WO2011080104A1

WO2011080104A1 - Flexible dental screwdriver and method of manufacturing the same

Info

Publication number: WO2011080104A1
Application number: PCT/EP2010/069933
Authority: WO
Inventors: Stéphane Courvoisier
Original assignee: Straumann Holding Ag
Priority date: 2009-12-29
Filing date: 2010-12-16
Publication date: 2011-07-07

Abstract

The present invention relates to a flexible dental screwdriver (1), comprising: a flexible shaft (2) having a proximal end and a distal end, a handle (3) coupled to the proximal end, and a drive tip (4) coupled to the distal end for driving a screw, wherein the flexible shaft (2) comprises a plurality of cylindrically shaped hollow shaft segments (5) having a height, an outside diameter, an inside diameter and first and second ends defined by a plurality of equidistant protrusions (6) and corresponding recesses (7) forming an undulated path (8), the protrusions (6) having a height, a base region (9) and a top region (10), at least a portion of the top region (10) being wider than the base region (9), whereby the protrusions (6) of adjacent shaft segments (5) interlock to join the adjacent shaft segments (5), the undulated paths of adjacent interlocked shaft segments defining a gap therebetween.

Description

FLEXIBLE DENTAL SCREWDRIVER AND METHOD OF

MANUFACTURING THE SAME

FIELD OF THE INVENTION

The present invention relates in general to devices for dental practices, in particular to a flexible dental screwdriver used for driving a screw of a dental implant and to methods of manufacturing this flexible dental screwdriver.

BACKGROUND OF THE INVENTION

In cases where the axis of a dental implant is going through the incision edge or the anterior plane of a tooth prosthesis it is usually not preferred, for aesthetic reasons, to realize a screw retained fixation on the prosthesis. Additionally, in some cases the available bone substance offers only limited flexibility for the placement of a dental implant. This results in a non optimal implant placement for screw retained prosthetics. In today's designs of screw retained fixations for dental implants the screw channel is a linear extension of the occlusal or basal screw. In cases of frontal teeth or between the cusps in molars, having such screw retained fixations requires the screw channel to end on the palatal/lingual surface. When this is not possible a cemented prosthesis, such as a cemented crown or bridge, must be used. Therefore, the use of screw retained crowns, for example, is limited to specific indications. For several reasons, it is highly desirable to have screw retained restorations. In particular, screw retained fittings enable the prosthesis to be removed, for example for cleaning purposes or abutment replacement, and then reapplied. This is not possible with cement retained prostheses as the prosthesis is usually damaged or destroyed during removal. Restorations having a non straight or even a bended screw channel could prevent the need for a cemented prosthesis and would allow for additional flexibility in designing screw retained crowns, for example. However, aside from the manufacturing difficulties involved in creating such abutments, current dental screwdrivers allow only for a very limited range of angulation. Thus, there is a need for a screwdriver that allows to drive and to tighten a screw through a non straight screw channel.

According to the invention these objectives are achieved by providing a flexible dental screwdriver and a method of manufacturing this flexible dental screwdriver as recited in claim 1 and claim 21, respectively.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a flexible screwdriver comprising: a flexible shaft having a proximal end and a distal end; a handle coupled to the proximal end; and a drive tip coupled to the distal end for driving a screw; wherein the flexible shaft comprises a plurality of cylindrically shaped hollow shaft segments having a height, an outside diameter, an inside diameter and first and second ends defined by a plurality of equidistant protrusions and corresponding recesses forming an undulated path, the protrusions having a height, a base region and a top region, at least a portion of the top region being wider than the base region, whereby the protrusions of adjacent shaft segments interlock to join adjacent shaft segments, the undulated paths of adjacent interlocked shaft segments defining a gap therebetween.

The gap between each segment forms an unbound joint permitting limited movement in any direction between the protrusions and the corresponding recesses of adjacent shaft segments, thereby providing limited flexibility in all directions for adjacent shaft segments, so that a flexible shaft is formed being able to transmit a torque from the handle to the drive tip, while conforming generally to a curvature along the longitudinal axis of the shaft.

