Accepted Article
Received Date : 20-Feb-2014 Revised Date : 05-Apr-2014 Accepted Date : 20-Apr-2014 Article type
: Original Scientific Article
Deformation and fracture incidence of Reciproc instruments: a clinical evaluation.
G. Plotino1, N. M. Grande1 & P.F. Porciani2.
1Private
Practice; Grande, Plotino & Torsello - Studio di Odontoiatria, Rome, 2Tuscan School of
Dental Medicine, University of Siena, Siena, Italy.
Running title: Deformation and fracture incidence of Reciproc.
Key words: Nickel-titanium, reciprocation, deformation, fracture.
Correspondance: Dr. Gianluca Plotino Via Calabria, 25 - 00187 Rome, Italy
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as an 'Accepted Article', doi: 10.1111/iej.12302 This article is protected by copyright. All rights reserved.
Accepted Article
Tel: +390642020595 email: [email protected]
Abstract Aim To investigate the incidence of fracture and deformation observed on Reciproc instruments after clinical use.
Methodology A total of 1696 Reciproc NiTi instruments that were discarded after normal clinical usage over 30 months were collected, 1580 instruments were R25 (93%), 76 were R40 (5%) and 40 were R50 (2%). The treatments included 3780 root canal preparations, 3023 primary treatments and 757 retreatments. Root canal preparation was standardized and followed the manufacturer's directions for use of Reciproc files without any prior glide path with hand instruments. In retreatment cases, Reciproc R25 instrument was used to remove all filling material and to complete the preparation. Each instrument was used for shaping only one tooth. All the instruments used were inspected under a microscope to assay signs of fracture or deformation and, if any fracture existed, the length of the files was measured. Data were analysed using a chi-square test with a level of significance set at P < .05.
Results A total of 8 Reciproc R25 instruments fractured during treatments, which represents 0.47% of the number of instruments used and 0.21% of the root canals treated. Five instruments fractured in primary treatment cases and three instruments during retreatments. Six Reciproc R25 deformed during clinical use (0.35% of the number of instruments used and 0.15% of the root canals treated), 4 during retreatments and 2 during primary treatments. The deformation reported was unwinding of the blades, one at 1mm from the tip and five between 2
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and 3 mm from the tip. No deformations or fracture were registered for the Reciproc R40 and R50 instruments.
Conclusions Root canal instrumentation following the manufacturer's instructions can be performed with Reciproc instruments with a very low incidence of instrument fracture and deformation.
Introduction Reciprocating movement has been used for stainless-steel instruments for many years (Frank 1967, Klayman & Brilliant 1975). This original movement could be defined as "complete oscillating reciprocation" in that the angle of reciprocation was the same in both clockwise and counter-clockwise directions. The reciprocation actually used with NiTi instruments is an alternating movement in which the file rotates a certain angle in the cutting direction and shortly after in the opposite direction over a much lower angle (Kim et al. 2012). Consequently, these instruments complete a full rotation over several cycles of reciprocating movements, and therefore this type of reciprocation may be defined as "partial reciprocation with a rotary effect".
Several studies have shown that the actual reciprocating movement of endodontic instruments promotes an extended cyclic fatigue instrument life in comparison with conventional rotation (De-Deus et al. 2010, Pedullà et al. 2013b). This suggests that such instruments could operate for a longer period of time before failure (Wan et al. 2010) and confirms that alternating rotation appears to be a valid and safe alternative to continuous rotary movement (VarelaPatiño et al. 2010).
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The advantage of a single-use instrument has been reported by Arens et al. (2003) who stated that defects could occur even with new files in the hands of experienced endodontists, and therefore they concluded that for absolute safety a single-use approach should be followed. These observations were confirmed by Shen et al. (2009d) who recommended the single-use of endodontic NiTi instruments in order to reduce instrument fatigue and the possibility of crosscontamination.
Following these concepts, new single-file and single-use reciprocating NiTi instruments have been introduced. However, so far there has been no study that evaluated the deformation and fracture of these instruments during clinical use. The aim of the present study was to investigate the incidence of fracture and deformation observed on Reciproc instruments (VDW, Munich, Germany) after clinical use.
Materials and methods A total of 1696 Reciproc NiTi instruments that were discarded after normal clinical usage over 30 months were collected. Three operators (GP, NMG, PFP) prepared 3780 root canals divided in 3023 primary treatments and 757 retreatments (Table 1).
Root canal preparation was standardized strictly following manufacturer's directions for use of Reciproc files (http://www.vdwdental.com/fileadmin/redaktion/downloads/presse/yared_reciproc_concept_en.pdf).
In primary treatment cases, the pulp chamber was opened using burs and ultrasonic tips and the coronal pulp tissue removed. Scouting of the root canals was made passively with a size 30
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and 20 stainless-steel K-file (VDW, Munich, Germany) in order to choose the correct size of the Reciproc file to be used: R25, R40 or R50. In cases in which R40 or R50 were used, a stainlesssteel K-file size 20 and 30 respectively reached the apex passively. In these cases working length was established using an electronic apex locator and patency was established with a size 10 stainless steel hand K-file (VDW, Munich, Germany).
In cases in which R25 was used, the coronal and middle thirds were initially prepared based on a working length estimated from the pre-operative radiograph, without any prior glide path with hand instruments. In all the cases, manufacturers instructions were followed in doing three up-and-down strokes advancing with the instrument, then removing it, cleaning the flutes and flushing the root canals with 5.25% sodium hypochlorite. These steps were repeated until the estimated working length of the two coronal thirds was reached by the instrument. When R40 or R50 instruments were used, this procedure was repeated until the entire root canal length previously established with the electronic apex locator was reached.
When preparation was performed with R25 instrument, a straight (not pre-bent) size 10 stainless-steel hand K-file was used to check apical patency and to determine the final electronic working
length
as
suggested
by
the
manufacturer
(http://www.vdw-
dental.com/fileadmin/redaktion/downloads/presse/yared_reciproc_concept_en.pdf). Preparation was completed with R25 as previously described until the entire root canal length. In cases in which a straight hand stainless-steel size 10 K-file did not reach the working length, the R25 instrument was used to the point where the hand instrument had reached and the apex was prepared by hand with stainless-steel and NiTi hand files.
