Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation application of U.S. application Ser. No. 10/302,070, filed Nov. 22, 2002 now U.S. Pat. No. 6,932,606 and entitled Abutment Screw With Spring-Washer, which claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No. 60/385,814, filed Jun. 4, 2002 and entitled Abutment Screw With Spring-Washer, both of these applications being hereby incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to the field of dental implantology and, more specifically, to retaining screws used to secure dental components, such as abutments, copings, and prosthesis to dental implants. 
   BACKGROUND OF THE INVENTION 
   Retaining screws in the field of dental implantology or dental prosthetics are very important since they are used to fasten and hold together various dental components. These retaining screws, for example, fasten the dental abutment to the dental implant. Unfortunately, prior dental retaining screws tend to loosen over time. The loosening of these screws has caused many problems, and much effort has been devoted to solving these problems. 
   Dental retaining screws are typically fabricated from titanium. On one hand, titanium is ideal for this indication since it is strong, light-weight, and biocompatible. On the other hand though, titanium has a high coefficient of friction that makes it very susceptible to loosening over time. Specifically, a large percentage of the torque applied to a dental retaining screw is lost to overcoming the high frictional contact between the screw threads and threaded bore of the implant and between the screw head and seating surface of the abutment. According to some estimates, approximately 50% of the applied torque is lost in overcoming the mating friction under the screw head; and 40% of the applied torque is lost in the threads. As such, only about 10% of the applied torque exerted on the screw head is actually exerted as preload or tensile force stretching and tightening the screw. 
   Retaining screws tend to loosen in dental applications also because these screws are exposed to large loads and extended vibrations. Occlusal forces from chewing, talking, grinding, brushing, etc. continuously load the prosthetic tooth and accompanying retaining screw. These forces, over time, can decrease the preload and loosen the screw. Once the screw loosens, the joint between the prosthetic components can open or form gaps. The dental components, such as the prosthesis, the abutment, and the screw, can then bend or even break. 
   Over the years, many solutions have been proposed to reduce the occurrence of titanium screws loosening in dental applications. One solution is to increase the applied torque to the screw. This solution has limitations since the retaining screws can be tighten or loaded above the yield point of the material. In this instance, the screw can be permanently damaged and elastically unable to return to its original shape and position. Further yet, the maximum, attainable preload can be lessened if the screw is permanently damaged and deformed. 
   Many other solutions have been devoted to reducing the coefficient of friction either between the screw head and the mating surface of the dental component or between the screw threads and threaded bore of the implant. In some instances, screws have been made of gold-alloy material to reduce the co-efficient of friction, but their soft material causes deformation of their threads upon tightening. 
   In other instances, surface coatings have been placed on the retaining screw to reduce the coefficient of friction. U.S. Pat. No. 6,447,295, entitled “Diamond-Like Carbon Coated Dental Retaining Screws” and incorporated by reference herein, teaches a retaining screw coated with diamond-like carbon. Further, U.S. Pat. No. 5,711,669, entitled “High Load Factor Titanium Dental Implant Screw” teaches a retaining screw coated with a soft, deformable, biocompatible material that is malleable and subject to cold flow. 
   These coatings reduce the coefficient of friction of the retaining screw, but the coatings have disadvantages. First, the coatings can be expensive. Additionally, they can wear over time or become removed or scraped during tightening. Further, although they can reduce the coefficient of friction, they do not prevent or inhibit the retaining screw from loosening or losing preload due to occlusal forces, vibrations during masticulation, and the like. 
   It would be advantageous to have a dental retaining screw that could be used to secure prosthetic components to a dental implant yet not be prone to loosen or lose preload. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed toward dental retaining screws used to secure dental components, such as abutments, copings, analogs, cuffs, healing members, and prosthesis to dental implants. The retaining screw has a proximal end with a head portion having a locking mechanism. This locking mechanism includes a spring-washer with an annular body and a plurality of resilient legs projecting downwardly from the body. Each leg has a distal end with a locking component shaped as a foot or projection extending outwardly from the leg. 
   The spring-washer is adapted to threadably engage the exterior threads on the retaining screw. The spring-washer can removably connect to the body of the screw with any one of various connections, such as a press-fit or snap-fit. In this regard, the outer surface of the retaining screw includes a housing adapted to receive the legs of the spring-washer. The housing is configured as a plurality of channels or grooves, wherein each channel receives one leg of the spring-washer. Once the spring-washer is connected to the body of the screw, the legs are adapted to flexibly move in an axial direction in the channels. 
