doi:10.1111/iej.12291
Comparative evaluation of the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files in severely curved root canals
€fer2 S. E. D. M. Saber1, M. M. Nagy1 & E. Scha 1
Department of Endodontics, Faculty of Dentistry, Ain Shams University, Cairo, Egypt; and 2Central Interdisciplinary Ambulance in the School of Dentistry, University of M€ unster, M€ unster, Germany
Abstract €fer E. Comparative evaluSaber SEDM, Nagy MM, Scha ation of the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files in severely curved root canals. International Endodontic Journal.
Aim To compare the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files during the preparation of severely curved root canals in extracted human molar teeth. Methodology Sixty mandibular molars with mesio-buccal canals having angles of curvature ranging from 25° to 35° were divided according to the instrument used into three groups of 20 teeth each: group PTN (ProTaper Next), group IR (iRaCe) and group HF (Hyflex CM). Using standardized pre- and post-instrumentation radiographs, straightening of canal curvature was determined using image analysis software. A double-digital standardized radiographic technique was used to determine apical transportation 0.5 mm from the working length (1.5-mm coronal of
Introduction The ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland) is the successor of the ProTaper Universal system (Dentsply Maillefer). It has an innovative off-centred rectangular cross section that gives the file
Correspondence: Shehab El Din Mohamed Saber, Department of Endodontics, Faculty of Dentistry, Ain Shams University, El-Rehab City. (81-11-11).11841, Cairo, Egypt (Tel.: 00201001413734; Fax: 002-022260983; e-mail: [email protected]).
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
the major foramen). Preparation time and instrument failures were also recorded. Data were analysed using one-way analysis of variance (ANOVA) and post hoc Tukey’s test, and significance was set at P < 0.05. Results During root canal preparation, no instruments fractured. The use of PTN resulted in significantly greater canal straightening than IR and HF (P < 0.05), with no significant differences between IR and HF (P > 0.05). There were no significant differences between the three groups with respect to apical transportation (P > 0.05). IR and HF were significantly faster than PTN (P < 0.05), with no significant differences between IR and HF (P > 0.05). Conclusions Under the conditions of this study, PTN, IR and HF respected original canal curvature well and were safe to use. Keywords: apical transportation, canal straightening, Hyflex CM, iRaCe, ProTaper Next, shaping ability. Received 25 January 2014; accepted 1 April 2014
a snake-like swaggering movement as it advances into the root canal. The manufacturer claims that the rotation of this cross section generates enlarged space for debris removal (ProTaper Next, directions for use). These instruments are manufactured from M-wire alloy that is claimed to improve file flexibility and resistance to cyclic fatigue whilst retaining cutting efficiency (Alapati et al. 2009, Zhou et al. 2013). iRaCe (FKG, La Chaux-de-Fonds, Switzerland) NiTi rotary files have been recently introduced as a simplified sequence of the RaCe system (FKG). These instruments have the same design features and have undergone the same surface treatment as RaCe
International Endodontic Journal
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Rotary NiTi instruments - Shaping and cleaning Saber et al.
instruments, and it is claimed by the manufacturer that this new sequence provides a quick, safe and effective protocol for preparation of curved root canals (FKG, iRaCe, instructions for use). Hyflex CM (Coltene-Whaledent, Altst€ atten, Switzerland) is a new NiTi rotary system. These files are produced by an innovative methodology (patent pending) that uses a unique process to control the material memory (a complex heating and cooling treatment) (Gutmann & Gao 2012). The CM-wire is a nearly equiatomic alloy composed of 52%wt Ni, whereas the majority of commercially available NiTi rotary instruments are composed of 54.5–57%wt Ni (Zinelis et al. 2010). The manufacturer claims that this alloy, together with the unique design features of the instruments, provides a superior flexibility allowing better maintenance of the original canal curvature and increased efficiency and safety (Zhao et al. 2013, Peters et al. 2012). Currently, very little information regarding the shaping ability of these new instruments is available. Thus, the aim of this investigation was to compare their shaping ability (straightening of curved root canals, apical transportation, preparation time, incidence of instrument separation) during the preparation of severely curved root canals in extracted human molar teeth. The null hypothesis tested was that there is no difference in the shaping ability between the tested rotary NiTi systems.
