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 (90° 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

Instruments tested with the kinematics EVO presented higher values of eta in all groups. 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.