A review of instrumentation kinematics of enginedriven nickel titanium instruments

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1 doi: /iej REVIEW A review of instrumentation kinematics of enginedriven nickel titanium instruments I. D. Cßapar 1 & H. Arslan 2 1 Department of Endodontics, Faculty of Dentistry, _Izmir Katip Cßelebi University, _Izmir; and 2 Department of Endodontics, Faculty of Dentistry, Atat urk University, Erzurum, Turkey Abstract Cßapar ID, Arslan H. A review of instrumentation kinematics of engine-driven nickel titanium instruments. International Endodontic Journal. Over the years, NiTi alloys have become indispensable materials in endodontic treatment. With technological advancements in metallurgy, manufacturers have attempted to produce instruments with enhanced features. In parallel with these developments, endodontic motors have undergone improvements in terms of torque control and kinematics that are adjustable in different directions. This review presents an overview of the advancements in instrumentation kinematics and the effect of instrumentation kinematics on root canal shaping procedures and instrument performance. The literature search for this narrative review was conducted in Google Scholar, Scopus, PubMed and Web of Science using the keywords kinematics and endodontics and reciprocation and endodontics. In addition, historical literature was searched using the keyword nickel titanium and endodontics. Overall, 143 articles were included up to Keywords: asymmetrical motion, instrumentation speed, kinematics, reciprocation, root canal instrumentation, torque. Received 28 August 2014; accepted 24 January 2015 Introduction Correspondence: Asst. Prof. Dr. _Ismail Davut Cßapar, Department of Endodontics, Faculty of Dentistry, _Izmir Katip Cßelebi University, Izmir, Turkey (Tel.: ; Fax: ; capardt@hotmail. com). Removing pulp tissue remnants, microorganisms and microbial toxins from the root canal system is essential for the success of root canal treatment (Basmadjian-Charles et al. 2002). Root canals can be cleaned by instrumentation supplemented with irrigants and intracanal medicaments (Bystr om & Sundqvist 1985). Several mechanical devices and techniques have been developed to further improve the effectiveness of instrumentation and to make canal preparation easier. The devices and techniques used for root canal instrumentation may be classified as either manual or machine-assisted. The use of machine-assisted endodontic instruments allows for easier and faster instrumentation (Sch afer et al. 2004). Machineassisted techniques consist of automated root canal preparation, sonic and ultrasonic preparation, laser systems and noninstrumental techniques (H ulsmann et al. 2005). Traditionally, stainless steel instruments have been used for root canal instrumentation. However, such instruments have a tendency to transport the prepared canal away from its original axis (Cheung & Liu 2009). With the introduction of the more flexible nickel titanium (NiTi) instruments (Walia et al. 1988), they have become indispensable. With technological advancements in metallurgy, manufacturers have attempted to improve the instruments (easier, faster and better root canal shaping, greater resistance to fracture), such as those made of M wire (Dentsply Tulsa Dental Specialties, Tulsa, OK, USA) or control memory wire (CM) (DS Dental, Johnson City, TN, USA), that incorporated several design features Published by John Wiley & Sons Ltd 1

2 Instrumentation kinematics Cß apar & Arslan Additionally, in parallel with these developments, endodontic motors have undergone enhancement regarding torque control and kinematics that are adjustable in several directions. A review of the literature reveals that the large number of studies on instrumentation kinematics carried out in the past decade has not yet been included in a review. This review presents an overview of the advancements in instrumentation kinematics and the effects of instrumentation kinematics on root canal shaping procedures and instrument performance. Literature search methodology A literature search for this narrative review was conducted in Google Scholar, Scopus, PubMed and Web of Science using the keywords kinematics and endodontics and reciprocation and endodontics. Over 2000 articles were found. In addition, historical literature searching was conducted using the keywords nickel titanium and endodontics. This resulted in the identification of over studies for preliminary analysis. Articles unrelated to the endodontic instruments were excluded. The included articles were checked to identify further relevant literature. Overall, 143 articles were included up to Endodontic machine-assisted instrumentation can be classified into five groups according to the instrumentation kinematics as follows: rotary motion, rotational reciprocating motion, vertical vibration plus rotational reciprocating motion, vertical vibration and rotary motion plus rotational reciprocating motion (adaptive). History of instrumentation kinematics Rotary instrumentation According to H ulsmann et al. (2005), the first reference to rotary instrumentation was made by Oltramare (1892), who used fine needles with rectangular cross sections that could be attached to a dental handpiece. Rollins (1899) developed the first endodontic handpiece for root canal instrumentation that was used with specially designed needles at 100 rpm (Milas 1987). After the introduction of NiTi endodontic hand instruments by Walia et al. (1988), many rotary NiTi instruments have been marketed. Recently, a new type of rotary motion, asymmetrical rotary motion, has been introduced (Diemer et al. 2013). Asymmetrical rotary motion (waves of motion travelling along the active part of the file) is produced by design features of the file, including having an off-centred cross section that is not related to endodontic motors. The first available systems enabling asymmetrical motion were Revo-S (Micro- Mega, Besancßon, France), followed by ProTaper Next (Dentsply Tulsa Dental Specialties), new generation OneShape (MicroMega) and more recently TRUShape 3D Conforming Files (Dentsply Tulsa Dental Specialties). Rotational reciprocating motion After