Patent Document

CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    The present application claims priority to Australian Provisional Patent Application No. PQ 8179, filed Jun. 16, 2000, which is herein incorporated by reference in its entirety for all purposes. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates to dental implants, and more particularly, to an abutment used to secure a dental prosthesis to an implant fixture.  
         BACKGROUND OF THE INVENTION  
         [0003]    A dental implant assembly is a device that is surgically attached to a patient&#39;s jawbone to replace one or more missing teeth. A typical dental implant includes an implant fixture that an oral surgeon inserts into the jawbone, and a prosthesis, which replaces the crown portion of a missing tooth. Currently, the most prevalent type of dental implant fixture is a root-form implant. As its name suggests, the root-form implant has an elongated shape reminiscent of the root portion of a tooth. Much like roots of natural teeth, the root-form implant penetrates the gum and anchors the prosthesis to the jawbone.  
           [0004]    The dental implant assembly also includes an abutment, which provides an interface or transition between the implant fixture and the prosthesis. Conventional abutments typically include a substantially axisymmetric base portion, which fits into a hole formed in the implant fixture, and a conical neck portion, which projects outward from the base portion of the abutment. Besides securing the prosthesis to the implant fixture, the abutment also compensates—with varying success—for any misalignment between the prosthesis and adjacent teeth. Misalignment can arise, for example, when the implant fixture has an orientation with respect to the gum surface that is substantially different than the adjacent teeth.  
           [0005]    Implant assemblies employ angled abutments, as opposed to straight abutments, to account for any misalignment. Straight and angled abutments have neck portions that project outward from their base portions in directions that are, respectively, substantially parallel or non-parallel to the symmetry axes of their corresponding base portions. Therefore, if the direction or orientation of the neck portion of the abutment is represented by a longitudinal axis that intersects the symmetry axis of the base portion (or implant fixture), the resulting orientation angle is about zero for straight abutments. In contrast, an angled abutment exhibits a nonzero orientation angle. For a discussion of straight and angled abutments, see U.S. Pat. No. 5,947,733 issued to Franz Sutter et al., which is herein incorporated by reference in its entirety for all purposes.  
           [0006]    Though widely accepted by dental practitioners, dental implants generally, and root-form implants in particular, are not without problems. For example, the neck portions of commercially available angled abutments have fixed angular displacements with respect to their base portions, which limits their usefulness. Once a patient has been fitted with an implant fixture, the dental practitioner must order an abutment having the requisite orientation angle to ensure proper alignment of the prosthesis. However, since only discrete orientation angles are available, it is often necessary to modify the abutment to achieve the requisite angular orientation, which can be a labor intensive and costly process. In some cases the necessary orientation angle may be significantly greater than what is commercially available, making it difficult to attain acceptable alignment of the prosthesis.  
           [0007]    Dental implants having adjustable orientation angles are known, but none appear to have achieved widespread use because of design deficiencies. See, for example, U.S. Pat. No. 5,890,902 issued to Sapian; U.S. Pat. No. 5,662,475 issued to Mena; U.S. Pat. No. 5,599,185 issued to Greenburg; U.S. Pat. No. 5,302,125 issued to Kownacki et al.; U.S. Pat. No. 4,793,808 issued to Kirsch; and U.S. Pat. No. 4,832,601 issued to Linden, which are herein incorporated by reference in their entirety for all purposes. Most of the disclosed implants are limited to modest orientation angles of about twenty-five degrees or less, and many do not readily permit removal of the prosthesis following installation. Some of the disclosed implants also fail to provide a smooth transition between the prosthesis and the implant fixture, which results in poor soft tissue adaptation. To ensure accurate alignment of the prosthesis with adjacent teeth, current practice provides for fabricating an abutment and prosthesis from a cast of the patient&#39;s mouth following insertion of the implant fixture. Some of the disclosed designs, however, do not include a mechanism for attaching the prosthesis to the abutment prior to installation, and therefore cannot take advantage of using a laboratory cast, if desired.  
