Abstract:
A dental implant system including an implant having an incisal portion for insertion into a alveolar receptor site formed in the jawbone to receive the implant, a collar having a beveled shape extending superiorly from the incisal portion with a smooth polished surface, a threadless cavity extending from the occlusal end of the implant partially into said embedded incisal portion with the cavity having a recessed groove adjacent the proximal end of the incisal portion, a removable healing cap adapted to be placed into the threadless cavity of said implant with said healing cap having a resilient shoulder projecting therefrom to engage said groove for forming a sealed interlock during an extended healing period and a single post abutment member for insertion into the threadless cavity of the implant after removal of the healing cap. An alternative embodiment of the implant system includes an implant having an incisal section with a vertical height of less than about 6mm for insertion into a very shallow bone receptor site formed in the jawbone of the patient, a plurality of projections laterally extending from a position near the apical end of the implant in a spider like arrangement so that they initially cover a broad subperiosteal surface adjacent mucosal tissue to give the implant lateral stability against lateral forces.

Description:
FIELD OF INVENTION 
     This invention relates to an improved dental implant system which minimizes or eliminates laboratory fees and accelerates healing in a shorter time period with greater predictability compared to conventional implant systems. 
     BACKGROUND OF THE INVENTION 
     A dental implant is a submergible structure which is inserted in the alveolar cavity of the jawbone to permit attachment of a dental prosthesis to the implant in an edentulous region. The implant requires a healing period of up to nine months to assure bone ingrowth and clinical ossiointergration at the bone implant interface. Once the healing period is over and the implant is firmly anchored to new bone, the mucosal gum tissue above the implant is penetrated for attachment of an upper post portion to which an artificial dental prosthesis is connected. 
     Conventional dental implants utilize a plurality of components commonly referred to as abutments which in combination with the embedded implant form the implant system. The abutments of a conventional implant system are externally and internally threaded to permit the components to be removably interconnected to one another. The proximal end of the abutments are typically shaped in the configuration of an hexagonal nut so that a wrench may be used to interconnect the abutment to the implant. The implant also contains a threaded recess to receive an abutment and has a projection at its occlusal end which is also in an hexagonal configuration. The implant may also be externally threaded to facilitate a self-tapping insertion of the implant into the cortical bone substructure. 
     The array of interconnecting abutments of a conventional implant system increase the installation expense of the implant and may necessitate the assistance of an outside dental laboratory to provide the component parts. More importantly, it has now been clinically established that the use of multi-threaded interconnecting abutments unavoidably leave clearance spaces or gaps at the interface between the internal and external threads of the implant and the interconnecting abutments. These gaps represent hollow crevices which allow for microbial leakage and also act as a trap for bacteria permitting microbial colonization at the juncture between the fittings. Microbial leakage can also cause inflammatory reactions in the peri-implant soft tissue. In addition, the use of many abutment components increase the procedure time and cause complications based upon the various parts needed. Furthermore there is an increased likelihood of the many parts not fitting accurately or loosening up from the occlusal forces during chewing which can result in excessive wear and breakdown. 
     In addition the post abutment may need to be placed at an angle with respect to the embedded implant in order to align the artificial dental prosthesis with the other teeth of the patient. To achieve this the post abutment is either bent after installation or is preangulated. Bending the post after installation is contraindicated and can cause fatigue and breakage. Although the use of a preangulated post is preferred this currently requires at least one additional screw-like member to secure the post to the implant. This complicates the design of the preangulated post since the design must account for how the screw is to be fastened through the post to the implant. Moreover if the post abutment, screw and implant are all threaded to facilitate their interconnection this will lead to the problem of microbial leakage referred to above. 
     The implant system of the preferred embodiment of the present invention is a two component system utilizing a narrow gauge implant which is preferably tapered and precisely contoured to press fit into the bone receptor site. A healing cap is removably inserted into a non-threaded cavity formed in the implant to form a seal within the cavity so as to permit healing of the implant without any potential for microbial leakage. Upon removal of the cap a single post abutment component is placed into the cavity for connecting the implant to a dental prosthesis. Since the implant is non-threaded the circumference of the implant may be significantly narrower in size relative to the circumference of the conventional threaded implant. In addition, the single post abutment is seated into the implant which permits it to be preangulated at an angle of from 0° to 30° to achieve parallelism with adjoining implant posts or other abutments without complicating its design. Once a preangulated post is selected with the desired preangulation it is fitted into the implant and then turned relative to the longitudinal axis of the implant to achieve the desired alignment. Thereafter the post is cemented in place to the implant. A plurality of horizontally spaced serrations are preferably formed around the circumference of the implant with the serrations spaced a fixed distance apart and extending over the entire vertical height of the embedded implant or a section thereof. 