reciprocation was first introduced in 1964 with the Giromatic system (MicroMega), various endodontic reciprocating handpieces have been manufactured (Prichard 2012). The Giromatic system, Endo-Gripper (Moyco Union Broach, Montgomeryville, PA, USA), Intra-Endo 3 LD (KaVo, Biberach, Germany) and Dynatrak (Dentsply DeTrey, Konstanz, Germany) operate with equal angles of 90 clockwise (CW) and clockwise (CCW) motion. Over time, the Giromatic system lost popularity because it produced greater procedural errors than hand filing (Weine et al. 1976). The M4 (SybronEndo, Orange, CA, USA), Endo-Eze (Ultradent Products Inc., South Jordan, UT, USA) and Endo-Express SafeSider (Essential Dental Systems, South Hackensack, NJ, USA) systems are current examples of reciprocating handpieces that utilize small, equal 30 angles of CW and CCW rotation. These handpieces enable the formation of an endodontic glide path using small stainless steel hand files (Gambarini et al. 2015). More recently, reciprocating motion regained popularity with the introduction of NiTi alloys and endodontic torque control motors. In 1985, a balanced-force technique for curved canals was described by Roane et al. (1985) and included unequal CW and CCW motions with hand files. Yared (2008) introduced the concept of single-file reciprocation, which was based on a balanced-force technique and used the ProTaper F2 instrument (Dentsply Tulsa Dental Specialties) (a flute-designed instrument with crosssectional geometry that aids in the cutting of the dentine in the CW direction) with unequal CW and CCW rotational motion (144 CW and 72 CCW). This development meant that the instruments required five rotations to complete a full 360 rotation. At the same time, the elastic limit of the instrument was not exceeded due to this motion (Kim et al. 2014). Based on these developments, manufacturers introduced single-file reciprocating systems including Published by John Wiley & Sons Ltd

3 Cß apar & Arslan Instrumentation kinematics WaveOne (Dentsply Tulsa Dental Specialities) and Reciproc (VDW, Munich, Germany). The major difference is that these instruments had a CCW cutting direction, so the instruments could cut if the CCW movement was greater than the CW movement. However, except for these reciprocating instruments, all of the instruments are designed for cutting in the CW direction. Thus, if a clinician tries to use these reciprocating instruments with CW rotating motors or tries to use CW cutting instruments with the reciprocating motors (CCW motion is greater than CW motion), the instrument will neither cut nor penetrate into the canal. Reciprocating endodontic motors can be classified as open or closed motors, with open motors [(ATR Vision; ATR, Pistoia, Italy), (iendo Dual; Acteon, Merignac, France), (SAF pro System; ReDent-Nova, Ra nana, Israel)] allowing modification of angles and speed and closed motors [(WaveOne), (Reciproc), (Elements motor; SybronEndo), (ATR Technika; ATR)] which do not allow such modifications. Vertical vibration plus rotational reciprocating motion Various manufacturers have produced handpieces that are able to produce an up-and-down motion of the file and a quarter turn rotation (e.g. Canal Finder System: Societe Endo Technic, Zurich, Switzerland; Endolift: SybronEndo). Although these handpieces were manufactured for use with stainless steel files, NiTi files are commercially available with the EndoPulse system (Societe Endo Technic), which is the new version of the Canal Finder ( Vertical vibration In 2010, the Self-Adjusting File system (SAF) (Re- Dent-Nova) was introduced. It is operated by vibrating a slightly abrasive lattice using an in-and-out motion to remove dentine and provide continuous irrigation during preparation (Metzger et al. 2010). Rotary motion plus rotational reciprocating motion (adaptive motion) In 2013, a new endodontic motor was introduced by Sybron Endo (Elements) that aims to combine the advantages of both rotary and reciprocating motions. When the instrument is not (or is minimally) stressed, the motion can be described as a rotation of 600 in the CW direction, a stop and then a restart in the CW direction. When the instrument engages dentine or the root canal filling, the motion of the instrument becomes reciprocal due to the increased stress. The reciprocal angles are not constant, and the motor modifies the CW/CCW angles from 600/0 to 370/ 50, depending on the intracanal stress ( axis.sybronendo.com/tfadaptive_confidence#tab 2). An overview of the asymmetrical rotary motion studies As mentioned previously, instruments having an offcentred cross section (Revo-S, ProTaper Next, new generation OneShape and TRUShape 3D Conforming Files) result in an asymmetrical rotary motion. However, there is no available study comparing instruments with similar cross-sectional geometry and metal alloy to determine the effect of pure asymmetrical motion. Thus, further studies comparing instruments with similar cross-sectional geometry are required to understand the effect of asymmetrical motion on debris extrusion, cutting efficacy, cyclic fatigue and root canal transportation. Debris extrusion Kocak et al. (2013) found no significant differences between Revo-S and other rotary and reciprocating systems with respect to debris extrusion. However, it has been found that the ProTaper Next instruments were associated with less debris extrusion than the ProTaper Universal instruments (Cßapar et al. 2014a, Kocak et al. 2014, Ozsu et al. 2014). The different cross-sectional geometry may lead to increased space between the file and the dentinal walls, allowing more coronal flow of the dentinal debris. In particular, ProTaper Universal instruments have a convex triangular cross-sectional geometry, whereas the ProTaper Next instruments have a rectangular geometry. Cutting efficacy With the aid of asymmetric rotary motion, instruments with an offset rotational mass may describe a larger envelope of motion than similarly sized files with symmetrical mass and axis of rotation. Consistent with this theory, Cßapar et al. (2014f) revealed that ProTaper Next X2 instrument that have a 0.06 apical taper Published by John Wiley & Sons Ltd 3

