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Study on the Effect and Mechanism of Synchronous Irrigation on the Cyclic Fatigue Resistance of Dental Rotary NiTi
Xinyu Fang1, Haixia Li2, Yuxian Cao3
1Department of Stomatology, the Fourth Medical Centre of PLA General Hospital, Beijing, China.
Objective:
To investigate the effect of synchronous irrigation on the cyclic fatigue resistance of rotary NiTi instruments, and to analyse the mechanism of their cyclic fatigue resistance through microtopography and phase transformation analyses.
Method:
Ten types of NiTi instruments-Protaper Universal F1 (PTU F1), Protaper Gold F1 (PTG F1), WaveOne (WO), WaveOne Gold (WOG), Reciproc (RPC), Reciproc Blue (RPCB), TF, TFA, HyFlex CM (HCM), HyFlex EDM (HEDM)-were used. 24 of each type were randomly divided into two groups (n = 12): irrigation group (synchronous irrigation on the instrument body during root canal preparation) and control group (non-irrigation). Dynamic cyclic fatigue testing was done in a metal-bending root canal model to record Time to fracture (TtF). Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used for fracture mechanism investigation.
Result:
The TtF of the same NiTi instrument in the irrigation group increased by 22% to 126% compared with that of the non-irrigation group (P < .01). SEM showed that the number of axial cracks and the maximum extension area ratio of the NiTi instrument in the irrigation group were significantly higher than that of the non-irrigation group (P < .05). Phase analysis showed that at 24°C, the matrix phase of PTU F1, TF and TFA was mainly austenite, while the other NiTi instruments were composed of mixed phases of R-phase, austenite and a small amount of martensite.
Conclusions:
Synchronous irrigation during root canal preparation can improve the dynamic cyclic fatigue performance of NiTi instruments by 22% to 126% and enhance the efficiency of root canal treatment. It functions by retarding the initiation and propagation of fatigue cracks and regulating phase composition through thermodynamic effects.
