Abstract:
An endosseous dental implant system having an implant body and an abutment. The implant body has a tapered cylindrical surface near its top end and an internally threaded or unthreaded passage extending into the implant body through an opening at the top of the implant. The abutment has an internal passage for receiving a fastener or, alternatively has a fastener as part of the abutment. The fastener threads into the implant body so that a tapered cylindrical cavity in the abutment mates with a matching tapered cylindrical surface of the implant to form an anti-rotational and locking junction with the implant when fastened by a screw or fastener. In addition to the anti-rotational and locking junction formed by the mating of external tapered cylindrical surface and internal tapered cylindrical surface, the dental implant system may also include an implant body having a multi-sided projection. In this embodiment, the abutment has a cavity for receiving the projection. The cavity and projection forms an additional anti-rotational junction between the implant body and the abutment.

Description:
RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 09/606,826, filed on Jun. 28, 2000, now abandoned incorporated herein by reference. 
    
    
     BACKGROUND OF THE PRESENT INVENTION 
     1. Field of the Invention 
     This invention relates to a dental implant system. More particularly, this invention relates to a dental implant system having an implant body and an abutment, wherein the implant body and abutment format least a first anti-rotational connection by frictional engagement of mating tapered surfaces. 
     2. Background of the Invention 
     Two-part endosseous dental implant systems for insertion in a wholly or partially edentulous region of the jawbone of a patient are known in the art. The implant systems may be completely embedded in a jawbone of a patient. Typically, a protective cover screw is attached to the top of the implant. The implant is then covered with mucosal tissue. Alternatively, the implants or a protective component affixed to the implant may protrude through the oral mucosa at the time of placement of the implant into the jawbone. Typically, the implants are permitted to remain in place while new bone grows around the implant. Once the implant has become firmly anchored in bone, the mucosal tissue must be reopened if the implant is covered. The protective component is then removed and an abutment or post is connected to the implant using a screw. A prosthesis can then be connected to the abutment or post. 
     Many two-part implant systems have an external, hexagonal projection, sometimes called a male hex, which projects upwardly from the top end of the implant. A shoulder surrounds the base of the male hex. An abutment or post having an outer diameter that substantially matches the outer diameter of the implant is seated on the male hex to form a substantially sealed connection. Some implants have an externally-threaded sidewall portion that can be screwed into an opening formed in the bone after bone tissue has been removed from the jawbone. Examples of such an implant may be found in U.K. Patent No. 1,291,470 or in U.S. Pat. No. 4,713,004. With implant systems of this kind, the male hex projection at the top of the implant is designed to engage an inserting device, e.g. a wrench, that is used to insert the implant in the jawbone. 
     Another kind of two-part, endosseous dental implant system with an external male hex is a cylindrical implant having a non-threaded, external body portion. These implants are pushed into an opening formed in bone tissue. An example of this type of implant is a BIO-VENT® implant available from Core-Vent Corporation, 15821 Ventura Boulevard, Suite 420 Encino, Calif. 91436. 
     In implants having external male heads, the male head is used to attach the implant to an abutment or post having a matching female hex-shaped cavity that receives and engages the male hex projection. Such male hex heads and female hex cavities are sometimes referred to as coupling surfaces. Typical implant systems have external male hexes and mating internal female hex cavities with walls of the hexagonal head and the hex-shaped cavity of the abutment being perpendicular to a longitudinal axis of the abutment and parallel to one another. 
     With such implant systems, the male hex of the implant is smaller in diameter than the diameter of the hex-shaped cavity of the abutment to permit the male hex to fit inside the female cavity. The difference in diameter is sufficiently large to allow for manufacturing variations while still allowing the coupling surfaces of the abutment to seat fully on the shoulder of the implant. Seating the coupling surfaces on the shoulder of the implant creates a sealed outer margin between abutment and implant. However, this leaves space between the coupling surfaces of the male and female hexes. 
