Abstract:
The implantable portion of the implant body includes a bone engaging surface ( 40 ) which, is spaced from the upper side of the implant body by a smooth coronal surface ( 42 ). The edge ( 62 ) of the bone engaging surface follows the crestal outline of the supporting bone tissue. The bone engaging surface could include (a) an externally threaded portion, (b) an acid etched, physically abraded or other roughened or textured peripheral surface, (c) a porous coated surface which for example, could consist of titanium, metal or ceramic beads and/or (d) a chemically coated portion. Chemical coatings for use with the bone engaging surface could comprise bioreactive coatings, (including coatings formed from hydroxyapatile and other compounds suitable for stimulating bone tissue growth) which facilitate the anchoring of the implant body by bone tissues following its placement.

Description:
[0001]     The present invention relates to a dental implant to be used in areas in the mouth where aesthetics are of a high concern, and more preferably an implant which has a bone engaging coated, textured and/or porous portion which has a contour selected to approximately mirror a predetermined surface contour of bone tissues at the site of implant placement.  
       BACKGROUND OF THE INVENTION  
       [0002]     Conventional implant constructions are generally of a two-part design and include a body portion which is adapted to be recessed into the patient&#39;s jaw, and a prosthesis in the form of a ceramic tooth which is adapted for coupling to a proximal end of the body. The implantable body which is made from stainless steel, titanium or other suitable metals or alloys is configured to be recessed into a suitable bore hole formed in the patient&#39;s jaw bone at the site of a lost tooth. Typically, the body has a threaded interior or is otherwise configured to mechanically receive thereto an attachment post which serves as a support for the ceramic tooth.  
         [0003]     U.S. Pat. No. 5,344,457 to Pilliar et al., entitled “Porous Surfaced Implant”, discloses a frustoconical shaped implant which is characterized by a porous coated bone engaging lower portion and a smooth non-porous upper bone attachment region or collar. The implant is press-fitted into a complementary sized bore formed in the patient&#39;s jaw bone at the site of placement and over time, bone tissues grow into and engage the porous coating on the lower portion of the implant to firmly anchor it in the place of a natural tooth. The implant which is the subject of U.S. Pat. No. 5,344,457 has achieved a significant degree of success in the market place, and is presently sold by Innova Corp. of Toronto, Canada, under the name Endopore®. Endopore® dental implants are used in the replacement of various teeth including, lost molars and bicuspid teeth in the anterior and posterior regions of the mouth.  
         [0004]     Other conventional implant constructions are characterized by the implantable body being cylindrical in shape and provided with a roughened lower exterior surface, texture, external thread configuration and/or coating, to facilitate the engagement of the implant body with the patient&#39;s surrounding bone tissues and its anchoring in place.  
         [0005]     A difficultly exists with conventional implants in that todate, they have achieved limited success in replacing incisors and teeth in the frontal-most regions of the mouth where high aesthetic demands exist. The abutment-implant interface, also termed “microgap”, is believed to harbor bacteria and bacterial products following exposure to the oral environment. This in turn results in the establishment of a “biological width” around the implant (i.e. the distance from the peri-implant bone crest to the microgap). The biological width is relatively constant and seems to be approximately 2 mm, similar to the biological width present around natural teeth. It has been found that following implantation, crestal bone remodeling occurs, whereby supporting bone tissues and the overlying bone tissues tend to recede to the uppermost peripheral edge of the textured or porous coated bone engaging portion of the implant body. A further variable that can play a role in crestal bone remodeling is lack of mechanical coupling around any smooth upper collar surface. For example, it has been demonstrated that the crestal bone resorption around Endopore® implants stops at the junction of the smooth collar and the porous surface. It has been suggested that the lack of mechanical coupling around the smooth collar surface results in “disuse atrophy” of the crestal bone to the level of the junction with the porous surface. This has been demonstrated also with other textured implant surfaces.  
         [0006]     The receding supporting tissues or crestal bone loss around dental implants has led to an aesthetic challenge when attempting dental restorations in that it may result in exposure of the metal implant body, greatly detracting from the natural appearance of the prosthesis. Conventional implants suffer the disadvantage in that the alveolar bone which encases the tooth root tends to gradually disappear along the portion of the implant where engagement of bone tissue with the implant body does not occur. This leads to a corresponding recession of the sulcus and overlying gum tissues which gradually results in the exposure of the stainless steel body of the implant. In the more aesthetically important regions of the mouth, the exposure of the stainless steel portion of the implant body greatly detracts from the natural look of the prosthesis.  
