Fracture Resistance of ProTaper UltimateTM Files Under Simulated Clinical Conditions

The objective of this study is to compare Torsional Force to Fracture (TFF) of ProTaper UltimateTM (PTU) Nickel-Titanium (NiTi) rotary instruments in as-received condition, after 1 and 3 simulated clinical uses in Endo-training blocs (ETB) and 3D printed teeth (3DT), respectively. Materials and Methods: A total of 5 sets of PTU NiTi files were used in simulated root canals (30-degree curvature) in ETB and 3DT per manufacturer instructions. File sets consisted of Slider (SL), Shaper (SH), F1, F2 and F3 files 25mm in length (N=5/size/group). Later, the mechanical properties of the files were evaluated according to ISO 3630-1 guidelines using a Torsiometer. (Sabri Dental Enterprises, Inc, Downers Grove, IL). For each tested file, measurements of peak torque (gm-cm) and angle rotation (°) were documented. The collected data was subjected to analysis using ANOVA and Tukey-Kramer tests (p<.05). Results: Peak torque was significantly lower after instrumentation of ETB compared to 3DT for SL and SH files (p<.05). There were no statistically significant differences in TFF in all simulated clinical conditions for F1, F2 and F3 files. For all files in all simulated clinical conditions, no statistically significant changes were observed in angle rotation. Conclusions: TFF of PTU NiTi rotary files decreased after use in ETB compared to 3DT. Within the limitations of this study, these findings may indicate a greater role of clinical conditions such as canal curvature and hardness rather than the number of uses (within 3 times).