EP1154729A2

EP1154729A2 - Screw connection device for osteo-integrated plants, method and apparatus for tightening this device

Info

Publication number: EP1154729A2
Application number: EP99959680A
Authority: EP
Inventors: Andrea Bazzurro; Giocondo Vianello
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-02-15
Filing date: 1999-12-03
Publication date: 2001-11-21
Also published as: WO2000047113A3; WO2000047113A2; ITTO990112A1; IT1307221B1

Abstract

A screw connection device, particularly for osteo-integrated plants, comprises a first element (I) and a second element (M) which are clamped to each other by means of a connection screw (9). Between the two elements (I, M) means (11) are interposed which are adapted to be deformed elastically and/or permanently as a result of the tightening of the connection screw (9), so as to enable the operator to carry out the tightening operation in a precise and controlled manner, untill reaching a predetermined force, which can be predetermined experimentally or by calculation, this reaching being signalled optically and/or acoustically by signalling means connected to the electronic processing means.

Description

"Screw connection device for osteo-integrated plants, method for tightening this device and apparatus for use in this method"

The present invention relates to a screw connection device which can be used for anchoring a prothesis to an osteo-integrated plant, such as a dental plant or a maxilla-facial plant. The invention also relates to a method for tightening this device, as well as an apparatus for use in this method. By the device and the method according to the invention, the value can be determined of the tightening torque which must be applied to this screw in order to obtain an axial force on the screw which is predetermined experimentally.

Screw connection devices for osteo-integrated plants are known which comprise: a first element, or plant element, which is to be integrated within a bone tissue, having a hole with a threaded portion, a second element, or support, for supporting a prothesis, which is mounted on said plant element, and having a through hole, and a connection screw, inserted with clearance through said through hole of the support and screwed within the threaded portion of said hole of the plant element, so as to hold the support in a final connected condition on the plant element.

Figure 1 of the annexed drawings shows, by way of example, a device according to the above indicated prior art, which is presently used for dental plants. Reference numeral 1 generally designates the plant element which is integrated by known techniques within the bone tissue 2 of a lower or upper jaw. In the illustrated example, the plant element 1 has a substantially elongated cylindrical body, with a blind cylindrical axial hole 3 which extends from an end surface la. In the illustrated example, the cylindrical hole 3 has an enlarged mouth portion 3a and an end threaded portion 3b. Within the mouth portion 3a a stem portion 4 of a support 5 is received. The stem portion 4 includes a polygonal cross-section 4a, such as an hexagonal cross-section, engaged within a portion having a co-operating cross-section of the hole 3 in order to prevent relative rotation between support 5 and plant element 1. The support 5 has a head 6 which rests against the end surface la of the plant element 1 in the final connected condition of the support 5 on the plant element 1. In the illustrated example, over support 5 there is fixed a further supporting element 7 on which the dental prothesis 8 is formed. Reference numeral 9 designates the connection screw, which is inserted with clearance through a through axial hole 10 of support 5 and having an end portion 9a screwed within the end cylindrical portion 3b of hole 3 of the plant element 1.

According to the prior art, the plant element 1, the support 5 and the connection screw 9 are usually made of titanium or a titanium alloy. The plant element 1 is pressed or screwed into the bone tissue 2. Naturally, the shape of the plant element 1 may be different, depending upon the application and the insertion method. Once the plant element 1 has been inserted into bone tissue 2 and after a waiting time, generally of some months, for integration of the plant element 1 within the bone tissue, the support 5 is secured to the plant element 1 by means of the screw 9. During the waiting time which is necessary for obtaining the osteo-integration, the hole 3 is covered by a covering screw. Naturally, when osteo-integration is achieved, the dental surgeon carries out the necessary operations for forming a mould and preparing the support 5 for the dental prothesis.

The technical problem which is encontered in the known devices of the above described type is a risk of a low efficienty of the connection of the support 5 to the plant element 1 because of insufficient tightening of the connection screw 9, which in turn is due to that it is impossible to carry out a precise control of the tightening operation when support 5 is installed and also because of the lack of efficient means preventing unscrewing. In particular, with the known devices the precise force induced on the screw, at the end of the tightening operation, by the applied tightening torque, can never be determined. Therefore, the dental surgeon carries out tightening of the screw without knowing the force induced in the screw by the applied tightening torque, which also is unknown if a manual screw driver is used. The loosening of screw 9 which may, and actually does, take place with the known devices involve the need of non-programmed interventions with resulting disturbance and difficulties.

