Influence of NiTi Wire Diameter on Cyclic and Torsional Fatigue Resistance of Different Heat-Treated Endodontic Instruments

Abstract

We compared the mechanical properties of 2Shape mini TS2 (Micro-Mega, Besançon, France) obtained from 1.0 diameter nickel-titanium (NiTi) wires and 2Shape TS2 from 1.2 diameter nickel-titanium (NiTi) wires differently thermally treated at room and body temperature. We used 120 NiTi TS2 1.0 and TS2 1.2 files made from controlled memory (CM) wire and T-wire (n = 10). Cyclic fatigue resistance was tested by recording the number of cycles to fracture (NCF) at room and body temperatures using a customized testing device. Maximum torque and angle of rotation at failure were recorded, according to ISO 3630-1. Data were analyzed by a two-way ANOVA (p < 0.05). The CM-wire files had significantly higher NCFs at both temperatures, independent of wire dimensions. Testing at body temperature negatively affected cyclic fatigue of all files. The 1.0-mm diameter T-wire instruments showed higher NCF than the 1.2-mm diameter, whereas no significant differences emerged between the two CM wires at either temperature. The maximum torque was not significantly different across files. The TS2 CM-wire files showed significantly higher angular rotation to fracture than T-wire files. The TS2 CM-wire prototypes showed higher cyclic fatigue resistance than T-wire prototypes, regardless of wire size, exhibiting suitable torsional properties. Torsional behavior appears to not be affected by NiTi wire size.

Cyclic fatigue resistance of different nickel‐titanium instruments in single and double curvature at room and body temperatures: A laboratory study

“…Comparing instruments with different dimensions, #20.05 files showed higher cyclic fatigue resistance than #25.06, in agreement with previous studies reporting that smaller instruments had high flexibility and fatigue resistance [33,34]. In particular, the HEDM #20.05 reported the highest values of cyclic fatigue resistance.…”

Impact of pecking amplitude on cyclic fatigue of new nickel–titanium files

“…Therefore, cyclic fatigue tests were conducted in an artificial stainless‐steel canal with the canal dimensions that have been used previously (La Rosa, Palermo, et al, 2021 ; Pedullà et al, 2018 ; Pedullà, Kharouf, et al, 2022 ). Furthermore, the customized apparatus guaranteed standardized laboratory conditions, permitting the reproducibility of the experiments carried out (La Rosa, Palermo, et al, 2021 ; La Rosa, Shumakova, 2021 ; Pedullà, Canova, et al, 2022 ; Pedullà, Kharouf, et al, 2022 ).…”

“…The #40/0.03 and #45/0.03 files probably benefit less from this advantage because of their larger size, which negatively impacts their cyclic fatigue behavior. Indeed, the cyclic fatigue is negatively affected by the diameter of the instruments at the point of maximum curvature (Pedullà, Canova, et al, 2022 ). This mechanism occurs because all of its points (except those in the center axis) are subjected to stress/compression cycles during the instrument's rotation.…”

“…In addition, the differences between static and dynamic tests seem to be significantly more for the smaller‐size instruments (i.e., #10/0.035, #17.5/0.045, and #25/0.05). This could be due to the lower metal mass at the maximum stress point, which increased their cyclic fatigue resistance by allowing them to rotate for more cycles before fracturing (Pedullà, Canova, et al, 2022 ).…”

“…Cyclic fatigue tests were carried out using a customized device (La Rosa, Palermo, et al, 2021 ; La Rosa, Shumakova, et al, 2021 ; Pedullà, Canova, et al, 2022 ; Pedullà, Kharouf, et al, 2022 ), upgraded with a moving stage to perform dynamic tests. Standardized positioning of each file within the artificial canal was enabled by a fixed platform block in which the electric handpiece was placed.…”