Dissolution of Nickel-Titanium Endodontic Files via an Electrochemical Process: A New Concept for Future Retrieval of Fractured Files in Root Canals

Microhardness and energy dispersive X-ray evaluation of dentinal walls following chemical and electrochemical dissolution of fractured nickel-titanium file: An in vitro study

Purpose

Chemical dissolution of nickel-titanium (NiTi) files involves the application of a fluoride solution in direct contact with a damaged instrument, whereas electrochemical dissolution involves the application of an electrical current to the electrolyte, which accelerates fragment dissolution. This study aimed to determine the hardness and concentration of calcium and phosphorus (Ca and P) ions in dentinal walls following chemical and electrochemical dissolution of fractured ProTaper F2 files with a novel chemical solution. Materials & Methods : Thirty human maxillary first molar palatal roots with fractured ProTaper F2 files in the middle third (length, 2.5 mm were divided into three groups according to the treatment techniques used with a novel solution (NaF 12 g/L + NaCl2 60 g/L + MgCl2 60 g/L + CaCl2 60 g/L) at pH 5: Group 1: distilled water (control group), Group 2: electrochemical dissolution, and Group 3: chemical dissolution using the novel solution. The novel solution was placed for 10 min using an electrochemical technique, and for 30 min in contact with the separated instrument in the chemical group. The Vickers microhardness test was performed in three areas: at 3, 6, and 9 mm from the apex, and an energy-dispersive X-ray test for both Ca and P ions was performed. The analysis of variance (ANOVA) and Tukey's tests were used for statistical analysis.

Results

According to the one-way ANOVA analysis, no difference was observed between the tested approaches (P > 0.05) in the three areas evaluated (3, 6, and 9 mm), with no difference in the Ca/P ratio between the tested groups.

Conclusion

Compared to the control group, the use of chemical and electrochemical dissolution methods with the novel solution did not affect dentin hardness or dentinal structure in terms of the Ca/P ratio, thereby indicating promising results while saving time.

Electrochemical dissolution and retrieval of broken NiTi endodontic files from root canal using chloride based isotonic fluids as electrolytes - An in vitro study

Objective

The electrochemical dissolution method of instrument retrieval emphasizes on the dissolution of the instrument rather than sacrificing dentine. Most of the studies conducted for electrochemical dissolution used fluoride-containing electrolytes and were performed inside a beaker. In this study, we used chloride-based fluids as electrolytes.

Materials and Methods

Fifty extracted mandibular first premolars were divided into five groups based on the electrolytes used. Canals were enlarged to ProTaper Universal F2, and files were intentionally broken inside the canal. These specimens were subjected to electrochemical characterization by applying the potential of 9V for 20 min. Optical images were taken to assess the change in surface topography. The results were analyzed statistically by one-way analysis of variance (analysis of variance [ANOVA]).

Results

The rate of dissolution based on the electrolyte used decreased in the following order, viz. Tyrode's solution>artificial saliva>normal saline>Ringer's lactate/physiological serum.

Conclusion

Apart from fluoride, chloride-based electrolytes could be an efficient alternative.

Navigating Separated Instrument Retrieval: A Case Report

Instrument separation during endodontic therapy is a complication occurring in 2% to 6% of cases. Focusing on the Masserann technique, the study presents a success rate of 55% in retrieving separated instruments. The technique's effectiveness is demonstrated through a case involving retrieving an instrument from the mandibular first premolar. The technique utilizes various tools, including trephine burs and an extractor, providing a reliable means to dislodge tightly wedged fragments. Despite limitations in specific tooth types and the necessity for frequent radiographic monitoring, the Masserann kit proves effective and underscores the importance of attempting retrieval before considering surgical interventions. The presented case exemplifies the technique's clinical applicability and positive outcomes in intricate scenarios, emphasizing its significance in endodontic practice.

