SCANNING VOL. 9999, 1–5 (2014) © Wiley Periodicals, Inc.
Evaluation of Microcrack Formation in Root Canals After Instrumentation With different NiTi Rotary File Systems: A Scanning Electron Microscopy Study ERSAN C¸IC¸EK, MUSTAFA MURAT KOC¸AK, BARAN CAN SAG˘LAM,
AND
SIBEL KOC¸AK
Bu¨lent Ecevit University, Faculty of Dentistry, Depertmant of Endodontics, Turkey
Summary: The aim of this study was to evaluate the dentinal microcrack formation of ProTaper Universal, ProTaper Next, and WaveOne. Sixty extracted mandibular molars were selected. The mesial roots were resected and randomly divided into four groups (n ¼ 15). The canals were prepared with hand files (group 1), ProTaper Universal (group 2), ProTaper Next (group 3), and WaveOne (group 4) instrument systems. The roots were separated horizontally at 3, 6, and 9 mm from the apex. Digital images were captured at 40 magnification using scanning electron microscopy to detect microcrack formation. Statistical analysis was performed by Pearson Chi-square test. The prevalence of microcracks in group 2, group 3, and group 4 were significantly higher when compared to group 1 (p < 0.001). Group 2, group 3, and group 4 demonstrated similar prevalence of microcracks without significant difference (p > 0.05) in all sections. All instruments caused microcracks except for hand file. The highest percentage of microcrack was recorded in 3 mm section for all groups. SCANNING 9999:XX–XX, 2014. © 2014 Wiley Periodicals, Inc. Key words: Instrumentation, microcrack, NiTi File, root dentin, scanning electron microscope
Introduction The aims of biomechanical preparation are enabling bacterial elimination, removing debris, and creating a Conflict of interest: none. Address for reprints: Ersan C¸I˙C¸EK, Bu¨lent Ecevit University, Faculty of Dentistry, Depertmant of Endodontics, Turkey E-mail: [email protected] Received 11 September 2014; Accepted with revision 31 October 2014 DOI: 10.1002/sca.21178 Published online XX Month Year in Wiley Online Library (wileyonlinelibrary.com).
canal form that allows a proper seal. However, complications such as perforations (Tsesis et al., 2010a), canal transportation, ledge and zip formation (Aydin et al., 2009), and separation of instruments (Cuje et al., 2010) are encountered during root canal preparation. Additionally, preparation procedures could damage the root dentine resulting in fractures or craze lines (Wilcox et al., 97). As a result of a microcrack or craze line that progresses with repeated stress application by occlusal forces, vertical root fracture and crack formation occur in root canal dentine during endodontic procedures. Vertical root fracture, which generally results in tooth extraction, is one of the frustrating complications of root canal treatment (Tsesis et al., 2010b). The amount of dentine removed during root canal preparation was associated with craze lines (Wilcox et al., 97). Bier et al. (2009) reported that the rotary nickel–titanium (NiTi) files caused high ratio of dentinal damage (microcrack), whereas no microcrack was observed with hand files. Recently, various new rotary NiTi file systems have been introduced and marketed by manufacturers. These systems mainly vary in cutting blades, body tapers, and tip configurations. Although systems possess some clinical advantages such as saving time (Vaudt et al., 2009) and better cutting efficiency (Scha¨fer and Lau, 99) than hand instrumentation, the influence of the design of the cutting blades is still controversial (Peters 2004; Bergmans et al., 2002) and could increase friction and stresses within the root canal (Blum et al., 2003). Furthermore, Kim et al. (Kim et al., 2010) reported the potential relationship between the design of NiTi instruments and the incidence of vertical root fractures. The efficacy of ProTaper Universal (PTU) rotary NiTi files in root canal treatment was evaluated in various studies (Versiani et al., 2013; Celik et al., 2013; Gonza´lez et al., 2012). Recently, ProTaper Next files (PTN) as a new generation of PTU system have been introduced by the same manufacturer. PTN files are available in five sizes: X1 (tip size 17 with a taper of
2
SCANNING VOL. 9999, 9999 (2014)
0.04), X2 (tip size 25 with a taper of 0.06), X3 (tip size 30 with a taper of 0.07), X4 (tip size 40 with a taper of .06), and X5 (tip size 50 with a taper of .06). They are manufactured using M-Wire NiTi alloy by an innovative thermal treatment process (Gambarini et al., 2008) to increase flexibility and cyclic fatigue resistance of the files. Recently, reciprocating files became popular in endodontic practice. WaveOne (WO) reciprocating files are available in three sizes: small (tip size 21 with a taper of 0.06), primary (tip size 25 with a taper of 0.08) and large (tip size 40 with a taper of 0.08) (Plotino et al., 2012). Introduction of scanning electron microscope (SEM) has proved to be valuable method for asesment of the abilty of the endodontic procedures to remove debris from root canals thus enabling comparison of instruments and techniques (Reddy et al., 2014). SEM images have been used to evaluate the effects of preparation methods on root canal surface (Prati et al., 2004), cleaning efficacy of various root canal instruments (Reddy et al., 2014), and formation of dentinal defects (Ashwinkumar et al., 2014) in endodontic practice. The aim of this study was to evaluate the dentinal microcrack formation of PTU, PTN, and WO NiTi files in comparison with NiTi hand files using SEM images.