4 Instrumentation kinematics Cß apar & Arslan removed similar amounts of dentine compared with other instruments that had a 0.08 apical taper and similar tip size. Thus, smaller and more flexible instruments can cut the same size of preparation as larger and more rigid files with centred mass and axis of rotation. Cyclic fatigue Diemer et al. (2013) reported that the axial stress on files decreased for asymmetrical prototype instruments. Asymmetrical motion produces different stress points during cyclic fatigue, which may contribute to the cyclic fatigue resistance of the instruments (Cßapar et al. 2014e). Numerous studies have reported that instruments with asymmetrical offset design have better cyclic fatigue resistance than instruments with a centred mass and axis of rotation (Cßapar et al. 2014c, Elnaghy 2014, Nguyen et al. 2014, Perez-Higueras et al. 2014). Torsional fatigue Pereira et al. (2013) compared ProTaper Universal and ProTaper Next instruments with respect to peak torque and force during root canal preparation; the ProTaper Next instruments had greater consistency in peak torque. Pereira et al. (2013) explained this result as being a consequence of the asymmetric contact between the ProTaper Next instrument and dentine. Dentinal defects The forces generated during instrumentation have been linked to an increased risk of root fracture (Kim et al. 2010), and it has been shown that the ProTaper Next instruments tended to cause fewer dentinal cracks compared with the ProTaper Universal instruments (Cßapar et al. 2014b, Karatas et al. 2015). However, Yoldas et al. (2012) reported that root canal instrumentation with Revo-S caused a similar incidence of dentinal cracks compared to instruments with a centred mass and axis of rotation. Root canal transportation and straightening of the canal curvature As mentioned previously no studies have evaluated the effect of pure asymmetrical motion on root canal transportation. However, it has been shown that instruments allowing asymmetrical motion caused similar (Cßapar et al. 2014f) or less root canal transportation (B urklein et al. 2014b, Zhao et al. 2014) compared with traditional instruments that have symmetrical motion. An overview of studies on reciprocating motion Reciprocating angle Knowing the actual reciprocating angles is important because it has been shown that decreasing the reciprocation range of the instruments results in increased cyclic resistance with less transportation but with longer preparation times (Saber & Abu El Sadat 2013). According to the manufacturers, the Wave- One ALL mode generates a rotation of 170 CCW and 50 CW, and the Reciproc ALL mode generates a rotation of 150 CCW and 30 CW (Kim et al. 2012). Recently, Fidler (2014) investigated the kinematics of reciprocating motors using a high-speed video camera and found that the actual angles of the WaveOne mode is 160 CCW and 41 CW, those of the Reciproc mode is 159 CCW and 35 CW, and those of ATR Technika s reciprocation mode is 1310 CW and 578 CCW. The ATR motors of two different models, the ATR Technika (old version) and ATR Vision (new version), were frequently used in previous studies (Yared 2008, De-Deus et al. 2010b, Varela-Patino et al. 2010, You et al. 2010, 2011, Paque et al. 2011, Stern et al. 2012, Perez-Higueras et al. 2013, Giuliani et al. 2014, Kansal et al. 2014). ATR Technika has only one reciprocating mode, such that the reciprocating angles are not adjustable, whereas the ATR Vision has an option to adjust the reciprocating angles. In the first study on the single-file reciprocation concept by Yared (2008), the ATR Vision was used, and the reciprocating angle was found to be four-tenths (144 ) and two-tenths (72 ) of a circle. Subsequently, ATR Technika was used in numerous studies, and conflicting angles (144 72, 60 45, ) were reported, although reciprocating angles could not be adjusted with the motor (De-Deus et al. 2010b, Varela-Patino et al. 2010, You et al. 2010, 2011, Stern et al. 2012, Kansal et al. 2014). Researchers should be aware of the actual angles of the reciprocating motion when undertaking further studies. Debris extrusion The literature includes conflicting results on the effect of reciprocating instrumentation on debris extrusion Published by John Wiley & Sons Ltd

5 Cß apar & Arslan Instrumentation kinematics Most of the studies are concerned with the effect of single-file reciprocating instrumentation on debris extrusion (B urklein & Sch afer 2012, Kocak et al. 2013, B urklein et al. 2014a, De-Deus et al. 2014) or extrusion of bacteria (Tinoco et al. 2014); however, there are few reports on pure reciprocating motion (De-Deus et al. 2010a). Previously, rotary instrumentation was associated with less debris extrusion compared with reciprocal instrumentation (B urklein & Sch afer 2012, B urklein et al. 2014a). In those studies, single-file reciprocating instruments are compared with full-sequence (B urklein & Sch afer 2012) or single-file rotary instrumentation (B urklein et al. 2014a). Similarly, Robinson et al. (2013) reported that root canal instrumentation with single-file reciprocating instruments induced greater debris accumulation than full-sequence rotary instrumentation. By contrast, it has been shown that single-file reciprocating instruments caused less extrusion of bacteria (Tinoco et al. 2014) and debris (De-Deus et al. 2014) than conventional multifile rotary systems. Kocak et al. (2013) found no significant differences between single-file reciprocating instruments and multifile rotary systems with respect to debris extrusion. Moreover, Caviedes-Bucheli et al. (2013) showed that Reciproc instruments produced lower levels of neuropeptide expression than WaveOne. These discrepancies may be caused by the use of differently designed instruments, a different number of files or differing root canal anatomy, and it is not possible to separate the influence of the reciprocating motion from the results of the aforementioned studies. In contrast to these studies, De-Deus et al. (2010a) compared debris extrusion associated with ProTaper instruments with fullsequence rotary motion up to size F2 with that of a single ProTaper F2 instrument with reciprocating motion and demonstrated no significant difference between the instrumentation