Patent Publication Number: US-6666684-B1

Title: Impression and foundation system for implant-supported prosthesis

Description:
This application is a continuation-in-part (CIP) of U.S. Ser. No. 08/811,494, filed Mar. 5, 1997, now U.S. Pat. No. 6,056,547, the content of all of which are incorporated by reference into the present application. 
     Throughout this application, various publications are referenced within parentheses. The disclosures of these publications are hereby incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to a system and method for forming a final oral, maxillofacial or cranial restoration consisting of implants, a framework made from individual foundation elements for attaching to the implant and a prosthesis supported on the framework. More specifically, the present invention relates to a system and method for forming a framework for taking an implant impression to more accurately determine the positions and alignment of the implant sites in a patient, and use of the same framework as a support for removable or fixed prostheses to form the final restoration. 
     BACKGROUND OF THE INVENTION 
     Osseointegrated implants have been developed as the result of the discovery of the ability of bone to make direct biological attachment to the surfaces of titanium implants. (See Dental Implants: Tissue-Integrated Prosthesis Utilizing the Osseointegration Concept” published in the Mayo Clinic Proceedings, vol. 61 February 1986, pp91-97). An example of osseointegrated. plants is osseointegrated dental implants used as an alternative to a single tooth, fixed bridge or removable dentures to form a final restoration. The procedure involves a first operation to surgically expose the bone and, to drill a hole in the bone where an implant, for example, a titanium anchor element, is to be inserted. An implant having a central aperture temporarily blocked by a covering plug is inserted into the drilled hole in the bone. A flap of skin is then sewn over the site. During the healing period, the bone tissue becomes biologically attached to the titanium implant by growth of the bone tissue. 
     After the implants have become biologically attached to the bone, the top surfaces of the implants are exposed in a second operation. Sometimes, a metal abutment or “spacer” is attached to each implant as an intermediate between the implant and the framework of the prosthesis, for example when there is a space between the patient&#39;s jawbone and the gum tissue above. The description that follows refers to the use of an abutment or spacer. 
     In order to achieve the desired arrangement of the prosthetic teeth on the implants in the final restoration, a negative impression is made of the patient&#39;s mouth which includes the implant sites, and any remaining teeth and gums. One method for making a negative impression involves attaching a temporary stud or a coping to each implant in place of the covering plug. An impression material contained in a dental impression tray is applied around the copings and the dental process. After the impression material cures, the tray with the impression material is then removed from the patient&#39;s mouth. The copings are either embedded in the impression material when it is removed from the patient&#39;s mouth or reinserted into the impression material after the impression material is removed from the patient&#39;s mouth. U.S. Pat. No. 4,693,683 to Lee and U.S. Pat. No. 4,432,728 to Sharkey describe dental trays and techniques for making impressions. 
     Another method for making a negative impression of the dental process is disclosed in U.S. Pat. No. 5,055,047 to Names. Names discloses a metal impression confirmation system for making an accurate impression for preparing an implant supported dental prosthesis. Individual foundation elements, which are affixed to adjacent elements with a bonding resin, are used to form a rigid metallic framework. An impression is taken of the framework and gums and any remaining teeth. The rigid metallic framework helps to minimize or prevent distortion of the impression material as it cures, and also to prevent distortion of the poured stone for the master model while it cures, to ensure a more accurate molded impression. After the impression material sets, the tray with the impression material and the framework, is then removed from the patient&#39;s mouth. 
     An abutment analog with an aperture and a top surface corresponding to the aperture and the top surface of the abutment attached to the implant is temporarily attached to each coping or foundation element embedded in the negative impression. A positive master stone cast model of the patient&#39;s mouth can then be made from the negative impression by embedding the abutment analogs into a material such as gypsum and removing the negative impression by unscrewing the copings or the foundation elements from the abutment analogs. This results in a master stone model that duplicates the location of the implants in the patient&#39;s mouth. The positive master model ensures that the prosthesis will match the top of the implants (with or without abutments attached) when the prosthesis is inserted onto the implants in the patient&#39;s mouth. 