Present status and future directions - Removal of fractured instruments

Success rate of fractured instrument retrieval varies because it is dependent mainly on several factors including the visibility of the fractured instrument, the length of the fractured instrument in relation to the curvature of the canal, and the techniques applied to each case. This review aims to update the present status on removal of fractured instruments to identify factors and variables that could affect the success of fractured instrument retrieval based on both the preparation techniques and the instrument retrieval techniques. On the other hand, future directions of fractured instrument retrieval should focus on management of non-visible fractured instruments since the removal of those instruments are deemed unpredictable with the current techniques, whereas the removal of visible fractured instruments are considered predictable now. Another possible direction of it is there might be no more instrument fracture due to possible significant changes in the root canal preparation technique which may dispense with the use of rotary instruments.

Electrochemical dissolution of nickel-titanium instrument fragments in root canals of extracted human maxillary molars using a small reservoir of electrolyte

AIM

To evaluate the viability of the electrochemical dissolution of fragments of fractured NiTi instruments in root canals of extracted human maxillary molars, using two electrodes and the solution restricted to a small reservoir coupled to the pulp chamber. The primary hypothesis was that this method enables the reduction of fragment volume and re-establishment of the root canal path with a size 08 K-file, both in simulated canals and in extracted human maxillary molars.

METHODOLOGY

Fragments of F1 ProTaper instruments were polarized in simulated root canals and in distobuccal root canals of extracted maxillary molars using a new method, with the solution restricted to a small acrylic microcell coupled to each resin block or pulp chamber. Two electrodes were used, where one was kept in contact with the intracanal fragment and another was positioned in the solution present in the acrylic microcell. After the tests, a size 08 K-file was used passively to verify the possibility of bypassing the fragment, which was also confirmed by radiographic analysis. Micro-CT analysis of the teeth was used before and after fragment dissolution to evaluate the volume, length and porosity of the fragments. The D'Agostino-Pearson normality test was used to verify the distribution of the data. A paired t-test (P < 0.05) was used to compare the volume, length and porosity of the fragments before and after the dissolution tests.

RESULTS

After dissolution, all fragments could be bypassed with a size 08 K-file in both simulated canals and in extracted teeth. The dissolution process did not result in significant reduction of neither the fragment length nor the fragment porosity. However, it resulted in a significant reduction of fragment volume (paired t-test, P < 0.05).

CONCLUSION

The electrochemical dissolution of fragments of NiTi files in root canals of extracted human maxillary molars using two electrodes, and the solution restricted to a small reservoir coupled to the pulp chamber resulted in a significant reduction of fragment volume. The re-establishment of the root canal path with the passive insertion of size 08 K-files was possible in all samples after the tests, both in simulated canals and in extracted teeth.

Comparative evaluation of the effectiveness of ultrasonic tips versus the Terauchi file retrieval kit for the removal of separated endodontic instruments

Objective

The aim of this study was to perform a comparative evaluation of the effectiveness of ultrasonic tips versus the Terauchi file retrieval kit (TFRK) for the removal of broken endodontic instruments.

Materials and Methods

A total of 80 extracted human first mandibular molars with moderate root canal curvature were selected. Following access cavity preparation canal patency was established with a size 10/15 K-file in the mesiobuccal canals of all teeth. The teeth were divided into 2 groups of 40 teeth each: the P group (ProUltra tips) and the T group (TFRK). Each group was further subdivided into 2 smaller groups of 20 teeth each according to whether ProTaper F1 rotary instruments were fractured in either the coronal third (C constituting the PC and TC groups) or the middle third (M constituting the PM and TM groups). Instrument retrieval was performed using either ProUltra tips or the TFRK.

Results

The overall success rate at removing the separated instrument was 90% in group P and 95% in group T (p > 0.05) The mean time for instrument removal was higher with the ultrasonic tips than with the TFRK (p > 0.05).

Conclusion

Both systems are acceptable clinical tools for instrument retrieval but the loop device in the TFRK requires slightly more dexterity than is needed for the ProUltra tips.

Evaluation of fluoride and sodium hypochlorite solutions during the electrochemical dissolution of conventional NiTi instruments and Gold thermomechanically treated NiTi instruments

AIM

To compare the dissolution time of two solutions, a fluoride solution and a sodium hypochlorite solution, both saturated with sodium chloride, during the electrochemical dissolution of instruments consisting of conventional nickel-titanium alloy and Gold thermomechanically treated nickel-titanium alloy.

