Influence of Fractured File Removal on Vertical Root Fracture Resistance

Fracturing instruments during endodontic treatments is a relatively common complication. The removal of fractured instruments is a technique-sensitive procedure necessary for adequate three-dimensional sealing of the root canal system and the success of the treatment. The quantity and quality of the remaining tooth tissues, the materials used, and the strength of bond between them have significant impact on the long-term survival of endodontically-treated teeth. Objectives: To investigate by means of 3D finite element analysis (3D-FEA) the influence of the removal of a fractured file on vertical root fracture resistance of an endodontically-treated canine tooth. Methods: An extracted human canine tooth was decoronated and scanned by micro-computed tomography (µ-CT, Skyscan, Belgium). 4mm F5 Protaper endodontic file (Dentsply, Switzerland) was deliberately fractured within the apical third of the root. Following the removal of the fractured file the root canal was obturated with gutta-percha (GP) and the scan repeated. Scans were imported by ScanIP (Simplware, UK) for 3D-reconstruction. Subsequently mesh generation was carried out in ScanFE (Simpleware, UK). The models were imported by Patran (MSCsoftware, USA) for pre and post-processing. FE analyses were carried out in Nastran (MSCsoftware, USA). Both models were subjected to 100N vertical occlusal loading.Materials were considered isotropic, elastic and homogeneous. Results: the results indicate that subsequent to the removal of the fractured file von Mises level increased (119MPa). The location of peak stresses was at the GP/dentine interface towards the coronal section prior to the file removal. Following the removal, peak stresses were concentrated towards the root/bone interface bucally. Root displacement was similar in both situations. Conclusions: This study indicated that fracture and subsequent removal of a file may be found to increase the risk of vertical root fracture in an endodontically-treated canine tooth, with the fracture most likely to be initiated in the buccolingual plane.