Materials and methods Selection of teeth A total of 60 extracted human permanent mandibular first molars with at least one curved root and curved root canal were selected. Coronal access was achieved using diamond burs, and the canals were controlled for apical patency with a size 10 K-file. Teeth with intact mature root apices were included. Teeth that did not allow the insertion of a size 10 Kfile to the major foramen or the passive placement of a size 15 K-file to within 1 mm of the foramen were discarded. Standardized digital radiographs were taken prior to instrumentation with a size 15 K-file inserted into the curved canal. Each tooth was placed in a radiographic mount made of silicone-based impression material (Optosil P Plus; Heraeus Kulzer, Hanau, Germany) to maintain a fixed film-object-source position. The radiographic mount compromised of a
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radiographic-sensor holding paralleling device (Howe, Kerr, Orange, CA, USA) which held the digital sensor (Sopro, Acteon, Merignac, France) and was aligned so that the long axis of the root canal was parallel and as near as possible to the surface of the sensor. The X-ray tube, and thus the central X-ray beam, was aligned perpendicular to the root canal. The exposure parameters (0.08s; 70 kV, 8 mA) were the same for all radiographs. The acquired digital radiographs were transferred to AutoCAD 2008 (Autodesk, San Rafael, CA, USA), and the angle and radius of curvature of each root canal were determined by following the methodology of Sch€ afer et al. (2002). Only teeth whose radii of curvature ranged between 4 and 9 mm and whose angles of curvature ranged between 25° and 39° were included. On the basis of the degree and the radius of curvature and the distance between the apex and the cementoenamel junction, the teeth were allocated into one of the three groups: ProTaper Next (PTN) group, Hyflex CM (HF) group and iRaCe (IR) group. The homogeneity of the groups with respect to the mentioned parameters was assessed using analysis of variance (ANOVA) and post hoc Tukey’s test (Table 1).
Root canal instrumentation The working length (WL) was established with a size 10 K-file, using 2.5% sodium hypochlorite as a lubricant, which was introduced into each canal until the file tip became visible at the major foramen under a surgical microscope (OMS 2350, Zumax, Jiangsu, China) set at a 6.99 magnification. Subsequently, the file was withdrawn until the tip was tangential to the major foramen. The rubber stop was adjusted to the nearest flat anatomic landmark on the tooth, which was chosen as a reference for the measurement of the root canal. The distance between the file tip and the rubber stop was measured under the same magnification with a millimetre ruler. Then, 1 mm was subtracted from this measurement, and the resulting value was taken as the WL. Instrumentation was performed by a single operator in strict accordance with the manufacturers’ recommendations for speed and torque using an electric motor with torque control (iEndo dual, Acteon, Merignac, France) using a gentle in-and-out motion. Each canal was prepared to the working length using three instruments. For ProTaper Next X1 (size 17, .04 taper), X2 (size 26, .06 taper) and X3 (size 30, .07 taper) files, for iRaCe size 15, .06 taper, size 25, .04 taper, and size 30, .04
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Saber et al. Rotary NiTi instruments - Shaping and cleaning
Table 1 Characteristics of curved root canals (n = 20 teeth per group) Curvature (degrees)
Radius (mm)
Instrument
Mean SD
Min
Max
Mean SD
Min
Max
ProTaper Next iRaCe Hyflex CM P-value
28.45 6.6 29.12 3.8 27.79 4.4 0.711
25 25 25
39 38 38
7.01 1.3 6.39 1.5 6.56 1.9 0.448
4 4.1 4.3
8.8 9 9
taper instruments, and for Hyflex-CM size 20, .04 taper, 25/04, and size 30, .04 taper instruments were used. Hence, the final apical preparation was set to size 30 in all groups. The flutes of the instruments were cleaned after three in-and-out-movements (pecks), and the root canal was flushed with 2 mL of a 2.5% NaOCl solution using a 30-gauge needle (NaviTip, Ultradent, South Jordan, UT, USA) that was inserted as deep as possible into the canal without binding. Apical patency was maintained using a size 10 K-file. Once the instrument had negotiated to the end of the canal and had rotated freely, it was removed. Each instrument was used to prepare four canals only. After shaping, the master apical rotary file was placed in the canal at WL and radiographed using the technique described above. Preparation time and the number of fractured instruments during enlargement were also recorded.
Evaluations Based on the canal curvatures assessed before and after instrumentation, canal straightening was determined as the difference between them. A double-digital standardized radiographic technique was used to compare apical transportation between groups. Adobe Photoshop (Adobe Systems, San Jose, CA, USA) was used to superimpose post- and the corresponding pre-instrumentation image. The central axes of the size 15 K-file and the master apical rotary file were superimposed. Small translation and rotation movements were used to achieve a perfect fit between the two images. ImageJ analysis software (ImageJ v1.44, U.S. National Institutes of Health, Bethesda, MD, USA) was used to measure apical transportation at 0.5 mm short of the WL (Fig. 1). The time for canal preparation was recorded using a digital chronometer (Timex, Middlebury, CT, USA) and included total active instrumentation, instrument changes within the sequence, cleaning of the flutes of the instruments and irrigation.