Materials and Methods Sixty extracted mandibular molars were selected and stored in purified filtered water. Teeth with severely curved mesial roots were excluded. The coronal portions and distal roots of all teeth were removed using a diamond coated bur under water cooling and mesial roots were used for the study. All roots were inspected with stereomicroscope under 12 magnification to detect any pre-existing craze lines or cracks. Canal patency was established with a #15 K-File (Dentsply Maillefer, Ballaigues, Switzerland) in mesiobuccal canals. A silicon impression material was used for coating the cemental surface of roots to simulate periodontal ligament space. Then, all roots were embedded in acrylic blocks. The teeth were randomly divided into four groups (n ¼ 15) as follows: In group 1, the canals were prepared with NiTi hand files (K-Flexofiles; Dentsply-Maillefer, Ballaigues, Switzerland) using balanced-force preparation technique to file# 25. Group 1 served as control. In group 2, the following sequence of PTU rotary files (Dentsply, Maillefer, Ballaigues, Switzerland) was used at 300 rpm to prepare the canals; an SX file was used to enlarge the coronal portion of the canal, and then all files were used up to working length: S1, S2, F1. The master apical file used was F2, which corresponds to file 25 with a taper 0.06 at the apical area. In group 3, the following sequence of PTN (Dentsply, Maillefer, Ballaigues, Switzerland) was used at 300 rpm
to prepare the canals, X1 and X2 were used up to the working length, which corresponded to file 25 with a taper 0.06 at the apical area. In group 2 and group 3, canal preparation was performed with rotational motion using a torque and speed-controlled motor (X-Smart; Dentsply Tulsa Dental, Tulsa, OK) In group 4, a primary reciprocating WO (Dentsply, Maillefer, Ballaigues, Switzerland) size 25 file with a taper of 0.08 was used in a reciprocating, slow in-andout pecking motion with a 6:1 contra- angle handpiece powered by a torque-limited electric motor (WaveOneTM motor, Dentsply, Maillefer, Ballaigues, Switzerland) according to the manufacturer’s instructions. The flutes of the instrument were cleaned after three pecks. No glide path was created prior to instrumentation. Only mesiobuccal canals were prepared and mesiolingual canals were unprepared to observe the presence of defect which occured before the experiment. In the presence of dentinal defect related to the mesiolingual canal, the specimen was excluded from the study. The irrigation was performed with a freshly mixed 2.5% sodium hypochlorite (NaOCl) solution.
Sectioning and SEM Analysis
All roots were cut horizontally at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling (Leica SP1600, Wetzlar, Germany). Digital image of each section was captured at 40 magnification using SEM (QuantaTM 450 FEG, FEI, Oregon, USA) (Figs. 1 and 2). The evaluation of dentinal defects was applied in a method which was previously described by Shemenesh et al. (2009). “No defect” was defined as root dentine devoid of any craze lines or microcracks at neither external surface of the root nor the internal root canal wall. “Defects” were defined as all other lines (e.g., a craze line, a partial crack, fractures or microcracks). For each group 45 slices were observed in the total of 180 sections.
Fig. 1. SEM sample demonstrating no microcrack formation after instrumentation in instrumented canal.
