Cyclic fatigue resistance of three rotary file systems in a dynamic model after immersion in sodium hypochlorite
Abstract
To
evaluate the effect of immersion in 3% sodium hypochlorite solution in
the resistance to cyclic fatigue of three nickel–titanium (NiTi) rotary
file systems, ProTaper Next (PTN), Hyflex CM (CM), and Hyflex EDM (EDM),
in a mechanical model featuring axial movement. Ninety instruments of
three different NiTi rotary file systems, PTN (size 25, 0.06 taper), CM
(25, 0.06), and EDM (25/~, variable taper), were randomly divided
according to a 3 × 3 factorial design and tested under dynamic immersion
in a 3% NaOCl solution (1 or 5 min) or without immersion, making a
total of 9 groups (n = 10). Files
were tested in an artificial root canal with 45° angle and 5 mm radius
apical curvature being submitted to back-and-forth movements until
fracture. Statistical analysis was performed using two-way factorial
ANOVA with Bonferroni post-hoc tests, at a significance level of 5%.
Instruments were evaluated for reliability using a Weilbull approach.
Regardless of the immersion treatment, PTN had on average 1200 ± 178
cycles to fracture, CM had 1949 ± 362, and EDM had 5573 ± 853, which was
a significantly different (P < 0.01). The NaOCl immersion promoted a significant reduction in the mean number of cycles to fracture (P = 0.01),
and was reflected in a significant reduction of the characteristic life
of the instruments of the CM end EDM groups. Within this study
conditions, EDM instruments performed better to cyclic fatigue followed
by CM and then PTN. Immersion in NaOCl decreased the resistance to
cyclic fatigue of all tested instruments, but affected more those
manufactured from CM wire.
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