Shaping of simulated root canals in resin blocks using files activated by a sonic handpiece

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Abstract
Summary. . A total of 50 simulated root canals in clear resin blocks with various degrees and positions of curvature were prepared by either K-files or Hedstrom files. Each file type was used to prepare 25 canals employing an in/out circumferential filing motion. The efficacy of the files was assessed by instrumentation time, deformation and fracture of instruments, and loss of working distance. The shape of the prepared canals was assessed by direct observation and from composite photographic prints produced by superimposing negatives of the canals obtained before and after preparation. Overall, canal shaping with Hedstrom files was quicker and more effective. Both file types prepared straight canals in an appropriate manner but the majority of prepared curved canals were hourglass in shape. In general, K-files created zips which were wider and thus more pronounced than those produced by Hedstrom files. Wide ‘danger zones’ were also regularly created. The location of the aberrations depended largely on the original shape of the canal and in particular on the position of the beginning of the canal curve. Under the conditions of this study, the manipulation of K-files and Hedstrom files in a simple in out circumferential filing motion proved an unsatisfactory method of shaping simulated curved root canals in resin blocks.