We evaluated the influence of manual preflaring and torque on the failure rate of rotary nickel-titanium ProTaper instruments Shaping 1 (S1), Shaping 2 (S2), Finishing 1 (F1), and Finishing 2 (F2). These factors were evaluated using an in vitro method by calculating the mean number of Endo-Training-Blocks shaped before file breakage under different conditions. Group A (S1 on simulators with no preflaring) shaped 10 blocks before failure, group B (S1 on manually preflared simulators) shaped 59 blocks (p<0.01 versus group A), group C (S2 with low torque) shaped 28 blocks, group D (S2 with high torque) shaped 48 blocks (p<0.01 versus group C), group E (F1 with low torque) shaped eight blocks, group F (F1 with high torque) shaped 23 blocks (p<0.01 versus group E), group G (F2 with low torque) shaped four blocks, and group H (F2 with high torque) shaped 11 blocks (p<0.01 versus group G). Manual preflaring creates a glide path for the instrument tip and is a major determinant in reducing the failure rate of these rotary nickel-titanium files. All instruments worked better at high torque.

During root canal instrumentation, nickel-titanium rotary instruments are subjected to continual stresses inside the canal due to its anatomy and the hardness of the dentin they must cut. They must therefore be both stress-resistant and elastic. This study aimed to compare the mechanical behavior of two nickel-titanium rotary instruments (ProTaper and ProFile) by applying the finite element analysis method to produce a numerical evaluation. The nonlinear mechanical behavior of the alloy was taken into account during the study. The distribution of stresses due to torsional and bending moments was compared in the two experimental models. The ProFile model was found to be more elastic than the ProTaper model. Under equal loads, the ProTaper model showed lower and better distributed stresses than the ProFile model.