In some embodiments the shaft segments may have differing heights such that a varying curvature along the longitudinal axis can be achieved. In one preferred embodiment the different height can be a height that constantly decreases from the proximal end to the distal end of the flexible shaft, which results in a curvature that increases in the direction of the distal end of the flexible shaft.

It is preferred however that the shaft segments have the same height such that a constant curvature along the flexible shaft can be achieved.

The flexible shaft is coupled at one end to the handle and at the other end to the drive tip. In a preferred embodiment the handle comprises a proximal end having a larger diameter than the flexible shaft. This is beneficial as it increases the torque that can be transmitted to the screwdriver shaft. Preferably at its widest point the handle has a diameter of greater than 5mm, preferably 7-9mm and most preferably 8mm. Preferably the ratio of the largest diameter of the handle to the diameter of the flexible shaft is between 4: 1 and 2: 1, most preferably around 3: 1.

In order to enable coupling to the flexible shaft it is preferable that the distal end of the handle comprises a coupling section having the same diameter as the shaft segment at the proximal end of the flexible shaft and comprising a plurality of equidistant protrusions and corresponding recesses forming an undulated path, whereby the protrusions interlock with the protrusions of the segment at the proximal end of the shaft. In a preferred embodiment the coupling section of the handle has a length less than or equal to the shaft segments, such that the flexible shaft effectively begins at the handle base.

In one embodiment the drive tip comprises, at its distal end, a non-rotationally symmetric drive nut shaped to engage a screw head and, at its proximal end a coupling portion having the same diameter as the shaft segment at the distal end of the flexible shaft and comprising a plurality of equidistant protrusions and corresponding recesses forming an undulated path, whereby the protrusions interlock with the protrusions of the segment at the distal end of the shaft. In some embodiments the length of the coupling section can be approximately equal to the shaft segments, such that the coupling section in effect forms the final segment of the flexible shaft. In other embodiments however this coupling section can be smaller in length than any of the shaft segments. Alternatively, in some embodiments the coupling section can be larger in length than any of the shaft segments. This longer, rigid length at the distal end of the screwdriver can make the screwdriver easier to insert into abutment screw channels.

In one preferred embodiment the coupling section of the drive tip has a length of between one half and one quarter the length of the flexible shaft, wherein the flexible shaft is defined as being the total length of the plurality of shaft segments. In another embodiment the length of the coupling section of the drive tip is approximately one third of the length of the flexible shaft. It is possible for at least part of the handle and the drive tip, for example the proximal end of the handle and/or the drive nut, to be attached to the screwdriver by way of plastic moulding, bonding, welding, friction fit etc. However, in a preferred embodiment the handle and/or drive tip are integrally joined to the flexible shaft.

In this preferred embodiment the screwdriver is therefore formed in one piece. This improves the strength of the device and also prevents the possibility of the handle or drive nut being disconnected from the screwdriver.

The present invention is further directed to a method of manufacturing a flexible dental screwdriver, comprising: providing a dental screwdriver having a handle, a rigid shaft and a drive tip; drilling a longitudinal hole through the rigid shaft; and cutting a plurality of circumferential undulated paths into the rigid shaft to form a plurality of shaft segments with a height, first and second ends defined by a plurality of equidistant protrusions and corresponding recesses, the protrusions having a height, a base region and a top region, the top region being wider than the base region, whereby the protrusions interlock to keep adjacent shaft segments joined, wherein the undulated paths define a gap between adjacent shaft segments, said gap having a sufficient width to form an unbound joint permitting limited movement in any direction between the protrusions and the corresponding recesses, thereby providing limited flexibility in all directions for adjacent shaft segments, so that a flexible shaft is formed being able to transmit a sufficient torque from the handle to the drive tip, while conforming generally to a curvature along the longitudinal hole.

