The aim of this study was to compare the completion and tightness of root canal fillings made with a calcium hydroxide root filling paste. Using seven different methods the paste was placed in ISO-standardized, simulated canal lumens in transparent plastic. The tightness of the root filling was assessed using digital radiographs and appropriate picture handling computer software. With a root filling spiral instrument, with a McSpadden Compactor and after injection of the material and vertical condensation a filling of the entire canal length could be achieved. Radiographs indicated that the greatest tightness was achieved using vertical condensation after initially injecting with a needle or applying with a root filling spiral instrument. It was concluded that calcium hydroxide root filling paste should be placed in root canals using an injection needle or a root filling spiral instrument, and that subsequent vertical condensation leads to complete filling of the apical region and additional compression of the material. These effects could also be expected with the application of other paste root filling materials (eg. chloropercha). Keywords: Zahnerhaltung, Kalziumhydroxid, Hypocal, ISO, Wurzelkanal, Wurzelfüllspirale, Lentulo, McSpadden-Compactor, Wattepellet, Injektion, Injektionskanüle, vertikale Kondensation, K-Feile, Papierspitze