Single File Reciprocating Technique Using Conventional Nickel Titanium Rotary Endodontic Files

Transcription

1 SCANNING VOL. 35, (2013) Wiley Periodicals, Inc. Single File Reciprocating Technique Using Conventional Nickel Titanium Rotary Endodontic Files SO YOUN JIN, 1 WOOCHEOL LEE, 2 MO K. KANG, 3 BOCK HUR, 1 AND HYEON CHEOL KIM 1 1 Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Pusan National University, Yangsan, Korea 2 Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Seoul National University, Seoul, Korea 3 Section of Endodontics, UCLA School of Dentistry, Los Angeles, California Summary: This study was aimed to evaluate the applicability of a reciprocating movement technique with conventional nickel titanium files for root canal preparation. Forty four simulated canals in resin blocks were used in this study and divided as following four groups according to the instruments used and preparation methods. Group CP (n ¼ 12) and CR (n ¼ 12) were instrumented with continuous rotation using four files of ProFile and RaCe, respectively. Group RP (n ¼ 10) and RR (n ¼ 10) were instrumented with a reciprocation movement by using a single ProFile and RaCe file, respectively. The resin blocks were scanned before and after instrumentation, and the images were superimposed. To compare the efficiency of canal shaping, the preparation time, and centering ratio were calculated. Morphologic changes of tested files were examined by scanning electron microscopy (SEM). Data were analyzed by ANOVA and Duncan s post hoc test at p < The preparation time was markedly shorter in Groups RP and RR than in Groups CP and CR. No significant difference in the centering ratio was noted between groups. Although the files used for Groups CP Grant sponsor: Pusan National University Dental Hospital. The first two authors contributed equally to this work and share first authorship. Conflict of interest: none. Address for reprints: Hyeon Cheol Kim, Department of Conservative Dentistry, School of Dentistry, Pusan National University, 20, Geumo ro, Mulgeum, Yangsan, Gyeongnam , Korea E mail: golddent@pusan.ac.kr Received 6 November 2012; Accepted with revision 17 December 2012 DOI /sca Published online 30 January 2013 in Wiley Online Library (wileyonlinelibrary.com). and CR showed no distortion under the SEM evaluation, the files used for Groups RP and RR had considerable torsional distortion. This study suggests that the reciprocating instrumentation technique using conventional nickel titanium rotary file systems might have a comparable efficacy for the root canal shaping with reduced shaping time. Although the reciprocating technique seems to be an effective alternative to the conventional rotation technique, the risk of torsional distortion and fracture should be considered before clinical application. SCANNING 35: , Wiley Periodicals, Inc. Key words: continuous rotation, nickel titanium endodontic rotary file, reciprocating, shaping efficacy, torsional fracture Introduction Effective cleaning and shaping of the root canal system is essential for achieving the biological and mechanical objectives of root canal treatment (Hülsmann et al., 2005). Shaping of root canals can be achieved by the manual use of stainless steel files or motor driven rotary movement of nickel titanium (NiTi) files. NiTi instruments offer many advantages over stainless steel files such as maintenance of the original root canal shape and prevention of zipping, ledge formation, and perforation (Walia et al., 1988; Kazemi et al., 2000; Hülsmann et al., 2005). Furthermore, the continuous reaming action by the rotary movement is more efficient of debris removal than manual preparation with stainless steel files and consequently reduces post operative pain (Cheung and Liu, 2009). However, these instruments have some disadvantages including fracture during rotation and high cost (Sattapan et al., 2000; Guelzow et al., 2005). In general, the NiTi rotary shaping technique requires the use of multiple files with different

2 350 SCANNING VOL. 35, 6 (2013) tapers and working lengths to enlarge root canals adequately. Therefore, it is not only a cost ineffective but also a complex procedure for the novice operator due to the use of multiple files in a sequence. Meanwhile, Yared (2008) reported the use of only one NiTi rotary file in a reciprocating shaping technique. In this simplified technique, one ProTaper F2 file (Dentsply Maillefer, Ballaigues, Switzerland) was used to shape the root canal in clockwise cutting and counterclockwise releasing direction. Recently, new reciprocating file systems have been introduced: Reciproc (VDW, Munich, Germany) and WaveOne (Dentsply Maillefer). Contrary to the reciprocating movement described by Yared (2008), these systems demonstrate counterclockwise cutting and clockwise releasing motions, and require