   The dental component includes an internal cavity with a locking mechanism along the interior surface of the cavity. Preferably, this locking mechanism is configured as a plurality of elongated channels that extend parallel to the longitudinal axis of the dental component. Preferably, the channels are formed along the interior surface and are equally spaced apart. 
   The retaining screw fits inside the interior cavity of the dental component and abuts a ledge to connect the dental component and implant. When the retaining screw is in place and appropriate torque and preload have been applied to it, the screw will not loosen while threadably connected to the implant. In this regard, the locking mechanism of the retaining screw and the locking mechanism of the dental component engage to prevent counterclockwise rotational movement of the retaining screw. Specifically, the legs of the spring-washer bias the locking component out of the housing and into the locking mechanism of the dental component. The projections or feet, thus, engage or lock with the channels along the interior surface of the dental component. As such, the retaining screw is prevented from rotating or losing preload while tightened and connected to the implant. 
   One important advantage of the present invention is that once the retaining screw is tightened to a selected torque level, the locking mechanisms of the dental component and retaining screw prevent or reduce the possibility that the retaining screw will loosen. The retaining screw will not tend to loosen even when exposed to large loads and extended vibrations, such as occlusal forces from chewing, clinching, grinding, talking, brushing, etc. Hence the stability of the dental implant system is improved and a secure and reliable fastening mechanism or coupling is provided between the dental component and the dental implant. 
   As another advantage, since the retaining screw is much less likely to loosen, then the joint between the prosthetic components is much less likely to form an opening or gap as a result of a loose retaining screw. Further, the dental components, such as the prosthesis, the abutment, and the screw, are not as likely to bend or even break. 
   As another important advantage of the present invention, the spring-washer body of the retaining screw is formed from titanium, and the spring-washer is formed from gold. The gold spring-washer advantageously provides a reduced coefficient of friction between the contacting surface of the retaining screw and the seating surface of the dental component, such as the abutment. As such, the screw is capable of obtaining a higher preload or clamping force between the dental component and implant. Further more, the coefficient of friction between gold and titanium is 60% less than titanium to titanium. This reduction in friction results in a higher preload. The spring washer can be made out of titanium and can be later anodized and or diamond coating can be applied to the surface to achieve the same affect as gold. 
   As a further advantage, the locking mechanisms of both the dental component and retaining screw are biocompatible and resistive to corrosion. The retaining screw is also relatively inexpensive to manufacture. 
   Another advantage is that the spring-washer ensures that the screw is retained in the abutment during shipping and placement of the abutment in the mouth without the need of internal threads inside the abutment. As such, the screw will not fall out from the abutment. 
   Accordingly, the present invention comprises a combination of features and advantages that overcome various problems, deficiencies, or shortcomings associated with prior devices. The various features and advantages of the invention will be readily apparent to those skilled in the art upon referring to the accompanying drawings and reading the following detailed description of the preferred embodiments of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more detailed description of preferred embodiments of the present invention, reference will now be made to the accompanying drawings, wherein: 
       FIG. 1  is a partial cross-sectional view of a dental implant system supporting a prosthetic tooth and having a retaining screw in accordance with a preferred embodiment of the invention. 
       FIG. 2  is a cross-sectional view of one embodiment of an abutment according to the invention. 
       FIG. 3  is a side view of a retaining screw according to the invention. 
       FIG. 4  is an exploded isometric view of the retaining screw of  FIG. 3 . 
       FIG. 5  is an enlarged isometric view of the spring-washer of  FIG. 4 . 
       FIG. 6  is a cross-sectional view along lines  6 - 6  of  FIG. 3 . 
       FIG. 7  is an enlarged, side, cross-sectional view along circle  7  of  FIG. 6 . 
       FIG. 8  is a partial cross-sectional view of an abutment and retaining screw according to the invention. 
       FIG. 9  is an enlarged cross-sectional view along lines  9 - 9  of  FIG. 8 . 
       FIG. 10  is an enlarged, cross-sectional view along circle  10  of  FIG. 9 . 
       FIG. 11  is a cross-sectional view of another embodiment of an abutment according to the invention. 
       FIG. 12  is a partial cross-sectional view of an alternate embodiment of the retaining screw connected to a spring-washer. 
       FIG. 13  is an enlarged, side, cross-sectional view along circle  13  of  FIG. 12 . 
       FIG. 14  is an enlarged isometric view of an alternate spring-washer. 
