The invention relates to impression coping for taking an open tray impression for making dental prosthesis. The essentially axially symmetric impression coping comprises a counterpart and a central screw guided through the counterpart for fixing the counterpart to the implant, the counterpart is provided with a positioning end unrotatably fitting into a positioning sleeve formed on the inner surface of the implant and the central screw comprises a head part, a shank and an end part. The end part of the central screw and the implant are connected to each other in releasable manner. That is, length of the central screw is selected so that its end portion at least partially overhangs the counterpart.

Taking impressions of steep conical and other implants imply several deficiencies. The geometry of the matching portion of the conventional impression copings does not make removal of the impression copings from the implants possible in a joint, tensionless manner. The implants in the mouth are always positioned in a different angle relative to each other. The conventional impression copings often cause self- closing during applying wax. In this case when the connected impression copings are removed from the implant they may move relative to each other. That is, when the impression copings are forced out from the wax by the hand they may be displaced by hundredths or even tenths of a millimetre in the wax which results in inaccurate fitting. In this manner the life span of the ceramic bridges decreases, they may break because of the internal stress. Due to the inaccurate fitting the implants may be exposed to stress too. In practice, this causes the so called see-saw movement of the bridges in spite of the fact that it was not perceptible during taking the sample (the sample carries the inaccuracy of the impression).

In case of flat implants and implants having a cone larger than 90° the length of the geometry (square, hexagon, special geometries, etc.) formed on the matching portion of the conventional impression copings in order to prevent them from turning may cause self-closure. In case of steep conical implants when the divergence between the axes of the implants is larger than the angle of the steep cone in the implant and also when the geometry for prevention of turning is too long self-closure may occur. (Thus, in case of implants having e.g. a cone of 12° if the divergence between the axes of two (or more) implants is more than 12° then self-closure takes place and the impression copings can be removed from the implants only if force is applied.) Generally, the known solutions only relate to the implants. The impression copings are formed in a conventional manner that is, they consist of a screw and a counterpart.

Patent application US 6283753 describes dental implant abutment systems, related devices and implantology processes and techniques. The abutment systems include a base that is adapted to mount in no-rotating fashion on any desired dental implant, root form or blade, from any supplier, together with a fixation screw which secures the base to the implant. A core to which an abutment is cast in customized shape and form is attached to the base in threaded fashion and secured with a non- rotational mechanism. The core and abutment may be formed using CAM processes. Such abutment systems unlike conventional systems do not require a central access bore in the core or abutment components and they occupy significantly less volume than conventional abutments.

This solution describes techniques for fixing prosthesis, generally a single tooth. In case of dental superstructures the superstructure is also attached to the base. This document does not deal with a sample taking method and does not describe an impression coping design.

Patent application US 6227856 describes an abutment and coping system for use with dental implants. The dental abutment forms an abutment post having a transmucosal base portion and a supra-gingival portion having a smaller transverse external cross-section than the proximal end of the base portion. The supra-gingival portion forms a through bore threaded at its proximal end and stepped to form an internal shoulder for seating the head of a screw for attaching the abutment post to the implant. The exterior surface of the abutment post forms a generally polygonal transverse cross-section for receiving hollow components having interior surfaces that can be telescoped over the abutment post. The abutment post is used in an abutment system that includes a healing cap, an impression coping and/or a prosthesis coping forming an interior surface that can be telescoped over the supra- gingival portion of the abutment post. The opposed surfaces of the abutment post and the coping have truncated corners that are very close to each other to maintain a coaxial relationship between the post and the coping, while the portions of the opposed surfaces adjacent to the truncated corners are spaced farther apart to permit limited angular movement of the post and coping relative to each other and to permit the entry of dental cement between the opposed surfaces.

This solution deals with external, protruding polygonal implants and uses gingiva shaper. This solution is used for a single artificial tooth in which case a possible angle divergence is of no importance. It does not give a solution for the case when impression must be taken of two angularly differently positioned implants.

