Influence of multiple clinical use on fatigue resistance of ProTaper rotary nickel-titanium instruments E. P. Vieira 1 , E. C. Franc ¸a 1 , R. C. Martins 2 , V. T. L. Buono 2 & M. G. A. Bahia 1 1 Department of Restoration Dentistry, Faculty of Dentistry, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil; and 2 Department of Metallurgical and Materials Engineering, Engineering School, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil Abstract Vieira EP, Franc ¸ a EC, Martins RC, Buono VTL, Bahia MGA. Influence of multiple clinical use on fatigue resistance of ProTaper rotary nickel-titanium instruments. International Endo- dontic Journal, 41, 163–172, 2008. Aim To examine the influence of clinical use on the occurrence of deformation and fracture and on the fatigue resistance of ProTaper rotary instruments. Methodology Root canal treatments were per- formed on patients using the ProTaper rotary system. Ten sets of instruments were used by an experienced endodontist, each set in five molars. Another 10 sets of instruments were used by the same operator, each set in eight molars. In addition, 10 sets of instru- ments were used, each set in five molars, by undergraduate students with no clinical experience with the system. After clinical use, S1, S2, F1 and F2 instruments were analysed for damage by optical and scanning electron microscopy. The used sets, along with a control group of 12 sets of new instruments, were then tested in a bench device for fatigue resistance. Results The use of the ProTaper rotary instruments by an experienced endodontist allowed for the cleaning and shaping of the root canal system of up to eight molars without fracture. During the students work, six instruments fractured. Fatigue resistance decreased upon clinical use for all instruments analysed. Conclusions Fatigue resistance of used instruments was reduced, but no significant change was observed amongst the instruments used for shaping the canals of five and eight molars. Operator experience affected the occurrence of fracture and plastic deformation during shaping. Keywords: clinical use, endodontic instruments, fatigue resistance, nickel-titanium, operator profi- ciency, ProTaper. Received 28 February 2007; accepted 6 August 2007 Introduction Since the introduction of nickel-titanium (NiTi) rotary instruments in root canal treatments, the shaping of curved canals has become more predictable, reducing operator fatigue and the time required to complete the preparation (Thompson & Dummer 1997). Moreover, procedural errors frequently found when using manual stainless steel instruments have been minimized (Glosson et al. 1995). Since then, an increasing num- ber of NiTi rotary systems have been marketed by various manufacturers. These systems differ from one another in the design of the cutting blades, body taper and configuration of the file tip. Despite the purported clinical advantages of the rotary techniques, unex- pected instrument fracture is not uncommon, especially for less-experienced operators (Mandel et al. 1999, Yared et al. 2001, 2002, 2003, Peters & Barbakow 2002). The fracture of rotary instruments takes place in different ways: due to torsion, fatigue flexure or by a Correspondence: Vicente T. L. Buono, Department of Metallurgical and Materials Engineering, Engineering School, Federal University of Minas Gerais, Rua Espirito Santo 35/206, 30160-030 Belo Horizonte, Minas Gerais, Brazil (Tel.: +55 31 3238 1859; fax: +55 31 3238 1815; e-mail: vbuo no@demet.ufmg.br). doi:10.1111/j.1365-2591.2007.01336.x ª 2007 International Endodontic Journal International Endodontic Journal, 41, 163–172, 2008 163