techniques. Conversely, in the study by De-Deus et al. (2010a), different numbers of files were compared, and it is not known whether the instruments would cause less debris extrusion when the instruments were used with a full-sequence reciprocating motion. Cutting efficacy The cutting efficacy of instruments involves a complex interrelationship of several factors such as crosssectional design, debris removal capacity, helical and rake angles, metallurgical properties and surface treatments (Sch afer & Lau 1999, Sch afer & Oitzinger 2008, Peters et al. 2014). The cutting efficacy of reciprocating single-file systems has previously been evaluated, and the Reciproc system was shown to be more effective than WaveOne instruments (Plotino et al. 2014) and other rotary instruments (Cßapar et al. 2014f). As mentioned above, these differences may be caused by the different cross-sectional designs rather than by different kinematics. It has been shown that heat-treated alloys have less stiffness (Gambarini et al. 2011) and a lower ultimate tensile strength than do conventional superelastic wires (Zhou et al. 2012), suggesting that heat-treated alloys are softer and therefore cut less effectively. The greater cutting efficacy of the Reciproc instrument is likely related to its S-shaped cross section having a double-cutting edge. It has recently been documented that Reciproc instruments can reach full working length without a glide path in a large proportion of straight or moderately curved canals in mandibular molar (De-Deus et al. 2013b). Stern et al. (2012) evaluated the effect of instrumentation kinematics on cutting efficacy and reported that the use of single ProTaper F2 Universal instruments with the reciprocating motion of ATR Technika motors removed a similar dentine volume to that produced when using a full sequence of the same instrument with rotational motions. Similarly, Giansiracusa Rubini et al. (2014) compared the cutting efficacy of Reciproc instruments with the Reciproc All motion and CCW rotary motion and found no significant differences between the motions. Saber & Abu El Sadat (2013) reported that decreasing the reciprocation range of the instruments resulted in increased cyclic resistance with less transportation but also in longer preparation times. Moreover, Plotino et al. (2014) showed that there were no significant differences between the Reciproc All and WaveOne All movements in terms of cutting effectiveness. Cyclic fatigue The cyclic fatigue resistance of single-file reciprocating systems has been evaluated previously, showing that reciprocating instruments had higher cyclic fatigue resistance than did instruments that used rotary motion (Castello-Escriva et al. 2012, Pedulla et al. 2013). Perez-Higueras et al. (2013) reported that K3 (SybronEndo), K3XF (SybronEndo) and Twisted File (SybronEndo) instruments had better cyclic fatigue resistance when moved with reciprocating motion (144 CW and 72 CCW) compared to rotary motion Published by John Wiley & Sons Ltd 5

6 Instrumentation kinematics Cß apar & Arslan Similarly, Kiefner et al. (2014) evaluated the cyclic fatigue resistance of Mtwo (VDW) and Reciproc instruments under rotary motion or reciprocating movement (Reciproc All mode) and concluded that the reciprocating movement increased cyclic fatigue resistance. Additionally, De-Deus et al. (2010b) reported the increased cyclic fatigue resistance of Pro- Taper Universal instruments under reciprocating movement (ATR Technika s mode). These results suggest that the cyclic fatigue resistance of different types of instruments (thermal treated or conventional NiTi) increases when using reciprocating motion. Gambarini et al. (2012) evaluated the effect of the reciprocating range on cyclic fatigue resistance of instruments and concluded that increasing the reciprocating range reduced resistance to cyclic fatigue. However, the rotational speed of reciprocating instruments may not be constant. Electrical engines have mechanical limitations for converting the rotation direction, resulting in acceleration and deceleration in both directions of rotation (Kim et al. 2012). Gambarini et al. (2012) stated that the differences in the cyclic fatigue resistance of different reciprocating angles may be related to this acceleration and deceleration phenomenon. In a recent study, Shin et al. (2014) evaluated the effect of different periodic angular increments on an instruments cyclic fatigue. The authors compared different stationary reciprocating motions (equal CW and CCW motion) and different progressive motions with different angular increments whenever an instrument completed different reciprocating cycles, a reciprocating motion similar to that used by Yared (2008) and rotary motion. It was found that a progressive reciprocating operation with a 45 reciprocating amplitude and a +7 progressive angular increment every 10 reciprocating cycles increased the cyclic fatigue life by 990% in rotary motion (Shin et al. 2014). Moreover, according to Shin et al. (2014), the use of the progressive reciprocating motion caused multiple fatigue crack initiation sites, whereas rotary motion and stationary reciprocating motions caused single crack initiation sites. Changing the stress point on the instruments with different angular increments appears to be a promising development in endodontic motors. Torsional fatigue Recently, Kim et al. (2014) investigated the torsional resistance of single-file reciprocating instruments and showed that the rotation angles at the beginning point of the plateau, which implicate permanent distortion, were >170. The authors concluded that both single-file reciprocating instruments should be relatively safe when operated with their own motions because the rotational deformation can be recovered upon unloading (Kim et al. 2014). Further studies will be needed to investigate the effect of reciprocating motion on the permanent deformation of different brands of NiTi instruments. Life span Varela-Patino et al. (2010) reported that root canal preparation using ProTaper Universal files with fullsequence reciprocation motion of ATR Technika motor resulted in a higher mean life span of the instrument compared with using the same instrument and