Influence of surface coatings on cutting efficiency and cyclic fatigue of nickel-titanium rotary endodontic files in artificial canals
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Since the endodontic files were introduced in the late 1980s, NiTi showed enhanced performance in root canal instrumentation when compared to stainless steel files. It was reported that NiTi files had a higher tendency to break inside root canals compared to stainless steel files. The aim of this research was to evaluate the cutting efficiency and the cyclic fatigue of Protaper® endodontic files and EndoSequence® endodontic files when their surface character was modified through coating the files with two types of silanes, as “dry” lubricants. The first coating was Octadecylsilane and the second was (3- Hepta-fluoroisopropoxy)propylsilane. Each file type was devided into 3 groups. A specially designed platform was made to test the cutting efficiency of 120 edodontic files in custom made epoxy resin blocks using a universal testing machine and an endodontic motor. The files rotated at 300rpm and were introduced into the blocks at 10mm/minute. Weight of the blocks was measured before and after testing and weight difference was recorded, maximum and minimum load that the files were subjected to during testing were measured and load difference was recorded. In the second part of this research 72 files were tested for cyclic fatigue in a specially designed platform that was built for this purpose. Files were tested with water flowing through a bent glass tube to flush away any resulting debris generated during testing. Files were rotated inside the tubes at 300rpm. Time to fracture, length of broken parts was recorded, and maximum strain amplitudes (MSA) were calculated. Broken files were examined under scanning electron microscope (SEM) to evaluate their broken edges. The results did not show significant difference in cutting efficiency between groups, this is acceptable since the coating was considered a monomolecular layer limited to the surface of the files, with no changes to the core properties or the cross section of the files. Results also did not show significant difference in the number of cycles to failure or length of broken part between the groups. EndoSequence® files broke at lower MSA than Protaper® files, because of the thinner diameter at which EndoSequence® files failed.