C ¸ ic¸ek et al.: Microcrack formation-NiTi file systems
already present before instrumentation of root canals. We observed no microcracks in contact with uninstrumented canals. This observation led to ensure that all microcracks occured during the preparation. In the previous studies, microcracks were evaluated by digital cameras at magnification of 10, 12, 20 and 40 (Bier et al., 2009; Yoldas et al., 2012; Liu et al., 2013; Barreto et al., 2012). However, SEM analysis appears to be an adequate method to investigate the influence of endodontic instruments on the morphology of dentine surfaces, and it has been well described (Prati et al., 2004). SEM offers high-resolution images and allows the observation of areas covered by debris and/or smear layer as well as the identification of patent dentinal tubules (Zmener et al., 2005). In the present study, SEM images at magnification of 40 were used to examine the presence of microcrack. The extent of defect formation was related to the tip design, cross-section geometry, constant or progressive taper type, constant or variable pitch, and flute form of the instruments (Yoldas et al., 2012). Consequently, the design and taper of the instruments, and the motion of instrumentation were the variables in the present study. No microcrack was observed in the NiTi hand K-files (0.02 taper) group. This result could be related to avoidance of the continuous rotational motion and 0.02 taper of hand files. This was in agreement with previous studies, which reported no defects in the hand file groups (Bier et al., 2009; Yoldas et al., 2012; Ashwinkumar et al., 2013). In the present study, all rotary and reciprocating NiTi files caused significantly more microcracks than hand instrumentation. This result could be related to the contact between the instrument and the dentinal walls. These contacts result in many momentary stress concentrations which could cause microcracks in the root canal surface. Our results supported the conclusion that the rotary NiTi instruments damage the dentine and create defects on the root canal (Shemenesh et al., 2009). Similarly, Bier et al. (Bier et al., 2009) reported that the root canal preparation with rotary NiTi files induced significantly more microcracks than hand files and they also underlined a difference in the extent of microcracks with different file designs.
Fig. 2. SEM sample demonstrating microcrack formation after instrumentation.
Statistical Analysis
Statistical analyses were performed with SPSS 18.0 software (SPSS Inc., Chicago, IL, USA). Descriptive statistics were expressed as frequency and percent. Pearson Chi-square test was used to determine the difference among three groups. p-Value of less than 0.05 was considered statistically significant for all tests.
Results The percentages of microcracks were shown in Table I. No defect was found in group 1. The prevalance of defect in group 2, group 3, and group 4 were significantly higher when compared to group 1 (p < 0.001). Group 2, group 3, and group 4 demonstrated similar prevalance of defects without significant difference (p > 0.05) in 3, 6, and 9 mm sections. The highest percentage of microcrack was observed in 3 mm section (apical) in these groups.
Discussion Only mesiobuccal canals of specimens were evaluated in terms of microcrack formation. The mesiolingual canals were not instrumented and served to observe the microcracks which were TABLE I
The percentages of microcrack formation after instrumentation Coronal (9 mm)
NiTi Hand File PTU PTN WO
3
Middle (6 mm)
0 (0%)*
0 (0%)* #
11 (73.3%) 9 (60%)# 5 (33.3%)#
0 (0%)* #
11 (73.3%) 10 (66.7%)# 6 (40%)#
*and # symbols indicate significant differences between groups (p < 0.05).
Apical (3 mm)
Total (%) 0
#
12 (80%) 10 (66.7%)# 8 (53.3%)#
75.55 64.44 42.22
SCANNING VOL. 9999, 9999 (2014)
4
PTU and PTN work in a continous rotational motion, whereas WO works in a reciprocating movement similar to the balanced force technique (Roane et al., 85). The reciprocating movement minimizes torsional and flexural stresses (Blum et al., 97) and reduces canal transportation (Roane et al., 85; Varela-Patin˜o et al., 2010; Franco et al., 2011). Furthermore, the reciprocating motion showed significantly higher resistance to cyclic fatigue (De-Deus et al., 2010; Kim et al., 2012). In this study, WO file with an apical size of #25 .08 caused less microcracks than the PTN files with an apical size of #25 .06 without significance. In conjunction with the difference in cross-sectional design, the result could be related to the reciprocating motion. The reciprocation could prevent continuous rotational force and constant torque applied by the NiTi rotary file on the root canal walls and resulted in less dentinal damage than the continuous rotational motion. Berutti et al. (2012a;b) reported that the reciprocating motion of WO aids the stress release before the file progresses within the canal. Both ProTaper files work in same continous rotation motion. To the authors knowledge, no previous study has evaluated the microcrack formation of the newly introduced PTN file system in mandibular molar teeth. PTN has progressive and regressive percentage tapers on a single file and is made from M-Wire technology (Capar et al., 2014). Having various percentages of taper function to decrease the screw effect and dangerous taper lock by minimizing the contact between a file and dentine (Capar et al., 2014). The comparison of both rotational ProTaper systems revealed that PTN caused decrease in the prevalance of microcracks than PTU files without significance. This finding supported the previous result which stated that the taper of instrument had a significant effect on microcrack formation (Rundquist & Versluis 2006). The lower prevalance of microcrack formation at the apical thirds could be the result of less taper of PTN files.
