The aim of this study was to determine the amount of Ca diffusion through radicular dentin from 4 calcium-hydroxide-based materials placed in root canals following different treatments. The materials studied were (U) Ultradent-Ultracal XS, (D) Diadent-Vitapex, (R) Roeko Calcium Hydroxide Plus points, and (M) Merck-pure calcium hydroxide. Ninety freshly extracted human teeth were decrowned to a standard length of 14 mm, instrumented, irrigated with 5.25% NaOCl and divided into 5 groups. Group 1 was divided into 4 subgroups that received one of the following treatments prior to obturation with U : (a) ultrasound, (b) 50% citric acid, (c) ultrasound and citric acid, and (d) no treatment. Groups 2, 3, and 4 were similarly treated with D, R and M, respectively. Group 5 acted as the control group and was divided into two subgroups : (a) biomechanical preparation only and (b) no preparation. Ca diffused (mg/dl) in water through dentin as a function of time (1, 3, 5 and 16d) and was measured by spectrophotometry. Ca diffusion (mean±SD.) through dentin from different materials as a function of different treatments and time covered a wide range (6.37-35.99). For all groups and time intervals, the amount of Ca diffused from different materials was the following : (U) 27.75±14.28, (D) 21.42±12.20, (R) 14.55±12.54, and (M) 26.74±14.14. From day 1 to day 16, there was a steady release of Ca from U, D, and M but not from R. Ultrasound and citric acid treatment yielded the highest (significant at p<0.0001) Ca diffusion (40.57±18.79) with R, followed by M (34.82±27.99), D (20.18±6.66) and U (18.32±6.21) at day 1. The highest diffusion of Ca ions for all materials occurred after the use of ultrasonic cavitation with citric acid irrigation. This study found Ca diffusion through dentin is influenced both by the nature of the material and type of treatment.