Influence of clinical use on physical-structural surface properties and electrochemical potential of NiTi endodontic instruments.
OBJECTIVE
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.


METHODS
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.
Department of Dental Clinic, Faculty of Dentistry, Federal University of Bahia, Salvador, BA, Brazil.
E S J
http://orcid.org/0000-0001-5504-6055
ESJ
Pereira
Department of Metallurgy and Materials, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
C C F
CCF
Amaral
Department of Metallurgy and Materials, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
J A C P
JACP
Gomes
Department of Endodontics, Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, CA, USA.
O A
OA
Peters
Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
V T L
VTL
Buono
Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
M G A
MGA
Bahia
D000497:Alloys / Q000627:therapeutic use; D004563:Electrochemistry; D006801:Humans; D008855:Microscopy, Electron, Scanning; D012390:Root Canal Therapy / Q000295:instrumentation*; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties
D000497:Alloys; C013616:nitinol
CM technology; NiTi alloy; electrochemical potential; oxide layer; shape memory technology