Efficacy of reciprocating and rotary NiTi instruments for retreatment of curved root canals assessed by micro-CT.

doi:10.1111/iej.12239

Efficacy of reciprocating and rotary NiTi instruments for retreatment of curved root canals assessed by micro-CT

€ dig1, P. Reicherts1, F. Konietschke2, C. Dullin3, W. Hahn4 & M. Hu € lsmann1 T. Ro 1

Department of Preventive Dentistry Periodontology and Cariology, University Medical Center, G€ ottingen; 2Department of 3 Medical Statistics, University Medical Center, G€ottingen; Department of Diagnostic and Interventional Radiology, University Medical Center, G€ottingen; and 4Private Dental Practice, G€ottingen, Germany

Abstract € dig T, Reicherts P, Konietschke F, Dullin C, Hahn Ro € lsmann M. Efficacy of reciprocating and rotary NiTi W, Hu instruments for retreatment of curved root canals assessed by micro-CT. International Endodontic Journal.

Aim To compare the efficacy of reciprocating and rotary NiTi-instruments in removing filling material from curved root canals using micro-computed tomography. Methodology Sixty curved root canals were prepared and filled with gutta-percha and sealer. After determination of root canal curvatures and radii in two directions as well as volumes of filling material, the teeth were assigned to three comparable groups (n = 20). Retreatment was performed using Reciproc, ProTaper Universal Retreatment or Hedstr€ om files. Percentages of residual filling material and dentine removal were assessed using micro-CT imaging. Working time and procedural errors were recorded. Statistical analysis was performed by variance procedures. Results No significant differences amongst the three retreatment techniques concerning residual filling material were detected (P > 0.05). Hedstr€om files

Introduction Complete removal of previous filling materials is the first important step of root canal retreatment to allow

Correspondence: Dr Tina R€odig, Departments of Preventive Dentistry, Periodontology and Cariology, University Medical Center G€ ottingen, Robert-Koch-Street 40, 37075 G€ ottingen, Germany (e-mail: [email protected]).

© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd

removed significantly more dentine than ProTaper Universal Retreatment (P < 0.05), but the difference concerning dentine removal between both NiTi systems was not significant (P > 0.05). Reciproc and ProTaper Universal Retreatment were significantly faster than Hedstr€ om files (P = 0.0001). No procedural errors such as instrument fracture, blockage, ledging or perforation were detected for Hedstr€ om files. Three perforations were recorded for ProTaper Universal Retreatment, and in both NiTi groups, one instrument fracture occured. Conclusions Remnants of filling material were observed in all samples with no significant differences between the three techniques. Hedstr€ om files removed significantly more dentine than ProTaper Universal Retreatment, but no significant differences between both NiTi systems were detected. Procedural errors were observed with ProTaper Universal Retreatment and Reciproc. Keywords: curved root canals, gutta-percha, micro-CT, ProTaper Universal Retreatment, Reciproc, retreatment. Received 23 August 2013; accepted 1 January 2014

thorough cleaning, disinfection and re-filling of the root canal system (Bergenholtz et al. 1979, H€ ulsmann et al. 2011). Usually, this objective can be accomplished using hand files (Imura et al. 1996, Betti & Bramante 2001) or rotary nickel-titanium (NiTi) instruments (Barrieshi-Nusair 2002, H€ ulsmann & Bluhm 2004, Gergi & Sabbagh 2007, Fariniuk et al. 2011) with or without the use of solvents (Friedman et al. 1990). Nevertheless, it is impossible to remove

