RU2782108C2 - Bioresorbable screw - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: bioresorbable screw contains thread for screwing in the bone, a head having a cap, and a drive part. The cap contains an essentially flat contact surface for an implant, and, between the drive part and the cap, there is a given breaking place, which is made in the form of narrowing between an upper side of the cap and the drive part. A screw rod increases in thickness in the direction of the cap. Thread is made so that thread gears are made flat or rounded from the outside, and a gear base with rounding goes to side gear surfaces.

EFFECT: invention provides a possibility of a convenient and reliable attachment of implants, which consist of not solid hard material.

12 cl, 11 dwg

Description

Technical field

The invention relates to a bioresorbable screw for fixing an implant, which is used, in particular, in the field of dentistry. In particular, the invention relates to screws for fixing bioresorbable membranes and implants that fill bone defects. In addition, the invention relates to a set of an implant and at least one bioresorbable screw.

Prior Art

Bioresorbable implants, such as, in particular, collagen films, are in practice reinforced with pins or wires, which, after dissolution of the implant, are subject to costly explantation.

The bioresorbable screws available on the market, such as those used for bone plates, are at least unsuitable for fixing implants in the jaw area. In particular, most of the screws available on the market are designed for fixing a solid and rigid element and are therefore not suitable for fixing thin, flexible flat structures, such as collagen films or membranes, or for porous shaped bodies.

The task of the invention

In view of the foregoing, the object of the invention is to provide a screw which, on the one hand, is bioresorbable and, on the other hand, allows convenient, secure fastening of implants that do not consist of a solid, solid material.

Disclosure of invention

The object of the invention is already solved by means of an implant fixation screw according to one of the independent claims.

Preferred embodiments and improvements of the invention are presented in dependent claims, description or drawings.

The invention relates to a screw for fixing an implant. In particular, the invention relates to a screw which is used in the field of dentistry, in particular in the field of oral surgery.

It is also entirely possible within the scope of the invention to use a screw for fixing tendons or ligaments, or for fixing small bone fragments, in particular also in upper and lower limb surgery. It is also possible to use it for bone ligament ruptures, for fixing the capsule in case of arthrosis of the shoulder or hip joints. The screw can also be used on the hip or shoulder, or in knee arthroscopy.

Other areas of use are the attachment of blocks of bone replacement material or blocks of sintered magnesium particles and/or sintered magnesium fibers, which can be introduced into defect sites and which should stimulate bone growth.

It is also possible to use in bone augmentation.

The screw is made of bioresorbable material.

The screw preferably consists of a metal, in particular magnesium or a magnesium alloy.

In a preferred embodiment, the screw consists of a magnesium alloy with yttrium, zinc, manganese and/or calcium, in particular, as the main components of the alloy. Yttrium-containing magnesium alloys have improved corrosion properties, i.e. screws corrode longer than pure magnesium.

The screw contains a thread for screwing into the bone, as well as a head having a drive part and a cap. The cap preferably contains a substantially flat contact surface for the implant. According to the invention, there is a predetermined break point between the drive part and the cap.

In order to achieve ease of insertion of the screw, the drive part is thus connected to a handling tool such as an electrically or pneumatically driven screwdriver (eg also a slowly rotating dental burr) or a mechanical screwdriver.

The drive part and the tools are preferably designed in such a way that the drive part is locked in the tool bore, in particular clamped or fixed.

In this way, the screw can be screwed in by means of a handling tool and, after screwing in, the drive part is removed by breaking off at the predetermined break point without any risk of falling out.

According to an embodiment, the predetermined fracture point is designed such that as soon as the contact surface of the cap comes into contact with the implant and thus blocks further screwing in, the drive part breaks off under the effect of a torsional moment during further screwing.

Another possibility is to break off the drive part by tilting the handling tool. If the patient's bone structure is too soft and threatens to break the screw, breaking off the drive part can also be done with an instrument.

After breaking off the drive part, the cap, preferably in the form of a mushroom cap, rests flat against the implant, as a result of which fragile or thin implants are also relatively securely fastened.

In particular, it is also possible to fix flexible surface materials, such as magnesium and/or collagen films.