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Distance Apex-CEJ (mm) Mean SD 9.75 0.8 9.85 0.9 9.7 0.7 0.835
An analysis of variance (ANOVA) and post hoc Tukey’s test were used for comparisons of the three groups. The level of statistical significance was set at P < 0.05.
Results During root canal preparation no instrument fractured. All canals remained patent following instrumentation. With all instruments, no canal showed overextension or underextension of the master apical rotary file. Statistical analysis of mean values for canal straightening, apical transportation (Fig. 2) and preparation time is summarized in Table 2. The use of PTN resulted in significantly greater canal straightening than IR and HF (P < 0.05), with no significant differences between IR and HF (P > 0.05). There were no significant differences between the three groups with respect to apical transportation (P > 0.05). IR and HF were significantly faster than PTN (P < 0.05). There were no significant differences between IR and HF (P > 0.05).
Discussion This study sought to evaluate canal transportation at the apical part of severely curved root canals. Failure to respect the canal anatomy in this particular area may result in zipping, ledging or perforation. In addition, irregular apical preparations promote the harbouring of infected debris and may prevent proper canal obturation (B€ urklein & Sch€ afer 2013, Metzger et al. 2013). To observe this effect, assessment of apical transportation was done 1.5-mm coronal of the major foramen. Three instruments were used for each system, and the final apical preparation was determined to be size 30 because larger preparations might result in canal straightening and undesirable weakening of the tooth
International Endodontic Journal
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Rotary NiTi instruments - Shaping and cleaning Saber et al.
(a)
(b)
(c)
(d)
Figure 1 Measurement of apical transportation using ImageJ software. (a) Preoperative radiograph showing a size 15 K-File inside the canal adjusted to working length. (b) Postoperative radiograph showing master apical rotary file adjusted to working length. (c) Superimposed pre- and postoperative radiographs. (d) Measurement of apical transportation (mm) at 0.5-mm coronal from working length.
structure, whereas smaller preparations may leave tissue remnants and infected dentin behind (Sch€ afer & Dammaschke 2009). The results of the present study revealed that the use of IR and HF instruments resulted in significantly less canal straightening than the use of PTN (P < 0.05). This finding can be attributed to the difference in instrument taper (4% for IR and HF vs. 7% for PTN). Values recorded for canal straightening in this study are lower than those obtained for Mtwo, Reciproc, WaveOne and ProTaper under similar
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International Endodontic Journal
experimental conditions (B€ urklein et al. 2011). Although statistically significant differences regarding canal transportation were obtained, from a clinical point of view, these differences are of limited importance (Fig. 2). Taking into account that severely curved canals were instrumented, the clinical relevance of a maximum difference in canal straightening of mere 0.42 mm caused by the different instruments remains questionable. Thus, it can be concluded that all three instruments tested maintained the original canal curvature well.
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Saber et al. Rotary NiTi instruments - Shaping and cleaning
(a)
(b)
(c)
Table 2 Statistical analysis of mean and standard deviation values for canal straightening, apical transportation and preparation time for experimental groups
Instrument ProTaper Next iRaCe Hyflex CM P value
Canal straightening (degrees)
Apical transportation (mm)
Preparation time (s)
1.30 0.39a
0.07 0.02
72.5 16.9a
0.88 0.28b 0.97 0.34b 0.0007
0.06 0.01 0.07 0.01 0.2043
53.8 9.2b 57.0 18.0b 0.0005
Values with the same superscript letters were not statistically different at P = 0.05.
(d)
(e)
(f)
(g)
(h)
(i)
Figure 2 Representative preoperative, postoperative and superimposed pre- and postoperative images of curved root canals prepared with ProTaper Next (a-c), iRace (d-f) and Hyflex CM (g-i).
