This study compared the sealing capacity of three different endodontic gutta-percha filling techniques. Forty-seven upper central incisors with straight canals were instrumented and randomly divided into three equal groups of 14. An additional group of five teeth with unobturated canals served as positive controls. The following gutta-percha filling techniques were evaluated: Trifecta (group A), lateral condensation (group B), and a combination of SuccessFil gutta-percha and lateral condensation (group C). Tubli-Seal was used as a sealer. The teeth were radiographed in mesiodistal and bucco-lingual directions to study the quality of the filling. Afterward, the teeth were immersed in India ink and subsequently cleared. The maximal depth of penetration was measured using a light microscope. The mean value of ink penetration for group A was 1.073 mm, for group B was 0.522 mm, and for group C was 0.765 mm. No statistically significant differences were seen among groups (p < 0.05).