full sequence with rotary motion. Moreover, You et al. (2010) showed that the use of single ProTaper F2 instruments with the reciprocating motion of the ATR Technika motor resulted in similar root canal transportation but shorter preparation time in curved canals compared with a full sequence with rotary motion. It also has been reported that a single F2 file can be used safely in curved canals at least six times with reciprocating motion (You et al. 2010). Recently, Plotino et al. (2015) investigated fracture incidence of the Reciproc instruments after clinical use and showed that the fracture incidence of the Reciproc instruments (single usage) was 0.47%. Similarly, Cunha et al. (2014) reported that the instrument fracture incidence was 0.42% of the teeth enlarged with the reciprocating WaveOne instrument. Based on these results, the file fracture incidence of reciprocating instruments is lower than that of rotary instruments (Ramirez-Salomon et al. 1997, Wu et al. 2011, Ehrhardt et al. 2012). Dentinal defects Root canal instrumentation with NiTi instruments has the potential to induce crack formation in roots (Bier et al. 2009, Liu et al. 2013, Ashwinkumar et al. 2014). However, there are conflicting results regarding the effect of reciprocating instruments on crack formation. In a study by B urklein et al. (2013b), reciprocating instruments were associated with more dentinal cracks than were full-sequence rotary systems. However, Liu et al. (2013) showed that Reciproc instruments caused fewer cracks than did Published by John Wiley & Sons Ltd

7 Cß apar & Arslan Instrumentation kinematics full-sequence rotary (ProTaper Universal) or single-file rotary instruments (OneShape). Similarly, Ashwinkumar et al. (2014) reported that WaveOne instruments caused fewer cracks than did the full-sequence rotary (ProTaper Universal) instrument. These conflicting findings may be due to the different instrument sizes (25 and 40) used in the studies. More recently, Kansal et al. (2014) compared the use of single ProTaper files F2 files with the reciprocating motion of the ATR Technika motor and full sequence with the rotary motion. The authors concluded that reciprocating motion with a single file caused fewer cracks (Kansal et al. 2014). However, the use of different numbers of instruments could affect crack formation. Abou El Nasr & Abd El Kader (2014) evaluated crack formation and fracture resistance of oval roots after being enlarged with the single ProTaper F2 instruments under rotary or reciprocating motion, and they found no significant differences between a single F2. However, in their study, the angles of the reciprocating motion were not stated; therefore, further studies should be conducted using the same numbers and brands of instruments with different motions (rotary and different range of reciprocation). Root canal transportation and straightening of the canal curvature During root canal preparation, particularly when preparing curved canals, there can be iatrogenic errors such as ledges, zips, perforations and root canal transportation (Weine et al. 1975). NiTi systems with different kinematics have been produced to maintain the original canal shape and thus keep it better centred (Sch afer & Florek 2003). Additionally, similar to studies on dentinal defect, there are conflicting results about the effects of reciprocating instruments on root canal transportation. Marzouk & Ghoneim (2013) reported that root canal instrumentation with rotary instruments (Twisted File) caused less transportation and similar straightening of the root canal compared with WaveOne instruments. B urklein et al. (2012) evaluated the shaping ability of Reciproc, WaveOne, Mtwo and ProTaper instruments in the curved root canals of extracted teeth and found no significant differences amongst the systems with respect to the straightening of canal curvature. More recently, B urklein et al. (2014c) evaluated the shaping ability of Reciproc, WaveOne, HyFlex CM (Coltene-Whaledent, Allstetten, Switzerland), F360 (Komet Brasseler, Lemgo, Germany) and OneShape single-file rotary systems in simulated S-shaped canals, and concluded that F360, OneShape and HyFlex CM caused less straightening than the reciprocating instruments. In another study by B urklein et al. (2013a) in severely curved canals of extracted teeth, no significant differences were found amongst Reciproc, OneShape, F360 and Mtwo with respect to root canal straightening. Similarly, Cßapar et al. (2014f) compared the effects of One- Shape, ProTaper Universal, ProTaper Next, Reciproc, Twisted File Adaptive (SybronEndo), and WaveOne rotary systems on transportation and canal curvature in the curved mesiobuccal root canals of mandibular molar teeth and found no significant differences amongst the groups. Recently, Saber et al. (2015) reported that WaveOne and Reciproc instruments respected the original canal curvature better than One- Shape instruments. These conflicting results may be related to the different instruments and methodologies used (simulated root canals versus natural root canals). You et al. (2011) investigated the effect of reciprocating motion on root canal transportation in curved canals of maxillary molar teeth and reported that the use of the ProTaper Universal instruments with full-sequence reciprocating motion of the ATR Technika motor caused less transportation than with the full-sequence rotary motion with the ProTaper Universal instruments, but no significant differences were obtained. Similarly, Paque et al. (2011) reported that the use of single ProTaper F2 instruments with reciprocating motion created by the ATR Technika motor was similar to rotary motion with respect to transportation, but the reciprocating motion with single instruments was faster. In a recent study, Giuliani et al. (2014) compared the WaveOne full-sequence reciprocating motion with ProTaper Universal instruments (144 CW and 72 CCW) and full-sequence rotary motion with ProTaper instruments in a simulated canal. The authors concluded that full-sequence reciprocating motion with ProTaper Universal instruments was superior to rotary motion with the same instruments or to WaveOne instruments with respect to the straightening of the canal curvature (Giuliani et al. 2014). Retreatment The complete removal of Gutta-percha from the root canal system during retreatment can be time consuming and challenging. Recent studies have shown that single-file reciprocating instruments are rapid and effective in root canal retreatment (Zuolo et al. 2013, Fruchi et al. 2014). Fruchi et al. (2014) reported that Published by John Wiley & Sons Ltd 7

