Abstract:
A transfer element for transferring the position of an implanted dental implant body to a master model including at least one element that can be fixed in an impression material for transferring the axial or rotational position of the implant to a dental impression. The invention aims at enhancing the transfer element to enable easy impression making and high precision during transfer of the vertical position of the implant in addition to ensuring anti-rotational blocking. The transfer element includes a core ( 2 ) that may be connected to the implant body, and a guide sleeve ( 4 ), and the core ( 2 ) and the guide sleeve ( 4 ) are provided with mutually engaging, corresponding positioning elements ( 22, 23; 24, 25 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a dental transfer element. 
     EP-A-0 727 193 discloses such a transfer element the guide sleeve of which can be connected by means of a core to the implant body previously implanted in the jaw bone. In the area of its coronal end, the implant body has a recess with guide faces aligned axially in parallel in the manner of a hexagon for anti-rotational blocking of a construct that can be connected to the implant body to which a superstructure, a crown or the like, can be fixed. When implant-supported superstructures, crown constructs or the like are created using a master model, a precise transfer of the axial as well as the circular implant position is very important. Corresponding to the hexagonal guide faces, the core is therefore also provided with hexagonally arranged positioning elements formed as outer surfaces aligned in parallel at the end of the core, which engage with the implant body. In other respects the core is essentially arranged within the guide sleeve, which in its area facing the coronal end of the implant body has further positioning elements corresponding to the positioning elements of the core. These further positioning elements are formed as interior hexagonal surfaces. Production of the further positioning elements of the guide sleeve formed as interior surfaces is quite costly. Very close tolerances must be met to permit the transfer of the angular position of rotation of the implant body to a master model by means of the guide sleeve and the impression material. Even slight differences or gaps between the hexagonal interior surface of the guide sleeve and the hexagonal outer surface of the core, which would normally be within tolerance, lead to a significant deviation in the rotational position of the guide sleeve. Despite high-precision production of the interior hexagonal surfaces of the positioning elements of the guide sleeve, transfer errors of the angular position of rotation are difficult to avoid in practice. 
     WO-A 93/20774 discloses such a transfer element whose core also has positioning elements in the form of hexagonal surfaces, which engage with a hexagon of the implant body. The core, which is capable of axial displacement within the guide sleeve, comprises an axially parallel flattened area, which fits against an axially parallel flattened interior surface of the guide sleeve. In other respects the outer surfaces of the core and the interior surfaces of the guide sleeve fitting against them are cylindrical. In this embodiment, too, the production of said flattened interior surfaces of the guide sleeve is quite costly and even slight deviations due to manufacturing tolerances cause a considerable angle error in the transfer of the angular position. 
     U.S. Pat. No. 4,758,161 discloses an insert element, which may be connected with the implant body. The insert element comprises a shaft, which may be inserted into an axial recess of the implant body and anchored therein, particularly with dental cement. The insert element further comprises a head for fastening a crown or superstructure. Said head has radial grooves, a constriction and a flattened area for defined localization of the crown or superstructure. 
     SUMMARY OF THE INVENTION 
     Based thereon, it is the object of the invention to ensure a simple impression procedure while nevertheless obtaining great precision in the transfer of the angular position. The handling in the dental practice and in the laboratory is also to be improved. 
     This object is attained by the invention as described and claimed hereinafter. 
     The transfer element according to the invention is distinguished by its functional construction, serves as a repositioning aid, and ensures with great precision the molding and transfer of the implant position in axial, radial and circumferential direction. The transfer element has two parts comprising on the one hand a core and on the other hand a guide sleeve with mutually corresponding positioning elements for a reciprocal positive-locking, defined fixation in circumferential as well as axial direction. The core is hollow on the inside so that a retaining screw can be guided through it, and it can be axially inserted into the sleeve. The positioning elements, which are advantageously formed as a radial projection and a radial recess, respectively, readily assure an exact mutual alignment. The core has a simple contour and/or geometry and is not costly to produce. The core is partly cylindrical and may be pushed into the sleeve. To take the impression, particularly with an open scoop, the core and the sleeve can be fixed to the implant body implanted into the jaw by means of the retaining screw. When the impression is taken with the open scoop, which is perforated in the implant region, the head of a correspondingly long retaining screw is guided through the perforation. After the scoop is removed, the transfer element remains in the impression and does not need to be repositioned. The core at its one end is advantageously provided with the positioning element and at its diametrically opposite end with the anti-rotational blocking element, particularly in the form of a hexagon, which may be engaged with a corresponding anti-rotational blocking element in the implant body. 
     The transfer of the circular and axial implant position to the master model by means of the transfer element is thus ensured, and a significantly improved overall accuracy of fit of the superstructure is achieved. The sleeve according to the invention extends up to the gum region and the axial end face fits directly against the axial front face of the implant body, with the end face and front face having substantially the same outside diameter. The axial length of the guide sleeve is at least 50%, particularly at least 65% of the axial core length. On its outer surface the sleeve has at least one constriction, recess, retention element or the like to ensure exact positioning in the impression material. The retention elements to secure the rotational position and/or the axial position in the impression material can advantageously be in the form of flattened areas arranged on the outer surface and produced particularly by milling, or in the form of longitudinal grooves or blind holes or the like. The constriction or recess is advantageously provided approximately in the center of the axial longitudinal extension of the sleeve. The part facing away from the implant body has a substantially cylindrical or approximately conical outer contour, the tip of which is also located on the side facing away from the implant body. The part of the sleeve facing toward the implant body has an outer contour corresponding to the dental construct element in the passage area of the gums and/or the corresponding gum former. 
