The aim of this study was to compare and evaluate the coronal microleakage following endodontic treatment of teeth restored with three different intracoronal restorations using calcium-45 radioisotope and autoradiography. A total of 48 extracted human mandibular premolars with single canals were divided into three experimental groups of 16 specimens each. The teeth were sectioned horizontally at the cementoenamel junction and at the middle-third of the root, orifices and canals were enlarged with Gates Glidden bur and finished using K files, and obturated with gutta-percha cones using lateral condensation technique. 3 mm of gutta-percha were removed from the coronal part of the teeth to prepare a clean 3 mm deep cavity for the coronal restorative material. Group 1 consisted of teeth restored with Ketac Molar Easymix; group 2 with Miracle Mix and group 3 with Filtek Z350. The teeth were then thermocycled and tested for microleakage using calcium-45 radioisotope. The results were analyzed using Kruskal-Wallis test and Mann-Whitney test. Filtek Z350 exhibited the least leakage followed by Ketac Molar Easymix and Miracle Mix, and the microleakage among the three restorative materials was statistically significant.