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In retreatment cases, after removal of restorations, the most coronal part of the root filling material was removed by Gates Glidden or ultrasonic tips. Reciproc R25 instruments were used to remove all filling material and to complete the preparation as previously described once the root canal was made patent with a size 10 stainless-steel hand K-file. In those retreatment cases in which it was not possible to reach the entire working length, Reciproc files were used to the point of the canal where the hand file reached. In all cases, a lateral brushing cutting action was performed in order to relocate the orifices and to prepare around the whole circumference.
All Reciproc files were used driven by an endodontic motor (Silver Reciproc or Gold Reciproc, VDW, Munich) with its specific reciprocating function (Reciproc ALL) and a 6:1 hand-piece (Sirona Dental Systems GmbH, Bensheim, Germany).
After canal preparation, irrigation using ultrasonically activated 5.25% sodium hypochlorite and 17% EDTA was used, and canals dried and then filled in the same or a subsequent visit.
Each instrument was used for shaping the canals of only one tooth. All the instruments used were ultrasonically cleaned and sterilized by autoclaving before inspection under an optical stereomicroscope at several magnifications to assess for signs of fracture or deformation. The discarded files were grouped according to the file size (R25, R40 and R50) and, if any fracture existed, the length of the files was measured from the shaft to the tip using a digital caliper, to determine the length of the fractured fragment. A database of all cases involving Reciproc instruments was maintained and included data on instrument fracture, such as tooth and canal involved, type of the treatment (primary treatment or retreatment), size of fractured instrument, length of the fractured fragment and resolution of the case, i.e. instrument removed, by-passed or remained in the canal.
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Data were analysed using a chi-square test with a level of significance set at P < .05.
Results A total of 1696 Reciproc NiTi instruments were discarded within 30 months of clinical practice. Overall, 1580 instruments were R25 (93%), 76 were R40 (5%) and 40 were R50 (2%).
No statistical significant differences were found between the number of fractured and deformed instruments (P = 0.44). A total of 8 Reciproc R25 instruments were fractured during treatments, which represents 0.47% of the number of instruments used and 0.21% of the root canals treated. Five instruments fractured in primary treatment cases, which represents 0.29% of the number of instruments used and 0.13% of the root canals treated and three instruments during retreatments, which represents 0.18% of the number of instruments used and 0.08% of the root canals treated. No significant difference was found for fractured instruments between treatment and retreatment cases (P = 0.31).
Five of the fractured fragments were removed (3 during primary treatments and 2 during retreatments) (Fig. 1), one of the instruments fractured during a primary treatment was bypassed and only two instruments remained inside the root canal. In 2 cases, the length of the fractured fragment was 16 mm from the tip of the instrument (1 in the palatal canal of a maxillary first molar, 1 in the single canal of a maxillary second premolar) and they were removed, while the other 6 fractures were reported between 2 and 3 mm from the tip. One of these instruments fractured 3 mm from the apex in the buccal canal of a maxillary first premolar (removed), one 5 mm from the apex in the disto-buccal canal of a maxillary second molar (removed) and another one at the canal terminus of the mesio-buccal canal in a maxillary
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first molar (not bypasssed nor removed). Three R25 instruments fractured in second mandibular molars, one inside a curvature in the middle portion of the distal canal (bypassed), one at the orifice of the mesio-lingual canal (removed) and the other one in the apical portion of the mesio-lingual canal in a C-shaped tooth (not bypasssed nor removed).
Six Reciproc R25 instruments deformed during clinical use (0.35% of the number of instruments used and 0.15% of the root canals treated), 4 during retreatments (0.23% of the number of instruments used and 0.10% of the root canals treated) and 2 during primary treatments (0.11% of the number of instruments used and 0.05% of the root canals treated). No significant difference was found for deformed instruments between treatments and retreatment cases (P = 0.24). The deformation reported was unwinding of the blades, one at 1mm from the tip and five between 2 and 3 mm from the tip.
No deformations or fracture were registered for the Reciproc R40 and R50 instruments.
Discussion The present study aimed to evaluate the deformation and fracture incidence of Reciproc NiTi instruments discarded after normal clinical use. The use of NiTi instruments for shaping root canals represents the gold standard of contemporary endodontic practice. It is very well established that rotary NiTi files are faster and produces equal or less canal transportation than stainless-steel hand files, reduce operator fatigue, procedural errors, and the duration of the canal preparation (Bergmans et al. 2001, Peters 2004, Peters & Paque 2010). The mechanical properties of NiTi have enabled endodontic files to be more flexible, to be better able to conform to canal curvature, to resist fracture, and to wear less than stainless-steel files (Plotino
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et al. 2009). Despite the advantages of NiTi rotary instruments, fracture can occur during clinical use (Parashos & Messer 2006). Malentacca & Lalli (2002) suggested that a reciprocating rotation might represent an advantage for the safer use of NiTi instruments, thus reducing fractures and deformations.
The results of the present study reveal a low percentage of fracture (less than 0.5%) and deformations (less than 0.4%) for Reciproc NiTi instruments. This percentage is much lower than most of the previously published fracture rates on rotary instruments (Table 2) and it is similar to that of De-Deus et al. (2013) in which only a single fracture (0.2% of 502 root canals instrumented with Reciproc) occurred in a root canal with moderate curvature. Therefore, the reciprocating movement may play a role in preventing instrument fracture, as the cyclical reversal of rotation seems to drastically reduce torsional stress. Furthermore, the reciprocating rotation that is a characteristic of the Reciproc movement may help the instrument in its advance towards the canal terminus, following a mechanical balanced force advance, as reported by De-Deus et al. (2013), while reducing the risk of blockage for the tip of the instrument (Gavini et al. 2012). In fact, the actual reciprocating rotation aims to minimize the risk of fracture of the instrument caused by torsional stress as the angle of rotation in the direction of cutting is designed to be less than the elastic limit of the instrument (Kim et al. 2012).
The very low frequency of R25 instrument fracture reported in the present study, can be possibly understood also as an improvement in cyclic fatigue resistance given by the reciprocation kinematics (Pedullà et al. 2013a, 2013b), the instrument cross-sectional design (Grande et al. 2006, Plotino et al. 2012) and the superelastic M-wire alloy (Johnson et al. 2008). Cross-sectional "S-shape" design may play a further role to provide great cutting ability to this instrument (Bürklein et al. 2012, Plotino et al. in press). Furthermore, the use of only one NiTi
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file in reciprocation to prepare the entire root canal, as provided by the Reciproc technique, may reduce the accumulation of metal fatigue, costs and avoid cross-infection (Shen et al. 2009d, DeDeus et al. 2010).