their own motors for the optimal rotational angles and speeds. Until now, many studies of reciprocation with ProTaper F2 files have been reported (De Deus et al., 2010a, b, c; You et al., 2010, 2011; Paqué et al., 2011). De Deus et al. (2010a) and You et al. (2010) reported that a reciprocating movement may lengthen the cyclic life of rotary files and preserve their clinical performance. However, the possibility of reciprocation usage with other conventional NiTi rotary instruments has not been reported. Therefore, the purpose of this study was to evaluate the applicability of a reciprocating shaping technique with NiTi rotary files for root canal preparation. Materials and Methods Forty four simulated root canals in clear resin blocks (Dentsply Maillefer) were used for this study. The simulated J shaped canals had a length of 16.5 mm and curvature of 40 as determined by Schneider s method. The resin blocks were divided into four groups according to the tested files and instrumentation methods: Groups CP, CR, RP, and RR. Groups CP (n ¼ 12) and CR (n ¼ 12) were instrumented with a continuous rotary movement by using four ProFile (Dentsply Maillefer) and RaCe files (FKG Dentaire Company, la Chaux de Fonds, Switzerland), respectively, operated by an electric motor (Tecnika; ATR, Pistola, Italy) set at a speed of 300 rpm and torque of 30 (Tecnika motor setting value) in a 16:1 reduction handpiece. The root canals in both groups were shaped in the crown down manner with the following file sizes and working lengths: #40/0.04 for the initial coronal shaping, #35/0.06 to 12.5 mm, #30/0.04 to 14.5 mm, and #25/0.06 to 16.5 mm (the final working length). Meanwhile, Group RP (n ¼ 10) and RR (n ¼ 10) were instrumented with a reciprocating movement by using only one ProFile and RaCe file (#25/0.06), respectively, operated by the same motor. This motor was set to ensure four tenths of clockwise and two tenths of counterclockwise rotations for the reciprocation movement at 300 rpm. For root canal preparation, slow pecking motions were used thrice with light apical pressure. During the instrumentation, canal wall was lubricated with the RCprep (Premier Dental, Plymouth Meeting, PA) to reduce the effect from the plastic blocks. The instrument was withdrawn from the canal when some resistance requiring more apical pressure was felt. Thereafter, the files were cleaned with gauze to remove resin debris, reinserted, and employed in the same manner until the working length was reached. The patency of the canals was verified with a #10 stainless steel K file (Mani, Inc., Shioya, Japan), followed by copious irrigation with saline. Each file used for Groups RP and RR was discarded after shaping one canal, and the files used for Groups CP and CR were discarded after shaping four canals to standardize their usage. After sufficiently practicing reciprocation with ProFile and RaCe files, a single clinically experienced operator prepared the canals in each group sequentially. The preparation time was recorded in seconds by an assistant. The time required for irrigation, changing instruments, and checking patency was excluded. Before root canal preparation, aqueous methylene blue dye was injected into the simulated canals to enhance the contrast of the pre instrumented images. The resin blocks were then scanned (HP Scanjet 7650; Hewlett Packard, Palo Alto, CA) in a reproducible position with the resolution of 2,400 dpi. The scanned images (2,960 1,160 pixel size) were stored in a personal computer. After root canal preparation, the canals (all blocks of Groups RP and RR and ten randomly selected blocks in Groups CP and CR each) were filled with Vitapex (Neo Dental Chemical Products Co., Ltd., Tokyo, Japan) and scanned again in the same position as for the pre instrumented image. Pairs of preinstrumented and post instrumented images were superimposed with the use of attached labels on the blocks by using Adobe Photoshop ver. 7.0 (Adobe, San Jose, CA; Fig. 1). These superimposed images were inspected by using the Adobe Photoshop program. The centering ratio was calculated to evaluate the change in the root canal center after instrumentation: the absolute value of the canal deviation (the difference between the inner and the outer instrumented width) was divided by the whole width of the post instrumented canal to obtain the centering ratio (Calhoun and Montgomery, 1988; Kuhn et al., 1997). The width was measured horizontally from a pre instrumented point to a post instrumented point both inward and outward at 1, 2, 3, 4, and 5 mm from the apical foramen with accuracy of 10 mm by counting the number of pixel manually using the Photoshop program. To evaluate the overall tendency of canal deviation, the mean value of the centering ratio of each canal was calculated by using the values from the five measurements.