           [0008]    The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems described above.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides a dental implant abutment incorporating a ball-and-socket joint, which can be constructed from standard elements to reduce costs. The abutment allows one to adjust the orientation angle of an attached prosthesis over a continuous and wide range of values (fifty degrees or more) before fixing the desired angular orientation. The abutment readily permits removal of the prosthesis following installation and provides a smooth transition between the prosthesis and the implant fixture, which results in good soft tissue adaptation. The claimed invention also allows for accurate transfer of the abutment from the laboratory cast to the jawbone.  
           [0010]    Thus, one aspect of the present invention provides an assembly for securing a permanent prosthesis to a root-form implant fixture. The implant fixture has a head portion, an adjoining root portion, and a hole extending from the head portion into the root portion of the implant fixture. The claimed assembly includes an abutment, which comprises a base and an attachable coping. The base has a first surface that is complementary to the head portion of the implant fixture, a second surface having a shape that approximates a section of a sphere, and a third surface that defines an aperture extending between the first and second surfaces of the base. The attachable coping has an exterior surface for receiving the permanent prosthesis, first and second openings in the exterior surface, and an interior surface that defines a cavity connecting the first and second openings. A portion of the interior surface of the attachable coping that is located adjacent to the first opening in the exterior surface is shaped to slidably engage the second surface of the base so that the attachable coping can be joined to the base at a desired angular orientation.  
           [0011]    Another aspect of the present invention provides a connector for securing the abutment to the implant fixture. The connector has a head portion and a shaft portion adjoining the head portion. The head portion of the connector has a lateral surface configured to engage the third surface of the base, and the shaft portion of the connector has external threads adapted to engage internal threads in the hole in the implant fixture. During installation, the first surface of the base of the abutment is disposed on the head portion of the implant fixture so that the respective aperture and hole of the base and the implant fixture are substantially aligned. The connector is placed in the aperture so that rotating the head of the connector using a tool inserted through the second opening in the exterior surface of the attachable coping drives the connector into the hole in the implant fixture, thereby securing the abutment to the implant fixture. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows a cross-sectional side view of one embodiment of an implant fixture.  
         [0013]    [0013]FIG. 2 shows an exploded, partial cross-sectional side view of an abutment adapted for use with the implant fixture shown in FIG. 1.  
         [0014]    [0014]FIG. 3 shows a cross-sectional side view of a connector.  
         [0015]    [0015]FIG. 4 shows a cross-sectional side view of a dental implant assembly.  
         [0016]    [0016]FIG. 5 shows a top view of the dental implant assembly shown in FIG. 4, in which the attachable coping has been removed for clarity.  
         [0017]    [0017]FIG. 6 shows a cross-sectional side view of a second embodiment of an implant fixture.  
         [0018]    [0018]FIG. 7 shows a partial cross-sectional side view of a base portion of an abutment adapted for use with the implant fixture shown in FIG. 6. 
     
    
     DETAILED DESCRIPTION  
       [0019]    [0019]FIG. 1 shows a cross-sectional side view of one embodiment of an implant fixture  10 , which a dental practitioner inserts into a patient&#39;s jawbone. The implant fixture  10  is a root-form implant fixture and includes a head portion  12  and an adjoining root portion  14 . The implant fixture  10  has a generally cylindrical shape and has external threads  16  formed along a section of an exterior surface  18  of the elongated root portion  14 . The external threads  18  help stabilize the implant fixture  10  in the patient&#39;s jawbone during healing, but other embodiments may employ grooves, lateral holes, and the like to minimize rotation. The exterior surface  18  may be machined smooth, plasma sprayed to increase surface area, or coated with hydroxylapatite to promote fusion to the jawbone (osseointegration). The implant fixture  10  can be made of any material having the requisite mechanical strength and the ability to integrate into the jawbone. Useful materials include commercially pure titanium.  
