doi:10.1111/iej.12292
Electrochemical-induced dissolution of stainless steel files
C. C. F. Amaral1, F. Ormiga2 & J. A. C. P. Gomes1 1 Department of Metallurgy and Materials, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; and 2Department of Endodontics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
Abstract Amaral CCF, Ormiga F, Gomes JACP. Electrochemicalinduced dissolution of stainless steel files. International Endodontic Journal, 48, 137–144, 2015.
Aim To investigate the effectiveness of the dissolution process when hand stainless steel files are polarized in solutions containing chloride and fluoride to promote their dissolution. Methodology Redox curves and anodic polarization curves were obtained to determine the conditions necessary for the dissolution of stainless steel endodontic files. Anodic polarization of sizes 20 and 30 files was performed, and a t-test (P < 0.05) was used to compare the weight loss, the time of dissolution and the electrical charge generated by both groups of files. Fragments were polarized in simulated root canals to evaluate the dissolution process. After the tests, a size 10 K-file was used to verify the possibility of bypassing the fragment. Radiographic analysis of
Introduction The fracture of endodontic files is of clinical concern for dental practitioners. This form of failure can impair the complete cleaning and shaping of the root canal system and result in failure of the treatment. Several methods have been described for removing fractured instruments from root canals (Masserann 1971, Feldman et al. 1974, Fors & Berg 1983, RoigGreene 1983, Weisman 1983, Krell et al. 1984,
Correspondence: Fabiola Ormiga, Rua Professor. Rodolpho Paulo Rocco 325 / 2° andar, Ilha da Cidade Universitaria, CEP 21941913 Rio de Janeiro, RJ, Brazil (e-mail: [email protected]).
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
the simulated canals was used before and after the tests to verify fragment dissolution. Results A progressive consumption of the sizes 20 and 30 files was observed with total polarization times of 7.0 and 9.0 min, respectively. Files with the larger diameters exhibited greater weight loss, longer times of dissolution and generated a greater electrical charge during the active dissolution process (t-test, P < 0.05). After 60 min, the anodic polarization of file fragments in simulated root canals resulted in their partial dissolution. Conclusion A 60-min anodic polarization of stainless steel K-file fragments in simulated root canals resulted in their partial dissolution. The fragments could be bypassed after the test. Keywords: active dissolution, endodontic instruments, fracture, stainless steel. Received 18 October 2013; accepted 2 April 2014
Nagai et al. 1986, Hulsmann 1993, 1994, Ruddle 1997, Suter 1998, Eleazer & O’Connor 1999, Okiji 2003, Terauchi et al. 2006, Parashos & Rahimi 2009). However, these methods are of varying success, and they may result in weakening and perforation of the root. In this context, it is important to investigate the effectiveness of new methods to remove fractured files from root canals without scarifying dentine. Ormiga et al. (2010) proposed a new method for the removal of metal fragments through active dissolution. The method requires the existence of 2 electrodes immersed in the solution: one acting as a cathode and the other as an anode. Contact between the fractured file and the electrode used as an anode is necessary because the dissolution of the fractured file is the
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objective of the process. An adequate electrochemical potential difference is imposed between the two electrodes, resulting in the migration of the electrons from the anode to the cathode and, consequently, the release of metallic ions into solution. This process corresponds to the progressive dissolution of the fragment inside the root canal. The partial dissolution of fragments of NiTi files embedded in resin in 6 h has been observed (Ormiga et al. 2011). However, this period is not clinically satisfactory, and an increase in the efficiency of the dissolution process is needed. Aboud et al. (2014) demonstrated that the application of a + 0.6 VSCE potential in a solution of [NaF 12 g L 1 + NaCl 1 g L 1] pH 5.0 caused more intense dissolution of the NiTi alloy than a + 0.7 VSCE potential in a solution of [NaF 5 g L 1 + NaCl 1 g L 1], pH 5.0, previously proposed (Ormiga et al. 2010). Aboud et al. (2014) observed the partial dissolution of NiTi file fragments inside simulated root canals after 60 min of anodic polarization, which allowed the recovery of the original path of the canal with a size 10 K-file. This fragment dissolution time is acceptable for clinical practice. With the development of rotary NiTi files, hand stainless steel files have become less commonly used for the shaping of root canals due to their poor shaping ability and the need for more time compared with NiTi files (Camara et al. 2008, Baratto-Filho et al. 2009). Nevertheless, fragments of stainless steel files still must be removed from root canals during nonsurgical root canal retreatment when the primary treatment has been performed using such instruments (Ruddle 2004). In this context, the aim of this study was to investigate the effectiveness of the dissolution process of hand stainless steel files in solutions containing chloride and fluoride to promote dissolution in the root canal during a period clinically acceptable.
Materials and methods Redox curves Redox curves were obtained for [NaF 12 g L 1 + NaCl 175.5 g L 1] solution at pH 5.0. An electrochemical cell was used containing a saturated calomel electrode as the reference, platinum as the counter electrode and another platinum electrode as the working electrode. The electrodes were immersed in the test solution and connected to a digital potentiostat (Metrohm Autolab, Herisau, Switzerland). Anodic and cathodic curves of the solution were obtained using the software GPES,
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version 4.9 (Eco Chemic B.V, Utrecht, The Netherlands), with a scanning speed of 1.6 mV s 1 and potential limits of 2.0 VSCE and +2.0 VSCE from the redox potential of the solution. This procedure was repeated thrice.
Anodic polarization curves Anodic polarization curves were obtained for a stainless steel flat electrode in a [NaF 12 g L 1 + NaCl 175.5 g L 1] solution at pH 5.0. An electrochemical cell containing a saturated calomel electrode was used as a reference, platinum as a counter electrode and a stainless steel flat electrode with an exposed surface equal to 1.0 cm2 as the working electrode (MemoryMetalle GmbH, Weil am Rhein, Germany). The electrodes were immersed in the test solution and connected to a digital potentiostat (Metrohm Autolab). The working electrode was submitted to anodic polarization to a potential of 1.3 VSCE using the software GPES, version 4.9 (Eco Chemic B.V) with a scanning speed of 0.8 mV s 1. This test was carried out thrice with the stainless steel electrode. The electrode surface was polished using 220, 400 and 600 grit (3 M, S~ ao Paulo, Brazil) sandpaper after each test.
Stainless steel file polarization Current register tests were conducted to evaluate the dissolution process of sizes 20 and 30 stainless steel hand K-files (Dentsply Maillefer, Ballaigues, Switzerland). A three-electrode electrochemical cell was used containing a stainless steel file as the working electrode, a saturated calomel electrode as the reference and platinum as the counter electrode. The solution was composed of [NaF12 g L 1 + NaCl 175.5 g L 1] and pH 5.0. The files were isolated using a polymeric coating, and a 6-mm-long section from the tip was exposed to the solution. The electrodes were immersed in 300 mL of the solution and connected to an AutoLab Potentiostat controlled by a computer. A constant anodic potential of +0.5 VSCE was applied to the stainless steel files, whilst the Potentiostat registered the anodic current. Four groups of six files each were tested. Groups 1 and 2 were composed of sizes 20 and 30 K-file, respectively, and were tested more than 30 min. The mean time for complete dissolution of the exposed portion of the file was calculated for each group. Groups 3 and 4 were composed of sizes 20 and 30 K-file, respectively, and were tested for half of mean times calculated in groups 1 and 2. The weight
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Amaral et al. Dissolution of stainless steel files
loss and length loss were measured to quantify the degree of file degradation. The electrical charge generated during the dissolution of each file was obtained from the respective current x time curves. After the tests, the files were observed at 6.59 magnification using an optical microscope.
