DENTAL SCREW AND DENTAL FASTENING TOOL

Abstract

The present disclosure provides a dental screw (10) for fixing dental components (1, 2) to each other, the dental screw having a proximal end (11), a distal end (12), and a longitudinal axis (LS), wherein the dental screw further comprises a screw head (13) including a tool engaging interface (20) for engaging a fastening tool (30) at the proximal end and distally to the screw head a screw shank (14), the screw shank comprising a torque limiting portion (15) and distally to the torque limiting portion a threaded portion (16) for engaging a dental component (1, 2, 3), wherein the dental screw is configured to transfer a minimum torque from the tool engaging interface to the threaded portion of 26 Ncm and the torque limiting portion is configured to limit the torque transferable to a maximum torque for preventing damage to the threaded portion. The disclosure also provides a dental fastening tool, a dental fastening set, and a dental support set.

Claims

1. A dental screw for fixing dental components to each other, the dental screw having a proximal end, a distal end, and a longitudinal axis, the dental screw comprising: a screw head including a tool engaging interface for engaging a fastening tool at the proximal end and a screw shank disposed distal to the screw head; a torque limiting portion; and a threaded portion disposed distal to the torque limiting portion for engaging a dental component, wherein the threaded portion is disposed distal to the torque limiting portion, and wherein the dental screw is configured to transfer a minimum torque of 26 Ncm and the torque limiting portion is configured to limit the torque transferable to a maximum torque for preventing damage to the threaded portion.

2. The dental screw of claim 1, wherein the torque limiting portion has the smallest section modulus along the shank.

3. The dental screw of claim 1, wherein the maximum torque transferable at the torque limiting portion is 38 Ncm, 36 Ncm, 34 Ncm, or 32 Ncm.

4. The dental screw of claim 1, wherein the torque limiting portion is configured to withstand a maximum tensile force in a range of 300 N to 500 N.

5. The dental screw of claim 1, wherein the tool engaging interface includes a torque transfer zone having a cross-section perpendicular to the longitudinal axis comprising a profile with at least one of four or five convex and planar sections alternating with four or five concave sections, respectively.

6. The dental screw of claim 5, wherein the convex sections and concave sections form longitudinal engagement protrusions (24) radially extending from a circle with a maximum inner diameter towards the longitudinal axis, the engagement protrusions having chamfers at their proximal ends.

7. The dental screw of claim 1, wherein the tool engaging interface includes a pick-up zone that tapers in a direction from the proximal end to the distal end of the dental screw, the pick-up zone being located adjacent, at least one of proximally to, and at least partially along the torque transfer zone.

8. The dental screw of claim 1, wherein the tool engaging interface further includes a verification zone for verifying the type of the dental screw, the verification zone being located at the distal end of the tool engaging interface.

9. A dental fastening tool, the dental fastening tool having a proximal end, a distal end, and a longitudinal axis, the dental fastening tool comprising a screw engaging interface at the distal end for engaging a dental screw, the dental screw comprising: a screw head including a tool engaging interface for engaging a fastening tool at the proximal end and a screw shank disposed distal to the screw head; a torque limiting portion; and a threaded portion for engaging a dental component, wherein the threaded portion is disposed distal to the torque limiting portion, wherein the torque limiting portion is configured to limit the torque transferable to a maximum torque for preventing damage to the screw engaging interface, and wherein the torque limiting portion is disposed proximal to the screw engaging interface.

10. The dental fastening tool of claim 9, wherein the torque limiting portion is configured to bear a maximum torque of 35 Ncm or less.

11. The dental fastening tool of claim 9, wherein the screw engaging interface includes a torque transfer zone with a cross-section perpendicular to the longitudinal axis comprising at least one of four or five convex and planar sections alternating with four or five concave sections, respectively, and at least one of the convex and planar sections and concave sections form an engagement structure about the longitudinal axis along the dental fastening tool, the engagement structure having a curved profile in a cross-section along the longitudinal axis.

12. The dental fastening tool of claim 11, wherein at least one of the convex and planar sections and concave sections are connected at points of transition, and at each point of transition an angle between a tangent to the profile of the concave section and a tangent to the convex section or the planar section is in a range of 90° to 180°.

13. The dental fastening tool of claim 9, wherein the screw engaging interface includes a pick-up zone for holding a dental screw, the pick-up zone being located adjacent, at least one of proximally to, and at least partially along the torque transfer zone.