     In another embodiment of the present invention the post abutment includes a shaft extending from the post abutment at any desired angle relative to the longitudinal axis of the implant. In this embodiment the desired angle is formed by connecting a threaded shaft into a threaded opening in the post abutment which can be done after the post abutment is seated in the implant. The threaded opening may be formed at any desired predetermined angle with the longitudinal axis of the implant thereby establishing a predetermined angle of inclination for the threaded shaft relative to the longitudinal axis of the implant. 
     In another two-component embodiment of the implant system of the present invention the vertical height of the implant may be shortened to a length of less than about 6 mm which facilitates insertion into a very shallow bone receptor site. In this embodiment the implant includes lateral projections extending from a position near the apical end of the implant to give the implant lateral stability. The use of a very short implant having lateral projecting arms at the occlusal end in a spider like arrangement permits the implant to avoid contact with the maxillary sinus or the mandibular nerve and may be used in the posterior portion of the mandible and maxilla in cases where minimum vertical height of bone is available. Two implants of this type having lateral projections in a spider like arrangement may also be inserted into the bone in tandem to provide additional strength and may be aligned so that the projections interdigitate. The use of two implants of this type in tandum is particularly suited for use where bone structure is minimal in the labialpalatal dimension in a posterior portion of the mandible or maxilla. 
     Yet another embodiment of the invention is a unitary narrow gauge implant having an integrated abutment post forming a unitary solid implant structure containing a post abutment for use in a posteria region of the mandible and/or maxilla where the jawbone is narrow. This implant is of a very narrow gauge with an extended length of over 18 mm and preferably between 18-22 mm. Two narrow gauge implants of this type may be used in tandem. 
     An additional embodiment of the present invention is an implant for use with a denture which permits a denture to be removably attached to either the upper or lower jawbone and to maintain the denture in a fixed position within a patients mouth. 
     In yet another embodiment of the present invention the distal end of the implant body is formed with a hollow interior adapted for the insertion of a bone morphogenic protein which is known to facilitate bone osseointegration. The distal end of the implant body surrounding the hollow area is defined by a plurality of projections extending lengthwise in a direction substantially parallel to the longitudinal axis of the implant permitting the distal end to be crimped so as to form an enclosure for the insertion of a bone morphogenic protein material composition. 
     SUMMARY OF THE INVENTION 
     One embodiment of the implant system of the present invention includes an implant having a tapered apical portion for insertion into an alveolar receptor site formed in the jawbone to receive the implant, a collar extending superiorly from the incisal portion with the collar having a beveled section, a threadless cavity extending through said collar and partially into the apical portion of the embedded implant, a recessed groove formed in the collar of the implant, a removable healing cap adapted to be placed into the threadless cavity of said implant with said healing cap having a resilient shoulder projecting therefrom in alignment with said recessed groove so as to form a sealed interlock upon insertion of the healing cap in said cavity and a single post abutment member for insertion into the threadless cavity of the implant after removal of the healing cap. The single abutment member may be preangulated at an angle of between 0° to 30° relative to the longitudinal axis of the implant to achieve parallelism with adjoining teeth in the mouth of the patient. A plurality of serrations are preferably formed around the circumference of the implant horizontally spaced apart from one another with the serrations extending over a section of the vertical height of the embedded portion of the implant to permit a plasma sprayed coating of hydroxyl apatite to be readily seated therein. 
     Another embodiment of the present invention comprises a dental implant having an apical portion for insertion into a very shallow bone receptor site formed in the jawbone with a vertical height corresponding to a length of less than about 8 mm, a plurality of projections laterally extending from a position near the apical end of the implant in a spider like arrangement for engaging the jawbone at the surface adjacent to mucosal tissue to give the implant lateral stability, a threadless cavity extending from the apical end of the implant at least partially through the embedded implant, a removable healing cap for placement into said cavity and a post abutment member for insertion into the cavity after removal of the healing cap. 
     Yet another embodiment of the present invention comprises a dental implant formed as a solid integrated single structure having an abutment post extending from a narrow gauge apical portion with said structure having a length of between 18-22 mm for insertion into a receptor site of a narrow jawbone. 