Intracanal fragment polarization Current register tests were used to evaluate the dissolution process of intracanal fragments according to the methodology described by (Aboud et al. 2014). An electrochemical cell was used containing a saturated calomel electrode as reference, platinum as counter electrode and a platinum wire with diameter equal to 0.1 mm as the working electrode. A support for the platinum wire was made according to the methodology described by Ormiga et al. (2011). The electrodes were immersed in a [NaF 12 g L 1 + NaCl 175.5 g L 1] solution at pH 5.0 and connected to a digital potentiostat (Metrohm Autolab). Flexural fatigue was utilized to obtain 3.0-mm fragments from the tip of sizes 20 and 30 stainless steel K-files (Dentsply Maillefer). Each fragment was positioned in a root canal simulated in a resin block (Dentsply Maillefer) with sufficient pressure to secure it. The files were introduced in the third middle of the simulated root canals following the experimental protocol previously published by Aboud et al. (2014). To validate this approach, the fragments were always inserted on the same position into the simulated root canals prior to the dissolution tests. The resin block models were previously prepared to this position using K3 rotary files (SybronEndo, Glendora, CA, USA) to a .02 taper and diameter corresponding to the fragment to obtain a more centralized and a regular preparation. A hand size 10 K-file (Dentsply Maillefer) was used to verify the canal obstruction by the fragment, where all the intracanal fragments could not be bypassed by size 10 K-file. The working electrode was used in contact with the file fragment. The simulated canal containing the fragment was immersed in the solution, in a manner that the surface of fracture of the fragment contacted the working electrode. An anodic potential of +0.5VSCE was applied to the fragment for 60 min, whilst the potentiostat registered the anodic current generated. The test was completed with ten file fragments of each size. After the tests, a size 10 K-file (Dentsply Maillefer) was used to verify the possibility of bypassing the fragment. The total electrical charge for each test was obtained from the corresponding
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
graph area. Radiographic analysis of the simulated canals was used before and after the tests to verify fragment dissolution.
Statistical analysis Group 1 was compared with group 2 using unpaired t-test (P < 0.05) with regard to weight loss, time of dissolution and the electrical charge generated. Group 1 was also compared with group 3 using the same test with regard to weight loss, length loss and the electrical charge generated. The same analysis was used to compare groups 2 and 4. This test was also used to compare the total electrical charges generated during the polarization of intracanal sizes 20 and 30 K-file fragments.
Results Figure 1a presents the redox curve of the [NaF12 g L 1 + NaCl175.5 g L 1] solution at pH 5.0 and the anodic polarization curve of the stainless steel flat electrode in the same solution. Reproducibility of the results was observed, and the graph shows the curve of the first test under each condition. The redox curves showed the stability of the solution to 0.2 VSCE, but above this potential, the solution was unstable due to oxidation reactions. The anodic polarization curves of the stainless steel flat electrode showed anodic current values close to 0.5 mA/cm2 from the electrode potential up to +0.2 VSCE. An increase in the anodic current was registered at a potential equal to +0.2 VSCE, which showed localized dissolution of the alloy due to the rupture of the protective passivation layer. This polarization behaviour of stainless steel implies that anodic dissolution of the alloy can be achieved using a + 0.5 VSCE potential. Above this range, the electrochemical process corresponds to the desired alloy dissolution and electrolyte oxidation occurring at the same time. This condition should be avoided due to the lower efficiency of the process. The anodic current records obtained during the polarization of the stainless steel files are shown in Fig. 1b. The current attained maximum values of approximately 30 mA and 35 mA during the polarization of sizes 20 and 30 hand K-file, respectively. The results exhibited good reproducibility. The total consumption of the exposed tips of the files required median times of 7.0 (1.13) min and 9 (2.49) min in groups 1 and 2, respectively, whereas the time in
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Figure 2 shows the optical microscope analysis of the files before the tests and after the dissolution of half of the immersed portion and after the total dissolution of the immersed portion. The optical microscope analysis revealed the progressive consumption of the files with increasing polarization time. Current values generated during the polarization of the intracanal fragments are presented in Fig. 3. The total mean electrical charge generated during the polarization of size 30 K-file fragments was 1.14 (0.31) C, which was significantly higher than that of 0.84 (0.20) C generated during the polarization of size 20 K-file fragments (t-test, P < 0.05). The radiographic images obtained before and after the polarization tests revealed a significant reduction in the fragment length due to polarization (Fig. 4). After the tests, all the intracanal fragments could be bypassed using a size 10 K-file (Fig. 4c,f).
(a)
(b)
Discussion
+ NaCl 175.5 g L ] pH 5.0 and Anodic Polarization Curve of the stainless steel flat electrode on the same solution. (b) Current registered during the application of + 0.5VSCE constant potential to sizes 20 and 30 stainless steel K- files in the same solution. Figure 1 (a) Redox curve of solution [NaF 12 g L
1
1
group 2 was significantly longer than in group 1 (P < 0.05). The weight loss values, the length loss and the electrical charge generated during the tests are summarized in Table 1. These results revealed the progressive consumption of the files with increasing polarization time. The larger the file diameter, the greater the weight loss and the electrical charge generated during the active dissolution process and the longer the time required for dissolution (P < 0.05). The weight loss, the length loss and the electrical charge were significantly higher at the time of total dissolution than for the half time of dissolution for all types of files (P < 0.05, Table 1).
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The removal of fractured files from root canals is difficult and occasionally impracticable, which impairs the cleaning and shaping of root canal systems. In this context, it is important to investigate the effectiveness of new methods to remove fractured files from the root canal without scarifying dentine. The present study evaluated the active dissolution process of stainless steel hand K-file to enable the application of the method developed by Ormiga et al. (2011) and improved by Aboud et al. (2014) in simulated root canals. The selection of the [NaF 12 g L 1 + NaCl 175.5 g L 1] pH 5.0 solution was based on the studies of Ormiga et al. (2010) and Aboud et al. (2014), who utilized [NaF 5 g L 1 + NaCl 1 g L 1] and [NaF 12 g L 1 + NaCl 1 g L 1] solutions, respectively. A higher chloride concentration was used to increase the intensity of stainless steel dissolution. The fluoride solution concentration was selected based on the studies of Aboud et al. (2014) and Saunders & McIntyre (2005), which used a 12.3 g L 1 fluoride solution. This concentration is acceptable for dental practitioners, because it does not alter the properties of dentine. The pH of 5.0 was chosen based on the studies of Marshall et al. (1997), Ormiga et al. (2010) and Aboud et al. (2014) because this pH has less chance of altering the dentinal structure of the root canal walls. Lower pH values are known to encourage tissue decalcification (Marshall et al. 1997).
