ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

MECHANICAL BAHAVIOR OF DIFFERENT NICKEL-TITANIUM
ROTARY ENDODONTIC INSTRUMENTS BY FINITE ELEMENT
ANALYSIS
1. ABSTRACT
L.A. Santos 1 , M.G.A. Bahia 2 , E.B.L. Casas 3 and V.T.L. Buono 4
The purpose of this study was to evaluate the flexibility and torsional strength of
different NiTi rotary endodontic instruments by using a finite element approach and
compare the numerical results with the experimental ones. Two commercially available
files were analyzed, ProTaper F1 and Mtwo. An accurate geometric model was created
for each instrument by micro-CT scanning and the nonlinear mechanical behavior of
NiTi was considered for the constitutive model. The boundary conditions were selected
according to specification ISO 3630-1 for flexibility and torsional experimental tests
and the simulations performed in ABAQUS 6.9-1. The calculated results were
compared with the experiment in order to validate the simulations. The results showed
smaller stress levels for the Mtwo instrument when simulated under bending conditions
and, consequently, higher flexibility. On the other hand, the Mtwo instrument presented
a higher tendency to fracture in torsional conditions when compared to ProTaper F1
instrument. The good fitting among the simulated and experimental results shows that
numerical methods may be helpful to understand the mechanical behavior of these
instruments during the root canal preparation.
2. INTRODUCTION
In recent decades nickel-titanium (NiTi) rotary endodontic instruments have gained
increasing popularity over stainless steel files in the endodontic field. Mainly due to the
superelastic behavior of the NiTi alloys, these files present a higher flexibility and better
preserve the root canal shape, with less canal aberrations (1). This superelastic behavior
is explained by a solid-solid phase transformation between two different
crystallographic structures, austenite and martensite, allowing the material to undergo
high reversible deformations.
Despite these advantages, fracture of NiTi files remains a concern in clinical practices.
The failure of these instruments may occur by torsional overloading or flexural fatigue
1 PhD Student, Metallurgical, Materials and Mineral Engineering Graduate Program, School of
Engineering, Universidade Federal de Minas Gerais (UFMG), Av. Antônio Carlos 6627, 31270-901, Belo
Horizonte, Brazil
2 Professor, Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas
Gerais (UFMG), Av. Antônio Carlos 6627, 31270-901, Belo Horizonte, Brazil
3 Professor, Department of Structural Engineering, School of Engineering, Universidade Federal de Minas
Gerais (UFMG), Av. Antônio Carlos 6627, 31270-901, Belo Horizonte, Brazil
4 Professor, Department of Metallurgical and Materials Engineering, School of Engineering, Universidade
Federal de Minas Gerais (UFMG), Av. Antônio Carlos 6627, 31270-901, Belo Horizonte, Brazil