M-Two

doi:10.1111/j.1365-2591.2011.01876.x

Flexibility and torsional resistance of three nickel–titanium retreatment instrument systems

R. P. Hussne1, L. C. Braga2, F. L. C. V. Berbert1, V. T. L. Buono3 & M. G. A. Bahia2
1 2

Department of Restorative Dentistry, School of Dentistry of Araraquara, University of the State of Sao Paulo, Araraquara, SP; ˜ Department of Restorative Dentistry,Faculty of Dentistry, Universidade Federal de Minas Gerais, Belo Horizonte, MG; and 3 Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil

Abstract
Hussne RP, Braga LC, Berbert FLCV, Buono VTL, Bahia MGA. Flexibility and torsional resistance of three Nickel–
titanium retreatment instrument systems.International Endodontic Journal.

Aim To assess the dimensional characteristics, flexibility and torsional behaviour of nickel–titanium retreatment instruments. Methodology Using image analysis software and high-resolution digital images, the instrument length, tip angle, diameter at 3 mm from the tip and the distance between the blades (pitch length) of the following eight instruments were measured (n =12 for each measurement parameter): the ProTaper Universal retreatment (PTU-R) D1, D2 and D3 instruments; the R-Endo R1, R2 and R3 retreatment instruments; and the Mtwo retreatment (Mtwo-R) sizes 25 and 15 retreatment instruments. Maximum torque and the angular deflection at fracture as well as the bending moment at 45° were measured (n = 12) according to the International Standards Organisation(ISO) specification number 3630-1. Data

were analysed using the analysis of variance (a = 0.05). Results The length of the active part of the instruments was found to vary according to the depth of the canal into which they were designed to reach. The pitch length also increased along the active length. The PTU-R D1 and the Mtwo-R instruments had active tips. Measurements of the bending moment at45° revealed that the Mtwo-R 15 instrument was the most flexible, whereas the PTU-R D1 was the least flexible. The maximum torque tended to increase as the instrument diameter at 3 mm from the tip increased, whereas the angular deflection at fracture varied in the opposite direction. Conclusions The geometrical characteristics of the retreatment instruments and their flexibility and torsion behaviourwere consistent with their intended clinical application. Keywords: endodontic retreatment instruments, flexibility, nickel–titanium, torsional resistance.
Received 30 March 2009; accepted 17 February 2011

Introduction
Nonsurgical root canal retreatment is undertaken in an attempt to re-establish healthy periapical tissue after ineffective treatment or reinfection of a filled root canal system(Schirrmeister et al. 2006a). The main causes of
Correspondence: Professor Vicente T. L. Buono, Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Av. Antonio Carlos, 6627 – Campus Pampulha, Escola de Engenharia – Bloco 2 – sala 2640, 31270-901 Belo Horizonte, MG, Brazil (e-mail: vbuono@demet.ufmg.br).

treatment failure are retained microorganismsthrough insufficient cleaning, root fractures, missed canals, inadequate filling and coronal or apical leakage (Siqueira 2001, Ruddle 2004, Nair 2006, Schirrmeister et al. 2006b). Endodontic retreatment is often indicated to eliminate or to substantially reduce the microbial load from the root canal by thoroughly removing the root filling to enable effective cleaning, shaping and refilling of the rootcanal system (Stabholz & Friedman 1988, Gu et al. 2008). Several techniques have been recommended for the removal of root filling materials during retreatment.

ª 2011 International Endodontic Journal

International Endodontic Journal

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Mechanical behaviour of retreatment instruments Hussne et al.

These include endodontic hand files combined with heat or chemical solvents, ultrasonic...