Objective: The recently introduced Vector system is recommended to be used in conjunction with a polishing fluid containing hydroxylapatite granules ( 10 µm). The aim of the present study was to assess morphologic alterations of the root surface after ultrasonic treatment with the polishing fluid. Method and Materials: Cementum of 30 freshly extracted human teeth was removed to a level of 4 mm below the cementoenamel junction. Surfaces were root-planed and conditioned with citric acid to remove the smear layer. Teeth were divided into 5 groups, with group 1 as the untreated control. Group 2 was solely treated with the ultrasonic system. In group 3, the ultrasonic system was used in conjunction with the polishing fluid. Group 4 was treated with a medium-hard toothbrush and the polishing fluid. Group 5 was treated only with the toothbrush. Specimens were evaluated by both light and scanning electron microscopy. Results: Dentinal tubules were not covered by a smear layer in the control group, whereas in group 2, a smear layer could be observed in some specimens. In group 3 dentinal tubules were always covered by a layer consisting of granules of about 2 µm. In group 4 all samples showed a layer containing granules of about 5 µm, and in group 5 a thin smear layer could be observed. Conclusion: The use of a polishing fluid containing hydroxylapatite granules during treatment of the root surface results in a granular layer covering the dentinal tubules. This layer may reduce hypersensitivity after ultrasonic subgingival scaling. Keywords: hydroxylapatite, hypersensitivity, smear layer, toothbrush, ultrasonic periodontal treatment, Vector system