14. The dental fastening tool of claim 9, wherein the screw engaging interface further includes a verification zone for verifying the type of a dental screw when engaging said dental screw, the verification zone being located at the distal end of the tool engaging interface.

15. A dental fastening set comprising: a dental screw comprising: a screw head including a tool engaging interface for engaging a fastening tool at the proximal end and a screw shank disposed distal to the screw head a torque limiting portion; and a threaded portion for engaging a dental component, wherein the threaded portion is disposed distal to the torque limiting portion; and a dental fastening tool, having a proximal end, a distal end, and a longitudinal axis, wherein the dental fastening tool comprises a screw engaging interface at the distal end for engaging the dental screw,  wherein the dental screw and the dental fastening tool each comprise a torque limiting portion, wherein the torque limiting portion of the dental screw is configured to bear a maximum torque that is higher than the maximum torque that is transferable by the torque limiting portion of the dental fastening tool.

16. The dental fastening set of claim 15, the dental screw comprising a tool engaging interface, wherein the tool engaging interface includes a torque transfer zone with a cross-section comprising at least one of convex and planar sections alternating with concave sections; and the dental fastening tool comprising a screw engaging interface, wherein the screw engaging interface includes a torque transfer zone with a cross-section comprising at least one of convex and planar sections alternating with concave sections, wherein in an engaged state of the dental screw and the dental fastening tool for transferring torque, at least an intermediate section of each of at least one of the convex and planar sections of the dental screw faces a profile of a concave section of the tool engaging interface at a distance.

17. The dental fastening set of claim 15, wherein the torque transfer zone of the dental screw and the torque transfer zone of the dental fastening tool have a rotational play when being engaged with each other, in particular a play in a range of 1° to 3.5°.

18. The dental fastening set of claim 15, wherein the dental screw and the dental fastening tool each comprise a pick-up zone configured to engage each other by friction.

19. The dental fastening set of claim 15, wherein the dental screw and the dental fastening tool each comprise a verification zone configured to allow engagement of the torque transfer zone (45b) of the dental fastening tool and the torque transfer zone of the dental screw when the dental fastening set is fully engaged.

20. A dental restoration support set comprising a dental screw according to claim 1, and a dental component, wherein the dental component is at least one of a dental implant, an abutment, and an artificial tooth.

21. The dental fastening tool of claim 9, wherein the dental screw is configured to transfer a minimum torque of 26 Ncm and the torque limiting portion is configured to limit the torque transferable to a maximum torque for preventing damage to the threaded portion.

22. The dental fastening set of claim 15, wherein the dental screw is configured to transfer a minimum torque of 26 Ncm and the torque limiting portion is configured to limit the torque transferable to a maximum torque for preventing damage to the threaded portion.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0082] The following figures illustrate preferred embodiments of the present invention. These embodiments are not to be construed as limiting but merely for enhancing the understanding of the invention in context with the following description. In these figures, same reference signs refer to features throughout the drawings that have the same or an equivalent function and/or structure. A repetitive description of these features is generally omitted for a concise description.

[0083] FIG. 1 is a cross-sectional view along the longitudinal axis of a dental screw and in particular of a tool engaging interface of the dental screw;

[0084] FIG. 2 is a plan view of the tool engaging interface of the dental screw illustrated in FIG. 1;

[0085] FIGS. 3a and 3b are cross-sectional views perpendicular to the longitudinal axis of the dental screw shown in FIGS. 1 and 2 illustrating the tool engaging interface in engagement with a screw engaging interface of a dental fastening tool;

[0086] FIG. 4 is a partial side view of the dental fastening tool shown in FIGS. 3a and 3b;

[0087] FIG. 5 is a cross-sectional view perpendicular to the longitudinal axis of the dental fastening tool shown in FIGS. 3 and 4 at the level of a torque transmission section of the fastening tool;

[0088] FIGS. 6a and 6b are cross-sectional views along the longitudinal axes of the dental screws at the level of the tool engaging interface and in engagement with a dental fastening tool;

[0089] FIG. 7 is a three-dimensional view of a dental screw according to another embodiment;

[0090] FIG. 8 is a three-dimensional view of a dental fastening tool according to another embodiment for fastening the dental screw shown in FIG. 7;

[0091] FIG. 9 is a detailed view of the screw engaging interface of the dental fastening tool of FIG. 8;

