Electrochemical-induced dissolution of stainless steel files

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.

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.