Guidelines for the prevention of fracture of root canal instruments

Abstract

1. Stainless steel reamers and files are preferable to carbon steel instruments because, while they may bend under excessive torque, they are less likely to break. 2. Root canal instruments should be examined both before and after use to make certain that the blades are regularly aligned. Too little or too much space between the blades is an indication that the instrument has been under strain and may break. 3. The smaller sizes of reamers and files (Nos. 10 to 30) should not be used more than twice (that is, instrumentation for more than two root canals). Rubber stops of different colors attached to the instrument are a convenient means of indicating how many times it has been used. 4. Dull instruments are likely to become lodged against dentine instead of cutting, and this promotes the chances of breakage. 5. Files break more often from the torque used in gaining a purchase on the dentine than from the act of filing against dentine. The degree of torque applied should be minimal. 6. Reamers should be twirled back and forth between the thumb and fingers, never exceeding a 180 degree are. 7. Instruments should be used in sequence of sizes, without ever skipping a size. 8. Because of the slight difference in diameter between a reamer and a file of a given size, both types of instrument should be used in narrow canals. Smaller stepwise increments in width will accrue than if either reamers or files alone are used, thus minimizing breakage of instruments. 9. Debris should be removed between the blades from time to time while one is operating with the same instrument in the root canal, as the accumulated debris retards cutting and so predisposes the instrument to breakage. 10. All root canal instruments should be used in a wet canal, preferably one which has been flooded with sodium hypochlorite, to facilitate cutting and thereby prevent breakage. 11. Chemical agents should be used along with instrumentation when necessary to facilitate cutting of dentine. 12. Where an instrument has been broken in the root canal, the prognosis is more favorable if an area of rarefaction is not present at the time of the accident.