     A further embodiment of the present invention comprises a dental implant designed to be interconnected to a denture to permit the denture to be removably attached to the upper or lower jawbone of a patient, said implant comprising an incisal portion for insertion into an alveolar receptor site formed in the upper or lower jawbone to receive the implant, a partial cavity formed in the implant extending from the apical end with a portion near the occlusal surface having a substantially spherical geometry for forming a female coupling adapted to receive a complementary male abutment extending from a denture with said complementary male abutment being in alignment with the cavity of the implant when the denture is seated over the jawbone, said complementary male abutment having a corresponding spherical shape and size for insertion into the socket of the implant. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings of which: 
     FIG. 1 is a view in perspective of a preferred embodiment of the implant of the present invention; 
     FIG. 1A is a modified version of the implant of FIG. 1; 
     FIG. 2 is an exploded cross sectional view of the implant of FIG. 1 with the implant shown embedded in a bone receptor site of a jawbone in combination with a healing cap which is removably inserted into the implant to permit the implant to heal before a post abutment as shown in FIG. 4 or FIG. 11 is substituted for the healing cap and cemented into the implant; 
     FIG. 3 is a cross sectional view of a modified embodiment of the implant shown in FIG. 2 having a tapered incisal body at least extending over the lower distal end region thereof; 
     FIG. 4 is a cross sectional view of the implant system of FIG. 2 in which the healing cap is removed and replaced with a preangulated post abutment over which a dental prosthesis is formed to match adjacent teeth; 
     FIG. 5 shows an alternative embodiment of an implant system in accordance with the present invention; 
     FIG. 6 is an exploded cross sectional view of the implant of FIG. 5 with the implant shown embedded in a bone receptor site of a jawbone in combination with a healing cap which is removably inserted into the implant to permit the implant to heal before a post abutment as shown in connection with FIG. 4 or FIG. 11 is substituted for the healing cap and is cemented into the implant; 
     FIG. 7 is a top view of a pair of the FIG. 5 type implants inserted into the jawbone with the arms from each of the implants arranged in an interdigitating relationship relative to one another; 
     FIG. 8 is a perpective view of another embodiment of the implant system of the present invention; 
     FIG. 9 is an exploded view in cross section of the distal end of the implant shown in FIG. 8; 
     FIG. 10 is a bottom view of the distal end of the implant of FIG. 9 taken along the lines  10 — 10  of FIG. 9; 
     FIG. 11 is another view of the distal end of the implant of FIG. 8 after crimping the slitted ends thereof so as to form an enclosure adapted for insertion of a conventional bone morphogenic protein; 
     FIG. 12 is a perspective view of yet another embodiment of the implant system of the present invention adapted for interconnection to a denture; 
     FIG. 13 is an enlarged cross sectional view of one of the implants shown in FIG. 12; 
     FIG. 14 shows the denture of FIG. 12 affixed to the jawbone through the implants; 
     FIG. 15 is a cross sectional view taken along the lines  15 — 15  of FIG. 14; 
     FIG. 16 shows another implant design of the present invention with the implant representing a solid integrated body having a post abutment extending therefrom; and 
     FIG. 17 is a cross sectional view of yet another embodiment of the implant system of FIG. 2 in which the healing cap is removed and replaced with a post abutment adapted to receive a threaded shaft which will extend from the post abutment in a given preangulated direction over which a dental prosthesis is formed to match adjacent teeth. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1-4 which correspond to a first preferred embodiment of the implant system of the present invention. As shown in FIGS. 1-3 the implant  10  comprises a narrow gauge body  12 , as narrow as 2.8 mm which is press fitted into a receptor site formed in the jawbone  14  of a dental patient. Before installation of the implant  10  an incision is made in the gum tissue of the patient and the underlying bone is exposed. A drill having a drill bit of a configuration matching the configuration of the implant is used to bore a hole in the jawbone  14  of a size slightly smaller than the circumference of the implant body  12 . This permits the implant  10  to be press fitted into the bored hole. The implant  10  should be composed of a biocompatible material preferably of titanium metal although any other biocompatible material may be used. Before the implant is press fitted into the bored hole a duplicate “test” or “try in” implant of slightly smaller diameter may be inserted into the bored hole to assure accuracy in fit. The duplicate “test” or “try in” implant may fit relatively loosely. The test implant should be highly polished and may have a head or knob (not shown) at the occlusal end thereof so that it may be easily retrieved before the implant  10  is press fitted into the bore. 
