The Authors evaluate four different techniques for root canal filling by means of a stereo-microscope analysis of extracted teeth sections. The results indicate that: 1) the single-cone technique shows poor apical seal; 2) the Mc Spadden thermomechanical condensation technique produces good apical seal but often causes overfilling; 3) the vertical condensation and 4) the lateral condensation of gutta-percha confirm their efficacy, nevertheless the Authors recommend the second one because it is easier and request shorter time of execution.