Abstract: PURPOSE: To evaluate the effect of continuous flushing out of the canal on fluid exchange in the root canal during mechanical preparation. METHODS: Sixty resin blocks with standardized root canals were divided into 5 experimental groups according to whether continuous flushing was performed during mechanical preparation. Injecting pure black ink into the root canals before each file preparation,the liquid exchange was calculated by measuring the absorbance value of the remaining liquid after performing different preparation and irrigation schemes. Meanwhile, computational fluid dynamics model was established which simulated the flow field in the canal when the file moved up-and-down. SPSS 19.0 software package was used for statistical analysis of the data. RESULTS: The absorbance value of the remaining fluid in the root canal of the three groups in which continuous flushing was performed during mechanical preparation differed significantly from the group without continuous flushing(P<0.05), but no significant difference among the three groups (P>0.05). Computer simulation confirmed that the “efficient regurgitation area” existed in the middle part of the root canal and fluid could be gradually transported to the apical area by the file's up-and-down motion. CONCLUSIONS: Continuous flushing out of the canal during mechanical preparation can replace the original solution in the canal partly, which is beneficial to conventional irrigation for cleaning of the root canal.

Key words: Continuous flushing out of the canal, Nickel titanium instrument, Computational fluid dynamics, Fluid replacement