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Amaral et al. Dissolution of stainless steel files
Table 1 Time of dissolution, weight loss, length loss and electrical charge generated during the dissolution process
Time (min)
Weight loss (mg)
Length loss (mm)
Electrical charge (C)
Group
File
Mean
SD
Mean
SD
Mean
SD
Mean
SD
1 2 3 4
20 30 20 30
7.0 9.0 3.5 4.5
1.13 2.49 – –
2.23 4.87 1.23 2.47
0.72 0.35 0.15 0.68
6 6 2 0
0 0 0 0
9.01 17.40 5.39 9.48
2.20 3.12 0.50 3.14
The dissolution times observed by Ormiga et al. (2010) and Aboud et al. (2014) were 53 and 30 min, respectively, which are longer than those observed in the present study. This discrepancy is likely related to the different alloy, such as NiTi, and the different file dimensions used. After calculating the mean polarization periods of 7.0 and 9.0 min for the sizes 20 and 30 K-file, respectively, the half intervals were considered for a detailed study of the progressive dissolution. Therefore, size 20 K-files were tested at intervals of 3.5 min and the size 30 K-file to a period of 4.5 in groups 3 and 4, respectively. These intervals were also based on the studies of Ormiga et al. (2010) and Aboud et al. (2014), and the total times were divided into four subintervals. In the present study, the electrical current values generated during the dissolution of the files were lower than those generated during the polarization of the flat electrode. These values are related to the smaller surface area exposed to the solution. However, the complex geometry of the files makes it difficult to estimate their area, and consequently, to calculate the current density. The results presented here showed significant differences between the two groups of files in relation to the weight loss, the time of dissolution and the electrical charge generated. The
The results presented herein are in agreement with previous studies demonstrating that chloride and fluoride act negatively on stainless steel and NiTi alloys to favour corrosion (Lopes 1994, Kim & Johnson 1999, Rondelli & Vicentini 1999, Menezes et al. 2006, Li et al. 2007, Barbosa et al. 2007, Kao & Huang 2010, Kondo & Nakasaga 2010, Lee et al. 2010, Masahiro 2010, Ormiga et al. 2010, Sun et al. 2011, Aboud et al. 2014). Based on the redox and the anodic polarization curves, a potential of +0.5 VSCE was selected for subsequent testing of the constant polarization of the files. At this potential, the dissolution of the material was observed with minimal solution instability. The study was based on those of Ormiga et al. (2010) and Aboud et al. (2014) in which similar polarization tests were performed to evaluate the weight loss of NiTi files. The initial programme to perform the anodic polarization tests determined duration of 30 min. However, the 6-mm files the tips that were immersed in the solution were completely dissolved before the established time. Thus, the experiments with sizes 20 and 30 K-file had a mean durations of 7.0 and 9.0 min, respectively. These results indicated that the active dissolution time is proportional to the file diameter, and larger file diameter requires more time for consumption.
(a)
(b)
Figure 2 Optical microscope analysis of stainless steel files aligned from the handle (6.59). (a1 - a3) Size 20 K-files as received,
submitted to constant potential of 3.5 min and 7 min, respectively. (b1 - b3) Size 30 K-files as received, submitted to constant potential of 4.5 min and 9 min, respectively.
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
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(a)
(b)
Figure 3 Current values registered during the polarization of intracanal file fragments. (a) Size 20 K-file fragment; (b) Size 30 K-file fragment.
larger the diameter of the files, the greater the weight loss, the time of dissolution and the electrical charge generated during the active dissolution. The most relevant aspect of these results is the longer time of total dissolution required by the files with greater diameter. This time varies according to the relation between the surface area and the bulk material to be dissolved, both depend on the diameter of the files but in different proportions. Once these files have greater mass and the same length immersed, it was expected that it would present greater weight loss and electrical charge after the total consumption. However, these values were important to establish the ratio between the weight loss and the electrical charge for each size
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of file. The weight loss and the electrical charge generated during the total dissolution time were significantly higher than those generated during the half time of dissolution for all groups of files tested with the 6 mm of the tip exposed to the solution. Simulated root canals on resin blocks were used to test polarization of intracanal fragments because this material has electrochemical properties similar to those of dentine and promotes electrical insulation (Nekoofar et al. 2006, Aboud et al. 2014). The resin blocks containing simulated root canals are transparent and allow visualization of the contact between the anode and the fragment, which enables an adequate comparison with extracted teeth. Consequently, the polarization conditions can be tested until the ideal conditions for dissolving fragments in the root canals of extracted teeth are established (Aboud et al. 2014). A limitation using extracted teeth is the necessity of a device that matches both electrodes in one tip. This tip must contact the fragment and guarantee contact between the fragment and the solution. Therefore, the teeth need not be immersed in the solution because both electrodes and the solution can be inserted into the root canal and the pulp chamber. Such conditions will closely approximate clinical conditions. The results presented here showed that 60 min was insufficient to attain the total dissolution of the 3.0-mm file fragment. This period of time is significantly longer than that used to dissolve 6.0 mm from the tip of the immersed files. Considering that the dissolution is directly related to the mass dissolved, a 3.0-mm file fragment would require less dissolution time than a 6.0-mm section from the tip of the immersed files (Aboud et al. 2014). This discrepancy can be related to the smaller surface area exposed to the solution during the polarization of intracanal fragments compared with that of the immersed files (Ormiga et al. 2011). It can be confirmed by the lower current values registered during the polarization of the intracanal fragments compared with the files immersed outside simulated canal, despite the same anodic polarization conditions imposed. The total mean electrical charges generated during the polarization of sizes 20 and 30 K-file fragments were 0.84 (0.20) C and 1.14 (0.31) C, respectively. The weight losses of the fragments are too low to be precisely measured using a precision balance. Aboud et al. (2014) calculated the theoretical values of mass loss of NiTi files fragments applying the
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Amaral et al. Dissolution of stainless steel files
(a)
(b)
(c)
(d)
(e)
(f)
Figure 4 Radiographic analysis of an intracanal file fragments. (a–c) Size 20 K-file fragment; (d–f) Size 30 K-file fragment. (a, d) Radiographies obtained before the test; (b, e) Radiographies obtained after polarization at 0.5 VSCE during 60 min; (c, f) Radiographies obtained after the polarization showing the fragment bypassed by a size 10 K-file.
Faraday’s law of electrolysis, considering the equivalent dissolution of Ni and Ti. According to this law, m = e.i.t, where m is the mass of the substance liberated at an electrode in grams, e is the electro electronic equivalent, i is the electrical current intensity in amperes, and t is the total time in seconds. However, this law could not be applied here because the rate of dissolution of the different metals of the stainless steel alloy is not known. Consequently, the use of this law would generate imprecise values of weight loss. Another way to estimate the weight loss of the file fragments inside simulated root canals is to use the ratio between the weight loss and the electrical charge obtained in the tests with immersed files. According to this ratio, the mean weight losses of sizes 20 and 30 K-file fragments were 0.21 mg and 0.32 mg, respectively. In the present study, stainless steel files with two different diameters were selected for the polarization tests because the file fragments of varying diameters are found in root canals during clinical practice. According to Ormiga et al. (2011), the diameter of the fragment surface exposed to the medium affects the currents used to promote dissolution; an exposed surface with a larger diameter cross-section has a higher total electrical charge. The results presented herein are in agreement with this statement because the electrical charges generated during the polarization of size 30 K-file fragments where significantly higher than those generated during the polarization of size 20 K-file fragments. In both groups, the partial dissolution of a file fragment enabled the recovering of the original canal pathway with a size 10 K-file after each 60 min; thus, 60 min can be considered a
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
clinically acceptable period of time (Aboud et al. 2014).
