Cyclic fatigue resistance and energy dispersive X‐ray spectroscopy analysis of novel heat‐treated nickel–titanium instruments at body temperature

Abstract

The aim of this study was to evaluate the cyclic fatigue resistance of Dia‐X, WaveOne Gold and One Curve files in a water bath at intracanal temperature (35°C). Thirty‐nine instruments Dia‐X, WaveOne Gold, and One Curve systems (n = 13) were tested in an artificial canal with a curvature angle of 60° and a radius of 3 mm. A water bath setup at a temperature of 35°C was used to simulate the intracanal temperature and time to fracture (TTF) as seconds was recorded. The mean data were analyzed statistically using one‐way ANOVA, and post hoc Tukey test (p = .05). The fractured surface of the instruments was examined with scanning electron microscopy (SEM) and chemical composition of the instruments were investigated with energy dispersive X‐ray spectroscopy (EDS). Statistically significant differences were detected in TTF values of all the systems as follows: One Curve > WaveOne Gold > Dia‐X (p < .05). One Curve instruments demonstrated the highest TTF values in all the tested instruments. The EDS microanalysis revealed similar NiTi composition of on the surface of One Curve, WaveOne Gold, and Dia‐X instruments. The novel manufacturing process, including C‐wire heat treatment and the variable cross‐section of the One Curve files, could be the main factors affecting the fatigue life of the instruments.

Influence of surrounding temperature and angle of file access on cyclic fatigue resistance of two single file nickel‐titanium instruments

“…More specifically, there is a connection between cross‐section and stress resistance whereas the larger the metal volume, the lower the fatigue resistance (27). S‐shaped cross‐section ensured better resistance to cyclic fatigue than triangular, horizontal or rectangular, cross‐sectional designs (28,29). F6ST files have a constant S‐shaped cross‐section (5,6,29) while OC instruments possess variable cross‐sections with a triangular one at 5‐mm from the tip (7,8,30).…”

Effects of Simultaneous Liquid or Gel Sodium Hypochlorite Irrigation on the Cyclic Fatigue of Two Single-File Nickel-Titanium Instruments

“…Nevertheless, in agreement with previous findings, the fatigue life of heat-treated NiTi files (OC) was longer than non-heat-treated files (F6ST) in all testing conditions. This behavior is probably due to the greater flexibility of OC files caused by the heat treatment [6,32,33].…”

Evaluation of the Cyclic Fatigue of Two Single Files at Body and Room Temperature with Different Radii of Curvature

“…Indeed, F6ST instruments are made with a traditional austenite 55-NiTi alloy with a modified S-shaped cross section along their entire working part [ 13 , 14 , 28 ]. OC files are produced with a novel heat treatment and possess, according to the manufacturer, a variable design which progressively changes from S-shaped design close to the shaft to a triangular cross section in the apical middle part, including at 5 mm and 3 mm as previously reported [ 11 , 15 , 16 ]. Although a dynamic model seems to mimic clinics better compared to the static one, it is challenging to guarantee repeatable and standardized laboratory conditions for each instrument.…”

“…This advantage was not significant at 37 °C, probably due to the fact it was compensated by the significant negative impact of increase of temperature. Therefore, on the basis of these results, it could be speculated that the cyclic fatigue of OC files, heat treated and with a triangular cross section at the apical level [ 15 , 16 ], is more affected by the small radius of curvature, while F6ST instruments made by traditional NiTi alloy and with an S-shaped cross section [ 13 , 14 ] are more influenced by temperature.…”

“…One Curve (Micro-Mega, Besançon, France) is also a single file rotary made of a C-Wire obtained through an innovative heat treatment process which should improve the file flexibility. The One Curve presents only one file (25.06) possessing a changeable cross-sectional design [ 15 , 16 ]. Although many previous investigations on cyclic fatigue have been performed at room temperature [ 11 , 17 ], body temperature (around 37 °C) may significantly affect the transformation temperatures of NiTi crystalline phase and thus the cyclic fatigue behavior of NiTi files [ 1 , 18 , 19 ].…”