[0092] FIGS. 10a and 10b illustrate the functionality of the screw engaging interface's verification zone;

[0093] FIG. 11 is a side view of another embodiment of a screw engaging interface of a dental fastening tool;

[0094] FIG. 12 is a frontal view of the screw engaging interface of the dental fastening tool shown in FIG. 11;

[0095] FIG. 13 is a schematic cross-sectional view of a threaded engagement between a dental screw and a dental implant; and

[0096] FIG. 14 is a cross-sectional view along the longitudinal axes of a dental screw, an abutment, and an implant in engagement according to yet another embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0097] FIG. 1 shows a cross-sectional view along the longitudinal axis LS of a dental screw 10 according to an embodiment. In the following, a cross-section along a longitudinal axis is also referred to as a longitudinal cross-section. The longitudinal cross-section of the dental screw 10 in FIG. 1 shows the screw head 13 and a part of the screw shank 14. The screw head 13 comprises a tool engaging interface 20. As shown in FIG. 1, the tool engaging interface 20 is preferably formed as a recess.

[0098] For transferring torque, the tool engaging interface 20 comprises an engagement structure. This engagement structure includes convex sections 21 and concave sections 22. The convex sections 21 alternate with the concave sections 22. There is an equal number of convex sections 21 and concave sections 22. As illustrated, these sections are arranged on an inner circumferential wall of the tool engaging interface 20 and form a torque transfer zone 25b.

[0099] The tool engaging interface 20 of the exemplary embodiment of a dental screw in FIG. 2 comprises five convex sections and five concave sections 22. As seen in a cross-section perpendicular to the longitudinal axis LS of the dental screw (also referred to in the following as a perpendicular cross-section), the convex sections 21 and concave sections 22 form longitudinal engagement protrusions 24 extending from a circle 26. This circle is defined by the maximum inner diameter of the tool engaging interface 20. In case of a tapered tool engaging interface 20 as further described below, the diameter of the circle 26 decreases from the proximal end to the distal end of the dental screw 10.

[0100] In order to achieve a compact yet durable design for the dental screw 10, it has been found to be advantageous to provide the tool engaging interface 20 with four or five concave and convex sections each. Preferably, the screw engaging interface of a dental fastening tool comprises numbers of concave and convex sections that corresponds to the numbers of the concave and convex sections of a dental screw to be engaged.

[0101] As will be described in more detail below, five sections of each of the convex and concave sections is preferred for a fastening tool that allows an efficient and an angular application of torque (i. e. an application of torque via an angle).

[0102] A number of four sections of each of the concave and convex sections has been found to be particularly advantageous for a combination of a dental screw and a fastening tool whose longitudinal axes are aligned during the application of torque. In such an embodiment, the geometry of the engagement structures results in a very precise engagement and efficient torque transfer.

[0103] In the exemplary embodiments of dental screws and fastening tools shown in the figures, the concave sections 22 and the convex sections 21 have a curved profile. Nonetheless and as previously described, the convex sections 21 may also be planar. The concave sections 22 and convex sections 21 form an engagement structure. Along the profile of the engagement structure in a perpendicular cross-section, the concave sections 22 and the convex sections 21 are connected at points of transition 23. In the embodiment of FIG. 2, the transition between the concave sections 22 and the convex sections 21 is continuous.

[0104] However and as described above, the transition between these sections may instead be a discontinuous transition. An example of a discontinuous transition along a profile of the engagement structure is shown in FIG. 5 for a fastening tool 30. Here, a point of transition 43 of a screw engaging interface 40 of the fastening tool 30 is discontinuous in terms of a change in slope. Due to this discontinuity, the point of transition 43 represents a corner along the profile of the screw engaging interface 40 as seen in a perpendicular cross-section in relation to the longitudinal axis LT of the dental fastening tool 30. In the engagement structure 44, this point of transition 43 of the profile results in a longitudinal edge (cf. FIG. 4).

[0105] At the point of transition 23, the transfer of torque from a fastening tool 30 to the dental screw 10 is most effective. The tangent to the profile of the tool engaging interface 20 at this point of transition 23 extends in a direction closest to a radial direction. As a result, a torque applied by means of a fastening tool results at this point along the engagement profile in the maximum force component perpendicular to the surface of the tool engaging interface 20 and the minimum force component parallel to this surface. Consequently, torque transfer is very efficient at this point between a dental fastening tool and the dental screw 10, whereas the amount of wear is relatively low. Thus, it is advantageous to transfer torque between a fastening tool and the dental screw 10 at and near the point of transition 23.