         [0020]    As shown in FIG. 1, the implant fixture  10  includes a longitudinal bore or hole  20 , which extends from an upper exterior surface  22  of the head portion  12  into the elongated root portion  14  of the implant fixture  10 . The hole  20 , which has a centerline substantially coincident with a symmetry axis  24  of the implant fixture  10 , includes an upper cavity  26 , which is adapted to receive an abutment, and a comparatively narrower lower cavity  28 , which is adapted to receive a connector. The upper  26  and lower  28  cavities are defined, respectively, by first  30  and second  32  lateral surfaces separated by an annular surface  34 . The first lateral surface  30  includes a pair  36 ,  38  of inverted conical surfaces, and an intermediate cylindrical surface  40 , but other embodiments may comprise a single inverted conical surface. The second lateral surface  32  has a cylindrical shape, and includes internal threads  42  that extend from the annular surface  34  to a region adjacent to the bottom  44  of the hole  20 .  
         [0021]    [0021]FIG. 2 shows an exploded, partial cross-sectional side view of an abutment  60 , which is adapted for use with the implant fixture  10  shown in FIG. 1. The abutment  60 , which secures a prosthesis (crown, bridge, etc.) to the implant fixture  10 , includes a base  62  and an attachable coping  64 . The base  62  of the abutment  60  has first  66  and second  68  surfaces which are separated by a skirt  70 , and a third (or inner) surface  72  that defines an aperture  74  which extends from the first surface  66  to the second surface  68  of the base  62 . The first surface  66  of the base  62  of the abutment  60  is complementary to the upper cavity  26  in the head portion  12  of the implant fixture  10 . The first surface  66  includes a pair  76 ,  78  of inverted conical surfaces, an intermediate cylindrical surface  80 , and a generally flat end surface  82 , but other embodiments may comprise a single inverted conical surface that terminates at the end surface  82  of the base  62  of the abutment  60 . Although the intermediate cylindrical surfaces  40 ,  80  of the implant fixture  10  and abutment  60  are substantially smooth, other embodiments may include complementary polygonal (hexagonal, octagonal, etc.) flat portions, grooves, and so on, which engage one another and prevent rotation of the base  62  of the abutment  60 .  
         [0022]    As shown in FIG. 2, the second surface  68  has a finite and approximately constant radius of curvature—i.e., has a shape that approximates a section of a sphere—and provides a surface for joining the attachable coping  64  to the base  62  of the abutment  60 . The third (inner) surface  72  of the base  62  has a pair of generally cylindrical surfaces  84 ,  86  that are separated by an annular surface  88  which slopes inward towards a symmetry axis  90  of the base  62  of the abutment  60 . The third surface  72  can be substantially smooth, but the embodiment depicted in FIG. 2 employs internal threads  92  along a portion of the cylindrical surface  86  adjacent to the end surface  82  of the base  62  of the abutment  60 . As described below, the third surface  72  is configured to receive a connector (see FIG. 4), which joins the base  62  of the abutment  60  to the implant fixture  10 . The internal threads  92  retain the connector in the base  62 , and aid in removing the abutment  60  from the implant fixture  10 . The base  62  can be constructed from any material that is compatible with the implant fixture  10  and the soft tissues within the patient&#39;s mouth. Suitable materials include titanium or titanium alloys, gold alloys, and the like, which are machined and milled to the requisite shape.  
         [0023]    Continuing with FIG. 2, the abutment  60  also includes an attachable coping  64 . Like the neck portion of a conventional abutment, the attachable coping  64  secures the prosthesis to the base  62  of the abutment  60 . The attachable coping  64  has an exterior surface  94  that provides a substrate for receiving the prosthesis. As shown in FIG. 2, the exterior surface  94  has a frustum-like shape that when viewed from bottom  96  to top  98  slopes inward towards a longitudinal axis  100 . The exterior surface  94  includes first  102  and second  104  openings located at the bottom  96  and top  98  of the attachable coping  64 , respectively, and an interior surface  106  that provides a cavity  108  that extends between the first  102  and second  104  openings. The interior surface  106  adjacent to the first opening  102  of the attachable coping  64  defines a depression  110  having a concave shape characterized by a finite and approximately constant radius of curvature. The depression  110  is shaped to slidably engage the second surface  68  of the base  62  of the abutment  60  so that the attachable coping  64  can be joined to the base  62  at a desired angular orientation.  
