Abstract:
A dental implant system comprising an implant member, an abutment member and a transfer key with cooperatively engaging structures for ensuring proper alignment and orientation of an abutment assembled on the implant member and for preparing an accurate dental impression and mold which represents the implantation site and its relationship to adjacent teeth structures. The abutment has the advantage of being easily removed for maintenance, repair or replacement with minimal or no discomfort to the patient. The invention also includes a dental implant with an improved bone-engaging structure for enhancing implant stability and fixation as well as an O-ring type abutment assembly with a reduced footprint in its assembled state when compared with similar conventional systems. Further, dental reconstruction and abutment installation methods utilizing the dental implant system and instruments of the invention are disclosed.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims benefit of U.S. Ser. No. 60/834,891, filed Aug. 1, 2006, which is incorporated herein by reference in its entirety. 
     
     FIELD AND BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates in general to a dental implant system and method, comprising components having improved surface and structural features for ensuring proper alignment and orientation of an abutment assembled on an implant and for preparing an accurate dental impression and mold representing the implantation site and its relationship to adjacent teeth structures. The present invention also relates to an implant having improved bone engaging surfaces for enhancing implant stability and fixation. The present invention further relates to a multi-component dental implant system with at least the implant and the abutment being detachably joined to one another with an improved, locking taper assembly designed for easy assembly and disassembly. The present invention further relates to an improved O-ring abutment assembly which offers a smaller footprint than existing O-ring attachment systems. The present invention further relates to an implant delivery method and its associated device(s) which reduces or eliminates, for example, slippage of the implant during implant surgery. 
       Abutment-to-Implant Connections 
       [0003]    Internal Morse taper connection, also referred to as the locking taper, is known in implant dentistry and is commonly used for securing an abutment to a dental implant. A widely used example is embodied in the implant described in U.S. Pat. No. 4,738,623 to Driskell. See also U.S. Pat. No. 5,888,066 to Morgan and U.S. Pat. No. 6,290,500 to Morgan, et al. for examples of other Morse taper abutment-to-implant connections. 
         [0004]    Known implant systems utilizing screw-less internal Morse taper connections have inherent disadvantages when compared to more widely used screw retained, internal or external hex dental implants. These disadvantages include: (1) the round shape of the female and male components makes it difficult to register the position of the prepared implant abutment; (2) the implant abutment may not travel in a straight line when tapped into the implant; (3) the round shape of the female and male components makes it difficult to prevent rotation of the implant abutment once the final restoration is under stress; (4) the implant abutment may be over-inserted into the implant as compared to the implant analog; and (5) the implant abutment may not be inserted into the implant as far as it was inserted into the implant analog. 
         [0005]    Locking engagement between complementary tapered surfaces of the implant and the abutment can be achieved through a tapping or threading operation. Some patients may find the use of tapping action to seat the abutment onto the implant uncomfortable. As an alternative, a dental implant system which utilizes a threaded fastener to seat the abutment onto the implant may be used. One example of a screw-assisted abutment connection is described in U.S. Pat. No. 6,726,481, issued to Zickmann, et al. There, a dental implant system is provided with an abutment post having an external tapered cylindrical surface, a projection extending from the top end of the abutment post and an abutment having complementary internal surfaces adapted to mate with the external cylindrical surface and projection of the abutment post. It is understood that the projection tends to increase the total height of the implant, subjecting the implant to more healing disrupting stress from mastication and tongue movements. The projection also makes fabrication of angled abutments more difficult. Also, the abutment of the aforementioned patent cannot be easily removed or replaced without damaging the abutment, crown or opposing dentition. In addition, it would be difficult if not impossible for the abutment and implant hex surfaces to mate accurately and for the conical or Morse tapered connection to operate properly at the same time. For example, the highest tolerance achieved by the machining process is no less than 12 microns. The Morse taper connection yields a 0.5 micron adaptation. In order to assure no interference with the Morse taper connection, the mating hex surfaces have to be manufactured to have significant tolerance to accommodate 12 microns margin of error for each mating surface. The gap between the external and internal hex must not be programmed to be less than 24 microns, but can be as large as 48 microns in the worst scenario. This would result in a significant rotational movement between the hexes during implant indexing and during abutment insertion. The error can be multiplied during the process of crown or bridge fabrication. The end result is most likely a restoration which does not fit properly. 
       Implant-Abutment Systems 
       [0006]    One typical prior art system is described in U.S. Pat. No. 5,527,183, issued to O&#39;Brien, which comprises an implant body having an externally threaded lower region and a plurality of tapered circumferentially extending members provided in an upper portion thereof. 
         [0007]    The present invention also improves upon existing O-ring attachments. The basic concept of the O-ring type attachment is described in U.S. Pat. No. 5,049,072, issued to Lueschen. It consists of a metal housing, an O-ring, which is placed inside the housing, and an O-ring abutment, which is attached to the implant. The mechanism of retention is presented as follows: the housing with the O-ring mounted therein is inserted over the spherical end of the abutment to detachably secure the housing to the abutment. The housing is designed to be encased within a denture or tooth (which can be natural or artificial). The O-ring must slip over the entire convexity of the spherical end in order to obtain good retention. Below the spherical end is a cylindrical spacer of a smaller cross-section, which needs to be of a certain length in order for the housing to have an appropriate range of movement. The housing includes a concave area on the inside wall adapted to receive the O-ring. This concave area needs to be sufficiently deep to incorporate most of the O-ring in order for O-ring not to come loose during denture insertion and removal. These two factors dictate the width and the height of the housing, apart from the diameter of the spherical end and the cross-sectional diameter of the O-ring. 
         [0008]    The size of the housing and O-ring abutment is critical because the available space inside the denture can be quite limited. Others have attempted to reduce the overall height of the dental attachment assembly by altering the curvature of spherical or ball-shaped end of the abutment. One example is the Brevis attachment manufactured by Bicon (http://www.bicon.com/tech/t_od01.html). While further reduction of the height and width can be accomplished by reducing the thickness of the O-ring and the diameter of the spherical end of the abutment, such modifications will lead to diminished retention capability. 
         [0009]    U.S. Pat. No. 6,981,871, issued to Mullaly, et al., describes a combination of a male abutment, a retaining housing and a soft liner with retentive protrusions. For this type of dental attachment assembly, the range of motion is limited to the amount of “give” the liner has. The liner, which must have a certain thickness to achieve any significant range of motion, will increase the width and height of the housing. Also, the cost of manufacturing the liner is higher when compared to O-rings. Further examples of O-ring type attachments can be found in U.S. patent application publication Nos. US 2006/0269903 of Bulard et al. and US 2002/0177103 of Pelak, and in U.S. Pat. No. 4,681,542, issued to Baum. The type of attachment described in Baum works well in situations where multiple teeth or implants are used to support removable denture. On the contrary, if few teeth or implants are used, the semi-rigid connection, which allows slight movement only along the vertical axis of the attachment, will apply too much stress on supporting teeth or implants and can lead to their failure. 
       Implant Delivery Method and Devices 
       [0010]    This invention further attempts to simplify implant placement procedures and improve patient safety during these procedures. It is desirable to store the implant in a sterile container, which would securely hold the implant in an upright position, ready to be removed from the container and placed into the patient&#39;s bone. The common practice is to utilize the implant carrier with larger than implant diameter to hold implant in a container. Implant carrier can have mechanical interlock or is frictionally fitted with container&#39;s side walls. Carriers typically protrude from the container and can be gripped with fingers to be transferred into the receiving site. In order to utilize the improved method of implant delivery, as described below, the implant&#39;s proximal end should not be obstructed. 
