# Patent

## Title
Screw and driver tool

## Abstract

The invention relates to a screw and corresponding screw driver for driving the screw into a dental implant at an angle from the longitudinal axis of the implant. The screw has a polygonal interface and the screw driver has a matching interface for driving the screw to rotate.

## Background
PRIORITY INFORMATION
This application is a national stage application under 35 U.S.C. §371 of PCT Application No. PCT/EP2012/002826, filed on Jul. 5, 2012, which published in English as WO 2013/004386 on Jan. 10, 2013, and which claims priority benefit of GB Patent Application No. 1111561.5, filed on Jul. 6, 2011, and GB Patent Application No. 1117590.8, filed on Oct. 12, 2011.
BACKGROUND
Field of the Invention
The present invention relates to methods and apparatus for fixing dental components to dental implants in a patient's jawbone. More specifically, the invention relates to the manipulation of screws into dental components with corresponding screw channels in order to secure the dental component to the dental implant.
Description of the Related Art
FIG. 1 shows an arrangement for a prosthetic single tooth replacement having angulated screw channels. Dental implant 110 comprises screw channel 130 having an inner thread configured to match the thread of screw 160 such that screw 160 can be fastened to the implant. Prosthesis 120 is fixed to the dental implant by means of screw 160. The prosthesis passes through the gum tissue to dental implant 110. The prosthesis has a screw channel 190 through which screw 160 is inserted. Screw channel 190 has a screw channel exit 180 and screw seat 140 at the base of the prosthesis, upon which the head 170 of the screw 160 is seated when the prosthesis is fastened to the implant with the screw. According to the present invention, the axis of screw channel 190 (i.e. the line described by the radial centre point of the channel at any point) does not follow the axis of channel 130. In fact, screw channel 190 may be mostly straight but orientated at a different angle to channel 130. Alternatively, the axis of screw channel 190 may be curving or S-shaped. As a result, the axis of screw channel 190 at the channel exit 180 does not match the axis of channel 130 or the axis of screw seat 140.
The problem arising from this arrangement is that of how to insert the screw through the angulated screw channel and, once the screw is engaged with the dental implant, how to drive the screw to rotate using a driver angled at a significant angle from the longitudinal axis of the screw.
What is needed is a way of interfacing the screw and a driver tool in a manner which allows the screw to be manipulated during insertion into the prosthesis and driven to rotate from an angle to the longitudinal axis of the screw.
US 2010167240 describes a driver tool for driving a screw to rotate from an angle from the axis of the screw. A ball-headed driver is described, wherein the ball shape of the driver head apparently provides an interface between the driver and the screw, even where the driver tool is presented at an angle from the axis of the screw.
SUMMARY
According to a first aspect of the invention, there is provided a screw for a dental application (in other words, a dental screw), the screw having a coronal end and an apical end and comprising a bore running from the coronal end of the screw along a portion of the screw towards the apical end of the screw, a first number of equally spaced recesses arranged circumferentially around an inside surface of the bore, each recess running a length from the coronal end of the bore towards the apical end of the bore. The length of each recess is angled relative to the longitudinal axis of the screw such that the recess is further from the longitudinal axis of the screw at a point parallel with the coronal end of the bore than at a point below the coronal end of the bore. Each pair of adjacent recesses is connected by a contact surface on the inside surface of the bore, each contact surface running a length from the coronal end of the bore towards the apical end of the screw. Each contact surface is angled away from the longitudinal axis of the screw such that the surface is further from the longitudinal axis of the screw at a point parallel with the coronal end of the bore than at a point below the coronal end of the bore.
At least a portion of the inside surface of the bore comprises a layer of Titanium Nitride. The apical end of the bore may be conical, having a widest point at the apical end of the recesses. In one embodiment, the screw is adapted to fasten a dental component to a dental implant. In another embodiment, the screw (itself) is a dental component directly attachable to a dental implant, wherein the dental component may be selected from the group comprising: a cover screw, a healing abutment, an impression coping, etc.
According to another aspect of the invention, there is provided a driver for driving a screw for fastening a dental component to a dental implant, the driver comprising a driver head having an apical and coronal end, the driver head comprising of at least a first and second portion having a polygonal cross-section in a radial plane of the longitudinal axis of the driver, a first portion having a substantially rounded cross-section in the axial plane of the longitudinal axis of the driver, a second portion connected apically relative to the first portion, the second portion having a substantially triangular shape tapered towards the apical end of the driver head in the axial plane of the longitudinal axis of the driver.
The driver head may comprise a tip portion at the apical end of the driver head having a polygonal cross-section in a radial plane of the longitudinal axis of the driver and a curved apical end. At least a portion of the surface of the driver head may comprise a layer of Titanium Nitride.
According to yet another aspect of the invention, a method of fastening a dental component to a dental implant comprising the steps of, inserting the driver head of a driver described above into the bore of any of the screws described above such that the edges of the driver head defined by the polygonal cross-section fit within the recesses of the screw, applying sufficient force to the driver so that the driver head grips the screw by means of a carry function, manipulating the screw through a screw channel of the dental component using the carry function until the screw is received by a threaded bore in the dental implant, driving the screw to rotate using the driver, such that the edges of the driver head defined by the polygonal cross section of the portions of the driver head smoothly convey rotational force to the screw regardless of the angle of the longitudinal axis of the driver relative to the longitudinal axis of the screw.



BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the present invention will now be described by way of example with reference to the accompanying drawing. In the drawings:
FIG. 1 shows a prosthesis having angulated screw channel and corresponding screw.
FIGS. 2A and 2B show the angle of the driver (not shown to scale) from the longitudinal axis of the screw during the process of inserting a screw into an prosthesis of FIG. 1.
FIGS. 3A-3D show an embodiment of the screw according to the invention.
FIGS. 4A-4C show an embodiment of the screw driver according to the invention.
FIGS. 5A-5C show the screw in co-operation with the screw driver head.
FIGS. 6A and 6B show an embodiment of a cover screw according to the invention.



DETAILED DESCRIPTION
Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements.
Screw
The present invention provides a method and apparatus for inserting a screw into a dental component having an angulated screw channel and securing the screw into a dental implant, thereby fixing the dental component to the dental implant.
A screw having a screw interface according to the preferred embodiment of the present invention is shown in FIGS. 3A to 3D. Screw 160 comprises screw head 310 having screw interface 300. The screw interface 300 comprises a bore in the head of the screw with a polygonal internal shape configured to co-operate with screw driver head 400, described later in the specification. As shown in FIG. 3A, screw interface 300 comprises tapered inner walls 320, conical section 330, chamfered or rounded interface edges 340 and recesses 350.
In the preferred embodiment, screw interface 300 comprises six equally spaced recesses 350 arranged circumferentially on the inside surface of the screw interface. An equivalent screw head with greater or fewer than six recesses is also envisaged. Each recess runs from the top surface of the screw head at a small angle (e.g. 2.5 degrees) inwards from the longitudinal axis of the screw towards conical section 330. In between the recesses are flat tapered surfaces 320, tapered outwardly towards the mouth of the screw interface. As a consequence, the internal surfaces 350 and 320 describe a slightly conical internal space such that the largest diameter at the mouth of the screw interface is greater than the largest diameter at the point where the tapered surfaces 320 meet the conical section below. In one embodiment, the tapered surfaces 320 are angled 2.5° from the longitudinal axis of the screw.
Conical section 330 comprises the bottom portion of the screw interface 300. At the widest point of the cone, conical section 330 meets the recesses 350 and tapered inner surfaces 320. The cone shape of section 330 then narrows to a truncated head 360 at the internal end of the screw interface. Cone 330 provides extra support to screw head edges 310 when the screw is inserted tightly into a screw seat. Whereas a flat lower surface (e.g. truncated portion 360 being the width of the interface) might allow the edges to plastically deform inwards as the screw was screwed tightly into a screw seat, conical shape 330 provides greater support to edges 310.
The mouth of the screw interface 300 comprises six chamfered or rounded edges 360 connecting the top surface of screw head 310 and tapered inner surfaces 320.
FIG. 6A is cross-sectional side view, and FIG. 6B is perspective view, of an embodiment of a cover screw 160′ according to the invention. The cover screw 160′ is generally adapted to completely cover the top (i.e. the coronal end) of a dental implant, for example the dental implant 110.
The cover screw 160′ comprises a screw head 310′. The screw head 310′ comprises a flat circumferential apical surface 370′. The surface 370′ is orthogonal to the longitudinal axis of the cover screw 160′. The surface 370′ is adapted to abut against and cover the top of the dental implant.
The screw head 310′ further comprises a screw interface 300. The screw interface 300 is of the same type as the screw interface of the screw 160 described in relation to FIGS. 3A to 3D. Therefore, the same driver or tool may be used to manipulate both the screw 160 and the cover screw 160′. The description of the screw interface 300 will not be repeated here.
Apically of the surface 370′, the cover screw 160′ comprises a conical section 380′, which narrows toward the apical end of the cover screw 160′. The conical section 380′ is adapted to abut against a corresponding conical section of the dental implant (internal conical connection), when the cover screw 160′ is screwed into the implant.
