Effectiveness of Nickel-Titanium Files for Retreatment of Molars Filled with Single-Cone Hydraulic Technique Using Bioceramic Sealers: An In Vitro Study

Recently single-cone hydraulic canal filling technique using bioceramic sealers brought a difficulty of retreatment due to the mechanical properties of the bioceramic sealers. This study assessed the effectiveness of four nickel-titanium rotary files in removing gutta-percha and bioceramic sealer from molar root canals in vitro. Eighty-eight root canals from extracted molars were instrumented with Vortex Blue rotary files and filled with gutta-percha and bioceramic sealer using a single-cone technique. After 30 days, the filled canals were randomly divided into four groups according to the file used for re-instrumentation: ProTaper Gold (PTG), Endo ReStart (ERS), XP-3D Shaper (XPD), and HyFlex Remover (HFR). The study assessed whether root canal filling material removal and patency were achieved within a 10-minute time frame, recording the time required in seconds. The rate of regaining patency and the time required to achieve patency were compared between groups using a generalized linear model. Scanning electron microscopy were used to evaluate the mechanical changes on the files. The patency rate of XPD and HFR was significantly higher than PTG. ERS and XPD demonstrated shorter patency times than HFR and significantly shorter patency times than PTG. SEM images revealed a varied range of reverse windings across file groups. PTG and ERS exhibited microcracks and fractured tips, while XPD and HFR did not display these mechanical alterations. The four file systems in this study displayed varying levels of effectiveness in the retreatment of root canals filled with bioceramic sealers.