         [0024]    The embodiment shown in FIG. 2 also includes a lateral opening  112 , which communicates with the cavity  108  in the attachable coping  64 . When the attachable coping  64  is joined to the base  62  of the abutment  60  and the connector is installed in the aperture  74  of the base  62 , the lateral opening  112  provides access to the connector. Alternatively or optionally, the second opening  104  of the attachable coping  64  may permit access to the connector following installation of the connector in the base  62  of the abutment  60 . In other embodiments, the second opening  104  may include internal threads (not shown) that are sized to engage a threaded connector, which joins the prosthesis to the coping  64 . The attachable coping  64  may be constructed from a variety of materials, including plastics that decompose upon heating, titanium and titanium alloys, gold alloys, and the like.  
         [0025]    [0025]FIG. 3 shows a cross-sectional side view of a connector  130  that secures the abutment  60  to the implant fixture  10 . The connector  130  includes a head portion  132  and an adjoining shaft portion  134 . The head portion  132  of the connector  130  has an outer lateral surface  136  that is configured to engage the third (or inner) surface  72  of the base  62  of the abutment  60  (FIG. 2). The outer lateral surface  136  thus includes a generally cylindrical surface  138  that intersects an annular surface  140 , which slopes inward towards the shaft portion  134  and a symmetry axis  142  of the connector  130 . The shaft portion  134  of the connector  130  includes external threads  144  formed along a section of its outer surface  146 . The external threads  144  are adapted to engage internal threads  42 ,  92  formed, respectively, in the lower cavity  28  of the implant fixture  10  (FIG. 1) and along the cylindrical surface  86  that defines part of the aperture  74  extending through the base  62  of the abutment  60 . The internal threads  92  in the aperture  74  retain the connector  130  in the base  62  of the abutment  60  when the abutment  60  is not installed on the implant fixture  10 .  
         [0026]    As can be seen in FIG. 3, the head portion  132  of the connector  130  further includes an end region  148  having a surface  150  that defines a recess  152 . The end region  148  of the surface  150  shown in FIG. 3 includes an inner lateral surface  154 , which delineates the width of the recess  152 , and a bottom surface  156 , which marks the depth of the recess  152 . The inner lateral surface  154  is sized and dimensioned to receive a tool for driving (e.g., rotating) the connector  130 . The inner lateral surface  154  may have polygonal flat portions (e.g., triangular flats) or similar structures formed on it, which provide contact surfaces for a driver tool (e.g., triangle-tipped screwdriver). The connector  130  can be fabricated from any material that is compatible with the abutment  60  and the implant fixture  10  and that has the requisite mechanical properties (e.g., tensile strength, elongation, and modulus). Useful materials include titanium, non-oxidizing alloys, and gold alloys.  
         [0027]    [0027]FIG. 4 shows a partial cross-sectional side view of a dental implant assembly  180 , which includes the implant fixture  10 , the abutment  60 , and the connector  130  shown in FIG. 1 through FIG. 3, respectively. After the implant fixture has been integrated into the jawbone, the head portion  12  of the implant fixture  10  is exposed (uncovered) by the oral surgeon. The first surface  66  of the base  62  of the abutment  62  is then disposed in the upper cavity  26  of the head portion  12  of the implant fixture  10  so that the respective aperture  74  and hole  20  of the base  62  and the implant fixture  10  are substantially aligned. Next, the connector  130  is placed in the aperture  74  of the base  62  to secure the abutment  60  to the implant fixture  10 . A tool, such as a screwdriver, is introduced through either the second opening  104  or the lateral opening  112  in the exterior surface  94  of the attachable coping  64  to engage the recess  152  in the head portion  132  of the connector  130 . Twisting or rotating the tool drives the connector  130  into the hole  20  in the implant fixture  10  as the external threads  144  on the shaft portion  134  of the connector  130  engage the internal threads  42  in the lower cavity  28  of the implant fixture  10 . Although not shown, the prosthesis joined to the exterior surface  94  of the coping  64  has one or more holes that allow the oral surgeon to access the appropriate openings  104 ,  112  in the exterior surface  94  of the attachable coping  64 . These holes are later filled in.  