         [0011]    There are several ways to transfer implant from a sterile container into the prepared or pre-drilled bone. Most of the methods involve the use of an implant carrier. Implant carrier can be attached to the implant with a retention screw or can be attached to it by means of mechanical interlocking. Since it is not possible to touch the implant, the operator grips the carrier with fingers, places the implant into the drilled socket, rotates the implant to achieve initial stability and then disengages the carrier. If the retentive screw is used to attach the carrier, it has to be unscrewed with a screw removal tool. Screw removal tool has to have sufficient height and diameter in order for operator to applied the required force. It is common for diameter to be 10-15 mm, while the height can be as much as 20 mm. Only two fingers of one hand are used to accomplish this task. If the work is done on upper back teeth, it is easily seen that the screw removal tool can slip out of fingers and end up being swallowed or inhaled by the patient. Having the tool of this size also requires a large space between the carrier and the opposing teeth. Implant insertion instrument is then placed into the implant&#39;s well and implant is inserted to the desirable depth. Thus, at least three instruments are used with unnecessary risk of the implant coming loose and falling out of socket before the implant is securely anchored to the bone. It is therefore desirable to have a single, dual- or multi-use instrument which can be utilized by the surgeon to handle and manipulate the implant. 
         [0012]    All cited references are incorporated herein by reference in their entireties. 
       SUMMARY OF THE INVENTION 
       [0013]    One aim of the present invention is to provide a dental implant system and method which is capable of eliminating the disadvantages of the prior art and in particular a dental implant system which has surface and structural features which provide accurate placement of the abutment and replication of the implantation site. 
         [0014]    It is an object of the present invention to provide a dental implant system comprising an implant member (or body), an abutment member (e.g., transfer coping/abutment or implant abutment) and a transfer key. 
         [0015]    The implant member generally has an anchoring portion on one end for anchoring the implant member in the patient&#39;s jaw bone, and an abutment receiving portion or post provided on the other end. At least a part or portion, or a cross-section, of the abutment receiving portion is tapered to a smaller diameter toward the top end of the abutment receiving portion. The abutment receiving portion has one or more spaced apart longitudinal grooves which extend downward from the top end thereof. 
         [0016]    The transfer key generally comprises one or more projecting members or projections, which extend axially outward from one end of the transfer key. The projection(s) are arranged and configured to detachably mate with the corresponding groove(s) of the abutment receiving portion. The transfer key also includes an elongated rail member formed on its circumferential or peripheral surface and extending substantially its entire length, or a portion thereof. 
         [0017]    The abutment member generally includes an axial bore formed therein along its long or central axis. The lower portion of the axial bore has a tapered cross-section, configured to receive and mate with the tapered part of the abutment receiving portion. The upper portion of the axial bore has a cross-section corresponding to the outer cross-section of the transfer key. 
         [0018]    Another object of the present invention is to provide an improved method of impression making and dental reconstruction utilizing the components of the dental implant system of the present invention. 
         [0019]    Another object of the present invention is to provide a dental implant (member) comprising an apical end, a top end, an anchoring portion adapted to engage bone and having an axial length, an abutment or prosthesis receiving portion, an externally threaded region extending upwardly from about the apical end of the dental implant and comprising about 50% to about 95% of the axial length of the anchoring portion, and at least one annular, implant-stabilizing member formed between the threaded region and abutment receiving portion and comprising about 5% to about 50% of the axial length of the anchoring portion, wherein the implant-stabilizing member and the threaded region together making up no more than about 100% of the axial length of the anchoring portion. Preferably, the anchoring portion comprises at least two implant-stabilizing members disposed in parallel, spaced apart relation, and the implant-stabilizing members have successively smaller cross sections in the direction of the apical end of the dental implant. 
         [0020]    Another object of the present invention is to provide a dental implant comprising an apical end, a top end, an anchoring portion adapted to engage bone and having an axial length, an abutment receiving portion having at least one spaced apart, longitudinal groove extending downwardly a predetermined length from the top end of the dental implant, and an internally threaded opening of a predetermined depth accessible from the top end of the dental implant. The dental implant may optionally include an annular shoulder formed between the anchoring portion and the abutment receiving portion, for example, when the diameter of the anchoring portion is greater than the diameter of the abutment receiving portion. If the diameter of the anchoring portion and the abutment receiving portion are approximately equal, then a shoulder is preferably not provided. Further, if the diameter of the anchoring portion is smaller than the diameter of the abutment receiving portion, then a “negative shoulder” may be incorporated into the anchoring portion. 
         [0021]    Another object of the present invention is to provide a transfer key for use with a dental implant of the present invention. The transfer key includes an outer wall, a threaded axial bore, at least one longitudinal protrusion, a first pin receiving opening, at least one axial projection extending outwardly from one end thereof and adapted to detachably mate with the corresponding longitudinal groove of the abutment receiving portion, wherein the longitudinal protrusion and the first pin receiving opening are formed on the outer wall of the transfer key. In an embodiment, the internally threaded opening of the dental implant has a smaller diameter than the threaded axial bore of the transfer key. 
         [0022]    Another object of the present invention is to provide an implant abutment (or member) for use with a dental implant of the present invention. The implant abutment includes a peripheral wall, a central bore extending through the implant abutment and having a lower part and an upper part, a cylindrical interior wall formed on the upper part of the central bore, a conical interior wall formed on the lower part of the central bore, a longitudinal channel formed on the cylindrical interior wall of the central bore and adapted to slidably mate with the longitudinal protrusion of the transfer key, and a second pin receiving opening formed on the peripheral wall, wherein the cylindrical interior wall is adapted to receive in a fittingly close relationship the transfer key, and wherein the conical interior wall is adapted to mate with the abutment receiving portion of the dental implant. The first and second pin receiving openings are adapted to be in alignment after the transfer key and the implant abutment are properly seated on the dental implant. This allows the use of the pin to connect the transfer key and the implant abutment, and permits the transfer key and the implant abutment to be disengaged from the dental implant in a single operation. 
         [0023]    Another object of the present invention is to provide a dental implant system comprising a dental implant and an implant abutment. The dental implant includes a top end, an anchoring portion adapted to engage bone, an abutment receiving portion having an external cylindrical surface which tapers toward the top end of the dental implant, and an internally threaded opening of a predetermined depth accessible from the top end of the dental implant. The implant abutment includes a lower part having an internal cylindrical surface which tapers outwardly toward a bottom end of the implant abutment, the internal cylindrical surface being adapted for secure mating engagement with the external cylindrical surface of the abutment receiving portion, and an upper part in communication with the lower part and having a threaded axial bore with a diameter larger than the internally threaded opening. 
         [0024]    Another object of the present invention is to provide a method of installing an implant abutment on a dental implant, which comprises providing an abutment insertion tool having a threaded end adapted to threadedly engage the internally threaded opening of the dental implant and a flat end having a larger cross section than the central bore of the implant abutment, inserting the transfer key into the implant abutment, placing the implant abutment and the transfer key on the abutment receiving post and engaging the corresponding projecting members and longitudinal grooves, inserting the abutment insertion tool through the threaded axial bore of the transfer key with the flat end of the abutment insertion tool abutting against an upper edge of the implant abutment, and turning the abutment insertion tool in an appropriate direction to urge the abutment receiving post and the corresponding conical interior wall of the implant abutment together to form a taper lock or Morse taper connection. 