Various solutions to the above mentioned problem have been proposed in the past, as disclosed for example in European Application EP-A-0 593 926, in US patent US-A-5 733 122 and in International Patent Application WO 93/06787. All the solutions proposed heretofore, however, are relatively complicated and/or not completely satisfactory, which is proved by that none of them have found a large diffusion so far.

The object of the present invention is that of providing a device of the type indicated at the beginning of the present description which is able to overcome the above mentioned drawbacks. In particular, the invention has the object of providing a device of the above indicated type which ensures the application of a tightening torque such that a predetermined axial force is obtained on the screw. A further object of the invention is that of providing a device which can be installed by extremely simple operations and yet in a precise and reliable manner.

In view of achieving this object, the invention provides a device of the type indicated at the beginning of the present description, characterized in that between said second element and said first element there are interposed means adapted to be deformed as a result of the tightening of the connection screw.

Theoretically, the above mentioned deformable means may be permanently deformable. However, in a preferred embodiment, the above mentioned deformable means are elastically deformable and are specifically constituted by a spring element comprising at least one Belleville washer. Preferably, this spring element is constituted by a single piece incorporating two Belleville washers with opposing cones. The above mentioned spring element is placed co-axially with the connection screw, between two facing surfaces of the support and the plant element and, due to its shape, is able to keep the support and the plant element co-axial with each other during the tightening operation, so as to then ensure a perfect contact between these elements .

Also in the case of the above mentioned preferred embodiment, the above mentioned spring element in form of double Belleville washer is interposed between the support and an auxiliary support resting on the plant element. The plant element and this auxiliary support have complementar portions mating with each other to prevent a relative rotation of said elements. The same 7113

applies to the support and the auxiliary support. Naturally, the auxiliary support may also be eliminated, in which case the spring element is directly interposed between the support and the plant element. However, it is always possible to make use of the same plant elements which are presently in use, with no modification.

A further advantage of the invention lies in that, once tightening has been carried out, said spring element acts also as an anti-unscrewing means.

According to a further feature, with the device according to the invention there is associated an electronic wrench adapted to transmit the value of the tightening torque applied to the screw during the tightening operation to electronic processing means, so as to enable the operator to carry out the tightening operation in a precise and controlled manner, untill a predetermined tightening force is reached. This predetermined force is located preferably experimentally, by making in use of a device which also forms part of the invention, which can be provided according to different embodiments, as indicated in the claims annexed hereto.

Finally, also the method for installing the above described connection device forms part of the invention, which method includes the use of the above mentioned electronic wrench as well as a preliminary experimental step in which the test device which also has been mentioned above is used. Further features and advantages of the invention will become apparent from the description which follows with reference to the annexed drawings, given purely by way of non limiting example, in which: 7113

figure 1 is a cross-sectional view of a device according to the prior art, which has been already described in the foregoing, figure 2 is a cross-sectional view showing the device according to the invention according to a preferred embodiment, in a first operative condition, figure 3 shows the cross-sectional of figure 2 in a second operative condition, figure 4 is a perspective exploded view of the device of figures 2, 3, figure 5 is a cross-sectional view of a preferred embodiment of the spring element forming part of the device according to the invention, figure 6 is an elevational view, partially in cross-section, of an apparatus in form of a dynamometric press which can be used for experimental determination of the tightening force which must be applied to the device according to the invention, figures 7, 8 are diagrams showing the principles at the basis of the invention, in the embodiment which makes use of the apparatus of figure 6, figure 9 is a cross-sectional view of a variant of figure 4, figure 10 is a view of an electronic wrench which can be used for installing the device according to the invention, figure 11 is a cross-sectional view taken along line XI-XI of figure 10, figure 12 is a cross-sectional view taken along line XII-XII of figure 10, figure 13 shows a variant of the electronic wrench, figure 14 is an elevational view, in cross- section, of a further embodiment of an apparatus which can be used m the preliminary experimental stage wnich is provided m the method according to the invention, figure 15 is a view at an enlarged scale of the detail indicated by arrow XV m figure 14, figure 16 is a top view of the device of figure 14, figure 17 is a diagram showing the relationship between tightening torque and axial force on the screw which can be determined by the apparatus of figure 14, figure 18 shows a variant of figure 14, and figure 19 is a cross-sectional taken along line IXX-IXX of figure 18.