         [0028]    [0028]FIG. 5 is a top view of the dental implant assembly  180  shown in FIG. 4, in which the attachable coping  64  has been removed to show the connector  130  following installation in the aperture  74  of the base  62  of the abutment  60 . The head portion  132  of the connector  130  includes a triangular recess  154 , which is sized to accommodate a triangle-tipped driver. In addition, the outer lateral surface  136  of the head  132  of the connector  130  includes one or more notches  182  that are adapted to receive locking pins  184  that help prevent rotation of the connector  130  following installation. After the connector  130  has been twisted into the implant fixture  10  to a requisite torque, the oral surgeon drills complementary notches  186  in the cylindrical surface  84  of the base  62  of the abutment  60  adjacent to the head portion  132  of the connector  130 . The locking pins  184  are then pressed or rotated into pairs of notches  182 ,  186 , and optionally held in place by applying a settable resin. The locking pins can be fabricated from a thermoplastic material or a metal alloy, such as a gold alloy, which the dental practitioner can easily remove by drilling if it is later necessary to remove the prosthesis and abutment  60  from the implant fixture  10 .  
         [0029]    Referring again to FIG. 4, the direction or orientation of the attachable coping  64  can be represented by an orientation angle, Φ. The orientation angle is formed by the intersection of the longitudinal axis  100  of the attachable coping  64  and the symmetry axis  90 ,  24  of the base portion  62  of the abutment  60  or of the implant fixture  10 . As noted above, the attachable coping  64  includes a depression  110  having a concave shape characterized by a finite and approximately constant radius of curvature. The depression  110  is shaped to slidably engage the second surface  68  of the base  62  of the abutment  60  so that the attachable coping  64  can be joined to the base  62  at the desired orientation angle. As can be seen in FIG. 4, the ball-and-socket joint allows Φ to vary between about zero degrees and about fifty degrees or more for any polar angle, θ. If necessary, a portion  188  of the exterior surface  94  of the attachable coping  64  can be removed to minimize interference between the skirt  70  of the abutment  60  and the attachable coping  64 .  
         [0030]    Once the implant fixture  10  has been integrated into the jawbone, the dental practitioner threads an impression coping into the implant fixture  10  and makes an impression of the patient&#39;s mouth. The impression coping is a type of straight abutment that projects outward from the patient&#39;s gum line and precisely locates the position and the orientation of the implant fixture  10  within the patient&#39;s mouth. A dental laboratory then prepares a cast of the patient&#39;s mouth from the dental impression. Using the cast as a guide, a laboratory technician positions the attachable coping  64  on the base  62  of the abutment  60 . If the attachable coping  64  is made of titanium or a titanium alloy, the technician can fix the orientation angle by laser welding the coping  64  to the base  62  of the abutment  60 . If the attachable coping  64  is instead made of a heat labile plastic, the technician first fixes the orientation angle by applying wax or resin to attach the coping  64  to the base  62  of the abutment  60 . Once the plastic coping  64  has been joined to the base  62 , any required alterations of the abutment  60  can be made, such as lengthening the coping  64 , tapping the second opening  104  of the coping  64 , etc. The technician then invests and casts an angled abutment (coping  64  and base  62 ) using the “lost wax” technique and appropriate dental materials (e.g. gold alloys).  