         [0025]    Another object of the present invention is to provide a method for obtaining an accurate translation of an orientation and position of an implant, which comprises providing an implant having a two or more spaced apart longitudinal grooves formed on an upper peripheral wall thereof, providing a threaded opening formed in an upper surface of the implant, providing an impression coping having axial projections corresponding to the longitudinal grooves of the implant and a threaded bore extending through the impression coping, seating the impression coping onto the implant, partially engaging the corresponding axial projections and longitudinal grooves, applying an axial force to the impressing coping with a fastener to urge the axial projections and the longitudinal grooves into a closely fitted engagement, applying a dental impression material to at least an area adjacent the impression coping so as to cover the impression coping to obtain an negative impression of said area, removing the fastener and then the impression material from the patient&#39;s mouth after the impression material has set, with the impression coping embedded in the impression material, detachably attaching the implant analog and the impression coping, pouring molding material into the negative impression formed in the impression material to form a dental cast model, and fabricating an implant abutment and/or dental prosthesis on the implant analog, wherein the fastener is adapted to cooperatively engage the threaded opening. Each longitudinal groove preferably has a larger cross section proximal portion, an apical portion having a smaller cross section than the proximal portion and a transition portion tapering between the proximal portion and the apical portion. In an embodiment, each proximal portion is adapted to freely receive the corresponding one of the axial projections until the transition portion, and the axial projections have sharp edges and are configured to provide at least two points of intimately engaging contact between the axial projections and the longitudinal grooves with the sharp edges of the axial projections biting into walls of at least the transition and apical portions. Further, the impression coping is preferably formed of a suitable biocompatible material which permits the axial projections to expand slightly outward when properly fitted into the longitudinal grooves. 
         [0026]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    In the drawings: 
           [0028]      FIG. 1  is a perspective view of a dental implant system or assembly of the present invention; 
           [0029]      FIG. 2  is a side cut-away elevational view of a dental implant system or assembly of the present invention; 
           [0030]      FIG. 3A  is a top plan and  FIG. 3B  is side elevational view of a dental implant of the present invention; 
           [0031]      FIG. 4A  is a side elevational and  FIG. 4B  is a bottom plan view of a transfer key of the present invention; 
           [0032]      FIG. 5A  is a top plan and  FIG. 5B  is a side cut-away elevational view of a transfer abutment of the present invention; 
           [0033]      FIG. 6A  is a top plan and  FIG. 6B  is a side cut-away elevational view of an implant abutment of the present invention; 
           [0034]      FIG. 7  is a side elevational view of an embodiment of a dental implant of the present invention; 
           [0035]      FIG. 8  is close-up view of inset A of  FIG. 7 ; 
           [0036]      FIG. 9  is a top plan view of another embodiment of a dental implant of the present invention; 
           [0037]      FIG. 10  is a perspective view of the dental implant of  FIG. 9 ; 
           [0038]      FIG. 11  is a perspective view of an embodiment of a transfer key and implant abutment of the present invention; 
           [0039]      FIGS. 12A and 12B  are two different perspective views of the implant abutment of  FIG. 11 ; 
           [0040]      FIG. 13  is perspective view of a locking pin of the present invention and the transfer key and implant abutment of  FIG. 11 ; 
           [0041]      FIG. 14  is a perspective view of an abutment insertion tool of the present invention; 
           [0042]      FIG. 15  is a perspective view of an abutment removal tool of the present invention; 
           [0043]      FIG. 16  is a perspective view of an implant placement tool of the present invention; 
           [0044]      FIGS. 17A to 17D  are bottom cut-away plan views of the implant-stabilizing members or fins with various bone ingrowth surfaces, openings or grooves; 
           [0045]      FIG. 18A  is a perspective view of an O-ring abutment of the present invention; 
           [0046]      FIG. 18B  is a perspective view of an O-ring with the O-ring abutment of  FIG. 19A ; 
           [0047]      FIG. 18C  is a top plan and  FIG. 19D  is a side elevational view of the O-ring abutment of  FIG. 19A ; 
           [0048]      FIG. 18E  is a perspective and  FIG. 19F  is a side cut-away elevational view of a retainer housing for use with the O-ring abutment of  FIG. 19A ; 
           [0049]      FIG. 19  is a side cut-away elevational view of another O-ring type abutment assembly in an assembled state; 
           [0050]      FIG. 20  is a perspective view of an abutment insertion tool and an O-ring abutment attached to a dental implant; 
           [0051]      FIG. 21  is a side cut-away view of an implant abutment of the present invention; 
           [0052]      FIG. 22  is a side elevational view of an implant holding vial of the present invention with an implant retained by the implant retaining member; and 
           [0053]      FIGS. 23A to 23C  show a perspective view of a device representing a transfer coping or a transfer key of the present invention being brought into engagement with a dental implant. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0054]    Referring now to the drawings, in which like reference numerals are used to refer to the same or similar elements,  FIG. 1  shows a dental implant system  1  comprising an implant member  4  or body/fixture, an abutment member  3  and a transfer key  5 . The implant member  4  includes an anchoring portion  16  on one end for anchoring the implant member  4  in the patient&#39;s jaw bone, and an abutment receiving portion  15  or post on the other end. The end of the anchoring portion  16  adjoining the abutment receiving portion  15  may be provided with a shoulder  18 , such as a downwardly and outwardly sloping shoulder. Preferably, the anchoring portion  16  is provided with external threads  17  ( FIG. 2 ). The anchoring portion  16  may be formed integrally with the abutment receiving portion  15 , or connected to each other to form the implant member  4 . The abutment member  3  may be straight or angled.  FIGS. 3A and 3B  respectively show a top and side view of an implant member of the present invention. 
         [0055]    At least a part or a cross-section of the abutment receiving portion  15  is tapered to a smaller diameter toward distal end  14 . The abutment receiving portion  15  is provided with a plurality of spaced apart longitudinal grooves  13  that extend a predetermined distance in a lengthwise direction away from distal end  14 . Preferably, the grooves  13  are equally spaced and/or parallel to each other. In one embodiment, the abutment receiving portion  15  has three equally spaced and generally parallel grooves  13 . 
         [0056]    The above mentioned transfer key  2  comprises a number of projecting members or projections  7 , which extend axially outward from one end of the transfer key  2 . The projections  7  are arranged and configured so as to allow mating engagement with the corresponding grooves  13  of the abutment receiving portion  15 . It is apparent to those skilled in the art that variations in the number, shape and size of the grooves and projections are possible, and that such changes, variations, modifications, and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, and are limited only by the claims which follow. 
         [0057]    The transfer key  2  also includes an elongated rail member  9  extending lengthwise along its circumferential or peripheral surface. The transfer key  2  is fabricated from a suitable ceramic, polymer, plastic or metallic material.  FIGS. 4A and 4B  respectively show a side and bottom view of a transfer key  2  of the present invention. 
         [0058]    The above mentioned abutment member  3 , or  21  in  FIGS. 5A and 5B , has an axial bore  10 , preferably, running through its center. The axial bore  10  includes a lower tapered or conical cross-section  12 , which is configured to receive and mate with the tapered part of the abutment receiving portion  15 , and an upper, cylindrical cross-section  11  corresponding to the outer cross-section of the transfer key  2 . Preferably, the tapered cross-section  12  and the tapered part of the abutment receiving portion  15  form a Morse taper connection. A lengthwise extending channel  24 , which corresponds to the rail member  9 , is formed on the inner circumferential surface of the abutment member  3 ,  21 , in the upper, cylindrical cross-section  11  of the axial bore  10 .  FIGS. 5A and 5B  respectively show a top and side cut-away view of abutment member  21  with retention members  19  or elements.  FIGS. 6A and 6B  respectively show a top and side cut-away view of abutment member  3 . 
         [0059]    In one embodiment, abutment member  21  (also referred to as a transfer coping or transfer abutment) is up to 0.25 mm longer than abutment member  3  (also referred to as an implant abutment). Abutment member  21  is adapted to cover up to 0.25 mm more of the length of the abutment receiving portion  15  or post than abutment member  3  when an impression of the abutment member  21  and the surrounding dentition is obtained. This is to ensure full insertion of abutment member  3  on the implant analog; otherwise, the master cast or mold may interfere with abutment seating. 
         [0060]    The transfer key  2  may also include a central bore  6  for engaging a suitable actuating or extraction tool therethrough, such as an endodontic file or a root canal reamer, to extract the transfer key  2  mounted on the abutment receiving portion  15  and within the axial bore  10  of the abutment member  3 ,  21 . 