         [0007]     This problem is particularly pronounced in the anterior regions of the mouth and when using two implants positioned adjacent to each other. Loss of inter-implant bone height (as a result of the normal crestal bone remodeling that is associated with each of the implants) results in the absence of a papilla between the two implants due to lack of bone support. This creates an aesthetic deformity, often termed “black triangle”, between the two implant crowns. “Black triangles” are particularly visible when present in the maxillary anterior region and the patient has a high lip line. The patient&#39;s perception of a successful implant-supported prosthesis depends not only on restoring function, but also on restoring normal anatomy and aesthetics. The lack of a papilla and the presence of a “black triangle” can lead to patients&#39; dissatisfaction with the whole implant treatment, even with patients having a low smile line. Heretofore, the dental profession has been forced to come up with techniques to deal with “black triangles”. Most commonly, pink acrylic or porcelain is added to the final restoration to replace the missing papilla. This solution is far from ideal since it is impossible to replicate the gingival tissue with acrylic or porcelain in terms of texture and colour. Several attempts have also been made in establishing surgical procedures that will regenerate the missing papilla; however, these procedures are very unpredictable and seldom result in 100% regeneration.  
         [0008]     Conventional implants are poorly suited to accommodate for the crestal bone remodeling which occurs with implants. With conventional implant designs, most often any bone engaging textured, porous or coated surface extends downwardly from an uppermost radial edge surface which is located a constant distance from the lower apex of the body. Conventional implant designs suffer the disadvantage that they fail to account for the fact that with natural incisor teeth, the surface contour of healthy supporting bone tissues tends to be higher along the distal and medial surfaces of the tooth than along the lingual and buccal regions. Heretofore, the bone engaging regions for conventional implants have either been limited by the lowermost extent of expected bone recovery, weakening the integrity of the dental implant attachment, or suffer the disadvantage that the lingual and buccal portions of the implantable portion of the implant body may be visible at the patient&#39;s gum line.  
       SUMMARY OF THE INVENTION  
       [0009]     To at least partially overcome the disadvantages of the prior art, the present invention seeks to provide an implant which includes an implantable body portion adapted to be at least partially recessed within a patient&#39;s alveolar bone, and which has a peripheral surface portion which is configured to stimulate and/or facilitate the engagement of bone tissues with the implant.  
         [0010]     In a healthy jaw, the root of the tooth is supported by alveolar bone, with lamellated bone surrounding the root of the tooth where periodontal ligament fibres attach. The shape and crestal outline of interdental bone will to a large extent depend upon the shape and size of the tooth roots, with the distance from the crest of the alveolar bone to the cementoenamel junction of the tooth in a healthy periodontium being about 2 mm and a healthy sulcus extending about 0.5 mm. The present implant construction preferably seeks to stimulate osteoblasts, namely the bone forming cells, so as to promote bone ingrowth into and otherwise engage the implantable portion of the implant, with the crestal surface of the regrown bone tissues substantially mirroring that of a healthy tooth, to firmly anchor the implant in place.  
         [0011]     Another object of the invention is to provide an improved dental implant body for use in the anterior regions of the mouth, and which provides bone engaging regions along one or more of the distal and/or mesial implant surfaces which are elongated relative to bone engaging regions on the lingual and/or buccal surfaces of the implant body.  
         [0012]     Another object of the invention is to provide an implant body configuration which is configured to stimulate crestal bone tissue remodeling to a normal pre-implant height.  
         [0013]     Another object of the invention is to provide a dental implant body which has a bone engaging porous, textured, threaded and/or coated exterior surface, which is applied to the peripheral surface of the implant body in a configuration which reflects the actual or a preselected optimum contour of the crest of the alveolar bone and/or lamellated bone tissues at the site of implant placement.  