In the present study, 6 out of the 8 fractured files were removed or by-passed. In these cases, file fracture seems to have no impact from a clinical point of view, as the treatments was completed normally. This is of particular importance in cases with primary infection (Ungerechts et al. 2014). Two R25 files fractured 16 mm from the tip of the instrument during the passive brushing action in the outward lateral movement. For this reason both instruments were outside the orifice, not engaged in the dentine and their retrieval was performed easily (Fig. 2).
As previously reported, the reciprocating technique was the most rapid method to effectively remove gutta-percha and sealer from the root canal space during retreatment (Zuolo et al. 2013). The results of the present study reveal that removal of old filling materials and repreparation of the root canals has been performed with a very low fracture rate using Reciproc R25 instrument in retreatment cases. Deformations occurred more frequently in retreatments than primary treatments (0.2% versus 0.1%), as during removal of filling materials too much pressure may be exerted in some cases.
Conclusions Root canal instrumentation can be performed with Reciproc system used as single instrument in all type of root canals with a very low incidence of instrument fracture and deformation.
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References Alapati SB, Brantley WA, Svec TA, Powers JM, Nusstein JM, Daehn GS (2005) SEM observations of nickel-titanium rotary endodontic instruments that fractured during clinical Use. Journal of Endodontics 31, 40-3. Ankrum MT, Hartwell GR, Truitt JE (2004) K3 Endo, ProTaper and Profile systems: breakage and distortion in severely curved roots of molars. Journal of Endodontics 30, 234-7. Arens FC, Hoen MM, Steiman HR, Dietz GC Jr (2003) Evaluation of single-use rotary nickeltitanium instruments. Journal of Endodontics 29, 664-6. Baumann MA, Roth A (1999) Effect of experience on quality of canal preparation with rotary nickel-titanium files. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 88, 714-8. Bergmans L, Van Cleynenbreugel J, Wevers M, Lambrechts P (2001) Mechanical root canal preparation with NiTi rotary instruments: rationale, performance and safety. Status report for the American Journal of Dentistry. American Journal of Dentistry 14, 324-33. Bürklein S, Hinschitza K, Dammaschke T, Schäfer E (2012) 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, 44961. Cheung GS, Peng B, Bian Z, Shen Y, Darvell BW (2005) Defects in ProTaper S1 instruments after clinical use: fractographic examination. International Endodontic Journal 38, 802-9. Cheung GS, Bian Z, Shen Y, Peng B, Darvell BW (2007) Comparison of defects in ProTaper handoperated and engine-driven instruments after clinical use. International Endodontic Journal 40, 169-78.
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De-Deus G, Moreira E, Lopes H, Elias C (2010) Extended cyclic fatigue life of F2 ProTaper instruments used in reciprocating movement. International Endodontic Journal 43, 1063–8. De-Deus G, Arruda TE, Souza EM, Neves A, Magalhães K, Thuanne E, Fidel RA (2013) The ability of the Reciproc R25 instrument to reach the full root canal working length without a glide path. International Endodontic Journal 46, 993-8. Di Fiore PM, Genov KA, Komaroff E, Li Y, Lin L (2006) Nickel-titanium rotary instrument fracture: a clinical practice assessment. International Endodontic Journal 39, 700-8. Gavini G, Caldeira C, Akisue E, Candeiro G, Kawakami D (2012) Resistance to flexural fatigue of Reciproc R25 files under continuous rotation and reciprocating movement. Journal of Endodontics 38, 684–7. Grande NM, Plotino G, Pecci R, Bedini R, Malagnino VA, Somma F (2006) Cyclic fatigue resistance and three-dimensional analysis of instruments from two nickel-titanium rotary systems. International Endodontic Journal 39, 755-63. Hulsmann M, Herbst U, Schafers F (2003) Comparative study of root-canal preparation using Lightspeed and Quantec SC rotary NiTi instruments. International Endodontic Journal 36, 74856. Inan U, Gonulol N (2009) Deformation and fracture of Mtwo rotary nickel-titanium instruments after clinical use. Journal of Endodontics 35, 1396-9. Johnson E, Lloyd A, Kuttler S, Namerow K (2008) Comparison between a novel nickel-titanium alloy and 508 nitinol on the cyclic fatigue life of ProFile 25/.04 rotary instruments. Journal of Endodontics 34, 1406-9. Kim H, Kwak S, Cheung G, Ko D, Chung S, Lee W (2012) Cyclic fatigue and torsional resistance of two new nickel-titanium instruments used in reciprocation motion: Reciproc versus WaveOne. Journal of Endodontics 38, 541–44.
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Knowles KI, Hammond NB, Biggs SG, Ibarrola JL (2006) Incidence of instrument separation using LightSpeed rotary instruments. Journal of Endodontics 32, 14-6. Malentacca A, Lalli F (2002) Use of nickel-titanium instruments with reciprocating movement. Italian Journal of Endodontics 16, 79-84. Parashos P, Messer HH (2006) Rotary NiTi instrument fracture and its consequences. Journal of Endodontics 32, 1031-43. Parashos P, Gordon I, Messer HH (2004) Factors influencing defects of rotary nickel-titanium endodontic instruments after clinical use. Journal of Endodontics 30, 722-5. Pedullà E, Grande NM, Plotino G, Palermo F, Gambarini G, Rapisarda E (2013a) Cyclic fatigue resistance of two reciprocating nickel-titanium instruments after immersion in sodium hypochlorite. International Endodontic Journal 46, 155-9. Pedullà E, Grande NM, Plotino G, Gambarini G, Rapisarda E (2013b) Influence of continuous or reciprocating motion on cyclic fatigue resistance of 4 different nickel-titanium rotary instruments. Journal of Endodontics 39, 258-61. Peng B, Shen Y, Cheung GSP, Xia TJ (2005) Defects in ProTaper S1 instruments after clinical use: longitudinal examination. International Endodontic Journal 38, 550–7. Peters OA (2004) Current challenges and concepts in the preparation of root canal systems: a review. Journal of Endodontics 30, 559-67. Peters OA, Paque F (2010) Current developments in rotary root canal instrument technology and clinical use: a review. Quintessence International 41, 479-88. Plotino G, Grande NM, Cordaro M, Testarelli L, Gambarini G (2009) A review of cyclic fatigue testing of nickel-titanium rotary instruments. Journal of Endodontics 35, 1469-76.