     The implant body  12  may be tapered as shown in FIG. 3 to facilitate its insertion into the jawbone  14  of the patient. This is particularly important for insertion into the posterior region of the mandible and maxilla where bone structure is minimal. Moreover, in cases where bone structure tapers downwardly which is usually the case for older patients which have lost considerable bone the implant taper may progress to form a relatively substantial tapered angle “α” at the lower distal end  15  of the shaft  12  as shown in FIG.  3 . The taper angle “α” at the lower distal end  15  of the implant can be as much as 10° to 15°. 
     The implant  10  has a beveled collar  16  extending superiorly from the shaft portion  12  of the implant  10  and a substantially upright section  17  of substantially cylindrical geometry at its proximal end. The beveled collar may be somewhat thicker in circumference at the occlusal surface abutting the porcelain superstructure  18  surrounding the post abutment  20  as shown in FIG.  4 . The beveled collar  16  and the upright section  17  of the implant  10  may have a smooth polished exterior surface. 
     A threadless cavity  22  is formed within the interior of the implant  10  extending from its proximal surface partly into the body of the implant  10 , i.e. a predetermined distance “d” beneath the occlusal surface  21  of the jawbone. The cavity  22  includes an annular recessed groove  23  formed around the beveled collar  16  preferably where the collar is relatively thick. The exterior of the implant body  12  should preferably have a plurality of serrations  24  which are spaced longitudinally apart along the vertical height of the implant  10  to facilitate the seating of a plasma sprayed coating of hydroxyl apatite “HA” before the implant  10  is press fitted into the jawbone  14 . The coating of HA may have a thickness of up to 50 microns to increase bony apposition at the interface between the implant  10  and bone  14 . In addition, a substantial vertical relief groove  25  as shown in FIG. 1A and 2 may be formed extending along the exterior of the implant body  12 . 
     Before the gingival tissue is replaced a healing cap  30 , as shown in FIG. 2, is inserted into the cavity  22  of the implant  10 . The healing cap  30  is an important attribute of the implant system of the present invention and is designed as a plug to permit the implant  10  to heal while clinical ossiointergration occurs at the bone implant interface over a predetermined healing period. During this healing period microbial leakage into the implant  10  is minimized by designing the healing cap  30  to also function as a seal. The healing cap  30  is removably inserted into the cavity  22  of the implant  10  without the complications of using multi-abutment components or tooling. The healing cap  30  is composed of a resilient plastic material having an annular shoulder  32  which snaps into the complementary annular recessed groove  23  of the cavity  22  thereby forming an interlocking seal. This secures the cavity  22  with the plug functioning to prevent microbial leakage. The healing cap  30  has a domed top  34  with two or more depressed areas  35  designed to permit a gripping tool such as a pair of conventional pliers to be used to pull the healing cap  30  out from the cavity  22  after completion of an adequate healing period. Because of the resiliency of the plastic composition of the cap  30 , the cap  30  readily disengages from the cavity  22 . 
     Upon removal of the healing cap  30  a post abutment  20 , as shown in FIG. 4, is placed into the open cavity  22 . The post abutment  20  has a proximal end  37 , a distal end  38  seated in the implant  12  and an annular shoulder  36  equivalent to the shoulder  32  of the healing cap  30  for engaging the annular recessed groove  23  of the implant  12  as discussed in connection with FIG.  2 . The post abutment  20  is preferably also formed with a collar  39  particularly when the post abutment  20  is to be preangulated. The collar  39  abuts the upright section  17  of the implant  12 . The post abutment is preangulated at a fixed angle relative to the longitudinal axis of the implant to achieve parallelism with adjoining teeth in the mouth of the patient. A plurality of fixed pre-angulated post abutments  20  at different angles preferably between 0° to 30° to the central axis of the implant provides the dentist with an adequate selection of angles to achieve parallelism with adjoining teeth in the mouth of the patient. After selecting a desired pre-angulated post abutment  20  the post abutment  20  is then further adjusted into position for proper alignment with adjoining teeth by turning the distal end  38  around its central axis. Thereafter the post abutment  20  is cemented in place to the implant  10 . 