A preferred embodiment of the device according to the invention is shown m figures 2, 3 and 4. As shown, also the device according to the invention comprises a first element I, which, in the case of an osteo- integrated plant, is an element to be integrated within a bone tissue, and a second element M which is a support for supporting a prothesis. The second element M is secured to the first element I by means of a connection screw 9 which is inserted into a through hole 10 of element M and is screwed into a threaded portion of an axial hole 3b of the first element I. In the illustrated example, the screw 9 has a head with a socket 10a of hexagonal shape or any other shape adapted to be engaged. Furthermore, m the case of the illustrated example, on the first element I there is mounted an auxiliary support S which is interposed between the first element I and the second element M. The auxiliary support S and the first element I have complementar portions 20, 23, e.g. of hexagonal cross- section, which engage with each other so as to prevent a relative rotation of these elements. Similarly, the second element M has a skirt 22 with an inner profile of hexagonal cross-section, mating with a head of hexagonal cross-section of the auxiliary support S, designated by 21, so that also any relative rotation between element M and the auxiliary support S is prevented. Figure 2 shows the unit according to the invention in a preassembled condition, before tightening. As shown, the auxiliary support S and the second element M have facing surfaces between which the spring element 11 is interposed (see figure 5) which incorporates two Belleville washers with opposing cones in a single piece. The element 11 is co-axial with screw 9.

The advantage of using a double spring made as a single piece derives from the need of keeping the support M and support S co-axial with each other during tightening, so as to ensure a contact thereof.

All the elements of the device are made of titanium alloy or any other suitable material.

In the condition shown in figure 2 the double Belleville washer 11 is free. Figure 3 shows the device according to the invention once tightening has been carried out. As shown, tightening of the connection takes place along with an elastic deformation of the double washer 11, which renders the tightening process adapted to be controlled precisely, due to the increase of the rotation which must be imparted to the screw for achieving full tightening, this rotation being proportional to the axial deformation travell of the double Belleville washer.

The variation of the axial force and the tightening torque as a function of the screw rotation is shown in figure 8. As shown, as a result of the elastic deformation of the spring element 11, the final tightened condition is reached gradually. Naturally, it would be possible to use any number of Belleville washers, or any other suitable type of spring. 7113

Preferably, with the device according to the invention there is associated an electronic wrench (figure 10) adapted to trasmit the value of the tightening torque applied to the screw during the tightening operation to electronic processing means, so as to enable the operator to follow the tightening operation in a precise and controlled manner, untill reaching a predetermined tightening force.

In a first embodiment of the method according to the invention, this tightening force is determined in a preliminary experimental stage by means of a dynamometric press (see figure 6) which measures the force necessary to deform the double Belleville spring 11 interposed between support S and support M (figure 7) . In figure 6, reference numeral 50 generally designates the dynamometric press, comprising a crank 51 which is used to rotate a screw 52. Scrue 52 applies a pressure on a piston 53, with the interposition of a load cell 54, which is able to output a signal proportional to the reached load on a cable 55. Piston 53 applies pressure on a specimen P which is constituted by the assembly of support S, support M and double Belleville spring interposed therebetween, these elements being those which will be then used for preparing the final prothesis. The load cell 54 in press 50 continously detects the applied force and tras its the value thereof to an electronic processor such as a personal computer, which is thus able to generate the diagram shown in figure 7 of the variation of the force causing deformation of the double Belleville spring 11, which is rectilinear and continuous up the point where support M comes in contact with support S (k point) . At this time, an increase in rotation generates an abrupt rise of the straight line representing the deformation force (which 7113

is substantially vertical beyond the diagram k point) since, once deformation of the double Belleville spring 11 is terminated, the applied force only causes a direct compression of support S on support M. This force at the end of the deformation of the double Belleville spring will represent the force applied on the screw when, after tightening thereof, support M comes in contact with support S, after deformation of the double Belleville spring 11. Press 50 also comprises an optical reader 152 co-operating with a disk 155 for detecting the rotation of screw 52.

