1) Background: One of the key factors for a successful endodontic therapy is to adequately fill the root canals. The aim of this in vitro study was to compare the quality of three different techniques of root canal obturation: tapered singlecone, cold lateral condensation, warm vertical condensation and injection system, using non-invasive Optical Coherence Tomography (OCT). 2) Materials and methods: A total of 30 extracted single-rooted teeth, prepared with Reciproc System (VDW, silver Reciproc ) were divided into three groups, based on the filling method: the first group obturated with “single-cone” (n=10) Reciproc guttapercha single-cone tapered according to the diameter, length and conicity of the preparation, the second group obturated with cold lateral condensation (n=10) and the third group, “combined-system” (EQ META BIOMED) (n=10). OCT technology can generate high-resolution cross-sectional imaging, capable to evaluate the micro-leakages of dental restorations and endodontic fillings. 3) Results: OCT showed that none of the root canal filled teeth were gape-free; the highest percentage of filling material was observed in the combined system group (warm vertical and injection system). 4) Conclusions: OCT represents a valuable method for investigation with high depth resolution which can be used for evaluation of endodontic fillings.