Objective: To determine the presence of certain bacterial species and their numbers in necrotic root canals in three treatment phases: pre-shaping, post-shaping and after placing calcium hydroxide into root canals. Subject and method: 13 teeth diagnosed with pulp necrosis were treated and taken samples at Hanoi Central Hospital of Dentistry and No.108 Military Central Hospital during period from 11/2011 to 08/2014. Calcium hydroxide was placed in the root canal 7 days for disinfection before sealing the root canal system. Tests for bacteria were performed before treatment (51 phase)
After shaping and irrigating of the canals (52 phase)
After placing antiseptic drug into canals (53 phase). This was an uncontrolled, interventional studies. Result and conclucion: Species appeared most frequently in each treatment phase were as follow: Veillonella sp (84.6 percent), S.oralis, M.micros (61.5 percent) in 51 phase
S.oralis, S.sanguinis (38.5 percent), S.mitis, Veillonella sp (30.8 percent) in 52 phase
and S.sanguinis (30.8 percent) in 53 phase. Species had the highest average number of bacteria in positive samples in each treatment phase were: S.sanguinis ( 1.6 x 105 CFU/ml) in 51 phase
Prevotella oralis, E.faecalis, M.micros, S.oralis ( 1 x 105 CFU/ml) in 52 phase
and S.sanguinis (2 x 104 CFU/ml) in 53 phase.