Priya Sinha

Abstract

Aim: The purpose of this study was to assess the effects of sodium hypochlorite (NaOCl) immersion and sterilization on the cyclic fatigue resistance of four heat-treated nickel-titanium (NiTi) rotary instruments.  Materials and Methods: Two hundred and forty new nickel-titanium endodontic files were tested for cyclic fatigue resistance in simulated canals. 25/.06 Twisted Files (Sybron Endo, Orange, CA, USA), 25/.06 Hyflex CM (Coltene Whaledent, Cuyahoga Falls, OH), 25/~ Hyflex EDM (Coltene, Whaledent Pvt Ltd) and 25/.06 EdgeFile X3 (EdgeEndo, Albuquerque, NM, USA) files were divided into 4 subgroups (n = 15) for each brand. Subgroup 1 (control group) included new instruments that were not immersed in NaOCl or subjected to autoclave sterilization. Subgroup 2 were composed of instruments dynamically immersed for 3 minutes in 5.25% NaOCl solution. Subgroup 3 consisted of instruments that underwent 3 cycles of autoclave sterilization at 121?C under 15 psi for 15 minutes. Subgroup 4 recruited instruments that received a cycle of both dynamic immersion in NaOCl solution for 3 minutes and 3 cycles of autoclave sterilization. All the files were rotated till fracture occurred. The means and standard deviations of the number of cycles to failure (NCF) were calculated and statistically analyzed using ANOVA with post-hoc Games Howell test. (P < .001).  Results: Comparison among the four investigated instruments indicated statistically significant difference of NCF (P > .001). EdgeFile X3 files exhibited highest cyclic fatigue resistance, followed by Hyflex EDM files, Hyflex CM files and lowest resistance exhibited by Twisted Files in all the subgroups. There was also statistical significant difference (P < .001) when comparing the instruments in respect to the four treatment protocols (subgroups). Instruments undergoing dynamic immersion in NaOCl solution for 3 minutes followed by 3 cycles of autoclave sterilization did influence the cyclic fatigue of NiTi files tested, which showed a significant increase of cyclic fatigue resistance for all the four different heat-treated instruments when compared with the control group. Conclusions: Within the limitations of this study, fracture resistance to cyclic fatigue was the highest for the EdgeFile X3 group followed by Hyflex EDM group, Hyflex CM group and lowest for Twisted File group in all the subgroups. Instruments undergoing dynamic immersion in NaOCl solution for 3 minutes followed by 3 cycles of autoclave sterilization did influence. Keywords: Cyclic fatigue controlled memory wire, Twisted File, Hyflex CM, Hyflex EDM, EdgeFile X3.

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