METHODOLOGY

Two solutions, an NaF solution consisting of 12 g L^-1 NaF with 180 g L^-1 NaCl and an NaOCl solution consisting of 2.5% NaOCl with 180 g L^-1 NaCl, were evaluated in a polarization test of a sample of 48 ProTaper Universal F1 (PTU F1) and WaveOne Gold Small (WOGS) instruments. The electric potentials were 0.5 V and 5 V for the NaF and NaOCl solutions, respectively. The electrochemical cell consisted of three electrodes for the polarization test of the PTU F1 and WOGS instruments, which had 6 mm of the tip immersed in the test solutions. The electric current was recorded for 540 s. If complete dissolution of the immersed tip occurred in less than the expected time, the experiment was considered complete. The time variations (in seconds) of the instruments in the solutions were measured. Data were subjected to statistical analysis using the Mann-Whitney, Kruskal-Wallis and Dunn tests. The corrosion patterns of the instruments were evaluated by scanning electron microscopy (SEM).

RESULTS

The NaF and NaOCl solutions were associated with significantly different (P = 0.000) dissolution times of the instrument, with mean values of 12.96 s and 83.63 s, respectively. There was no significant difference (P = 0.649) in dissolution time between the PTU F1 and WOGS instruments.

CONCLUSIONS

NaF and NaOCl solutions were able to electrochemically dissolve PTU F1 and WOGS instruments. However, the NaF solution achieved dissolution in significantly less time.

Separated Instrument in Endodontics: Frequency, Treatment and Prognosis

Instrument separation during endodontic therapy is a frequent accident with rotary instruments being more likely to separate than manual ones. The treatment of cases with a separated instrument can be either conservative or surgical. A conservative approach involves the following treatment choices: a) bypass of the fragment, b) removal of the fragment, c) instrumentation and obturation coronally to the fragment. Concerning the removal of a separated instrument, a variety of techniques and systems have been developed. Ultrasonics, in combination with the operative microscope constitute the most effective and reliable tools for removing a separated endodontic instrument from a root canal. The likelihood of successful removal depends on: the level of separation (coronal, middle or apical third); location in relation to the root canal curvature; the type of separated instrument; its length; the degree of canal curvature and the tooth type. Several complications may occur during the management of a separated instrument: separation of the ultrasonic tip or file used for bypassing or removing the instrument; further separation of the fragment; perforation; ledge; extrusion of the file into periapical tissues; tooth weakening due to dentin removal, as well as excessive temperature rise in periodontal tissues. Prognosis for a tooth retaining a separated instrument depends on the presence of a periapical lesion, the microbial load of the root canal during the time of separation and the quality of the obturation.

Evaluation of the effects of the solution used for electrochemical dissolution of nickel-titanium endodontic files on dentine structure, microhardness and cell viability

AIM

To evaluate the effects of the [NaF 12 g L^-1  + NaCl 1 g L^-1 ] solution used in the electrochemical dissolution process of fractured endodontic files, as well as its NiTi-containing product, on dentine hardness, topography and human fibroblast viability.

METHODOLOGY

Sixty single-rooted human teeth were evaluated for dentine microhardness using the Vickers hardness test and the area and number of dentinal tubules by scanning electron microscopy. The samples were divided according to the dentine surface treatment: distilled water; 17% EDTA; [NaF 12 g L^-1  + NaCl 1 g L^-1 ]; and 17% EDTA + [NaF 12 g L^-1  + NaCl 1 g L^-1 ]. Thirty-six single-rooted human teeth were divided according to the irrigation protocol: Dulbecco's Modified Eagle's Medium + 10% foetal bovine serum; 5.25% NaOCl; [NaF 12 g L^-1  + NaCl 1 g L^-1 ]; and [NaF 12 g L^-1  + NaCl 1 g L^-1  + NiTi]. The extracts in contact with the apical foramen were used in the MTT assay to evaluate human fibroblast viability, with dilutions of 100%, 50%, 25% and 12.5%. Statistical tests used were paired t-tests, one-way anova, Tukey's test, Kruskal-Wallis test and Dunn's post-test.