     Caps may then be attached to the abutment analogs embedded in the master positive model and a bridge body wax model on the caps, reinforced by a supporting plastic plate, is then produced. The bridge body wax model (the bite template) is placed in the patient&#39;s mouth and the caps are screwed onto the abutments. This step checks the accuracy of the impression and determines the height of the bite and the shape of the tooth curvature. After returning the bite template to the master positive model, the positive master model is matched to a positive master model of the opposite jaw and the two positive master models are mounted in an articulator. 
     In the bite template, teeth of plastic material (acrylate) matching the teeth of the opposite jaw, if any, are attached. The bite template with the teeth is tested in the patient&#39;s mouth and then is returned to the master positive model in the articulator. After the positions of the teeth are determined by pre-molding the teeth in soft plastic material, the teeth are removed from the bite template. New wax, connecting the caps on the bite template and built to a suitable dimension, and the caps are then embedded into gypsum. The new wax is melted and removed from the gypsum mold and molten cast gold is poured into the gypsum mold cavity, the caps being embedded into the gold as it sets. 
     The gold bridge body is removed from the gypsum mold and secured via the caps to the abutment analogs of the master positive model in the articulator. The teeth, the positions of which had been determined by the soft plastic pre-molding, are then attached to the gold bridge body by means of wax. The connection of the gold bridge body to the abutments via the caps is tested in the patient&#39;s mouth. If the fit is acceptable, the wax retaining the teeth to the gold bridge body is replaced by plastic material (acrylate) which permanently attaches the teeth to the gold bridge body by means of a pressing method. The gold bridge body with teeth is then screwed onto the abutments attached to the implants via the caps molded in the gold bridge body. 
     The entire process for preparing a final restoration as described above using fixed implants and a prosthesis involves numerous steps and materials and is tedious and time-consuming. Accordingly, there remains a need in the art for an improved system and method which simplifies the overall process by eliminating some of the steps and materials and thereby decreases the time and cost requirements for preparing the final restoration. 
     There remains a further need in the art for a system and method for accurately establishing the locations and orientations of the implants and preserving the accuracy throughout the entire process of preparing a final restoration. 
     There remains yet a further need in the art for a system and method for providing a foundation onto which a removable or fixed prosthesis is attached that is simple to produce, and is readily adjusted to confirm the fit of the prosthesis on the fixed implants. 
     SUMMARY OF THE INVENTION 
     The system and method according to the present invention is intended for use not only with dental prostheses but also with oral, maxillofacial and cranial prostheses of other kinds, such as ear, nose and eye socket prostheses, which are supported on foundation elements implanted in bone tissue in a patient. The description of the preferred embodiments are described in connection with dental restorations consisting of prostheses (teeth) which are supported on implants surgically inserted into the jawbone of a patient. 
     Preferred embodiments of the present invention meet the foregoing needs by providing an impression system that also serves as the foundation for a prosthesis to form the final restoration. The system and method of the present invention provide foundation elements that form a framework for taking an impression for accurate determination of the positions and orientations of the implants and for serving as a foundation on which the prosthesis is supported. 
     In one embodiment, the system of the present invention comprises individual foundation elements made of a prosthetic material which is similar or the same as the material used to make the prosthesis and is of sufficient strength and flexibility to withstand the stresses and strains transferred to the implant in actual operational environments. The individual foundation elements are attachable to each implant in the patient and bonded together to form a single framework. The framework provides a rigid base around which impression material may be molded. The rigidity of the framework ensures that the molded impression is dimensionally stable. 
     Each foundation element comprises a base member with a central bore so that a threaded permanent screw can be inserted through the bore and screwed into an implant thereby allowing aligned attachment of the base member to the implant. A final, permanent screw seats on a metal insert collar. The insert collar is located inside the base member with a central bore to receive three screws. The impression screw, the fabricating screw and the permanent screw. The impression and fabricating screws seat on a smooth inside ring. The permanent screw seats on the outer edge ring which contains the anti-rotation mechanism. The bottom of the insert collar is designed to interface with all dental implants. An elongated element extends from the surface of the base member and, when attached to a dental implant, the elongated element extends along the gum line. The opposite free end of the elongated element may be rigidly bonded to an adjacent foundation element with a small amount of a bonding material such as a resinous bonding material. If necessary, the elongated member may be cut to meet the adjacent base member and the bonding material can be added to complete the connection. 
