Preventing rotary file separation: glide path, torque settings and when to retire a file

In short

Rotary files separate for two reasons: cyclic fatigue from rotating in a curve, and torsional overload when the tip binds while the shaft keeps turning. Prevent both with a glide path to working length before any rotary file, the motor speed and torque the file maker specifies, a light pecking motion with irrigation, heat-treated files in curved canals, and a firm limit on how many times a file is reused.

• Cyclic fatigue accumulates every rotation in a curved canal; the sharper the curve and the larger the file diameter, the fewer rotations to fracture.
• Torsional failure happens when the tip locks in dentine and the shaft twists beyond its elastic limit; a glide path and a torque-limited motor with auto-reverse are the defences.