FIELD OF THE INVENTION AND PRIOR ART

This invention is related to a device for anchoring prostheses, in particular dental prostheses, in accordance with the pre¬ amble of the appendent claim 1.

A device of this nature is described in EP-A-0 288 702, where the element comprising the convex surface is shaped as a complete ball received in a socket formed by a base part and a part releasably connected thereto, said latter releasable part forming the peripherical edge portion of the socket. The means for securing the ball/socket coupling comprises a screw arran¬ ged so as to tend to actuate the ball in a direction outwardly from the socket, said actuation however being prevented by the releasable socket part.

A disadvantage with this known solution is that it is limited to the use of a complete ball, which causes a relatively bulky design. Furthermore, it involves a relatively complicated embodiment to form the socket intended for the ball by two mutually releasable parts. Finally, the securing technique used in EP-A-0 288 702 involves that a locking screw or the like has to act upon a surface of the socket proper or alternatively on the ball, which may cause problems to make readjustments after a first tightening of the screw and after releasing thereof.

SUMMARY OF THE INVENTION

The object of the present invention is to reduce the disadvan¬ tages discussed hereinabove and provide a device, wherein the tightening operation of the connection means is based upon co-operation between complementary convex/concave surfaces having relatively large areas.

This object is according to the invention achieved primarily by means of that defined in the characterizing parts of the enclosed claim 1.

Preferable developments of the concept according to the inven¬ tion are subject for the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the enclosed drawings, a more close descrip¬ tion of an embodiment example of the invention will follow hereinafter.

In the drawings:

Fig 1 is an illustration of the complete device according to the invention, Fig la being an exploded side view of the device, Fig lb an end view thereof viewed from below in Fig la, and Fig lc an end view of the device in Fig la viewed from above;

Fig 2 is a longitudinal section through the device according to Fig la, however in an assembled state;

Fig 3 is a view similar to Fig 2 but illustrating a possibility to inclination between parts of the device; and

Fig 4 is a view similar to Fig 2 but illustrating an alterna¬ tive principle for holding together the parts of the device.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The device according to the invention will hereinafter be described as particularly intended for anchoring prostheses in the form of dental prostheses. However, is should be noted that the device according to the invention may be used for anchoring of other prostheses.

As appears from Fig 1, the device comprises a securing member 1 to be secured in bone tissue and a support member 2 for sup¬ porting the prosthesis in question. As will be more closely described hereinafter, means for interconnecting the securing member 1 and support member 2 preferably comprise a screw 3.

The securing member 1 is provided with a thread 4 in the form of a trapezoidal thread or round thread. A trapezoidal thread is illustrated as an example in Fig 1. The advantage in using a trapezoidal thread or a round thread is that these two thread types allow a much larger amount of material between adjacent thread revolutions than conventionally used fine threads. Since anchoring is to occur in a relatively porous material (the skeleton bone) a trapezoidal thread or a round thread cause a much better chance for a good attachment and homogenizing with the bone tissue due to the larger amount and height of material.

The securing member 1 according to the invention is designed so as to be self-tapping upon screwing into a prebored hole in the bone tissue. In order to achieve this the securing member 1 is as appears from the end view in Fig lb provided with cuts 5 extending axially in relation to the securing member 1 while forming tapping cutting edges 6 on the thread of the securing member.

It is preferred that the securing member 1 comprises guide means 7 to simplify alignment of the securing member 1 in a axial position relative to the prebored hole in the bone tissue. Said guide means 7 has in the embodiment the character

of a cylindrical end portion on the securing member 1, said end portion being without thread. This guide means 7 also simpli¬ fies the first phase of the tapping operation in the prebored hole.

In order to provide a place to escape for the tissue material released in the tapping operation, a cavity 8 is arranged in the securing member 1, the volume of the cavity corresponding to the volume of the tissue material release. Thus, the cavity 8 will receive the tissue material released during the tapping operation as it proceeds. The cavity 8 has preferably the character of a transverse hole through the securing member 1 in the area of its tapping cutting edges 6. In addition, it should be emphasized that the cavity 8 also contributes favourably to obtaining securing of the securing member 1 and adjacent bone tissue.

The securing member 1 comprises preferably at its outer end means 9 for non-rotatable co-operation with a tool. The means 9 has preferably the character of a key grip, which may have a polygonal cross section for co-operation with the corresponding tool. The securing member 1 may be screwed into the hole in question by the means 9 and furthermore, the means 9 may serve for co-operation with a tool while the support member 2 is secured to the securing member 1, said tool having the purpose to avoid rotation of the securing member 1 when the support member 2 is connected thereto.

As appears from Figs 2 and 3, the support member 2 and securing member 1 have co-operating surfaces which are complementary concave and convex respectively and arranged to allow adjust¬ ment of the position of the support member 2 relative to secu¬ ring member 1, the adjusted position being fixable by means of the connection means. Said adjustability has the purpose to allow, as is immediately apparent from a comparison between Figs 2 and 3, mutual inclination of the support member 2 and securing member 1.