The present finding that Hyflex CM files maintained the original canal curvature well is corroborated by recent studies conducted under similar experimental
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
conditions (B€ urklein et al. 2014) and using microcomputed tomography evaluation (Zhao et al. 2013). The good shaping ability can be attributed to the increased flexibility of these instruments. Hyflex CM files have been reported to be significantly more flexible than ProFile, Hero 642 (Micro Mega, Besancßon, France), FlexMaster (VDW, Munich, Germany) and EndoSequence (Brasseler USA, Savannah, GA, USA) instruments (Testarelli et al. 2011), and less stiff than Profile Vortex (Dentsply Tulsa Dental, Johnson City, TN, USA) and RaCe (Pongione et al. 2012). The improved flexibility of Hyflex CM files may be due to the thermal pre-treatment of the CM-alloy during manufacturing making the alloy more ductile and thereby reducing the magnitude of the restoring forces (Pongione et al. 2012). A recent study has shown that Hyflex CM files were highly bendable and displayed similar torsional resistance and higher fatigue resistance than files made of conventional NiTi (Peters et al. 2012). In the present study, also iRaCe instruments demonstrated a good shaping ability. This can be explained by their small cross-sectional area, which increases their flexibility and gives more space for debris removal. Another relevant design feature that might have a beneficial impact on the shaping ability of iRaCe is the design of the working part with alternating cutting edges. This design feature is claimed to prevent the screwing in effect thus reducing intra-operative torque values (Paque et al. 2005). RaCe instruments allowed preparation of curved root canals to apical diameters larger than those normally achieved when using other rotary NiTi instruments with only minimal canal transportation and adequate centring ability (PasternakJunior et al. 2009).
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Conclusions Within the limitations of this study, it can be concluded that ProTaper Next iRaCe and Hyflex CM instruments respected original canal curvature well and were safe to use.
References Alapati SB, Brantley WA, Iijma M et al. (2009) Metallurgical characterization of a new nickel-titanium wire for rotary endodontic instruments. Journal of Endodontics 35, 1589– 93. B€ urklein S, Sch€ afer E (2013) Critical evaluation of root canal transportation by instrumentation. Endodontic Topics 29, 110–24. B€ urklein S, Hinschitza K, Dammaschke T, Sch€ afer E (2011) Shaping ability and cleaning effectiveness of two single-file systems in severely curved root canals of extracted teeth: reciproc and WaveOne versus Mtwo and ProTaper. International Endodontic Journal 45, 449–61. B€ urklein S, B€ orjes L, Sch€afer E (2014) Comparison of preparation of curved root canals with Hyflex CM and Revo-S rotary nickel-titanium instruments. International Endodontic Journal 47, 470–6. FKG: iRaCe, instructions for use: available at http:/www.fkg. ch/products/root-canal-preparation-and-retreatment/irace. Accessed March 27, 2014 Gutmann JL, Gao Y (2012) Alteration in the inherent metallic and surface properties of nickel-titanium root canal instruments to enhance performance, durability and safety: a focussed review. International Endodontic Journal 45, 113–28. Metzger Z, Solomonov M, Kfir A (2013) The role of mechanical instrumentation in the cleaning of root canals. Endodontic Topics 29, 87–109. Paque F, Musch U, H€ ulsmann M (2005) Comparison of root canal preparation using RaCe and ProTaper rotary Ni-Ti instruments. International Endodontic Journal 38, 8–16.
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Pasternak-Junior B, Sousa-Neto MD, Silva RG (2009) Canal transportation and centring ability of RaCe rotary instruments. International Endodontic Journal 42, 499– 506. Peters OA, Gluskin AK, Weiss RA, Han JT (2012) An in vitro assessment of the physical properties of novel Hyflex nickel– titanium rotary instruments. International Endodontic Journal 45, 1027–34. Pongione G, Giansiracusa A, Lisotti F, Milana V, Testarelli L (2012) Mechanical properties of endodontic instruments made with different nickel titanium alloys: a stiffness test. ENDO-Endodontic Practice Today 6, 41–4. ProTaper Next: directions for use: available at http:/www. protaperbext.com/benefits-concept.html. Accessed March 27, 2014. Sch€ afer E, Dammaschke T (2009) Development and sequelae of canal transportation. Endodontic Topics 15, 75–90. Sch€ afer E, Diez C, Hoppe W, Tepel J (2002) Roentgenographic investigation of frequency and degree of canal curvatures in human permanent teeth. Journal of Endodontics 28, 211–6. Testarelli L, Plotino G, Al-Sudani D et al. (2011) Bending properties of a new nickel–titanium alloy with a lower percent by weight of nickel. Journal of Endodontics 37, 1293–5. Zhao D, Shen Y, Peng B, Haapasalo M (2013) Micro– computed tomography evaluation of the preparation of mesiobuccal root canals in maxillary first molars with Hyflex CM, Twisted Files, and K3 instruments. Journal of Endodontics 39, 385–8. Zhou H, Peng B, Zheng YF (2013) An overview of the mechanical properties of nickel-titanium endodontic instruments. Endodontic Topics 29, 42–54. Zinelis S, Eliades T, Eliades G (2010) A metallurgical characterization of ten endodontic Ni-Ti instruments: assessing the clinical relevance of shape memory and superelastic properties of Ni-Ti endodontic instruments. International Endodontic Journal 43, 125–34.