Patent application US 6290499 describes a set of impression components that may be used for either open tray or closed tray impression moulding techniques. The components are used with an impression material to fabricate a model at a site in a jawbone where an implant has been osseointegrated. The solution of this document can be used for making a single prosthetic tooth and it is different from the solution of the present invention as it does not eliminate the disadvantages described here.

Patent application US 6332777 describes a device for forming a dental prosthesis. The device includes a support and an element which can be attached thereto, such as an impression element. The support has an anchoring part for anchoring in a bone or a master model, a shoulder with an annular shoulder face, and a head. The impression element has an elastically deformable fixing agent. When the device is assembled, the fixing agent jams and/or latches with the support, either externally on the support on the side of the shoulder facing the anchoring part, or in an axial hole of the support. The element can be quickly detachably connected to the support by placing it on top of the support, and can be quickly separated from the support by moving the support away. When the device is assembled, the support and the element can lay on top of each other with annular surfaces. The annular surfaces have fully circular outer edges which are visible from the outside in an approximately radial viewing direction.

This solution describes an elastic implant, but it is not clear from the document how displacement of the master pieces can be eliminated in case of two differently angled implants.

To sum it up, none of the known solutions ensures that during removal of the counter parts of the sample taking device the correct positions are kept. None of the known solutions not even their combinations can provide the solution of the present invention. The aim of the present invention is to eliminate the disadvantages of the known impression taking devices.

It has been realised that if the counterparts are separated from the impression taking device before the wax pattern is removed after taking the sample, the disadvantages of the known impression taking procedures can be eliminated.

Accordingly, the present invention is an impression coping for taking open tray impression for making dental prosthesis. The essentially axially symmetric impression coping comprises a counterpart provided with a positioning end unrotatably fitting into a positioning sleeve formed on the inner surface of the implant and a central screw which is guided through the counterpart for fixing the counterpart to the implant, the central screw comprises a head part, a shank and an end portion. The end portion of the central screw can be connected to the implant in a releasable manner. That is, the length of the central screw is selected so that its end portion at least partially overhangs the counterpart. The shank of the central screw is guided through a tubular screw and the counterpart. The tubular screw comprises an internal screw and an external screw which is shorter than the internal screw. The internal screw and the external screw are fixed to each other in unreleasable manner. The tubular screw and the counterpart are arranged on the central screw. They can be moved along and rotated around the axis of the central screw. The inner surface of the counterpart has an internal positioning surface and a threaded seat. On the tubular screw an axially movable and rotatable moving element comprising an upper moving element and a lower moving element is arranged. The external screw is guided through the upper moving element and its end distant from the implant is provided with a flange. On the other end of the external screw that is on its end adjacent to the implant an arrester provided with threads is formed. On the inner surface of the upper moving element internal threads mating with threaded arrester of the external screw are provided. The lower moving element is positioned on the internal screw in such a manner that a slider is installed between them. The slider is axially movable between the internal screw and the lower moving element. The internal positioning surface is also provided on the inner surface of the lower moving element, while on the outer superficies of the slider an external positioning surface matching the internal positioning surface is formed. The lower moving element and the slider are fitted into each other unrotatably relative to each other. The end of the internal screw adjacent to the implant is connected to the threaded seat of the counterpart in releasable manner. The upper moving element and the lower moving element are secured to each other in unreleasable manner.

Preferred embodiments of the impression coping according to the present invention will be defined by the appended claims and the following description.