     After assembly of the framework in the patient&#39;s mouth, impression material is injected around the dental process, including the framework, and a dental tray is pressed onto the overcoated framework. The dental tray is provided with openings at locations corresponding to the locations of the impression screws such that the tops of the impression screws extend through the openings. After the impression material has cured, the impression screws are detached from the implants by unscrewing at the tops of the impression screws extending through the openings of the dental tray. The dental tray, the cured impression material mold and the framework of foundation elements imbedded in the mold are then removed from the patient&#39;s mouth. The entire assembly is then used to make a master mold using standard procedures. 
     The master model and a master model of the opposing side of the jaw are placed in an articulator, the relative positions of the upper and lower jaw master models being established by a bite registration. The framework is then removed from the cured impression material mold and attached via fabricating screws to the master model in the articulator. Prosthetic material is then directly molded and sculpted onto the framework to form prosthetic teeth, leaving holes for access to the fabricating and permanent screws. 
     The final restoration system, comprising the impression framework of foundation elements, the permanent screws, and the prosthetic teeth, is detached from the master model and attached to the implants in the patient&#39;s mouth via the permanent pins inserted through the bore of each foundation element. The fit is be confirmed in the patient&#39;s mouth and the dentist can make any final adjustments to the prosthesis and if necessary by cutting at one or more specific locations on the prosthesis and reluting the prosthesis. After establishing a satisfactory fit, additional prosthetic material is then applied to the prosthesis to complete the prosthesis. Alternatively, removable dentures may be attached to the framework of the foundation elements via attachments such as ball and sockets and/or bar-to-clips. 
     In an alternative embodiment, the foundation elements are constructed of a material that can be used for lost wax casting. In this embodiment the foundation elements are joined together to form a framework on the implants in the patient&#39;s mouth as described above, and transferred during the impression process to a stone model. The framework is then removed by evaporation or melting to form a metallic framework. This metallic framework is then attached to the implants in the patient&#39;s mouth and used to support a prosthesis to form the final restoration. 
     In addition, the invention provides unshaped pontics that fit over the elongated foundation element to replace missing teeth. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B is a perspective view ( 1 A) and a cross section ( 1 B) of a foundation element according to an embodiment of the present invention. 
     FIGS. 2A,  2 B,  2 C and  2 D is a side view of a foundation element attached to an implant ( 2 A), shown in partial cross-section, inserted into implants, shown in partial cross-section and the three screws, fabrication, impression and final placement screw, inserted into implants shown in partial cross-section ( 2 A), and details of the impression screw ( 2 B), details of the screw heads ( 2 C) and a bottom view of the permanent screw ( 2 D). 
     FIG. 3 shows details of the final placement screw and internal seat in the foundation element shown in FIG.  1 . 
     FIGS. 4A and 4B is a side view of two adjoining foundation elements of FIG. 1 attached to two adjacent implants ( 4 A) in a patient&#39;s mouth and a top view of the two adjoining foundation elements ( 4 B). 
     FIG. 5 is a perspective view of a dental tray for making an impression of the dental process. 
     FIGS. 6A and 6B is perspective views of the framework of foundation elements embedded in an impression tray and attached to a stone master model via impression screws screwed into analogs embedded in the model ( 6 A) and  6 B is a perspective view of a framework of foundation elements attached to a master model via impression screws screwed into analogs embedded in the stone master model with the impression tray removed. 
     FIG. 7 is a perspective view of a final restoration consisting of a prosthesis supported on a framework of foundation elements attached to the implants. 
     FIG. 8 is a perspective view of the framework foundation elements serving as a foundation for a removable prosthesis in an alternative embodiment of the present invention. 
     FIG. 9 depicts the reverse threaded filler plug used to fill the access hole over the permanent screw. 
     FIG. 10 depicts a movable pontic (false tooth) form positioned on the wing of the foundation element. 
     FIG. 11 is views of alternative embodiments of pontics. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The structure and function of the preferred embodiments can best be understood by reference to the drawings. Where the same reference numerals appear in multiple figures, the numerals refer to the same or corresponding structure in those figures. 