International Endodontic Journal

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€ dig et al. Retreatment of curved root canals Ro

filling material completely from root canals irrespective of the retreatment technique (Wilcox et al. 1987, Sae-Lim et al. 2000, Barrieshi-Nusair 2002, Zmener et al. 2006, Takahashi et al. 2009, Rached-J unior et al. 2013). Especially in curved root canals, retreatment is a challenge and procedural errors such as alterations of root canal anatomy or instrument fracture are more likely to occur than in straight canals (Schirrmeister et al. 2006). The efficacy of ProTaper Universal Retreatment files (Dentsply Maillefer, Ballaigues, Switzerland) that were specifically developed for retreatment purposes has been confirmed in straight root canals (Giuliani et al. 2008, S o et al. 2008, Takahashi et al. 2009, Bramante et al. 2010, Ersev et al. 2012) but information on the effectiveness and safety of these instruments in € curved canals is limited (C et al. 2009, R€ odig ß elik Unal et al. 2012, Beasley et al. 2013). A recently introduced concept for root canal preparation using a single-file NiTi system with reciprocating motion (Reciproc; VDW, Munich, Germany) was shown to have superior mechanical properties compared to a full-sequence rotary NiTi system (Gavini et al. 2012). Additionally, this reciprocating technique was significantly more effective than rotary files in removing filling material from straight canals (Zuolo et al. 2013). However, no data on the efficacy of Reciproc files in the retreatment of curved canals are available. Micro-computed tomography (micro-CT) allows three-dimensional quantitative evaluation of residual filling material (Hammad et al. 2008, Roggendorf et al. 2010, Ma et al. 2012, R€odig et al. 2012, Solomonov et al. 2012). This technique also facilitates the measurement of dentine removal during retreatment (R€ odig et al. 2012), which is an important factor as excessive removal of dentine should be avoided, thus reducing the risk of vertical root fracture or perforation (H€ ulsmann et al. 2011). Therefore, the purpose of this study was to compare remaining filling material and volumes of dentine removed after retreatment of curved canals with Reciproc, ProTaper Universal Retreatment and Hedstr€ om files using micro-CT imaging.

Material and methods Specimens One hundred and nine extracted human molars without previous endodontic treatment, caries, cracks

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and resorptions were collected. Roots with double curvatures and immature apices were discarded. After gaining access, a size 10 K-file (VDW, Munich, Germany) was inserted into the root canal until the tip of the instrument was just visible at the apical foramen. The molars were separated in the furcation to allow radiographic examination of the root canals without superimposition. Digital radiographs in bucco-lingual and mesio-distal directions were performed, and canal curvatures and radii were measured in both directions (Schneider 1971, Sch€ afer et al. 2002) by two calibrated operators, and mean values were calculated. Root canals with a canal curvature between 20° and 40° and a radius between 3 and 12 mm in at least one direction were included in the study, and these parameters were defined as ‘curvature 1’ and ‘radius 1’. The corresponding measurements in the second radiographic direction were defined as ‘curvature 2’ and ‘radius 2’. Overall, 60 curved mesio-buccal and palatinal roots from maxillary as well as mesial and distal roots from mandibular molars that fulfilled the criteria were finally available and then stored in tap water throughout the study.

Root canal preparation All roots were decoronated to obtain a standardized root length of 18 mm with a working length (WL) of 17 mm. Root canal preparation was performed using FlexMaster NiTi instruments (VDW) in a crown-down technique with size 30, 0.06 taper, size 25, 0.06 taper, size 20, 0.06 taper, size 30, 0.04 taper, size 25, 0.04 taper, size 20, 0.04 taper and size 20, 0.02 taper. Apical enlargement was performed with instruments of 2% taper to a size 30. During instrumentation, root canals were irrigated with 2 mL NaOCl (1%) between each file, delivered by a syringe and a 30-gauge needle (NaviTip; Ultradent, South Jordan, UT, USA). After completion of preparation, a final rinse with 5 mL EDTA (20%) and 5 mL NaOCl (1%) was performed and the root canals were dried with paper points.