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Plotino G, Grande NM, Testarelli L, Gambarini G (2012) Cyclic fatigue of Reciproc and WaveOne reciprocating instruments. International Endodontic Journal 45, 614-8. Plotino G, Giansiracusa Rubini A, Grande NM, Testarelli L, Gambarini G (in press) Cutting efficiency of Reciproc and WaveOne reciprocating instruments. Journal of Endodontics. Ramirez-Solomon M, Soler-Bientz R, de la Garza-Gonzalez R, Palacios-Garza CM (1997) Incidence of Lightspeed separation and the potential for bypassing. Journal of Endodontics 23, 586-7. Sattapan B, Nervo GJ, Palamara JE, Messer HH (2000) Defects in rotary nickel-titanium files after clinical use. Journal of Endodontics 26, 161-5. Shen Y, Cheung GS, Bian Z, Peng B (2006) Comparison of defects in ProFile and ProTaper systems after clinical use. Journal of Endodontics 32, 61-5. Shen Y, Haapasalo M, Cheung GS, Peng B (2009a) Defects in nickel-titanium instruments after clinical use. Part 1: Relationship between observed imperfections and factors leading to such defects in a cohort study. Journal of Endodontics 35, 129-32. Shen Y, Cheung GS, Peng B, Haapasalo M (2009b) Defects in nickel-titanium instruments after clinical use. Part 2: Fractographic analysis of fractured surface in a cohort study. Journal of Endodontics 35, 133-6. Shen Y, Coil JM, Haapasalo M (2009c) Defects in nickel-titanium instruments after clinical use. Part 3: a 4-year retrospective study from an undergraduate clinic. Journal of Endodontics 35, 193-6. Shen Y, Coil JM, McLean AG, Hemerling DL, Haapasalo M (2009d) Defects in nickel-titanium instruments after clinical use. Part 5: single use from endodontic specialty practices. Journal of Endodontics 35, 1363-7.
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Tzanetakis GN, Kontakiotis EG, Maurikou DV, Marzelou MP (2008) Prevalence and management of instrument fracture in the postgraduate endodontic program at the Dental School of Athens: a five-year retrospective clinical study. Journal of Endodontics 34, 675–8. Ungerechts C, Bårdsen A, Fristad I (2014) Instrument fracture in root canals - where, why, when and what? A study from a student clinic. International Endodontic Journal 47, 183-90. Varela-Patiño P, Ibañez-Párraga A, Rivas-Mundiña B, Cantatore G, Otero XL, Martin-Biedma B (2010) Alternating versus continuous rotation: a comparative study of the effect on instrument life. Journal of Endodontics 36, 157-9. Wan J, Rasimick BJ, Musikant BL, Deutsch AS (2011) A comparison of cyclic fatigue resistance in reciprocating and rotary nickel-titanium instruments. Australian Endodontic Journal 37, 122-7. Wei X, Ling J, Huang X, Liu L (2007) Modes of failure of ProTaper nickel-titanium rotary instruments after clinical use. Journal of Endodontics 33, 276-9. Wolcott S, Wolcott J, Ishley D, Kennedy W, Johnson S, Minnich S, Meyers J (2006) Separation incidence of ProTaper rotary instruments: a large cohort clinical evaluation. Journal of Endodontics 32, 1139-41. Wu J, Lei G, Yan M, Yu Y, Yu J, Zhang G (2011) Instrument separation analysis of multi-used ProTaper Universal rotary system during root canal therapy. Journal of Endodontics 37, 758-63. Zuolo AS, Mello JE Jr, Cunha RS, Zuolo ML, Bueno CE (2013) Efficacy of reciprocating and rotary techniques for removing filling material during root canal retreatment. International Endodontic Journal 46, 947-53
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Figure legends Figure 1. A) Radiograph of a mandibular second molar with a fragment of fractured instrument; B) Radiograph in which the fragment was partially removed; C) Radiograph with gutta-percha cones after complete removal of the fractured fragment; D) Post-operative radiograph after three-dimensional filling of the root canal and direct restoration with a fiber post in the distal canal; E) Photograph of the access cavity after root canal filling; F) Photograph immediately after the coronal reconstruction; G) 1-year radiographic control; H) 1-year control photograph.
Figure 2. A) Radiograph of a maxillary first molar with a 16mm fragment of fractured instrument in the palatal canal; B) Intra-operative radiograph of the working length after removal of the fractured instrument; C) Photograph of the access cavity with the fractured instrument protruding outside the orifice of the palatal canal; D) Photograph of the fragment after removal using the Instrument Removal System; E) Photograph of the access cavity after removal of the fractured instrument; F) Post-operative radiograph after three-dimensional filling of the root canal system; G) Photograph of the indirect lithium disilicate onlay immediately after cementation; H) 1-year radiographic control.
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Table 1 Number of teeth treated in the present study. Central Incisors
Lateral Incisors
Canines
Premolars
Molars
Maxillary
80
75
53
298
509
Mandibular
18
47
32
142
394
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Table 2 Fracture and deformation rate of rotary instruments reported in previous studies. Fractures Ramirez-Solomon et al. (1997)
3.7%
Baumann et al. (1999)
9.4%
Sattapan et al. (2000)
21%
Deformations
28%
Hulsmann et al. (2003)
6-10%
Parashos et al. (2004)
5%
12%
Ankrum et al. (2004)
1.7-6%
2.4-15.3%
Alapati et al. (2005)
3-23%
7-22%
Peng et al. (2005)
23%
Cheung et al. (2005)
23%
Shen et al. (2006)
7-14%
Wolcott et al. (2006)
2.4%
Di Fiore et al. (2006)
1.9%
Knowles et al. (2006)
1.3%
Cheung et al. (2007)
14%
0.3-5%
Wei et al. (2007)
12.9%
Tzanetakis et al. (2008)
1.8%
Inan et al. (2009)
16%
10%
Shen et al. (2009a, 2009b)
5%
3%
Shen et al. (2009c)
0.3%
1%
Shen et al. (2009d)
0.26%
2.9%
Wu et al. (2011)
2.6%
De-Deus et al. (2013)
0.2%
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Received Date : 20-Feb-2014 Revised Date : 05-Apr-2014 Accepted Date : 20-Apr-2014 Article type
: Original Scientific Article
Deformation and fracture incidence of Reciproc instruments: a clinical evaluation.