Conclusion It was possible to obtain a significant dissolution of stainless steel K-file using the method proposed by Ormiga et al. (2010). The anodic polarization of stainless steel K-file fragments in simulated root canals more than 60 min resulted in their partial dissolution. The fragments could be bypassed after the test.
Acknowledgements The authors deny any conflict of interests and would like to acknowledge the support of COPPE-TEC Foundation and CNPq.
References Aboud LR, Ormiga F, Gomes JACP (2014) Electrochemical induced dissolution of fragments of a nickel–titanium endodontic files and their removal from simulated root canals. International Endodontic Journal 47, 155–62. Baratto-Filho F, Leonardi DP, Zielak JC, Vanni JR, SayaoMaia SM, Sousa-Neto MD (2009) Influence of ProTaper finishing files and sodium hypochlorite on cleaning and shaping of mandibuldar central incisors-a histological analysis. Journal of Applied Oral Science 17, 229–33. Barbosa FOG, Gomes JACP, Ara ujo MCP (2007) Influence of sodium hypochlorite on mechanical properties of K3 nickel-titanium rotary instruments. Journal of Endodontics 33, 982–5. Camara AC, Aguiar CM, de Figueiredo JA (2008) Evaluation of the root dentine cutting effectiveness of the HERO 642,
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143
Dissolution of stainless steel files Amaral et al.
HERO Apical and HERO Shaper rotary systems. Australian Endodontic Journal 34, 94–100. Eleazer PD, O’Connor RP (1999) Innovative uses for hypodermic needles in endodontics. Journal of Endodontics 25, 190–1. Feldman G, Solomon C, Notaro P, Moskowitz E (1974) Retrieving broken endodontic instruments. Journal American Dental Association 88, 588–91. Fors UG, Berg JO (1983) A method for the removal of broken endodontic instruments from root canals. Journal of Endodontics 9, 156–9. Hulsmann M (1993) Methods for removing metal obstructions from the root canal. Endodontics Dental Traumatology 9, 223–37. Hulsmann M (1994) Removal of fractured instruments using a combined automated/ultrasonic technique. Journal of Endodontics 20, 144–7. Kao C, Huang T (2010) Variations in surface characteristics and corrosion behaviour of metal brackets and wires in different electrolyte solutions. The European Journal of Orthodontic 1, 142. Kim H, Johnson J (1999) Corrosion of stainless steel, nickeltitanium, coated nickel-titanium, and titanium orthodontic wires. Angle Orthodontic 69, 39–44. Kondo M, Nakasaga T (2010) Corrosion of reduced activation ferritic martensitic steel JLF-1 in purified Flinak at static and flowing conditions. Fusion Engineering and Design 85, 1430–6. Krell K, Fuller M, Scott G (1984) The conservative retrieval of silver cones in difficult cases. Journal of Endodontics 10, 269–73. Lee TH, Huang TK, Lin SY, Chen LK, Chou MY, Huang HH (2010) Corrosion resistance of different nickel-titanium archwires in acidic fluoride-containing artificial saliva. Angle Orthodontic 80, 547–53. Li X, Wang J, Han EH, Ke W (2007) Influence of fluoride and chloride on corrosion behavior of NiTi orthodontic wires. Acta Biomaterialia 3, 807–15. Lopes HP (1994) Corros€ao em limas endod^ onticas de acßo inoxid avel. Revista Brasileira de Odontologia 51, 26–8. Marshall GW Jr, Inai N, Wu-Magidi IC et al. (1997) Dentin demineralization: effects of dentin depth, pH and different acids. Dental Materials 13, 338–43. Masahiro I (2010) Corros~ao de ions de NiTi implantados em orio bucal com fios ortod^onticos em solucß~oes de enxaguat fluoreto. Jornal Materiais Dentarios 29, 53–8. Masserann J (1971) Translation of Entfernen metallischer fragment aus wurzelkan€alen, by Jean Masserann, which describes a technique for the removal of metallic fragments which remain lodged in root canals. Journal of the British Endodontic Society 5, 55–9.
144
International Endodontic Journal, 48, 137–144, 2015
Menezes LM, Lima EMS, Rizzatto SMD (2006) Evaluation of titanium brackets surface after immersion in sodium fluoride. Revista Dental Press de Ortodontia e Ortopedia Facial 11, 93–103. Nagai O, Tani N, Kayaba Y, Kodama S, Osada T (1986) Ultrasonic removal of broken instruments in root canals. International Endodontic Journal 19, 298–304. Nekoofar MH, Ghandi MM, Hayes SJ, Dummer PM (2006) The fundamental operating principles of electronic root canal length measurement devices. International Endodontic Journal 39, 595–609. Okiji T (2003) Modified usage of the Masserann kit for removing intracanal broken instruments. Journal of Endodontics 29, 466–7. Ormiga F, Gomes JACP, Ara ujo MCP (2010) Dissolution of nickel-titanium endodontic files via an electrochemical process: a new concept for future retrieval of fractured files in root canals. Journal of Endodontics 36, 717–20. Ormiga F, Gomes JACP, Ara ujo MCP, Barbosa AOG (2011) An initial investigation of the electrochemical dissolution of fragments of nickel-titanium endodontic files. Journal of Endodontics 37, 526–30. Parashos P, Rahimi M (2009) A novel technique for the removal of fractured instruments in the apical third of curved root canals. International Endodontic Journal 42, 264–70. Roig-Greene J (1983) The retrieval of foreign objects from root canals: a simple aid. Journal of Endodontics 9, 394–7. Rondelli G, Vicentini B (1999) Localized corrosion behaviour in simulated human body fluids of commercial Ni-Ti orthodontic wires. Biomaterials 20, 785–92. Ruddle CJ (1997) Micro-endodontic nonsurgical retreatment. Dental Clinics of North America 41, 429–54. Ruddle CJ (2004) Nonsurgical retreatment. Journal of Endodontics 30, 827–45. Saunders JG, McIntyre JM (2005) The ability of 1.23% acidulated phosphate fluoride gel to inhibit simulated endogenous erosion in tooth roots. Australian Dental Journal 50, 263–6. Sun XT, Kang ZX, Jiang HJ, Guan RF, Zhang XP (2011) A comparative study on the corrosion behavior of porous and dense NiTi shape memory alloys in NaCl solution. Electrochimica Acta 56, 6389–96. Suter B (1998) A new method for retrieving silver points and separated instruments from root canals. Journal of Endodontics 24, 446–8. Terauchi Y, O’Leary L, Suda H (2006) Removal of separated files from root canals with a new file-removal system: Case reports. Journal of Endodontics 32, 789–97. Weisman MI (1983) The removal of difficult silver cones. Journal of Endodontics 9, 210–1.