         [0061]    In one embodiment, the outer surface of abutment member  3  is provided with at least one anti-rotational element or feature, such as a groove, recess or projection, to provide secure attachment of the implant prosthesis to abutment member  3 . Abutment member  21  may have disposed on its outer surface at least one retention member  19  or element to provide secure attachment of abutment member  21  to the dental impression material used, for example, in the “pick-up” modelling of the patient&#39;s mouth. This type of modelling technique is described in the background section of U.S. Pat. Nos. 6,824,386 and 6,951,460, both issued to Halldin, et al., the disclosures of which are incorporated herein by reference in their entireties. 
         [0062]    When assembled, the components of the dental implant system, such as the grooves  13 , projections  7 , rail member  9  and channel  24 , operate cooperatively with each other to prevent unwanted movement or rotation of the abutment member  3 ,  21  relative to the implant member  4  or the implant analog. The arrangement of the various components of the dental implant system of the present invention also, in addition to the above mentioned advantages, provides accurate three-dimensional abutment registration and modelling of the implant site, ensures abutment member  3 ,  21  travels in a straight line, e.g., when tapped into place, during abutment seating, and/or prevents over-insertion of the abutment member  3 ,  21 . 
         [0063]    The exemplary method for performing dental reconstruction using the dental implant system of the present invention will be described below in more detail. However, it will be apparent to one of ordinary skill in the art that other embodiments are also possible in which various steps are added, combined, modified, substituted, automated or omitted. 
         [0064]    The anchoring portion  16  of the implant member  4  is implanted in the patient&#39;s jaw bone. Preferably, the anchoring portion has threads  17  for securing the implant member  4  to the bone. 
         [0065]    The transfer abutment  21  is then placed over the abutment receiving portion  15 . Preferably, the transfer abutment  21  covers slightly more of the abutment receiving portion  15 . This is to prevent the master cast from interfering with the seating of the implant abutment  3  on the implant analog. The transfer abutment  21  may include retention element(s)  19  for retention of the transfer abutment  21  in the impression material. 
         [0066]    The transfer coping key is inserted into the axial bore  10  of the transfer abutment  21  with the rail member  9  sliding within channel  24  of the transfer abutment  21 . 
         [0067]    The transfer abutment  21  is rotated to align the axially extending projections on the transfer coping key with the corresponding grooves  13  of the abutment receiving portion  15  and to engage the projections with the grooves. In this way, an accurate three-dimensional implant position registration is obtained. 
         [0068]    Slight pressure is applied to the transfer abutment  21  to engage the Morse taper abutment-to-implant connection formed by the respective male and female mating surfaces on the abutment receiving portion  15  and the transfer abutment  21 . 
         [0069]    Impression material is applied to the patient&#39;s mouth to obtain a negative impression of the transfer abutment  21  and the surrounding dentition. 
         [0070]    Impression material is removed from the patient&#39;s mouth with the transfer abutment  21  and transfer coping key embedded therein. 
         [0071]    The implant analog (post) is inserted into the transfer abutment  21 . The distal end of the implant analog is provided with grooves which correspond to and engage with the projections of the transfer coping key. Preferably, the respective male and female mating surfaces on the implant analog and the transfer abutment  21  form a Morse taper connection. The transfer coping key retained in the impression material also acts as stop to prevent over-insertion of the implant analog. 
         [0072]    Molding material is poured into the negative impression of the surrounding dentition and around the transfer abutment  21 . 
         [0073]    The impression material is removed from the hardened molding material. The transfer abutment  21  remains embedded in the impression material. 
         [0074]    The desired implant abutment  3  is placed over the distal end of the implant analog protruding from the hardened mold. 
         [0075]    A transfer key is inserted into the axial bore  10  of the implant abutment  3 , in particular the upper cross-section  11  of the axial bore  10 , with the rail member  9  slidably engaging channel  24  of the implant abutment  3 . The transfer coping key, or a different key but similar to the transfer coping key, may be used as the transfer key. The transfer key has axially extending projections corresponding to the grooves  13  of the abutment receiving portion  15  of the implant member  4 . 
         [0076]    The implant abutment  3  is rotated to align the projections  7  on the transfer key with the corresponding grooves on the implant analog and to engage the projections with the grooves. The upper end  5  of the key is trimmed to a length of preferably 1-2 mm above the occlusal surface  8  of the implant abutment  3 . 
         [0077]    Slight pressure is applied to the implant abutment  3  to engage the Morse taper connection formed by the respective male and female mating surfaces on the implant analog and the implant abutment  3 . Preferably, seating of the implant abutment  3  is also performed with a hollow cylindrical tapping instrument so as not to interfere with the transfer key. The instrument may have a striking surface which corresponds to the occlusal surface  8  of the implant abutment  3 . The transfer key registers the vertical position of the implant abutment  3 , which ensures that the implant abutment  3  (and similarly in the case of transfer abutment  21 ) travels in a straight line when it is tapped into place. Optionally, with the transfer key remaining inside the implant abutment  3 , the implant abutment  3  may be prepared to the desired shape. 
         [0078]    An implant prosthesis or crown is made over the implant abutment  3 . Crown can be made as a separate piece to be cemented on implant abutment by the dentist at later date, or it can be incorporated directly on implant abutment and be tapped over the implant post. 
         [0079]    The transfer key is removed from the implant abutment  3 . Preferably, an extraction tool adapted to engage the central bore  6  of the transfer key is used to extract the transfer key. 
         [0080]    The implant abutment  3  is removed from the implant analog using rotational movement. The implant abutment  3 , transfer key, and/or dental prosthesis fabricated in the manner described above is then sent or provided to the dental practitioner for installation into the dental implant or fixture installed in the patient&#39;s jaw bone. 
         [0081]    Alternatively, the implant abutment and the transfer are permanently joined together while they are still seated on the implant analog. Preferably, the side walls of the implant abutment and the transfer key are provided with pin holes, and the implant abutment and the transfer key are joined together by aligning the pin holes on their respective side walls and applying a suitable resin to the pin holes. It will be appreciated that the implant abutment and the transfer key may also be joined together by soldering, gluing or any other suitable joining technique. 
         [0082]    The implant abutment  3  is first placed on the abutment receiving portion  15  of the implant member  4  implanted in the patient&#39;s jaw bone. The transfer key is inserted into the implant abutment  3  with the rail member  9  slidably engaging channel  24  of the implant abutment  3 . 
         [0083]    The implant abutment  3  is then rotate to align the projections  7  of the transfer key with the grooves  13  of the abutment receiving portion  15  and to permit engagement of the corresponding projections  7  and grooves  13 . 
         [0084]    Slight pressure may be applied to the implant abutment  3  to engage, e.g., the Morse taper abutment-to-implant connection formed by the respective male and female mating surfaces provided on the abutment receiving portion  15  and the implant abutment  3 . The transfer key aligns the implant abutment  3  and the implant, and ensures that the implant abutment  3  travels in a straight line during abutment seating. 
         [0085]    Preferably, abutment seating is performed until the occlusal surface  8  of the implant abutment  3  is at the same level as the upper end of the transfer key  5 . 
         [0086]    Finally, the dental prosthesis or crown is securely attached to the implant abutment  3 . 
       Alternate Preferred Dental Implant Systems 
       [0087]      FIGS. 9-16  illustrate an alternate embodiment of the dental implant system or assembly of the present invention, which comprises a dental implant  100 , a transfer key  102 , an implant abutment  121 , an abutment insertion tool  205 , an abutment removal tool  206  and an implant insertion and removal tool  207 . Unless otherwise specified, it is to be understood that all of the components of the alternate embodiments are substantially the same as the other embodiments discussed above. 