Detailed description of the impression coping of the invention will be given with reference to the accompanying drawings in which:

Figure 1 a is the side view of the assembled impression coping;

Figure 1 b shows the cross-section of the impression coping of Figure 1 a taken along line A-A;

Figure 2a is the side view of the separated component parts of the impression coping;

Figure 2b is the sectional view of Figure 2a taken along line A-A;

Figure 3 shows the process of assembling the tubular screw, the upper moving element and the slider of the impression coping as viewed from the side;

Figure 4a is the side view of the tubular screw, the upper moving element and the slider of the impression coping when they are assembled;

Figure 4b is the sectional view of Figure 4a taken along line A-A;

Figure 5 shows the process of assembling the lower moving element and the elements of the impression coping shown in Figure 4a as viewed from the side;

Figure 6 shows the possible travel path of the slider within the lower moving element;

Figure 7 is a partial cross-section showing the process of installing the central screw into the assembled elements of Figure 5 as viewed from the side;

Figure 8a is the side view of the assembled impression coping without the central screw;

Figure 8b is the cross-section of Figure 8a taken along line A-A;

Figure 9a is the side view of the disassembled impression coping; and

Figure 9b is the cross-section of the disassembled impression coping of Figure 9a as viewed from the side.

The impression coping 1 according to the invention is suitable for taking open tray impressions for making dental prosthesis (Figures 1 a and 1 b). The impression coping 1 comprises essentially axially symmetric component parts. On the inner surface of the implant 2 a positioning sleeve 20 is formed in a known manner into which the counterpart 4 is fitted unrotatably by means of its positioning end 3. A central screw 8 is guided through counterpart 4 in order to fix counterpart 4 to implant 2. Central screw 8 comprises a head part 5, a shank 6 and a threaded end part 7. The end part 7 of the central screw 8 is fixed into a threaded sleeve in implant 2 while the positioning end 3 of the counterpart 4 is fitted into positioning sleeve 20 of implant 2. The length of the central screw 8 is selected so that its threaded end part 7 at least partially overhangs counterpart 4 in this manner it can be introduced into threaded sleeve of implant 2. In order to realize the aim of the present invention in the preferred embodiment of the invention further component parts are installed on central screw 8.

Namely, between the head part 5 and counterpart 4 a tubular screw 1 1 is placed on the shank 6 of central screw 8. Tubular screw 1 1 consists of an internal screw 9 and an external screw 10, the external screw 10 is shorter than internal screw 9 and they are fixed to each other in unreleasable manner (Figures 2a, 2b and 3). On the inner surface of counterpart 4 internal positioning surface 12 and threaded seat 13 are formed. On the rim of the counterpart 4 distant from implant 2, arched flange 25 is provided for making disconnection of impression copy 1 easier at counterpart 4 after the pattern is taken. Internal screw 9 and external screw 10 can be fitted into each other. Prior to fitting them together the external screw 10 is guided through an upper moving element 14. The outer superficies 21 of the upper moving element 14 is ribbed and/or cornered so that it cannot get blocked in the wax used for making the pattern and it cannot turn aside. A flange 24 formed on external screw 10 prevents the upper moving element 14 from slipping off the external screw 10. At the end of external screw 10 adjacent to implant 2 a threaded arrester is formed and on the inner surface of the upper moving element 14 internal threads 22 mating with threaded arrester 17 of the external screw 10 are provided. The internal screw 9 is guided through slider 18 (Figure 3). Sliding off the slider 18 is prevented by means of threaded portion formed at the end of the internal screw 9 adjacent to the implant 2. This threaded portion is formed so that it mates with threaded seat 13 of the counterpart 4 (Figure 4a). Thereafter the internal screw 9 is placed into external screw 10 in such a manner that their ends distant from counterpart 4 are set level with each other and they are fixed together through welding 23 (Figure 4b). In this manner internal screw 9 and external screw 10 form a tubular screw 1 1 . Thereafter the lower moving element 15 is pulled onto internal screw 9 and slider 18 (Figure 5) in such a manner that the internal positioning surface 12 formed in the lower moving element 15 mates with the external positioning surface 19 formed on the superficies of slider 18 and slider 18 at least partially slides into lower moving element 15 (Figure 6). Namely, the lower moving element 15 and slider 18 are placed into each other unrotatably relative to each other. Then the upper moving element 14 and the lower moving element 15 are fixed together through welding 23. In this manner moving element 16 is formed (Figures 7, 8a, 8b, 9a and 9b).