     Further developments and specific embodiments of the invention are set forth in the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in greater detail, by way of example, with reference to, but not limited to, specific embodiments shown in the drawing in which 
     FIG. 1 is a side elevation of the transfer element in an exploded view, 
     FIG. 2 shows the transfer element in its assembled state of the guide sleeve and core, 
     FIG. 3 is an axial longitudinal section through a further embodiment including the implant body and the retaining screw, 
     FIG. 4 is a view of the further embodiment according to FIG. 3 in a position rotated by 90° in relation to the longitudinal axis, 
     FIG. 5 shows the embodiment according to FIG. 3, with the retaining screw and the core partly detached, 
     FIG. 6 is a perspective view in accordance with FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The exploded view depicted in FIG. 1 shows the core  2 , which comprises an axial through-bore  20  for a retaining screw, as well as the guide sleeve or sleeve  4  with an end-to-end central opening  6 . The outside diameter of core  2  is at maximum equal to the diameter of the opening  6  of the sleeve  4 , so that the core  2  can be pushed into the sleeve in the direction of the longitudinal axis  8 , or the sleeve  4  can be pushed over the core  2 , with substantially no radial play. Preferably, the outside diameter of the outer surface of the core  2  and the inside diameter of the inner surface of the sleeve  4  match in such a way that the core can be inserted into sleeve  4  with a sliding fit and then removed therefrom again. In the outer surface  9  of sleeve  4  there is a radial constriction  10  permitting a defined and secure fixation in the impression material. In addition, or as an alternative to the radial constriction  10 , sleeve  4 , within the scope of the invention, may also have other retention elements, openings or the like for positioning and fixation in the impression material . Preferably, anti-rotational blocking means or retention elements are provided in the area of the outer surface of the sleeve  4 , particularly at least one flattened area  11 , a longitudinal groove or the like, to ensure a rotationally stable anchoring with in the impression material. The retention elements according to the invention, which form a radially inward pointing indentation or recess in relation to the otherwise substantially rotationally symmetrical outer surface of sleeve  4 , ensure axial and radial fixation of the position of the sleeve in the impression material. Thus, they assure a precise transfer of the anti-rotational blocking as well as the axial position from the implant body to the sleeve and the impression material and, ultimately, for the construct, the superstructure or the like. 
     Core  2  has a length  12 , which is greater than length  14  of sleeve  4 . Length  14  is advantageously at least half as long as length  12  of the core  2 . A specified length  14  of the sleeve  4  of at least 70% of the core length  12  has proven advantageous. At its end facing toward the implant body (not shown) core  2  has an element  16  for anti-rotational blocking or for the transfer of the circular implant position. The anti-rotational blocking element  16  in this case takes the form of a hexagon and may be inserted into a correspondingly shaped recess in the implant body. In the assembled state, the end of core  2  with its blocking element  16  protrudes from sleeve  4 . 
     Instead of element  16  or the hexagon provided on the outer surface  2 , other elements may be provided for anti-rotational blocking within the scope of the invention, for example in the area of the front face  18  or in the vicinity thereof in the axially continuous inner surface  19  of the core. It should be noted that, on the inside, core  2  has an axial through-bore  20  permitting the passage of a retaining screw by means of which core  2  and the combined sleeve  4  can be connected for removal with the implant body, which is implanted into the jaw bone. The axial end face  21  of the sleeve  4  fits directly against the opposite front face of the implant body to ensure defined axial alignment. 
     The core  2  has at least one first positioning element  22 , which is associated with a second positioning element  24  of the sleeve  4 . The positioning elements are provided in the area of the ends of the core  2  or sleeve  4  facing away from the implant body. As may be seen, the core  2  has preferably two such positioning elements  22 ,  23  which are diametrically opposite in radial direction. Correspondingly, the sleeve  4  also has two diametrically opposite positioning elements  24 ,  25 . The first positioning element or elements  22 ,  23  of core  2  are advantageously formed as radial projections of core  2 , while the second positioning elements  24  are formed as preferably continuous slots in radially outward direction into which the positioning elements  22 ,  23  or projections of the core  2  can be inserted for a precise fit. The positioning elements  22 ,  23  advantageously have axially parallel lateral faces  26  and the second positioning elements  24 ,  25  of the sleeve  4  have associated lateral faces  28 . Preferably, the lateral faces  26  or  28  of core  2  or sleeve  4 , respectively, have a snug fit to ensure a defined transfer of the circular implant position. To permit insertion of the first positioning element  22 ,  23  of core  2 , the second positioning element  24 ,  25  is open toward the end face  30  or the sleeve end. In addition, core  2  and sleeve  4  have mutually associated and corresponding axial support faces  32 ,  34 , so that a defined transfer of the axial position is also ensured. 