         [0088]    As shown in  FIG. 10 , the dental implant  100  is formed as an elongated body having an anchoring portion  116 , an abutment receiving portion  115  and an internally threaded opening  114 A of a predetermined depth, which is accessible from the top end  114  of the dental implant  100 . Preferably, the dental implant  100  has a cylindrical shaped body, and/or an annular shoulder  118  disposed between the anchoring portion  116  and the abutment receiving portion  115 . The size and shape of the dental implant  100  may vary, depending on, for example, the surgeon&#39;s needs or preferences and/or the anatomical conditions present at the implant site. The abutment receiving portion  115  includes at least one longitudinal groove  113 , and an external, conically tapered surface. Each longitudinal groove  113  is machined or formed (e.g., cast or molded) into the tapered surface of the abutment receiving portion  115 , and preferably extends a predetermined distance from top end  114  toward the anchoring portion  116  of the implant  100 . While the implant shown in  FIGS. 9 and 10  is provided with three circumferentially equally spaced apart grooves  113 , it will be appreciated that the number, shape, length, depth and arrangement of the longitudinal grooves  113  may vary, depending on the number, shape, length and arrangement of the axial projection(s)  107  of the transfer key  102 . Further, the inclination angle of the conically tapered surface is selected to form a taper connection, such as a Morse taper connection, with the conical interior wall in the conical bore section  110 B ( FIG. 11 ) of the abutment  121 . 
         [0089]    Generally, a Morse taper is defined, in a non-limiting fashion, as a taper connection having a taper surface making an angle of about 1 to 12 degrees relative to the longitudinal axis of the component. Morse taper connections can be made between interpenetrating parts, with, e.g., a first of the parts having a tapered bore, and a second of the parts having a frusto-conical shape for securement in the tapered bore of the first part. The tapered bore and the frusto-conical shape can have slightly different sizes or taper angles to facilitate securement of the parts via the mating taper connection as described below. To assemble mating taper connections, including Morse taper connections, items having a mating taper structure are interference fit one to the other to cause co-integration or locking of the items. See, e.g., U.S. published application number US 2004/0111861 of Barrette, et al. 
         [0090]    As shown in  FIG. 11 , the transfer key  102  has a cylindrical outer wall, a longitudinal protrusion  109  disposed along the entire length (or a portion) of the outer wall, a pin receiving opening  102 B which can be a blind hole or a through-passage opening, a threaded axial bore  102 A, and projections  107  which extend axially outward from one end of the transfer key  102 . The transfer key  102  preferably has one or more circumferentially equally spaced projections  107  configured for detachable engagement with the corresponding number of correspondingly dimensioned longitudinal grooves  113  of the implant  100 . It will be appreciated that the transfer key  102  can also have more than one longitudinal protrusion  109  which can respectively mate with the corresponding longitudinal channels  124  in the implant abutment  121  ( FIGS. 11-13 ). 
         [0091]    As shown in  FIGS. 11-13 , the implant abutment  121  has an outer peripheral wall, a pin receiving opening  121 C and a central bore  110 . The central bore  110  is comprised of a cylindrical bore section  110 A and a conical bore section  110 B. The cylindrical bore section  110 A has a cylindrical interior wall which is configured to receive in a fittingly close relationship the transfer key  102 . Formed on the cylindrical interior wall is at least one longitudinal channel  124  for sliding engagement with the longitudinal protrusion  109  and for guiding the insertion of the transfer key  102  through cylindrical bore section  110 A of the central bore  110 . Although the transfer key  102  and the cylindrical bore section  110 A are shown as having a circular cross-section, it will be appreciated that they may have other suitable cross-sectional shapes. Further, it will also be appreciated that the cross-sectional size and height of transfer key and the cylindrical bore section can be selectively varied by one skilled in the art as may be appropriate to improve the form-fitted engagement between the transfer key and the cylindrical bore section of the implant abutment. 
         [0092]    The outer peripheral wall of the implant abutment  121  may be optionally provided with anti-rotational elements. Although the outer peripheral wall of the implant abutment  121  is shown with flatten areas  121 A and non-continuous, annular grooves  121 B (see  FIG. 11 ), it is contemplated that other suitable patterns of surface protuberances, recesses or treatments may be use. 
         [0093]    In an embodiment, the abutment receiving portion  115 , the implant abutment  121  and the transfer key  102  are precisely machined or formed to at least provide approximate alignment for the pin receiving openings  102 B,  121 C when the implant abutment  121  and the transfer key  102  are properly seated on the implant  100 . Although not required, pin receiving opening  102 B can have a slightly larger diameter than opening  121 C and may be formed over the longitudinal protrusion  109  of the transfer key  102  (see  FIGS. 11-13 ). Preferably, opening  102 B does not penetrate through the cylindrical inner wall of the transfer key  102 . 
         [0094]    The pin receiving openings  102 B,  121 C are used to releasably connect the transfer key  102  and the implant abutment  121  with a locking pin, such as the one shown at reference numeral  204  in  FIG. 13 . By joining the implant abutment  121  and the transfer key  102 , they can be disengaged from the dental implant  100  with a single operation. This is usually sufficient to remove the abutment, unless the transfer key and the abutment are joined together in which case the locking pin is not required. The pin receiving openings  102 B,  121 C may be position at any suitable location on peripheral wall of the implant abutment  121  and the transfer key  102 , provided that the openings do not interfere with the form-fitted engagement of the implant abutment  121 , transfer key  102  and dental implant  100 . 
         [0095]    Referring now to another embodiment of the implant abutment of the present invention which will be discussed with reference to  FIG. 21 , implant abutment  621  is provided with a central bore  610  which is comprised of a cylindrical bore section  610 A, a threaded bore section  610 C and a conical or tapered bore section  610 B. Implant abutment  621  can be seated or removed from the abutment receiving portion of an implant using an abutment insertion and removal tool, respectively, in a manner as discussed below. The conical or tapered bore section  610 B of the implant abutment  621  is configured to mate with a complementary tapered surface of the implant to preferably form a Morse taper connection. Bore section  610 C has a larger diameter than bore  114 A in the abutment receiving end  115  and is threaded to cooperatively engage with the threads on the abutment removal tool. The implant abutment  621  may include grooves or other types of texturing, indentations or elevations for resisting slippage of the crown or dental prosthesis attached to the implant abutment  621 . 
         [0096]    Installation of the alternate preferred dental implant system will be described below. First, a dental implant  100  made of a biocompatible material such as titanium alloy, pure titanium or ceramic is implanted into a patient&#39;s jawbone. Installation of the dental implant  100  may be performed with an implant placement instrument  208  as shown in  FIG. 16 . The lower end of the implant placement instrument  208  is provided with axially extending projections  208 B, resembling those found on the transfer key  102 , for engaging the longitudinal grooves  113  on the dental implant  100 . The upper end  208 C of the implant placement instrument  208  may be formed with tool engagement surfaces or recesses for engagement with a torque applying tool, such as a torque wrench. 
         [0097]    An opening  208 A extends longitudinally through the implant placement instrument  208  and is configured to receive a threaded fastener  207  for threadedly securing the implant placement instrument  208  to the dental implant  100 . The threaded fastener  207  has a rod shaped member  207 A which is threaded at one end  207 B for cooperatively engaging the threads of the internally threaded opening  114 A of the dental implant  100 . An enlarged head member  207 C is formed at the other end of the rod shaped member  207 A to provide a gripping surface for rotating the rod shaped member  207 A. To form a tight connection between the implant placement instrument  208  and the implant, longitudinal grooves of the same size as grooves  113  can be placed in member  207 C. A placement tool, similar to tool  208  can engage those grooves and rotate fastener  207 . Alternatively a hex or other shaped socket or retentive cavity can be placed on the top of member  207 C. 
         [0098]    The implant placement instrument  208  can be used to retrieve the implant from its storage container and thereafter carry the implant to the patient&#39;s mouth for insertion. This advantageously reduces the number of manipulative steps that need to be performed and the number of loose pieces that need handling during implant installation. 
