The main objective of endodontic treatment is the prevention of infection of the endodontium and the elimination of already existing infection. Witzel established as early as 1879 that the reason for a failed endodontic procedure is mainly the presence of bacteria. The foundation of endodontics has therefore always been to ensure that the canal system is free from bacteria. The modern cornerstones of endodontics are based on this foundation: an optimal view of the inner aspects of the tooth by magnification and light, preparation using nickel-titanium instruments, disinfection using efficient activation techniques and as dense filling as possible of all cavities of the canal system as well as adhesive coronal sealing.