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Comparative evaluation of the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files in severely curved root canals
€fer2 S. E. D. M. Saber1, M. M. Nagy1 & E. Scha 1
Department of Endodontics, Faculty of Dentistry, Ain Shams University, Cairo, Egypt; and 2Central Interdisciplinary Ambulance in the School of Dentistry, University of M€ unster, M€ unster, Germany
Abstract €fer E. Comparative evaluSaber SEDM, Nagy MM, Scha ation of the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files in severely curved root canals. International Endodontic Journal.
Aim To compare the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files during the preparation of severely curved root canals in extracted human molar teeth. Methodology Sixty mandibular molars with mesio-buccal canals having angles of curvature ranging from 25° to 35° were divided according to the instrument used into three groups of 20 teeth each: group PTN (ProTaper Next), group IR (iRaCe) and group HF (Hyflex CM). Using standardized pre- and post-instrumentation radiographs, straightening of canal curvature was determined using image analysis software. A double-digital standardized radiographic technique was used to determine apical transportation 0.5 mm from the working length (1.5-mm coronal of
Introduction The ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland) is the successor of the ProTaper Universal system (Dentsply Maillefer). It has an innovative off-centred rectangular cross section that gives the file
Correspondence: Shehab El Din Mohamed Saber, Department of Endodontics, Faculty of Dentistry, Ain Shams University, El-Rehab City. (81-11-11).11841, Cairo, Egypt (Tel.: 00201001413734; Fax: 002-022260983; e-mail: [email protected]).
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
the major foramen). Preparation time and instrument failures were also recorded. Data were analysed using one-way analysis of variance (ANOVA) and post hoc Tukey’s test, and significance was set at P < 0.05. Results During root canal preparation, no instruments fractured. The use of PTN resulted in significantly greater canal straightening than IR and HF (P < 0.05), with no significant differences between IR and HF (P > 0.05). There were no significant differences between the three groups with respect to apical transportation (P > 0.05). IR and HF were significantly faster than PTN (P < 0.05), with no significant differences between IR and HF (P > 0.05). Conclusions Under the conditions of this study, PTN, IR and HF respected original canal curvature well and were safe to use. Keywords: apical transportation, canal straightening, Hyflex CM, iRaCe, ProTaper Next, shaping ability. Received 25 January 2014; accepted 1 April 2014
a snake-like swaggering movement as it advances into the root canal. The manufacturer claims that the rotation of this cross section generates enlarged space for debris removal (ProTaper Next, directions for use). These instruments are manufactured from M-wire alloy that is claimed to improve file flexibility and resistance to cyclic fatigue whilst retaining cutting efficiency (Alapati et al. 2009, Zhou et al. 2013). iRaCe (FKG, La Chaux-de-Fonds, Switzerland) NiTi rotary files have been recently introduced as a simplified sequence of the RaCe system (FKG). These instruments have the same design features and have undergone the same surface treatment as RaCe
International Endodontic Journal
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Rotary NiTi instruments - Shaping and cleaning Saber et al.
instruments, and it is claimed by the manufacturer that this new sequence provides a quick, safe and effective protocol for preparation of curved root canals (FKG, iRaCe, instructions for use). Hyflex CM (Coltene-Whaledent, Altst€ atten, Switzerland) is a new NiTi rotary system. These files are produced by an innovative methodology (patent pending) that uses a unique process to control the material memory (a complex heating and cooling treatment) (Gutmann & Gao 2012). The CM-wire is a nearly equiatomic alloy composed of 52%wt Ni, whereas the majority of commercially available NiTi rotary instruments are composed of 54.5–57%wt Ni (Zinelis et al. 2010). The manufacturer claims that this alloy, together with the unique design features of the instruments, provides a superior flexibility allowing better maintenance of the original canal curvature and increased efficiency and safety (Zhao et al. 2013, Peters et al. 2012). Currently, very little information regarding the shaping ability of these new instruments is available. Thus, the aim of this investigation was to compare their shaping ability (straightening of curved root canals, apical transportation, preparation time, incidence of instrument separation) during the preparation of severely curved root canals in extracted human molar teeth. The null hypothesis tested was that there is no difference in the shaping ability between the tested rotary NiTi systems.