       FIG. 15  is a side view of an alternate retaining screw connected to the spring-washer of  FIG. 14 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a dental prosthetic implant system  10  having features in accordance with one preferred embodiment of the present invention. The dental implant system  10  generally comprises a dental component  12  (shown as an abutment), a retaining screw or bolt  14  (shown as an abutment retaining screw), and a dental implant, fixture, or root  16 . The dental implant  16  is adapted to be received in a hole, osteotomy, or alveolar cavity in a jawbone of a patient. The retaining screw  14  serves the purpose of fastening and holding the abutment  12  to the implant  16 . 
   The dental component  12  and retaining screw  14  can be commercialized as a dental kit. This dental kit may further include additional dental components known to those skilled in the art. Such dental components include dental copings, analogs, healing collars, healing abutments, cuffs, prosthesis, and the like. 
   In one preferred embodiment, the dental implant system  10  further comprises a dental restoration, prosthesis, or artificial tooth  18 . The abutment  12  supports the restoration  18  in the mouth of a patient. The restoration  18  can be cemented to the abutment  12 . Alternatively, or in addition, a separate screw (not shown) can be used to mount and retain the prosthesis  18  on the abutment  12 . 
   As shown in  FIGS. 1 and 2 , the abutment  12  is generally elongated in shape and can have a variety of shaped exterior surfaces  21  adapted to seat and retain the prosthesis  18 . For example, the abutment exterior surface  21  can be tapered, conical, cylindrical, straight, angled, contoured, or combinations thereof. 
   As the skilled artisan will recognize, the present invention can be embodied utilizing a wide variety of commercially available abutments. Thus, the abutment  12  can comprise, for example, the UCLA abutment or abutments sold by Centerpulse Dental Inc. of Carslbad, Calif. 
   The abutment  12  has a top end  22 , a bottom seating end/surface  24  for interfacing or abutting with the implant  18 , and an internal, through cavity or bore  26 . This cavity has a generally circular opening  28  at the top end  22  and is adapted to receive the retaining screw  14 . The cavity  26  further includes an internal seating surface, shoulder, seat, or ledge  32  that serves as a seating surface for the head of the screw  14 . Preferably, the shoulder  32  is generally flat, annular or ring-like in shape, but other embodiments are known to those skilled in the art. 
   The shoulder or abutting surface  32  divides or partitions the through cavity  26  into an upper generally cylindrical cavity, portion, or surface  34  and a lower (or middle) generally cylindrical cavity, portion, or surface  36 . The cavity  34  and cavity  36  are in communication with one another with the cavity  34  having a diameter larger than that of the cavity  36 . 
   The cavity  36  is further in communication with a generally hexagonal socket, portion, or surface  38  at the bottom end  24  of the abutment  12 . The hexagonal socket  38  permits anit-rotational mating, coupling, or attachment between the abutment  12  and implant  16 . 
   As shown in  FIG. 2 , cavity  26  includes a locking mechanism  27  formed along the interior surface of the bore. Preferably, the locking mechanism is formed above a threaded section  29 . This locking mechanism includes a plurality of locking members  31 . In this embodiment, these locking members are formed as elongated channels or grooves that extend in a longitudinal or axial direction in the interior surface of the cavity  26 . Preferably, the locking members are spaced about 6° to 18° apart. 
   Turning back to  FIG. 1 , the implant  16  can be any one of a wide variety of dental implants, for example, a threaded implant, a cylindrical implant, or a tapered implant, as are known in the art, such as a tapered or straight Screw-Vent implant of Centerpulse Dental Inc. The implant  16  comprises a body or root portion  40  adapted to engage an osteotomy or alveolar cavity in the jawbone of a patient. The implant includes a hexagonal post or protrusion  42  at a top end  44 . A blind internal threaded socket or bore  46  originates from the top end  44  and into the implant body portion  40 . The threaded socket  46  is adapted to threadably engage the abutment retaining screw  14 . A seating surface  48  generally circumscribes the hexagonal post  42  to engage, contact, or abut against the opposing abutment seating surface  24 . The implant body portion  40  may include a passage  50  formed to permit in-growth of bone and tissue for locking or anchoring the implant  16  in the osteotomy. 
   The hexagonal post  42  of the implant is configured to provide anti-rotational engagement with the abutment hexagonal socket  38  ( FIG. 2 ). Alternatively, a mating post may be provided at the bottom end of the abutment  12  to interlock with a corresponding mating socket at the top end of the implant  16 . 
