Endodontic instrument fracture during root canal treatment occurs in 2% to 5% of cases. Removal of instrument fragments in infected root canals or the coronal third of canals should be attempted if they cannot be successfully bypassed, because resultant persistent periapi-cal infection and additional surgi-cal treatment can increase patient morbidity and raise treatment costs. The American Association of Endodontists and the American Academy of Oral and Maxillofacial Radiology recommend cone beam computed tomography use to assess separated endodontic instruments.

Empirical risk evaluation may be established with 2-dimensional (2D) periapical radiography, used to evalu­ate major factors affecting the retrieval of separated instruments, such as the angle of canal curvature, the depth of the fragment and the fragment posi­tion relative to the curvature of the canal. Only the radius of the canal curvature cannot be measured using a 2D modality.

Tordai et al from the University of Pécs, Hungary, conducted an in vivo study to evaluate the value of periapical radiographs taken during treatment of separated endodontic instruments to assess preoperative case difficulty and predict instrument removal success. They studied results in 115 patients (123 instruments in 120 root canals in 115 teeth) treated between March 2005 and March 2015. Before treatment, teeth were assessed for the type of tooth and root canal; site of the fragment in the root canal and in relation to the root canal curvature; type and length of the fragment; degree of root canal curvature; and radius of the root canal.

Fragments were removed using a microsonic technique. After the canal was enlarged coronally to the broken fragment, ultrasonic K-files mounted in a piezoelectric scaler were used to trephine around the obstruction. Successful cases saw complete removal of the fragment without perforation of the root canal.

Of the 123 fractured instruments, 97 fragments were removed. Three variables had a statistically significant impact on removal success:

  • site of fragment in relation to the root canal curvature
  • angle of the root canal curvature measured with the Schneider technique
  • angle of the root canal curvature measured with the canal access angle technique

No variables were statistically associated with the failed cases. Root canal fillings with an ideal taper had significantly better outcomes with respect to obturation length.


Microsonic removal successfully retrieved and removed fragments of separated instruments. Perioperative radiographs can help evaluate the potential for treatment success but cannot precisely predict outcomes.

Tordai B, Schreindorfer K, Lempel E, Krajczár K. Factors affecting ultrasonic removal of separated endodontic instruments: a retrospective clinical study. Quintessence Int 2018;49:257-266.