The aims of this retrospective analysis are (1) to evaluate the success rate of a non-surgical retreatment of teeth with broken file instrument into the canal using ultrasounds, microscope and a modified spinal needle, (2) to assess the outcome of the treatment if the remaining fragment was left, bypassed or removed from the root canal in terms of survival rate of the treated teeth after a 5-years follow up period.

The fracture of an endodontic instrument is a frustrating phenomenon, both for practitioners and patients, that can compromise the cleaning and shaping procedures of the root canal treatment, with a potential impact on the treatment outcome. In the past decades, the advent of rotary nickel titanium instruments resulted in an increased incidence of instrument separation.

Two mechanisms have been reported in order to describe the fracture of an endodontic instrument inside the root canal: torsional stress and cyclic fatigue. Cyclic failure is due to the constant tension and compression which insists on the file when it shapes the maximal root canal curvature area. Torsional failure occurs when the tip of the instrument locks on the wall of the root canal while the shafts keeps rotating, and the torque exceeds the plastic limit of the metal.

Several studies focused on causes and factors influencing the weakening of endodontic instrument after clinical use, and some recommendation were given trying to minimized the risk of instruments breakage. Nevertheless, this problem can still occur, even to an experienced operator, making the achievement of a correct and predictable root canal final treatment uncertain.

Due to their complexity, many of these cases are approached by extraction and implant replacement of the so evaluated "hopeless" tooth. Treatment decisions can vary widely among dentists and dental specialists and may be based more on personal values and experience than an objective analysis of treatment benefits, risks, costs, prognosis, and alternatives.

At present, there is no standardized procedure for safe and consistently successful instrument fragment removal in the dental literature.

Different devices, techniques, methods, and protocols used for removal of separated instruments are described in literature. Unfortunately, there is a lack of high-level evidence, since most of the papers refer to clinical case report.

Until the beginning of endodontics, dentists have had to face this problem and already in the last century Masserann invented an instrument to remove obstacles in the root canals. Some authors believe that Masserann instrument used by expert hands does not expose the tooth to the root fracture, but this risk remains very high. Several other instruments were invented as a result, many of them similar to the Masserann extractor, others using micro tweezers or cyanoacrylate glue.

To solve the problem of root canal obstruction due to fragments of root canal instruments, some authors make use of the technique of intentional reimplantation after retreatment of the tooth out of the mouth. Recently, some authors have also used the Nd: YAG laser to remove broken instruments in the canals. Laser energy has been used to melt the solder, connecting the separated instrument with the brass tube.

Furthermore, the literature is not clear about the actual need to remove the instruments from the root canals, neither about the percentage of successes in case of bypassing the fragment or about the persistence of the instrument in the root canal.

Independently from the technique, the optimal management of instrument fragments during root canal treatment is crucial in order to enable sufficient debridement and obturation of the root canal system. However, all clinicians agree that the best help in this procedure came by the combined use of ultrasound and the operative microscope. These two devices used in combination allow a more efficient and accurate work, lowering the risk of weakening the canal wall or create root perforations.

The aims of this retrospective analysis are (1) to evaluate the success rate of a non-surgical retreatment of teeth with broken file instrument into the canal using ultrasounds, microscope and a modified spinal needle, (2) to assess the outcome of the treatment if the remaining fragment was left, bypassed or removed from the root canal in terms of survival rate of the treated teeth after a 5-years follow up period.

Inclusion Criteria:

All patients who received an endodontic retreatment due to a separated instrument inside a root canal were included in this study.

Exclusion Criteria:

Exclusion criteria were unavailability of complete clinical data or the use of other retreatment techniques.

All patients needing an endodontic retreatment due to a separated instrument inside a root canal.