As already indicated in the foregoing, the double Belleville spring 11 (see figure 5) is shaped so as to ensure that the two contact planes of elements M and S are kept parallel to each other during tightening, so as to reach a full contact of these elements at the end of the tightening operation.

Figures 10, 11 and 12 show an embodiment of the electronic wrench, designated by reference numeral 70, which can be used for installing and tightening the screw 9. Wrench 70 has one end 71 where the wrench body defines a housing containing a worm screw 72 / helical wheel 73 coupling. The worm screw 72 can be actuated by manually rotating a hand-wheel 74 which is rotatably mounted inside the body of wrench 70 and connected by a shaft 74a to worm screw 72. The rotation of hand-wheel 74 is transmitted by shaft 74a, worm screw 72 and helical wheel 73 to a shaft 75 having a cross-section complementar to that of socket 10a of screw 9, so as to be able to cause screwing. An optical reader 73 cooperating with the toothed wheel 78 which is connected in rotation to shaft 74a, is able to generate a signal indicative of the rotation angle of hand-wheel 74, whereas a load cell 79 detects the force generated by the axial reaction due to the rotation torque applied to worm screw 72. The load cell 79 is therefore able to generate a signal proportional to the applied tightening torque, whereas the value of the screwing rotation is signalled by the optical reader 77. Naturally, the electronic processing means to which the wrench is connected may be programmed so as to generate an optical and/or acoustic signal when a predetermined tightening force is reached. More precisely, the signals coming from the electronic wrench may be sent to an electronic processing and displaying system, such as a personal computer.

During the tightening operation, the personal computer continuously displays the value of the applied torque as signalled by the electronic wrench 70. When contact between support S and support M is reached, actuation of the screw does not cause any further deformation of the double Belleville spring 11, and only tends to apply a further load on the screw, thus causing a great increase in the torque which will be simultaneosly perceived both by the hand of the operator and the personal computer. Indeed, the tension directly applied to the screw becomes much greater than that which was previously necessary to deform the double Belleville spring. The personal computer immediately displays the above mentioned abrupt increase in the torque, by showing an abrupt variation in direction of the straight line in the diagram of figure 8, the k point corresponding to the force at the end of the deformation of the double Belleville spring 11. When the k point is reached, the torque applied has induced the same force on the screw which is necessary to deform the double Belleville spring and which was previously experimentally measured by the above described dynamometric press 50. The diagram of figure 8 shows the tightening torque in a hypothetical example where the k point is located at a force of 300 N and a torque of 150 Nmm. Obviously, the tightening torque is proportional to the tightening force. It is thus possible to obtain a greater force by a proportionally greater torque.

As a further advantage, spring 11 acts also as an anti-unscrewing means adapted to intervene any time that the screw may be engaged by a force greater than the mounting force, so as to keep elements S, M in contact with each other.

Also in order to reach the objects which are ... of the present invention, an alternative embodiment is provided to the device for controlling the screwing data and the components thereof. This alternative device comprises both the same prothesis elements which have been described with reference to figures 2, 3, 4, 5, and the wrench shown in figures 10 - 12, or that which will described in the following with reference to figure 13; however, in liew of the dynamometric press of figure 6, the apparatus shown in figures 14 - 16 is used. This apparatus is a screwing data detector by which the tightening torque can be determined which is necessary to deform the double Belleville spring 11 untill reaching contact between support M and support S, the same apparatus also being used to determine to axial force which is induced in the connection screw 9, the whole as a function of the angular rotation of the wrench 70 which causes screwing. The screwing data detecting apparatus is generally designated by reference numeral 100 and comprises a framework 101 supporting a bush 102 having its upper surface with a portion 102a (see figure 15) with an identical shape as that of the plant which is to receive elements S, M which are being tested in apparatus 100. Portion 102a constitutes a projection with hexagonal cross-section corresponding to the hexagonal portion of plant I which prevents rotation thereof (see element 20 in figure 2) . On the hexagonal portion 102a there is inserted support S which carries the double Belleville spring 11 and support M. Screw 9 (see figure 15) is pre-screwed, so as to apply a light force on the above mentioned elements, within a cylindrical body 103 which is slidably mounted within bush 102 and is prevented to rotate therewithin by an end portion 103a thereof having a square cross-section corresponding to the cross-section of bush 102. Body 103 has a plate 105 at its lower end to which a load cell 106 is secured. When screwing of the screw 9 into element 3 is initiated by means of wrench 111, so as to generate a tension in this screw, the load cell 106 comes in contact with the tip of a dowel 107 and tras its a signal to the personal computer representing the force induced in the screw 9. At the same time, the wrench 111 trasmits the value of the applied torque. Any control of the rotation may take place simply by means of a position detector actuated by the movement of the electronic wrench 111 (figure 16), this detector been diagrammatically shown and designated by 104, or by using other suitable systems, such as reading the rotation angle of wrench 111 by means of an optical reader (not shown) .