Root canal filling A standardized gutta-percha master cone size 30 was fitted with tug-back at WL. This master cone was lightly covered with an epoxy resin-based sealer (2Seal, VDW) and slowly inserted into the root canal until it reached WL. Cold lateral compaction with a size 20 finger spreader and size 15 accessory gutta-percha cones was performed until these could



not be introduced more than 5 mm into the root canal. The coronal gutta-percha was removed with a heated plugger to assure a standardized length of the root fillings (10 1 mm). Subsequently, specimens were digitally radiographed in bucco-lingual and mesio-distal directions to assess the quality and apical extent of the root canal filling. Filling was determined adequate when it appeared to be homogeneous without any voids. Inadequate root fillings were recondensed. Access cavities were temporarily sealed with Cavit (Espe, Seefeld, Germany), and specimens were stored for 14 days at 37 °C and 100% humidity. All endodontic procedures were performed by a single operator (P. R.).

Root canal retreatment Based on root canal curvatures and radii in both radiographic directions and the preoperative volumes of filling material, the roots were assigned with regard to homogenous mean values to three groups of 20 specimens. Each group comprised four mesio-buccal and six palatal roots of maxillary molars and seven mesial and three distal roots of mandibular molars. As a sensitivity analysis, the equality of the mean values amongst the groups was evaluated using Kruskal–Wallis test (P < 0.05). The test results, mean values and standard deviations are shown in Table 1. After the removal of the temporary restorations, retreatment was performed according to the following groups. Group 1: Hedstr€om files The coronal third of the root canal fillings were removed using Gates-Glidden drills size 3 and 2 at 4000 rpm. The canals were re-instrumented with Hedstr€ om files sizes 30, 25 and 20 in a circumferential quarter-turn push-pull filing motion to remove gutta-percha and sealer until WL was achieved.

Apical enlargement was performed with pre-curved Hedstr€ om files to size 40. Group 2: ProTaper Universal Retreatment instruments ProTaper Universal Retreatment files were used with 500 rpm and a torque of 2 N cm 1 with minimal apical pressure as recommended by the manufacturer. D1 (size 30, 0.09 taper) was used for the removal of the coronal third of the root filling, followed by D2 (size 25, 0.08 taper) for the middle third. Finally, D3 (size 20, 0.07 taper) was used at working length. Apical preparation was performed with ProTaper instruments F2 (size 25, 0.08 taper), F3 (size 30, 0.09 taper) and F4 (size 40, 0.06 taper). Group 3: Reciproc According to the manufacturer’s instructions, the coronal third of the root canal fillings were removed using Gates-Glidden drills similar to group 1. Reciproc files were operated in a reciprocating, slow in-and-out pecking motion with an amplitude of approximately 3 mm. Gentle apical pressure was combined with a brushing motion against the lateral root canal walls. The instrument was cleaned with a sterile gauze after three pecks. A R25 file (size 25 with a taper of 0.08 over the first apical millimetres) was used for the removal of filling material until working length was reached followed by apical enlargement with a R40 file (size 40 with a taper of 0.06 over the first apical millimetres). In all groups, irrigation was performed with 2 mL NaOCl (1%), using a syringe and a 30-gauge needle after each instrument or after three pecks with the reciprocating files. NiTi instruments were used in a torque-controlled motor (Silver Reciproc; VDW) and were discarded after four uses or if a visible deformation occured. Time to reach working length (T1) as well as time needed for complete gutta-percha removal and preparation to size 40 (T2) were recorded. Time for instrument changes and irrigation

Table 1 Characteristics of curved root canals (n = 20 roots per group)

Group € m files Hedstro ProTaper UR Reciproc

Curvature 1 (°)

Radius 1 (mm)

Curvature 2 (°)

Radius 2 (mm)

Volume of filling material (mm3)

25.6 4.8 25.4 3.9 25.4 4.0 P = 0.9995

8.1 2.2 8.1 1.6 7.9 1.5 P = 0.9303

12.7 7.3 12.5 6.1 12.1 5.7 P = 0.9852

21.6 19.8 20.7 13.3 19.7 13.5 P = 0.9891

4.8 2.1 4.6 1.6 4.8 2.1 P = 0.9989

Data shown as mean standard deviation. Statistical analysis for the equality of the mean values amongst the three groups was evaluated using Kruskal–Wallis test (P < 0.05). Roots were included in the study according to parameters ‘curvature 1’ and ‘radius 1’. Corresponding parameters in the second radiographic direction were defined as ‘curvature 2’ and ‘radius 2’.