Tubular screw 1 1 and counterpart 4 are movable along the axis of central screw 8 and rotatable around the axis of central screw 8. The moving element 16 comprising upper moving element 14 and lower moving element 15 is axially movable on tubular screw 1 1 and rotatable around the axis of tubular screw 1 1 .

The positioning end 3 of the counterpart 4 can be shaped to have any form which fits to positioning sleeve 20 of implant 2.

The counterpart 4 and the internal positioning surface 12 of the lower moving element 15 can be a socket head sleeve e.g. a hexagon socket, a star-shaped socket. The external positioning surface 19 of slider 18 is formed as a stud formed as a hexagon screwdriver tip or a star-shaped screwdriver tip which fits to internal positioning surface 12. Internal positioning surface 12 and external positioning surface 19 are always formed to fit into each other. In order to prevent turning an arrester of any design can be used. The head part 5 of central screw 8 and flange 24 are provided with e.g. a polygonal or roughened or ribbed surface which makes their turning easier. The outer superficies 21 of the upper moving element 14 is at least partially ribbed and/or cornered. The head part 5 of the central screw 8 may be e.g. a socket cap or a cornered screw head.

During use of impression coping 1 according to the invention the impression copings 1 assembled according to Figure 1 a are fixed in implants 2 as it is shown in Figure 1 b. The positioning ends 3 of the counterparts 4 are fitted into the positioning sleeves 20 of implants 2 then they are fixed in the threaded portions of implants 2 by means of end part 7 of the central screw 8. After that the outer superficies 21 of the upper moving elements 14 of moving elements 16 are bond together at their ribbed portions or at the portions between them using the known Paten Resin plastic material or some other known binding material in order to ensure firm positioning. Then the impression material is placed in the open tray and the pattern is taken in the known manner. The pliable impression material entirely fills in the space between the impression copings 1 . The open tray is placed on the impression copings 1 in such a manner that the head parts 5 of the central screw 8 of the impression copings 1 and the flange 24 of the external screw 10 of tubular screw 1 1 protrudes from the impression material and the open tray. After setting of the impression material the central screw 8 is driven out. In a following step the external screw 10 of the tubular screw 1 1 is driven out by means of flange 24. During this the threaded portion of the internal screw 9 of the tubular screw 1 1 (which on the one hand ensures the connection to counterpart 4, on the other hand prevents slider 18 from sliding off) is unscrewed from counterpart 4 and at the same time the slider 18 is partially raised from counterpart 4. The threaded arrester 17 provided on external screw 10 engages with the internal threads 22 provided in the upper moving element 14 fixed in the impression material. By turning external screw 10 with the help of flange 24 tubular screw 1 1 is unscrewed. In this manner slider 18 is entirely removed from counterpart 4 (Figures 9a and 9b). Then connection between counterparts 4 and central screws 8 and between the elements of the central screws 8, namely the tubular screw 1 1 and the moving element 16 is terminated. After that the open tray with the impression material in it, the tubular screw 1 1 and the moving element 16 fixed in the impression material can be removed from implants 2 and counterparts 4 as a single unit while the angular positions of the counterparts 4 do not change. Removal of the other parts of the sample taking device from counterparts 4 is further made easier by arched flange 25 formed at the rim of counterpart 4. Then counterparts 4 can be removed in a simple manner. During laboratory work the impression copings 1 are re-assembled by placing central screws 8 and counterparts 4 back to tubular screw 1 1 provided in moving element 16 included in the impression material. Then the laboratory analogue and on the basis of it the prosthesis are made in the known manner.

The advantage of the impression coping according to the invention is that for making a plaster cast only one impression must be taken. It is not necessary to decide in advance whether a single superstructure or a bridge will be produced. The plaster cast produced by using the all-purpose impression coping includes the axis, the position and the orientation of the implants at the same time. Accordingly, the superstructure system of the invention can be placed on in a simple manner. It can compensate the axis divergence of the implant and the crown or prosthesis. Loosening of the fixing screw is prevented. Replacing of the dental prosthesis becomes possible. Thereby time, energy and cost can be saved.