RESULTS

The [NaF 12 g L^-1  + NaCl 1 g L^-1 ] solution did not modify dentine microhardness or the average dentinal tubule area. However, EDTA induced changes in dentine structure and microhardness (P < 0.05). The [NaF 12 g L^-1  + NaCl 1 g L^-1 ] solution, and its NiTi-containing product had lower cytotoxicity than NaOCl at dilutions of 25% and 50% (P < 0.01).

CONCLUSIONS

The [NaF 12 g L^-1  + NaCl 1 g L^-1 ] solution did not alter dentine microhardness or damage the dentine structure. It also demonstrated lower cytotoxicity than NaOCl.

Electrochemical dissolution of fractured nickel-titanium instruments in human extracted teeth

AIM

To assess the effect of sodium chloride concentration in fluoridated solutions during the electrochemical dissolution of fractured rotary endodontic instruments.

METHODOLOGY

Two solutions were assessed (solution 1: NaF 12 g L^-1  + NaCl 1 g L^-1 , pH = 5.0; and solution 2: NaF 12 g L^-1  + NaCl 180 g L^-1 , pH = 5.0) using two tests: the ProTaper Universal F1 (PTU F1) instrument polarization test and the polarization test for intracanal PTU F1 fragments fractured in mandibular incisors. In the first test, two sets of five instruments were separately and partially immersed in each solution, and the electrical current was evaluated over 30 min. In the second test, 45 PTU F1 instruments were fractured within the root canals of mandibular incisors and subjected to potentiodynamic polarization for 30 min. The electrical current and the variations in the length of PTU F1 fragments were measured. The data were analysed statistically (anova and Wilcoxon and Mann-Whitney tests, respectively).

RESULTS

Solution 2 was associated with more corrosive effects in both tests. In the first test, the PTU F1 instruments immersed in solution 2 had a higher electrical current (P < 0.001) and had a total dissolution time of approximately 540 s. In the second test, a larger difference between the baseline and final lengths of the fragments was noted in solution 2 (P = 0.011).

CONCLUSION

Saturation of fluoridated solution with sodium chloride led to an increase in electrical current and microscopic reductions in the length of fractured instrument fragments subjected to electrochemical dissolution.

Electrochemical-induced dissolution of nickel-titanium endodontic instruments with different designs

AIM

To compare the active dissolution process of K3, ProTaper and Mtwo NiTi endodontic rotary instruments in chloride and fluoride containing solutions.

METHODS

Anodic polarization of K3 size 20, 0.06 taper, ProTaper size F1 and MTwo size 20, 0.06 taper instruments was performed, and anova (P < 0.05) was used to compare the weight loss, the time of dissolution and the electrical charge generated by the groups of instruments. Fragments of the instruments were polarized in simulated root canals to evaluate the dissolution process. After the tests, a size 10 K-file was used to verify whether the fragment could be bypassed. Radiographic analysis of the simulated canals was used before and after the tests to verify fragment dissolution.

RESULTS

A progressive consumption of the instruments was observed. K3 and ProTaper instruments had significantly greater weight loss than Mtwo instruments after 30 min of polarization. K3 instruments had the highest values of total electrical charge, and MTwo instruments the lowest (P < 0.05). After 60 min, the anodic polarization of instrument fragments in simulated root canals resulted in their partial dissolution.

CONCLUSION

The anodic polarization of K3, ProTaper and MTwo instruments resulted in their progressive consumption with increasing polarization time. Sixty minutes anodic polarization of the various NiTi instrument fragments in simulated root canals resulted in their partial dissolution.

Electrochemical-induced dissolution of stainless steel files

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 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.

Electrochemical induced dissolution of fragments of nickel-titanium endodontic files and their removal from simulated root canals

AIM

To improve the dissolution process of NiTi endodontic rotary files aiming at fragment removal and the recovery of the original path of the root canal during a clinically acceptable period of time.