         [0014]     The implantable portion of the implant body could for example include about all or only part of its periphery, a bone engaging surface which, when the implant body is fully seated within the patient&#39;s jaw bone, extends from a distal portion of the implant body to a remote proximal-most edge. The proximal-most edge has a contour selected to generally follow a predetermined crestal outline of the supporting bone tissue. The bone engaging surface could take a number of possible forms including without restriction: an externally threaded portion, in which the proximal-most thread patterns are configured to generally follow the surface contour of alveolar and/or lamellated bone; an acid etched, physically abraded or other roughened or textured peripheral surface of the implant body; a porous coated surface which, for example, could consist of titanium, metal or ceramic beads and/or a chemically coated portion. Suitable chemical coatings for use with the bone engaging surface would typically comprise bioreactive coatings, including coatings formed from hydroxyapatite and other compounds suitable for stimulating bone tissue growth, and which facilitate the anchoring of the implant body by bone tissues following its placement.  
         [0015]     The predetermined crestal outline could by way of non-limiting example, be selected as a crestal outline of the patient&#39;s own alveolar and/or lamellated bone tissues at the site of implant placement or at the site of one or more of the patient&#39;s own teeth, or the crestal outline of alveolar and/or lamellated bone tissues of a typical healthy jaw, and more preferably the crestal outline at the site of or proximate to the intended site of implant placement.  
         [0016]     The bone engaging portion of the implant body could, for example, consist of a narrow band between the proximal exposed end of the implant body, and the distalmost end tip of the implant which is recessed into the patient&#39;s jaw. The bone engaging portion may further extend partially or completely about the circumference of the implant body. More preferably, however, the bone engaging region extends from approximately adjacent to the distalmost apex of the implant body to a proximal edge surface which, following placement of the implant body, approximately coincides with the crest of the alveolar bone of either the patient&#39;s missing tooth or a healthy tooth.  
         [0017]     In one aspect, the “aesthetic implant” design features of the present invention are therefore based on the principles governing peri-implant crestal bone loss, and aim at maintaining the interproximal bone at a level that is coronal to the buccal and lingual bone levels. In one simplified construction, the implant is designed to be inserted in a single stage surgery, thereby ensuring adequate biological width between the microgap and the crest of the bone.  
         [0018]     Although not essential, the implant body could be generally frustoconical in shape and, for example, be provided with a porous coated and/or textured bone engaging exterior surface which is designed to be “press-fit” in a specific buccal/lingual and mesial/distal orientation. In such an embodiment, the invention is directed to an improved dental implant which is suitable for use in aesthetic regions of the mouth, including as replacement for upper incisor teeth, and may be developed as a modification of the Endopore® implant disclosed in U.S. Pat. No. 5,344,457. The implantable portion of the implant may optionally be provided with a smooth upper collar portion which, for example, is provided to prevent or minimize the accumulation of oral bacteria. The smooth collar portion could, in a first embodiment, be provided as a smooth band which extends from the proximal edge of the bone engaging surface to a proximal end of the implant body which is provided with a substantially constant width, extending from the bone engaging surface to a contoured implant end surface which also follows the general contour of the crestal surface of the alveolar bone. In an alternate embodiment, the smooth collar of the implant body could extend from the proximal-most edge of the lower bone engaging portion to a generally flat proximal implant body surface.  
         [0019]     In another construction, the present invention seeks to provide an improved cylindrical implant body which is characterized by a bone engaging portion which, by way of non-limiting example, could comprised helical threads, ribs and/or a roughened implant surface formed by grit blasting and/or acid etching. The bone engaging portion most preferably extends from a lowermost distal end of the implant to a contoured upper edge which at least generally follows the contour of the patient&#39;s crestal bone or a pre-selected typical contour of healthy bone tissue at the site where the implant is to be used.  
         [0020]     A further construction of the invention provides an improved implant coating which is selected to provide enhanced engagement between the bone tissue and the implant body, and which for example could comprise a hydroxyapatite or other dentally active coating used to facilitate the anchoring of the implant in situ in a patient&#39;s jaw. The dentally active coating is applied about at least part of the circumference of the implant body, and depending upon the intended site of implant placement, extends from a distalmost end portion of the implant body to a proximal-most edge. The coating is applied so as to be elongated along one or more of the lingual, distal mesial and/or buccal sides of the implant body. More preferably, the coating is applied such that its proximal edge of the coating generally mirrors the typical crestal surface contour of either the patient&#39;s own or healthy bone tissues at the site at which the implant is to be used.  
