Evaluation of Flexibility, Microstructure and Elemental Analysis of Some Contemporary Nickel-Titanium Rotary Instruments

Abstract

Background: Contemporary nickel-titanium (NiTi) rotary endodontic instruments had a revolutionary impact on the success of root canal treatment.

Aim: To evaluate the flexibility, microstructure and elemental analysis of four different recent NiTi rotary instruments, namely; Wave One Gold, TF adaptive, HyFlex EDM and Gr_Reciproc Blue compared to conventional Protaper Universal (F2).

Material and methods: The NiTi rotary files were subjected to cantilever bending test to evaluate their flexibility. The microstructural characteristics and elemental analysis were examined via scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDX).

Results: The TF adaptive, HyFlex EDM and Wave One Gold endodontic files showed significantly lower cantilever bending values (i.e., higher flexibility) than Protaper F2 and Gr_Reciproc Blue (p < 0.05). The SEM micrographs showed that the bulk of all examined files showed multiple striations due to the cutting process, on the other hand, their external surfaces were different: The Protaper Universal F2 showed multiple voids, while the TF Adaptive surface exhibited more uniform structure. The Hyflex EDM had a crater-like surface, whereas Wave one Gold showed machining grooves with minimum defects, while Reciproc Blue displayed machining grooves with random scratch lines. There was a significant difference in bulk and surface elemental analysis of the various examined files, yet composed mainly of the same elements.

Conclusion: Chemical composition, heat treatment, manufacturing process and geometrical design of the NiTi rotary instrument have a great influence on their flexibility and microstructure.

Keywords: Elemental analysis; Endodontic files; Flexibility; Heat treatment; Microstructure; NiTi instruments.

Figure 1

Rotary NiTi instruments: A) ProTaper Universal F2; B) TF adaptive; C) HyFlex EDM; D) Wave One Gold; E) Reciproc Blue

Figure 2

Bar chart showing mean cantilever bending values among the different endodontic files

Figure 3

Representative SEM micrograph and EDX spectrum from a Protaper Universal F2 instrument; A) SEM micrograph of file cross-section after cutting, red arrow pointed to cut part of bulk and white arrow directed to external surface, magnification 400 X; B) SEM micrograph of cut part of bulk, magnification 8000 X; C) SEM micrograph of external surface, magnification 8000 X; D) EDX of cut part of bulk; E) EDX of external surface

Figure 4

Representative SEM micrograph and EDX spectrum from a TF Adaptive instrument; A) SEM micrograph of file cross-section after cutting, red arrow pointed to cut part of bulk and white arrow directed to external surface, magnification 400 X; B) SEM micrograph of cut part of bulk, magnification 8000 X; C) SEM micrograph of external surface, magnification 8000 X; D) EDX of cut part of bulk; E) EDX of external surface

Figure 5

Representative SEM micrograph and EDX spectrum from a Hyflex EDM instrument; A) SEM micrograph of file cross-section after cutting, red arrow pointed to cut part of bulk and white arrow directed to external surface, magnification 400 X; B) SEM micrograph of cut part of bulk, magnification 8000 X; C) SEM micrograph of external surface, magnification 8000 X; D) EDX of cut part of bulk; E) EDX of external surface

Figure 6

Representative SEM micrograph and EDX spectrum from a Wave one Gold instrument; A) SEM micrograph of file cross-section after cutting, red arrow pointed to cut part of bulk and white arrow directed to external surface, magnification 400 X; B) SEM micrograph of cut part of bulk, magnification 8000 X; C) SEM micrograph of external surface, magnification 8000 X; D) EDX of cut part of bulk; E) EDX of external surface

Figure 7

Representative SEM micrograph and EDX spectrum from a Reciproc Blue instrument; A) SEM micrograph of file cross-section after cutting, red arrow pointed to cut part of bulk and white arrow directed to external surface, magnification 400 X; B) SEM micrograph of cut part of bulk, magnification 8000 X; C) SEM micrograph of external surface, magnification 8000 X; D) EDX of cut part of bulk; E) EDX of external surface

Figure 8

Bar chart showing elemental analysis (EDX) of bulk material of the different endodontic files

Figure 9

Bar chart showing elemental analysis (EDX) of external surfaces of the different endodontic files