Objectives: The aim of this study was to apply to a model of simplified root canal, the physical laws which generate the penetration of dyes to the interface canal walls-obturation materials, in order to determine the relative importance of the various parameters driving dye transport Methods: To describe these phenomena we have used a simplified representation of the experimental condition as well of the endodontic treatment. There are two ways to transport the dye through the apex slit, in one case the root is completely wet and in a second case the root is dry. In the former case the movement of dye solution is driven by capillary law and in the first case the dye is transported inside slit by diffusion. Results: In wet condition the only mechanism of dye transport into interfaces is the diffusion if we assume that the size of the dye probe is much smaller than the interface slit width. The description of the diffusion of colloidal dye becomes much more complicated when the size of the dye particle is comparable with the width of the interfaces. Then the diffusion coefficient of particle depends on the dimension of the channel or capillary. In dry condition ie –dentin channels, cement pores and interface slit- are initially dry filled with gas under atmospheric pressure, when tooth is placed in contact with aqueous dye solution, it penetrates the tooth interior mainly by capillary force. As it is shown the crucial parameter determining the degree of penetration is whether the air entrapped in the tooth pores can be freely removed after the immersion of the specimen in the dye solution. Conclusions: This study is a milestone toward new endodontic leakage tests based either on control dye penetration either on gas permeability.