3 S. Y. Jin et al.: Reciprocating usage of conventional NiTi files 351 Fig 1. Representative images from the Group RR. Pre instrumented image (left), post instrumented image (middle), and superimposed image (right). Morphologic changes, such as deformation or fracture, in the tested files were examined by scanning electron microscope (SEM; S 4800 II; Hitachi High Technologies America, Inc., Pleasanton, CA). The preparation time and centering ratio were analyzed by two way ANOVA and Duncan s multiplerange tests for post hoc comparison. The level of significance was set at p < Results Among the tested files, one file (RaCe) used for Group RR fractured during shaping. Therefore, forty three canals were prepared completely and 39 superimposed images were evaluated. The preparation time was markedly shorter in Groups RP and RR than in Groups CP and CR (p < 0.05). The ProFile instruments required significantly longer preparation time than the RaCe files irrespective of the instrumentation methods (p < 0.05; Table 1). Two way ANOVA revealed no significant differences in the centering ratio between the groups, regardless of Fig 2. Representative SEM images (30) shows (A) ProFile samples without distortion from the Group CP, (a) distorted ProFile from Group RP, (B) RaCe samples without distortion from the Group CR, and (b) with distorted RaCe file from the Group RR. the instrumentation methods and tested files (p > 0.05; Table 1). Under SEM, the files used for Groups CP and CR did not show any distortion. However, six and five files (overall, 11/19) used for Groups RP and RR, respectively, showed torsional distortion of the reverse wound (reverse helix) type and/or distorted flutes (Fig. 2) including one fractured RaCe file (Fig. 3). Discussion Considering the importance of canal shaping in root canal treatment, research on the shaping efficiency TABLE 1 The preparation time (s) and centering ratio (%) in the study after root canal preparation (mean SD) Groups Preparation time Centering ratio Method ProFile RaCe ProFile RaCe Continuous rotation aa 57 8 ba Reciprocation ab bb The different lowercase letters indicate significant differences in preparation time between the tested files independently of the instrumentation methods. The different uppercase letters indicate significant differences in preparation time between the instrumentation methods independently of the tested files (p < 0.05). The centering ratio was not significantly different between the groups (two way ANOVA, p > 0.05).

4 352 SCANNING VOL. 35, 6 (2013) Fig 3. One fractured RaCe file from the Group RR. A: Black arrow indicates the torn crack from torsional load, (B) and (C) show typical characteristics of torsional fracture of concentric abrasion mark (black circular arrow) and fibrous dimples area (white circle). of a new technique is compulsory. After Yared (2008) introduced reciprocation by using ProTaper F2 files, studies have been conducted on the efficiency of this single file shaping technique (De Deus et al., 2010a, b, c; You et al., 2010, 2011; Paqué et al., 2011). However, single file reciprocating shaping techniques are not well known yet, and clinicians have little information about them. Although new file systems (Reciproc and WaveOne) specially designed for reciprocating movement have been recently introduced in the market, some authors have still conducted experiments with ProTaper F2 files for evaluating reciprocating movement and reported its comparability or superiority to the conventional continuous rotary movement (De Deus et al., 2010a; You et al., 2010, 2011; Paqué et al., 2011). The new reciprocating file systems have opposite direction of screwing to conventional NiTi rotary files and these new systems need their own motor to make reciprocating movement. Meanwhile conventional endodontic motor cannot operate the new reciprocating files. Thus, in this study, we tried to use the RaCe and ProFile instruments with a single file reciprocating technique using the Tecnika engine which is able to move files reciprocally. RaCe files have similar active features to ProTaper files, but their triangular cross sectional area is smaller than that of ProTaper files, which have a convex triangular shape. ProFile instruments have radial lands and exhibit passive cutting characteristics (Shen et al., 2006). Reciprocating movement, in terms of changing the direction of rotation, seems to imitate the balanced force technique, which maintains the curvature of the root canal with minimal distortion (Roane et al., 1985; You et al., 2011). While the balanced force technique basically had the greater angle of rotation in counterclockwise against the spiral directions which are actually the key of balanced force to cut the root dentin, the greater angle in the reciprocating movement has to be inwards in line with the flutes in order to move a rotary into the canal. Although the effectiveness of balanced force technique using stainless files, it inherently show some aberrations during instrumentation (Moore et al., 2009). Contrarily, the alternative reciprocating shaping technique with ProTaper F2 files reportedly demonstrates comparable results to the continuous rotary shaping technique with multiple files used in the crown down manner (De Deus et al., 2010a; You et al., 2010, 2011; Paqué et al., 2011). The present results show that the single file reciprocating shaping technique not only significantly shortened the preparation time but also maintained a similar centering ratio to that achieved by