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Electrochemical-induced dissolution of stainless steel files
C. C. F. Amaral1, F. Ormiga2 & J. A. C. P. Gomes1 1 Department of Metallurgy and Materials, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; and 2Department of Endodontics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
Abstract Amaral CCF, Ormiga F, Gomes JACP. Electrochemicalinduced dissolution of stainless steel files. International Endodontic Journal, 48, 137–144, 2015.
Aim To investigate the effectiveness of the dissolution process when hand stainless steel files are polarized in solutions containing chloride and fluoride to promote their dissolution. Methodology Redox curves and anodic polarization curves were obtained to determine the conditions necessary for the dissolution of stainless steel endodontic files. Anodic polarization of sizes 20 and 30 files was performed, and a t-test (P < 0.05) was used to compare the weight loss, the time of dissolution and the electrical charge generated by both groups of files. Fragments were polarized in simulated root canals to evaluate the dissolution process. After the tests, a size 10 K-file was used to verify the possibility of bypassing the fragment. Radiographic analysis of
Introduction The fracture of endodontic files is of clinical concern for dental practitioners. This form of failure can impair the complete cleaning and shaping of the root canal system and result in failure of the treatment. Several methods have been described for removing fractured instruments from root canals (Masserann 1971, Feldman et al. 1974, Fors & Berg 1983, RoigGreene 1983, Weisman 1983, Krell et al. 1984,
Correspondence: Fabiola Ormiga, Rua Professor. Rodolpho Paulo Rocco 325 / 2° andar, Ilha da Cidade Universitaria, CEP 21941913 Rio de Janeiro, RJ, Brazil (e-mail: [email protected]).
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
the simulated canals was used before and after the tests to verify fragment dissolution. Results A progressive consumption of the sizes 20 and 30 files was observed with total polarization times of 7.0 and 9.0 min, respectively. Files with the larger diameters exhibited greater weight loss, longer times of dissolution and generated a greater electrical charge during the active dissolution process (t-test, P < 0.05). After 60 min, the anodic polarization of file fragments in simulated root canals resulted in their partial dissolution. Conclusion A 60-min anodic polarization of stainless steel K-file fragments in simulated root canals resulted in their partial dissolution. The fragments could be bypassed after the test. Keywords: active dissolution, endodontic instruments, fracture, stainless steel. Received 18 October 2013; accepted 2 April 2014
Nagai et al. 1986, Hulsmann 1993, 1994, Ruddle 1997, Suter 1998, Eleazer & O’Connor 1999, Okiji 2003, Terauchi et al. 2006, Parashos & Rahimi 2009). However, these methods are of varying success, and they may result in weakening and perforation of the root. In this context, it is important to investigate the effectiveness of new methods to remove fractured files from root canals without scarifying dentine. Ormiga et al. (2010) proposed a new method for the removal of metal fragments through active dissolution. The method requires the existence of 2 electrodes immersed in the solution: one acting as a cathode and the other as an anode. Contact between the fractured file and the electrode used as an anode is necessary because the dissolution of the fractured file is the
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objective of the process. An adequate electrochemical potential difference is imposed between the two electrodes, resulting in the migration of the electrons from the anode to the cathode and, consequently, the release of metallic ions into solution. This process corresponds to the progressive dissolution of the fragment inside the root canal. The partial dissolution of fragments of NiTi files embedded in resin in 6 h has been observed (Ormiga et al. 2011). However, this period is not clinically satisfactory, and an increase in the efficiency of the dissolution process is needed. Aboud et al. (2014) demonstrated that the application of a + 0.6 VSCE potential in a solution of [NaF 12 g L 1 + NaCl 1 g L 1] pH 5.0 caused more intense dissolution of the NiTi alloy than a + 0.7 VSCE potential in a solution of [NaF 5 g L 1 + NaCl 1 g L 1], pH 5.0, previously proposed (Ormiga et al. 2010). Aboud et al. (2014) observed the partial dissolution of NiTi file fragments inside simulated root canals after 60 min of anodic polarization, which allowed the recovery of the original path of the canal with a size 10 K-file. This fragment dissolution time is acceptable for clinical practice. With the development of rotary NiTi files, hand stainless steel files have become less commonly used for the shaping of root canals due to their poor shaping ability and the need for more time compared with NiTi files (Camara et al. 2008, Baratto-Filho et al. 2009). Nevertheless, fragments of stainless steel files still must be removed from root canals during nonsurgical root canal retreatment when the primary treatment has been performed using such instruments (Ruddle 2004). In this context, the aim of this study was to investigate the effectiveness of the dissolution process of hand stainless steel files in solutions containing chloride and fluoride to promote dissolution in the root canal during a period clinically acceptable.
Materials and methods Redox curves Redox curves were obtained for [NaF 12 g L 1 + NaCl 175.5 g L 1] solution at pH 5.0. An electrochemical cell was used containing a saturated calomel electrode as the reference, platinum as the counter electrode and another platinum electrode as the working electrode. The electrodes were immersed in the test solution and connected to a digital potentiostat (Metrohm Autolab, Herisau, Switzerland). Anodic and cathodic curves of the solution were obtained using the software GPES,
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version 4.9 (Eco Chemic B.V, Utrecht, The Netherlands), with a scanning speed of 1.6 mV s 1 and potential limits of 2.0 VSCE and +2.0 VSCE from the redox potential of the solution. This procedure was repeated thrice.
Anodic polarization curves Anodic polarization curves were obtained for a stainless steel flat electrode in a [NaF 12 g L 1 + NaCl 175.5 g L 1] solution at pH 5.0. An electrochemical cell containing a saturated calomel electrode was used as a reference, platinum as a counter electrode and a stainless steel flat electrode with an exposed surface equal to 1.0 cm2 as the working electrode (MemoryMetalle GmbH, Weil am Rhein, Germany). The electrodes were immersed in the test solution and connected to a digital potentiostat (Metrohm Autolab). The working electrode was submitted to anodic polarization to a potential of 1.3 VSCE using the software GPES, version 4.9 (Eco Chemic B.V) with a scanning speed of 0.8 mV s 1. This test was carried out thrice with the stainless steel electrode. The electrode surface was polished using 220, 400 and 600 grit (3 M, S~ ao Paulo, Brazil) sandpaper after each test.
Stainless steel file polarization Current register tests were conducted to evaluate the dissolution process of sizes 20 and 30 stainless steel hand K-files (Dentsply Maillefer, Ballaigues, Switzerland). A three-electrode electrochemical cell was used containing a stainless steel file as the working electrode, a saturated calomel electrode as the reference and platinum as the counter electrode. The solution was composed of [NaF12 g L 1 + NaCl 175.5 g L 1] and pH 5.0. The files were isolated using a polymeric coating, and a 6-mm-long section from the tip was exposed to the solution. The electrodes were immersed in 300 mL of the solution and connected to an AutoLab Potentiostat controlled by a computer. A constant anodic potential of +0.5 VSCE was applied to the stainless steel files, whilst the Potentiostat registered the anodic current. Four groups of six files each were tested. Groups 1 and 2 were composed of sizes 20 and 30 K-file, respectively, and were tested more than 30 min. The mean time for complete dissolution of the exposed portion of the file was calculated for each group. Groups 3 and 4 were composed of sizes 20 and 30 K-file, respectively, and were tested for half of mean times calculated in groups 1 and 2. The weight
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Amaral et al. Dissolution of stainless steel files
loss and length loss were measured to quantify the degree of file degradation. The electrical charge generated during the dissolution of each file was obtained from the respective current x time curves. After the tests, the files were observed at 6.59 magnification using an optical microscope.