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was not included. Total working time was calculated by adding T1 and T2. Removal was considered complete when no residual filling material was observed in the instrument flutes or in the irrigation solution. All teeth were treated by the same operator. Procedural incidents such as ledges, blockages, perforations and instrument fractures were recorded. If an instrument fracture occurred, removal of the fragment was performed with hand files, but this time was not added to working time. Final irrigation was performed with 5 mL EDTA (20%) and 5 mL NaOCl (1%), and root canals were dried with paper points.

Micro-CT scanning procedures and evaluation Specimens were scanned pre- and postoperatively using the eXplore locus SP micro-CT (GE Medical Systems, Toronto, ON, Canada) with the following parameters: 90 kVp, 80 lA, 900 projections within a full rotation (McNamara et al. 2005). Three-dimensional reconstruction resulting in data sets with 29 lm resolution that were analysed (MicroView 2.1.2; GE Medical Systems) using post-threshold-based segmentation. As segmentation threshold, the inflection point of the CT absorption histogram between dentine and filling material compartments was used. Pre- and postoperative volumes of filling material and dentine were measured in mm3 by two blinded observers, and mean values for each specimen were assessed. The mean percentage of residual filling material and the mean amount of dentine removal were calculated.

curvature (P = 0.9995, P = 0.9852), radii (P = 0.9303; P = 0.9891) and volume of filling material (P = 0.9989) could be detected. Remaining filling material was observed in all specimens (Fig. 1). Mean percentages of residual material are shown in Table 2. All retreatment techniques left 5.1–8.3% of the filling material in the root canal with no significant differences between the groups (P = 0.143). Hedstr€ om files removed significantly more dentine than ProTaper Universal Retreatment (P = 0.014). No significant differences between the two NiTi systems (P = 0.839) and between Hedstr€ om files and Reciproc (P = 0.058) were observed. The mean retreatment times are presented in Table 2. T1 and T2 as well as total working time were significantly shorter for both NiTi systems than for Hedstr€ om files (P = 0.0001) with no significant difference between ProTaper Universal Retreatment and Reciproc (P > 0.48). No procedural errors were detected for Hedstr€ om files. Three perforations in the coronal third towards the furcation were recorded in the ProTaper Universal Retreatment group with file D1. In both NiTi groups, one instrument fractured (D3 after two uses and a new R25).

Discussion As in previous studies on curved root canals (Schirr€ meister et al. 2006, Barletta et al. 2007, C ß elik Unal et al. 2009, Abramovitz et al. 2012), none of the retreatment techniques allowed complete removal of filling material. The percentage of residual material (5.1–8.3%) was similar to a recent micro-CT study

Statistical analysis For the analysis, SAS 9.2 (SAS Institute Inc., Cary, NC, USA) was used. As multivariate data are apparent, Wilk’s Lambda was computed to investigate differences within the filling material and dentine removal and working time (P < 0.05). Using analysis of covariance, the impact of the time on the filling material and dentine removal was investigated. No significant results could be detected (P > 0.05). Subsequently, the end-points were analysed separately using analysis of variance and t-tests. Tukey’s adjustment was applied to account for multiplicity.

Results The mean values for degree and radius of curvature of each group are displayed in Table 1. No significant differences between the groups concerning angles of

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Figure 1 Pre- and postoperative micro-CT images in mesiodistal direction of one selected specimen prior (left) and after (right) retreatment with remaining filling material in the apical third. The bar represents 3 mm.



