Freshly extracted human single-rooted teeth with a single root canal were used to study the effects of 2 irrigation regimens and the effect of cementum on the diffusion of corticosteroid and antibiotic tracer molecules from Ledermix paste placed in the pulp space. An irrigation regime that combined the use of 15% EDTAC and 1% NaOCl resulted in a significant increase in the permeation of the trace molecules through dentine compared with teeth that were irrigated with Savlon solution. Mechanical removal of the cementum also resulted in a significant increase in the permeation of the trace molecules. This study demonstrated that neither the smear layer nor the cementum were complete barriers to diffusion. The data obtained appeared to be of clinical relevance and provided further understanding of the dynamics of drugs in tooth roots.