     Referring generally to FIGS. 1-8, the system and method of the present invention comprises generally three stages. The first stage involves attaching foundation elements  10  to implants  26   a  and  26   b  embedded in the patient&#39;s mouth and connecting foundation elements  10  together to form a rigid framework as shown, for example, in dashed lines in FIG.  7 . As shown in FIG. 6A, impression material  56  is applied around the framework thereby embedding the framework in impression material  56 , forming a negative impression which includes elements  10  and material  56 . Thus, the rigid framework becomes a component of the negative impression of the location of implants  26  in the patient&#39;s mouth, from which accurate master model  64  may be made (FIG.  6 B). The second stage involves producing master model  64  and placing master model  64  and a corresponding master model of the opposite side of the jaw in an articulator, the relative positions of the master models being established by a bite registration or a bite block, using known procedures (not illustrated in the drawings). After removing impression material  56  from the rigid framework and placing the framework on master model  64  in the articulator, a prosthetic material is molded or sculpted as prosthetic teeth onto the rigid framework, where foundation elements  10  are made of the same or similar prosthetic material. Thus, the framework becomes the foundation supporting prosthetic teeth  68  of final restoration  70  (FIG.  7 ). The third and last stage involves attaching final restoration prosthesis  70  into the patient&#39;s mouth and filling any gaps and holes in the prosthesis with the same prosthetic material. Each of these three stages will be described in further detail below. 
     As shown in FIGS. 1A and B, foundation element  10  has base member  12  and elongated member  14  extending from base member  12 . Base member  12  may be cylindrical, rectangular or any other suitable shape. Base member  12  has top surface  19 , bottom surface  21  which flares upward to form seat  23  near bottom surface  21 , and defines bore  20 , generally perpendicular to elongated member  14 . Seat  23  supports the final prosthesis formed around the framework in the final restoration. Bore  20  near bottom surface  21  of base member  12  may be made to be of any shape to match or mate with implants  26  (FIG. 2A) manufactured by different manufacturers. 
     Elongated member  14  is attached to base member  12  at end  16  and also has top surface  15 , opposing surfaces  17  and free end  18 . Preferably, elongated element  14  has a generally trapezoidal cross-section with opposing surfaces  17  at a slight taper of at least approximately 2°. Although elongated element  14  may have other cross-sectional shapes, such as a cylindrical cross-section, a generally trapezoidal cross-section has the advantage of providing a flat top surface  15  for receiving prosthetic material for molding or sculpting prosthetic teeth onto foundation elements  10 . In addition, this shape ensures a good male-female fit with removable prosthetic teeth such as dentures, if dentures rather than fixed prosthetic teeth  68  are to be attached to foundation elements  10 . Foundation element  10  may be of unitary construction or of multiple elements. For example, base member  12  and elongated member  14  may be formed as a unitary element or as two separate components and bonded together, and therefore may be made of the same or different materials such as alumina or zirconium, or similar materials, which are used as a substructure coated with a material such as porcelain and/or fiber re-enforced composite resin. 
     As shown in FIG. 2A, there can be three different screws. The impression screw  24   a  is used to secure the impression cylinder  12  to the implant  26   a . The shape of this screw  24   a  permits it to be placed and pre-tightened with the thumb and forefinger of the user. The fabrication screw  24   b  (FIG. 2B) is used only during construction of the prosthesis and for confirming the fit intra-orally. The nature of this “working” screw allows it to seat passively on the smooth surface of the small diameter internal bore  20  of the cylinder  75   b , and to be placed and removed repeatedly. The permanent screw  24   c  has two surface variations on the underside of its head (FIG. 2D) which work in tandem as a sealer and to prevent counterclockwise rotation ( 75   b  and  76 ). The first surface  75   a  is a hollow area designed to house sealing material such as gold or gold with a binder and/or silicone. The second surface variation is the outer ring  75   b  which engages the raised metal counter rotation grooves  76  that are located in the seating surface  75   c ,  75   d  of the insert  73  (FIG.  1 B). This permanent screw  24   c  is used only once to retain the final prosthesis permanently in place. All three screw heads preferably have a screwdriver slot in the head with a centered square hole  74  to help retain the screw on the screwdriver and to reduce stripping. 
