Abstract: Objective: To evaluate the effect of positive pressure irrigation on the clearance rate of bacterial infection during the root canal preparation using nickel titanium file, as well as pain rates after operation, to provide a new method for improving the effect of root canal treatment. Method: 80 cases of single root canal with chronic periapical periodontitis were collected and randomly divided into two groups according to with or without positive pressure irrigation during nickel titanium files preparation. The root canals were instrumental with M3 system using crown-down technique. Before and after root canal preparation, samples were taken and cultured under anaerobic condition for 48h to compare the number of colonies. The pain rates after operation were recorded. Results: Compared to the unprepared root canal, the number of bacterial colony was significantly decreased after root canal preparation (P < 0.05). The clearance rate of bacterial infection was significantly increased in the group with positive pressure irrigation compared to the group without positive pressure irrigation (P < 0.05). The 24h pain rate was statistically decreased in the group with positive pressure irrigation compared to the group without positive pressure irrigation (P < 0.05). Conclusions: Root canal preparation with positive pressure irrigation can reduce the bacterial infection in the root canal as well as pain rates after operation.

Key words: Four-handed operation, Positive pressure flushing, Root canal preparation, Nickel titanium file