In the embodiment the securing member 1 comprises a concave surface 10 for co-operation with a complementary convex surface 11 on the support member 2. More specifically, the surfaces 10 and 11 are spherically concave and convex respectively, which involves a possibility to universal inclination of the support member 2 relative to the securing member 1.

Said connection means comprise a first member 12, which suppor- tingly bears on a surface portion 13 of the securing member 1, a second member 14, which supportingly bears on a surface portion 15 of the support member 2, and a third member 16, which interconnects the first and second members 12, 14. The mutual distance of the -first and second members 12, 14 is variable so as to fix and release respectively the support member 2 and securing member 1 relative to each other. More specifically, the device is such that the securing member 1 and support member 2 are tightened relative to each other when the distance between the connection members 12 and 14 is reduced.

The surface portion 13 of the securing member 1 and a surface 17 of the first member 12 co-operating therewith are complemen¬ tary concave and convex respectively. It is also here preferred that the surfaces 13, 17 are spherical so as to achieve the universal possibility to inclination already discussed herein- above. More specifically, the surface portion 13 of the secu¬ ring member 1 is convex whereas the surface 17 of the first member 12 co-operating therewith is concave.

The third member 16 has the character of a shank projecting through holes 18 and 19 respectively in the co-operating surfaces of the securing member 1 and support member 2.

The connection member 12 is in the example formed by a washer having a threaded hole. The connection member 14 is formed by a head of the screw 3 already mentioned in connection with Pig 1 and the third member 16 is formed by a shank of the screw, said

shank having a threaded end portion 20 engaging with the threaded hole of the washer 12.

The securing member 1 comprises an element 21, which on a first side has the surface 10, which is complementary to the surface 11 of the support member 2, and on a second side the surface portion 13, which is complementary to the surface 17 of the washer 12. The element 21 is intended to be attached relative to the securing member 1 in the mounted state of the device. As appears from the drawings, the element 21 may be formed by a washer mounted in a hole in the securing member 1. As an example, the washer 21 may be pressed into an upper portion of said hole 22 in the securing member 1 so that the washer 21 is retained therein by a press fit.

The washer 12 co-operating with the thread of the screw shank 16 is inserted into the hole 22 of the securing member inwardly of the washer 21.

As can be seen, the support member 2 has the character of a sleeve with a hole portion 23 having a relatively large dia¬ meter and receiving the head 14 of the screw 3. In the transi¬ tion between this hole portion 23 and the hole 19 previously mentioned there is formed a shoulder forming the surface portion 15, on which the head 14 of the screw supportingly bears. The hole portion 23 of the supporting member 2 may comprise an internal thread or other suitable, arbitrary means for connecting a prosthesis in the form of a tooth, a bridge or other design to the support member 2.

The bottom 24 of the hole 22 of the securing member 1, the upper side 17 and the lower side 25 of the washer 12 and the lower side 13 of the washer 21 are serrated or otherwise provided with a friction increasing design to avoid rotation of the washer 12 when the threaded shank 16 of the screw" 3 is screwed into and out of the washer 12.

The device according to the invention is used in the following way. Initially, a suitable hole is bored in the bone tissue and thereafter the securing member 1 is screwed into the same. After healing, the support member is mounted on the securing member 1 anchored in the bone tissue by causing the screw 3 to engage with the thread in the washer 12 by means of its threa¬ ded shank 16. As a consequence of the co-operating spherical surfaces, the support member 2 may be adjusted into varying angle relative to the securing member 1 so that the best position of the support member 2 for mounting the prosthesis is obtained. The adjusted position is fixed by final tightening of the screw 3. When readjustment is needed, such can easily be carried out without any need for releasing the securing member 1. Releasing of the support member 2 relative to the securing member 1 may easily be carried out since the screw head 14, which is provided with a suitable means for rotation, here in the form of a transverse groove, is easily accessible via the hole portion 23 of the support member 2.

From what is stated it appears that the washer 12 is inserted into the hole 22 of the securing member 1 before putting the washer 21 in its place.

In order to achieve a favourable surface contact between the respective spherical surfaces, the centers of curvature for the surfaces 10, 11, 13, 17 should coincide as viewed in the mounted state of the device. This causes the radius of curva¬ ture for the surfaces 10, 11 to be smaller than the one for the surfaces 13, 17.

It is illustrated in Fig 4 that the washer 12 illustrated in Figs 2 and 3 may be left out if the purpose is to locate the securing member 1 and the support member 2 in only one mutual position, namely aligned with each other. In such a case a screw 3 is used which has a larger length than the screw illustrated in Figs 1-3 and the free end portion of the screw engages with a threaded hole 26 provided in the bottom of the hole 22 of the

securing member 1. As before, the washer 21 forms a cup shaped spherical surface turned towards the support member 2 and this surface co-operates with a complementary spherical, convex surface on the support member.

The device described may of course be modified in several ways within the scope of the appendent claims. As an example there¬ on, it may be mentioned that the surface 11 of the support member 2 could be concave whereas the surface 10 of the secu¬ ring member 1 could be convex. A corresponding inversion could also be made as far as the surfaces 13, 17 are concerned.