This application is a continuation of application Ser. No. 08/498,188 filed Jul. 5, 1995 now abandoned.

This invention relates generally to the field of dental implants and their use, more particularly to the preparation of crestal bone surrounding an implant at the site of installation for receiving a dental restoration on the implant.

U.S. Pat. No. 5,338,196 (which is owned by the Assignee of the present application) teaches, among other things, a second-stage healing abutment for forming and preserving in the mucosa above a dental implant a transmucosal opening large enough to receive an artificial tooth which faithfully replicates a natural tooth being restored. This opening expands in size from the implant to the outer surface of the overlying gingiva, where the opening has width approximating that of the lost natural tooth being replaced, where it emerged from the gums. During the first stage of dental implantation, however, when the implant with its cover screw is left unloaded in the jawbone for a time interval while osseointegration proceeds, the crestal cortical bone tends to grow over the periphery of the cover screw, and this overgrowth must be removed at the beginning of the second stage, if only to permit the cover screw to be removed from the implant. Removing this bone overgrowth is now done by hand. This practice is tedious and imprecise, and potentially harmful to the patient.

According to the present invention an expanding hole is formed in the crestal bone surrounding the gingival surface of the implant, the shape of which hole preferably matches and mates with the expanding hole in the overlying gingiva. In this preferred embodiment of the invention there is presented to the restoring dentist a continuous tapered hole from the gingival surface through the gingiva and the underlying crestal bone to the surface of the implant, through which to instal an artificial tooth on the implant. The present invention further provides improved means for forming a desired hole in the crestal bone accurately and precisely shaped and positioned with relation to the implant, and without damaging the bone or the implant surface. More particularly, the present invention teaches a new bone mill using teeth with a negative rake to provide a passive cutting action which minimizes damage to the bone and to the surface of the implant, together with a method of using it which emphasizes low speed turning. The present invention provide means to limit the progress of the bone mill toward the implant surface, which further safeguards the surface of the implant.

The present invention improves and enhances the utility of the second-stage healing abutment which is taught in the '196 patent, which is now provided with improved access to the implant and can be seated with assured precision on the implant. Since the process of making an artificial tooth begins with the healing abutment, these benefits flow through to the artificial tooth that will ultimately be installed on the implant.

FIG. 1 is a transverse section of jawbone with a dental implant and cover screw installed, in the first stage of osseointegration;

FIG. 2 is a similar section with the cover screw removed showing crestal bone removed to give access to the cover screw, as done heretofore;

FIG. 3 is a section similar to FIG. 2 showing a healing abutment according to the '196 patent being fitted to the implant as prepared in FIG. 2;

FIG. 4 is a section similar to FIG. 2 showing a guide pin according to the present invention being fitted to the implant;

FIG. 5 is a section similar to FIG. 4 showing the guide pin in place and a bone mill according to the invention being fitted to it;

FIG. 6 is a section similar to FIG. 5 showing the bone mill being turned to for a tapered opening in the crestal bone above the implant;

FIG. 7 is a section similar to FIG. 2 showing the tapered opening formed by the present invention in the crestal bone;

FIG. 8 is a section similar to FIG. 3 showing the healing abutment seated on the implant through the tapered opening of the present invention;

FIG. 9 is a partial schematic view of the bone mill showing locations of its teeth;

FIG. 10 is an enlarged isometric schematic view of the bone mill; and

FIG. 11 is a longitudinal section through the bone mill with the guide pin in place.

FIGS. 1 and 2 illustrate the background situation described above. In FIG. 1 the implant 10 is installed in jawbone 12, composed of cortical bone 14 surrounding cancellous bone 16. The supragingival (top) surface 20 of the implant is located to penetrate the crestal cortical bone 22. A cover screw 24, placed on the implant to seal its interior receiving bore (not shown) prior to starting the first stage healing process (osseointegration) lies within ther opening through the crestal bone. At the end of the first stage, when the overlying gum tissue (not shown) is opened to access the cover screw the dentist will usually find that the crestal bone 22 has grown over the cover screw, as is shown in FIG. 1, and must be removed, as by chipping it away, before the cover screw can be removed from the implant. The result of this initial procedure is shown in FIG. 2. A roughly round, somewhat tubular opening 26 is produced, giving access to the top surface 20 and to the non-rotational fitting 18 which may be an integral part of the implant.

In the circumstances of this background (prior-art) situation an attempt to fit to the implant a second-stage healing abutment according to the '196 patent may encounter difficulty, as is illustrated in FIG. 3. The healing abutment 30 has a tapered section 32 that is shaped for the purpose of forming in the overlying mucosa 34 a transmucosal opening as is described in the '196 patent. The opening 26 must be altered to provide passage for the abutment to the supragingival surface 20 of the implant. This might be done by further chipping away crestal bone, resulting in most cases in a larger rough opening in the crestal bone 22. The present invention provides a better way, starting with the fitting of a guide-pin 36 to the implant, as is shown in FIG. 4.

A bone mill 38 according to the invention is fitted over the guide-pin 36, which centers the bone mill on the implant 10 and guides it to the crestal bone opening 26 and the surface 20 of the implant., as is shown in FIGS. 5 and 6. The bone mill may be fitted with a driving stem 40 of a known design for connecting it to a dental driving tool (not shown). An arrow 42 indicates the driving direction, The bone mill (to be described in greater detail with reference to FIGS. 9 and 10) is fitted with cutting teeth 48 on a tapered side 44 and on its end 46 confronting the surface 22. With this bone mill an accurately centered and shaped tapered hole 50 is formed in the crestal bone 22, as is shown in FIG. 7. The angle of taper of the bone mill surface 44 is chosen substantially to match to angle of taper of the tapered surface 32 of the healing abutment 30, so that the healing abutment fits snugly into the tapered hole 50 and seats on the implant top surface 20. Desirably, the taper of the hole 50 in the crestal bone 22 and the taper of the hole through the gum tissue 34 may be on the same angle, so that the present invention used with the invention of the '196 patent will produce in essence a single continuous tapered hole from the outer gingival surface through the mucosa and the crestal bone to the top surface 20 of the implant.

FIG. 9 is a partial side view of the bone mill 38 showing the negative rake of the cutting teeth 48 relative to the turning direction indicated by the arrow 42. As is here illustrated the shorter approaching face 43 has a negative rake of 20 degrees measured from the turning axis A—A. The longer receding face 45 has an angle of 80 degrees measured from the same axis. The angle between the two faces of a tooth is thus 100 degrees. The teeth 48 when turned at a slow speed of about 1,000 to 1,500 rpm will gently abrade the crestal bone 22 and will not dig into or damage the surface 20 of the implant.

FIG. 10 is a greatly magnified isometric schematic view of the bone mill 42 showing the locations of the cutting teeth on the tapered side surface 44 and on the end surface 46. The angles of the teeth are the same on both surfaces.

FIG. 11 is a longitudinal side view of an implant 10, guide pin 36 and bone mill 42 as they would be assembled to do the work of the invention. The bone mill is generally tubular in shape, and the driving stem partially fills its interior bore 56. The remainder of the bore, which opens through the end 46, receives the guide pin 36. A round recess 58 in the end 46 serves to receive the non-rotational fitting 18 of the implant, without engaging it, so that the bone mill is freely rotatable on the implant. The top surface 62 of the guide pin, inside the bore 56 confronts a stop 60 across the bore when the milling teeth 48 meet the implant surface 20, for limiting the advance of the bone mill with relation to the implant surface. The stop 60 can be provided by the driving stem 40, as shown, or if desired by a separate shoulder 64 within the bore 56.