         [0021]     It is envisioned that the dental implant could also be placed in the patient&#39;s alveolar bone in two stages. During the first stage surgery, the implant body is submerged into a complementary size bone formed in the bone to the level of a proximal end cap or platform used as a temporary cover over the proximal end of the implant. Following initial placement, a period of time is provided to allow bone tissue regrowth so as to grow into and engage the bone engaging surface and firmly anchor the implant body in place. As a next stage the proximal end platform is removed, and an abutment and suitable prosthesis are then coupled to the proximal end of the implant body in a mechanical and/or chemically bonded fit arrangement.  
         [0022]     Accordingly, in one aspect the present invention resides in a dental implant for use in replacing a missing tooth in a patient&#39;s jaw bone comprising, 
        an implant body adapted to be at least partially recessed into a portion of said patient&#39;s jaw bone, said implant body extending longitudinally along an axis from a distalmost apex to a proximal end portion,     a bone engaging surface provided about at least a portion of a peripheral surface of said implant body, said bone engaging surface selected to promote bone tissue ingrowth or attachment thereto and extending longitudinally along said periphery of said implant body to a proximal edge spaced towards said proximal end portion, wherein at least a portion of said proximal edge having a contour selected to generally follow a crestal surface contour of preselected bone tissues.        
 
         [0025]     In another aspect, the present invention resides in a dental implant for use in replacing a missing tooth in a patient&#39;s jaw bone comprising, 
        an implant body portion adapted to be recessed into a portion of said patient&#39;s jaw bone, said implant body extending longitudinally along an axis from a distalmost apex to a proximal end portion,     a bone engaging surface providing a peripheral surface of said implant body, said bone engaging surface selected to promote bone tissue ingrowth or attachment thereto and extending longitudinally along said periphery of said implant body to a proximal edge spaced towards said proximal end portion, wherein the proximal edge of the bone engaging surface has a contour selected to generally follow a crestal surface contour of a pre-selected jaw bone adjacent said missing tooth.        
 
         [0028]     In a further aspect, the present invention resides in a dental implant for use in replacing a natural tooth in a patient&#39;s jaw bone comprising, 
        an implant body extending longitudinally along an axis from a lowermost apex to an upper end portion and including, 
            a bone engaging surface providing a peripheral surface of said implant body adapted to be recessed into said patient&#39;s jaw bone, said bone engaging surface selected to promote bone tissue ingrowth or attachment thereto and extending longitudinally along said periphery of said implant body substantially from said apex to an upper edge spaced towards said upper end portion, wherein the upper edge of the bone engaging surface has a contour selected to generally follow a crestal surface contour of healthy bone tissues at a site of implant placement, and     a smooth peripheral portion intermediate said bone engaging surface and said upper end portion, and     an abutment for supporting a prosthesis thereon.   
               
 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0033]     Reference may be now had to the accompanying detailed description, together with the accompanying drawing pages in which:  
         [0034]      FIG. 1  illustrates an exploded view of a dental implant construction in accordance with a first embodiment of the invention;  
         [0035]      FIG. 2  shows an enlarged schematic side view of the distal surface of the implant body used in the implant construction of  FIG. 1 ;  
         [0036]      FIG. 3  shows an enlarged plan view of the proximal end of the implant body shown in  FIG. 2 ;  
         [0037]      FIG. 4  shows a schematic side view of the lingual surface of the implant body of  FIG. 2  seated within a patient&#39;s jaw bone;  
         [0038]      FIG. 5  shows a schematic view of the implant construction shown in  FIG. 1  seated in place within a patient&#39;s jaw bone;  
         [0039]      FIG. 6  shows a schematic side view of a distal/mesial side of an implant body in accordance with a second embodiment of the invention;  
         [0040]      FIG. 7  illustrates a schematic view of a distal/mesial side of an implant body in accordance with a third embodiment of the invention; and  
         [0041]      FIG. 8  illustrates a schematic view of a distal/mesial side of an implant body construction in accordance with a fourth embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]      FIG. 1  illustrates an exploded implant construction  10  used in the replacement of a lost anterior or maxillary tooth, in accordance with a first preferred embodiment of the invention. The implant construction  10  consists of an implantable titanium or stainless steel body  12 , a stainless steel abutment assembly  14 , a stainless steel retaining screw  16 , and a ceramic tooth prosthesis  18  which has a profile and size selected to mimic the patient&#39;s natural tooth which is to be replaced. As will be described, the implant construction  10  is adapted to be recessed at the site of a missing anterior or maxillary tooth within the lamellated and alveolar bone tissues  20 , 22  of the patient&#39;s jaw  24  ( FIG. 4 ) in the place of the lost natural tooth.  