     Each of the screws, impression screw  24   a , fabrication screw  24   b  and final, permanent screw  24   c  and threaded plug  80 , all have a combination screw/slot top with a square driver placed in the middle and protruding beyond the screw slot  74  (FIGS. 2A,  2 B). Square drivers have the advantage of retaining the screw while the professional is working in the oral cavity of the patient. The screw slot favors the application of torque without stripping. 
     The first stage of the method of the invention involving the process of making an accurate impression of the dental process, where the system of the present invention is utilized as a component of the impression, will now be discussed as can be understood and appreciated by one of ordinary skill in the art. 
     As shown in FIGS. 1 through 3, to attach foundation element  10  to implant  26   a , impression screw  24   a  with threads  34   b  is inserted through bore  20  into insert  73  in base member  12  and screwed into implant  26   a . Preferably, impression screw  24   a  has a tapered or round head  32   b  (FIG. 2A) which provides additional distance from tapered heads of adjacent foundation elements already attached to adjacent implants (see FIG.  6 A). Head  32   b  of impression screw  24   a  may have a machined internal hexagon, square, circle with a screw slot, combination thereof, or other shape that permits removal with or without the use of a correspondingly shaped tool. Because implants  26   a ,  26   b  are rarely implanted perfectly parallel to each other in the bone tissue, due to various factors such as human placement of the implants and jaw and bone ridges, angulation of implants  26   a ,  26   b  may result in foundation elements  10   a ,  10   b  being angled with respect to each other. Thus, the additional distance provided by tapered heads  32   a ,  32   b  allows foundation element  10   b  to be placed closer to adjacent foundation element  10   a  without interference between adjacent tapered heads  32   a ,  32   b , even where implants  26   a ,  26   b  are at extreme angles toward each other. Furthermore, the additional space provided by tapered heads  32   a ,  32   b  also allows easier handling and attachment of foundation element  10   b  by a dentist or technician. 
     In a preferred embodiment, foundation element  10  may be made of a biocompatible prosthetic material compatible with the same or a similar prosthetic material used to form the prosthesis to be sculpted or molded directly onto the framework of foundation elements  10 . Suitable prosthetic material may be, for example, ceramic optimized polymers, polymer ceramics, polyglass/crystal polymers, or any other suitable material of similar qualities. Ceramic optimized polymers combine the advantages of ceramics (such as strength, durable aesthetic quality, abrasion resistance, and high stability) with the advantage of composites, such as ease of final adjustment, polishability, effective bond with luting composites, low degree of brittleness and susceptibility to fracturing, and ability to repair the restorations in the mouth. One example of ceramic optimized polymers is Targis, manufactured by Ivoclar Williams, composed of fine particle closely packed ceramic fillers embedded in a temperable organic polymer matrix. Targis has enamel-like translucency, fluorescence and hardness, has high flexural strength, and is biocompatible. 
     Fiber-reinforced composites may also be mixed with a ceramic optimized polymer to produce the material for foundation elements  10  and final teeth prosthesis  68 . An example of a fiber-reinforced composite is Vectris, a polymerized fiber/matrix, also manufactured by Ivoclar Williams, which is dentin-colored and translucent, has high strength and high stability, and is biocompatible. 
     Another material which may be used for foundation elements  10  and final teeth prosthesis  68  is crystal polymers. An example of crystal polymers is Sculpture, manufactured by Jeneric/Pentron, which combines polycarbonate dimethacrylate-containing resins with optically correct glass fillers. The crystal polymer has low water sorption for better color stability and is cured by using a combination of visible light and heat/vacuum. 
     The foregoing examples of materials which may be used as the material for foundation elements  10  and final teeth prosthesis  68  is merely illustrative and is not meant to be limiting. Any other suitable biocompatible material of similar qualities may be used. A suitable material is to be of high strength sufficient to withstand the stresses and strains which the final restoration system for implant-fixed prosthesis would be subjected to in actual operational environments. The material is also appropriately workable and has enamel-like translucency and hardness, high flexural strength and stability, low degree of brittleness and low water sorption. In addition, the material is cured by any combination of light, pressure, temperature and/or vacuum, biocompatible, and compatible with the interfacing implants and can be effectively bonded with luting composites. Furthermore, while foundation elements  10  and final teeth prosthesis  68  need not be made of the same prosthetic material, prosthetic material for foundation elements  10  must be compatible with prosthetic material used to construct final teeth prosthesis  68 . 
