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

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 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.

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.

Microscopic evaluation of the dentinal walls of extracted human teeth following electrochemical dissolution of fragmented nickel-titanium instruments

Electrochemical dissolution is a method in which fluoridated solution in direct contact with the fractured instrument receives an electrical current that speeds up fragment dissolution. The aim of this study was to assess the integrity of dentinal walls during the electrochemical dissolution of fractured rotary endodontic instruments in extracted human teeth. Forty-five human mandibular incisors subjected to the electrochemical dissolution process using fluoride solution with low NaCl concentration (LC group: NaF 12 g/L + NaCl 1 g/L, pH = 5.0), fluoride solution with saturating NaCl concentration (SC group: NaF 12 g/L + NaCl 180 g/L, pH = 5.0) and distilled water (control group) were evaluated. For each group, 15 incisors were submitted for the scanning electron microscopy (SEM) evaluation. The roots were sectioned longitudinally; each hemisection was analyzed (n = 30), and energy-dispersive spectroscopy (EDS) was performed. The amount of dentinal tubule openings was analyzed by SEM. Statistical analyses were performed. The test solutions did not alter the amount of dentinal tubule openings when compared with the control group. No Ni or Ti was impregnated into the dentinal tubules after electrochemical techniques. The dentinal structure remained unchanged following the electrochemical dissolution method.

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.