The endodontic space forms the central part of the tooth and consists of a pulp chamber and one or more root canals. Root canal morphology is often extremely complicated and such as presents a major challenge in endodontic treatment. Vertucci described eight types of possible morphological variations of root canals that provide basic information about their number and possible merging or branching on their way from the bottom of the pulp chamber to the root apex. Nevertheless, according to recent researches of root canal system it has been established that its configration is much more complex. A prerequisite for any endodontic treatment is a thorough knowledge of the internal anatomy of each tooth, including the position of the pulp chamber, the number and the position of root canals, their cross-sectional shape and direction, but also possible variations that can be found in each tooth. Missed root canal is often the cause of a poor therapy outcome. Not recognizing a demanding anatomy can be the cause of many procedural errors during endodontic procedures. The success of endodontic treatment depends on efficient chemomechanical treatment and canal shaping, as well as on the complete three-dimensional filling by which this space is sealed. These procedures eliminate microorganisms as the main causes of pulp and periapical disease and prevent canal reinfection. Microorganisms inhabit not only the main root canal, but also hard-to-reach areas such as isthmuses, ramifications, dentinal tubules and recessions, which significantly complicates the efficient treatment of the canal. By adhering to effective protocols for cleaning these areas, the number of microorganisms is reduced below the critical level, whereas adequate filling to the apical stop and good coronary sealing prevents the influx of nutrients and their consequent survival and multiplication.