Instrument fractures - Prophylaxis

All instruments must be used with a correct technique and with little force. For example, Hedstroem files unpredictably break when used in a rotary motion against resistance, while proper use in filing motion with the instrument passively placed in the canal hardly ever results in fracture. Instruments typically fracture in obliterated/narrow canals. When too large instruments are used early (e.g. #15 in canal requiring #08), the force applied to the instrument is often too high resulting in fracture.
The first years experiences with rotary (mechanical) nickel-titanium instruments, used at speeds of 150 to 1200 rpm depending on the type of instrument, indicate that they may have a greater risk for fracture than most instruments in manual preparation. Use of excessive force and using instruments in more than the recommended number of teeth are probably the most common reasons for fracture. This emphasises the importance of correct use of each technique.