Intracanal fragment polarization Current register tests were used to evaluate the dissolution process of intracanal fragments according to the methodology described by (Aboud et al. 2014). An electrochemical cell was used containing a saturated calomel electrode as reference, platinum as counter electrode and a platinum wire with diameter equal to 0.1 mm as the working electrode. A support for the platinum wire was made according to the methodology described by Ormiga et al. (2011). The electrodes were immersed in a [NaF 12 g L 1 + NaCl 175.5 g L 1] solution at pH 5.0 and connected to a digital potentiostat (Metrohm Autolab). Flexural fatigue was utilized to obtain 3.0-mm fragments from the tip of sizes 20 and 30 stainless steel K-files (Dentsply Maillefer). Each fragment was positioned in a root canal simulated in a resin block (Dentsply Maillefer) with sufficient pressure to secure it. The files were introduced in the third middle of the simulated root canals following the experimental protocol previously published by Aboud et al. (2014). To validate this approach, the fragments were always inserted on the same position into the simulated root canals prior to the dissolution tests. The resin block models were previously prepared to this position using K3 rotary files (SybronEndo, Glendora, CA, USA) to a .02 taper and diameter corresponding to the fragment to obtain a more centralized and a regular preparation. A hand size 10 K-file (Dentsply Maillefer) was used to verify the canal obstruction by the fragment, where all the intracanal fragments could not be bypassed by size 10 K-file. The working electrode was used in contact with the file fragment. The simulated canal containing the fragment was immersed in the solution, in a manner that the surface of fracture of the fragment contacted the working electrode. An anodic potential of +0.5VSCE was applied to the fragment for 60 min, whilst the potentiostat registered the anodic current generated. The test was completed with ten file fragments of each size. After the tests, a size 10 K-file (Dentsply Maillefer) was used to verify the possibility of bypassing the fragment. The total electrical charge for each test was obtained from the corresponding
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
graph area. Radiographic analysis of the simulated canals was used before and after the tests to verify fragment dissolution.
Statistical analysis Group 1 was compared with group 2 using unpaired t-test (P < 0.05) with regard to weight loss, time of dissolution and the electrical charge generated. Group 1 was also compared with group 3 using the same test with regard to weight loss, length loss and the electrical charge generated. The same analysis was used to compare groups 2 and 4. This test was also used to compare the total electrical charges generated during the polarization of intracanal sizes 20 and 30 K-file fragments.
Results Figure 1a presents the redox curve of the [NaF12 g L 1 + NaCl175.5 g L 1] solution at pH 5.0 and the anodic polarization curve of the stainless steel flat electrode in the same solution. Reproducibility of the results was observed, and the graph shows the curve of the first test under each condition. The redox curves showed the stability of the solution to 0.2 VSCE, but above this potential, the solution was unstable due to oxidation reactions. The anodic polarization curves of the stainless steel flat electrode showed anodic current values close to 0.5 mA/cm2 from the electrode potential up to +0.2 VSCE. An increase in the anodic current was registered at a potential equal to +0.2 VSCE, which showed localized dissolution of the alloy due to the rupture of the protective passivation layer. This polarization behaviour of stainless steel implies that anodic dissolution of the alloy can be achieved using a + 0.5 VSCE potential. Above this range, the electrochemical process corresponds to the desired alloy dissolution and electrolyte oxidation occurring at the same time. This condition should be avoided due to the lower efficiency of the process. The anodic current records obtained during the polarization of the stainless steel files are shown in Fig. 1b. The current attained maximum values of approximately 30 mA and 35 mA during the polarization of sizes 20 and 30 hand K-file, respectively. The results exhibited good reproducibility. The total consumption of the exposed tips of the files required median times of 7.0 (1.13) min and 9 (2.49) min in groups 1 and 2, respectively, whereas the time in
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Figure 2 shows the optical microscope analysis of the files before the tests and after the dissolution of half of the immersed portion and after the total dissolution of the immersed portion. The optical microscope analysis revealed the progressive consumption of the files with increasing polarization time. Current values generated during the polarization of the intracanal fragments are presented in Fig. 3. The total mean electrical charge generated during the polarization of size 30 K-file fragments was 1.14 (0.31) C, which was significantly higher than that of 0.84 (0.20) C generated during the polarization of size 20 K-file fragments (t-test, P < 0.05). The radiographic images obtained before and after the polarization tests revealed a significant reduction in the fragment length due to polarization (Fig. 4). After the tests, all the intracanal fragments could be bypassed using a size 10 K-file (Fig. 4c,f).
(a)
(b)
Discussion
+ NaCl 175.5 g L ] pH 5.0 and Anodic Polarization Curve of the stainless steel flat electrode on the same solution. (b) Current registered during the application of + 0.5VSCE constant potential to sizes 20 and 30 stainless steel K- files in the same solution. Figure 1 (a) Redox curve of solution [NaF 12 g L
1
1
group 2 was significantly longer than in group 1 (P < 0.05). The weight loss values, the length loss and the electrical charge generated during the tests are summarized in Table 1. These results revealed the progressive consumption of the files with increasing polarization time. The larger the file diameter, the greater the weight loss and the electrical charge generated during the active dissolution process and the longer the time required for dissolution (P < 0.05). The weight loss, the length loss and the electrical charge were significantly higher at the time of total dissolution than for the half time of dissolution for all types of files (P < 0.05, Table 1).
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The removal of fractured files from root canals is difficult and occasionally impracticable, which impairs the cleaning and shaping of root canal systems. In this context, it is important to investigate the effectiveness of new methods to remove fractured files from the root canal without scarifying dentine. The present study evaluated the active dissolution process of stainless steel hand K-file to enable the application of the method developed by Ormiga et al. (2011) and improved by Aboud et al. (2014) in simulated root canals. The selection of the [NaF 12 g L 1 + NaCl 175.5 g L 1] pH 5.0 solution was based on the studies of Ormiga et al. (2010) and Aboud et al. (2014), who utilized [NaF 5 g L 1 + NaCl 1 g L 1] and [NaF 12 g L 1 + NaCl 1 g L 1] solutions, respectively. A higher chloride concentration was used to increase the intensity of stainless steel dissolution. The fluoride solution concentration was selected based on the studies of Aboud et al. (2014) and Saunders & McIntyre (2005), which used a 12.3 g L 1 fluoride solution. This concentration is acceptable for dental practitioners, because it does not alter the properties of dentine. The pH of 5.0 was chosen based on the studies of Marshall et al. (1997), Ormiga et al. (2010) and Aboud et al. (2014) because this pH has less chance of altering the dentinal structure of the root canal walls. Lower pH values are known to encourage tissue decalcification (Marshall et al. 1997).