         [0099]    Implants, generally designated as  100 , may be individually stored in implant holding vials or open end sleeves, such as the vial shown at reference numeral  601  in  FIG. 22 . The vial is preferably made of a plastic material. The vial can have any suitable shape such as cylindrical, triangular, square, etc. An implant supporting member  601 A, made of plastic, ceramic pure titanium or titanium alloy, with a disk-, cylindrical-, square- or any suitably shaped body is placed inside the vial and preferably spaced above the bottom of the vial to keep the implant  100  from coming into contact with the sidewalls and the bottom of the vial. The implant supporting member  601 A may include a threaded bore with the thread pitch and shape corresponding to that of the implant  100  for retaining the implant  100  in a substantially vertical orientation. Alternatively, member  601 A can have a conical internal chamber corresponding in size to the tapering end of the implant. This way, the implant  100  can be easily retrieved from the vial using, for example, the implant placement instrument  208 . 
         [0100]    It will be appreciated that the implant insertion tool  208  is readily adaptable to serve as an implant removal tool. 
         [0101]    After the implant is securely affixed to the patient&#39;s bone and sufficient healing has occurred, the crown or dental prosthesis, transfer key  102  and implant abutment  121  are then prepared according to the method of the present invention, as is disclosed herein. 
         [0102]    The transfer key  102  is inserted into the cylindrical bore section  110 A of the implant abutment  121 . In one embodiment, the transfer key  102  and the implant abutment  121  are joined together into one piece in the manner as described herein above. Next, the implant abutment  121  is placed over the abutment receiving portion  115  and rotated to engage the corresponding projections  107  and longitudinal grooves  113 . 
         [0103]    It will be appreciated that these steps may be performed in any appropriate order. For example, the implant abutment  121  may be placed on the dental implant  100  before the transfer key  102  is inserted into the implant abutment  121 . 
         [0104]    After the implant abutment  121  is placed over the dental implant  100 , namely over the abutment receiving portion  115 , and the axial projections  107  are engaged with the longitudinal grooves  113 , an abutment insertion tool, such as the one shown at reference numeral  205  in  FIG. 14 , is lowered through the axial bore  102 A of the transfer key  102 . It is contemplated that the axial bore  102 A forms a passage with a cross-section larger than that of the internally threaded opening  114 A of the dental implant  100  so as not to interfere with the insertion and rotation of the abutment insertion tool  205 . 
         [0105]    Abutment insertion tool  205  is provided with a rod shaped member  205 C having threads at one end  205 A for cooperatively engaging the threads in the internally threaded opening  114 A of the dental implant  100 . The rod shaped member  205 C extends outward from a flat surface  205 B which is dimensioned to have a larger cross-section than the abutment opening  110 A (see  FIG. 12B ) of the implant abutment  121 . 
         [0106]    By rotating the abutment insertion tool  205  in a thread engaging direction, an axial seating force is applied to urge the respective tapered surfaces of the implant abutment  121  and the abutment receiving portion  115  tightly together, preferably forming a Morse taper connection. The flat surface  205 B of the abutment insertion tool  205  abuts and slidably rotates against the occlusal surface  108  of the implant abutment  121  as the abutment insertion tool  205  is turned into the internally threaded opening  114 A by rotation against the threads in said opening. If the top of the abutment is shortened or if there is a large gap between occlusal surface  108  and flat surface  205 B, a spacer of an appropriate thickness may be placed between the implant abutment  121  and the flat surface  205 B of the abutment insertion tool  205 . The transfer key  102  registers the vertical position of the implant abutment  121 , which ensures that the implant abutment  121  travels in a straight line during abutment seating. It will be appreciated that the height of the transfer key  102  is proportional or related to the height of the implant abutment  121 , and that the height of the transfer key  102  should not interfere with the proper seating of the implant abutment  121 . Further, the rotation of the abutment insertion tool  205  may be accomplished with a torque applying tool, such as a torque wrench, and the upper extremity of the abutment insertion tool  205  may be adapted to accept the torque applying tool. 
         [0107]    After the implant abutment  121  is properly seated, the abutment insertion tool  205  is removed by rotation in a thread disengaging direction. If the dentist desires to reinforce the implant abutment  121 , then the transfer key  102  can be removed from the abutment with, e.g., tool  205  to apply a thin layer of glue or a suitable adhesive to the outside surface of the transfer key  102 . Afterwards, the transfer key  102  is inserted back into the implant abutment  121 . Glue can also be placed into holes  102 B and  121 C to improve the connection between the transfer key  102  and the implant abutment  121 . Finally, the crown or dental prosthesis is fabricated and attached (e.g., cemented) over the implant abutment  121 . 
         [0108]    Abutment removal is accomplished as follows. A hole is placed on the occlusal surface of the crown or dental prosthesis to gain access to the axial bore  102 A of the transfer key  102 . The threaded end  206 A of the abutment removal tool  206  is threadedly directed into the axial bore  102 A of the transfer key. If the transfer key  102  and the implant abutment  121  were separately mounted on the abutment receiving portion  115 , the cement used to attach the crown or dental prosthesis to the implant abutment  121  will permeate into the pin receiving openings  102 B,  121 C and join the implant abutment  121  and the transfer key  102  together. The combined implant abutment  121  and transfer key  102  can be detached from the abutment receiving portion  115  by applying an axial and/or rotational force using the abutment removal tool  206 . 
       Alternate Implant Anchoring Structure 
       [0109]    The implants of the present invention may alternately employ a blade-type or a press-fit fixture. It will be appreciated that the size, shape and arrangement of the blade-type or a press fit fixture can vary. 
         [0110]    A further embodiment of the invention is depicted in  FIG. 7 , which shows a dental implant  400  provided with an anchoring portion  116  having three annular, implant-stabilizing members  200 A (or fins) and a threaded region  201 . The number of implant-stabilizing members  200 A may vary from one to three or more as desired, and preferably comprises about 5% to about 50% of the axial length of the anchoring portion  116 . While the anchoring portion  116  has a generally cylindrical shape and is tapered at its lower extremity, other shapes or profiles (such as frusto-conical, conical and uniformly cylindrical profiles) of the anchoring portion may be used. Unless otherwise specified, it is to be understood that all of the components of the alternate embodiments are substantially the same as the other embodiments discussed above. 
         [0111]    The threaded region  201  extends from about the apical end  203  toward the abutment receiving portion  115  of the dental implant  400  (see  FIG. 7 ), and preferably comprises about 50% to about 95% of the axial length of the anchoring portion  116 . The implant-stabilizing member(s)  200 A is disposed between the threaded region  201  and the abutment receiving portion  115 . Although the apical end  203  is shown as being flat, other shapes such as bullet or concave or convex shapes are within the scope and spirit of the present invention. The threads  117  ( FIG. 8 ) in the threaded region  201  can be continuous or non-continuous and uniform or non-uniform, and the ends of the threads  117  can be flat or tapered. The continuity, uniformity, shape, pitch, depth, and spacing of the threads  117  may be varied to obtain the best holding power and screwing/cutting characteristics. If non-continuous threads are employed, the ends of the thread segments are preferably aligned to form at least one longitudinal extending passage or groove for allowing bone tissue growth and enhancing implant stability. 
         [0112]    If the diameter of the abutment receiving portion  115  is smaller then the diameter of the anchoring portion  116 , an annular shoulder  118  may be disposed between the anchoring portion  116  and the abutment receiving portion  115 , and may optionally comprise a continuous or non-continuous, circumferentially extending groove  118 A (see  FIG. 8 ) formed on an annular surface  118 B thereof. While the annular surface  118 B is shown as having a downward slope, which forms an acute angle with the lower edge of the annular shoulder  118 , it will be appreciated that the annular surface  118 B can be oriented at about 90 degrees or at any suitable acute or obtuse angle relative to the lower edge of the annular shoulder  118 . If the diameter of the abutment receiving portion  115  is greater than the diameter of the anchoring portion  116 , which is likely to occur with transitional or mini-implants, then a “reversed” shoulder will be employed to generate the transition between the above-mentioned portions. If the diameters of the abutment receiving portion  115  and the anchoring portion  116  are approximately equal, then a cylindrical collar is provided between portion  115  and  116 . 
