Abstract: In apicoectomies, which are carried out after reaming out a bone cavity, treatment of a root is very often necessary. The corresponding fillings must be dry, and thus material separation of the exposed bone surface from the resection area is necessary so that no blood can enter the root region to be filled and, on the other hand, solid particles and any reagents which are necessary (for example for root canal irrigations) are unable to contact the bone cavity. An appliance is provided to allow complete lining of the bone cavity and to separate the latter materially from the root region to be filled. The lining has two layers of different and complementary function. The lining is pushed into the bone cavity using a suitable tool and, at the same time, is shaped to the surface of the cavity.