Table 2 Mean percentage of residual root canal filling, volume of dentine removal and time used for instrumentation [time to reach working length (T1), time for complete guttapercha removal and preparation to size 40 (T2) and total time (T total)]

Residual root canal filling (%) Dentine removal (mm3) T1 (s) T2 (s) T total (s)

€ m files Hedstro

ProTaper UR

Reciproc

5.1 4.2

6.4 4.3

8.3 6.4

6.5 2.2

4.7 1.6

5.0 2.0

207 67 251 97 458 127

66 17 56 13 122 25

81 21 44 15 125 23

Data shown as mean standard deviation.

that detected 3.7–11.3% of filling debris in curved canals after retreatment with Hedstr€om files and two NiTi retreatment systems, ProTaper Universal Retreatment files and D-RaCe instruments (FKG Dentaire, La Chaux-de-Fonds, Switzerland) (R€ odig et al. 2012). In this study, no significant differences regarding cleanliness were found amongst the experimental groups. This is consistent with the results by R€odig et al. (2012), who also found ProTaper Universal Retreatment and Hedstr€om files to be equally effective in € curved canals. In contrast, C et al. (2009) ß elik Unal demonstrated that ProTaper Universal Retreatment files were less effective than hand instruments in curved canals. They initially prepared the root canals to an apical size 30 with 0.06 taper, whilst the tip of D3 has a size of 20 with a 0.07 taper. In that case, the manufacturer of ProTaper Universal Retreatment recommends that removal of residual filling material should be accomplished with additional instruments whenever the apical diameter of the root canal is larger than the tip of the D3 file. Retreatment in the manual group was completed at size 30 preparations, which contributes to more effective removal of filling € material (C et al. 2009). In the current ß elik Unal study, apical enlargement by two sizes beyond the initial preparation size was performed to reduce the amount of residual filling material (Hassanloo et al. 2007, Roggendorf et al. 2010) and to create sufficient space for effective irrigation (H€ ulsmann et al. 2011). No data are available on the retreatment efficacy of Reciproc in curved canals. A recent study evaluated the effectiveness of Reciproc in straight root canals and showed that the percentage of remaining material was significantly higher for Mtwo R (12.17%) compared with Reciproc (4.57%) and hand files (7.19%), which performed statistically similar


(Zuolo et al. 2013). These authors assessed the percentages of remaining filling material by longitudinal splitting of the teeth, and remnants were quantified using an imaging software. Nevertheless, the results of the present study performed in curved root canals were within the range of this previous investigation. Assessment of residual filling debris has been performed using radiographic examination (Ferreira et al. € 2001, Zanettini et al. 2008, C et al. 2009) or ß elik Unal longitudinal sectioning prior to photographic or microscopic analysis (Sae-Lim et al. 2000, de Oliveira et al. 2006, S o et al. 2008). Due to shortcomings of these two-dimensional imaging techniques, three-dimensional micro-CT scanning has been used to calculate the volume of residual material (Hammad et al. 2008, R€ odig et al. 2012, Solomonov et al. 2012). Moreover, this technique allows measurement of the amount of dentine removal during primary instrumentation (Peters et al. 2000) or retreatment (R€ odig et al. 2012, 2014). In retreatment cases, re-preparation of the root canal is necessary to establish sufficient space for effective irrigation and filling (H€ ulsmann et al. 2011). However, excessive removal of dentine should be avoided to reduce additional weakening of the root and thereby the risk of vertical root fracture or perforation (H€ ulsmann et al. 2011). In this study, the amount of dentine removal was significantly higher for Hedstr€ om files compared with ProTaper Universal Retreatment, whereas no significant differences were found between ProTaper Universal Retreatment and Reciproc which might be due to similar dimensions of these instruments. The results differ from that of a recent study, in which ProTaper Universal Retreatment removed approximately twice as much dentine (13.1 mm3) as Hedstr€ om files (6.3 mm3) in curved canals (R€ odig et al. 2012). These contrary findings may be explained by operator-related variables such as intensity of brushing motion or determination of the end-point of filling removal which affects working time. It might be speculated that dentine removal is influenced by instrument size and taper as well as several operator-dependent factors. Moreover, in the aforementioned study, four ProTaper Universal Retreatment files fractured and had to be removed resulting in additional dentine loss prior to micro-CT imaging (R€ odig et al. 2012). However, the micro-CT software allowed a quantitative evaluation of the volume of dentine removal but no visualization of the corresponding root canal area. Furthermore, it is unknown what amount of dentine removal is favourable during root canal re-preparation.


