A comparison between clinical operative torque and in vitro torsional resistance

Operative torque indicates the real-time stresses exerted on Nickel-Titanium Rotary Instruments (NTRs) during clinical application, whereas torsional resistance denotes a file’s maximum capacity to withstand torsional stresses prior to fracture. A comprehensive understanding of both parameters is essential for enhancing instrument safety and informing the development of next-generation rotary systems. Consequently, the present study aimed to evaluate the “in vivo” operative torque values of new NiTi rotary instruments (I-file, Henry Schein Endodontics, China) and to compare these with the in vitro torsional resistance of each instrument. Twenty instruments, representing the following sizes (i-File 25.07, I-Follow 15.04, and I-Finish 25.04), were selected and divided into two groups. The first group (n=10 for each size) was evaluated for torsional resistance in accordance with ISO Standard 3630-1. The second group involved instruments used clinically to prepare a molar case. Data were collected and subjected to statistical analysis. The results demonstrated statistically significant differences among the three files in both tests; however, their behavior was similar. No values exceeded the torsional strength, indicating a proper balance between the two properties. The findings of the study confirmed an ideal distribution of intracanal operative loading, with all instruments exhibiting operative torque values below the maximum torque at failure.