         [0043]     The abutment assembly  14  serves as the base support for the prosthesis  18  and has an exterior shape selected for fitted engagement within a complementary sized recess  30  formed in the bottom of the prosthesis  18 . A central bore  32  is formed through the center of the abutment  14  which is sized to receive therein the screw  16  while preventing the screw head  34  from moving therethrough. It is to be appreciated that although  FIG. 1  illustrates a one-part abutment assembly  14 , its individual abutment components and configuration may vary having regard to the configuration of the prosthesis  18 . In the final assembly of the implant construction  10 , the prosthesis  18  is secured in place over the abutment assembly  14  by a suitable dental cement.  
         [0044]     As shown best in  FIG. 1 , the implantable body  12  is formed with an internally threaded axial bore  36  which extends downwardly from a proximal surface  38  of the implant body to which the abutment assembly  14  is mounted approximately three-quarters along its longitudinal length. The internal threads of the bore  36  are selected for threaded engagement with the retaining screw  16 , to enable the mechanical coupling of the assembly  14  to the implant body by means of the retaining screw  16 . As will be described, following the positioning of the body  12  in a complementary sized bore formed in the patient&#39;s jaw  24 , the abutment assembly  14  is coupled to the implant body  12  by inserting the screw through the bore  32  and into threaded engagement with the internal treads of the bore  36 .  
         [0045]      FIG. 2  shows best the implant body  12  construction in accordance with the first embodiment of the invention where the implant body  12  is configured for use with a conventional abutment  14  and prosthesis  18 , as for example is shown in  FIG. 1 . Although not essential, the implant body  12  most preferably has a tapered frustoconical shape. The body  12  has two principle portions or surfaces, namely a distalmost porous coated surface  40  for primary fixation of the implant (i.e. bone-engagement) with the patient&#39;s bone tissues, as well as a non-porous smooth upper or coronal surface  42 . The coronal surface  42  is provided to prompt the maintenance of bone surrounding the surface of the implant  10 . As shown best in  FIGS. 2 and 3 , a hexagonal mount  44  projects upwardly from the proximal end surface  38  of the implant body  12 . The hexagonal mount  44  is centered on the elongated central axis A-A 1  ( FIG. 2 ) of the implant body. As seen best in  FIG. 3 , the central bore  36  extends downwardly through the center of the hexagonal mount  44  in the axial direction. The hexagonal mount  44  more preferably has a size and shape selected for fitted placement within a complementary sized recess  46  ( FIG. 1 ) which is formed in the bottom of the abutment assembly.  FIG. 2  further shows best the proximal end surface  38  as comprising a substantially flat surface extending radially generally normal to the axis A-A 1 .  
         [0046]     The implant body  12  is shown as frustoconically shaped along its entire length, however, the invention is not so limited and other implant configurations which taper only partially along their axial length are also possible. Preferably, the implant body  12  tapers inwardly from the proximal end surface  38  to a distalmost apex  46 , which, as seen best in  FIG. 4 , orients in a downwardmost position in a complementary bore  48  formed in the patient&#39;s jaw  24  at the site of implant placement. The implant body  12  tapers toward the distalmost apex  46  at an angle of between about 1 and 20 degrees, preferably 2 and 10 degrees, and still more preferably at approximately 3 to 5 degrees.  