According to a preferred embodiment of the invention, the predetermined fracture point is in the form of a constriction, preferably in the form of a constriction, the smallest diameter of which is smaller than the smallest diameter of the shank and/or the inner diameter of the thread. In particular, the constriction has a diameter of 0.7 to 0.99.

It has been found that already a taper diameter of 0.9 - 0.99 of the smallest diameter of the shank or of the inner diameter of the thread is sufficient to ensure that in each case the breaking occurs at the given fracture point without the risk that the screw will fail elsewhere, in particular at bar or thread area.

The cap is preferably made in the form of a plate. The cap has a maximum height to a given fracture point, preferably less than 2 mm, particularly preferably less than 1 mm and most preferably less than 0.8 mm.

By means of a breakable drive part, the cap can be made with a lower height, since it is not necessary to equip it with form-fitting elements for engagement with a tool.

In an embodiment of the invention, the smallest diameter of the screw shaft is at most equal to the inside diameter of the thread. In particular, the smallest diameter of the shank is approximately equal to the inside diameter of the thread.

As a result, the shaft and thread profile cavities form a circular cylinder, at least in its sections. From this circular cylinder, the teeth of the threads extend.

As a rule, osteosynthesis screws are reliably used only in the cortical layer of the bone. If the cortical layer of the bone is made too thin, as often happens in elderly patients, this can lead to the fact that when the screw is fully screwed in, only the rod is fixed in the cortical layer of the bone, but not the thread. The thread is thus screwed only up to and including the spongy tissue and is not retained in it.

However, due to the fact that there is now a hole in the cortical layer, the diameter of which approximately corresponds to the internal diameter of the thread and which thus contains threads communicating exclusively with the thread of the screw, the screw, even if it is "turned", at least protected from axial displacement, that is, it does not fall out without jamming the thread in the cortical layer.

In a preferred embodiment of the invention, the thread is provided with a self-tapping point.

In a further embodiment of the invention, the screw is designed to be driven in. In particular, the tip of the screw has a taper angle of less than 60°, preferably less than 40°.

In accordance with one embodiment, the thread is made single-start. However, variants with multiple, in particular double threads are also possible, in particular in one embodiment in which the screw can also be driven in instead of being screwed in.

In a preferred embodiment of the invention, the screw comprises a self-tapping point that cuts into the bone tissue when the screw is screwed in.

However, before screwing in the screw, a hole is preferably drilled, in particular with a bur, the diameter of which differs from the inner diameter of the thread by up to 25%.

According to one embodiment, the self-tapping point is designed, however, such that the blade is present in only one edge region, but not in the center of the point.

In particular, at least one blade of the self-tapping point extends from 10 to 80%, preferably from 20 to 60%, of the outside diameter of the thread.

Thus, it is not necessary to do all the drilling work with the self-tapping tip of the screw, which reduces the resulting screw-in torques.

In addition, according to one embodiment, the screw may be provided with a centering cone in the region of which there is no blade. Thus, the screw can be conveniently inserted into the drilled hole and centered.

In another embodiment, the self-tapping point is rubbed to the front end of the screw. This embodiment is most suitable for driven screws.

According to one embodiment, the cap has a diameter of 1 to 6 mm, preferably 2 to 4 mm.

The diameter of the cap is preferably 1.5 to 5 times, particularly preferably 2 to 4 times the diameter of the shaft and/or the inside diameter of the thread.

The thread pitch is preferably 0.5 to 1.6 mm. In an embodiment in which the screw can be driven, the thread pitch is preferably over 1.6 mm, in particular between 1.6 and 2.5 mm.

According to a preferred embodiment, the thread teeth are externally flat or rounded.

The teeth of the thread can be made so that the base of the tooth passes with a rounding into the side surfaces of the tooth.

In particular, the thread is made as a single or double trapezoidal thread with a rounded tooth base. The flanks of the tooth preferably merge with a rounding into the tops of the tooth.

This avoids sharp thread edges that corrode more quickly after implantation.

In particular, the thread teeth have a width of at least 0.5, preferably 0.7 of the tooth root width.

In an improvement of the invention, the screw contains a coating. In particular, the screw contains a coating of magnesium fluoride. This kind of passivating coating, which initially inhibits corrosion after installation, can be simply created by immersing a magnesium or magnesium alloy screw in hydrofluoric acid.