[0106] A dental fastening tool 30 for transferring torque to a dental screw 10 comprises an engagement structure 44 that corresponds to the engagement structure 24. FIG. 5 shows an exemplary embodiment of such a dental fastening tool 30 with an engagement structure 44 in a perpendicular cross-section in relation to a longitudinal axis LT of this tool. The engagement structure 44 of the dental fastening tool 30 is part of a torque transfer zone 45b (cf. FIG. 4). Corresponding to the dental screw 10, the cross-sectional profile of the engagement structure 44 comprises convex sections 41 and concave sections 42. The convex sections 41 and the concave sections 42 merge or transition into each other at points of transition 43. Like the points of transition 23 of the torque transfer zone 25b of the dental screw 10, the point of transition 43 may be continuous or discontinuous points of transition 43. As already explained above, the point of transition 43 of the dental fasting tool illustrated in FIG. 5 is a discontinuous point of transition.

[0107] Further, the concave section 42 is preferably curved. The convex section 41 may be curved and/or planer. In the exemplary embodiment illustrated in FIG. 5, the convex section 41 is curved and, more specifically, has a circular shape.

[0108] As described above, the angle at the point of transition 43 between a tangent to the convex section 41 and a tangent to the concave section 42 is preferably in a range of 90° to 180° or to 160°, preferably 95° to 150°. The closer this angle is to 90°, the more efficient is the torque transfer from the dental fastening tool 30 to the dental screw 10 at the point of transition 43. At 90°, the transfer of torque is basically performed in a circumferential direction. There is basically no force component acting in a direction parallel to the surface of the engagement structure 44 (which extends radially) and, as a result, wear of this surface caused by torque transfer can basically be prevented. For example, the dental fastening tools 130, 230 shown in FIGS. 8 to 11 are designed for such an efficient torque transfer.

[0109] FIG. 3 show a dental fastening tool 30 that has been inserted into a dental screw 10 (see FIG. 3a). The dental fastening tool 30 is then rotated about its longitudinal axis LT so that the engagement structure 44 of the dental fastening tool 30 is brought into engagement with the engagement structure 24 of the dental screw 10 (see FIG. 3b). As described above, this rotational play provides haptic feedback to a dental professional and facilitates insertion of the screw engaging interface 40 of the fastening tool 30 into the tool engaging interface 20 of the dental screw 10. The rotation of the screw engaging interface 40 within the tool engaging interface 20 about the aligned longitudinal axes LT and LS from the intermediate position in FIG. 3a to the engagement position in FIG. 3b is about 0.5 times β. As described above, the rotational play β between rotational engagement orientations, i. e. an engagement orientation for fastening and an engagement orientation for loosening is preferably 1° to 3.5° and preferably 1.5° to 3°.

[0110] Once in engagement, torque is transferred across the concave section 42 of the dental fastening tool 30 to the convex section 21 of the dental screw 10. This is schematically indicated in FIG. 3b by means of thick black lines. More specifically, torque is transferred along the profiles of the engagement structures 24, 44 between the transition points 23, 43 to intermediate positions, preferably the middle position, along the concave sections 42 of the fastening tool 30 and the convex sections 21 of the dental screw 10. In other words, there is essentially no transfer of torque along the profile in the region of the convex sections 41 of the fasting tool 30 and the convex sections 21 of the dental screw 10. This is due to a gap being present between the convex sections 41 and the concave sections 22 facing each other while being engaged state. As a result, no wear is caused in this area. Further, torque is provided in an efficient way at the transition point and its vicinity. Transfer of torque also takes place in an area further away from the outer wall of the dental screw 10, i. e. in an area with a higher wall thickness. Due to this and the torque transfer along the curved concave section 42 and the correspondingly curved convex section 21, stress concentrations are avoided. Consequently, these features also enable a more compact design of the dental screw.