         [0113]    If two or more implant-stabilizing members  200 A are employed, each successive member, toward the apical end of the implant, preferably has an incrementally smaller cross section than its preceding member. Also, the width or diameter of the uppermost, implant-stabilizing member and the lower edge of the annular shoulder  118  and maximum diameter of the threads  117  of the threaded region  201  are preferably substantially equal to each other. In the non-limiting embodiment shown in  FIG. 7 , three implant-stabilizing members  200 A are disposed on the dental implant  400  between the annular shoulder  118  and the threaded region  201  in generally parallel spaced apart relation. The number and arrangement of the implant-stabilizing member(s) may vary, depending on, for example, the surgeon&#39;s needs or preferences and/or the anatomical conditions present at the implant site. 
         [0114]    If the uppermost, implant-stabilizing member is formed integrally with the annular shoulder  118  below its lower edge, an annular groove  200 B is optionally provided between the uppermost, implant-stabilizing member and the annular shoulder  118 . None or one or more implant-stabilizing members  200 A may be provided with an annular groove  200 C around the outer edge. Further, at least one annular groove may be provided on the axial wall of the anchoring portion below at least one implant-stabilizing member  200 A or between at least one pair of neighboring, implant stabilizing members  200 A. The depth and width of annular grooves  118 A,  200 C,  200 B of the annular shoulder  118 , the implant-stabilizing member(s)  200 A and the axial wall of the anchoring portion  116 , respectively, preferably ranges from about 0.01 mm to about 0.2 mm. It is contemplated that annular grooves  118 A,  200 C,  200 B and the implant-stabilizing member  200 A can have continuous or non-continuous surfaces or structures. 
         [0115]    In one embodiment, the implant-stabilizing member  200 A has a curved peripheral edge  200 E which helps to displace or expand the bone tissue to facilitate passage of the implant-stabilizing members  200 A into the bore hole in the patient&#39;s jaw bone. Preferably, axially, longitudinally, or circumferentially continuous or non-continuous ribs or grooves  200 F or combinations thereof are formed on the apical surface  200 D of the implant-stabilizing member  200 A for promoting bone ingrowth (see  FIGS. 17A-17D ).  FIGS. 17A-17D  show cutaway views of the implant stem  116 A and examples of different surface structures that can be employed in the apical surfaces  200 D of the implant-stabilizing member  200 A. The ribs or grooves  200 F on the apical surface  200 D may be formed to extend entirely through the implant-stabilizing member  200 A. The ribs or grooves  200 F can be either machined (e.g., laser cutting or engraving) or cast into the apical surface  200 D. 
         [0116]    O-Ring Abutment Assembly 
         [0117]    In  FIGS. 18A to 18F , another aspect of the present invention is illustrated. In this embodiment of the invention, an O-ring abutment assembly (which can also be an attachment for natural tooth), generally designated  530  and employed in removable denture, tooth (natural or artificial) or dental prosthesis, is provided with an O-ring  537 , an abutment  503  and a retainer housing  535 . The abutment  503  is comprised of a downwardly tapering seat member  532  having an upper end  532 A and a lower end  532 B, an anchoring portion  533  extending downwardly from the lower end  532 B of the seat member  532 , an upwardly extending spacing member  531  having one end connected to the upper end  532 A of the seat member  532 , a plate member  538  connected to the spacing member  531  opposite the seat member  532  and a having a plurality of peripherally-disposed axial grooves  513 , and a circumferential cavity  536  defined by the upper end  532 A of the seat member  532 , the spacing member  531  and the plate member  538 . The cavity  536  is configured to receive and releasably retain a major portion of the cross section the O-ring  537 , preferably at least 70% of the cross-sectional area of the O-ring  537  is disposed within the cavity  536 . In another preferred embodiment, at least 85% of the cross-sectional area of the O-ring  537  is disposed within the cavity  536 . The abutment  503  may be formed (e.g., machined, cast or by other suitable means) as a single piece or as a plurality of permanently or detachably connected pieces. 
         [0118]    The remaining peripheral portion of the O-ring  537  that extends beyond the peripheral edge  536 A of the cavity  536  is operable to engage the circumferentially extending groove  535 A formed on the interior cavity wall  535 B of the retainer housing  535  to provide an interference fit between the abutment  503  and the retainer housing  535 . Alternatively, instead of using the retainer housing  535  as an intermediate mounting collar, a groove, similar to groove  535 A of  FIG. 18F , can be provided on the interior cavity wall of an artificial tooth or denture and mounted directly on the abutment  503 . 
         [0119]    The amount (or the cross-sectional area) of the O-ring  537  received within the cavity  536  is selected to minimize the peripheral portion of the O-ring  537  that is received by groove  535 A of the retainer housing  535 , while providing an interference fit between the abutment  503  and retainer housing  535  that can withstand a desired minimum, axial pull-out force (or separation force). In this way, the overall cross-section of the abutment is reduced. A preferred reduced height of the abutment is achieved by selecting a minimum thickness for the plate member  538  for providing a desired mechanical stability. Preferably, the thickness of the plate member  538  is selected such that it does not deform under the stresses of normal usage, installation and removal. 
         [0120]    The plate member  538  may comprise a flat  534  or rounded top surface or a combination of both. Employing a plate member  538 , which is frusto-conical-, bullet-, or dome-like shaped, is also possible. One or more axial grooves  513  may be formed on the edges of the plate member for engaging the projections  508 A of an abutment insertion tool such as tool  508  shown in  FIG. 20 . The axial grooves  513  are preferably arranged to be in axial alignment with the peripherally-disposed, longitudinal grooves  500 A in implant  500  or one of the implants of the invention as described herein above. This way, only one set of tools is needed for implant and abutment placement. 
         [0121]    External threads may be provided on the anchoring portion  533  for securing the abutment  503  in the threaded opening of the implant  500  (see  FIG. 20 ). A Morse-type taper connection can also be used. As shown in  FIG. 19 , the respective male and female taper surfaces of the anchoring portion  533 ′ of the abutment and abutment receiving portion  515  of the implant are sized and configured for mutual taper-locked interconnection. 
         [0122]    As best seen in  FIG. 18D  and  FIG. 19 , the seat member  532  tapers to the cross-section of the anchoring portion  533  adjacent the bottom end  532 B of the seat member  532 , and at least a part of the seat member  532  is depressed into the abutment receiving opening of the implant. The implant preferably comprises a countersunk conical area at an upper region of the abutment receiving opening for receiving a part of the seat member thereon. 
         [0123]    In a further embodiment of the abutment assembly  530 , the seat member, the anchoring portion and the plate member have an equal, uniform circular cross section, and optionally, the plate member has a rounded top surface. 
       Improved Impression Coping System 
       [0124]    There is a need to accurately transfer position information of the dental implant installed in the patient&#39;s mouth to a model used to prepare a dental prosthesis. Thus, it is desirable to have an impression coping suitable for use with the dental implant of the present invention which provides closely matched, complementary mating surfaces to permit precise impression-taking and modeling, despite current manufacturing limitations and tolerances. 