In particular, the intensity of corrosion is reduced by increasing the chloride concentration of the collagen membrane swollen in sodium chloride solution, which is attached with a screw.

It is also possible to reduce the formation of galvanic cells as a result of adjoining metals and the associated increased initial corrosion.

The invention also relates to a screw, in particular a screw with one or more of the features described above.

The screw consists in particular of a bioresorbable material and has a thread for screwing into the bone.

In addition, the screw may, but need not, comprise a breakable drive portion.

The screw also contains a rod, to which a head with a cap adjoins.

According to a further aspect of the invention, the cap preferably comprises a substantially flat contact surface for the implant, the shaft increasing in thickness towards the cap, which optionally, together with the drive part, forms the head of the screw.

Thus, the shaft is made thicker in the area immediately below the cap than in the area adjacent to it in the direction of the thread.

This leads to the fact that at the end of the screwing process, the thickened area comes into contact with the upper side of the implant, as a result of which the torque required for subsequent screwing in increases abruptly and further screwing in of the screw by the user stops.

This ensures that, when screwing in, the contact surface of the cap is not pressed against the implant with such great force that damage occurs.

This applies in particular to implants that are made in the form of flexible planar structures.

Due to the thickening below the cap between the bone and the contact surface, as it were, a gap is created in which a flat structure is placed.

The thickened area is made, in particular, so that the rod contains a cone-shaped part adjacent to the head. As a result, the screw is clamped at the end of the screwing process, with the screw cap still at a distance from the cortical layer, thus preventing the implant from being trepanned by the cap.

Thus, due to the cone-shaped part, in contrast to the step in the implant, as a rule, the drilled hole is expanded until the screw is wedged. This reduces the torques that can be transmitted to the implant via the contact surfaces in the sense of the friction clutch and thus lead to trepanation.

The cone-shaped part can be made, in particular, in the form of a truncated cone.

With the improvement of the invention, the steepness of the angle of the cone-shaped part in the transition area in the direction of the cap relative to the central axis is increased. In particular, the transition region between the cone-shaped part and the bordering cap is made in the form of a fillet.

As a result, the diameter of the shaft directly in front of the contact surface is significantly increased, so that at the latest when this region comes into contact with the implant, the screw is wedged.

The transition region preferably has a length of 0.5 to 2 mm (along the central axis of the screw). Thus, the screw is most successfully suitable for fixing flat structures used as implants.

According to one embodiment of the invention, the cone-shaped portion may comprise, with respect to the central axis, a generatrix that extends at an (average) angle of 20 to 40°, preferably 35 to 45° to the central axis of the screw. The conical part has an axial length preferably from 0.2 to 10 mm, preferably from 0.4 to 0.6 mm.

The conical part has a diameter which is preferably 1.1 to 2.5 times greater than the smallest diameter of the rod, particularly preferably 1.3 to 1.8 times.

The invention also relates to a kit with at least one screw of the type described above and one implant.

In particular, the implant is made in the form of a flexible flat structure, in particular in the form of a collagen membrane and/or a magnesium film.

The kit may comprise, as defined in accordance with one embodiment, in addition, a pilot drill, the diameter of which is approximately equal to, preferably, the diameter of the shank and/or the internal diameter of the screw thread.

Depending on the state of the bone substance, drilling can be carried out with a pilot drill whose diameter is smaller than the inner diameter of the thread, or the pilot drill can be omitted altogether, in particular in the case of a driven screw.

The set may also include a holder for a plurality of screws and/or a template for positioning the pilot drill. The holder serves as an intermediate storage for the screws and is preferably sterilizable. In particular, the holder consists of a metal-free sterilizable material, such as polysiloxane. In this way, the screws can be fixed sterile without touching them.

In addition, the kit may include a screw adapter that contains a sleeve for connection to a hand screw handle or a dental burr.

Brief description of the drawings

The invention is explained in more detail below with reference to exemplary embodiments based on the drawings in FIG. 19.

