Summary: Results of root canal treatment may be influenced by presence of accessory root canals and apical ramifications. Root canals of 120 extracted teeth were treated by step-back technique. The canals were irrigated with 5% solution of NaOCl, physiological saline was used in the control group. The irrigation solutions were applied by an ultrasonic or syringe techniques. The shaped and cleaned root canals were split open and routinely prepared for SEM and TEM ivestigation. Apical ramifications in upper central incisors were found in 11.5%, in upper lateral incisors in 25%. The smear layer covered part of the root canal and its presence was dependent on the irrigant and application technique used. TEM study demonstrated that the smear layer covered openings of dentine tubules and the inner part of the smear layer penetrated into dentine tubules for a different distance. Obturation was not, however, complete and the smear layer did not close dentine tubules hermetically.

        Key words: accessory canals – dentine tubules – smear layer