         [0047]      FIG. 2  shows the distal side face  50  of the implant oriented in a forwardmost direction, with the mesial side face  51  ( FIG. 3 ) having substantially the mirror construction, and the lingual and buccal implant side faces identified by reference numerals  52  and  54 , respectively. As seen best in  FIG. 2 , the non-porous coronal surface  42  of the implant body  12  adjacent to the end surface  38  is provided with a smooth polished texture which minimizes the possibility that bacteria could be trapped thereabouts. Preferably, the smooth coronal surface  42  extends in the axial direction a distance of approximately 2 to 4 mm. The distalmost three-quarters of the implant body  12  which functions as a bone engaging surface is provided with the porous coated surface  40  formed by spray coating the implant with titanium beads. The porous surface  40  of the bone-engaging region of the implant body  12  may be in the form of a coating comprised of discrete titanium beads or particles adhered to a remainder of the implant body  12  into which the patient&#39;s bone tissues  20  and/or  22  may grow. Other porous coatings and/or constructs may also be used including porous coatings formed by mechanical abrasion, or a roughened portion of the implant. Preferably, the porous surface  40  is formed having a porosity of from about 10 to 800 microns, with the porous coated surface having a porosity similar to that of the Endopore® implants. Differing porosities are, however, also possible.  
         [0048]     As shown best in  FIGS. 2 and 4 , the porous coated surface  40  is characterized by two axially elongated and proximally extending regions  60   a , 60   b  which extend on each of the opposing distal and mesial sides  50 , 51  of the implant body  12 . In each of the regions  60   a , 60   b , the porous coated surface  40  extends an increased distance from the distal apex  46  of the implant body  12  towards its proximal end surface  38  relative to the portions of the porous coated surface  40  along the lingual and buccal implant sides  52 , 54 . More preferably, the regions  60   a , 60   b  extend approximately 2 to 4 mm closer to the end surface  38  of the implant body  12  than the coated surface  40  at the buccal and lingual surfaces  52 , 54 . As seen best in  FIG. 2 , in this manner the upper edge  62  of the porous coated surface  40  which is spaced closest to the implant body end  38  rides upwardly into the collar  42  along both the distal and mesial sides  50 , 51  of the implant  10 . Most preferably, the proximal-most edge  62  of the porous surface  40  is formed so as to follow a predetermined profile, as for example the profile of the crestal ridge of typical healthy bone tissue  20  and/or alveolar tissues  22  at the site of intended implant use.  
         [0049]     It is to be appreciated that providing the proximal edge  62  of the porous coated portion  40  of the implant body  12  with a profile which generally follows the profile of healthy bone tissue advantageously stimulates bone tissues to engage the dental implant body  12  in the identical manner that occurs with natural teeth. As such, sites of higher bone tissue  20 , 22  engagement occur along the mesial and distal side portions  51 , 50  of the implant body  12 . It is to be appreciated that the sites of higher bone tissue  20 , 22  engagement in turn maintain the shape and crestal outline of interdental bone and overlying gum tissues  66  ( FIG. 4 ) at the optimum spacing from the cementoenamel junction of the tooth, eliminating “black triangles” between implants  10  and adjacent natural teeth. In addition, the higher sites of bone tissue  20 , 22  attachment reduce the likelihood of alveolar bone tissue  22  loss which may otherwise result in the exposure of the collar  42  of the implant body  12 .  
         [0050]     To ensure proper orientation of the implant body  12  seated within the bore  48 , the proximal surface  38  of the body  12  may further include visual indicia  68  (see stamped letters D and M) or other striations, grooves, guides or posts used to assist in orienting the implant body  12  following its placement in the patient&#39;s jaw  24 .  
         [0051]     In installation of the implant  10 , a frustoconical shaped bore  48  is formed in the patient&#39;s jaw  24  at the site of intended tooth replacement, as for example is shown in  FIG. 5 . The bore  48  is formed to a depth selected so that the cementoenamel junction of the prosthesis  18  and collar  42  locates at a position corresponding to that of a natural healthy tooth. The implant body  12  is then inserted in the bore  48  in a press fit arrangement and the indicia  68  is used to facilitate in orienting the implant body  12  so that the distal and mesial sides  50 , 51  assume the desired orientation in the patient&#39;s jaw bone. Following placement of the implant, a temporary cap (not shown) is secured over the hexagonal mount  44  and proximal end  38  and the implant body  12  is sutured over and allowed to heal for several weeks.  
