there are things that can kill some of the bacteria in root canals, but those bacteria have to be removed from the cavity. the souce of the bacteria cannot be removed unless the tooth itself is removed. as far as abcesses, they do not reverse is the general of thumb. i have heard of people saying they had an abcess and did various things and they don't have them any longer, but i cannot comment on that because i have not seen any actual cases and go with what i have been taught and have experienced.