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As in previous studies, retreatment with enginedriven instruments required less time than hand instruments (H€ ulsmann & Bluhm 2004, Giuliani et al. 2008, Takahashi et al. 2009, Zuolo et al. 2013). Overall, working time was considerably shorter in this study compared with other investigations on curved canals (Ferreira et al. 2001, Schirrmeister et al. 2006, € C et al. 2009), which might be explained by ß elik Unal higher rotational speeds resulting in plasticization of gutta-percha and easier removal of the softened material (H€ ulsmann & Bluhm 2004). Despite differences in instrument number, both NiTi systems performed similar regarding working time. As in previous studies, no procedural errors were observed during manual retreatment (H€ ulsmann & Bluhm 2004, Schirrmeister et al. 2006, R€ odig et al. 2012). Three lateral perforations in the coronal third of the root canals occurred in the ProTaper Universal Retreatment group with D1, which might be attributed to the cutting tip of this file. Although ProTaper Universal Retreatment and Reciproc were used according to the manufacturer’s instructions and with a torque-controlled motor, one instrument fractured in each group (5%). These results are considerably lower than in a recent study (R€ odig et al. 2012), in which four ProTaper Universal Retreatment (20%) and five D-RaCe files fractured (25%). Similarly, C ß elik € Unal et al. (2009) reported a high incidence of procedural errors for ProTaper Universal Retreatment in curved canals (36% instrument fractures, 14% perforations).

Conclusion Neither retreatment technique could render root canals completely free of filling debris. Nevertheless, under the conditions of the present study, Hedstr€ om files, ProTaper Universal Retreatment and Reciproc were equally effective in removing filling material from curved canals. Hedstr€ om files removed significantly more dentine than ProTaper Universal Retreatment, whilst retreatment with full-sequence or reciprocating NiTi files resulted in the same amount of dentine removal. The engine-driven files were significantly faster than hand instrumentation but were associated with an increased risk of procedural errors.

Acknowledgements This study was supported by VDW. Donation of ProTaper Universal Retreatment instruments by Dentsply

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Maillefer is gratefully acknowledged. The authors deny any conflict of interest related to this study.

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Fatigue life enhancement of NiTi rotary endodontic instruments by progressive reciprocating operation.

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Efficacy of 3D conforming nickel titanium rotary instruments in eliminating canal wall bacteria from oval-shaped root canals.

Comparative evaluation of the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files in severely curved root canals.

Effectiveness of ProTaper Universal retreatment instruments used with rotary or reciprocating adaptive motion in the removal of root canal filling material.

Efficacy of reciprocating instruments for removing filling material in curved canals obturated with a single-cone technique: a micro-computed tomographic analysis.

CBCT Evaluation of the Root Canal Filling Removal Using D-RaCe, ProTaper Retreatment Kit and Hand Files in curved canals.

Success Rate and Time for Bypassing the Fractured Segments of Four NiTi Rotary Instruments.

Cyclic fatigue testing of three different rotary nickel titanium endodontic instruments in simulated curved canals - an in vitro sem analysis.

Wear and metallographic analysis of WaveOne and reciproc NiTi instruments before and after three uses in root canals.

Evaluation of Apically Extruded Debris during Root Canal Retreatment Using ProTaper Next and Reciproc in Severely Curved Canals.

An analytical mechanical model to describe the response of NiTi rotary endodontic files in a curved root canal.

Fitness of gutta-percha cones in curved root canals prepared with reciprocating files correlated with tug-back sensation.

Comparison of retreatment ability of full-sequence reciprocating instrumentation and 360° rotary instrumentation.

Evaluation of microcrack formation in root canals after instrumentation with different NiTi rotary file systems: a scanning electron microscopy study.

A comparative study on the shaping ability of k3, profile and protaper instruments in simulated curved root canals.