Cutting Efficiency of Conventional and Martensitic Nickel-Titanium Instruments for Coronal Flaring Renata Dornelles Morgental, DDS, MS, PhD,* † Fabiana Vieira Vier-Pelisser, DDS, MS, PhD,* Patr ıcia Maria Poli Kopper, DDS, MS, PhD, ‡ Jose Antonio Poli de Figueiredo, DDS, MS, PhD,* and Ove A. Peters, DMD, MS, PhD † Abstract Introduction: This study aimed at evaluating the influ- ence of rotational speed and number of uses on the cutting efficiency of 4 nickel-titanium coronal flaring instruments against 2 substrates, bovine dentin and acrylic blocks. Methods: BioRaCe BR0, HyFlex CM1, ProFile OS#2, and ProTaper Sx were used in simulated lateral action against both substrates at 250 and 500 rpm up to 5 times, producing 5 notches in each block. Notch areas and lengths were measured under a stereo- microscope, and data were compared by using para- metric tests (a = 0.05). Results: Against both substrates, HyFlex CM1 and ProFile OS#2 were the most and the least cutting efficient instruments, respec- tively (P < .05). Against acrylic, area and length values at 500 rpm were significantly higher than those at 250 rpm for all brands. Against dentin, significant differ- ences were detected between 250 and 500 rpm for Hy- Flex CM1 and ProTaper Sx (area) and for BioRace BR0, HyFlex CM1, and ProTaper Sx (length). Regarding cutting efficiency loss, area and length for notches 1 and 2 (first notches) and 4 and 5 (last notches) were similar against acrylic. Against dentin, length values for notches 1 and 2 were significantly higher than those for notches 4 and 5 in ProFile OS#2 and ProTaper Sx. A strong correlation was detected between the overall results obtained on acrylic and dentin for area and length (P < .0001), although further analysis showed that data against acrylic were a poor predictor of data against dentin after repeated use. Conclusions: HyFlex CM1 was the most cutting efficient instrument in lateral action. An increase in rotational speed improved the cutting efficiency. Results against acrylic showed a high correlation to data against dentin, but acrylic may not be a proper substrate when the intention is to assess cutting efficiency loss with repeated use. (J En- dod 2013;39:1634–1638) Key Words Coronal flaring, cutting efficiency, martensitic nickel-titanium T he introduction of nickel-titanium (NiTi) to endodontics (1) significantly changed the way root canal preparation is performed. NiTi rotary instruments have enabled clinicians to obtain tapered preparations with little or no procedural errors even in curved canals (2). New instrument designs, surface, and alloy treatments have been developed over the years. Thus, several brands are available on the market, and directions of use for most of them recommend a crown-down approach. A so-called coronal flaring procedure is typi- cally performed by more tapered instruments and is claimed to be advantageous during the cleaning and shaping phase of the root canal treatment (3). It is commonly accepted that such instruments should act laterally, avoiding the danger zone described by Abou- Rass et al (4). Also, the crown-down technique may decrease fracture risks by preventing a large portion of an instrument from engaging root dentin (5). NiTi rotary instruments should have some desirable mechanical properties, such as shaping ability, flexibility, resistance to breakage, and cutting efficiency (6). Different methodologies have been used to evaluate the cutting efficiency of endodontic instru- ments, such as weight loss analysis (7–9), profilometry (10, 11), and micro– computed tomography (6). Moreover, several substrates have been used for such purpose: human dentin (9), bovine bone (6, 10–12), and acrylic or plastic blocks (7, 8, 13–18). It appears that there is no consensus regarding the most adequate criteria to assess cutting efficiency of endodontic instruments. However, in principle, the quantification of material removed in a specific time seems a rational way to determine cutting efficiency. Despite the extensive literature, there is a lack of information about the behavior of NiTi coronal flaring instruments related to lateral cutting action. Several design factors may affect cutting efficiency of rotary instruments (6), but the influence of rotational speed and number of uses on this property has yet to be investigated further. Thus, the aims of this study were as follows: 1. To compare the cutting behavior of 4 NiTi rotary instruments in lateral action 2. To compare 2 different substrates 3. To analyze the influence of rotational speed and number of uses in the cutting efficiency From the *Department of Endodontics, School of Dentistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil; † Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, California; and ‡ Department of Endodontics, School of Dentistry, Federal University of Rio Grande do Sul, Porto Alegre, Brazil. Renata Dornelles Morgental was supported by MEC/CAPES (Brazilian Federal Agency for Support and Evaluation of Graduate Education) as an exchange scholarship at the University of the Pacific, Arthur A. Dugoni School of Dentistry. Address requests for reprints to Dr Renata Dornelles Morgental, Pontifical Catholic University of Rio Grande do Sul – PUCRS, Av. Ipiranga 6681, Predio 6, 90619-900 Porto Alegre, RS, Brazil. E-mail address: remorgental@hotmail.com 0099-2399/$ - see front matter Copyright ª 2013 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2013.08.016 Basic Research—Technology 1634 Morgental et al. JOE — Volume 39, Number 12, December 2013