Conclusions Within the limitations of this study the following conclusions can be drawn:
NiTi hand K-files (2% taper) did not produce microcracks in the root canals at any level.
Rotational and reciprocating NiTi files caused significantly increased percentage of microcrack formation than NiTi hand file. Fewer microcracks were seen with WO Primary reciprocating files in comparison with both ProTaper rotary files. PTN files caused less microcracks than PTU files without significance.
References Ashwinkumar V, Krithikadatta J, Surendran S, Velmurugan N. 2013. Effect of reciprocating file motion on microcrack formation in root canals: an SEM study. Int Endod J Sep 21 doi: 10.1111/iej.12197. Aydin B, Kose T, Caliskan MK. 2009. Effectiveness of HERO 642 versus Hedstrom files for removing gutta-percha fillings in curved root canals: an ex vivo study. Int Endod J 42:1050– 1056. Barreto MS, Moraes Rdo, Rosa A, Moreira RA, So´ CH, Bier MV. 2012. Vertical root fractures and dentin defects: effects of root canal preparation, filling, and mechanical cycling. J Endod 38:1135–1139. Bergmans L, Van Cleynenbreugel J, Beullens M, Wevers M, Van Meerbeek B, Lambrechts P. 2002. Smooth flexible versus active tapered shaft design using NiTi rotary instruments. Int Endod J 35:820–828. Berutti E, Paolino DS, Chiandussi G, Alovisi M, Cantatore G, Castellucci A, Pasqualini D. 2012a. Root canal anatomy preservation of WaveOne reciprocating files with or without glide path. J Endod 38:101–104. Berutti E, Chiandussi G, Paolino DS, Scotti N, Cantatore G, Castellucci A, Pasqualini D. 2012b. Canal shaping with WaveOne Primary reciprocating files and ProTaper system: a comparative study. J Endod 38:505–509. Bier CA, Shemesh H, Tanomaru-Filho M, Wesselink PR, Wu MK. 2009. The ability of different nickel-titanium rotary instruments to induce dentinal damage during canal preparation. J Endod 35:236–238. Blum JY, Machtou P, Esber S, Micallef JP. 1997. Analysis of forces developed during root canal preparation with the balanced force technique. Int Endod J 30:386–396. Blum JY, Machtou P, Ruddle C, Micallef JP. 2003. Analysis of mechanical preparations in extracted teeth using ProTaper rotary instruments: value of the safety quotient. J Endod 29:567–575. Capar ID, Ertas H, Ok E, Arslan H, Ertas ET. 2014. Comparative Study of Different Novel Nickel-Titanium Rotary Systems for Root Canal Preparation in Severely Curved Root Canals. J Endod 40:852–856. Celik D, Tas¸demir T, Er K. 2013. Comparative study of 6 rotary nickel-titanium systems and hand instrumentation for root canal preparation in severely curved root canals of extracted teeth. J Endod 39:278–282. Cuje J, Bargholz C, Hulsmann M. 2010. The outcome of retained instrument removal in a specialist practice. Int Endod J 43:545–554. De-Deus G, Moreira EJL, Lopes HP, Elias CN. 2010. Extended cyclic fatigue life of F2 ProTaper instruments used in reciprocating movement. Int Endod J 43:1063–1068. Franco V, Fabiani C, Taschieri S, Malentacca A, Bortolin M, Del Fabbro M. 2011. Investigation on the shaping ability of nickeltitanium files when used with a reciprocating motion. J Endod 37:1398–1401. Gambarini G, Grande NM, Plotino G, Somma F, Garala M, De Luca M, Testarelli L. 2008. Fatigue resistance of enginedriven rotary nickel–titanium instruments produced by new manufacturing methods. J Endod 34:1003–1005. Gonza´lez Sa´nchez, Duran-Sindreu JA, de Noe´ F, Mercade´ S, Roig M. 2012. Centring ability and apical transportation after overinstrumentation with ProTaper Universal and ProFile Vortex instruments. Int Endod J 45:542–551. Kim HC, Kwak S-W, Cheung GS-P, Ko DH, Chung SM, Lee W. 2012. Cyclic fatigue and torsional resistance of two new nickel-titanium instruments used in reciprocation motion: reciproc versus WaveOne. J Endod 38:541–544. Kim HC, Lee MH, Yum J, Versluis A, Lee CJ, Kim BM. 2010. Potential relationship between design of nickel-titanium rotary instruments and vertical root fracture. J Endod 36:1195–1199.