         [0052]     After a passage of time which is selected to permit the bone tissue  20 , 22  ingrowth into the bone engaging porous coated surface  40 , so as to sufficiently anchor the implant body, the temporary cap is removed. The abutment assembly  14  is then secured to the implant body  12  by means of the threaded engagement of the screw  16  within the bore  36 . The prosthesis  18  is thereafter positioned over and affixed over the abutment  14  by a suitable dental cement.  
         [0053]     The implant body  12  is constructed such that it may be placed in a press-fit manner with the raised regions  60   a , 60   b  of the porous portions  40  oriented in a distal/mesial alignment, and the buccal and lingual sides  54 , 52  of the positioned implant body  10  characterized by the porous coated regions of a comparably shorter length. In an optimum construction, the implant body  12  is constructed such that: 
        The proximal edge  62  of the porous coating  40  is curved or follows a contour whereby the buccal/lingual side portions  54 , 52  are more apical relative to the mesial/distal side portions  50 , 51  by 2 to 4 mm.     The implant body  12  is adapted to be “press fitted” in the patient&#39;s jaw.     The smooth collar  42  of the body  12  is at least 1.5-2 mm wide.     The implant can be offered in the same diameters and lengths as the Endopore® implants.        
 
         [0058]     Although FIGS.  1  to  4  illustrates the implant body  12  as having a bone engaging porous coated surface  40  which includes elongated regions  60   a , 60   b  extending towards the proximal end surface  38  and into the collar  42  along the distal and mesial sides  50 , 51  of the positioned implant  10 , the invention is not so limited. It is to be appreciated that in an alternate configuration, the proximal edge  62  of bone engaging porous surface  40  of the implant body  12  could include only one elongated porous coated region extending into the collar  42  along only one of the distal side  50  or mesial side  52  of the implant. In an alternate construction, the porous surface  40  could have elongated regions extending proximally along the lingual and/or buccal sides  52 , 54  of the implant body  12 .  
         [0059]     Although FIGS.  1  to  4  illustrate the implant body  12  as having a generally flat proximal end surface  38 , the invention is not so limited. Reference may be had to  FIG. 6  which shows an alternate implant body construction in which like reference numerals are used to identify like components. In  FIG. 6 , the proximal end  38  of the implant body  12  is contoured so as to generally follow the same contour as the proximal edge  62  of the bone engaging porous surface  40 . It is to be appreciated that with the contoured proximal end surface  38 , a modified abutment assembly is provided which is adapted to substantially mate with the contoured end  38  in assembly of the implant  10 . In the construction shown, the non-porous coronal surface  42  follows the uppermost edge  62  of the porous coated surface  40  as a smooth band having a substantially constant width, which most preferably is selected at about 1.5 to 2.5 mm in width. It is to be appreciated, however, that a coronal surface  42  could also be provided which narrows in width at each raised region  60   a , 60   b  of the porous surface  40 .  
         [0060]     Although FIGS.  1  to  5  illustrate the implant  10  as having a tapered implant body  12 , the invention is not so limited. It is to be appreciated that the present invention is also operable with an implant body  12  which, for example, could be parallel sided or for that matter which could include a combination of parallel sided and tapered portions, without departing from the spirit and scope of the present invention.  
         [0061]     Reference is made to  FIG. 7  which illustrates a further embodiment of the invention wherein like reference numerals are used to identify like components. In  FIG. 7 , the dental implant body  12  is cylindrical in shape. The body  12  includes a distalmost bone engaging portion  140  which is provided with external helical threads  80  as the means by which bone engagement and anchorage of the implant body  12  is achieved. As with the porous coating  40  of the implant body  12  shown in  FIG. 1 , the helical threads  80  of the implant body  12  of  FIG. 5  extend from a distalmost apex  40  upwardly to a proximal-most edge  62 . The external threads  80  extend axially in the proximal direction further along the distal side ( 50 ) and mesial side (not shown) of the implant body  12  than the regions of the external threads in the lingual and buccal  52 , 54  side portions. As with the raised porous region  60   a , 60   b , the elongated threaded region  60   a  shown in  FIG. 5  thus extends closer to the proximal end surface  38  of the implant body and further proximally into the smooth collar  42  than the threads  80  of the implant body  12  along its lingual and buccal sides  52 , 54 .  