the continuous rotary shaping technique. With regard to the tested files, the RaCe files enabled a shorter preparation time than the ProFile instruments regardless of the instrumentation method, possibly because of their active cutting characteristics. These results indicate that the singlefile reciprocating shaping technique may be a suitable alternative to the conventional NiTi rotary shaping technique. However, under the SEM evaluation, many tested files (11/19) used with the reciprocating movement demonstrated gross deformations morphologically such as unwinding (Fig. 2). To explain this phenomenon, the continuous cyclic change in the direction of rotation during the motor driven reciprocating movement might have caused torsional fatigue and/or fracture (Figs. 2, 3). It seemed that the files were pre fatigued, indeed due to the periodic change in direction. Moreover, the tip of the file was taper locked and the programmed reciprocating movement, in this study, might be too great, and consequently produced torsional load high enough to

5 cause plastic deformation. The currently introduced reciprocating instruments (Reciproc and WaveOne) are operated by their own motors at the optimal speeds and rotational angles. The manufacturers of these reciprocating instruments state that their reciprocating angles are within the elastic limits of the files. Information on the torsional elastic limit of NiTi instruments is insufficient; further, evidence on the most appropriate angle for reciprocation with the conventional rotary instruments is lacking. This issue should be investigated further. The file taper should be considered for torsional deformation. The basic Reciproc R25 and WaveOne Primary files have an 8% apical taper, similar to ProTaper F2 files. A large apical taper may endure torsional stress during reciprocating movements. However, the files used in this study had a 6% apical taper, which may have led to torsional deformation after reciprocation because they have less cross sectional area and volume than the reciprocating systems with 8% apical taper. Furthermore, ProFile instruments may be subjected to increased torsional stress from the contacts between the radial lands and the canal walls. Although the simulated canals used in this study allowed direct comparison of the shaping efficiency of different methods and instruments (Dummer et al., 1991; Tharuni et al., 1996), they did not permit evaluation of the instruments performance on natural teeth because of differences in surface texture, hardness, and cross sectional shape. The greater torsional stress from the resin material may have resulted in larger torsional deformation of the instruments. However, under the conditions of this study, many files showed distortion, including one fractured file, only in the reciprocating groups. Possibly, the single files used for reciprocation accumulated torsional fatigue whereas the multiple files used for continuous rotary instrumentation showed stress distribution among the files. The alternating movements of reciprocation should theoretically reduce the incidence of torsional fracture due to taper lock or screwing by minimizing the torsional stress during the reverse rotation before increasing stress (Franco et al., 2011). The clockwise and counterclockwise angles programmed in the new reciprocating systems seem to be significantly narrower than the angles at which such instruments usually fracture. In this respect, the single file reciprocating shaping technique should be safer than the continuous rotary shaping technique while maintaining the shaping efficacy. However, before the clinical application of the reciprocating shaping technique with the conventional NiTi rotary files, further research on extracted teeth under different conditions is highly recommended to determine the optimal size (tip size and taper), reciprocating angle, and rotational speed for reducing torsional deformation or fracture. Especially the SEM evaluation of tested files may provide information of fracture susceptibility by the reciprocating usage. S. Y. Jin et al.: Reciprocating usage of conventional NiTi files 353 Although the present study had the limited conditions of only one canal curvature and final apical preparation size of #25 by using 6% sized file, the single file reciprocating shaping technique using conventional NiTi rotary files seems to be a potentially alternative to the general continuous rotary shaping technique. However, the risk of torsional deformation and fracture should be considered during clinical application. Acknowledgement This work was supported by clinical research grant from Pusan National University Dental Hospital (2012). References Calhoun G, Montgomery S The effects of four instrumentation techniques on root canal shape. J Endod 14: Cheung GS, Liu CS A retrospective study of endodontic treatment outcome between nickel titanium rotary and stainless steel hand filing techniques. J Endod 35: De Deus G, Moreira EJ, Lopes HP, Elias CN. 2010a. Extended cyclic fatigue life of F2 ProTaper instruments used in reciprocating movement. Int Endod J 43: De Deus G, Barino B, Zamolyi RQ, et al. 2010b. Suboptimal debridement quality produced by the single file F2 ProTaper technique in oval shaped canals. J Endod 36: De Deus G, Brandão MC, Barino B, Di Giorgi K, Fidel RA, Luna AS. 2010c. Assessment of apically extruded debris produced by the single file ProTaper F2 technique under reciprocating movement. 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