Also in the case of apparatus 100, all data relating to force, torque, and necessary rotation angle, are transmitted to electronic processing means in order to provide the operator with an optical, acoustic and printed information about all the tightening data as experimentally detected. Obviously, these data are used by the operator during the actual mounting of the prothesis to the osteo-integrated plant, with the following further advantage. The operator, with the aid of the apparatus 100, is able to determine simultaneosly both the value of the tightening torque and the value of the force induced in the screw, during the whole tightening operation as simulated with apparatus 100. The processing means connected to the apparatus will be thus able to define a diagram of the type shown in figure 17, on the basis of which the relationship is determined between the applied tightening torque and the force consequently induced in the screw. This relationship cannot be calculated, since it varies case by case depending upon the friction forces between the walls which are in friction mutual contact during tightening. Once the above mentioned relationship has been determined with the aid of apparatus 100 with reference to the specific device which must be installed, the same device can then be mounted on the osteo-integrated element. The processing means will attend to calculating the value of the force induced in the screw as a function of the applied tightening torque, whose value will be signalled to the processing means by the same wrench which is used by the dentist to carry out the tightening operation. This processing means will thus be able to emit an acoustic and/or optical signal when a predetermined force is reached in this screw. In other words, on the basis of the diagram of figure 17, the dentist will be able to choose the value of the tightening torque to be applied for obtaining a desired force. Figure 17 shows both the line which is obtained experimentally, representing the force/torque relationship, and two further lines which are defined above and below the experimental line, by adding and subtracting, respectively, an error such as in the order of 10 %. Therefore, for each value of the tightening torque, the diagram provides a minimum and maximum value of the force correspondingly induced in the screw.

Figure 13 shows an alternative embodiment of the wrench, which in this case is generally designated by reference numeral 60, which can be used to tighten screw 9. Wrench 60 has one end 61 with a shaft having a cross-section corresponding to the cross-section of the socket 10a of the screw, for engaging this socket to actuate the screw. The rotation of the end portion of the wrench takes place by means of a free-wheel system or a ratchet-and-pawl system. At the other end, the wrench 60 has a hollow handle 62, inside which a rod 63 is slidably mounted which has one end pushing against a load cell 64. The latter outputs a signal on a cable 65, which is indicative of the force applied thereon (which is proportional to the tightening torque) . The opposite end of rod 63 is in engagement against an element 66 rigidly connected to the active end 61 of the wrench. Element 66 is articulated at an out-of axis point 67 to the body of the handle 62 and is subject to the action of a return spring 68. Due to the distance of pivot 67 from the axis, when the key is used to rotate screw 9, an oscillation of element 66 around pivot 67 is obtained which causes the rod 63 to push against the load cell 64. The load cell is thus able to output a signal proportional to the applied tightening torque.

