The results of the present study indicates that the tooth can act as a barrier for medication diffusion and does not block it completely, because not only Ca2+ and OH- can diffuse through dentine and reach the external root surface but other components of the vehicle used can also diffuse and reach the external surface. Each medicament presents different diffusion characteristics, which will be directly related to its interaction with the tooth structure. Thus, more research is needed to determine which components of vehicles permeate the dentine, in what quantity they permeate, and whether these components have any effect on the periodontium.