Effects Of Different Flushing Liquids On Root Canal Preparation Capacity Of Rotary Ni-Ti Instrument

Background: In recent years, the instruments of root canal preparation has been greatly developed. Different materials and design of instruments continue to emerge, of which the nickel-titanium root canal instrument is the most representative. It has the advantages of large taper, superelasticity, abrasion resistance, excellent flexibility and superior memory performance. It can not only reduce the deviation and the step formation in the preparation of curved root canal, but also can make a root canal shape easier to irrigate and fill in,improve the efficiency of preparation significantly. However, nickel-titanium instrument also has its unavoidable shortcomings. It is more likely to break compared to traditional manual stainless steel instrument.Objective: By studying the number of prepared root canals and the preparation efficiency when rotary Ni-Ti instrument is flushed with different liquids, to find out the most effective way to improve its root canal preparation capacity.Methods: Eighy rotary Ni-Ti files, ProTaper Universal (PTU) F1, were divided into four groups randomly, with 20 files in each group: water group, saline group, 1% sodium hypochlorite group and 5% sodium hypochlorite group. The files were used to prepare the root canals in the simulated curved root canal resin module, and, continuously flushed with the punching machine of different liquids during the preparatory process. The number of prepared root canals for each file, the total times of pull before broken, and the times of pull required to complete each root canal were record. The differences between groups were compared.Results: The number (x±s) of prepared root canals for each file under four different flushing conditions: water group(7.13±3.48),saline group(6.24±1.76),1% sodium hypochlorite group(6.88±3.20) and 5% sodium hypochlorite group(4.31±2.34). The statistical results showed that 5% sodium hypochlorite group were statistically different from the other three groups (P <0.05). There were no statistically significant differences among the other three groups. Comparison of the number of prepared root canals in the four groups: water group ≈ saline group ≈ 1% sodium hypochlorite group > 5% sodium hypochlorite group.The times(x±s) of pull required to complete each root canal under four different flushing conditions: water group(17.98± 1.70),saline group(17.85±0.73),1% sodium hypochlorite group(17.47±1.10) and 5% sodium hypochlorite group(18.31 ± 1.44). There was no significant difference between the four groups by ANOVA (P> 0.05).Conclusion: Among four different flushing liquids,water,saline and 1% sodium hypochlorite are more conducive to increase the number of prepared root canals for each rotary Ni-Ti file than 5% sodium hypochlorite, but the times of pull required to complete each root canal are similar in the four groups. Taking into account the economic,environmental and other factors, water is the most conducive flushing liquid to improve the rotary Ni-Ti file root canal preparation capacity.