الفهرس 
Metallurgical influence of separated endodontic instruments on the retrieval capability of katana sword ultrasonic tip under different lubricants (in vitro study)
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Abstract
The aim of the present study was to assess the retrieval capability of katana sword ultrasonic tip on two different alloys (M-wire and electric discharge machining EDM) using two different lubricants (EDTA and olive oil) as regards to the remaining dentin thickness, cracks development and time of retrieval procedure.
Methodology: Eighty-five extracted premolar teeth with moderately curved roots (15-30° angle of curvature and 4-8 mm radius of curvature) were used in the current study to have a total of forty successfully retrieved samples. The apical 4mm of ProTaper Next (ProTaper Next®, Dentsply Tulsa Dental) (n=20) and Neoniti (Neolix, Raoul Vadepied, FR-53600 Chatres la Foret, France) (n=20) rotary NiTi instruments were fractured at the apical portion of the root canals. Under the magnification of the dental operating microscope, and after staging platform creation, a modified katana sword ultrasonic tip was used to retrieve the separated instruments under EDTA (Prevest DenPro, USA) or olive oil (RS, Rafael Salgado, Spain) as an intracanal lubricant. CBCT scans were taken preoperatively after instruments separation, and postoperatively after retrieval attempts in all samples.
For samples with successful retrieval, CBCT scans were used to assess the changes in root dentin thickness, at 4 and 6mm from every root apex, then teeth were sectioned horizontally at apical and middle levels and viewed under the scanning electron microscope to detect the presence of dentinal cracks. The retrieval time was also recorded in minutes from the beginning of staging platform creation until retrieval was successfully achieved. As for samples with unsuccessful retrieval, CBCT scans were used to assess the incidence of perforations and secondary fractures. All data were collected and tabulated for statistical analysis.
Results: There was no statistically significant difference in the retrieval capability of katana sword ultrasonic tip between the different groups. Regarding the changes in root dentin thickness, there was a significant decrease in the dentin thickness in all tested groups postoperatively, with the greatest dentin loss observed at 6mm from the root apex. There was no statistically significant difference of the alloy type or the intracanal lubricant on the overall percentage of dentin thickness change. Additionally, there was no statistically significant effect of the different alloys or intracanal lubricants on the presence of dentinal cracks.
Regarding the retrieval time, there was no statistically significant difference between the different alloys. However, using olive oil as an intracanal lubricant had a statistically significant decrease in the retrieval time
Conclusion: Within the limitations of this study, it could be concluded that:
1. Katana sword ultrasonic tip proves to be efficient enough to retrieve apically separated instruments in curved canals.
2. Katana sword ultrasonic tip and high viscosity lubricants fail to omit the incidence of cracks during separated instruments retrieval, but reduce the retrieval time, which in turn reduce the incidence of cracks and amount of dentin removed during retrieval.
3. Metallurgical make up of endodontic instruments presents minimal effect on the retrieval capability of separated endodontic files.