[0111] FIG. 4 illustrates a partial view of a dental fastening tool 30 in a longitudinal cross-section. The dental fastening tool 30 is also illustrated in the longitudinal cross-section in FIG. 6 referred to further below. As illustrated in FIG. 4, the torque transfer zone 45b of the screw engaging interface 40 is curved. More specifically, it is in particular at least partly a basically circular profile. Further, at the distal end 32, the dental fastening tool 30 preferably has a rounded tip 33. This geometric configuration allows to tilt the dental fastening tool 30 while transferring torque from the dental fastening tool 30 via the screw engaging interface 40 to the tool engaging interface 20 of the dental screw 10. This is, for example, illustrated in FIG. 6, where the longitudinal axis LS of the dental screw is inclined in relation to the longitudinal axis LT of the fastening tool 30. Further, above-described curved and rounded configuration of the screw engaging interface 40 prevents damage or scratches to the surface of the engagement structure 24, which may otherwise reduce the strength of the dental screw 10. Similar to the dental screw 10, the torque transfer zone 45b also acts as pick-up zone 45a as will be described in more detail further below.

[0112] The dental fastening tool of FIG. 4 also comprises proximally to the screw engaging interface 40 a torque limiting portion 35. Preferably, a shank 36 is arranged between the screw engaging interface 40 and the torque limiting portion 35 so that the dental fastening tool 30 does not break within the tool engaging interface 20 of the dental screw 10 during failure. This facilitates removal of the part of the dental fastening tool 30 comprising a portion that remains inside the tool engaging interface 20.

[0113] As already described above, the torque limiting portion 35 is configured to fail if a torque applied exceeds a predefined maximum value. Preferably, the torque limiting portion is configured to bear a maximum torque of 35 Ncm or less, and preferably in a range of 27.5 Ncm to 34 Ncm and more preferably in a range of 28 Ncm to 33 Ncm.

[0114] As illustrated in FIG. 4, the torque limiting portion 35 may be designed with a reduced cross-section so that the strength at this cross-section is reduced. In other words, the torque limiting portion 35 has the lowest section modules along the dental fastening tool 30. Consequently, the torque limiting portion 35 has a section modulus that is lower than the section modulus of the waisted portion adjacent to the screw engaging interface 40 and the shank 36.

[0115] As illustrated in FIG. 1, the convex sections 21 of the tool engaging interface 20 that form the tip of the longitudinal engagement protrusions 24 are chamfered at their proximal ends, i.e. at the entrance for the dental fastening tool to the tool engaging interface 20. The resulting chamfers 27 facilitate insertion of a dental fasting tool. On the one hand, they allow an initial insertion of a dental fastening tool without the engagement structure 44 of the dental fastening tool 30 being correctly aligned with the engagement structure 24 of the dental screw 10 in a rotational direction. On the other hand, the longitudinal axis LS of the dental screw 10 may initially have too much inclination in relation to the longitudinal axis LT of the fastening tool 30. Here, the chamfers 27 have a guiding function.

[0116] Further, the dental screw 10 in FIG. 1 comprises a tapered tool engaging interface 20. More specifically, the tool engaging interface 20 becomes narrower in a direction from the proximal end 11 to the distal end of the dental screw 10. In other words, the tool engaging interface 20 may have a substantially conical shape. Due to the tapered shape, the tool engaging interface 20 forms a pick-up zone 25a for picking-up and retaining a dental screw. In this exemplary embodiment of a dental screw and as illustrated in FIGS. 1, 2, and 6, the pick-up zone 25a and the torque transfer zone 25b overlap each other.

[0117] The pick-up function will be explained in the following in more detail under reference to FIG. 6. As illustrated in FIG. 6a, a fastening tool 30 may engage the dental screw 10 by friction when the fastening tool 30 is inserted along the longitudinal axis LS into the recess of the tool engaging interface 20. Since the tool engaging interface 20 is tapered, the friction caused due to insertion of the fastening tool 30 enables the pickup function. More specifically, the dental screw 10 can be retained by the fastening tool 30.

[0118] As described above, the angle of the taper is preferably chosen in a range of 5° to 12°, in particular 6° to 9°, or may be substantially 7°. Alternatively, it may be in a range of 10° to 12°, or may be substantially 11°. These values allow to safely retain a dental screw and at the same time allow the connection between a fastening tool 30 and the dental screw 10 to be easily releasable. Thus, these angles also prevent unnecessary wear from occurring.