Figure 9 shows a variant in which the auxiliary support has been eliminated. In the example illustrated in this figure, the first element I has a front socket 24 with hexagonal cross-section where a front hexagonal appendage 25 of support M is received. A variant of the screwing data detecting apparatus of figures 14, 15 is shown in figures 18, 19. In these figures, the parts common to figures 14, 15 are designated by the same reference numeral. The main difference of the apparatus shown in figures 18, 19 with respect to that of figures 14, 15 lies in that in this case the load cell 106 is located co-axially with screw 9 and element 103, thus ensuring a more balanced assembly. In the example illustrated with reference to figures 18, 19, to the lower end of the movable body 103 there is fixed by means of a screw 200 an elongated plate 201, whose ends are free to move within two slots 202, diametrically opposite to each other, formed on the upper edge of a bush 203, clamped within tubolar body 201 and resting on a further fixed bush 204. To plate 201 there is secured a U-shaped bracket 210, having a horizontal bracket 210a with a threaded through whole engaged by a screw 208, locked by a nut 209 and whose tip is in contact with cell 106. The latter is received within a seat 206 formed in the lower surface of an elongated plate 205, perpendicular to plate 201, having the ends received in slots 207 diametrically opposite to each other, formed in the upper edge 204. The ends of plate 205 are locked between the bottom of slots 207 and the lower edge of bush 203. Due to this arrangement, the cell 106 always remains in a fixed position relative to structure 101, whereas screw 208 moves rigidly with element 103 following screwing of the screw 9, thus applying the same force to this cell as that to which screw 9 is subjected due to its tightening. The apparatus 100 is also able to measure the torsion torque acting on screw 9. The rotation which will be transmitted by screw 9 to plate 201 is opposed by a rod 220 which is guided through hole 221 of structure 101 and acting against a load cell 222 carried by bracket 223. The personal computer can thus calculate the composite stress 7113

deriving from the axial force and the torque acting on the screw 9, so that it can take them into account for determining the tightening torque to be applied. The apparatus also comprises a potentiometric sensor 224 which signals the rotation of wrench 111.

It is clearly apparent that the principle at the basis of the invention is that of interposing means adapted to be deformed as a result of the tightening of the connection screw between the two elements of the connection which must come in contact with each other, so as to enable the operator to carry out the tightening operation in a precise and controlled manner, untill reaching a predetermined tightening force. Obviously, the above mentioned deformable means may be constituted by any type of spring means, also different from that illustrated with reference to the preferred embodiment of the invention, or also by means adapted to undergo a permanent deformation. For instance, it is possible to provide a plug-and-socket coupling between two parts of the connection by arranging an interference between these parts so as to give rise to an exstrusion deformation of the plug portion within the socket portion. Alternatively, any other type of mutual connection may be arranged which causes a permanent deformation of one or both the parts of the connection as a result of the tightening of the screw.

Furthermore, although in the case of the preferred embodiment the predetermined force corresponding to completion of the tightening operation is found experimentally, it is also possible, according to the invention, that this value of the force is determined by calculation.

Naturally, while the principle of the invention remains the same, the details of construction and the embodiments may widely vary with respect to what has been described and illustrated purely by way of example, without departing from the scope of the present invention.

Claims

1. Screw connection device for osteo-integrated plants comprising: a first element (I), or plant element, which is to be integrated within a bone tissue, said first element having an axial hole with a threaded portion (3b), a second element (M) , or support, for supporting a prothesis, said second element (M) being mounted on said first element (I) and having a through hole (10), a connecting screw (9), inserted with clearance through the through hole (10) of the second element (M) and screwed within the threaded portion (3b) of the hole of the first element, so as to hold the second element (M) in a final connected condition on said first element (I), characterised in that between the said second element (M) and said first element (I) there are interposed means (11) adapted to be deformed as a result of the tightening of the connecting screw (9) .

2. Screw connection device according to claim 1, characterised in that said deformable means (11) are elastically deformable.

3. Screw connection device according to claim 1, characterised in that said deformable means are permanently deformable.

4. Screw connection device according to claim 2, characterised in that said elastically deformable means are constituted by a spring element incorporating two Belleville washers with opposite cones in one piece, said spring element (11) being arranged co-axially to the connecting screw (9), between the second element (M) and the first element (I) .

5. Screw connection device according to claim 4, characterised in that said spring element in form of double Belleville washer is interposed between the second element (M) and an auxiliary support (S) resting on the first element (I) .

6. Screw connection device according to claim 5, characterised in that the first element (I) and said auxiliary support (S) have complementar portions (20, 23) mating with each other to prevent a relative rotation of said elements.

7. Screw connection device according to claim 5, characterised in that the second element (M) and the auxiliary support (S) have complementar portions (21, 22) mating with each other to prevent a relative rotation of said elements.