   Turning now to  FIGS. 3-7 , the abutment retaining screw  14  is generally dimensioned and configured to adapt to a particular implant-abutment pair. The retaining screw  14  generally comprises an elongated body  53  and a spring-washer  55 . The body further includes an upper head or cap portion  60  in mechanical communication with a shank portion  62  that extends downwardly therefrom. The shank  62  comprises a threaded portion  64  having external threads  66  adapted to threadably engage the threaded socket  46  of the implant  16  ( FIG. 1 ). The threaded portion  64  is in mechanical communication with an upper non-threaded portion  68  and a lower non-threaded portion  70  at the distal tip of the shank  62 . 
   The screw head  60  is preferably generally cylindrical in shape and includes a lower contacting, seating, or abutting surface  72  at the bottom of the spring-washer  55  for engaging the opposed seating surface, or shoulder  32  of the abutment  14  ( FIG. 2 ). Preferably, the contacting surface  72  is generally annular or ring-like in shape to generally conform to the shape of the abutment shoulder  32  ( FIG. 2 ). Additionally, the screw head  60  preferably has a generally hexagonal cavity or socket  74  for receiving a torque wrench or other suitable tool. 
   The retaining screw  14  includes a locking mechanism  76  adapted to prevent the screw from loosening while tightened to the implant. The locking mechanism generally includes the spring-washer  55  and corresponding housing  78 . The housing is formed along the external surface of the body  53  on the head  60 . Preferably, the housing is formed as a plurality of elongated channels, slots, or grooves  80 . These channels extend from the distal end of the head  60  toward the proximal end where the socket  74  is located. As shown best in  FIGS. 6 and 7 , the channels  80  have a rectangular or square shape in cross section. 
   As best shown in  FIGS. 4 and 5 , the spring-washer  55  has a ring-shape or annular body  82 . In cross section, this body is generally rectangular. The body  82  has a plurality of legs  84  that extend downwardly and that are equally spaced around the body  82 . These legs are resilient or spring-like and have an elongated configuration with a proximal end connected to the body  82  and a distal end with a locking component  86 . As best shown in  FIG. 7 , the locking component  86  is formed as a foot or protrusion  88  that extends outwardly from the distal end of each leg  84 . 
   As shown in  FIGS. 4 and 5 , the outer surface  90  of the spring-washer  55  is smooth, while the inner surface  92  is threaded. These threads are adapted to threadably engage the threaded portion  64  of the body of the screw. As such, the spring-washer is captured along shank portion  62  between the threaded portion  64  and head  60 . The spring-washer could be captured in other ways as well. For example, the outer diameter of the head of the screw could be larger than the inner diameter of the spring-washer. 
   As best shown in  FIGS. 6 and 7 , the legs  84  of the spring-washer  55  fit inside the channels  80 . A small gap or space  95  exists between the inner, threaded surface  92  of each leg  84  and the bottom surface  96  of each channel  80 . This gap enables each leg to move in an axial or radial direction (arrows A-A) toward and away from the body  53 . The legs, thus, have a resilient or flexible movement while the spring-washer is connected to the body. Further, while the legs  84  are positioned in the housing  78 , the foot or protrusion  88  extends partially out of the channels  80 . 
   The housing  78  and the legs  84  may have various configurations known to those skilled in the art. The figures show a generally rectangular configuration, but other shapes which ensure proper bearing, including polygonal shapes (such as square, hemi-spherical, frusto-conical, etc.), are also contemplated. 
   Preferably, the body of the retaining screw is formed of a biocompatible, corrosive resistant material such as titanium Other materials may work as well, such as steal or other biocompatible, corrosive resistant materials. Preferably, the spring-washer, however, is formed from a second material, different than the material of the body of the abutment. Preferably, this second material is gold. The spring-washer can also be formed a material that is different than the body of the screw. Further yet, the spring-washer can be gold and then coated with titanium. 
   The gold spring-washer has an advantage in that it provides a reduced coefficient of friction between the contacting surface of the retaining screw and the seating surface of the dental component, such as the abutment. As such, the screw is capable of obtaining a higher preload or clamping force between the dental component and implant. 
   The spring-washer may be formed from other materials that also reduce the coefficient of friction between contacting surface of the retaining screw and the seating surface of the dental component. For example, the spring-washer can be formed from titanium or other suitable materials and then coated with a diamond-like carbon coating or other coatings or oxidized surfaces, as described in U.S. Pat. No. 6,447,295. 
