Extension piece for a dental implant, transmission aid, and method for preparing a base for a retention piece

Extension piece for a dental implant with a head portion (20) which serves as basis for a retention element (7), and with a threaded shank (29) which can be screwed the extension piece (2) the dental implant (1), wherein the extension piece (2) has at least one reference form (27b, 24) defining the peripheral position of the extension piece (2) and through which can be transferred the peripheral position of the extension piece (2) to a working model (M), characterized in that the extension piece (2) has, between the reference form (27b, 24) and threaded shank (29), one non-cylindrical outer contour with screw surfaces (21) through which can be screwed the extension piece (2) into the dental implant (1) with a tool (3) engaging in said part.