     It is understood that other alignment or fixation means in axial and radial direction of core  2  and sleeve  4  may be specified within the scope of the invention. For example, the first positioning element of core  2  may be constructed as a radial slot for corresponding engagement with a radially inward directed projection of sleeve  4  as the second positioning element. Furthermore, other retention elements, such as gear teeth or gear-like positioning elements, which establish a positive locking connection or positioning of core and sleeve, may be provided. 
     The previously mentioned radial constriction  10  of sleeve  4  is approximately in the center of the longitudinal extension. The area of sleeve  4  adjacent to constriction  10  and facing away from the implant body preferably has an approximately conical outer contour  36 , with the tip of the cone also pointing away from the implant body. The outer surfaces  38  of the radial projections  22 ,  23  are preferably adapted to the outer contour  36  of sleeve  4 . Toward the implant side, sleeve  4  has an initially approximately cylindrical outer contour  40 , which adjoins the axial end face  21  via a rounded transition area  42  with a predefined radius. 
     FIG. 2 shows the transfer element with core  2  and sleeve  4  in its assembled state. The end region of core  2  together with element  16  for anti-rotational blocking projecting beyond the axial end face  21  is clearly visible. The outer surface  38  of the positioning element  22  corresponds to the outer contour  36  of sleeve  4 . It can also be readily seen that the two mutually corresponding positioning elements  22 ,  25 , namely the projection and the recess, fit precisely against one another to preclude relative motion in circumferential or axial direction. 
     FIG. 3 is an axial longitudinal section depicting a further embodiment of the two-part transfer element with core  2  and sleeve  4 , including implant body  44  and retaining screw  46 . For anti-rotational blocking of a construct or superstructure, the implant body  44 , in the area of its coronal end, has preferably internal securing means  48 , preferably designed as a hexagon, with which the antirotational blocking element  16  of core  2  engages. At its apical end the retaining screw  46  contains a thread  50 , which is screwed into a corresponding female thread of the implant body  44 . At its coronal end, the implant body  44  has an outside diameter  52  corresponding to the outside diameter of the adjacent axial end face  21  of sleeve  4 . The two positioning elements  22 ,  23  of the core  2  enter the corresponding elements or recesses  24 ,  25  of the sleeve  4 . Sleeve  4  extends up to the support shoulder  54  of the retaining screw  46 , which fixes it in relation to the implant body  44 . 
     According to the invention, the retaining screw  46  comprises a first drive element  56 , which is formed, in particular, as a male thread. The axial through-bore  20  of the core  2  comprises a corresponding second drive element  58 , which is advantageously formed as a female thread matching the male thread  56  of the retaining screw  46 . In the depicted locking position of core  2  and guide sleeve  4  in relation to the implant body  44  to take the impression, the first drive element  56  is advantageously closer to the implant body  44  than the second drive element  58 . Advantageously no engagement between the two drive elements  56  and  58  is provided. As will be explained below, after the impression has been taken, as the retaining screw  46  is unscrewed, the core  2  is also readily released in axial direction from the implant body  44  due to the two drive elements  56 ,  58 . 
     FIG. 4 is a side elevation of the transfer element with core  2  and guide sleeve  4  as well as implant body  44  and retaining screw  46  as viewed in direction B according to FIG.  3 . Sleeve  4  has two lateral diametrically opposite flattened areas  11 , which can be produced very simply, particularly by milling an otherwise substantially cylindrical part, the outer contour of which is indicated by broken lines  60 . Sleeve  4  further comprises retention elements  62  into which the impression material penetrates as the impression is being taken, and which thus serve for both rotational and axial blocking of sleeve  4  in the impression material and thus for the transfer of the circular and axial position of the implant body  44 . 
     FIG. 5 is an axial longitudinal section in the same plane as FIG. 3, with the retaining screw  46  now being partly unscrewed from the implant body  44  in the direction of arrow  64 . As may be seen, the first drive element  56  of the retaining screw  46  and the second drive element  58  of the core  2  are engaged in such a way that when the retaining screw  46  is unscrewed, the core  2  is also already partly released from sleeve  4 . This substantially facilitates handling after taking the impression, especially since core  2  can also be readily detached in the direction of longitudinal axis  8  or arrow  64  either simultaneously with or after the complete unscrewing of retaining screw  46 . It should be noted that the first positioning elements  22 ,  23  of the core  2  and the associated positioning elements  24 ,  25  of the sleeve  4  are matched to one another in such a way that on the one hand anti-rotational blocking is ensured while on the other hand axial release is readily possible based on the aforementioned associated axially parallel lateral faces of core  2  and sleeve  4 . The retention elements  62  of guide sleeve  4  are also clearly visible. 
     FIG. 6 is a perspective view of the core  2 , which has been partly detached by means of the retaining screw  46 , corresponding to FIG.  5 . The section plane in accordance with FIG. 5 is indicated by the broken line  66 . The retention elements  62 , which are provided in the lateral flattened area  11  of the sleeve  4 , are clearly visible.