8 Instrumentation kinematics Cß apar & Arslan Reciproc and WaveOne instruments removed 94% and 93% of the root fillings in the canals of curved molars, respectively. A study comparing the retreatment effectiveness of the Reciproc and Mtwo rotary NiTi instruments revealed that Reciproc instruments removed more filling material from the canal wall than did Mtwo instruments (Zuolo et al. 2013). The effectiveness of reciprocating instruments in root canal retreatment may be due to many factors, the most likely being the engagement of the filling material with the first motion and the dislodging of the filling from the canals via the second motion. In contrast to the aforementioned studies, R odig et al. (2014) and Rios Mde et al. (2014) demonstrated no significant differences between the single-file reciprocating instruments and the ProTaper Universal retreatment instruments (Dentsply Tulsa Dental Specialties). These conflicting results may be due to the use of differently designed instruments in the removal of root canal filling material. Further studies should be conducted to evaluate the effectiveness of pure reciprocating motion with the same type of instrument to clarify this issue. Bacterial elimination Numerous studies have reported that single-file reciprocating systems and full-sequence rotary systems have similar disinfection performance (Alves et al. 2012, Machado et al. 2013, Siqueira et al. 2013, Ferrer-Luque et al. 2014, Marinho et al. 2014, Martinho et al. 2014). Marinho et al. (2014) showed that Reciproc, Mtwo, ProTaper and Race (FKG Dentaire, La Chaux-de-Fonds, Switzerland) instruments produced highly significant reductions of the bacterial load, but no significant differences in endotoxin levels were found. However, there are no available data concerning the effect of pure reciprocating motion on bacterial reduction. An overview of vertical vibration plus rotational reciprocating motion There are limited data about this motion in the current literature. H ulsmann & Meyer (1989) reported that the Canal Finder System was a good and suitable device for the initial instrumentation of narrow and severely curved canals. However, in another study, H ulsmann et al. (1997) demonstrated that the Canal Finder and Endolift systems resulted in insufficiently cleaned root canal walls. An overview of vertical vibration A finite elemental analysis revealed that the stress created by the SAF system during operation is less than the stress resulting from rotary instrumentation (Kim et al. 2013). Several studies have shown that root canal instrumentation with SAF caused a lower incidence of dentinal cracks compared with rotary systems (Yoldas et al. 2012, Hin et al. 2013, Liu et al. 2013). SAF was introduced to achieve a complete three-dimensional root canal shaping, cleaning and irrigation (Metzger et al. 2010). This system allows for continuous irrigation during preparation and has beneficial effects for activating the final irrigation once the canal preparation has been completed (Metzger et al. 2010). The continuous flow of the irrigating solution through the file, combined with the vibrating motion, may affect the cleaning ability of the file (Metzger et al. 2010). Metzger et al. (2010) showed that using the SAF system combined with NaOCl and EDTA resulted in a dentinal surface that was mostly free of a smear layer in all parts of the root canal. Several recent studies have shown that using the SAF system enhanced the removal of calcium hydroxide medicament from apical grooves (Cßapar et al. 2014d), residual Gutta-percha after retreatment (Abramovitz et al. 2012), bacterial population from oval shaped canals (Siqueira et al. 2010) smear layer from the root canal wall (Cßapar & Ari Aydinbelge 2014), and biofilm bacteria from within apical grooves (Lin et al. 2013), as well as increasing pulp tissue debridement (De-Deus et al. 2011) and the bond strength of root fillings (De-Deus et al. 2013a). Moreover, Kocak et al. (2013) showed that the SAF system extruded similar amounts of debris compared with rotary instruments. The details of the SAF system can be found in previous reviews (Metzger et al. 2013, Metzger 2014). An overview of the adaptive motion studies This motion is recommended for the Twisted File Adaptive instrument, which aids in the cutting of dentine in the CW direction. Most of the rotary instruments are designed for CW cutting; thus, the adaptive motion may be used with other instruments. The speed of the instruments used with adaptive motion may be reduced due to the changes in the angle of reciprocating motion, depending on the intracanal stress (particularly in the treatment of curved canals, retreatment, or calcified or narrow Published by John Wiley & Sons Ltd

9 Cß apar & Arslan Instrumentation kinematics canals). To date, there are limited data about adaptive motion. Debris extrusion Kirchhoff et al. (2015) reported that Twisted File Adaptive instruments used with adaptive motion caused similar debris extrusion compared with ProTaper Next and WaveOne instruments. Another recent study reported that Twisted File Adaptive instruments used with adaptive motion caused less debris extrusion than the ProTaper Universal and HyFlex systems (Cßapar et al. 2014a). Postoperative pain Gambarini et al. (2013) compared Twisted File and Twisted File Adaptive instruments (Twisted File and Twisted File adaptive instruments have similar file designs but are used with different motions) and found no differences with respect to postoperative pain. Cyclic fatigue Gambarini & Glassman (2013) reported that adaptive motion increased an instrument s time to fracture compared with rotary motion under cyclic fatigue testing. Dentinal defects Karatas et al. (2015) reported that ProTaper Next and Twisted File Adaptive systems caused fewer cracks than the WaveOne system. Root