G. Plotino1, N. M. Grande1 & P.F. Porciani2.
1Private
Practice; Grande, Plotino & Torsello - Studio di Odontoiatria, Rome, 2Tuscan School of
Dental Medicine, University of Siena, Siena, Italy.
Running title: Deformation and fracture incidence of Reciproc.
Key words: Nickel-titanium, reciprocation, deformation, fracture.
Correspondance: Dr. Gianluca Plotino Via Calabria, 25 - 00187 Rome, Italy
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as an 'Accepted Article', doi: 10.1111/iej.12302 This article is protected by copyright. All rights reserved.
Accepted Article
Tel: +390642020595 email: [email protected]
Abstract Aim To investigate the incidence of fracture and deformation observed on Reciproc instruments after clinical use.
Methodology A total of 1696 Reciproc NiTi instruments that were discarded after normal clinical usage over 30 months were collected, 1580 instruments were R25 (93%), 76 were R40 (5%) and 40 were R50 (2%). The treatments included 3780 root canal preparations, 3023 primary treatments and 757 retreatments. Root canal preparation was standardized and followed the manufacturer's directions for use of Reciproc files without any prior glide path with hand instruments. In retreatment cases, Reciproc R25 instrument was used to remove all filling material and to complete the preparation. Each instrument was used for shaping only one tooth. All the instruments used were inspected under a microscope to assay signs of fracture or deformation and, if any fracture existed, the length of the files was measured. Data were analysed using a chi-square test with a level of significance set at P < .05.
Results A total of 8 Reciproc R25 instruments fractured during treatments, which represents 0.47% of the number of instruments used and 0.21% of the root canals treated. Five instruments fractured in primary treatment cases and three instruments during retreatments. Six Reciproc R25 deformed during clinical use (0.35% of the number of instruments used and 0.15% of the root canals treated), 4 during retreatments and 2 during primary treatments. The deformation reported was unwinding of the blades, one at 1mm from the tip and five between 2
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and 3 mm from the tip. No deformations or fracture were registered for the Reciproc R40 and R50 instruments.
Conclusions Root canal instrumentation following the manufacturer's instructions can be performed with Reciproc instruments with a very low incidence of instrument fracture and deformation.
Introduction Reciprocating movement has been used for stainless-steel instruments for many years (Frank 1967, Klayman & Brilliant 1975). This original movement could be defined as "complete oscillating reciprocation" in that the angle of reciprocation was the same in both clockwise and counter-clockwise directions. The reciprocation actually used with NiTi instruments is an alternating movement in which the file rotates a certain angle in the cutting direction and shortly after in the opposite direction over a much lower angle (Kim et al. 2012). Consequently, these instruments complete a full rotation over several cycles of reciprocating movements, and therefore this type of reciprocation may be defined as "partial reciprocation with a rotary effect".
Several studies have shown that the actual reciprocating movement of endodontic instruments promotes an extended cyclic fatigue instrument life in comparison with conventional rotation (De-Deus et al. 2010, Pedullà et al. 2013b). This suggests that such instruments could operate for a longer period of time before failure (Wan et al. 2010) and confirms that alternating rotation appears to be a valid and safe alternative to continuous rotary movement (VarelaPatiño et al. 2010).
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Accepted Article
The advantage of a single-use instrument has been reported by Arens et al. (2003) who stated that defects could occur even with new files in the hands of experienced endodontists, and therefore they concluded that for absolute safety a single-use approach should be followed. These observations were confirmed by Shen et al. (2009d) who recommended the single-use of endodontic NiTi instruments in order to reduce instrument fatigue and the possibility of crosscontamination.
Following these concepts, new single-file and single-use reciprocating NiTi instruments have been introduced. However, so far there has been no study that evaluated the deformation and fracture of these instruments during clinical use. The aim of the present study was to investigate the incidence of fracture and deformation observed on Reciproc instruments (VDW, Munich, Germany) after clinical use.
Materials and methods A total of 1696 Reciproc NiTi instruments that were discarded after normal clinical usage over 30 months were collected. Three operators (GP, NMG, PFP) prepared 3780 root canals divided in 3023 primary treatments and 757 retreatments (Table 1).
Root canal preparation was standardized strictly following manufacturer's directions for use of Reciproc files (http://www.vdwdental.com/fileadmin/redaktion/downloads/presse/yared_reciproc_concept_en.pdf).
In primary treatment cases, the pulp chamber was opened using burs and ultrasonic tips and the coronal pulp tissue removed. Scouting of the root canals was made passively with a size 30
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and 20 stainless-steel K-file (VDW, Munich, Germany) in order to choose the correct size of the Reciproc file to be used: R25, R40 or R50. In cases in which R40 or R50 were used, a stainlesssteel K-file size 20 and 30 respectively reached the apex passively. In these cases working length was established using an electronic apex locator and patency was established with a size 10 stainless steel hand K-file (VDW, Munich, Germany).
In cases in which R25 was used, the coronal and middle thirds were initially prepared based on a working length estimated from the pre-operative radiograph, without any prior glide path with hand instruments. In all the cases, manufacturers instructions were followed in doing three up-and-down strokes advancing with the instrument, then removing it, cleaning the flutes and flushing the root canals with 5.25% sodium hypochlorite. These steps were repeated until the estimated working length of the two coronal thirds was reached by the instrument. When R40 or R50 instruments were used, this procedure was repeated until the entire root canal length previously established with the electronic apex locator was reached.
When preparation was performed with R25 instrument, a straight (not pre-bent) size 10 stainless-steel hand K-file was used to check apical patency and to determine the final electronic working
length
as
suggested
by
the
manufacturer
(http://www.vdw-
dental.com/fileadmin/redaktion/downloads/presse/yared_reciproc_concept_en.pdf). Preparation was completed with R25 as previously described until the entire root canal length. In cases in which a straight hand stainless-steel size 10 K-file did not reach the working length, the R25 instrument was used to the point where the hand instrument had reached and the apex was prepared by hand with stainless-steel and NiTi hand files.
