![]() Files that separate higher up on the shank, such as 5 to 6 mm are the result of cyclic fatigue. It has been our experience that rotary files that separate in the apical 1 to 3 mm are usually the result of excessive torque. The only way to monitor cyclic fatigue is to discard an instrument after it has been used in a troublesome canal or tooth. Cyclic fatigue accumulates to a point where the next bend will separate the instrument. It is a result of a repetitive bending motion, similar to bending a clothes hanger. Cyclic fatigue, on the other hand, cannot be seen. Naturally, when we see this, we immediately discard the instrument. We actually can see excessive torque as an unwinding of a rotary file. ![]() Torque is a result of a twisting motion, similar to twisting a pencil in opposite directions. The most common factors that can result in file separation are excessive force (torque) and the build-up of cyclic fatigue (metal fatigue). 1) Understanding torque and cyclic fatigue The following discussion points are tips that we believe will help you to minimize the separation of any rotary file. ![]() While we may never be able to totally eliminate separation, the key to minimizing separation is to understand what causes it. Excellent though they may be, there is always the possibility of an unpredicted separation. Their introduction is perhaps one of the great technological advances in the recent history of dental medicine. The past 15 years has seen the acceptance of nickel titanium rotary files to perform endodontic procedures. ![]() By Kenneth Koch, DMD, and Dennis Brave, DDS ![]()
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