Search

Abstract: Aim: To investigate the surface morphology and electrochemical potential of superelastic (SE), M‐Wire (MW) and shape memory technology (SMT) NiTi instruments before and after single clinical use in vivo. Methodology: A total of 60 ProTaper Universal F2 (PTU‐SE), ProTaper Next X2 (PTN‐MW), Typhoon (TYP), Hyflex (HF) and Vortex Blue (VB), the last three SMT, and size 25, .06 taper (n = 6 of each type) files were examined. Scanning electron microscopy (SEM), X‐ray energy‐dispersive spectroscopy (EDS) and electrochemical potential analysis were employed before and after clinical use. Statistical analysis was performed with one‐way analysis of variance and Bonferroni's post hoc test. Significance was determined at the 95% confidence level for both tests. Results: SEM observations of new instruments indicated the presence of marks left by the machining process during manufacturing and EDS revealed the existence of an oxide coating on shape memory instruments. After clinical use, the five types were associated with propagation of transverse cracks 3 mm from the tip. The surface oxide layer of TYP, HF and VB instruments had microcracks in multiple directions, whilst TYP and HF had fragmentation in chip form of the oxide layer. EDS analysis demonstrated a significant reduction of the oxide layer in shape memory instruments, except for VB. Electrochemical potentials were higher for shape memory instruments than for M‐Wire and superelastic NiTi instruments, respectively (P < 0.05). Conclusions: It appears that shape memory technology NiTi instruments have a dysfunctional oxide layer after clinical use. Additionally, they featured higher electrochemical potential relative to NiTi instruments manufactured from M‐Wire, and conventional superelastic NiTi alloy. [ABSTRACT FROM AUTHOR]

Aim To assess and compare the flexibility and torsional resistance of PathFile, Ra Ce ISO 10 and Scout Ra Ce instruments in relation to stainless steel K- File hand instruments. Methodology Rotary Path File (sizes 13, 16 and 19; .02 taper), Race ISO 10 (size 10; 0.02, 0.04 and 0.06 tapers), Scout Ra Ce (sizes 10, 15 and 20; 0.02 taper) and hand K- File (sizes 10, 15 and 20; 0.02 taper) instruments were evaluated. Alloy chemical composition, phases present and transformation temperatures were determined for the Ni Ti instruments. For all instruments, diameters at each millimetre from the tip as well as cross-sectional areas at 3 mm from the tip were measured based on ANSI/ ADA Specification No. 101 using image analysis software. Resistance to bending and torsional resistance were determined according to specification ISO 3630-1. Vickers microhardness measurements were also taken in all instruments to assess their strength. Data were analysed using analysis of variance (α = 0.05). Results The alloys used in the manufacture of the three types of Ni Ti instruments had approximately the same chemical composition, but the Path File instruments had a higher Af transformation temperature and contained a small amount of B19' martensite. All instruments had diameter values within the standard tolerance. The bending and torsional resistance values were significantly increased relative to the instrument diameter and cross-sectional area. Conclusions PathFile instruments were the most flexible and the least torque resistant, whilst the stainless steel instruments were the least flexible although they were more torque resistant than the Ni Ti instruments. [ABSTRACT FROM AUTHOR]

Endodontic files made of nickel–titanium (NiTi) superelastic wires can be employed in rotary techniques for cleaning and shaping curved root canals, suffering tensile–compressive strain cycles with maximum amplitudes between 3 and 5%. The aim of this work was to study the fatigue behaviour of this material under such high deformation conditions, using NiTi instruments and superelastic wires taken from their production line. One hundred load–unload tensile cycles in the superelastic regime (4% elongation) were applied to NiTi wires. New endodontic instruments were fatigue-tested simulating the geometrical conditions found in their clinical use. It was found that only small changes took place in the parameters describing the mechanical behaviour of the cycled wires. The measured average number of cycles to failure varies inversely with the maximum tensile strain amplitude in the fatigue tests ( r= 0.993). [ABSTRACT FROM AUTHOR]