Torsional behaviour of rotary NiTi ProTaper Universal instruments after multiple clinical use.

AIM: To assess the influence of multiple clinical uses on the torsional behaviour of ProTaper Universal rotary NiTi instruments. METHODOLOGY: Root canal treatments were performed on patients using the ProTaper Universal rotary system to prepare canals. Ten sets of instruments were used by an experienced endodontist, each set being used in five molar teeth. After clinical use, S1, S2, F1 and F2 instruments were analysed for damage by optical and scanning electron microscopy. The used sets, along with a control group of 10 sets of new instruments, were then torsion tested based on the ISO 3630-1 specification. Data obtained were subjected to a one-way analysis of variance (anova) with alpha = 0.05. RESULTS: The use of the ProTaper Universal rotary instruments by an experienced endodontist allowed for the cleaning and shaping of the root canal system of five molar teeth without fracture. The maximum torque for instruments S2, F1 and F2, and the angular deflection at fracture for instruments S2 and F1 were significantly lower following clinical use. The largest decrease in maximum torque was 18.6% (P = 0.014) for S2 instruments. The same maximum percent decrease was found for angular deflection at fracture for F1 instruments (P = 0.009). CONCLUSIONS: Torsional resistance and angular deflection of used instruments, as compared to that of new instruments, were reduced following clinical use.