In FIG. 1 shows a screw according to a first embodiment, which is adapted in particular for oral surgery, in particular for fixing sheet structures such as collagen membranes or magnesium films, in side view;

in fig. 2 – screw tip, top view;

in fig. 3 is a sectional view along plane A-A in accordance with FIG. 2;

in fig. 4 is a sectional view along plane B-B in FIG. one;

in fig. 5 is a screw according to another exemplary embodiment, made longer and adapted, in particular, for fixing blocks with which to fill bone defects, side view;

in fig. 6 is an enlarged view of FIG. 5;

in fig. 7 shows schematically how the implant can be fixed with one of the screws;

in fig. 8 and 9 - driven screw according to the embodiment;

in fig. 10 and 11 is an adapter for one of the screws, which can be connected to a dental drill or a hand screwdriver.

Embodiments of the invention

In FIG. 1 shows a screw 1 according to a first exemplary embodiment of the invention, seen from the side.

The total length of the screws (including the head 2 with the drive part 7) is generally preferably 3 to 20 mm. The shorter variant shown here, compared to the variant in FIG. 5 and 6 has an overall length preferably between 5 and 10 mm.

The screw 1 has a head 2 which consists of a cap 5 and a drive part 7. Attached to the head 2 is a shaft 4 which, in this exemplary embodiment, goes directly into the thread 3.

The cap 5 is made in the form of a plate and in this exemplary embodiment is rounded on the upper side 9.

The underside forms a preferably even contact surface 6 which protects the implant when used for the intended purpose.

The drive part 7 adjoins the cap 9.

Through the drive part 7, the screw 1 can be inserted into a manipulation tool (not shown). In this case, the drive part 7 is protected against falling out by means of a manipulation tool.

Between the upper side 9 of the cap 5 and the drive part 7 is made narrowing, which forms a predetermined place 8 fracture.

In the region of the given break point 8, the diameter of the screw 1 is the smallest.

In particular, the diameter of the specified fracture point 8 can be 5–10% less than the diameter of the thinnest point of the rod 4 or the inner diameter of the thread 3.

The predetermined break point 8 is adjacent directly to the cap 5, so that when the drive part 7 is broken off, only the flat cap 5 remains.

From a predetermined fracture point 8, which can in particular be in the form of a rounding, the diameter of the screw 1 increases in the direction of the drive part 7, in this embodiment in the form of a truncated cone in the region 21 with an acute angle, for example, from 40 to 80° .

Thread 3 is single threaded. Around the core preferably less than 10, particularly preferably less than 6 times the cut 16 of the thread. Thus screw 1 can be screwed in with fewer turns.

The tip 17 of the screw 1 is made, on the one hand, self-tapping and contains a blade 14. When the screw 1 is screwed into a pre-drilled hole, the threads are inserted into the bone using the blade 14.

In addition, the tip 17 includes a centering cone 13, which in this example embodiment contains a generatrix that occupies a steeper angle relative to the central axis 23 of the screw 1 than the cutting edge 22 of the blade 14.

The cutting edge 22 can be positioned relative to the central axis 23, in particular at an angle of 10 to 30°.

The thread 3 extends in this example embodiment almost to the head 2 of the screw 1. In this example embodiment of the screw 1, the tapered portion 10 of the shaft 4 is adjacent directly to the thread 3.

Near the bottom side, i.e. the contact surface 6 of the cap 5, the diameter of the rod 4 increases, starting from the thread 3 in the direction of the cap 5.

In this exemplary embodiment, there is a tapered portion 10 which comprises a generatrix with an angle preferably between 20° and 40° with respect to the central axis 23.

In the area of the cone-shaped part 10, the diameter of the rod 4 increases preferably up to 1.2-1.7 times the smallest diameter of the rod 4 and/or the inner diameter of the thread 3.

The region 11 of the transition from the cone-shaped part 10 of the rod to the head 2 in this exemplary embodiment is made in the form of a fillet.

In the transition area 11, which can in particular have a radius of 0.1 to 0.5 mm, the diameter increases sharply, so that when the screw 1 is screwed in, it is locked at the latest by this transition area 11 .

The transition region 12 of the tapered portion 10 is preferably rounded on the thread side.

In this way, in particular when fixing flexible planar structures such as collagen membranes or films, contact surface 6 is prevented from being pressed against the implant in such a way that penetration occurs.

The diameter of the cap 5 is preferably 2 to 4 mm, the diameter of the stem is preferably 0.6 to 1.5 mm.