In accordance with this method the handle, shaft and drive tip can be separate components joined together after individual manufacture. However, preferably the handle, rigid shaft and drive tip are integrally formed. According to an alternative, preferred method of manufacture a metal rod is provided having a longitudinal blind bore. This bore can be produced by, for example, drilling or electro-erosion. The rod is then machined, for example via grinding, cutting etc, to form a handle, rigid hollow shaft and drive tip wherein the blind bore extends along the longitudinal axis of the screwdriver from the handle to the drive tip. Finally, a plurality of circumferential, undulated paths are cut into the rigid shaft to form a plurality of segments. Preferably the undulated paths are formed by laser cutting or electro erosion. Although metal is the preferred material other materials, such as ceramic or plastic could also be used to form the screwdriver.

A flexible screwdriver manufactured in accordance with this preferred method is therefore an integral component, wherein a blind bore extends longitudinally from the handle to the drive tip. The blind bore must extend to the coupling section of the drive tip in order to ensure that the plurality of segments are hollow and thus flexible relative to one another. The drive nut is preferably solid however to ensure a suitable strength for torque transfer. This blind bore extending through the screwdriver allows a holding rod to be inserted into the screwdriver to maintain this in a straight, unbent position during storage. This is beneficial as it can prevent damage to the screwdriver and also enables the user to quickly identify a screwdriver having the desired length.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic representation of a flexible dental screwdriver according to an embodiment of the present invention; and Fig. 2A and 2B show representations of a shaft segment of Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Fig. 1, 2A and 2B, an embodiment of a flexible dental screwdriver 1 according to the present invention includes a flexible shaft 2 having a proximal end and a distal end, a rotatable handle 3 coupled to the proximal end and a drive tip

4 coupled to the distal end for driving a screw. The flexible shaft 2 includes a plurality of cylindrically shaped hollow shaft segments 5. Each of the shaft segments

5 have a height, an outside diameter, an inside diameter and first and second ends. The respective first and second ends of the shaft segments 5 are defined by a plurality of equidistant protrusions 6 and corresponding recesses 7 that form an undulated path 8. The protrusions 6 have a height, a base region 9 and a top region 10. The top region 10 of the protrusions 6 is wider than the base region 9 of the protrusions 6, whereby the protrusions 6 of adjacent shaft segments 5 interlock for joining such adjacent shaft segments 5. A gap is defined between the undulated paths 8 of adjacent shaft segments 5. Although the segments 5 are shown in the figures as having the top region 10 and the corresponding non-referenced bottom region perpendicular to the segment axis, the invention also envisages embodiments thereof having segments with the top and bottom regions inclined with respect to the segment axis, i.e. the top and bottom regions forming an angle other than 90° with the segment axis.

In an aspect of the present invention the gap has a sufficient width to form a joint permitting limited movement in any direction between the protrusions 6 and the corresponding recesses 7 of adjacent segments. This provides limited flexibility in all directions for adjacent shaft segments 5, so that the flexible shaft 2 is able to transmit a sufficient torque from the rotatable handle to the drive tip, while conforming generally to a curvature along a longitudinal axis (L).

Handle 3 comprises a proximal end 31 , having a larger diameter than the flexible shaft 2. In use this is gripped either by hand or via a driving device such as a ratchet or dental handpiece and rotated in order to supply torque to the screwdriver 1. For this reason the proximal end 31 may comprise recesses 32 to assist in gripping. In an alternative embodiment the proximal end 31 may have a non-rotationally symmetric external contour, such as a hexagon.

The handle 3 has a larger diameter than the flexible shaft 2 in order to facilitate gripping or connection to a driving device as well as to enable a larger amount of torque to be transmitted to the screwdriver 1. In this preferred embodiment the largest diameter of the handle 3 is approximately three times the diameter of the flexible shaft 2.