Apically of the conical section 380′, the cover screw 160′ comprises an externally threaded portion 390′ for engagement with a corresponding internally threaded portion of the dental implant, so that the cover screw 160′ can be secured to the dental implant.
The screw interface 300 may also be applied to other dental components than cover screws, such as healing abutments, impression copings, etc.
Driver
According to the preferred embodiment of the invention shown in FIGS. 4A-4C, the screw driver head 400 comprises a polygonal shape in the radial plane (i.e. the plane normal to the longitudinal axis of the driver) and a ball shape in the axial plane.
In particular, the preferred embodiment of the driver head 400 has a polygonal cross section as shown in FIG. 4A. In the preferred embodiment, the polygonal cross section has six sides. However, an equivalent driver head with greater or fewer than six sides (corresponding to the number of recesses in the screw interface) is envisaged. The sides of the polygons form surfaces 410, spanning between edges 420
In FIG. 4B, the screw driver head is shown in a side perspective. In order to describe the driver head, it is divided up into portions 430, 440, 450, 460, and 470.
Edges 410 of apical end portion 470 describe a circular curve where all the edges 410 meet. The circular curve of the edges at apical end portion 470 describe a rounded head in the axial plane.
Edges 410 of portion 460 describe a straight line, such that the portion 460 comprises the shape of a truncated polygonal pyramid, truncated towards apical end 470 such that the surfaces of portion 460 smoothly meet the surfaces of portion 470.
Edges 410 of apical end portion 450 describe a circular curve connecting the edges of portion 460 to portion 440. The circular curve is that which give portion 450 a truncated ball shape in the axial plane.
Edges 410 of portion 440 describe a straight line, such that the portion 460 comprises the shape of a truncated polygonal pyramid, narrowing away from apical end 470 such that the surfaces of portion 450 smoothly meets the surfaces of portion 430.
Portion 430 is where surfaces 420 meet the cylindrical shaft of the driver tool.
Co-operation Between the Driver Head and the Screw Interface
As shown in FIGS. 5A to 5C, the features of the driver head and corresponding screw interface are configured to allow the driver head to be inserted into the screw interface and for the screw to be driven to rotate by the driver at an angle from the longitudinal axis of the screw.
Upon initial insertion of the driver head into the screw interface, chamfered (or rounded) edges 340 of the mouth of the screw interface guide the tip of the driver head into the bore of the screw. This makes the process of loading the driver head into the screw more simple and require less precise spatial co-ordination from the person manipulating the driver/screw.
The driver head is then rotated until edges 410 align with recesses 330. At this point, edges 410 will fit into recesses 330 and the driver head will obtain rotational grip with the screw head. The recesses allow the driver head to be smoothly rotated at an angle from the longitudinal axis of the screw without a locking collision between the surfaces of the driver head and the screw interface causing the driver head to become rotationally fixed to the screw.
As shown in FIG. 5A, if the screw head is inserted into the screw interface at an angle matching, or close to, the longitudinal axis of the screw, the conical portion 460 will rest against internal cone 330 to provide a comfortable fit and the driver may be driven to rotate the screw.
If, as shown in FIGS. 5B and 5C, the screw head is inserted into the screw interface at a significant angle from the longitudinal axis of the screw (i.e. greater than 5 degrees), rounded apical end 470 meets internal cone 330 at a point above the truncated end 360 of the internal cone. This prevents the screw head from entering the screw interface as deeply as when the screw head is inserted into the screw interface at an angle close to the longitudinal axis of the screw. At the same time, rounded edges 410 of portion 450 fit with recesses 350. In the preferred embodiment, the gradient angle of the internal cone 330 is chosen to ensure that depth to which the driver head enters the screw head is dependent on the angle from the longitudinal axis of the screw that the driver head is inserted. By controlling the depth to which the screw head enters the screw interface, rounded edges 410 of portion 450 can be controlled