[0119] Besides the pick-up function, the taper of the tool engaging interface 20 also ensures optimum engagement between the engagement structures of the dental fastening tool 30 and the dental screw 10. This is schematically shown in FIGS. 6a and 6b. In FIG. 6a, the dental fastening tool 30 has its initial size, i.e. it has not been subject to wear. As a result, engagement between the dental fastening tool 30 or more specifically the screw engaging interface 40 occurs on the proximal side of the tool engaging interface 20 of the dental screw 10.

[0120] Preferably, the dental fastening tool 30 is configured to be reusable and is preferably made of metal, in particular steel. As a result, wear occurs during continued use and reuse of this tool. Wear occurring at the engagement structure 44 of the dental fastening tool 30 results in a decrease of the size of this structure. However, since the tool engaging interface of the dental screw 10 is tapered, the dental fastening tool 30 will simply be pushed further into the tool engaging interface 20. This achieves the same quality of engagement, which ensures an efficient transfer of torque. This is shown in FIG. 6b, where the dental fastening tool 30 that has been subject to wear is now engaging the tool engaging interface 20 of the dental screw 10 more distally.

[0121] FIG. 7 illustrates another embodiment of a dental screw 110. As illustrated in FIG. 7, the dental screw 110 comprises a torque limiting portion 115 that is directly adjacent to the screw head 113. The skilled person will appreciate that such a torque limiting portion 115 may also be present along the screw shank 14 in the embodiment of a dental screw 10 illustrated in FIG. 1, either at the same position or at a different position along the screw shank 14.

[0122] Similar to the torque limiting portion 35 described in relation to the dental fastening tool 30, the torque limiting portion 115 has the smallest section modulus along the part of the body of the dental screw 110 that transfers torque, i.e. the part of the body that is subject to increasing shear stresses and tensile stresses during fastening of the dental screw 110.

[0123] The torque limiting portion 115 is part of and arranged along the screw shank 114. At the end of the screw shank 114, i. e. at the distal end 112 of the dental screw 110, is a threaded portion 116. The threaded portion 116 is for engaging a dental component such as a dental implant 401 or an abutment 402 (cf. FIG. 14). For example, the dental screw 110 may be used to attach an abutment 402 to a dental implant 401.

[0124] As already defined above, the minimum torque that the torque limiting portion 115 of the dental screw 110 should withstand and transfer is preferably 26 Ncm. When exceeding the maximum torque value, the torque limiting portion 115 should particularly prevent failure of any part of the dental screw 110 distally of the torque limiting portion 115, in particular a failure of the threaded portion 116. Controlling the failure of the dental screw in this manner ensures that the dental component, which is in engagement with the dental screw 110, remains intact. This is particularly advantageous in case of the dental component been a dental implant that is anchored within the bone tissue of a patient since a revision of the implant is prevented.

[0125] FIG. 8 illustrates another embodiment of a dental fastening tool 130. The screw engaging interface 140 at the distal end 132 of the dental fastening tool 130 also comprises convex sections 141 and concave sections 142, which form a circumferential engagement structure 144. The dental fastening tool 130 is configured for a dental screw preferably comprising an engagement structure with a corresponding number of convex and concave sections. As described above, the convex sections may also be at least partially planar.

[0126] Nonetheless, the dental fastening tool 130 particularly differs from the dental fastening tool 30 of the previous figures in terms of the screw engaging interface 140. In particular, the screw engaging interface comprises four of each of the convex and concave sections instead of five.

[0127] Turning to FIG. 9, the screw engaging interface 140 of the dental fastening tool 130 also differs in relation to the previous embodiments in that the pick-up zone 145a is separate from the torque transfer zone 145b. More specifically, the torque transfer zone 145b is located adjacent and distally to the pick-up zone 145a. In other words, the pick-up zone 145a does not overlap with the torque transfer zone 145b. The pick-up zone 145a basically has a conical shape for engagement with a corresponding pick-up zone of a dental screw by friction to facilitate handling of a dental screw as has already been described above.

[0128] Although the torque transfer zone 145b of the dental fastening tool 130 of FIG. 9 has a concave shape similar to the pick-up zone 145a, it may alternatively have a cylindrical form as shown in another embodiment of a dental fastening tool 230 illustrated in FIGS. 11 and 12 and described further down below.

