RESUMO
The aim of the study was to evaluate the adhesive forces for removing iatrogenically fractured endodontic nickel-titanium instruments using a modified tube technique with various pre-treatment agents in combination with a light-curing composite. 120 Nickel-Titanium-Mtwo instruments were cut at its parallel shaft and fixed in a vise with an overlap of 2 mm. The surfaces were treated with different agents: A) GC Metalprimer; B) Prime and Bond active; C) NaOCl (3%); D) citric acid (15%); E) phosphoric acid (37%) and group (F) was not pretreated (control). One end of a matching microtube, filled with light-curing composite, was placed over the instrument and a transmitting glass fiber inserted from the opposite side guaranteed polymerization. Pull-out tests (1 mm/min) were performed and failure load was measured digitally. Data were statistically analyzed using the ANOVA and Student-Newman-Keuls tests. Interfaces were subjected to SEM analysis. Prime and Bond active created significant higher pull-out values (mean 30.5 N) compared to all other groups (p < 0.001) and Metalprimer (18.5 N) was significantly superior to the untreated (12.6 N) and NaOCl (11.7 N) group (p < 0.05). No significant differences were obtained between the other groups (p > 0.05). Thus, adhesives improved bonding to fractured NiTi instruments.
RESUMO
INTRODUCTION: The aim of this in vitro study was to assess an alternative method using light-curing composite for removing fractured endodontic instruments with a tube technique. METHODS: Two different stainless steel endodontic instruments (ISO 20: Hedstrom files, K-files; VDW, Munich, Germany) were cut at the diameter of 0.4 mm. These fragments were fixed in a vise leaving a free end of 1 or 2 mm. Cyanoacrylate (Instant Fix; Henry Schein Dental, Melville, NY), dual-curing Rebilda DC (VOCO, Cuxhaven, Germany), and light-curing SureFil SDR (Dentsply, York, PA) were placed into microtubes (N'Durance Syringe Tips; Septodont, Saint-Maur, France) and shifted over the instruments (n = 20 in each group). After polymerization, pull-out tests were performed with a constant speed of 2 mm/min; failure load was measured digitally. Data were analyzed using the Kruskal-Wallis test followed by the Dunn test for pairwise comparison. RESULTS: The median failure load was up to 62.5 N for SDR, 35.8 N for Rebilda, and 14.7 N for cyanoacrylate, respectively. Both tested composites yielded significantly higher values in pull-out tests than cyanoacrylate. The disconnecting force was highest when light-cured composite SDR was used for fixation. Removing Hedstrom files resulted in higher values than removing K-files. The median force when using SDR was 79.7 N (interquartile range, 66.0-86.8 N) in Hedstrom files and 53.3 N (interquartile range, 47.1-58.5 N) in K-files. CONCLUSIONS: Within the limitations of this study, the use of light-curing composite inside of the microtube was superior compared with the use of cyanoacrylate or chemically cured composite, which are being used presently.