     Within the hex head region, and extending into the implant itself, there is in such implants a threaded hole for receiving an attachment screw of a mating abutment. The abutment typically has an interior abutment passage centered on its hex cavity. When attaching the abutment to the implant, the screw is inserted through the abutment passage and is screwed into the threaded implant hole. Tightening the screw tightens the abutment against the implant. When the screw is tightened until the external hex of the implant mates with the matching female hex cavity in the abutment, the system is secured against axial displacement of the abutment from the implant. 
     The seating of the external hex of the implant within the female hex cavity of the abutment, where both the external hex and the internal hex cavity have parallel walls, results in the full seating of the abutment onto the shoulder surrounding the external male hex of the implant. However, according to reported studies, the seating of the external hex of the implant within the female hex cavity of the abutment of existing implant systems fails to completely prevent rotational displacement of the implant with respect to the abutment. 
     For example, a scientific study presented by Dr. Paul Binion at the Academy of Osseointegration meeting in San Diego, Calif. in Mar. 1993, documented that the coupling surfaces of commercially-available implants allow four to five degrees of rotation between the abutment and the implant. Dr. Binion later reported that certain implant/abutment assemblies exhibit up to nine degrees of rotation between the implant and the abutment. The relative rotation of the abutment and implant result in an attachment that is unstable. Lateral forces from biting are transmitted to the screw joining the abutment to the implant rather than the coupling surfaces of the external hex projection on the implant and the internal hex cavity in the abutment. As a result, the screw that joins the implant to the abutment may break or loosen. Rotational instability may also adversely affect the accuracy of transfer procedures needed for the indirect fabrication of a final prosthetic restoration on such implant/abutment assemblies. 
     Attempts have been made to remedy the problem of rotational instability in implant/abutment assemblies. For example, U.S. Pat. No. 4,547,157 discloses an implant having a conical projection for mating with an abutment having a matching cavity. A small degree of taper of the two surfaces results in a friction fit between the parts that tends to maintain the connection. These systems do not use a screw that passes through the abutment to lock the abutment to the implant. The tapered, cylindrical coupling surface makes direct contact and fully seats on the mating cavity in the implant, which results in a good connection. However, a drawback with this type of connection is that a ledge is formed as the outer walls of the internal cavity fit over the conical projection of the implant. This ledge can trap food particles and irritate gum tissues. Moreover, it is necessary to use a hammering action to seat the abutment onto the implant, which is uncomfortable for a patient. Further, it is not possible to quantify the force of hammering, which varies greatly from one practitioner to the other. 
     Other implants exist that have an internal taper connection. One example is the ITI® Dental Implant System available from Straumann Holding AG, CH-4437 Waldenburg, which has a very wide implant head to accommodate the abutment. Therefore, the ITI® dental implant is not suitable for narrow spaces. In addition, the marginal area of the restoration is cemented directly onto the implant. As a result, the top of the implant must remain exposed after healing of the soft tissues. A disadvantage of this arrangement is that it is not possible to modify the marginal area, which leaves a visible unaesthetic silver margin around the restoration. 
     There is, therefore, a need for improvements in dental implant systems, particularly, endosseous dental implant systems which overcome the above and other disadvantages. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an endosseous dental implant system that includes at least two parts: a first part called a implant body, and a second part called an abutment, post or insert. The implant body may have a threaded external sidewall surface or a non-threaded external sidewall surface, and the implants themselves may be generally cylindrical or tapered in shape. The external sidewall surface may also have one or more longitudinally extending grooves. 
     A part or all of the external surfaces of the implant system may be treated by applying a coating consisting of hydroxyl apatite or titanium plasma spray. Alternatively, part or all of the external surfaces may be roughened by blasting or acid etching or a combination of the above-mentioned methods. 