canal transportation and straightening of the canal curvature There are conflicting results on the effect of adaptive motion on root canal transportation. Recent studies have shown that Twisted File Adaptive instruments caused less (Gergi et al. 2014, 2015) or similar (Cßapar et al. 2014f, Ordinola-Zapata et al. 2014) root canal transportation compared with other instruments. Retreatment Cßapar et al. (2015) used the ProTaper Universal retreatment instruments with adaptive motion and reported that adaptive motion removed more filling materials from the root canals than rotary motion. Instrumentation kinematics includes instrumentation speed and torque and the following sections describe these factors. An overview of instrumentation speed and torque studies Several factors can affect instrument failure, including the experience of the operator, the radius of the root canal curvature, electro-polishing, the diameter of the instrument, repeated use of the instrument and the instrumentation speed, force and torque values (Haikel et al. 1999, Yared & Kulkarni 2003, Schrader & Peters 2005, Bahia et al. 2006, Anderson et al. 2007). Instrumentation speed The optimal speed of rotary instrument varies from instrument to instrument according to the manufacturer s recommendations. To advance to the canal terminus safely, using the optimal speed for the instrument is important. Numerous factors, such as an instrument s cross-sectional designs, diameter, taper, helical angle, pitch number, alloy and tip design, could affect its advancement in root canals (Diemer & Calas 2004, McSpadden 2007, R odig et al. 2014). Thus, to determine the optimal speed of the instruments, all of these factors should be considered. Therefore, each instrument and design should be evaluated separately to obtain its optimal speed. Many studies have evaluated instrument speed, though with conflicting findings. According to the study by Yared et al. (2001), the use of ProFile instruments (Dentsply Maillefer, Ballaigues, Switzerland) with a lower speed (150 rpm) did not result in locking, deformation or fracture; however, instruments used at higher speeds (250 and 350 rpm) locked frequently. Consequently, Yared et al. (2001) concluded that higher rotational speeds increased the probability of instrument fracture. However, Zelada et al. (2002) concluded that whereas both the instrument rpm and the curvature of the root canal contribute to an increased risk of breakage of NiTi rotary instruments, the curvature was found to be the most important factor. Based on these data, Zelada et al. (2002) stated that the instrument rpm is not an independent factor but is instead related to curvature. A study by Daugherty et al. (2001) used mature molars and evaluated Published by John Wiley & Sons Ltd 9

10 Instrumentation kinematics Cß apar & Arslan the fracture rate, deformation rate and efficiency of rotary endodontic instruments driven at 150 rpm and 350 rpm. Their findings indicated that ProFile instruments could be used at 350 rpm to produce nearly double the efficiency and half the deformation rate compared with the results obtained at 150 rpm. The study by Bardsley et al. (2011) found that using ProFile Vortex instruments (Dentsply Tulsa Dental Specialties) at 400 rpm generated less torque and force compared with their use at 200 rpm, but an additional speed increase to 600 rpm did not provide any further benefit. Moreover, Pruett et al. (1997) reported that the number of cycles to failure was not affected by speed when used in artificial metal canals. Recently, Peters et al. (2014) reported that increased rotational speed was associated with increased cutting efficiency. Poulsen et al. (1995) evaluated root canal morphology after instrumentation using Lightspeed instruments (Lightspeed Inc., San Antonio, TX, USA) rotating at 750, 1300 or 2000 rpm and found that there was no significant difference in instrumentation at the various rotational speeds in respect of the amount of dentine removed, canal transportation or the ability of the instrument to remain centred in the canal. Torque values Torsional loading, also referred to as torsional fracture or resistance, is expressed as the maximum torque, and the angular distortion when instrument failure occurs is caused by torsional overload (Yum et al. 2011). Gambarini (2000) discussed the rationale for selecting lower torque values in endodontic motors. If a high-torque motor is used, the instrument-specific torque limit (fracture limit) is often exceeded, thus increasing the risk of intracanal fracture. The author suggested that a specific torque limit (close to the limit of elasticity) be set for each instrument size and type, such that the motor stops if its load reaches this instrument-specific torque limit. Torque influences the incidence of locking of the instrument and thus results in instrument fracture (Yared et al. 2001). Endodontic motors at a higher torque setting can result in excessive stress. This stress is unimportant in straight root canals because the resistance of dentine removal is very low (Gambarini 2000). However, the resistance can be high in curved or narrow root canals, resulting in the instrument locking near the apical terminus. If the clinician does not stop or retract the instrument, it will be subjected to excessive torque (Gambarini 2000). This problem can be prevented by the use of a low-torque endodontic motor that operates below the maximum torque limit of each instrument (Gambarini 2000). Such torque-controlled motors are designed to stop and reverse the rotation of the instrument when its torque value is reached, thus preventing instrument breakage (Suffridge et al. 2003). Conversely, the reduced cutting efficiency of the instrument would be problematic for endodontic motors at lower torque settings. This makes instrument progression in the root canal difficult and results in the operator being more likely to force the instrument. The force applied by the operator would result in the instrument locking, followed by deformation and fracture (Yared et al. 2001). A retrospective clinical study by Iqbal et al. (2006) revealed that there was no significant difference in instrument fracture between torque-controlled and