At its distal end the handle 3 comprises a coupling section 33. This section 33 has the same diameter as the flexible shaft 2 and comprises at its distal end a plurality of protrusions 6 and corresponding recesses 7 identical to those of the shaft segments 5. The coupling section 33 of the handle 3 is thus interlocked with the proximal most segment 5 of the flexible shaft 2.

In the present embodiment the coupling section 33 is linked to the proximal end 31 of the handle by way of a transitional portion 34 that tapers inwardly in the distal direction. However, in other embodiments the proximal end 31 may join directly to the coupling section 33. Drive tip 4 comprises, at its distal end, drive nut 41. This nut is sized and shaped to connect in a non-rotational manner to a screw head. For this reason the nut has a non-rotationally symmetric cross-section, for example a cross, bar or polygon shape. In the present embodiment the drive nut 41 has a TORX® shape. In order to improve the connection between the drive nut 41 and screw, the nut can taper inwards slightly towards its distal end. This improves the retention of the screw on the nut 41 and reduces the likelihood of the screw being dropped and potentially lost or damaged.

At its proximal end drive tip 4 comprises coupling section 43. In a similar manner to the coupling section 33 of the handle 3, coupling section 43 has the same external diameter as the flexible shaft 2 and comprises at its proximal end a plurality of protrusions 6 and corresponding recesses 7 identical to those of the segments 5. This enables the drive tip 4 to be interlocked with the distal most segment of the flexible shaft 2.

In the present embodiment coupling section 43 is similar in length to the segments 5. However, in other embodiments this section 43 can be longer, creating a rigid shaft section at the distal end of the screwdriver 1.

In another aspect of the present invention the height of the shaft segments 5 can be in the range from 1.5 mm to 6 mm. The total length of the flexible shaft 2, namely the total length of the plurality of shaft segments 5, is between 10 and 20mm, most preferably 12mm. The length of the coupling section 43 of the drive tip 4 can be, preferably, between 1 and 6mm and may or may not correspond to the height of the shaft segments.

The height of the shaft segments 5 is one of the parameters that can determine the curvature along the longitudinal axis L. Generally, a smaller height of the shaft segments 5 results in a stronger curvature along the longitudinal axis L and hence a small height is usually preferred. The shaft segments 5 of the present invention can have the same, different or mixed heights. In the case of the same height of the shaft segments 5, as shown in the preferred embodiment of FIG 1, it is goes without saying that a constant curvature along the longitudinal axis L can be achieved. In the case of different heights of the shaft segments 5, it is clear for the person skilled in the art that a varying curvature along the longitudinal axis L can be achieved. The different height can be a height that constantly decreases from the proximal end to the distal end of the flexible shaft, which can result in a curvature that increases in the direction to the distal end of the flexible shaft 2. The case of mixed heights of the shaft segments 5 can result in portions of the flexible shaft 2 that have a different curvature compared to each other, wherein the curvature can be a constant and/or an increasing curvature. Thus, in another aspect of the present invention the curvature can be a non-uniform curvature. In another aspect of the present invention the curvature can be in the range from 0° to 90°.

In another aspect of the present invention the outside diameter of the shaft segments 5 can be in the range from 1 mm to 5 mm.

In another aspect of the present invention the ratio of the outside diameter to the inside diameter of the shaft segments 5 can be in the range from 0.3 to 0.8.

Basically, this ratio defines a wall thickness of the shaft segments 5. It is to be understood that the shaft segments 5 require a wall thickness that is sufficient to be able to transmit the torque needed to drive and to tighten a screw. Accordingly, the sufficient wall thickness of the shaft segments 5 can be in the range from 0.05 mm to 0.8 mm. It goes without saying that the sufficient wall thickness also depends on the material of the shaft segments 5. Any suitable material can be used to

manufacture the screwdriver, particularly favored are biocompatible materials that can be re-sterilized. Metals, such as steel or titanium are good choices, for example steel material number 1.4441.

In another aspect of the present invention the number of the protrusions 6 can be from 2 to 5.

