Background and Aim: The final objective of root canal therapy is to create a hermetic seal along the length of the root canal system from the coronal opening to the apical termination and to accomplish the best adaptation of obturation material with canal walls. The purpose of this study was to compare the microleakage during lateral condensation of 0.04 and 0.02 tapered gutta-percha master cones.

Materials and Methods: In this experimental in vitro study, seventy two single canal teeth were selected and the crowns were removed. Canals were prepared using a step-back technique. Patency of the apical foramen was maintained and the teeth were divided into two experimental groups of 31 each Ten teeth were used as control group, out of which five served as negative and five as positive controls. The first and second groups were obturated with 0.02 and 0.04 tapered master cones respectively. All the teeth were obturated using lateral condensation technique. The teeth were placed in 100% humidity and 37^oc for three days. The roots were coated with two layers of nail varnish and one layer of stick wax except for the apical 2 mm. Teeth were placed in Pelikan ink for one week and sectioned vertically. The maximum depth of dye penetration for each tooth was recorded by two evaluators with stereomicroscope. The results were statistically analyzed using t-test with p<0.05 as the level of significance.

Results: The mean linear dye penetration for the first and second groups was 2.53 0.88mm and 4.89 1.20 mm respectively. The difference was statistically significant (P<0.001).

Conclusion: The results of this study showed that 0.02 tapered gutta-percha master cone, provided a significantly better apical seal than 0.04 tapered gutta-percha master cone.