The centering cone 13 may have a vertex angle of 70 to 110°.

The thread of the osteosynthesis screw according to the invention preferably has a length of 2 to 18 mm, in this embodiment of the short screw preferably 2 to 5 mm.

Around the screw 1 less than five, particularly preferably less than four times the cut 16 of the thread. Thus, the screw can only be screwed in with a small number of turns.

In FIG. 2 shows the tip of the screw 1, top view.

In FIG. 3 shows a section along the plane A-A in Fig. 2, detailed view.

It can be seen here that the thread cuts 16 are made in the form of rounded recesses, the side surfaces 18 of which are preferably located at a profile angle α from 90 to 150°. The thread teeth 15 are preferably flat, in particular they have an axial length of 0.2 to 0.5 mm.

In this exemplary embodiment, the thread 3 is made as a single start trapezoidal thread with a rounded tooth base.

The width b1 of the thread tooth 15 is at least 0.5 times the width b2 of the base of the tooth (including the sides of the tooth).

The teeth 15 of the thread do not form a point, since the point would initially be subject to high corrosion and thus the strength of the threaded connection would quickly decrease.

In FIG. 4 shows a section along the B-B plane in FIG. one.

In this exemplary embodiment, the drive portion 7 is triangular in cross section with rounded tops. It is clear that the shape of the drive part 7 can be arbitrary. It should only ensure that sufficient torque is transmitted. For example, a hexagonal or star design (not shown) is also possible.

In FIG. 5 shows, in side view, a screw according to an alternative embodiment which is longer than the screw shown in FIG. 1 to 4. It preferably has an overall length of more than 8 mm, particularly preferably more than 12 mm.

Also in this exemplary embodiment, the screw 1 comprises a head 2 which includes a drive part 7 and a flat cap 5.

The unthreaded shaft 4 of the screw 1 has a length which is at least twice, preferably at least three times, the length of the thread 3. The shaft 4 and the thread 3 together preferably have a length of 8 to 18 mm.

However, the screw is similar to the screw shown with reference to FIG. 1 - 4, and includes, in particular, also a cone-shaped part 10 at the end of the rod 4 from the side of the head, as well as a point 17 with a blade 14.

In FIG. 6 is a detailed view according to FIG. 5, in which it can be seen that the long version of the screw 1 shown here essentially corresponds to the shorter version according to FIG. fourteen.

The shaft 4 of the screw 1, as well as the internal diameter of the thread 3, however, preferably have a greater thickness. In particular, it has a diameter of 1.0 to 1.3 mm.

It has been found that already a recess with only a slightly smaller diameter compared to the rod 4, in particular with a smaller diameter of 0.01-0.05 mm, leads to a sufficiently reliable predetermined fracture point 8.

Also, the tip 17 is made in accordance with FIG. 1 and contains a blade 14 for inserting threads, as well as a centering cone 13 without a blade.

In FIG. 7 schematically shows an implant 19 in the form of a planar structure, such as a collagen film. It is applied to a wound, for example, to close a bone defect. After that, the drill holes 20 are drilled, which essentially correspond to the diameter of the screw shaft and/or the inside diameter of the thread.

Finally, the implant 19 is secured with at least one screw.

In this case, the screw is screwed into the drilled hole 20 until the rotation is stopped at the end of the cone-shaped part (10 in Figs. 1 and 6).

After this, either the drive part breaks off due to the screwing torque if the screw head comes into contact with the implant and/or the bone. However, the user can also break off the drive part by breaking.

The screws preferably consist of a magnesium alloy. If a magnesium film is used as the implant 19, due to the small stress difference, no increased corrosion occurs, so that both the implant 19 and the screw degrade only after treatment.

In FIG. 8 and 9 show a screw 1 according to an alternative embodiment, which can also be driven in.

As shown in FIG. 8, the self-tapping point 17 extends to the front end of the screw 1. The self-tapping point has a taper angle of less than 45°, preferably less than 40°. There is no separate centering cone with a different opening angle of the cone (13 in Fig. 1).

In addition, the thread 8 is multi-start, in particular double-start, and has a thread pitch larger than the thread according to the embodiments of FIG. 16.