[0129] In addition to the pick-up zone 145a and the torque transfer zone 145b, the dental fastening tool 130 comprises adjacent to its distal end 132 a verification zone 145c. On the one hand, this verification zone 145c has the function to prevent engagement with the tool engaging interface 120b of a dental screw 110b that does not comprise a verification zone with a corresponding shape (cf. FIG. 10b). Further, a dental screw 110b without a corresponding verification zone may also prevent engagement of a pick-up zone 145a since it will not be possible to insert the dental fastening tool 130 far enough into the tool engagement interface of this dental screw 110b for bringing these zones into engagement.

[0130] On the other hand, if a dental screw 110a comprises a corresponding verification zone such as the dental screw 110a in FIG. 10a, the dental fastening tool 130 is able to engage the tool engaging interface 120a of this screw.

[0131] FIGS. 11 and 12 illustrate yet another embodiment of a dental fastening tool 230 with a screw engagement interface 240 similar to the screw engaging interface 140 of the previous embodiment. However, in difference to the previous embodiment, the dental fastening tool 230 does not comprise a verification zone. Instead, the screw engaging interface 240 may only comprise a pick-up zone 245a and a torque transfer zone 245b. Although in the embodiment of a dental fastening tool 230 shown in FIG. 11 and in the embodiment of a dental fastening tool 130 shown in FIG. 10 the torque transfer zones 145b, 245b are located adjacent and distally to the pickup zones 145a and 245a, the skilled person will appreciate that this sequence may well be reversed. Thus, the pick-up zones 145a, 245a may be located distally to the torque transfer zones 145b, 245b. Further, the pick-up zones 145a, 245a and the torque transfer zones 145b, 245b do not have to be adjacent to each other but may be spaced apart from each other.

[0132] For a cost-efficient production, the concave sections 242 are machined in a proximal direction beyond the screw engaging interface 240. As a result, the pick-up zone 245a basically has a conical shape that is interrupted by concave sections. However, this is functionally not necessary although it may provide a more defined friction between the pick-up zone 245a and a corresponding dental screw. The same applies to the dental fastening tools of the previous embodiments.

[0133] FIG. 12 illustrates a frontal view of the dental fastening tool 230 as seen from the distal end 232. As illustrated in this figure, the screw engaging interface 240 comprises four convex sections 241 alternating with four concave sections 242. As already noted in relation to the previous embodiments, the convex sections 241 may instead be planar sections. In this exemplary embodiment, the convex sections 241 are curved and have in particular a circular shape as seen in a perpendicular cross-section in relation to the longitudinal tool axis LT.

[0134] As shown by way of example in FIG. 12, the angle α between a tangent to the convex sections and a tangent to the concave sections is at least close to the optimal angle of approximately 90° for transfer as explained above. In other words, the angle α is in above-noted lower range. Thus, the configuration of the torque transfer zone 245b of the screw engaging interface 240 provides for an efficient transfer of torque and is less prone to wear during continued use and reuse. For keeping wear of the dental fastening tools of this disclosure low, at least the screw engaging interfaces and preferably the fastening tool is made of metal, in particular steel.

[0135] In difference to the dental fastening tool 30 of the previous figures, the screw engaging interface 240 is only engageable with the tool engaging interface of a dental screw if the longitudinal tool axis LT and the longitudinal axis are basically in alignment. As described above, this alignment may be facilitated by providing chamfers at the entrance to the tool engaging interface of a dental screw.

[0136] FIG. 13 is a schematic longitudinal cross-section of a threaded engagement between a dental component, in particular a dental implant 301, and a dental screw 310. Naturally, this configuration is applicable for any combination of a dental component and a dental screw.

[0137] In a tightened state, a distal flank 303 of the dental implant's thread is in tight contact with a proximal flank 318 of the dental screws threaded portion 316. Thus, the force provided by tightening the dental screw 310 to fasten another dental component to the dental implant 301 is transferred as contact force between the thread flanks 303 and 318.

[0138] In the configuration of this disclosure, the threaded hole of the implant 301 and the outer thread of the dental screw 310 are dimensioned so that the overlap of the dental flanks, indicated in FIG. 13 as black continuous lines, is at least 70% of the length of each of the thread flanks in a radial direction. The length of the thread flanks in a radial direction is defined as the length between the tip of a thread and its root that allows for transfer of forces in a longitudinal direction of the threaded screw shaft of the dental screw or threaded hole of the dental component. For comparison, normal threads such as threads according to the ISO-standard only have an overlap of at least 60%.