         [0031]    It may be necessary to remove the prosthesis following installation on the implant fixture  10 . In such cases, the dental practitioner accesses the head portion  132  of the connector  130  by drilling into the prosthesis, if necessary. Next, the dental practitioner removes the locking pins  184  (e.g., by drilling), and twists the connector  130  out of the implant fixture  10  using the requisite tool, such as a triangle-tipped screwdriver. As the connector  130  recedes, the external threads  144  along the shaft portion  134  of the connector  130  engage the internal threads  92  on the cylindrical surface  86  that defines a portion of the aperture  74  extending through base  62  of the abutment  60 . Because the external threads  144  also engage a section of the internal threads  42  of the hole  20  in the implant fixture  10 , the connector  130  exerts a force in the direction of its longitudinal axis  142  against the base  62  of the abutment  60 . The force pushes the base  62  out of the upper cavity  26  of the implant fixture  10 .  
         [0032]    [0032]FIG. 6 and FIG. 7 show, respectively, cross-sectional side views of second embodiments of an implant fixture  10 ′ and a base portion  62 ′ of an abutment, respectively. Like the embodiment shown in FIG. 1, the implant fixture  10 ′ is also a root-form implant fixture and includes a head portion  12 ′ and an adjoining root portion  14 ′. In addition, the implant fixture  10 ′ has a generally cylindrical shape and has external threads  16 ′ formed along a section of an exterior surface  18 ′ of the elongated root portion  14 ′. The implant fixture  10 ′ includes a longitudinal bore or hole  20 ′, which extends from an upper exterior surface  22 ′ of the head portion  12 ′ into the elongated root portion  14 ′ of the implant fixture  10 ′. The hole  20 ′, which has a centerline substantially coincident with a symmetry axis  24 ′ of the implant fixture  10 ′, includes a cavity  28 ′ defined by an interior surface  32 ′, which is adapted to receive the connector  130  (FIG. 2). The interior surface  32 ′ has a cylindrical shape, and includes internal threads  42 ′ that extend from the head portion  12 ′ to a region adjacent to the bottom  44 ′ of the hole  20 ′. The exterior surface  22 ′ of the head portion  12  of the implant fixture  10 ′ has a polygonal (e.g., hexagonal) shape, which is adapted to receive a tool (e.g., hex head socket driver) for rotating the implant fixture  10 ′ into the jawbone.  
         [0033]    As can be seen in FIG. 7, the base  62 ′ of the abutment has first  66 ′ and second  68 ′ surfaces which are separated by a skirt  70 ′, and a third (or inner) surface  72 ′ that defines an aperture  74 ′ which extends from the first surface  66 ′ to the second surface  68 ′ of the base  62 ′. The first surface  66 ′ of the base  62 ′ of the abutment  60 ′ is complementary to the exterior surface  22 ′ of the head portion  12 ′ of the implant fixture  10 ′ shown in FIG. 6. The second surface  68 ′ has a finite and approximately constant radius of curvature—i.e., has a shape that approximates a section of a sphere—and provides a surface for joining the attachable coping  64 ′ (FIG. 2) to the base  62 ′ of the abutment  60 ′. The third (inner) surface  72 ′ of the base  62 ′ has a pair of generally cylindrical surfaces  84 ′,  86 ′ that are separated by an annular surface  88 ′ which slopes inward towards a symmetry axis  90 ′ of the base  62 ′ of the abutment  60 ′. As described above, the third surface  72 ′ is configured to receive the connector  130  (FIG. 3), which joins the base  62 ′ of the abutment  60 ′ to the implant fixture  10 ′.  
         [0034]    The above description is intended to be illustrative and not restrictive. Many embodiments and many applications besides the examples provided would be apparent to those of skill in the art upon reading the above description. The scope of the invention should therefore be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are hereby incorporated by reference in their entirety for all purposes.

Technology Category: 1