AIM: To investigate the microleakage of two different root canal obturation systems, using the nuclear medicine approach.METHODS: Twenty-six single-rooted extracted teeth were selected. The crowns were sectioned to obtain 15-mm long root segments and each tooth was prepared using rotary Pro File instruments. The roots were divided into 2 experimental groups using Real Seal 1 and Real Seal sealer or Thermafil and Top Seal sealer as well as two control groups. On the 7th and the 28 th day the apices were submersed in a solution of 99 m TcPertechnetate during 3 h. The radioactivity was counted using a γ camera. RESULTS: The present study showed that none of the root canal-filled teeth was leakage free. The statistical analyses were made using Kruskal-Wallis and statistical significance was assessed using α = 0.05. Although apical leakage measured in counts per minute(cpm) in the Thermafil/Top Seal group was lower than in the Real Seal/Real Seal group(363 916 ± 180 707.7 cpm vs533 427 ± 414 020.6 cpm) on 7th day and(1 678 200 ± 567 217.4 cpm vs 2 240 518 ± 383 356.7 cpm) on 28 th day, there was no statistical difference(P > 0.05). In the Thermafil/Top Seal group and Real Seal 1/Real Seal group it was found that over time, the number of counts increased between 7 d and 28 d(363 916 ± 180 707.7 cpm vs 1 678 200 ± 567 217.4 cpm) and(533 427 ± 414 020.6 cpm vs 2 240 518 ± 383 356.7 cpm), respectively, with statistically significant differences(Thermafil/Top Seal group, P = 0.015 and Real Seal 1/Real Seal group, P = 0.036).CONCLUSION:Both carrier-based Realseal 1 and Thermafil techniques showed a similar sealing effect,but none of the materials was leakage free. To investigate the microleakage of two different root canal obturation systems, using the nuclear medicine approach. METHODS: Twenty-six single-rooted extracted teeth were selected. The crowns were sectioned to obtain 15-mm long root segments and each tooth was prepared using rotary Pro File instruments. The roots were divided into 2 experimental groups using Real Seal 1 and Real Seal sealer or Thermafil and Top Seal sealer as well as two control groups. On the 7th and the 28th day the apices were submersed in a solution of 99 m Tc Pertechnetate during 3 h. The radioactivity was counted using a gamma camera. RESULTS: The present study showed that none of the root canal-filled teeth was leakage free. The statistical analyzes were made using Kruskal-Wallis and statistical significance was assessed using α = 0.05. Although apical leakage measured in counts per minute (cpm) in the Thermafil / Top Seal group was lower than in the Real Seal / Real Seal group (363 916 ± 180 707.7 cpm vs 534 42 7 ± 414 020.6 cpm) on 7th day and (1 678 200 ± 567 217.4 cpm vs 2 240 518 ± 383 356.7 cpm) on 28 th day, there was no statistical difference (P> 0.05). In the Thermafil / Top Seal group and Real Seal 1 / Real Seal group it was found that over time, the number of counts increased between 7 d and 28 d (363 916 ± 180 707.7 cpm vs 1 678 200 ± 567 217.4 cpm) and (533 427 ± 414 020.6 cpm vs 2 240 518 ± 383 356.7 cpm), respectively, with statistically significant differences (Thermafil / Top Seal group, P = 0.015 and Real Seal 1 / Real Seal group, P = 0.036) .CONCLUSION: Both carrier-based Realseal 1 and Thermafil techniques showed a similar sealing effect, but none of the materials was leakage free.