Cyclic fatigue resistance of Nickel-Titanium reciprocating instruments tested with an innovative kinematics

Aim: To evaluate cyclic fatigue resistance of different Nickel-Titanium instruments tested with an innovative reciprocating kinematics. Methodology: Eighty Nickel-Titanium reciprocating instruments were tested in cyclic fatigue resistance: WaveOne Primary (n = 20), WaveOne Gold Primary (n = 20), Reciproc R25 (n = 20) and Reciproc Blue R25 (n = 20). The cyclic fatigue of each brand was measured with two different motors and kinematics settings: (1) X-Smart Plus (Denstply Maillefer) used in ‘‘WaveOne All’’ or ‘‘Reciproc All’’ setting, according to manufacturer’s instruction; (2) a 4:1 contra-angle (Cefla, Imola, Italy) with an experimental kinematics (Goldspeed EVOE4 — Cefla, Italy) (EVO) with different rotation angles and based on a sinusoidal acceleration. The time to fracture in an artificial stainless-steel canal (908 angle and a 5-mm radius of curvature) was digitally recorded. Mean life, beta (failure rate) and eta (characteristic life i.e. the number of seconds at which 63.2% of the product has failed) were calculated for each group and compared with Weibull analysis. Results: InstrumentstestedwiththekinematicsEVOpresentedhighervaluesofetainallgroups. Reciproc Blue showed the highest eta value (233.05) and Wave One Gold the lower failure probability (46.98%). Wave One instruments showed similar fatigue resistance when tested with EVO or X-Smart. Conclusion: Tested kinematics with different angles and based on sinusoidal reciprocating acceleration had a positive impact on fatigue lifetime of reciprocating instruments. Present findings suggest the possibility of future improvements in the clinical use of reciprocating files.