C ¸ ic¸ek et al.: Microcrack formation-NiTi file systems Liu R, Hou BX, Wesselink PR, Wu MK, Shemesh H. 2013. The Incidence of Root Microcracks Caused by 3 Different Singlefile Systems versus the ProTaper System. J Endod 39:1054– 1056. Peters OA. 2004. Current challenges and concepts in the preparation of root canal systems: a review. J Endod 30: 559–567. Plotino G, Grande NM, Testarelli L, Gambarini G. 2012. Cyclic fatigue of Reciproc and WaveOne reciprocating instruments. Int Endod J 45:614–618. Prati C, Foschi F, Nucci C, Montebugnoli L, Marchionni S. 2004. Appearance of the root canal walls after preparation with NiTi rotary instruments: a comparative SEM investigation. Clin Oral Investig 8:102–110. Reddy JM, Latha P, Gowda B, Manvikar V, Vijayalaxmi DB, Ponangi KC. 2014. Smear layer and debris removal using manual Ni-Ti files compared with rotary Protaper NiTi files An In-Vitro SEM study. J Int Oral Health 6:89–94. Roane JB, Sabala CL, Duncanson MG, Jr. 1985. The “balanced force” concept for instrumentation of curved canals. J Endod 11:203–211. Rundquist BD, Versluis A. 2006. How does canal taper affect root stresses. Int Endod J 39:226–237. Scha¨fer E, Lau R. 1999. Comparison of cutting efficiency and instrumentation of curved canals with nickel-titanium and stainless-steel instruments. J Endod 25:427–430. Tsesis I, Rosen E, Tamse A, Taschieri S, Kfir A. 2010a. Diagnosis of vertical root fractures in endodontically treated teeth based on clinical and radiographic indices: a systematic review. J Endod 36:1455–1458.
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Tsesis I, Rosenberg E, Faivishevsky V, Kfir A, Katz M, Rosen E. 2010b. Prevalence and associated periodontal status of teeth with root perforation: a retrospective study of 2,002 patients’ medical records. J Endod 36:797–800. Varela-Patin˜o P, Iban˜ez-Pa`rraga A, Rivas-Mundin˜a B, Cantatore G, Otero XL, Martin-Biedma B. 2010. Alternating versus continuous rotation: a comparative study of the effect on instrument life. J Endod 36:157–159. Vaudt J, Bitter K, Neumann K, Kielbassa AM. 2009. Ex vivo study on root canal instrumentation of two rotary nickeltitanium systems in comparison to stainless steel hand instruments. Int Endod J 42:22–33. Versiani MA, Leoni GB, Steier L, De-Deus G, Tassani S, Pe´cora JD, de Sousa-Neto MD. 2013. Micro-computed tomography study of oval-shaped canals prepared with the self-adjusting file, Reciproc, WaveOne, and ProTaper universal systems. J Endod 39:1060–1066. Wilcox LR, Roskelley C, Sutton T. 1997. The relationship of root canal enlargement to finger-spreader induced vertical root fracture. J Endod 23:533–534. Yoldas O, Yilmaz S, Atakan G, Kuden C, Kasan Z. 2012. Dentinal microcrack formation during root canal preparations by different NiTi rotary instruments and self-adjusting file. J Endod 38:232–235. Zmener O, Pameijer CH, Banegas G. 2005. Effectiveness in cleaning oval-shaped root canals using Anatomic Endodontic Technology, ProFile and manual instrumentation: a scanning electron microscopic study. Int Endod J 38: 356–363.