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In retreatment cases, after removal of restorations, the most coronal part of the root filling material was removed by Gates Glidden or ultrasonic tips. Reciproc R25 instruments were used to remove all filling material and to complete the preparation as previously described once the root canal was made patent with a size 10 stainless-steel hand K-file. In those retreatment cases in which it was not possible to reach the entire working length, Reciproc files were used to the point of the canal where the hand file reached. In all cases, a lateral brushing cutting action was performed in order to relocate the orifices and to prepare around the whole circumference.
All Reciproc files were used driven by an endodontic motor (Silver Reciproc or Gold Reciproc, VDW, Munich) with its specific reciprocating function (Reciproc ALL) and a 6:1 hand-piece (Sirona Dental Systems GmbH, Bensheim, Germany).
After canal preparation, irrigation using ultrasonically activated 5.25% sodium hypochlorite and 17% EDTA was used, and canals dried and then filled in the same or a subsequent visit.
Each instrument was used for shaping the canals of only one tooth. All the instruments used were ultrasonically cleaned and sterilized by autoclaving before inspection under an optical stereomicroscope at several magnifications to assess for signs of fracture or deformation. The discarded files were grouped according to the file size (R25, R40 and R50) and, if any fracture existed, the length of the files was measured from the shaft to the tip using a digital caliper, to determine the length of the fractured fragment. A database of all cases involving Reciproc instruments was maintained and included data on instrument fracture, such as tooth and canal involved, type of the treatment (primary treatment or retreatment), size of fractured instrument, length of the fractured fragment and resolution of the case, i.e. instrument removed, by-passed or remained in the canal.
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Data were analysed using a chi-square test with a level of significance set at P < .05.
Results A total of 1696 Reciproc NiTi instruments were discarded within 30 months of clinical practice. Overall, 1580 instruments were R25 (93%), 76 were R40 (5%) and 40 were R50 (2%).
No statistical significant differences were found between the number of fractured and deformed instruments (P = 0.44). A total of 8 Reciproc R25 instruments were fractured during treatments, which represents 0.47% of the number of instruments used and 0.21% of the root canals treated. Five instruments fractured in primary treatment cases, which represents 0.29% of the number of instruments used and 0.13% of the root canals treated and three instruments during retreatments, which represents 0.18% of the number of instruments used and 0.08% of the root canals treated. No significant difference was found for fractured instruments between treatment and retreatment cases (P = 0.31).
Five of the fractured fragments were removed (3 during primary treatments and 2 during retreatments) (Fig. 1), one of the instruments fractured during a primary treatment was bypassed and only two instruments remained inside the root canal. In 2 cases, the length of the fractured fragment was 16 mm from the tip of the instrument (1 in the palatal canal of a maxillary first molar, 1 in the single canal of a maxillary second premolar) and they were removed, while the other 6 fractures were reported between 2 and 3 mm from the tip. One of these instruments fractured 3 mm from the apex in the buccal canal of a maxillary first premolar (removed), one 5 mm from the apex in the disto-buccal canal of a maxillary second molar (removed) and another one at the canal terminus of the mesio-buccal canal in a maxillary
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first molar (not bypasssed nor removed). Three R25 instruments fractured in second mandibular molars, one inside a curvature in the middle portion of the distal canal (bypassed), one at the orifice of the mesio-lingual canal (removed) and the other one in the apical portion of the mesio-lingual canal in a C-shaped tooth (not bypasssed nor removed).
Six Reciproc R25 instruments deformed during clinical use (0.35% of the number of instruments used and 0.15% of the root canals treated), 4 during retreatments (0.23% of the number of instruments used and 0.10% of the root canals treated) and 2 during primary treatments (0.11% of the number of instruments used and 0.05% of the root canals treated). No significant difference was found for deformed instruments between treatments and retreatment cases (P = 0.24). The deformation reported was unwinding of the blades, one at 1mm from the tip and five between 2 and 3 mm from the tip.
No deformations or fracture were registered for the Reciproc R40 and R50 instruments.
Discussion The present study aimed to evaluate the deformation and fracture incidence of Reciproc NiTi instruments discarded after normal clinical use. The use of NiTi instruments for shaping root canals represents the gold standard of contemporary endodontic practice. It is very well established that rotary NiTi files are faster and produces equal or less canal transportation than stainless-steel hand files, reduce operator fatigue, procedural errors, and the duration of the canal preparation (Bergmans et al. 2001, Peters 2004, Peters & Paque 2010). The mechanical properties of NiTi have enabled endodontic files to be more flexible, to be better able to conform to canal curvature, to resist fracture, and to wear less than stainless-steel files (Plotino
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et al. 2009). Despite the advantages of NiTi rotary instruments, fracture can occur during clinical use (Parashos & Messer 2006). Malentacca & Lalli (2002) suggested that a reciprocating rotation might represent an advantage for the safer use of NiTi instruments, thus reducing fractures and deformations.
The results of the present study reveal a low percentage of fracture (less than 0.5%) and deformations (less than 0.4%) for Reciproc NiTi instruments. This percentage is much lower than most of the previously published fracture rates on rotary instruments (Table 2) and it is similar to that of De-Deus et al. (2013) in which only a single fracture (0.2% of 502 root canals instrumented with Reciproc) occurred in a root canal with moderate curvature. Therefore, the reciprocating movement may play a role in preventing instrument fracture, as the cyclical reversal of rotation seems to drastically reduce torsional stress. Furthermore, the reciprocating rotation that is a characteristic of the Reciproc movement may help the instrument in its advance towards the canal terminus, following a mechanical balanced force advance, as reported by De-Deus et al. (2013), while reducing the risk of blockage for the tip of the instrument (Gavini et al. 2012). In fact, the actual reciprocating rotation aims to minimize the risk of fracture of the instrument caused by torsional stress as the angle of rotation in the direction of cutting is designed to be less than the elastic limit of the instrument (Kim et al. 2012).
The very low frequency of R25 instrument fracture reported in the present study, can be possibly understood also as an improvement in cyclic fatigue resistance given by the reciprocation kinematics (Pedullà et al. 2013a, 2013b), the instrument cross-sectional design (Grande et al. 2006, Plotino et al. 2012) and the superelastic M-wire alloy (Johnson et al. 2008). Cross-sectional "S-shape" design may play a further role to provide great cutting ability to this instrument (Bürklein et al. 2012, Plotino et al. in press). Furthermore, the use of only one NiTi
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file in reciprocation to prepare the entire root canal, as provided by the Reciproc technique, may reduce the accumulation of metal fatigue, costs and avoid cross-infection (Shen et al. 2009d, DeDeus et al. 2010).