     The advantages of using such materials include that they transfer less stress and strain to the implants in the patient&#39;s mouth during use and are aesthetically more like natural teeth. In addition, such materials are easier to manipulate and adjust as described in the system and methods herein. 
     Referring now to FIG.  6 A and FIGS. 4-7 generally, a dentist would first attach foundation element  10   a  via impression screw  24   a  to implant  26   a  which is the implant located furthest back in the patient&#39;s mouth, and on the patient&#39;s right side if working on the lower jaw and on the patient&#39;s left side if working on the upper jaw. The dentist would then attach second foundation element  10   b  to implant  26   b  adjacent to implant  26   a  and continue along in a clockwise or counter-clockwise direction along the patient&#39;s gum line in the lower or upper jaw. 
     After attaching foundation elements  10   a ,  10   b , foundation element  10   a  is oriented such that elongated member  14   a  optimally contacts base member  12   b  of adjacent foundation element  10   b , on the side of base member  12   b  closer to the dentist, as shown by phantom lines in FIG.  7 . Because foundation elements  10  are made of a material which can be easily cut and shaped while in place in the patient, elongated member  14   a  is then cut to a length such that foundation element  10   a  can be further rotated so that new free end  18   a ′ of elongated member  14   a  optimally contacts base member  12   b  of adjacent foundation element  10   b  and that elongated member  14   a  extends over a portion of the gum line between implants  26   a ,  26   b.    
     Alternatively, as discussed above, because implants  26   a ,  26   b  are rarely implanted perfectly parallel to each other, angulation of implants  26   a ,  26   b  away from each other may result in elongated member  14   a  being of insufficient length to contact base member  12   b  of adjacent foundation element  10   b . Thus, because foundation element  10  is of a material which can be easily cut by a dentist or technician in a patient&#39;s mouth, the dentist or technician may sever elongated member  14   a  from base member  12   a  and reattach elongated member  14   a  via a compatible luting composite to base member  12   a  such that elongated member  14   a  is closer to seat  23   a  or such that elongated member  14   a  rests upon seat  23   a . Alternatively, elongated member  14   a  may be extended using additional material luted to elongated member  14   a  so that end  18   a  optimally contacts base member  12   b.    
     In addition, because adjacent implants  26   a ,  26   b  in a patient&#39;s mouth may be at different levels, due to various factors such as human placement of the implants and jaw and bone ridges, foundation elements  10   a ,  10   b  attached to implants  26   a  and  26   b  may also be at different levels. As a result, elongated member surface  15   a  would not be at substantially the same level as top surface  19   b  of foundation element  10   b . For example, as shown in FIGS. 6A and B, if the level of top surface  19   a  of a first foundation element extends beyond the level of the adjacent elongated member top surface  15   b , top surface  19   a  may be cut so as to create a slope extending from the level of elongated member  14   a  to the level of elongated member  14   b  and thereby creating a continuous surface comprising surfaces  15   a ,  19   a ,  15   b  and  19   b . This process may be repeated for all or some foundation elements  10  attached to implants  26 . 
     As shown in FIG. 4B, once elongated member  14   a  is cut and rotated so as to optimally contact base member  12   b  of adjacent foundation element  10   b , elongated member  14   a  is attached to base member  12   b  by applying a suitable bonding material such as bonding resin  40  at the interface between elongated member  14   a  and base member  12   b . Bonding resin  40  is selected to be compatible with the material of foundation elements  10  and is preferably a light cured luting composite or bonding resin. After foundation elements  10  have been attached to all implants  26  and bonding resin  40  at all interfaces between base member  12  and elongated member  14  has cured, a single rigid framework is thereby created. Note that elongated member  14  of foundation element  10  attached to the last implant  26  which is the furthest left or the right implant in the patient&#39;s mouth, may be cut to a desired length sufficient to support the desired number and size of prosthetic teeth  68  to be attached thereon. 