In FIG. 9 shows a section along the B-B plane in FIG. 8. The drive part 7 has a different shape than the drive part according to FIG. 1 - 6, namely the shape of a circular cylinder truncated on one side. It will be understood, however, that the drive part may also have the shape shown in FIG. four.

Otherwise shown in FIG. 8 and 9 the screw essentially corresponds to the exemplary embodiment according to FIG. one.

In FIG. 10 shows a screw adapter 24 that can be fitted to a dental burr or hand screwdriver (not shown) in sectional view.

To this end, the adapter 24 comprises a sleeve that can be connected to a dental burr or a hand screwdriver, which, depending on the bur or hand screwdriver used, can be made in any way.

In addition, the adapter contains, in particular, a holder 25 for the drive part of the screw, similar to the holder for the insert cutter.

As seen in the end-side top view according to FIG. 11, the holder 25 in this exemplary embodiment corresponds in shape to the screw drive portion shown in FIG. four.

The drive part of the screw can be clamped or fixed in the holder 25. After the screw is completely screwed in, the broken off drive part remains in the holder 25.

According to one embodiment (not shown), the drive part can then be knocked out with a manipulation tool, for example by means of a rod axially movable in the adapter 24, which presses out the drive part, or by releasing the lock.

EFFECT: invention provides simple and reliable fastening, in particular, of dental implants.

List of reference designations

1 - Screw

2 - Head

3 - Thread

4 - Rod

5 - Cap

6 - Contact surface

7 - Power part

8 - Predetermined break point

9 - Upper side

10 - Tapered part

11 - Transition area

12 - Transition area

13 - Centering cone

14 - Blade

15 - Thread tooth

16 - Threading

17 - Point

18 - Side

19 - Implant

20 - Drilled hole

21 - Region

22 - Cutting edge

23 - Central axis

24 - Adapter

25 - Holder

26 - Coupling

Claims (15)

1. A bioresorbable screw containing a thread for screwing into the bone, a head having a cap and a drive part, and the cap contains a substantially flat contact surface for the implant, and between the drive part and the cap there is a given break point, which is made in the form of a narrowing between the top side of the cap and the drive part, while the screw shaft increases in thickness in the direction of the cap, the thread is made so that the teeth of the thread are made flat or rounded on the outside, and the base of the tooth with rounding passes into the side surfaces of the tooth. 2. The screw according to claim 1, in which the specified fracture point is made in the form of a narrowing. 3. A screw according to claim 1 or 2, wherein the cap is made in the form of a plate, preferably the cap has a maximum height to a given fracture point of less than 2 mm, preferably less than 1 mm and particularly preferably less than 0.8 mm. 4. Screw according to one of paragraphs. 1-3, containing a rod, and the smallest diameter of the rod is as much as possible equal to the inner diameter of the thread, in particular, the smallest diameter of the rod is equal to the inner diameter of the thread. 5. Screw according to one of paragraphs. 1-4, in which the thread contains a self-tapping point. 6. Screw according to one of paragraphs. 1-5, in which the cap has a diameter of 1 to 6 mm, preferably 2 to 4 mm, and/or the cap has a diameter equal to 1.5-5 times, preferably 2-4 times the diameter of the shaft and/or the inner diameter of the thread, and/or the thread pitch is between 0.5 and 1.6 mm, and/or the screw contains a centering point. 7. Screw according to one of paragraphs. 1-6, consisting of magnesium or a magnesium alloy, in particular a magnesium alloy with yttrium, zinc, manganese and/or calcium. 8. Screw according to one of paragraphs. 1-7 containing a coating, in particular a magnesium fluoride coating. 9. Screw according to one of paragraphs. 1-8, in which the stem comprises a cone-shaped, in particular truncated-conical part adjacent to the head. 10. The screw according to claim 9, in which the steepness of the angle of the conical part increases in the region of transition to the cap relative to the central axis, in particular, the transition region is made in the form of a rounding. 11. Screw according to claim 10, in which the transition region has a length of 0.5 to 2 mm. 12. Screw according to one of paragraphs. 1-11, in which, below the cap, the screw comprises a tapered portion which forms an angle of 20 to 40°, preferably 35 to 45°, with respect to the central axis of the screw, and/or which has a length of 0.2 to 10 mm, preferably 0 .4 to 0.6 mm.

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