Observations of chips produced by NiTi files and hand files

Objectives: The purpose of this study was to compare NiTi files and hand files concerning the chips produced after preparation of teeth and resin blocks. Methods: Eight maxillary buccal roots were obtained from extracted human molars and prepared up to #10 size canal with 11.0mm length. The eight roots and eight transparent plastic blocks (VDW, Munich, Germany) which had curvature of 30 degrees were prepared up to #35 size by either 21mm stainless K-files or Flexmaster made of NiTi. The file and the prepared object were put into a 2ml cryovial with 1ml distilled water, and taken off the chips with ultrasonic vibration. The 0.2ml water containing the chips was observed with a microscope and taken digital photographs. The chip sizes were measured with commercialized computer software and analyzed by Student's t-test. Result: The amount of chips by hand files increased along with increasing of the file number. In NiTi files, the initial file that had a great taper created the most large amount of chips, and amounts of chips were decreased along with increasing of the file number in crown-down technique. The chips by hand files clogged the canals in many cases, therefore there was not seen in NiTi.The dentin chips by NiTi were almost same size to hand files, but the averages (62.4 μm) of the plastic chip by hand files were was twice greater than NiTi. The chips in plastic models by large number of hand file made a long threadlike shape chips. The sizes of plastic chips by NiTi were significantly small against hand file, and there was no significant difference in dentin chips. Conclusion: The chips produced in mechanical preparation were differential shapes and size in plastic and dentin. NiTi files make small chips and are safer against to clogging root canals.