In case of inflammation or infection of the tooth pulp, root treatment is required. The cause of infections or inflammations may be dental caries, dental tissue damage, or a dental intervention itself. The microorganism associated with unsuccessful endodontic treatments is Enterococcus faecalis, which is considered one of the most resistant bacteria against antimicrobial agents and other methods of bacteria removal. It can survive extreme conditions due to its significant growth range which also contributes to high resistance of the bacterium. This thesis tests the probiotic strain Enterococcus faecalis Symbioflor 1, which also shows significant growth range and antimicrobial resistance. Optimal physico-chemical conditions for the growth of the strain in the planktonic form were tested and the biofilm growth on various surfaces (regular glass slide, plexiglass slide, model of a tooth canal, dentine) was monitored. The effectiveness of the 5 % sodium hypochlorite solution in removing the biofilm was also examined. The results demonstrated successful formation and growth of the biofilms on all test surfaces. It was discovered that washing with the sodium hypochlorite solution removes most of the cells and even alters the mechanical properties of the dentine. Washing was equally effective on other surfaces, except on the regular slide where defects were present.