Evaluation of Microcrack Formation in Root Canals After Instrumentation With different NiTi Rotary File Systems: A Scanning Electron Microscopy Study ERSAN C¸IC¸EK, MUSTAFA MURAT KOC¸AK, BARAN CAN SAG˘LAM,
AND
SIBEL KOC¸AK
Bu¨lent Ecevit University, Faculty of Dentistry, Depertmant of Endodontics, Turkey
Summary: The aim of this study was to evaluate the dentinal microcrack formation of ProTaper Universal, ProTaper Next, and WaveOne. Sixty extracted mandibular molars were selected. The mesial roots were resected and randomly divided into four groups (n ¼ 15). The canals were prepared with hand files (group 1), ProTaper Universal (group 2), ProTaper Next (group 3), and WaveOne (group 4) instrument systems. The roots were separated horizontally at 3, 6, and 9 mm from the apex. Digital images were captured at 40 magnification using scanning electron microscopy to detect microcrack formation. Statistical analysis was performed by Pearson Chi-square test. The prevalence of microcracks in group 2, group 3, and group 4 were significantly higher when compared to group 1 (p < 0.001). Group 2, group 3, and group 4 demonstrated similar prevalence of microcracks without significant difference (p > 0.05) in all sections. All instruments caused microcracks except for hand file. The highest percentage of microcrack was recorded in 3 mm section for all groups. SCANNING 9999:XX–XX, 2014. © 2014 Wiley Periodicals, Inc. Key words: Instrumentation, microcrack, NiTi File, root dentin, scanning electron microscope
Introduction The aims of biomechanical preparation are enabling bacterial elimination, removing debris, and creating a Conflict of interest: none. Address for reprints: Ersan C¸I˙C¸EK, Bu¨lent Ecevit University, Faculty of Dentistry, Depertmant of Endodontics, Turkey E-mail: [email protected] Received 11 September 2014; Accepted with revision 31 October 2014 DOI: 10.1002/sca.21178 Published online XX Month Year in Wiley Online Library (wileyonlinelibrary.com).
canal form that allows a proper seal. However, complications such as perforations (Tsesis et al., 2010a), canal transportation, ledge and zip formation (Aydin et al., 2009), and separation of instruments (Cuje et al., 2010) are encountered during root canal preparation. Additionally, preparation procedures could damage the root dentine resulting in fractures or craze lines (Wilcox et al., 97). As a result of a microcrack or craze line that progresses with repeated stress application by occlusal forces, vertical root fracture and crack formation occur in root canal dentine during endodontic procedures. Vertical root fracture, which generally results in tooth extraction, is one of the frustrating complications of root canal treatment (Tsesis et al., 2010b). The amount of dentine removed during root canal preparation was associated with craze lines (Wilcox et al., 97). Bier et al. (2009) reported that the rotary nickel–titanium (NiTi) files caused high ratio of dentinal damage (microcrack), whereas no microcrack was observed with hand files. Recently, various new rotary NiTi file systems have been introduced and marketed by manufacturers. These systems mainly vary in cutting blades, body tapers, and tip configurations. Although systems possess some clinical advantages such as saving time (Vaudt et al., 2009) and better cutting efficiency (Scha¨fer and Lau, 99) than hand instrumentation, the influence of the design of the cutting blades is still controversial (Peters 2004; Bergmans et al., 2002) and could increase friction and stresses within the root canal (Blum et al., 2003). Furthermore, Kim et al. (Kim et al., 2010) reported the potential relationship between the design of NiTi instruments and the incidence of vertical root fractures. The efficacy of ProTaper Universal (PTU) rotary NiTi files in root canal treatment was evaluated in various studies (Versiani et al., 2013; Celik et al., 2013; Gonza´lez et al., 2012). Recently, ProTaper Next files (PTN) as a new generation of PTU system have been introduced by the same manufacturer. PTN files are available in five sizes: X1 (tip size 17 with a taper of
2
SCANNING VOL. 9999, 9999 (2014)
0.04), X2 (tip size 25 with a taper of 0.06), X3 (tip size 30 with a taper of 0.07), X4 (tip size 40 with a taper of .06), and X5 (tip size 50 with a taper of .06). They are manufactured using M-Wire NiTi alloy by an innovative thermal treatment process (Gambarini et al., 2008) to increase flexibility and cyclic fatigue resistance of the files. Recently, reciprocating files became popular in endodontic practice. WaveOne (WO) reciprocating files are available in three sizes: small (tip size 21 with a taper of 0.06), primary (tip size 25 with a taper of 0.08) and large (tip size 40 with a taper of 0.08) (Plotino et al., 2012). Introduction of scanning electron microscope (SEM) has proved to be valuable method for asesment of the abilty of the endodontic procedures to remove debris from root canals thus enabling comparison of instruments and techniques (Reddy et al., 2014). SEM images have been used to evaluate the effects of preparation methods on root canal surface (Prati et al., 2004), cleaning efficacy of various root canal instruments (Reddy et al., 2014), and formation of dentinal defects (Ashwinkumar et al., 2014) in endodontic practice. The aim of this study was to evaluate the dentinal microcrack formation of PTU, PTN, and WO NiTi files in comparison with NiTi hand files using SEM images.
