Permeability of root dentin to epinephrine released from gingival retraction cord

The permeation of racemic epinephrine across roots of human molar crown segments was studied in vitro. Permeation was measured in the presence of cementum, with cementum removed (dentin exposed), and with and without dentin smear layers. Epinephrine was initially detected at 10 minutes and reached a steady state in 70 minutes. Epinephrine flux (the product of concentration and the flow rate per unit of dentin surface area) significantly increased when both the cementum and dentin smear layers were removed. The T1/2 (half-time in minutes necessary to reach steady-state diffusion) was zero with intact cementum and increased to approximately 40 minutes in dentin with and without smear layers. This study suggests that the permeation of epinephrine across root surfaces is prevented by the presence of cementum and retarded by the presence of dentin smear layers. Also, the data suggest that root dentin is another source of absorption when epinephrine-impregnated retraction cord is applied to the gingival sulcus.