Impact of a modified kinematic on the fatigue life of reciprocating instruments

Aim To evaluate the impact of a modified kinematic on the fatigue life of the existing reciprocating instruments. Summary Cyclic fatigue of 80 nickel-titanium reciprocating instruments was tested by measuring the time to fracture in an artificial stainless steel canal with an angle of 90° and a 5-mm radius of curvature, using two different kinematics. Instruments were divided as follows: Group 1 (n=10) WaveOne Primary; Group 2 (n=10) WaveOne Gold Primary; Group 3 (n=10) Reciproc R25; Group 4 (n=10) Reciproc Blue R25. X-Smart Plus (Maillefer) endodontic motor was used respectively in “WaveOne All” or “Reciproc All” setting, according to manufacturer’s instruction. Other four groups of the same instruments (n=10) were tested using an innovative reciprocating kinematics (EVO) with different rotation angles and based on a sinusoidal acceleration, using a specific motor handpiece with a 4:1 contra-angle (CEFLA, Imola, Italy). The mean half-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. At a number of seconds corresponding to the mean half-life, 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%). Key Learning Points • The modified kinematic 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.