     A tapered cylindrical surface is provided at the top end of the implant body for engaging and interlocking anti-rotationally with a matching tapered cavity inside the abutment. The anti-rotational connection is formed when the abutment is fully seated and fastened to the implant body by means of screw or fastener. On top of the implant, there may be an additional projection, preferably a multi-sided projection. In the preferred embodiment, the projection consists of multiple sides that are parallel to the longitudinal axis of the implant body. The optional projection forms a second anti-rotational connection with a corresponding internal cavity in the abutment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the method and apparatus of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein: 
     FIG. 1 is an exploded cross-sectional side view of a first embodiment of the dental implant system of the invention; 
     FIG. 2 is an exploded cross-sectional side view of a second embodiment of the dental implant system of the invention; 
     FIG. 3 is a cross-sectional side view of an embodiment of a threaded implant body that may be used with the dental implant system of FIGS. 1 and 2; 
     FIG. 4 is a cross-sectional side view of another embodiment of a threaded implant body that may be used with the dental implant system of FIGS. 1 and 2; 
     FIG. 5 is a cross-sectional side view of the components of the dental implant system of FIG. 1 assembled; 
     FIG. 6 is a cross-sectional side view of an alternate embodiment of a tapered implant body pursuant to the teachings of the present invention; 
     FIG. 7 is a cross-sectional side view of the tapered implant body of FIG. 6 with a projection affixed thereto; 
     FIG. 8 is a cross-sectional side view of the tapered implant body of FIG. 7 with threads; 
     FIG. 9 is a cross-sectional side view of the tapered implant body of FIG. 6 with threads; 
     FIG. 10 is a cross-sectional side view of an alternate embodiment of the present invention having a blade portion affixed to the implant body; and 
     FIG. 11 is a cross-sectional side view of the bladed implant body of FIG. 10 with a projection affixed thereto. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     Referring now to FIGS. 1-4, shown is a multi-part, endosseous dental implant system, generally designated by the reference numeral  10 . It should be understood that common components of the various embodiments for practicing the instant invention retain the same numerical designation in each of the Figures. The dental implant system  10  has an implant body, generally designated by the reference numeral  12  (FIGS.  1 - 4 ), and an abutment, generally designated by the reference numeral  14  (FIGS.  1  and  2 ). 
     With reference now to FIG. 1, the implant body  12  has an external sidewall  16  having a generally-cylindrical shape, and an external tapered cylindrical surface  18  that tapers towards top end  20  of implant body  12 . In one embodiment, the external sidewall  16  of the implant body  12  may include a plurality of external screw threads  22 , as illustrated and described in more detail in connection with FIGS. 3 and 4, having a substantially constant pitch. The external screw threads  22  may be either self-tapping or non-self-tapping, as is understood in the art. The external screw threads  22  may extend along the entire length of external sidewall  16  or only partly along the length of the external sidewall  16 . The external sidewall  16  of the implant body  12  above the external screw threads  22  may either be substantially cylindrical, may taper upwardly and outwardly or may taper upwardly and inwardly toward the top end. Additionally, at the bottom end  24  of the implant body  12 , the external sidewall  16  of the implant body  12  may be substantially cylindrical, or may taper toward the bottom end  24  of the implant body  12 . 
     With reference now to FIG. 1, abutment  14  preferably has a generally tapered shape also. The bottom end  26  of the abutment  14  has a primary cavity  28  therein to receive the aforedescribed top end  20  of the implant body  12  when the abutment  14  is seated on implant body  12 . 
     When implant body  12  and abutment  14  of the instant invention are secured together, at least one anti-rotational component  30  or connection is formed, as illustrated in FIG.  5 . The first anti-rotational connection  30  is formed in part by the aforedescribed external tapered cylindrical surface  18  of the implant body  12 . As illustrated in FIG. 1, the external tapered cylindrical surface  18  tapers upwardly and inwardly near the top end  20  of the implant body  12 . The external tapered cylindrical surface  18  frictionally engages a mating internal tapered cylindrical surface  32  within the primary cavity  28  of the abutment  14  when components  12  and  14  are fully seated and form the first anti-rotational connection  30 . As is well understood to those skilled in the art, friction between the external tapered cylindrical surface  18  and the internal tapered cylindrical surface  32  increases as the abutment  14  is fastened to the implant body  12 . As shown in FIG. 1, the abutment  14  has an outer diameter  34  at the bottom end  26  of the abutment  14  that is substantially the same as the outer diameter  35  of the top end  20  of the implant body  12  before installation of the abutment  14  on the implant body  12 . 
     Preferably, the degree of taper of the external tapered cylindrical surface  18  of the implant body  12  and the corresponding internal tapered cylindrical surface  32  on the inside of the abutment  14  is in the range of about one to about eight degrees. 
