A fixture which is intended to be screwed firmly into bone tissue. The fixture includes a generally cylindrical anchoring portion provided with an external screw thread. The anchoring portion includes a cavity which extends from the insertion end of the anchoring portion. A number of slots which connect the cavity with the outside of the anchoring portion extend from the insertion end of the anchoring portion. Each slot is delimited by a leading slot wall and a trailing slot wall, the leading and trailing slot walls rotating in the direction defined by the screw thread when screwing in the anchoring portion. At least the radially outermost part of the trailing slot wall defines an angle with the radial direction and is inclined obliquely forward from within and outward in the direction of rotation.