In another aspect of the present invention the height of the protrusions 6 can be in the range from 0.3 mm to 1 mm. The height of the protrusions 6 is another one of the parameters that can determine the curvature along the longitudinal axis.

Generally, a smaller height of the protrusions results in a stronger curvature along the longitudinal axis.

In another aspect of the present invention the width ratio of the widest region of the top region 10 to the narrowest region of the base region 9 of the protrusions 6 can be in the range from 1.1 to 1.8. It is obvious that the ratio has to be greater than 1 for the protrusions being able to interlock with each other.

In another aspect of the present invention the top region 10 of the protrusions can be flat. However, it is also possible for the top region 10 of the protrusions to be curved, tapered etc. In such embodiments the top of protrusion 6 may be narrower than the base region 9. A portion of the upper region 10 will always be wider than the base portion however in order to enable interlocking.

In another aspect of the present invention the height ratio of the shaft segments 5 to the protrusions 6 can be at least 3 : 1 and preferably in the range from 3: 1 to 6: 1.

In another aspect of the present invention the sufficient width of the gap defined by adjacent undulated paths 8 can be in the range from 0.02 mm to 0.3 mm. As a matter of fact, the width of the gap defined by the undulated path 8 is another one of the parameters that can determine the curvature along the longitudinal axis L.

Generally, a bigger gap results in a stronger curvature along the longitudinal axis L. However, it goes without saying that there has to be a minimum value of the gap to provide for sufficient flexibility of the flexible shaft 2 and that the maximum value of the gap should not be exceeded in order to maintain the structural stability of the flexible shaft 2.

In another aspect of the present invention the flexible shaft 2 is able to transmit the torque in clockwise and counterclockwise directions to the same extent. In another aspect of the present invention the flexible shaft 2 is able to transmit the torque in the range from 15 Ncm to 200 Ncm and preferably in the range from 15 Ncm to 120 Ncm.

The above dimensions enable a flexible screwdriver to be created that is particularly suited to use in the dental implant field. In particular, these dimensions enable the shaft to be inserted into a narrow screw channel within a dental abutment or prosthesis while retaining a sufficient strength to transfer the torque necessary to effectively pre-load dental screws and other components. The curvature of the shaft is also beneficial in allowing a practitioner to more easily undertake work in the posterior of the mouth, while increasing the comfort of the patient.

In another aspect of the present invention a flexible sheath (which is not shown in the drawings) can be disposed about the entire flexible shaft 2. The flexible sheath can provide for protection against body fluids during invasion, easier cleaning and an additional support for shaft segments 5. Preferably, the flexible sheath is substantially inert to standard sterilizing methods. In another aspect of the present invention the flexible sheath can include germicides. For example, in the form of an anti-infective coating.

The present invention provides also a method of manufacturing the flexible dental screwdriver which includes providing a dental screwdriver having a handle, a rigid shaft and a drive tip, drilling a longitudinal hole through the rigid shaft and cutting a plurality of circumferential undulated paths 8 into the rigid shaft to form a plurality of shaft segments 5 with a height, first and second ends defined by a plurality of equidistant protrusions 6 and corresponding recesses 7, the protrusions 6 having a height, a base region 9 and a top region 10, at least a portion of the top region 10 being wider than the base region 9, whereby the protrusions 6 of adjacent shaft segments 5 interlock to keep such adjacent shaft segments 5 joined, wherein the undulated paths 8 of adjacent shaft segments define a gap, said gap having a sufficient width to form an unbound joint permitting limited movement in any direction between the protrusions 6 and the corresponding recesses 7, thereby providing limited flexibility in all directions for adjacent shaft segments 5, so that a flexible shaft 2 is formed being able to transmit a sufficient torque from the rotatable handle to the drive tip, while conforming generally to a curvature along the longitudinal hole.

