Objectives. To evaluate the cytotoxicity of Shellac F, a new fluoride varnish, and its effects on human dentin hydraulic conductance. Methods. Shellac F was compared to another fluoride varnish (Duraphat ®) and a fluoride containing desensitizing agent (Isodan ®). The cytotoxicity test was performed on human gingival fibroblasts and through dentin slice on human pulp fibroblasts. The hydraulic conductance (Lp) was recorded by fluid filtration with a Flodec device under a constant pressure (15 cm H 2 O). The treated surface of the dentin disks and their sections were also investigated with SEM. Results. The cytotoxicity test on gingival fibroblasts revealed that Duraphat ® was the least cytotoxic material, followed by Shellac F then Isodan ®. With dentin slice interposition, a lower level of cytotoxicity was obtained. All of them showed a lower cytotoxicity decreasing on further dilutions (p < 0.001). The measurement of hydraulic conductance showed that all materials resulted in a significant decrease in dentin permeability after 24 h comprising between 60 and 76%, but there was no statistically significant difference among the materials. This decrease was still over 50% of the initial values after 7 days for all three materials. SEM investigation showed dentin tubules covered with a thick layer of Shellac F or Duraphat ® whilst no material was observed on dentin surfaces treated with Isodan ®. Significance. Shellac F showed an adequate cellular compatibility and a significant effect on human dentin hydraulic conductance. This indicates that the new material is safe and seemstobeeffectiveasapotentialdesensitizingagent.