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Amaral et al. Dissolution of stainless steel files
Table 1 Time of dissolution, weight loss, length loss and electrical charge generated during the dissolution process
Time (min)
Weight loss (mg)
Length loss (mm)
Electrical charge (C)
Group
File
Mean
SD
Mean
SD
Mean
SD
Mean
SD
1 2 3 4
20 30 20 30
7.0 9.0 3.5 4.5
1.13 2.49 – –
2.23 4.87 1.23 2.47
0.72 0.35 0.15 0.68
6 6 2 0
0 0 0 0
9.01 17.40 5.39 9.48
2.20 3.12 0.50 3.14
The dissolution times observed by Ormiga et al. (2010) and Aboud et al. (2014) were 53 and 30 min, respectively, which are longer than those observed in the present study. This discrepancy is likely related to the different alloy, such as NiTi, and the different file dimensions used. After calculating the mean polarization periods of 7.0 and 9.0 min for the sizes 20 and 30 K-file, respectively, the half intervals were considered for a detailed study of the progressive dissolution. Therefore, size 20 K-files were tested at intervals of 3.5 min and the size 30 K-file to a period of 4.5 in groups 3 and 4, respectively. These intervals were also based on the studies of Ormiga et al. (2010) and Aboud et al. (2014), and the total times were divided into four subintervals. In the present study, the electrical current values generated during the dissolution of the files were lower than those generated during the polarization of the flat electrode. These values are related to the smaller surface area exposed to the solution. However, the complex geometry of the files makes it difficult to estimate their area, and consequently, to calculate the current density. The results presented here showed significant differences between the two groups of files in relation to the weight loss, the time of dissolution and the electrical charge generated. The
The results presented herein are in agreement with previous studies demonstrating that chloride and fluoride act negatively on stainless steel and NiTi alloys to favour corrosion (Lopes 1994, Kim & Johnson 1999, Rondelli & Vicentini 1999, Menezes et al. 2006, Li et al. 2007, Barbosa et al. 2007, Kao & Huang 2010, Kondo & Nakasaga 2010, Lee et al. 2010, Masahiro 2010, Ormiga et al. 2010, Sun et al. 2011, Aboud et al. 2014). Based on the redox and the anodic polarization curves, a potential of +0.5 VSCE was selected for subsequent testing of the constant polarization of the files. At this potential, the dissolution of the material was observed with minimal solution instability. The study was based on those of Ormiga et al. (2010) and Aboud et al. (2014) in which similar polarization tests were performed to evaluate the weight loss of NiTi files. The initial programme to perform the anodic polarization tests determined duration of 30 min. However, the 6-mm files the tips that were immersed in the solution were completely dissolved before the established time. Thus, the experiments with sizes 20 and 30 K-file had a mean durations of 7.0 and 9.0 min, respectively. These results indicated that the active dissolution time is proportional to the file diameter, and larger file diameter requires more time for consumption.
(a)
(b)
Figure 2 Optical microscope analysis of stainless steel files aligned from the handle (6.59). (a1 - a3) Size 20 K-files as received,
submitted to constant potential of 3.5 min and 7 min, respectively. (b1 - b3) Size 30 K-files as received, submitted to constant potential of 4.5 min and 9 min, respectively.
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(a)
(b)
Figure 3 Current values registered during the polarization of intracanal file fragments. (a) Size 20 K-file fragment; (b) Size 30 K-file fragment.
larger the diameter of the files, the greater the weight loss, the time of dissolution and the electrical charge generated during the active dissolution. The most relevant aspect of these results is the longer time of total dissolution required by the files with greater diameter. This time varies according to the relation between the surface area and the bulk material to be dissolved, both depend on the diameter of the files but in different proportions. Once these files have greater mass and the same length immersed, it was expected that it would present greater weight loss and electrical charge after the total consumption. However, these values were important to establish the ratio between the weight loss and the electrical charge for each size
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of file. The weight loss and the electrical charge generated during the total dissolution time were significantly higher than those generated during the half time of dissolution for all groups of files tested with the 6 mm of the tip exposed to the solution. Simulated root canals on resin blocks were used to test polarization of intracanal fragments because this material has electrochemical properties similar to those of dentine and promotes electrical insulation (Nekoofar et al. 2006, Aboud et al. 2014). The resin blocks containing simulated root canals are transparent and allow visualization of the contact between the anode and the fragment, which enables an adequate comparison with extracted teeth. Consequently, the polarization conditions can be tested until the ideal conditions for dissolving fragments in the root canals of extracted teeth are established (Aboud et al. 2014). A limitation using extracted teeth is the necessity of a device that matches both electrodes in one tip. This tip must contact the fragment and guarantee contact between the fragment and the solution. Therefore, the teeth need not be immersed in the solution because both electrodes and the solution can be inserted into the root canal and the pulp chamber. Such conditions will closely approximate clinical conditions. The results presented here showed that 60 min was insufficient to attain the total dissolution of the 3.0-mm file fragment. This period of time is significantly longer than that used to dissolve 6.0 mm from the tip of the immersed files. Considering that the dissolution is directly related to the mass dissolved, a 3.0-mm file fragment would require less dissolution time than a 6.0-mm section from the tip of the immersed files (Aboud et al. 2014). This discrepancy can be related to the smaller surface area exposed to the solution during the polarization of intracanal fragments compared with that of the immersed files (Ormiga et al. 2011). It can be confirmed by the lower current values registered during the polarization of the intracanal fragments compared with the files immersed outside simulated canal, despite the same anodic polarization conditions imposed. The total mean electrical charges generated during the polarization of sizes 20 and 30 K-file fragments were 0.84 (0.20) C and 1.14 (0.31) C, respectively. The weight losses of the fragments are too low to be precisely measured using a precision balance. Aboud et al. (2014) calculated the theoretical values of mass loss of NiTi files fragments applying the
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
Amaral et al. Dissolution of stainless steel files
(a)
(b)
(c)
(d)
(e)
(f)
Figure 4 Radiographic analysis of an intracanal file fragments. (a–c) Size 20 K-file fragment; (d–f) Size 30 K-file fragment. (a, d) Radiographies obtained before the test; (b, e) Radiographies obtained after polarization at 0.5 VSCE during 60 min; (c, f) Radiographies obtained after the polarization showing the fragment bypassed by a size 10 K-file.
Faraday’s law of electrolysis, considering the equivalent dissolution of Ni and Ti. According to this law, m = e.i.t, where m is the mass of the substance liberated at an electrode in grams, e is the electro electronic equivalent, i is the electrical current intensity in amperes, and t is the total time in seconds. However, this law could not be applied here because the rate of dissolution of the different metals of the stainless steel alloy is not known. Consequently, the use of this law would generate imprecise values of weight loss. Another way to estimate the weight loss of the file fragments inside simulated root canals is to use the ratio between the weight loss and the electrical charge obtained in the tests with immersed files. According to this ratio, the mean weight losses of sizes 20 and 30 K-file fragments were 0.21 mg and 0.32 mg, respectively. In the present study, stainless steel files with two different diameters were selected for the polarization tests because the file fragments of varying diameters are found in root canals during clinical practice. According to Ormiga et al. (2011), the diameter of the fragment surface exposed to the medium affects the currents used to promote dissolution; an exposed surface with a larger diameter cross-section has a higher total electrical charge. The results presented herein are in agreement with this statement because the electrical charges generated during the polarization of size 30 K-file fragments where significantly higher than those generated during the polarization of size 20 K-file fragments. In both groups, the partial dissolution of a file fragment enabled the recovering of the original canal pathway with a size 10 K-file after each 60 min; thus, 60 min can be considered a
© 2014 International Endodontic Journal. Published by John Wiley & Sons Ltd
clinically acceptable period of time (Aboud et al. 2014).