non-torque-controlled handpieces. This result was confirmed by Zarrabi et al. (2010), who concluded that the use of a torque-controlled handpiece is not an important factor compared with the instrumentation technique. Moreover, previous studies (Yared & Kulkarni 2004a,b,c) evaluated torque output and examined the accuracy of various torque-controlled motors, concluding that the actual torque deviated from the pre-set torque value and was higher than the torque reported at the fracture of several NiTi rotary instruments. These results call the usefulness of low-torque motors into question (Yared & Kulkarni 2004a,b,c). However, another study evaluated the failure incidence of ProFile NiTi rotary instruments when used by inexperienced operators as high, low or very low-torque-control motors or as air-driven handpieces (Yared & Kulkarni 2002). The authors concluded that when used by an inexperienced operator, very low-torque-control motors were safer than hightorque-control motors, low-torque-control motors or air-driven handpieces (Yared & Kulkarni 2002). By contrast, other studies reported that all of those types of motors were safe when used by an experienced operator (Yared 2002, Yared & Sleiman 2002). Moreover, Berutti et al. (2004) reported that the use of high torque applied to the NiTi instruments significantly extended the time before instrument failure when used by endodontists. The torque generated by a rotating instrument during root canal instrumentation depends on the preoperative canal volume, the apical force applied by the operator (operator experience), the instrument s Published by John Wiley & Sons Ltd

11 Cß apar & Arslan Instrumentation kinematics diameter, the cross-sectional design, repeated use of the instrument, the manufacturing process and the contact area between the instrument and the root canal walls (Turpin et al. 2000, Peters et al. 2003, Yared & Kulkarni 2003, Schrader & Peters 2005, Bahia et al. 2006). Moreover, subjecting instruments to cyclic fatigue influences their torsional resistance, particularly in curved root canals (Yared & Kulkarni 2003, Bahia et al. 2006). There have been several attempts to understand and reduce the torque values generated by instrumentation. One study showed that torque at failure values increased regularly with increased file size (Camps & Pertot 1994). Another study by Peters et al. (2005) evaluated the effects of lubrication on torque generated during the rotary preparation of simulated root canals in dentine using various NiTi instruments. In that study, the maximum torque values were significantly reduced by the aqueous solutions compared with paste-type products. Similarly, a study by Boessler et al. (2007) concluded that an aqueous chelating lubricant reduced torque values. The effect of torque settings on canal transportation was evaluated previously. Sch afer et al. (2005) compared the shaping ability of FlexMaster (VDW) instruments in simulated curved canals with three different torque-limited automated devices and concluded that torque-limited rotary handpieces were suitable for preparing curved root canals. Similarly, B urklein & Sch afer (2006) compared the shaping ability of Mtwo instruments in simulated curved canals with two different torque-limited automated devices and found that the torque-limited rotary handpiece was safe and suitable for preparing curved root canals. Canal centring was compared after the instrumentation using the ProTaper Universal system with an electric torque-control motor or an air-driven handpiece. It was concluded that NiTi instruments can be used with air-driven motors without any considerable changes in the root canal anatomy, but the clinician must be an expert (Zarei et al. 2013). Gambarini (2001) evaluated the cyclic fatigue resistance of NiTi rotary instruments that were operated clinically and had either a high-torque motor or a low-torque electric motor. Using an endodontic motor with lower torque values tended to increase resistance to cyclic fatigue. Apart from these reports, there are studies evaluating the effects of different torque settings on dentinal crack formation, cutting efficacy and further studies should be conducted. Conclusions Endodontic motors have undergone a revolution regarding torque control and adjustable kinematics in different directions; Adaptive motion is a novel modified reciprocating motion that aims to combine the advantages of rotary and reciprocating motions; The literature suggests that adaptive motion has advantages over simple rotary motion in terms of removal of filling material and cyclic fatigue; The actual speed and angles of reciprocation may differ from the manufacturers declared values; Changing the stress point on the instruments with different angular increments appears to be a promising development in endodontic motors; The instrumentation speed, force, kinematics and torque values are several factors that affect instrument failure; The actual torque deviated from the pre-set torque and could be higher than the torque reported at the fracture of several NiTi rotary instruments; Decreased axial stress on the file and enhanced debris removal appear to be advantages of instruments with asymmetrical motion; Conflicting results amongst the studies on reciprocating motion may be related to the use of different instruments. Thus, further studies should be conducted to evaluate the effectiveness of different instrumentation kinematics with standardized prototypes of instruments that are designed for use with both working motions and that are equal in all design features and alloy properties. Acknowledgement The authors deny any conflict of interests related to this study. References Abou El Nasr HM, Abd El Kader KG (2014) Dentinal damage and fracture resistance of oval roots prepared with singlefile systems using different kinematics. Journal of Endodontics 40, Abramovitz I, Relles-Bonar S, Baransi B, Kfir A (2012) The effectiveness of a Self-Adjusting File to remove residual gutta-percha after retreatment with rotary files. International Endodontic Journal 45, Alves FR, Rocas IN, Almeida BM, Neves MA, Zoffoli J, Siqueira JF Jr (2012) Quantitative molecular and culture Published by John Wiley & Sons Ltd 11