     A variation of a post abutment design of FIG. 4 is shown in FIG. 17 in which the post abutment  80  has a proximal end  81  and a distal end  82 . The distal end  82  is adapted to be fitted into the cavity  22  formed in the implant body  12 . The abutment  80  may include an annular shoulder  36  equivalent to the annular shoulder  36  in FIG. 4. A shaft  84  is threadably connected into a threaded opening  85  in the abutment  80 . The threaded opening  85  should be formed at any desired angle to the longitudinal axis of the abutment so that the shaft  84  will always extend ninety degrees from the face  86  of the abutment  80 . The dotted lines about the shaft  84  in FIG. 17 show different position of the shaft  84  forming different angles between the threaded opening  85  and the longitudinal axis of the abutment. In this way a porcelain superstructure such as  18  in FIG. 4 may be formed over the shaft  84  with the shaft  84  aligned to achieve parallelism with adjoining teeth in the mouth of the patient. Before forming the porcelain superstructure over the shaft  84  a fused aluminum oxide sleeve  87  may be placed thereon to circumvent metal shadows particularly for anterior teeth. 
     Another embodiment of the two component implant of the present invention, preferably for use in cases where minimum vertical height of bone is available, is illustrated in FIGS. 5 through 7. In the embodiment of FIG. 5 an implant  40  is shown comprising a shaft  41  with a vertical height no greater than about 6 mm so that it will not involve contact with the maxillary sinus or the mandibular nerve. This implant embodiment is designed for use in the posterior portion of the mandible and maxilla, where their is minimum vertical height of bone. The shaft  41  of the implant  40  has a beveled collar  43  extending superiorly from the shaft  41  with a smooth polished outer surface. The exterior surface of the implant  41  may have a plurality of serrations  42  which are spaced longitudinally apart along the height of the implant body  41  to facilitate the seating of a plasma sprayed coating of hydroxyl apatite “HA” before the implant  40  is press fitted into a receptor site  44  formed in the jawbone  14  to receive the implant  40 . 
     The implant  40  may be cylindrical or tapered in a shape similar to the geometry of the implant  10  and may be of a similar composition preferably of titanium metal. A plurality of projections  46  extend laterally from a position adjacent the upper end of the body  41  in a spider like arrangement and may terminate to form a plurality of bent outer tips  47  directed downwardly to engage openings  48  formed in the jawbone  14  surrounding the receptor site  44 . Alternatively, the outer projections  46  may be straight and not form bended tips  47 . In FIG. 7 a pair of implants  40  are shown inserted in the jawbone  14  in tandem to one another so that the projections  46  from each implant  40  mesh in a gear-like arrangement. The projections  46  should lie on the subperiosteal surface of the jawbone  14  at the interface between the jawbone  14  and mucosal tissue  45  as shown in FIG.  6 . During the healing period ossiointegration will occur to cover the projections  46 . The plurality of bent outer tips  47  which extend into the jawbone  14  become integrated with the bone to form a unitary endosseous implant. A receptor site is formed in the jawbone  14  to receive each implant  40  using a drill in the same fashion as the receptor site formed in the jawbone  14  of FIG. 2. A single tool may be used to form the receptor hole and multiple surrounding openings  48  into which the tips  47  are placed. The projections  46  and depending tips  47  give the implant  40  lateral stability to anchor the short body  41  of the. implant  40  in the jawbone  14  throughout the healing period and afterwards. 
     During the healing period a healing cap  30  as shown in FIG. 2 is inserted into the cavity  22 . The cavity  22  formed in the implant body  41  has a recessed annular groove  23  which interlocks with the complementary annular shoulder  32  of the healing cap  30  shown in FIG.  2 . After the healing cap is removed from the cavity  22  a post abutment  52  as shown in FIG. 6 is seated in the cavity  22  and cemented in place. The post abutment  52  is constructed similarly to the post abutment  20  of FIG.  4  and may include the collar  39  of FIG. 4 to facilitate formation of a plurality of fixed preangulated post abutments  54  at different typical angles preferably between 0° to 30° to the central axis of the implant similar to preangulated post abutments  20 . A porcelain superstructure is formed over the preangulated proximal end  54  of the post abutment  52  before the post abutment  52  is cemented in place following conventional practice. 
     The projections  46  extending from the implant  40  distribute the load from biting forces over a relatively broad subperiosteal jawbone surface. The bent ends  47  of the implant  40  provide stability to lateral forces, since the perimeter is supported against and/or within the cortical bone. The implant  40  requires only one surgical procedure without the necessity for an impression. 