[0139] Further, the overlap of the threaded connection according to this embodiment is up to 90%, 93%, and preferably 96%. Nonetheless, it is particularly the difference in minimum overlap of 10% in comparison to ISO-threads that allows for a significantly improved strength of the thread. This result enables a more compact design of the dental screw 310 since the transfer of compressive forces within this threaded connection is more effective.

[0140] FIG. 14 shows a partial cross-sectional view in a longitudinal direction along the longitudinal screw axis LS. It illustrates an abutment 402 that is fastened to a dental implant 401 via a dental screw 410. As described above, the torque limiting portion of a dental screw according to the present disclosure is dimensioned to transfer at least a minimum amount of torque. Further, the dental screw is configured for a controlled failure at torque values that exceed a maximum torque value.

[0141] When fastening the dental screw 410 of FIG. 14 to the dental implant 401, a support surface 417 of the screw head 413 at the distal end of the screw head 113 is pressed against a screw seat 404 of the dental abutment 402. As a result of the contact established between the support surface 417 and the screw seat 404, a part of the torque transferred from a dental fastening tool (not shown) via the tool engaging interface 420 of the dental screw 410 is transferred to the abutment 402.

[0142] As also shown in FIG. 14, the screw seat 404 and the support surface 417 have a conical shape. The conical shape of the screw seat 404 and the conical shape of the support surface 417 have cone angles that differ from each other. Preferably, the cone angle of the support surface 417 is larger than the cone angle of the screw seat 404. However, a configuration, in which the cone angles are dimensioned vice versa is alternatively possible. The difference between the cone angles of the support surface 417 and the screw seat 404 is indicated as γ in FIG. 14.

[0143] Due to this angle γ, a contact between the support surface 417 and the screw seat 404 is essentially established by a line contact. This is on the one hand advantageous since such a line contact causes less torque to be transferred from the dental screw 410 to the abutment 402. On the other hand, the torque transferred and not used to tighten the threaded connections can be more accurately determined. Both advantages allow for a more predictable behavior of a torque limiting portion of the dental screw 410. In other words, this configuration renders the failure of the dental screw 410 at the torque limiting portion more reliable and, thus, may contribute to a more compact design of the dental screw 410.

[0144] As previously described, the gap created due to the difference γ between the cone angles may at least partially be closed at the end of fastening process of the dental screw 410. This closure of the gap is caused by deformation of the screw seat 404 and the support surface 417 and further decreases the amount of torque that is transferred towards the threaded portion of the dental screw 410 in relation to the amount of torque that is transferred to the abutment 402. This change in transfer ratio has a dampening effect during the application of torque and enables a more precise adjustment of the maximum torque at the end of fastening the threaded connection between the dental screw 410 and the dental implant 401. Thus, these features of the screw seat 404 and the support surface 417 and their configuration in a dental assembly also enable a more compact design for the dental screw 410.

REFERENCE SIGNS

[0145] The following lists the last two digits of the reference signs used in the description and the drawings. Throughout the drawings these digits refer to features that have the same or an equivalent function and/or structure. The preceding digit represents the embodiment. [0146] 1 dental implant [0147] 2 abutment [0148] 3 flank of threaded hole [0149] 4 screw seat [0150] 10 dental screw [0151] 11 proximal end [0152] 12 distal end [0153] 13 screw head [0154] 14 screw shank [0155] 15 torque limiting portion [0156] 16 threaded portion [0157] 17 support surface [0158] 18 flank of threaded portion [0159] 20 tool engaging interface [0160] 21 convex section [0161] 22 concave section [0162] 23 point of transition [0163] 24 engagement structure of dental screw [0164] 25a pick-up zone [0165] 25b torque transfer zone [0166] 25c verification zone [0167] 26 circle with maximum inner diameter [0168] 27 chamfer [0169] 30 fastening tool [0170] 31 proximal end [0171] 32 distal end [0172] 33 rounded tip [0173] 35 torque limiting portion [0174] 36 shank [0175] 40 screw engaging interface [0176] 41 convex section [0177] 42 concave section [0178] 44 engagement structure of fastening tool [0179] 45a pick-up zone [0180] 45b torque transfer zone [0181] 45c verification zone [0182] LS longitudinal axis of screw [0183] LT longitudinal axis of fastening tool [0184] α angle at point of transition between tangent to convex section and tangent to concave section [0185] β rotational play between dental screw and fastening tool [0186] γ difference in cone angle between screw seat and support surface of screw head