In the present study, 6 out of the 8 fractured files were removed or by-passed. In these cases, file fracture seems to have no impact from a clinical point of view, as the treatments was completed normally. This is of particular importance in cases with primary infection (Ungerechts et al. 2014). Two R25 files fractured 16 mm from the tip of the instrument during the passive brushing action in the outward lateral movement. For this reason both instruments were outside the orifice, not engaged in the dentine and their retrieval was performed easily (Fig. 2).
As previously reported, the reciprocating technique was the most rapid method to effectively remove gutta-percha and sealer from the root canal space during retreatment (Zuolo et al. 2013). The results of the present study reveal that removal of old filling materials and repreparation of the root canals has been performed with a very low fracture rate using Reciproc R25 instrument in retreatment cases. Deformations occurred more frequently in retreatments than primary treatments (0.2% versus 0.1%), as during removal of filling materials too much pressure may be exerted in some cases.
Conclusions Root canal instrumentation can be performed with Reciproc system used as single instrument in all type of root canals with a very low incidence of instrument fracture and deformation.
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References Alapati SB, Brantley WA, Svec TA, Powers JM, Nusstein JM, Daehn GS (2005) SEM observations of nickel-titanium rotary endodontic instruments that fractured during clinical Use. Journal of Endodontics 31, 40-3. Ankrum MT, Hartwell GR, Truitt JE (2004) K3 Endo, ProTaper and Profile systems: breakage and distortion in severely curved roots of molars. Journal of Endodontics 30, 234-7. Arens FC, Hoen MM, Steiman HR, Dietz GC Jr (2003) Evaluation of single-use rotary nickeltitanium instruments. Journal of Endodontics 29, 664-6. Baumann MA, Roth A (1999) Effect of experience on quality of canal preparation with rotary nickel-titanium files. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 88, 714-8. Bergmans L, Van Cleynenbreugel J, Wevers M, Lambrechts P (2001) Mechanical root canal preparation with NiTi rotary instruments: rationale, performance and safety. Status report for the American Journal of Dentistry. American Journal of Dentistry 14, 324-33. Bürklein S, Hinschitza K, Dammaschke T, Schäfer E (2012) 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, 44961. Cheung GS, Peng B, Bian Z, Shen Y, Darvell BW (2005) Defects in ProTaper S1 instruments after clinical use: fractographic examination. International Endodontic Journal 38, 802-9. Cheung GS, Bian Z, Shen Y, Peng B, Darvell BW (2007) Comparison of defects in ProTaper handoperated and engine-driven instruments after clinical use. International Endodontic Journal 40, 169-78.
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De-Deus G, Moreira E, Lopes H, Elias C (2010) Extended cyclic fatigue life of F2 ProTaper instruments used in reciprocating movement. International Endodontic Journal 43, 1063–8. De-Deus G, Arruda TE, Souza EM, Neves A, Magalhães K, Thuanne E, Fidel RA (2013) The ability of the Reciproc R25 instrument to reach the full root canal working length without a glide path. International Endodontic Journal 46, 993-8. Di Fiore PM, Genov KA, Komaroff E, Li Y, Lin L (2006) Nickel-titanium rotary instrument fracture: a clinical practice assessment. International Endodontic Journal 39, 700-8. Gavini G, Caldeira C, Akisue E, Candeiro G, Kawakami D (2012) Resistance to flexural fatigue of Reciproc R25 files under continuous rotation and reciprocating movement. Journal of Endodontics 38, 684–7. Grande NM, Plotino G, Pecci R, Bedini R, Malagnino VA, Somma F (2006) Cyclic fatigue resistance and three-dimensional analysis of instruments from two nickel-titanium rotary systems. International Endodontic Journal 39, 755-63. Hulsmann M, Herbst U, Schafers F (2003) Comparative study of root-canal preparation using Lightspeed and Quantec SC rotary NiTi instruments. International Endodontic Journal 36, 74856. Inan U, Gonulol N (2009) Deformation and fracture of Mtwo rotary nickel-titanium instruments after clinical use. Journal of Endodontics 35, 1396-9. Johnson E, Lloyd A, Kuttler S, Namerow K (2008) Comparison between a novel nickel-titanium alloy and 508 nitinol on the cyclic fatigue life of ProFile 25/.04 rotary instruments. Journal of Endodontics 34, 1406-9. Kim H, Kwak S, Cheung G, Ko D, Chung S, Lee W (2012) Cyclic fatigue and torsional resistance of two new nickel-titanium instruments used in reciprocation motion: Reciproc versus WaveOne. Journal of Endodontics 38, 541–44.
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Knowles KI, Hammond NB, Biggs SG, Ibarrola JL (2006) Incidence of instrument separation using LightSpeed rotary instruments. Journal of Endodontics 32, 14-6. Malentacca A, Lalli F (2002) Use of nickel-titanium instruments with reciprocating movement. Italian Journal of Endodontics 16, 79-84. Parashos P, Messer HH (2006) Rotary NiTi instrument fracture and its consequences. Journal of Endodontics 32, 1031-43. Parashos P, Gordon I, Messer HH (2004) Factors influencing defects of rotary nickel-titanium endodontic instruments after clinical use. Journal of Endodontics 30, 722-5. Pedullà E, Grande NM, Plotino G, Palermo F, Gambarini G, Rapisarda E (2013a) Cyclic fatigue resistance of two reciprocating nickel-titanium instruments after immersion in sodium hypochlorite. International Endodontic Journal 46, 155-9. Pedullà E, Grande NM, Plotino G, Gambarini G, Rapisarda E (2013b) Influence of continuous or reciprocating motion on cyclic fatigue resistance of 4 different nickel-titanium rotary instruments. Journal of Endodontics 39, 258-61. Peng B, Shen Y, Cheung GSP, Xia TJ (2005) Defects in ProTaper S1 instruments after clinical use: longitudinal examination. International Endodontic Journal 38, 550–7. Peters OA (2004) Current challenges and concepts in the preparation of root canal systems: a review. Journal of Endodontics 30, 559-67. Peters OA, Paque F (2010) Current developments in rotary root canal instrument technology and clinical use: a review. Quintessence International 41, 479-88. Plotino G, Grande NM, Cordaro M, Testarelli L, Gambarini G (2009) A review of cyclic fatigue testing of nickel-titanium rotary instruments. Journal of Endodontics 35, 1469-76.
