There is a variety of protocols for rotary root canal instrumentation. Frustration of rotary file separation can be avoided by proper training for mastering instrumentation and improving operator competence through learning and experience .

Various studies around the globe has reported that the most important factor the rotary instrument seperation was the operator. This is probably attributed to their clinical skills or their decision either to use instruments for a specific number of times or until defects were evident.

Another important factor for rotary instrument seperation is the root canal morphology. M ore complicated the root canal morphology, the greater the risk of dental endodontic instruments breakage. A higher prevalence of rotary instrument separation has been reported in molars particularly in the mesial roots of mandibular molars.

Further, the risk of instrument seperation in the apical third of the canal is higher when compared with coronal and middle thirds. Rotary files undergo greater fatigue as the curvature increases and the contact surface with the dentinal walls is greater since most curved canals are narrow. Clinically, fatigue of an instrument may be related to the degree of instrument flexure when placed in a curved root canal. When the curvature of canals is pronounced, the cyclical fatigue of the instrument is greater and thus its life expectancy is lower.

The parameters of the angle and the radius of curvature are independent in such a way that even if two canals have the same angle of curvature they may have different radii of curvature, which indicates that some curves are sharper than others.

Therefore , the radius of canal curvature is more important than the curvature angle itself. Further, the rate of file separation increases as the radius of curvature decreases. When several variables, including those related to root canal anatomy, are considered, the radius of curvature is the most significant factor in rotary file seperation.

As a result, their resistance to defect formation and fracture differ.Cross-sectional shape determines the bulk of the file and the contact area between the file and dentinal walls, as well as its cutting efficiency. The greater the area of file contacting the dentinal walls, the greater the quantity of cut dentine. Consequently there is greater friction and a fatiguedrotary file has a reduced life span.

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