Abstract: For the production of a core for a root-filled prepared tooth the root canal (11) of the prepared tooth (10) is filled with an impression material (27) which is injected at the bottom of the root canal to successively fill the root canal from the bottom thereof and outwardly under expulsion of air therefrom. The injection is carried out with the aid of an injection needle (23) with an injection syringe cylinder (24) with piston (25) attached thereto, the cylinder being filled with said impression material and the injection needle serving as reinforcing element for the impression material, permitting extraction of the cast from the root canal after the impression material has set.