8. Screw connection device according to claim 4, characterised in that said double Belleville washer (11) is directly interposed between the second element (M) and the first element (I) .

9. Apparatus for installing a device according to any of the previous claims, characterised in that it comprises an electronic wrench (60) for tightening said device, provided with sensor means adapted to emit a signal indicative of the value of the tightening torque applied to the screw (9) during the tightening operation, said apparatus further comprising electronic processing means for processing said signal, and optical and/or acoustic signalling means connected for said processing means, so as to enable the operator to carry out the tightening operation in a precise and controlled manner, untill reaching a predetermined tightening force.

10. Apparatus for installing a device according to claim 9, characterised in that said electronic wrench (70) is provided also with sensor means (77, 78) for sensing the rotation angle imparted to the wrench.

11. Apparatus for installing a device according to claim 9, characterised in that said processing means are constituted by a personal computer.

12. Apparatus for installing a device according to any of claims 1 - 8, characterised in that it comprises a dynamometric press (50) which can be used to predetermine the force necessary to deform said spring element (11) untill reaching full contact between the two elements (I, M) of the connection, said press comprising a support adapted to receive a specimen (P) constituted by parts of the device which are to be installed on the plant element, and screw compression means (51, 52), adapted to apply a pressure on the specimen (P) with the interposition of a load cell (54) which is adapted to output a signal indicative of the axial force applied on the specimen (P) , said press (50) further comprising means for sensing the rotation angle of the screw compression means.

13. Apparatus for installing a device according to any other of claims 1 -8, characterised it comprises a screwing data detection device (100) which can be used to predetermine the tightening torque which is necessary to deform said spring elements (11) untill reaching full contact between the two elements (I, M) of the connection, as well as the corresponding tightening force induced in the screw, said data detection device comprising: a fixed support (102, 102a) adapted to receive and hold against rotation a specimen constituted by the parts of the device which are to be installed on the plant element (I), said fixed support (102, 102a) fulfilling the function of the plant element, a body (103) slidably guided relative to said support (102), having a threaded hole engaged by the screw (9) of the specimen, an electronic wrench for operating the screw (9), provided with sensor means for sensing the applied tightening torque, feeler means (107) in contact with said slidable body (103) and subjected to an axial force imparted by said slidable body as a result of the screwing of the screw (9) therewithin, a load cell interposed between said slidable body (103) and said feeler means (107) to detect the tightening axial force, and processing means connected to said electronic key and said load cell (106) .

14. Apparatus according to claim 13, characterised in that it further comprises means (201, 220, 222) for measuring the torque acting on the screw (9) .

15. Method for tightening a screw connection, which can be used particularly in an osteo-integrated plant of the type comprising a first element, or plant element (I) , which is to be integrated within a bone tissue, said first element having an axial hole with a threaded portion (3b), a second element or support (M) , for supporting a prothesis, said second element (M) being mounted on said first element (I) and having a through hole (10), a connection screw (9), inserted with clearance through the through hole (10) of the second element (M) and screwed within the threaded portion (3b) of the hole of the plant element, so as to hold the second element (M) in a final connected condition on said plant element (I), said method being characterised in that between said second element (M) and said plant element (I) there are interposed means (11) adapted to be deformed as a result of the screwing of the connection screw, and in that said screw is tightened while continuously measuring the applied tightening torque and then the 3

axial force deriving therefrom, and finally in that the tightening operation is interrupted when a predetermined value of the force is reached.

16. Method according to claim 15, characterised said predetermined value is found experimentally, with the aid of a dynamometric press (50) , by locating the value of the axial force which causes a deformation of said deformable means (11) up to reaching the full contact condition between the two elements (I, M) of the connection.

17. Method according to claim 15, characterised in that before installing the device, the parts of the device which are to be mounted on the plant element are located on a support fulfilling the function of the plant element and forming part of a screwing data detection device (100) which simulates the tightening of the connection device, by continouosly measuring the variation both of the applied tightening torque and the tightening force induced on the screw during the tightening operation.

18. Operation according to claim 15, characterised in that installation of the connection device and the tightening thereof are carried out with the aid of electronic processing means connected to means for optically and/or acoustically signalling the reaching of a predetermined tightening condition.

The whole substantially as described and illustrated and for the specified objects.