     The body  12  of each of the implant embodiments of the present invention may include a modified distal end constuction as shown in FIGS. 8-11 inclusive. In this embodiment the distal end  60  of the implant  12  contains a hollow area  61 . A plurality of slitted sections  63  having a shape  62  corresponding to an inverted “V” are formed in the distal end  60  of the implant  12 . The slitted sections  63  surround the hollow area  61  and extend lengthwise substantially parallel to the longitudinal axis of the implant. Each section  63  has an open ended tip  64  which is slightly bent in the lateral direction to facilitate crimping the sections  63  of FIG. 9 toward one another into the configuration shown in FIG.  11 . With the tips  64  crimped as shown in FIG. 11 the hollow area  61  is substantially closed at the bottom end  66  of the implant  12 . A bone morphogenic protein  67  which is known to facilitate bone osseointegration is inseted into the area  61  of the implant  12 . Any known bone morphogenic protein  67  may be used and may be combined with collagen in a micro or macro encapsulated form to be absorbed by receptor cells once introduced into the surrounding bone. The distal end  60  of the implant should also have a plurality of openings  65 , preferably four or more, laterally extending through the sections  63  into the area  61 . Use of the hollow area  61  at the distal end of the implant as a reservoir reservoir for a gel or for micro or macro encapsulation of a bone morphogenic protein  67  is a unique feature of this invention. 
     In addition a grooved pathway  69  may be formed as shown in FIG. 8 in the implant  12  extending preferably from the openings  65  upwardly to the upright section  17  of the implant  12 . The combination of openings  65  and the grooved pathways  69  provide a path for movement of the bone morphogenic protein  67  from the area  61  over the surface of the implant  12  allowing the bone morphogenic protein  67  to surround the implant  12  after it is implanted. The bone morphogenic protein  67  may be injected into the area  61  or may be placed in a porous vessel or bag  68  which is inserted into the area  61  before crimping the ends  64 . The grooved pathway  69  functions as a feeder groove to a groove  79  surrounding the collar  17  of the implant  12  as shown in FIG. 8 to control die back at the occlusal or incisal aspect of the bone where the implant enters the bone. 
     Another implant design in accordance with the present invention which is designed primarily for use in the posterior portion of the mandible and/or maxilla where the jawbone is narrow but sufficiently deep to accommodate a long shaft is shown in FIG. 16 in which the implant  55  is a solid structure combining an elongated narrow gauge shaft  56  of at least between 18-22 mm adapted for insertion into an elongated cavity (not shown) formed in the jawbone and a post abutment structure  57  extending from the shaft  56  as an integral unit. The post abutment structure  57  may be preangulate to define a fixed pre-angulated post abutment at any desired angle of preferably between 0° to 30° to the central axis of the implant. This narrow gauge implant  55  may be used as a provisional implant or an a permanent implant. 
     A further embodiment of the present invention is shown in FIGS. 12-15 respectively. in this embodiment the implant system of the present invention comprises an implant  71  which is implanted in the upper or lower jawbone of a patient and a male plug  78  representing an abutment which is permanently affixed to a denture  72  to permit the denture  72  to be removably attached to the upper or lower jawbone containing the implant  71 . In FIG. 12 the denture  72  is shown adapted for removable attachment to the lower jawbone  14  containing an implant  71  and in FIG. 14 the denture  72  is shown affixed to the lower jawbone  14  by the interlocking of the implant  71  and the male plug  78 . Although one implant  71  will satisfy the requirements of this embodiment of the present invention two or more implants  71  are preferred. Each implant  71  as more fully shown in FIGS. 13 and 15 has a shaft portion  12  directly corresponding to the body  12  of the implant  10  of FIG.  1 . The length of the shaft  12  can also be reduced to conform to the length of the shaft  41  of the implant  40  of FIG.  5 . The shaft  12  of the implant  71  includes a beveled collar  73  extending superiorly from the shaft and a substantially upright section  74  of substantially cylindrical geometry at its proximal end. A threadless cavity  76  is formed extending from its proximal surface partly into the implant shaft  12  to a desired depth beneath the occlusal surface of the jawbone  14 . The cavity  76  has a substantially spherical shape forming a spherically shaped socket into which the male plug  78  extending from the denture  72  is mounted. The male plug  78  may be permanently affixed to the denture  72  in any conventional fashion such as by insertion into an opening formed in the denture which is then closed using an adhesive cement or by molding the denture  72  with the male plug affixed thereto. Alignment between the male plug  78  and implant  71  is preestablished before the implant  71  is implanted in the jawbone  14  so that insertion of the male plug  78  into the implant  71  automatically maintains the denture  71  in a desired position on the jawbone  14 . The male plug  78  has a substantially spherical shape which is complementary to the spherical geometry of the cavity  76  to cause interlocking engagement of the male plug  78  and the cavity  76 . The male plug  78  can be manually disengaged from the cavity  76  by lifting the denture off the jawbone  14 .