The fracture of endodontic instruments during root canal treatment is a complication every endodontist must have to deal with. The reported frequency rate for fractured instruments varies from 0.7% to 6% of cases. Stainless steel instrument fracture can be prevented mostly by discarding instruments that show signs of metal fatigue however, NiTi instrument separation can happen without any sign of fatigue. The single use of rotary NiTi instruments reduces the chance of breakage to 0.9% but does not prevent the chance of fracture entirely. Common reasons for fracture of rotary NiTi files are flexural and/or torsional fatigue. Unfortunately, it is theoretically impossible to create nonbreaking instruments because of the fact that more flexible instruments, that are more resistant to cyclic fatigue, have been assumed to be less resistant to torsional load and vice versa.
The common approach for dealing with a broken instrument is its removal. The use of an operative microscope to facilitate canal widening to the level of the broken fragment and its removal by ultrasonic tips and/or some type of grasping equipment is accepted worldwide.
The rate of successful fragment removal is high but can it be defined as endodontic treatment success? Immediate untoward results of dentin removal may be perforation or strip perforation at the danger zone. Removal of healthy dentin and especially peri-cervical dentin decreases root strength and can predispose the root to vertical root fracture.The first principle of medicine is do not hurt your patient, please remember it. The goal of endodontics is to treat or prevent apical periodontitis. The most common cause of periapical lesions is intra-radicular infection. A broken file by itself does not induce inflammation. We often see teeth with fractured instruments that were treated many years ago and have no clinical or radiologic signs of periapical inflammation. Periapical healing takes place if during endodontic treatment disinfection decreases microbial load beneath the specific threshold. Nowadays, total sterilization of canals is still a utopic goal. If the broken instrument prevents effective disinfection and the apical lesion does not heal or a new lesion is developed, apical surgery can be used without sacrificing peri-cervical dentin.
Successful removal of fractured instruments may risk the long-term outcome of the tooth by sacrificing sound peri-cervical dentin, which may lead to perforations and predispose the tooth to vertical root fracture. The clinician should consider the micro-biological and biomechanical aspects during clinical decision making.