         [0125]    One preferred impression coping  702  is depicted in  FIGS. 23A to 23C , and described as follows. Impression coping  702  has a generally elongated body having spaced apart, axial projections  707  extending outwardly from one end of the body, and a bore  710  extending axially through the body. At least a part of bore  710  can be threaded. The axial projections  707  are preferably provided with sharp edges. The impression coping  702  shares some similarities with the transfer key of the present invention, except that the impression coping  702  does not have a longitudinal protrusion or rail member or a pin receiving opening. The peripheral wall of the impression coping  702  may be provided with grooves, flat surfaces, raised ribs, recesses, apertures or other suitable surface structures to provide anti-rotation while the impression coping  702  is embedded in the impression material. Accurate fit of the impression coping  702  to the implant  700  is achieved by fabricating the longitudinal grooves  713  of the implant  700  with a larger cross section proximal portion  713 A, an apical portion  713 C having a smaller cross section relative to the proximal portion  713 A and a transition portion  713 B which tapers between the proximal portion  713 A and the apical portion  713 C. This allows the axial projections to be inserted into the proximal portion of the longitudinal grooves  713  without experiencing any, or with relatively small, friction force until the axial projections  707  are at the transition portion  713 B. The axial projections  707  are fitted into the transition  713 B and apical  713 C portions of the longitudinal grooves  713  by exerting an axial force on the impression coping  702  using a threaded screw or bolt, thereby forming at least two points of contact between the axial projections  707  and the longitudinal grooves  713 . The screw or bolt is threaded into the threaded opening provided in the top surface of the implant  700 . It is preferred, although not necessary, that the threaded opening of the implant  700  has a smaller cross section than bore  710  of the impression coping  702 . Preferably, the corners of the axial projection  707  become blunt or dig or bite into the walls of the longitudinal grooves  713 , and the axial projections  707  are slightly bent, deflected or displaced outward. In an embodiment, the impression coping  702  is made of a softer material (e.g., pure titanium) than the implant  700 , which can be a titanium alloy, to provide the axial projections  707  with the flexibility to bend when axial projections  707  are press-fitted into the respective engaging longitudinal grooves  713 . 
         [0126]    It will be appreciated that the structures of the cooperating mating surfaces of the impression coping  702  and the axial projections  707  can be readily implemented in the transfer keys and dental implants of the present invention as described herein. 
         [0127]    The axial projections  707  of the impression coping  702  may correspond to longitudinal grooves  713  of the implant  700  in dimension, shape, number and spacing. In a preferred embodiment, the axial projections  707  are essentially square in shape, while the grooves  713  are semicircular. The inward corners of projections  707  are made to passively fit inside the proximal  713 A portions and actively engage the  713 B and  713 C portions. The walls of the proximal  713 A and apical  713 C portions of the longitudinal grooves  713  can be parallel. Further, at least a section of the walls of the proximal  713 A and apical  713 C portions of the longitudinal grooves  713  may be formed at an incline, preferably having the same inclination angle (for example, 1-10°) as the peripheral wall of the abutment post or abutment receiving portion of the implant. Further, it is possible to preserve the benefits of the invention by having the proximal portion with parallel grooves and the apical portion formed at an incline, omitting the transition portion. 
         [0128]    A suggested procedure for obtaining precise translation of the orientation of the dental implant to a model utilizing impression coping  702  is described below. However, it will be apparent to one of ordinary skill in the art that other embodiments are also possible in which various steps are added, combined, modified, substituted, automated or omitted. 
         [0129]    The impressing coping  712  is placed over the implant  700  and orientated to engage the corresponding axial projections  707  and longitudinal grooves  713 . A fastener (e.g., threaded screw) is used to urge the axial projections  707  and the longitudinal grooves  713  into a closely fitting engagement and to temporarily secure the impression coping  702  to the implant  700 . 
         [0130]    Impression material is applied over the impression coping  702 A and surrounding dentition utilizing, e.g., standard open tray technique. 
         [0131]    Once the impression material sets, the fastener is removed, followed by the removal the impression material from the patient&#39;s mouth. The impression coping  702  may be picked up by the impression material or may remain on the implant  700 . If the impression coping  702  is not picked up by the impression material, an abutment removal tool, such as the one shown at reference numeral  206  in  FIG. 15 , can be connected to the threaded bore  710  to remove the impression coping  702  from the implant  700 . 
         [0132]    With the impression coping  702  placed or remaining in the impression material, an implant analog (post) is brought into engagement with the impression coping  702 . The distal end of the implant analog is provided with longitudinal grooves which are substantially similar those provided on the implant  700  and which correspond to and engage with the axial projections  707  of the impression coping  702 . A fastener is again used to temporarily secure the impression coping  702  to the implant analog. 
         [0133]    Soft model material is poured into the negative impression (formed in the impression material) into the area immediately surrounding the impression coping  702 , while the area surrounding the implant analog is filled with the hard material. The fastener, impression coping  702  and impression material are removed from the implant analog and the hardened model material. The soft model material can be trimmed back from the implant analog to allow the seating of the implant abutment. The implant abutment and/or the dental prosthesis can be fabricated on the implant analog. 
         [0134]    It will be understood and appreciated that the concept embodied within the mating structures of the impression coping and the implant body described in a preceding section of this application can be readily applied to various types of two-part dental implant systems (e.g., those with an implant abutment and an implant body), whether now known or later developed, to substantially prevent rotation of the abutment when the abutment is seated on the implant body. A typical dental implant utilized in a two-part dental implant system is generally provided with a hexagonal or tri-lobed projection (or a suitable polygonal protrusion) for engaging the correspondingly configured cavity in the abutment. Alternatively, the projection may be formed on the abutment, and the internal cavity formed in the implant. See U.S. Design Pat. No. D446,859, issued to Hurson, for an example of this type of dental implant system. To provide an interference fit which will substantially inhibit relative rotation between the abutment and the implant, the internal cavity is provided with an upper region of a larger cross-section, a lower region of a smaller cross-section relative to the upper region, and a transition region tapering from the upper region to the lower region. The upper region is configured to permit the protrusion to passively mate with the internal cavity. When the lower edge of the projection reaches the transition region, an axial force will be required to fully insert the projection into and engage the internal cavity. The smaller cross-section of the lower region of the internal cavity causes the (axially-extending) edges of the projection to bite into the inner wall of the lower region to form a relatively rotation-free engagement. Alternatively, the transition region can be omitted. In this case the lower region would have inclined surfaces to mate with the projections. Preferably, the relative rotation between the implant and the abutment, or the impression coping and an implant, is reduced to 0 degree. It is also possible to realize a mating arrangement whose rotation is limited only by the capability of the manufacturing machinery or process. The above-described coupling surfaces, when employed in the implant-mating recess or projection of an impression coping device in conjunction with an implant having complementary mating surfaces, are especially advantageous for procuring highly accurate dental impressions of a patient&#39;s mouth and teeth during a dental reconstruction procedure due to the substantially rotationally-inhibited connection that results. 
         [0135]    The principles and concepts of the present invention enumerated herein can be readily implemented in an existing or later developed dental implant system that includes an implant body and an abutment coupled together by means of a taper connection and/or a threaded fastener. For example, U.S. Pat. No. 6,726,481 describes various abutments which are attached to the implant body using a threaded connection (e.g., threaded fastener) and a friction-fit connection formed by complementary, tapered mating surfaces. However, these types of abutments cannot be easily removed for repair or replacement. By providing or configuring the upper section of the axial bore of the abutment with internal threads having a diameter larger than the fastener-receiving opening on the implant body, an abutment removal tool, such as the one disclosed in  FIG. 15  at reference numeral  206  can be connected to the abutment, and disengage the abutment from the implant body. 
         [0136]    It is also contemplated that the present invention includes implant-abutment systems that, in addition to the novel features described herein above, utilize complementary projecting and recessed hex or polygonal (e.g., with 4-8 side walls) surfaces, or keyed surfaces having a suitable irregularly shaped configuration, as indexing means for ensuring accurate placement and orientation of the abutment relative to the implant body. Preferably (although the reverse configuration is also acceptable), the raised keyed surface is formed on the top surface the implant and the corresponding recessed cavity is formed within the abutment. 
         [0137]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.