METHODOLOGY

Anodic polarization curves and redox curves were obtained to determine the conditions necessary for the dissolution of endodontic files. Anodic polarization of K3 files was performed, and analysis of variance (P < 0.05) was used to compare different test times in relation to weight loss, length loss and electrical charge generated in each solution. The polarization of fragments in simulated root canals was undertaken to evaluate the dissolution process. After the tests, a size 10 K-file was used to verify the possibility to bypass the fragment. The total electrical charge of each test was obtained from the corresponding graph area. Radiographic analysis of the simulated canals was used before and after the tests to verify fragment dissolution.

RESULTS

The weight loss values, the length loss values and the total values of electrical charge in each period of time were significantly higher (P < 0.05) in the tests using the selected solution compared with the solution previously proposed. A progressive consumption of the K3 file tip was observed up to 30 min. The anodic polarization of file fragments in simulated root canals for 60 min resulted in their partial dissolution and enabled the recovery of the original canal pathway with size 10 K-files.

CONCLUSIONS

Increasing fluoride concentration resulted in greater active dissolution of NiTi files. The dissolution of fractured files in simulated root canals enabled the recovery of its original path during a clinically acceptable period of time.

Management of intracanal separated instruments

INTRODUCTION

Intracanal separation of endodontic instruments may hinder cleaning and shaping procedures within the root canal system, with a potential impact on the outcome of treatment. The purposes of this narrative review of separated instruments were to (1) review the literature regarding treatment options, influencing factors, and complications and (2) suggest a decision-making process for their management.

METHODS

An online search was conducted in peer-review journals listed in PubMed to retrieve clinical and experimental studies, case reports, and review articles by using the following key words: instruments, files, obstructions, fractured, separated, broken, removal, retrieval, management, bypassing, and complications with or without root canal and endodontic.

RESULTS

There is a lack of high-level evidence on management of separated instruments. Conventional conservative management includes removal of or bypassing the fragment or filling the root canal system to the coronal level of the fragment. A surgical intervention remains an alternative approach. These approaches are influenced by a number of factors and may be associated with complications. On the basis of current clinical evidence, a decision-making process for management is suggested.

CONCLUSIONS

Guidelines for management of intracanal separated instruments have not been formulated. Decisions on management should consider the following: (1) the constraints of the root canal accommodating the fragment, (2) the stage of root canal preparation at which the instrument separated, (3) the expertise of the clinician, (4) the armamentaria available, (5) the potential complications of the treatment approach adopted, and (6) the strategic importance of the tooth involved and the presence/or absence of periapical pathosis. Clinical experience and understanding of these influencing factors as well as the ability to make a balanced decision are essential.

Electrochemical dissolution of nickel-titanium endodontic files induces periodontal ligament cell death

INTRODUCTION

Fractured endodontic files present a major problem. A novel method has been proposed to retrieve fractured nickel-titanium (NiTi) endodontic files by using electrochemical dissolution. However, the effect of file dissolution on adjacent soft tissues such as the periodontal ligament (PDL) has not been investigated. The aim of this study was to determine the effects of the dissolution products on PDL fibroblasts.

METHODS

Endodontic files were dissolved in sodium fluoride (NaF) by passing a 50-mA current through the NiTi files while immersed in the NaF solution. NaF/NiTi solutions were diluted with minimal essential medium-α media containing 10% serum. PDL cells were treated for up to 24 hours, and cell viability was quantified by using calcein AM to label live cells and ethidium homodimer to label dead cells. This was repeated by using artificial saliva (AS) as an alternative to NaF.

RESULTS

NaF solution reduced PDL cell survival, and the NaF/NiTi solution further reduced PDL cell survival. AS alone did not reduce cell survival, whereas AS/NiTi solution reduced PDL cell survival. Particles that resulted from the electrochemical dissolution of NiTi files were highly cytotoxic.

CONCLUSIONS

Electrochemically dissolving NiTi files in NaF results in solutions that are cytotoxic to PDL fibroblasts. AS may be a less toxic alternative for dissolving NiTi files.