Alternatively, the longitudinal hole can be provided first, prior to the formation of the handle, shaft and drive tip. In accordance with this method a longitudinal blind bore is first drilled or otherwise produced in a metal rod. The rod is then machined to create an integral handle, rigid shaft and drive tip, wherein the longitudinal hole forms a blind bore running along the longitudinal axis from the handle to the drive tip. A plurality of circumferential paths are then cut into the rigid shaft to form a plurality of shaft segments 5 with a height, first and second ends defined by a plurality of equidistant protrusions 6 and corresponding recesses 7, the protrusions 6 having a height, a base region 9 and a top region 10, at least a portion of the top region 10 being wider than the base region 9, whereby the protrusions 6 of adjacent shaft segments 5 interlock to keep such adjacent shaft segments 5 joined, wherein the undulated paths 8 of adjacent shaft segments define a gap, said gap having a sufficient width to form an unbound joint permitting limited movement in any direction between the protrusions 6 and the corresponding recesses 7, thereby providing limited flexibility in all directions for adjacent shaft segments 5.

The flexible screwdriver 1 created in accordance with either method may be an integrally formed component having a longitudinal blind bore extending from the handle 3 to the drive tip 4. Although it is possible to close the blind bore, preferably this is left open so that a rod can be inserted into the blind bore to straighten the flexible shaft when desired, for example during storage.

In an aspect of the present invention the cutting of the circumferential paths can be carried out by a laser or electro erosion.

The advantages achieved by the present invention can be substantially described as follows:

- The specific design of the shaft of the dental screwdriver is capable to transmit sufficient torque and is flexible. In comparison to known flexible shafts made from coiled wires it allows to transmit more torque.

- A further advantage is that it is possible to transmit identical torque in both clockwise and counterclockwise directions.

- A further advantage is that the screwdriver can be an integrally formed component, which increases the strength and structural integrity of the device.

- A further advantage is that the flexible shaft has a small enough diameter for insertion into dental prostheses and abutment screw channels.

As a result, the flexible dental screwdriver of the present invention allows to drive and to tighten a screw through a bended or angled screw channel. This enables the opening of the screw channel to be placed in an appropriate region of the crown where no functional or aesthetic problems occur. The specific design of the flexible dental screwdriver offers enough angular freedom whilst still being able to transmit sufficient torque.

List of reference numbers flexible dental screwdriver

flexible shaft

rotatable handle

1 proximal end of handle

2 recesses

3 coupling section of handle

4 transitional portion of handle

drive tip

1 drive nut

3 coupling section of drive tip

shaft segment

protrusion

recess corresponding to protrusion

undulated path

base region of protrusion

top region of protrusion

longitudinal axis

Claims

1. A flexible dental screwdriver (1), comprising:

a flexible shaft (2) having a proximal end and a distal end,

a handle (3) coupled to the proximal end, and

a drive tip (4) coupled to the distal end for driving a screw,

wherein the flexible shaft (2) comprises

a plurality of cylindrically shaped hollow shaft segments (5) having a height, an outside diameter, an inside diameter and first and second ends defined by a plurality of equidistant protrusions (6) and corresponding recesses (7) forming an undulated path (8), the protrusions (6) having a height, a base region (9) and a top region (10), at least a portion of the top region (10) being wider than the base region (9), whereby the protrusions (6) of adjacent shaft segments (5) interlock to join the adjacent shaft segments (5), the undulated paths of adjacent interlocked shaft segments defining a gap therebetween.

2. The flexible dental screwdriver (1) as claimed in claim 1, wherein the gap has a sufficient width to form a joint permitting limited movement in any direction between the protrusions (6) and the corresponding recesses (7) of adjacent shaft segments, thereby providing limited flexibility in all directions for adjacent shaft segments (5), so that the flexible shaft (2) is able to transmit a sufficient torque from the rotatable handle (3) to the drive tip (4), while conforming generally to a curvature along a longitudinal axis (L).

3. The flexible dental screwdriver (1) as claimed in claim 1 or 2, wherein the plurality of shaft segments (5) all have the same height.