   Turning now to  FIGS. 8-10 , the coupling or engagement between the retaining screw  14  and abutment  12  is shown in detail. The locking mechanism  76  of the retaining screw engages or locks with the locking mechanism  27  of the abutment. Specifically, when the abutting surface  72  of the screw seats or engages with the abutting surface  32  of the abutment, the locking component  86  of the spring-washer  55  is biased into the locking members  31  of the dental component  12 .  FIG. 10  shows how the foot or protrusion  88  engages or locks with the channels or grooves of the locking member  31 . Here, each leg biases the foot in a radial direction so it abuts against a back wall or surface  100  of the locking member  31 . The connection or engagement between the locking component  86  and locking members  31 , thus, prevents the screw from backing out. 
   The spring-washer is adapted to threadably engage the exterior threads on the retaining screw. The spring-washer can removeably connect to the body of the screw with any one of various connections, such as a press-fit or snap-fit. Alternatively, the spring-washer can be permanently connected to the body of the retaining screw. 
   The rotational force or torque required to disengage the locking mechanism  76  of the screw from the locking mechanism  27  of the abutment would be greater than the forces tending to loosen the screw, such as vibrational and occlusal forces like chewing, grinding talking, brushing, etc. 
   Looking to  FIG. 10 , the locking member  31  includes the back wall  100 , a tapered entry wall or surface  102 , and a perpendicular, flat, stop wall or surface  104 . When the retaining screw is rotated in a clockwise direction (shown as arrow A) or is being tightened, the feet  88  slide up and along the tapered wall  102 . When the screw, however, is rotated in a counterclockwise direction (shown as arrow B) or is being loosened, the feet abut against flat, stop surface  104 . This stop surface prevents the locking component  86  from disengaging from the locking mechanism  27  or, more particularly, the locking members  31 . 
   One skilled in the art will appreciate that the locking mechanism  27  of the dental component  12  and the locking mechanism  76  of the retaining screw  14  can have various configurations to provide a locking or anti-rotational engagement. The locking members  31 , for example, have a generally rectangular configuration with three surfaces  100 ,  102 , and  104 , but other polygonal shapes (such as square, hemi-spherical, frusto-conical etc.) are also contemplated. Further too, the locking component  86  can have various configurations to correspondingly mate with the locking members. The locking component, for example, can be a pin, a button, a cylinder, other geometric configurations, or combinations thereof. 
   It will be appreciated too that the present invention could incorporate multiple legs and locking components on the spring-washer. Preferably, the spring-washer has three legs, one or more legs can work too. 
   Further, although  FIG. 2  shows the locking members  31  as channels, one skilled in the art will appreciate that the locking mechanism  27  can have various configurations without departing from the scope of the invention.  FIG. 11 , for example, shows an abutment  120  similar to the abutment  12  in  FIG. 2 . This abutment  120 , however, has a different locking mechanism  122 . Here, the locking mechanism  122  includes a plurality of locking members  124  formed as circular indentations or partial spherical indentations. These indentations could have various configurations, such as squares, spheres, rectangles, or other polygonal formations. 
   Turning now to  FIGS. 12 and 13 , an alternate embodiment is shown. Here, the retaining screw  140  and spring-washer  142  are generally configured as the retaining screw  14  and spring-washer  55  described in connection with  FIGS. 3-5 . As one important difference, the retaining screw  140  has a projection or single thread  144  right below the screw head  146 . This projection  144  engages with the internal threads  148  of the spring-washer  142  to hold and maintain the spring-washer against the screw head  146 . 
   When a screw is tighten it acts like a clamp that resists the forces that are trying to pry open the joint. When the abutment screw is tightened, it stretches (within elastic limits) and thus generates axial compressive forces. Therefore, the abutment screw acts like a spring. As soon as the screw tightening process is stopped, some of the pre-load is lost. 
     FIGS. 14 and 15  show an alternate embodiment of the spring-washer that is adapted to prevent preload from being lost. Here, the retaining screw  160  and spring-washer  162  are generally configured as the retaining screw  14  and spring-washer  55  described in connection with  FIGS. 3-5 . As one important difference, the spring-washer  162  is configured to have an axial biasing ability. Specifically, the body  164  of the spring-washer has coils or springs  166  that are moveable in an axial direction. These coils are adapted to bias the body  164  as they are compressed. The coils will become compressed when the retaining screw is seated and tightened against a seating surface. 
   The present invention can be used with various dental implants and dental accessories, such as abutments, heating components, fixture mounts, copings, analogs, cuffs, or other dental components. Further, as understood by those skilled in the art, the precise configuration and dimensions of the various components of the retaining screw may vary depending upon the size of the implant or dental component. The principles of the present invention can be applied to these various components. Further yet, while preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention.

Technology Category: 1