Epinephrine permeation across dentin in vitro

The permeation of epinephrine across human dentin discs was studied in vitro. Permeation was measured across dentin of two different thicknesses, with and without the presence of smear layers. Epinephrine was readily detected at the earliest measured time (10 min) and reached peak concentrations between 30 and 50 min. Epinephrine flux (concentration multiplied by the volume of the effluent per min) increased with decreasing thickness of the discs and increased significantly with the removal of the smear layer. The T 1/2 (half-time in min necessary to reach steady-state diffusion of epinephrine) decreased as dentin thickness was reduced and fell further in the absence of the smear layer. This study suggests that the permeation of epinephrine across dentin is inversely related to dentin thickness and retarded by the presence of a smear layer. Also, the topical use of 1 mg/ml epinephrine produced therapeutically useful drug concentrations, but the rate of permeation was relatively slow.