A new idea was lately realized for nickel-titanium (NiTi) rotary instruments: it consists of using just one instrument with different working motions with the aim to prepare root canals.1e4 Diverse single-file systems have been promoted with the ability to prepare root canals with just one instrument. The recently introduced NiTi files Reciproc (VDW, Munich, Germany) and WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) are made of a special NiTi-alloy called M-Wire which is created by an innovative thermaltreatment process. The benefits of this M-Wire NiTi are based on increased flexibility of the instruments and on improvement of resistance to cyclic fatigue.5 These files must be used in a reciprocal motion that requires special automated devices. Reciproc files are available in sizes 25e0.8, 40e0.6, and 50e0.5, and WaveOne are available in sizes 21e0.6, 25e0.8, and 40e0.8. The reciprocation working movement lies in a counterclockwise (cutting direction) and a clockwise movement (instrument release), whilst the counterclockwise cutting direction angle is greater than the instrument release one. Because the angle of counterclockwise is greater than the angle of clockwise, it is expressed that the instrument continually progress in the direction of the root canal apex. The One-Shape New Generation file by Micro-Mega (Besancon Cedex, France) is another single-file system, but used in continuous clockwise rotation; in addition to the size 25e0.6, there are Apical files in sizes 30e0.6 and 37e0.6. These instruments, having an innovative design, with three diverse cross-sectional areas above the entire length of the working part do not have a fixed pitch and a noncutting safety tip.6 The design features of Reciproc, WaveOne,3 and OneShape have been previously described in detail.6 Some data are present in literature on the shaping ability of these systems,2,6 but a comparative evaluation in canals with curvatures of over 35
is still missing. Therefore, the aim of the present study was to compare the shaping ability of WaveOne, Reciproc, and OneShape single-file systems in severely curved root canals of extracted human molar teeth. The null hypothesis tested was that there is no difference among different single-file systems regarding canal straightening, apical transportation, or preparation time when preparing severely curved root canals.