     Implant body  12  preferably has a flat surface  36  on top end  20 , as shown in FIG.  1 . The flat surface  36  of the implant body  12  is perpendicular to a longitudinal axis A of the implant body  12 . Preferably, the flat surface  36  should not make contact with the abutment  14  when the implant body  12  is secured to the abutment  14 . Instead, the external tapered cylindrical surface  18  and the internal tapered cylindrical surface  32  should mate to create the aforementioned first anti-rotational connection  30 . When the abutment  14  is fully seated, space between the bottom end  26  of the abutment  14  and the top end  20  of the implant body  12  is completely sealed off from the environment. 
     In one embodiment, as illustrated in FIGS. 1,  2  and  4 ,  5 ,  7 , and  11  a second anti-rotational connection is formed by a projection  38  from the top end  20  of implant body  12  that preferably has a substantially flat upper surface thereof. The projection  38  has a plurality of sidewall surfaces, generally designated by the reference numeral  39 , and numbering four (square) to eight (octagon) most preferably six (hexagon). 
     In preferred embodiments, the projection  38  is sized to fit inside a secondary cavity  40 , as illustrated in FIG. 1, located on an upper internal surface  41  of the primary cavity  28  inside of abutment  14 , thereby creating a second anti-rotational connection by the frictional interface of the projection  38  into the secondary cavity  40 . The anti-rotational property of the second anti-rotational connection is, however, not typically adequate to prevent all rotational movement of abutment  14 , although enough to locate the position of the abutment  14  with sufficient accuracy for further restoration with a prosthetic component. 
     With reference again to FIG. 1, the abutment  14  may include an abutment passage  42  therein. Abutment passage  42  is preferably cylindrically-shaped for receiving a fastener, generally designated by the reference numeral  44 , therein which passes through the abutment  14 . The fastener  44  may be a screw, bolt, or other suitable device for securing abutment  14  to implant body  12 . The fastener  44  preferably passes through the aforementioned abutment passage  42  and preferably screws into a threaded implant passage  46  in the implant body  12 . The threaded implant passage  46  in the implant body  12  extends downwardly into the implant body  12  from the top end  20 , and is preferably substantially centered through the aforedescribed projection  38  at the top end  20  of the implant body  12 . A flange surface  48 , as shown in FIG. 1, is preferably provided in the abutment  14  for engaging a head portion  50  of the fastener  44 . Tightening of the fastener  44  seats the abutment  14  substantially fully upon the implant body  12 , thereby creating the aforementioned first anti-rotational connection, as illustrated by the conjoined component  30  in FIG.  5 . Additionally, in certain embodiments of the invention, tightening of the fastener  44  additionally creates the second anti-rotational connection. 
     In a further alternate embodiment, illustrated in FIG. 2, a modified abutment, generally designated by the reference numeral  52 , may have an attached fastener portion  54  that extends from the aforementioned upper internal surface  41  of the primary cavity  28 . The attached fastener  54  screws into the aforedescribed threaded implant passage  46  in the implant body  12 . Tightly securing the modified abutment  52  to implant body  12  with the attached fastener  54  seats the modified abutment  54  upon the implant body  12  and frictionally engages the internal and external tapered cylindrical surfaces  18 ,  32  of the modified abutment  52  and implant body  12 , respectively, thereby creating the aforementioned first anti-rotational connection. 
     With reference now to FIG. 6, there is illustrated an alternate embodiment of the present invention in which the external sidewall  16  of the implant body  12  is tapered inward toward axis A, as opposed to the substantially cylindrically-shaped configuration of the external sidewall  16  illustrated in FIGS. 1-5. As shown in FIG. 6, external sidewall  16  and the external tapered cylindrical surface  18  meet at a juncture  17 . In one embodiment, the radial diameter of the external sidewall  16  at the bottom end  24  of the implant body  12  is less than the radial diameter of the external tapered cylindrical surface  18  at the top end  20  of the implant body  12 . 