Materials and Methods Sixty extracted mandibular molars were selected and stored in purified filtered water. Teeth with severely curved mesial roots were excluded. The coronal portions and distal roots of all teeth were removed using a diamond coated bur under water cooling and mesial roots were used for the study. All roots were inspected with stereomicroscope under 12 magnification to detect any pre-existing craze lines or cracks. Canal patency was established with a #15 K-File (Dentsply Maillefer, Ballaigues, Switzerland) in mesiobuccal canals. A silicon impression material was used for coating the cemental surface of roots to simulate periodontal ligament space. Then, all roots were embedded in acrylic blocks. The teeth were randomly divided into four groups (n ¼ 15) as follows: In group 1, the canals were prepared with NiTi hand files (K-Flexofiles; Dentsply-Maillefer, Ballaigues, Switzerland) using balanced-force preparation technique to file# 25. Group 1 served as control. In group 2, the following sequence of PTU rotary files (Dentsply, Maillefer, Ballaigues, Switzerland) was used at 300 rpm to prepare the canals; an SX file was used to enlarge the coronal portion of the canal, and then all files were used up to working length: S1, S2, F1. The master apical file used was F2, which corresponds to file 25 with a taper 0.06 at the apical area. In group 3, the following sequence of PTN (Dentsply, Maillefer, Ballaigues, Switzerland) was used at 300 rpm
to prepare the canals, X1 and X2 were used up to the working length, which corresponded to file 25 with a taper 0.06 at the apical area. In group 2 and group 3, canal preparation was performed with rotational motion using a torque and speed-controlled motor (X-Smart; Dentsply Tulsa Dental, Tulsa, OK) In group 4, a primary reciprocating WO (Dentsply, Maillefer, Ballaigues, Switzerland) size 25 file with a taper of 0.08 was used in a reciprocating, slow in-andout pecking motion with a 6:1 contra- angle handpiece powered by a torque-limited electric motor (WaveOneTM motor, Dentsply, Maillefer, Ballaigues, Switzerland) according to the manufacturer’s instructions. The flutes of the instrument were cleaned after three pecks. No glide path was created prior to instrumentation. Only mesiobuccal canals were prepared and mesiolingual canals were unprepared to observe the presence of defect which occured before the experiment. In the presence of dentinal defect related to the mesiolingual canal, the specimen was excluded from the study. The irrigation was performed with a freshly mixed 2.5% sodium hypochlorite (NaOCl) solution.
Sectioning and SEM Analysis
All roots were cut horizontally at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling (Leica SP1600, Wetzlar, Germany). Digital image of each section was captured at 40 magnification using SEM (QuantaTM 450 FEG, FEI, Oregon, USA) (Figs. 1 and 2). The evaluation of dentinal defects was applied in a method which was previously described by Shemenesh et al. (2009). “No defect” was defined as root dentine devoid of any craze lines or microcracks at neither external surface of the root nor the internal root canal wall. “Defects” were defined as all other lines (e.g., a craze line, a partial crack, fractures or microcracks). For each group 45 slices were observed in the total of 180 sections.
Fig. 1. SEM sample demonstrating no microcrack formation after instrumentation in instrumented canal.
C ¸ ic¸ek et al.: Microcrack formation-NiTi file systems
already present before instrumentation of root canals. We observed no microcracks in contact with uninstrumented canals. This observation led to ensure that all microcracks occured during the preparation. In the previous studies, microcracks were evaluated by digital cameras at magnification of 10, 12, 20 and 40 (Bier et al., 2009; Yoldas et al., 2012; Liu et al., 2013; Barreto et al., 2012). However, SEM analysis appears to be an adequate method to investigate the influence of endodontic instruments on the morphology of dentine surfaces, and it has been well described (Prati et al., 2004). SEM offers high-resolution images and allows the observation of areas covered by debris and/or smear layer as well as the identification of patent dentinal tubules (Zmener et al., 2005). In the present study, SEM images at magnification of 40 were used to examine the presence of microcrack. The extent of defect formation was related to the tip design, cross-section geometry, constant or progressive taper type, constant or variable pitch, and flute form of the instruments (Yoldas et al., 2012). Consequently, the design and taper of the instruments, and the motion of instrumentation were the variables in the present study. No microcrack was observed in the NiTi hand K-files (0.02 taper) group. This result could be related to avoidance of the continuous rotational motion and 0.02 taper of hand files. This was in agreement with previous studies, which reported no defects in the hand file groups (Bier et al., 2009; Yoldas et al., 2012; Ashwinkumar et al., 2013). In the present study, all rotary and reciprocating NiTi files caused significantly more microcracks than hand instrumentation. This result could be related to the contact between the instrument and the dentinal walls. These contacts result in many momentary stress concentrations which could cause microcracks in the root canal surface. Our results supported the conclusion that the rotary NiTi instruments damage the dentine and create defects on the root canal (Shemenesh et al., 2009). Similarly, Bier et al. (Bier et al., 2009) reported that the root canal preparation with rotary NiTi files induced significantly more microcracks than hand files and they also underlined a difference in the extent of microcracks with different file designs.