4. The flexible dental screwdriver (1) as claimed in claim 1, 2 or 3 wherein the height of the shaft segments (5) is in the range from 1.5 mm to 6 mm.

5. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the drive tip (4) comprises, at its distal end, a non-rotationally symmetric drive nut (41) shaped to engage a screw head and, at its proximal end a coupling section (43) having the same external diameter as the shaft segment (5) at the distal end of the flexible shaft (2) and comprising a plurality of equidistant protrusions (6) and corresponding recesses (7) forming an undulated path, whereby the protrusions interlock with the protrusions of the segment at the distal end of the shaft.

6. The flexible dental screwdriver (1) as claimed in claim 5, wherein the coupling section (43) of the drive tip (4) has a length of between one half and one quarter the length of the flexible shaft (2).

7. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the handle (3) comprises a proximal end having a larger diameter than the flexible shaft (2) and, at its distal end, a coupling section (33) having the same diameter as the shaft segment (5) at the proximal end of the flexible shaft (2) and comprising a plurality of equidistant protrusions (6) and corresponding recesses (7) forming an undulated path, whereby the protrusions interlock with the protrusions of the segment at the proximal end of the shaft.

8. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the handle (3) and/or drive tip (4) are integrally joined to the flexible shaft (2).

9. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein a blind bore extends longitudinally from the handle (3) to the drive tip (4).

10. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the outside diameter of the shaft segments (5) is in the range from 1 mm to 5 mm.

11. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the ratio of the outside diameter to the inside diameter of the shaft segments (5) is in the range from 0.3 to 0.8 or wherein the wall thickness of the shaft segments (5) is in the range from 0.05 mm to 0.8 mm.

12. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the number of the protrusions (6) is from 2 to 5.

13. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the height of the protrusions (6) is in the range from 0.3 mm to 1 mm.

14. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the width ratio of the widest region of top region (10) to the narrowest region of the base region (9) of the protrusions (6) is in the range from 1.1 to 1.8.

15. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the top region (10) of the protrusions (6) is flat.

16. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the height ratio of the shaft segments (5) to the protrusions (6) is at least 3 : 1 and preferably in the range from 3: 1 to 6: 1.

17. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the sufficient width of the gap is in the range from 0.02 mm to 0.3 mm.

18. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein the flexible shaft (2) is able to transmit the torque in the range from 15 Ncm to 200 Ncm and preferably in the range from 15 Ncm to 120 Ncm.

19. The flexible dental screwdriver (1) as claimed in any preceding claim, wherein a flexible sheath is disposed about the entire flexible shaft (2).

20. The flexible dental screwdriver (1) as claimed in claim 19, wherein the flexible sheath comprises germicides.

21. A method of manufacturing a flexible dental screwdriver (1 ) as claimed in any preceding claim, comprising the steps of:

providing a longitudinal blind bore in a rod;

machining said rod to form a handle (3), rigid hollow shaft and drive tip (4) wherein the longitudinal blind bore runs along the longitudinal axis of the

screwdriver from the handle into the drive tip; and

cutting a plurality of circumferential undulated paths (8) into the rigid shaft to form a plurality of shaft segments (5) with a height, first and second ends defined by a plurality of equidistant protrusions (6) and corresponding recesses (7) having a height, a base region (9) and a top region (10), at least a portion of the top region being wider than the base region (9), whereby the protrusions (6) of adjacent shaft segments (5) interlock for keeping adjacent shaft segments joined, wherein the undulated paths (8) of adjacent shaft segments define a gap, said gap having a sufficient width to form an unbound joint permitting limited movement in any direction between the protrusions (6) and the corresponding recesses (7) of adjacent segments, thereby providing limited flexibility in all directions for adjacent shaft segments (5), so that a flexible shaft (2) is formed being able to transmit a sufficient torque from the handle (3) to the drive tip (4), while conforming generally to a curvature along the longitudinal axis.

22. The method as claimed in claim 21, wherein the cutting is carried out by a laser or electro erosion.