K-file ( endodontic instrument ) Uses and Safety Tips
K-file: Design & Structure
K-files are manufactured from square or sometimes triangular steel wire that is twisted to give the typical shape of a K-file. The angle between the long-axis and the cutting blade is greater than in a reamer, and therefore preparation by a K-file is effective both in rotary and filing motion.
The tip of the instrument is cutting which makes the K-file best suited for the preparation of straight canals. Small K-files (ISO 06 – 15) can be also used in curved canals without the risk of ledging. Small K-files are particularly good for the initial preparation of very narrow canals.
K-file: Sizes & Codes
K-files are produced in sizes 06 – 140, all with a taper of 0.02. K-file design is identified by the square symbol on the handle.
K-file: Recommended use
The K-file is suited for the preparation of straight canals. It prepares dentin effectively both in filing motion (up and down) and when rotated. In slightly curved canals the recommended techniques are continuous rotation (lower picture) when the resistance is small and balanced force (upper picture) against greater resistance. Compared to reamers, the use of continuous rotation is limited because of the screwing effect typical of K-files.
K-file: Safety tips
K-files can be rotated only using moderate pressure. Use of force, particularly with smaller sized instruments may result in distortion of the helical structure and ultimately in fracture. Balanced force technique and filing instead of continuous rotation should be used with sizes 06 – 15 to minimize fracture risk. Each instrument should be checked for symmetry by rotating it against an even background before introducing it into the canal.
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