     Referring now to FIG. 6A for making negative impression  58 , dental tray  50 , as shown in FIG. 5 with curved trough  52  and access holes  54  corresponding to locations of implants  26  through which heads  32  of connecting pins  24  extend, is provided. Curved trough  52  is filled with impression material  56 . Impression material  56  is also applied areas immediately adjacent to the framework. Dental tray  50  is then pressed against the framework with heads  32  of connecting pins  24  extending through access holes  54 . 
     Impression material  56  is preferably a material that is soft and pliable, such as alginate or other materials of similar qualities. Soft, rather than hard impression material  56  may be used, because the system of the present invention provides a rigid framework around which impression material  56  is applied and thus there is less concern for deformation or distortion of impression material  56 . Because soft impression material  56  easily “gives”, it is also preferred for taking impressions with the system of the present invention as it produces minimum compression in the gums. Thus, deformation and distortion in impression  58  is minimized or avoided and a more accurate impression  58  of the location of the implants in the patient&#39;s mouth is thereby produced. 
     After impression material  56  has cured, impression screws  24  are unscrewed from implants  26  and analogs  28 . Impression screws  24  and impression  58 , comprising dental tray  50 , cured impression material  56  and the rigid framework embedded in impression material  56 , are then removed from the patient&#39;s mouth. 
     Because the rigid framework of foundation elements  10  is embedded in cured impression material  56 , the framework preserves impression  58  and thereby minimizes or prevents distortion of impression material  56  as it cures. The molded impression  58  containing the framework is thus sturdy and reliable and may be used as a negative in the construction of master model  64 . The relative locations and orientations of foundation elements  10  accurately match those of implants  26 . Thus, misalignment of the final restoration prosthesis on implants  26  in the patient is minimized or avoided. 
     The second stage involving molding or sculpting prosthetic teeth  68  onto the rigid framework of foundation elements  10 , while the framework is attached to master model  64  placed in an articulator (FIG.  6 B), will now be discussed in detail. 
     As shown in FIG. 6B, each foundation element  10  is attached to the analog  28 , via impression screw  24 . Analogs  28  may be those manufactured by manufactures such as Nobel BioCare, ITI or BIOMET or other companies. Master positive model  64  is then made from the impression by embedding analogs  28  into a modeling material such as gypsum. Because impression material  56  completely surrounds the framework of foundation elements  10  thereby providing a rigid and stable negative impression  56 , as the gypsum of master model  64  sets, there is no distortion or loss of accuracy of the locations and orientations of analogs  28  in master model  64  which reflect the locations and orientations of implants  26  embedded in the patient&#39;s mouth. Thus, a more accurate master model  64  can thereby be produced. 
     After gypsum  62  has set, impression  58  is removed from master model  64  by unscrewing impression screws  24  from analogs  28 . Master model  64  and a master model of the opposite side of the jaw are then placed in an articulator and a bite block or bite registration is used to determine the correct spatial relationship between the two master models (not shown). Impression material  56  is removed from the rigid framework and the framework is placed in the articulator and secured to analogs  28  embedded in master model  64  via fabrication screws  24   b . Fabrication screws  24   b  may provide multiple top interfaces, for example, hexagonal interface and slot-type interface, for compatibility with different tools which may used in screwing fabrication screws  24   b.    
     The framework is prepared for receiving the prosthesis. For example, the surface of the framework is abraded and shaped for accommodating the fixed prosthesis or removable dentures and to form a stable bond therewith. 
     Prosthetic teeth  68  are then molded or sculpted directly onto the rigid framework such that seat  23  of the foundation element  10  provides support for prosthetic teeth  68 . During this stage, prosthetic teeth  68  provides holes for access to fabrication screws  24   b  such that fabrication screws  24   b  can be unscrewed from analogs  28  of master model  64  and removed from master model  64  and such that fabrication screws  24   b  can be screwed into implants  26   a  and  26   b  and/or analogs  28  in the model. Thus, the framework of framework elements  10  is the foundation for and a component of the final restoration  70 . 
     The material for prosthetic teeth  68  is the same or compatible with the material used for foundation elements  10 . Compatible as used herein means that the materials, in addition to being biocompatible and of sufficient strength and flexibility to withstand stress when located in the final restoration in the patient, cooperate to form a stable bond between the framework and the prosthesis. 