     With reference now to FIG. 7, there is illustrated a modified version of the embodiment shown in FIG. 6 having a projection  38  affixed at said top end  20  of implant body  12  and having hexagonal walls  39 . 
     With reference now to FIG. 8, there is shown a still further modified version of the embodiment shown in FIG. 7 having external screw threads  22  along said external sidewall  16  of the implant body  12  for engaging bone. 
     Similarly, shown in FIG. 9 is the embodiment illustrated in FIG. 6 with the external threads  22  along the external sidewall  16  of the implant body  12 . 
     With reference now to FIG. 10, there is illustrated an alternative structure for the implant body  12 . In particular, the implant body in this embodiment contains a narrow blade-shaped body portion  56  affixed to the heretofore bottom end  24  of the implant body  12 . The thin blade body portion  56  has a razor or sharpened edge  58  opposite the fixture of the implant body  12 . In use, the blade and implant arrangement is pounded into the jawbone of the patient, securing the implant body  12  portion into bone. A number of holes  60  through the blade  56  allow bone-and tissue growth therethrough, further securing the placement of the implant body  12 . 
     Lastly, shown in FIG. 11 is a modified embodiment of the configuration of FIG. 10 including a projection portion  38  affixed to the top end  20  of the implant body  12 , which engages the aforementioned secondary cavity  40  in the manner described hereinabove. 
     The invention has numerous advantages. One advantage is that the external taper of the external tapered cylindrical surface  18  allows for a narrower implant to be used than may currently be used. In the apparatus of the invention, the abutment  14  surrounds the implant body  12 . In some related art devices, the implant system has the opposite configuration, i.e., where the implant body surrounds the abutment. When the implant body surrounds the abutment, it is necessary to make the walls of the implant body very wide to give the implant body enough structural strength to prevent breaking. Further, when the implant body surrounds the abutment, the margin of a prosthesis or crown is on the implant body, which cannot be modified. 
     In the apparatus of the invention on the other hand, the external taper  18  of the implant body  12  allows for an implant body  12  that is narrow and an abutment  14  that is wider. The wider abutment  14  can be bulky to provide for strength and for aesthetic purposes. Furthermore, the weakest portion of the assembly  30  lies in the abutment  14 . In the apparatus of the invention, the abutment  14  is changeable. A changeable embodiment is advantageous because an implant body  12  is difficult to change, i.e., the implant body  12  requires removal if fractured. An externally tapering implant body  12  allows the use of modifiable abutments  14  at a patient&#39;s gingival margin. For aesthetic purposes and for creating a shape that does not trap food, it is necessary to have flexibility in the gingival area of the assembly. An externally tapering implant body  12  combined with modifiable abutments  14  is aesthetically desirable and allows for the creation of an implant system that does not trap food. 
     An additional advantage of the device of the invention is that the device uses a friction-fit taper connection for an anti-rotational connection. A friction-fit taper connection is leak-proof, prevents rotation and provides a connection that takes load off of the fastener  44 , thereby preventing micro-movement of the abutment  14 . A friction fit connection is less likely to experience problems associated with loosening or breakage of the fastener  44  than with non-friction fit connections. The apparatus of the invention possesses the advantages of a friction fit taper connection without the disadvantages associated with an implant body  12  that surround the abutment  14 . 
     A further advantage of the apparatus of the invention is that an externally tapering implant body  12  with an abutment  14  that is secured to the implant by means of a screw  44  with a torque-wrench is more precise and more comfortable to the patient than existing implants that require a non-quantifiable tapping or hammering force to seat the abutment  14 . 
     Another advantage is that an optional projection  38 , e.g., a hexagonal projection, provides an additional anti-rotational component, which also allows for precise capturing of orientation of the abutment  14  by means of commonly used impression components, which aids in the fabrication of a prosthesis. The external hexagonal projection  38  is not necessarily engaged because the main stability of the device derives from the tapered friction fit of the anti-rotation connection. All of the positioning advantages of the projection component  38  are available but the disadvantages of loosening or breakage of the screw  44  are eliminated. 
     While only several forms of the invention have been shown and described, it should be apparent to those skilled in the art that the invention is not so limited, but is susceptible to various changes without departing from the scope of the invention.