         [0062]     In  FIG. 7 , the implant body  12  is similarly provided with a hexagonal or other polygonally shaped mount  44 . In addition to serving as a mount for the abutment assembly  14 , the mount  44  advantageously may be used to assist in theadedly inserting the implant body  12  into the patient&#39;s jaw bone. If desired, the external hexagonal mount  50  on the implant body  12  could be provided with grooves, slots or other visual indicia which facilitate the positioning of the implant body  12  so that the elongated threaded regions  60  are in alignment with the mesial and distal surfaces of the patient&#39;s immediately adjacent teeth.  
         [0063]      FIG. 8  illustrates a further embodiment of the invention in which like reference numerals are used to identify like components. In  FIG. 8 , the implant body  12  includes a conventional externally threaded bone engaging portion  140 . In the embodiment as shown, the implant body  12  further includes an enlarged flared non-porous upper portion  142 . A threaded bore (not shown) is formed in the proximal end surface  38  of the implant body  12  and is adapted for the mechanical coupling of an abutment assembly and prosthesis (not shown) thereto in a conventional manner. To provide an enhanced bone engaging surface, a bioreactive coating  144  is provided over the externally threaded portion  140  and part of upper portion  142  of the implant body  12 . The coating  144  extends further towards the proximal surface  38  along the lingual side  52  and buccal side  54  of the implant body as regions  160   a ,  160   b . It is to be appreciated, however, that the coating  144  could equally extend further along the mesial and/or distal sides of the implant in the similar manner as the porous coated surface  40  shown in  FIG. 1 . The bioreactive coating  144  which is selected to facilitate the engagement of bone tissues with the implant and suitable coatings include without restriction, hydroxyapatite coatings and the like. As with the embodiments shown in FIGS.  1  to  5 , the proximal-most edge  162  of the bioreactive coating  144  has a contour which is selected to follow a predetermined contour, as for example, which follows the profile of the crestal surface of either a healthy jaw bone or the patient&#39;s own jaw bone.  
         [0064]     While it may be preferred that the implant body  12  include two opposed elongated coated regions  160   a ,  160   b  on both the distal/mesial sides  50 , 51  of the implant body  12 , the invention is not so limited. If desired, the body  12  could be modified to include only a single elongated coated region  160   a  where for example, the implant  10  is to be placed in a position interposed between a natural tooth and a second implant. In this construction, any proximally extending or elongated portion of the coating  144  would be located adjacent to the second implant alone. Alternately, it is envisioned that the implant having two or more non-opposed discrete elongated coated regions  160   a ,  160   b  could be provided for specific orientation, where the loss of supporting bone height may otherwise occur.  
         [0065]     Although FIGS.  1  to  4  illustrate the implant body  12  as including a hexagonal mount or projection  44  sized for complementary insertion within the bore  46  of the abutment assembly  14 , the invention is not so limited. Other forms and configurations of mounts may also be used and will now become apparent. In a less preferred embodiment, the mount may be omitted in its entirety or alternately, a complementary form recess could be provided within the implant body  12 . The hexagonal projection  44 , however, is believed to represent a preferred construction in that it acts to correctly seat the abutment  14 , preventing any rotational movement thereof once secured against the implant body surface  38 . The hexagonal projection  44  most preferably is of a standard size so as to provide compatibility with a variety of prosthetic systems from a variety of different manufacturers.  
         [0066]     Although  FIG. 1  illustrates the abutment assembly  14  as comprising a single piece, the invention is not so limited. It is to be appreciated that the present invention is suitable for use with a variety of abutment configurations including, without restriction, other single, two-piece and multiple-piece abutments.  
         [0067]     Although the preferred embodiments of the invention disclose and describe the bone engaging regions of the implant body  12  as comprising a porous coated surface, an externally threaded surface or a biochemically coated surface, the invention is not so limited. It is to be appreciated that other bone engaging surfaces could also be used with the present invention, including, without restriction, the use of other textured or roughened surfaces which are provided with a contoured profile selected to follow the crestal surface of a patient&#39;s or other preselected jaw bone tissues.  
         [0068]     Although the preferred embodiment of the invention describes and illustrates various preferred aspects of the invention, the invention is not so limited. Many modifications and variations will now occur to persons skilled in the art. For a definition of the invention, reference may be had to the appended claims.