Materials and methods Selection of teeth A total of 60 extracted human permanent mandibular first molars with at least one curved root and curved root canal were selected. Coronal access was achieved using diamond burs, and the canals were controlled for apical patency with a size 10 K-file. Teeth with intact mature root apices were included. Teeth that did not allow the insertion of a size 10 Kfile to the major foramen or the passive placement of a size 15 K-file to within 1 mm of the foramen were discarded. Standardized digital radiographs were taken prior to instrumentation with a size 15 K-file inserted into the curved canal. Each tooth was placed in a radiographic mount made of silicone-based impression material (Optosil P Plus; Heraeus Kulzer, Hanau, Germany) to maintain a fixed film-object-source position. The radiographic mount compromised of a
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International Endodontic Journal
radiographic-sensor holding paralleling device (Howe, Kerr, Orange, CA, USA) which held the digital sensor (Sopro, Acteon, Merignac, France) and was aligned so that the long axis of the root canal was parallel and as near as possible to the surface of the sensor. The X-ray tube, and thus the central X-ray beam, was aligned perpendicular to the root canal. The exposure parameters (0.08s; 70 kV, 8 mA) were the same for all radiographs. The acquired digital radiographs were transferred to AutoCAD 2008 (Autodesk, San Rafael, CA, USA), and the angle and radius of curvature of each root canal were determined by following the methodology of Sch€ afer et al. (2002). Only teeth whose radii of curvature ranged between 4 and 9 mm and whose angles of curvature ranged between 25° and 39° were included. On the basis of the degree and the radius of curvature and the distance between the apex and the cementoenamel junction, the teeth were allocated into one of the three groups: ProTaper Next (PTN) group, Hyflex CM (HF) group and iRaCe (IR) group. The homogeneity of the groups with respect to the mentioned parameters was assessed using analysis of variance (ANOVA) and post hoc Tukey’s test (Table 1).
Root canal instrumentation The working length (WL) was established with a size 10 K-file, using 2.5% sodium hypochlorite as a lubricant, which was introduced into each canal until the file tip became visible at the major foramen under a surgical microscope (OMS 2350, Zumax, Jiangsu, China) set at a 6.99 magnification. Subsequently, the file was withdrawn until the tip was tangential to the major foramen. The rubber stop was adjusted to the nearest flat anatomic landmark on the tooth, which was chosen as a reference for the measurement of the root canal. The distance between the file tip and the rubber stop was measured under the same magnification with a millimetre ruler. Then, 1 mm was subtracted from this measurement, and the resulting value was taken as the WL. Instrumentation was performed by a single operator in strict accordance with the manufacturers’ recommendations for speed and torque using an electric motor with torque control (iEndo dual, Acteon, Merignac, France) using a gentle in-and-out motion. Each canal was prepared to the working length using three instruments. For ProTaper Next X1 (size 17, .04 taper), X2 (size 26, .06 taper) and X3 (size 30, .07 taper) files, for iRaCe size 15, .06 taper, size 25, .04 taper, and size 30, .04
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Saber et al. Rotary NiTi instruments - Shaping and cleaning
Table 1 Characteristics of curved root canals (n = 20 teeth per group) Curvature (degrees)
Radius (mm)
Instrument
Mean SD
Min
Max
Mean SD
Min
Max
ProTaper Next iRaCe Hyflex CM P-value
28.45 6.6 29.12 3.8 27.79 4.4 0.711
25 25 25
39 38 38
7.01 1.3 6.39 1.5 6.56 1.9 0.448
4 4.1 4.3
8.8 9 9
taper instruments, and for Hyflex-CM size 20, .04 taper, 25/04, and size 30, .04 taper instruments were used. Hence, the final apical preparation was set to size 30 in all groups. The flutes of the instruments were cleaned after three in-and-out-movements (pecks), and the root canal was flushed with 2 mL of a 2.5% NaOCl solution using a 30-gauge needle (NaviTip, Ultradent, South Jordan, UT, USA) that was inserted as deep as possible into the canal without binding. Apical patency was maintained using a size 10 K-file. Once the instrument had negotiated to the end of the canal and had rotated freely, it was removed. Each instrument was used to prepare four canals only. After shaping, the master apical rotary file was placed in the canal at WL and radiographed using the technique described above. Preparation time and the number of fractured instruments during enlargement were also recorded.
Evaluations Based on the canal curvatures assessed before and after instrumentation, canal straightening was determined as the difference between them. A double-digital standardized radiographic technique was used to compare apical transportation between groups. Adobe Photoshop (Adobe Systems, San Jose, CA, USA) was used to superimpose post- and the corresponding pre-instrumentation image. The central axes of the size 15 K-file and the master apical rotary file were superimposed. Small translation and rotation movements were used to achieve a perfect fit between the two images. ImageJ analysis software (ImageJ v1.44, U.S. National Institutes of Health, Bethesda, MD, USA) was used to measure apical transportation at 0.5 mm short of the WL (Fig. 1). The time for canal preparation was recorded using a digital chronometer (Timex, Middlebury, CT, USA) and included total active instrumentation, instrument changes within the sequence, cleaning of the flutes of the instruments and irrigation.
