fracture susceptibility or corrosion, but should not be immersed in NaOCl overnight. Milton's solution is much more corrosive than bleach with the same NaOCl concentration.
O'Hoy
P Y Z
PY
School of Dental Science, University of Melbourne, Melbourne, Australia.
Messer
H H
HH
Palamara
J E A
JE
D000704:Analysis of Variance; D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry*; D004202:Disinfectants / Q000627:therapeutic use; D004203:Disinfection / Q000379:methods*; D004868:Equipment Failure; D006801:Humans; D007101:Immersion; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D012965:Sodium Chloride; D012973:Sodium Hypochlorite / Q000627:therapeutic use; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*; D019415:Torque; D014465:Ultrasonics
D003722:Dental Alloys; D004202:Disinfectants; C040654:titanium nickelide; D012965:Sodium Chloride; D009532:Nickel; D014025:Titanium; D012973:Sodium Hypochlorite