Aim: The current study was intended to compare the impact of various taper designs of different NiTi rotary instruments on the fracture resistance of endodontically treated mandibular molar teeth.
Materials and methods: 90 mature mesial roots with 13 mm length were collected from permanent mandibular molars after removal of its crowns and distal roots. All mesial roots were then embedded in self-cure acrylic resin blocks. Samples were randomly divided into control group and five groups (n = 16) at which the roots were prepared as follows: RaCe EVO #25/0.04, RaCe EVO 25/0.06, RaCe EVO 30/0.04, ProTaper Gold F2, and WaveOne Gold Primary file. Samples were obturated using single cone obturation technique. All specimens were subjected to an increasing compressive force applied perpendicularly to the roots. The forces required to induce vertical root fracture in the root samples were recorded and analyzed.
Results: One way ANOVA test revealed significant difference between the tested group regarding required force to fracture. Paire wise comparison with Tukey's postHOC test revealed that there were significant differences between control group and the tested groups except with 25/0.04 group (p=0.89). However, ProTaper Gold group demonstrated the least resistance in comparison with the test groups. there were no significant differences between 25/0.04, 25/0.06 30/0.04 groups, and WaveOne Gold.
Conclusion: Preparation of root canal using greater taper NiTi rotary files would affect root resistance toward fracture. However, it safer to consider constant taper instruments over progressive taper instruments during preparation of root canals.