AimThe aim of this study was to assess whether an obturation, combining a custom gutta-percha cone with the BIOROOT™-RCS sealer, displays similar sealing quality to the orthograde apical plugs of MTA CAPS® in immature teeth with irregular wide apices. MethodologyThirty-four immature permanent premolars with apical diameter varying between (1–3mm) were chosen for this study and were divided into two groups. They were imbedded in wet sponge, which simulated the periapex. In the first group; 5mm orthograde plugs of MTA were placed using an appropriate plugger. In the second group; a custom gutta-percha cone was fabricated and used for root canal filling with the BIOROOT™-RCS sealer. The specimens were stored at 37°C and 100% humidity during five weeks to allow the complete set of the filling materials. The apical leakage was evaluated using a dye penetration test with 50%-weight silver-nitrate. The teeth were then embedded in a transparent resin and sectioned transversally at 1 and 3mm from the apex. The slices were examined under optical microscope and were given scores from (0) to (4). When scoring a slice was difficult, spectroscopy for energy dispersion using a scanning electron-microscope was used to confirm the score. The results were compared using the Fisher test with p<0.05. ResultsSilver-nitrate was found in both groups in all slices at 1mm. At 3mm, the difference of micro-leakage was not significant. ConclusionsThe custom gutta-percha cone combined with BIOROOTtm-RCS sealer displays similar leakage resistance to the orthograde MTA plugs.