Impact of Root Canal Taper on Fracture Resistance of Endodontically Treated Teeth Prepared by Hero Shaper and RaCe File Systems: An In-vitro Study

Introduction: Tooth fracture is one of the most undesirable phenomena in Endodontically Treated Teeth (ETT) and usually leads to tooth extraction. Basically, removal of any hard tissue from the canal walls raises the chance of root fracture. Aim: To evaluate the impact of root canal taper on fracture resistance of ETT prepared by two different file systems (Hero Shaper and RaCe file systems). Materials and Methods: This in-vitro study was conducted in the Department of Conservative Dentistry and Endodontics at Bharati Vidyapeeth (Deemed to be University) Dental College and Hospital, Sangli and Praj Metallurgical Laboratory Pune, Maharashtra, India, frome February 2021 to November 2021. The study included 44 freshly extracted mandibular premolar teeth were randomly divided into four groups. Group 1a had Hero Shaper 4%, group 1b had 6% Hero Shaper, group 2a had RaCe 4% and group 2b had RaCe 6% file system. After cleaning and shaping the root canals, obturation was completed using cold lateral compaction and root canals were embedded in standardised autopolymerising acrylic resin blocks, subjected to a vertical load in universal testing machine to cause vertical root fracture. The forces required to induce fractures were measured in Newtons. Data was analysed by using independent t-test and two-way Analysis of Variance (ANOVA) test for intergroup comparison. A p-value <= 0.05 was considered as statistically significant. Results: Among instrumented groups, group 1a (Hero Shaper 4%) showed higher fracture resistance of 372.5 Newtons and group 2b (RaCe 6%) showed lowest fracture resistance of 314.56 Newtons as compared to other groups. Statistically significant difference (p-value=0.026) was seen in the mean fracture resistance among the group 1a and 1b, and group 2a and 2b. At pair wise comparison there was statistically significant difference in group 1a and group 2a (p-value=0.016). Conclusion: Amongst the instrumented groups, Hero Shaper file system showed the higher fracture resistance, than RaCe file system. Marked reduction in fracture resistance of ETT was seen with the use of greater taper instruments.