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Distance Apex-CEJ (mm) Mean SD 9.75 0.8 9.85 0.9 9.7 0.7 0.835
An analysis of variance (ANOVA) and post hoc Tukey’s test were used for comparisons of the three groups. The level of statistical significance was set at P < 0.05.
Results During root canal preparation no instrument fractured. All canals remained patent following instrumentation. With all instruments, no canal showed overextension or underextension of the master apical rotary file. Statistical analysis of mean values for canal straightening, apical transportation (Fig. 2) and preparation time is summarized in Table 2. The use of PTN resulted in significantly greater canal straightening than IR and HF (P < 0.05), with no significant differences between IR and HF (P > 0.05). There were no significant differences between the three groups with respect to apical transportation (P > 0.05). IR and HF were significantly faster than PTN (P < 0.05). There were no significant differences between IR and HF (P > 0.05).
Discussion This study sought to evaluate canal transportation at the apical part of severely curved root canals. Failure to respect the canal anatomy in this particular area may result in zipping, ledging or perforation. In addition, irregular apical preparations promote the harbouring of infected debris and may prevent proper canal obturation (B€ urklein & Sch€ afer 2013, Metzger et al. 2013). To observe this effect, assessment of apical transportation was done 1.5-mm coronal of the major foramen. Three instruments were used for each system, and the final apical preparation was determined to be size 30 because larger preparations might result in canal straightening and undesirable weakening of the tooth
International Endodontic Journal
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Rotary NiTi instruments - Shaping and cleaning Saber et al.
(a)
(b)
(c)
(d)
Figure 1 Measurement of apical transportation using ImageJ software. (a) Preoperative radiograph showing a size 15 K-File inside the canal adjusted to working length. (b) Postoperative radiograph showing master apical rotary file adjusted to working length. (c) Superimposed pre- and postoperative radiographs. (d) Measurement of apical transportation (mm) at 0.5-mm coronal from working length.
structure, whereas smaller preparations may leave tissue remnants and infected dentin behind (Sch€ afer & Dammaschke 2009). The results of the present study revealed that the use of IR and HF instruments resulted in significantly less canal straightening than the use of PTN (P < 0.05). This finding can be attributed to the difference in instrument taper (4% for IR and HF vs. 7% for PTN). Values recorded for canal straightening in this study are lower than those obtained for Mtwo, Reciproc, WaveOne and ProTaper under similar
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International Endodontic Journal
experimental conditions (B€ urklein et al. 2011). Although statistically significant differences regarding canal transportation were obtained, from a clinical point of view, these differences are of limited importance (Fig. 2). Taking into account that severely curved canals were instrumented, the clinical relevance of a maximum difference in canal straightening of mere 0.42 mm caused by the different instruments remains questionable. Thus, it can be concluded that all three instruments tested maintained the original canal curvature well.
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Saber et al. Rotary NiTi instruments - Shaping and cleaning
(a)
(b)
(c)
Table 2 Statistical analysis of mean and standard deviation values for canal straightening, apical transportation and preparation time for experimental groups
Instrument ProTaper Next iRaCe Hyflex CM P value
Canal straightening (degrees)
Apical transportation (mm)
Preparation time (s)
1.30 0.39a
0.07 0.02
72.5 16.9a
0.88 0.28b 0.97 0.34b 0.0007
0.06 0.01 0.07 0.01 0.2043
53.8 9.2b 57.0 18.0b 0.0005
Values with the same superscript letters were not statistically different at P = 0.05.
(d)
(e)
(f)
(g)
(h)
(i)
Figure 2 Representative preoperative, postoperative and superimposed pre- and postoperative images of curved root canals prepared with ProTaper Next (a-c), iRace (d-f) and Hyflex CM (g-i).
The present finding that Hyflex CM files maintained the original canal curvature well is corroborated by recent studies conducted under similar experimental
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
conditions (B€ urklein et al. 2014) and using microcomputed tomography evaluation (Zhao et al. 2013). The good shaping ability can be attributed to the increased flexibility of these instruments. Hyflex CM files have been reported to be significantly more flexible than ProFile, Hero 642 (Micro Mega, Besancßon, France), FlexMaster (VDW, Munich, Germany) and EndoSequence (Brasseler USA, Savannah, GA, USA) instruments (Testarelli et al. 2011), and less stiff than Profile Vortex (Dentsply Tulsa Dental, Johnson City, TN, USA) and RaCe (Pongione et al. 2012). The improved flexibility of Hyflex CM files may be due to the thermal pre-treatment of the CM-alloy during manufacturing making the alloy more ductile and thereby reducing the magnitude of the restoring forces (Pongione et al. 2012). A recent study has shown that Hyflex CM files were highly bendable and displayed similar torsional resistance and higher fatigue resistance than files made of conventional NiTi (Peters et al. 2012). In the present study, also iRaCe instruments demonstrated a good shaping ability. This can be explained by their small cross-sectional area, which increases their flexibility and gives more space for debris removal. Another relevant design feature that might have a beneficial impact on the shaping ability of iRaCe is the design of the working part with alternating cutting edges. This design feature is claimed to prevent the screwing in effect thus reducing intra-operative torque values (Paque et al. 2005). RaCe instruments allowed preparation of curved root canals to apical diameters larger than those normally achieved when using other rotary NiTi instruments with only minimal canal transportation and adequate centring ability (PasternakJunior et al. 2009).