Fig. 2. SEM sample demonstrating microcrack formation after instrumentation.
Statistical Analysis
Statistical analyses were performed with SPSS 18.0 software (SPSS Inc., Chicago, IL, USA). Descriptive statistics were expressed as frequency and percent. Pearson Chi-square test was used to determine the difference among three groups. p-Value of less than 0.05 was considered statistically significant for all tests.
Results The percentages of microcracks were shown in Table I. No defect was found in group 1. The prevalance of defect in group 2, group 3, and group 4 were significantly higher when compared to group 1 (p < 0.001). Group 2, group 3, and group 4 demonstrated similar prevalance of defects without significant difference (p > 0.05) in 3, 6, and 9 mm sections. The highest percentage of microcrack was observed in 3 mm section (apical) in these groups.
Discussion Only mesiobuccal canals of specimens were evaluated in terms of microcrack formation. The mesiolingual canals were not instrumented and served to observe the microcracks which were TABLE I
The percentages of microcrack formation after instrumentation Coronal (9 mm)
NiTi Hand File PTU PTN WO
3
Middle (6 mm)
0 (0%)*
0 (0%)* #
11 (73.3%) 9 (60%)# 5 (33.3%)#
0 (0%)* #
11 (73.3%) 10 (66.7%)# 6 (40%)#
*and # symbols indicate significant differences between groups (p < 0.05).
Apical (3 mm)
Total (%) 0
#
12 (80%) 10 (66.7%)# 8 (53.3%)#
75.55 64.44 42.22
SCANNING VOL. 9999, 9999 (2014)
4
PTU and PTN work in a continous rotational motion, whereas WO works in a reciprocating movement similar to the balanced force technique (Roane et al., 85). The reciprocating movement minimizes torsional and flexural stresses (Blum et al., 97) and reduces canal transportation (Roane et al., 85; Varela-Patin˜o et al., 2010; Franco et al., 2011). Furthermore, the reciprocating motion showed significantly higher resistance to cyclic fatigue (De-Deus et al., 2010; Kim et al., 2012). In this study, WO file with an apical size of #25 .08 caused less microcracks than the PTN files with an apical size of #25 .06 without significance. In conjunction with the difference in cross-sectional design, the result could be related to the reciprocating motion. The reciprocation could prevent continuous rotational force and constant torque applied by the NiTi rotary file on the root canal walls and resulted in less dentinal damage than the continuous rotational motion. Berutti et al. (2012a;b) reported that the reciprocating motion of WO aids the stress release before the file progresses within the canal. Both ProTaper files work in same continous rotation motion. To the authors knowledge, no previous study has evaluated the microcrack formation of the newly introduced PTN file system in mandibular molar teeth. PTN has progressive and regressive percentage tapers on a single file and is made from M-Wire technology (Capar et al., 2014). Having various percentages of taper function to decrease the screw effect and dangerous taper lock by minimizing the contact between a file and dentine (Capar et al., 2014). The comparison of both rotational ProTaper systems revealed that PTN caused decrease in the prevalance of microcracks than PTU files without significance. This finding supported the previous result which stated that the taper of instrument had a significant effect on microcrack formation (Rundquist & Versluis 2006). The lower prevalance of microcrack formation at the apical thirds could be the result of less taper of PTN files.
Conclusions Within the limitations of this study the following conclusions can be drawn:
NiTi hand K-files (2% taper) did not produce microcracks in the root canals at any level.
Rotational and reciprocating NiTi files caused significantly increased percentage of microcrack formation than NiTi hand file. Fewer microcracks were seen with WO Primary reciprocating files in comparison with both ProTaper rotary files. PTN files caused less microcracks than PTU files without significance.
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