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Plotino G, Grande NM, Testarelli L, Gambarini G (2012) Cyclic fatigue of Reciproc and WaveOne reciprocating instruments. International Endodontic Journal 45, 614-8. Plotino G, Giansiracusa Rubini A, Grande NM, Testarelli L, Gambarini G (in press) Cutting efficiency of Reciproc and WaveOne reciprocating instruments. Journal of Endodontics. Ramirez-Solomon M, Soler-Bientz R, de la Garza-Gonzalez R, Palacios-Garza CM (1997) Incidence of Lightspeed separation and the potential for bypassing. Journal of Endodontics 23, 586-7. Sattapan B, Nervo GJ, Palamara JE, Messer HH (2000) Defects in rotary nickel-titanium files after clinical use. Journal of Endodontics 26, 161-5. Shen Y, Cheung GS, Bian Z, Peng B (2006) Comparison of defects in ProFile and ProTaper systems after clinical use. Journal of Endodontics 32, 61-5. Shen Y, Haapasalo M, Cheung GS, Peng B (2009a) Defects in nickel-titanium instruments after clinical use. Part 1: Relationship between observed imperfections and factors leading to such defects in a cohort study. Journal of Endodontics 35, 129-32. Shen Y, Cheung GS, Peng B, Haapasalo M (2009b) Defects in nickel-titanium instruments after clinical use. Part 2: Fractographic analysis of fractured surface in a cohort study. Journal of Endodontics 35, 133-6. Shen Y, Coil JM, Haapasalo M (2009c) Defects in nickel-titanium instruments after clinical use. Part 3: a 4-year retrospective study from an undergraduate clinic. Journal of Endodontics 35, 193-6. Shen Y, Coil JM, McLean AG, Hemerling DL, Haapasalo M (2009d) Defects in nickel-titanium instruments after clinical use. Part 5: single use from endodontic specialty practices. Journal of Endodontics 35, 1363-7.
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Tzanetakis GN, Kontakiotis EG, Maurikou DV, Marzelou MP (2008) Prevalence and management of instrument fracture in the postgraduate endodontic program at the Dental School of Athens: a five-year retrospective clinical study. Journal of Endodontics 34, 675–8. Ungerechts C, Bårdsen A, Fristad I (2014) Instrument fracture in root canals - where, why, when and what? A study from a student clinic. International Endodontic Journal 47, 183-90. Varela-Patiño P, Ibañez-Párraga A, Rivas-Mundiña B, Cantatore G, Otero XL, Martin-Biedma B (2010) Alternating versus continuous rotation: a comparative study of the effect on instrument life. Journal of Endodontics 36, 157-9. Wan J, Rasimick BJ, Musikant BL, Deutsch AS (2011) A comparison of cyclic fatigue resistance in reciprocating and rotary nickel-titanium instruments. Australian Endodontic Journal 37, 122-7. Wei X, Ling J, Huang X, Liu L (2007) Modes of failure of ProTaper nickel-titanium rotary instruments after clinical use. Journal of Endodontics 33, 276-9. Wolcott S, Wolcott J, Ishley D, Kennedy W, Johnson S, Minnich S, Meyers J (2006) Separation incidence of ProTaper rotary instruments: a large cohort clinical evaluation. Journal of Endodontics 32, 1139-41. Wu J, Lei G, Yan M, Yu Y, Yu J, Zhang G (2011) Instrument separation analysis of multi-used ProTaper Universal rotary system during root canal therapy. Journal of Endodontics 37, 758-63. Zuolo AS, Mello JE Jr, Cunha RS, Zuolo ML, Bueno CE (2013) Efficacy of reciprocating and rotary techniques for removing filling material during root canal retreatment. International Endodontic Journal 46, 947-53
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Figure legends Figure 1. A) Radiograph of a mandibular second molar with a fragment of fractured instrument; B) Radiograph in which the fragment was partially removed; C) Radiograph with gutta-percha cones after complete removal of the fractured fragment; D) Post-operative radiograph after three-dimensional filling of the root canal and direct restoration with a fiber post in the distal canal; E) Photograph of the access cavity after root canal filling; F) Photograph immediately after the coronal reconstruction; G) 1-year radiographic control; H) 1-year control photograph.
Figure 2. A) Radiograph of a maxillary first molar with a 16mm fragment of fractured instrument in the palatal canal; B) Intra-operative radiograph of the working length after removal of the fractured instrument; C) Photograph of the access cavity with the fractured instrument protruding outside the orifice of the palatal canal; D) Photograph of the fragment after removal using the Instrument Removal System; E) Photograph of the access cavity after removal of the fractured instrument; F) Post-operative radiograph after three-dimensional filling of the root canal system; G) Photograph of the indirect lithium disilicate onlay immediately after cementation; H) 1-year radiographic control.
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Table 1 Number of teeth treated in the present study. Central Incisors
Lateral Incisors
Canines
Premolars
Molars
Maxillary
80
75
53
298
509
Mandibular
18
47
32
142
394
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Table 2 Fracture and deformation rate of rotary instruments reported in previous studies. Fractures Ramirez-Solomon et al. (1997)
3.7%
Baumann et al. (1999)
9.4%
Sattapan et al. (2000)
21%
Deformations
28%
Hulsmann et al. (2003)
6-10%
Parashos et al. (2004)
5%
12%
Ankrum et al. (2004)
1.7-6%
2.4-15.3%
Alapati et al. (2005)
3-23%
7-22%
Peng et al. (2005)
23%
Cheung et al. (2005)
23%
Shen et al. (2006)
7-14%
Wolcott et al. (2006)
2.4%
Di Fiore et al. (2006)
1.9%
Knowles et al. (2006)
1.3%
Cheung et al. (2007)
14%
0.3-5%
Wei et al. (2007)
12.9%
Tzanetakis et al. (2008)
1.8%
Inan et al. (2009)
16%
10%
Shen et al. (2009a, 2009b)
5%
3%
Shen et al. (2009c)
0.3%
1%
Shen et al. (2009d)
0.26%
2.9%
Wu et al. (2011)
2.6%
De-Deus et al. (2013)
0.2%
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