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Rotary NiTi instruments - Shaping and cleaning Saber et al.
Conclusions Within the limitations of this study, it can be concluded that ProTaper Next iRaCe and Hyflex CM instruments respected original canal curvature well and were safe to use.
References Alapati SB, Brantley WA, Iijma M et al. (2009) Metallurgical characterization of a new nickel-titanium wire for rotary endodontic instruments. Journal of Endodontics 35, 1589– 93. B€ urklein S, Sch€ afer E (2013) Critical evaluation of root canal transportation by instrumentation. Endodontic Topics 29, 110–24. B€ urklein S, Hinschitza K, Dammaschke T, Sch€ afer E (2011) Shaping ability and cleaning effectiveness of two single-file systems in severely curved root canals of extracted teeth: reciproc and WaveOne versus Mtwo and ProTaper. International Endodontic Journal 45, 449–61. B€ urklein S, B€ orjes L, Sch€afer E (2014) Comparison of preparation of curved root canals with Hyflex CM and Revo-S rotary nickel-titanium instruments. International Endodontic Journal 47, 470–6. FKG: iRaCe, instructions for use: available at http:/www.fkg. ch/products/root-canal-preparation-and-retreatment/irace. Accessed March 27, 2014 Gutmann JL, Gao Y (2012) Alteration in the inherent metallic and surface properties of nickel-titanium root canal instruments to enhance performance, durability and safety: a focussed review. International Endodontic Journal 45, 113–28. Metzger Z, Solomonov M, Kfir A (2013) The role of mechanical instrumentation in the cleaning of root canals. Endodontic Topics 29, 87–109. Paque F, Musch U, H€ ulsmann M (2005) Comparison of root canal preparation using RaCe and ProTaper rotary Ni-Ti instruments. International Endodontic Journal 38, 8–16.
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International Endodontic Journal
Pasternak-Junior B, Sousa-Neto MD, Silva RG (2009) Canal transportation and centring ability of RaCe rotary instruments. International Endodontic Journal 42, 499– 506. Peters OA, Gluskin AK, Weiss RA, Han JT (2012) An in vitro assessment of the physical properties of novel Hyflex nickel– titanium rotary instruments. International Endodontic Journal 45, 1027–34. Pongione G, Giansiracusa A, Lisotti F, Milana V, Testarelli L (2012) Mechanical properties of endodontic instruments made with different nickel titanium alloys: a stiffness test. ENDO-Endodontic Practice Today 6, 41–4. ProTaper Next: directions for use: available at http:/www. protaperbext.com/benefits-concept.html. Accessed March 27, 2014. Sch€ afer E, Dammaschke T (2009) Development and sequelae of canal transportation. Endodontic Topics 15, 75–90. Sch€ afer E, Diez C, Hoppe W, Tepel J (2002) Roentgenographic investigation of frequency and degree of canal curvatures in human permanent teeth. Journal of Endodontics 28, 211–6. Testarelli L, Plotino G, Al-Sudani D et al. (2011) Bending properties of a new nickel–titanium alloy with a lower percent by weight of nickel. Journal of Endodontics 37, 1293–5. Zhao D, Shen Y, Peng B, Haapasalo M (2013) Micro– computed tomography evaluation of the preparation of mesiobuccal root canals in maxillary first molars with Hyflex CM, Twisted Files, and K3 instruments. Journal of Endodontics 39, 385–8. Zhou H, Peng B, Zheng YF (2013) An overview of the mechanical properties of nickel-titanium endodontic instruments. Endodontic Topics 29, 42–54. Zinelis S, Eliades T, Eliades G (2010) A metallurgical characterization of ten endodontic Ni-Ti instruments: assessing the clinical relevance of shape memory and superelastic properties of Ni-Ti endodontic instruments. International Endodontic Journal 43, 125–34.
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
