The invention relates to a device for penetratingly extending a blind hole into a hard tissue, particularly a jawbone. The device is characterized in that it comprises a tubular body (1) having a distal working opening (2) and an inlet (3) opposite the working opening (2), said inlet being closed by a sealing element (4) that is penetrated by a shaft (5) of a working tool, for example a milling tool (5, 6), and allows at least a feed motion, a drive motion and a steering motion of the working tool (5, 6), the tubular body (1) being provided with a connection (8) for applying an internal pressure.