The study was aimed to conduct a morphological assessment of the influence exerted by a certain method of activation of endodontic rinsing liquid on the root dentin structure and canal cleaning effectiveness in an ex vivo experiment. The study was performed on 20 single-rooted teeth removed due to complicated caries in people aged 25—44 years. A devised method of vacuum-jet irrigation was used to carry out the final antiseptic treatment and to activate a rinsing liquid in the group No. 1 (n=10), and an endodontic syringe with ultrasonic activation was used in the group No. 2 (n=10). Optical and scanning electron microscopy data were used to assess dentin histostructure, presence or absence of organic inclusions in the root canal lumens, quality of preparation and contour lines of their sides. An analysis of scans demonstrates that the vacuum-jet irrigation method effectively cleans the root canal lumen in the apical area in 90% of the cases, while irrigation with an endodontic syringe and ultrasound activation has been effective in 67% of the cases. The smear layer throughout the root canals in the samples of the group No. 1 was removed in 100% of the cases. At the same time, the smear layer in the canal apical area was not completely removed in either of the samples of the group No. 2. An analysis of photomicrographs of histotopographic cross sections of the dental roots in group No. 2 under consideration revealed numerous cavities in the circumpulpal dentin, which form nidi of destruction up to 10—15 mcr in diameter merging in the cervical and middle third of the root. At the same time, a typical structure of the circumpulpal dentin with a well-developed network of dentinal tubules and intact peritubular and intertubular matrix was observed throughout the dental roots in the samples of the group No. 1. These investigational studies allow us to conclude that vacuum-jet irrigation of root canals provides better cleaning, completely removes the smear layer and does not damage the root dentin structure.