Conclusion It was possible to obtain a significant dissolution of stainless steel K-file using the method proposed by Ormiga et al. (2010). The anodic polarization of stainless steel K-file fragments in simulated root canals more than 60 min resulted in their partial dissolution. The fragments could be bypassed after the test.
Acknowledgements The authors deny any conflict of interests and would like to acknowledge the support of COPPE-TEC Foundation and CNPq.
References Aboud LR, Ormiga F, Gomes JACP (2014) Electrochemical induced dissolution of fragments of a nickel–titanium endodontic files and their removal from simulated root canals. International Endodontic Journal 47, 155–62. Baratto-Filho F, Leonardi DP, Zielak JC, Vanni JR, SayaoMaia SM, Sousa-Neto MD (2009) Influence of ProTaper finishing files and sodium hypochlorite on cleaning and shaping of mandibuldar central incisors-a histological analysis. Journal of Applied Oral Science 17, 229–33. Barbosa FOG, Gomes JACP, Ara ujo MCP (2007) Influence of sodium hypochlorite on mechanical properties of K3 nickel-titanium rotary instruments. Journal of Endodontics 33, 982–5. Camara AC, Aguiar CM, de Figueiredo JA (2008) Evaluation of the root dentine cutting effectiveness of the HERO 642,
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143
Dissolution of stainless steel files Amaral et al.
HERO Apical and HERO Shaper rotary systems. Australian Endodontic Journal 34, 94–100. Eleazer PD, O’Connor RP (1999) Innovative uses for hypodermic needles in endodontics. Journal of Endodontics 25, 190–1. Feldman G, Solomon C, Notaro P, Moskowitz E (1974) Retrieving broken endodontic instruments. Journal American Dental Association 88, 588–91. Fors UG, Berg JO (1983) A method for the removal of broken endodontic instruments from root canals. Journal of Endodontics 9, 156–9. Hulsmann M (1993) Methods for removing metal obstructions from the root canal. Endodontics Dental Traumatology 9, 223–37. Hulsmann M (1994) Removal of fractured instruments using a combined automated/ultrasonic technique. Journal of Endodontics 20, 144–7. Kao C, Huang T (2010) Variations in surface characteristics and corrosion behaviour of metal brackets and wires in different electrolyte solutions. The European Journal of Orthodontic 1, 142. Kim H, Johnson J (1999) Corrosion of stainless steel, nickeltitanium, coated nickel-titanium, and titanium orthodontic wires. Angle Orthodontic 69, 39–44. Kondo M, Nakasaga T (2010) Corrosion of reduced activation ferritic martensitic steel JLF-1 in purified Flinak at static and flowing conditions. Fusion Engineering and Design 85, 1430–6. Krell K, Fuller M, Scott G (1984) The conservative retrieval of silver cones in difficult cases. Journal of Endodontics 10, 269–73. Lee TH, Huang TK, Lin SY, Chen LK, Chou MY, Huang HH (2010) Corrosion resistance of different nickel-titanium archwires in acidic fluoride-containing artificial saliva. Angle Orthodontic 80, 547–53. Li X, Wang J, Han EH, Ke W (2007) Influence of fluoride and chloride on corrosion behavior of NiTi orthodontic wires. Acta Biomaterialia 3, 807–15. Lopes HP (1994) Corros€ao em limas endod^ onticas de acßo inoxid avel. Revista Brasileira de Odontologia 51, 26–8. Marshall GW Jr, Inai N, Wu-Magidi IC et al. (1997) Dentin demineralization: effects of dentin depth, pH and different acids. Dental Materials 13, 338–43. Masahiro I (2010) Corros~ao de ions de NiTi implantados em orio bucal com fios ortod^onticos em solucß~oes de enxaguat fluoreto. Jornal Materiais Dentarios 29, 53–8. Masserann J (1971) Translation of Entfernen metallischer fragment aus wurzelkan€alen, by Jean Masserann, which describes a technique for the removal of metallic fragments which remain lodged in root canals. Journal of the British Endodontic Society 5, 55–9.
144
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Menezes LM, Lima EMS, Rizzatto SMD (2006) Evaluation of titanium brackets surface after immersion in sodium fluoride. Revista Dental Press de Ortodontia e Ortopedia Facial 11, 93–103. Nagai O, Tani N, Kayaba Y, Kodama S, Osada T (1986) Ultrasonic removal of broken instruments in root canals. International Endodontic Journal 19, 298–304. Nekoofar MH, Ghandi MM, Hayes SJ, Dummer PM (2006) The fundamental operating principles of electronic root canal length measurement devices. International Endodontic Journal 39, 595–609. Okiji T (2003) Modified usage of the Masserann kit for removing intracanal broken instruments. Journal of Endodontics 29, 466–7. Ormiga F, Gomes JACP, Ara ujo MCP (2010) Dissolution of nickel-titanium endodontic files via an electrochemical process: a new concept for future retrieval of fractured files in root canals. Journal of Endodontics 36, 717–20. Ormiga F, Gomes JACP, Ara ujo MCP, Barbosa AOG (2011) An initial investigation of the electrochemical dissolution of fragments of nickel-titanium endodontic files. Journal of Endodontics 37, 526–30. Parashos P, Rahimi M (2009) A novel technique for the removal of fractured instruments in the apical third of curved root canals. International Endodontic Journal 42, 264–70. Roig-Greene J (1983) The retrieval of foreign objects from root canals: a simple aid. Journal of Endodontics 9, 394–7. Rondelli G, Vicentini B (1999) Localized corrosion behaviour in simulated human body fluids of commercial Ni-Ti orthodontic wires. Biomaterials 20, 785–92. Ruddle CJ (1997) Micro-endodontic nonsurgical retreatment. Dental Clinics of North America 41, 429–54. Ruddle CJ (2004) Nonsurgical retreatment. Journal of Endodontics 30, 827–45. Saunders JG, McIntyre JM (2005) The ability of 1.23% acidulated phosphate fluoride gel to inhibit simulated endogenous erosion in tooth roots. Australian Dental Journal 50, 263–6. Sun XT, Kang ZX, Jiang HJ, Guan RF, Zhang XP (2011) A comparative study on the corrosion behavior of porous and dense NiTi shape memory alloys in NaCl solution. Electrochimica Acta 56, 6389–96. Suter B (1998) A new method for retrieving silver points and separated instruments from root canals. Journal of Endodontics 24, 446–8. Terauchi Y, O’Leary L, Suda H (2006) Removal of separated files from root canals with a new file-removal system: Case reports. Journal of Endodontics 32, 789–97. Weisman MI (1983) The removal of difficult silver cones. Journal of Endodontics 9, 210–1.
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