     The third and final stage involving attaching final prosthesis  70  into the patient&#39;s mouth and filling the access holes in prosthetic teeth  68  will now be discussed. As shown in FIG. 7, permanent screw  24   c , is inserted through each access hole provided in prosthetic teeth  68  and through bore  20  of each foundation element  10  and screwed into threaded aperture  30  of implant  26  and analog  28 . The fit of prosthesis  70  on implants  26  is tested in the patient&#39;s mouth. If adjustments need to be made, because foundation elements  10  and teeth  68  are made of a prosthetic material which can be easily cut, the dentist can easily make any necessary final adjustments by cutting and reluting prosthesis  70 . 
     After the fit of prosthesis  70  on implants  26  has been confirmed, a material compatible with the material used for foundation elements  10  and prosthetic teeth  68  is then applied to and thereby sealing any space in bore  20  not occupied by permanent screw  24   c  and access holes provided in prosthetic teeth  68 . The material is then light cured and the final restoration consisting of implant supported prosthesis  70  and implants  26  is complete. 
     Alternatively, as shown in FIG. 8, removable dentures  90 , rather than fixed prosthetic teeth  68 , may be provided for removable attachment to the rigid framework of foundation elements  10  by addition and/or subtraction of material; such as wax that is subsequently cast into metal (lost wax method) over and around the metal sleeve  21  of the foundation elements. A portion of elongated member  14  may be removed from surface  15  and denture interface  72  may be bonded in place of the removed portion with a bonding resin, such as a luting composite, compatible with foundation elements  10 . The interface  72  to secure the dentures on the framework, may be, for example, a ball and joint  72   a  or of a cylindrical configuration  72   b , which is received in a mating recess in the denture, and is generally of a metallic material bonded to the foundation element  10 . Prosthetic dentures are typically made of a material, such as acrylic, compatible with the prosthesis material, or composite resins and/or ceramics. These materials can be used to attach the removable dentures to the foundation framework using connecting means such as ball and sockets and/or bar-to-clips. 
     In an alternative embodiment, the foundation elements  10  can be made of a suitable material such as a plastic material, for example Duralay, which can be evaporated without producing contaminants. In this embodiment, referring to FIGS. 1-8, the framework is constructed of plastic foundation elements  10  on implants  26  which are joined and adjusted for optimal fit on the implants as described above. An impression is then taken as described above, and the impression containing the plastic framework is removed from the patient&#39;s mouth. A master stone model is then formed from the impression and having the plastic framework attached, using procedures as described above. Articulation and jaw relationships are also established as described above. A procedure such as lost wax casting is performed, in which the plastic framework is eliminated and replaced with a suitable metal such as gold or metal alloy. The framework can be further modified to have the ideal shape. 
     Referring to FIGS. 7 and 8, after the framework of foundation elements has been removed from the impression it can be further modified to have an ideal shape ( 21 ) to support the addition of tooth colored materials. The modification is accomplished, for example, by reducing foundation elements to create a more natural tooth shape, using a burr or other instrument. In addition, wax or other material may be used to prepare the final shape. 
     A method for quickly providing material for missing teeth in the prosthetic involves the use of tooth shapes or “pontics” as shown in FIGS. 7,  10  and  11 . The pontic  85  can be made in the shape of a tooth as part of a bridge. In order to fill spaces of missing teeth in an implanted supported bridge (FIG. 7) an inverted U-shaped pontic unit  86  may be used that fits over the elongated wing extension  14  (FIG. 10) of the foundation element  10  of the invention. There is an opening  87  to permit ideal placement of the pontic unit  86  for appearance and function for the individual patient. The opening  87  is filled between the pontic unit  86  and the wing extension  14  to attach to the foundation element  10 . Additional filling material  88  can be used to on the pontic unit  86  to provide additional support for the final tooth colored materials  91  (FIG.  11 ). Holes  89  may also be made in the pontic unit  86  (FIG. 11) to permit the final tooth colored materials  91  to bond to the pontic unit  86 . Another advantage is that there is less expansion and contraction between two similar materials. 
     The present invention has been described in terms of preferred embodiments. The invention, however, is not limited to the embodiments depicted and described. For example, other materials may be used to form the foundation elements, provided the materials have properties as described herein for supporting the prosthesis and forming the final restoration. Rather, the scope of the invention is defined by the appended claims.