to contact recesses 350 within an optimal range of the length of recesses 350, i.e. not too close to the mouth of the screw interface such that the driver head slips out of rotational grip with the screw, and not so close to the internal end of the screw interface that the rounded portion 450 contacts internal conical portion 330 and introduces extra friction or forces the screw head back out of the screw interface. In one embodiment, the range of optimal contact for rounded portion 450 on recesses 350 is between points describing 25% and 75% of the length of the recess. By ensuring that a section of the rounded edges contacts the conical portion 330 within this range, an optimal play between the screw and the driver is achieved to allow angulated rotation of screw. Once the driver head is moved to rotate, the rounded aspect of portion 450 in recesses 350 allows the screw to be rotated at an angle from the longitudinal axis from the driver.
Surface 460 of the driver also provides extra contact surface during the driving process. For a rounded driver head, each edge in the recess would curve out of the recess after the point at which the edge and the recess surface were contacting. The straight surface does not curve out of the recess and provides some degree of surface contact until the end of the recess.
In the preferred embodiment of the invention, the slight angling of the recesses 350 and the surfaces 320 from the longitudinal axis of the screw provides a carry function for the driver head. The slight angle means that, if the screw head is pushed into the screw interface with a certain force, edges 450 are pushed into recesses 350 with an increasingly tighter fit. Once a certain point is reached, the surfaces of the driver head are pressed against the inner surface of the screw interface so tightly that the resultant friction fit allows the screw to be picked up by the driver head and carried without any support for the screw. This is called a carry function and can be vital for simplifying the process of installing the screw in a dental implant. In the preferred embodiment, the configuration of the preferred driver head and interface allows this carry function to exist even when the driver head is inserted at an angle from the longitudinal axis of the screw. This is particularly advantageous when inserting a screw into an angulated screw channel (as shown in FIGS. 2A and 2B). Furthermore, the configuration of the preferred driver head and interface allows the contact position of rounded portion 450 to be controlled to be within the optimal range, and so the optimal amount of friction to achieve the carry function can also be controlled.
In a preferred embodiment of the invention, either or both of the surfaces of the driver head or the internal surface of the screw interface are applied with a coating, such as Titanium Nitride, which increases the friction between the components. This provides an enhanced carry function between the driver head and the screw interface and reduces the risk of the screw being dropped.
In an alternative embodiment of the invention, the number of recesses in the screw interface is greater than six. An increased number of recesses provides a smoother action between the co-operating surfaces of the screw interface during rotation of the screw by the driver head.

## Claims

1. A combination of a screw for a dental application, and a driver for driving the screw for fastening a dental component to a dental implant:
the screw having a coronal end and an apical end, the screw comprising:
a bore running from the coronal end of the screw along a portion of the screw towards the apical end of the screw,
a first number of equally spaced recesses arranged circumferentially around an inside surface of the bore, each recess running a length from the coronal end of the bore towards the apical end of the bore,
wherein the length of each recess is angled relative to the longitudinal axis of the screw such that the recess is further from the longitudinal axis of the screw at a point parallel with the coronal end of the bore than at a point below the coronal end of the bore, wherein each pair of adjacent recesses are connected by a contact surface on the inside surface of the bore, each contact surface running a length from the coronal end of the bore towards the apical end of the screw, and wherein each contact surface is angled away from the longitudinal axis of the screw such that the surface is further from the longitudinal axis of the screw at a point parallel with the coronal end of the bore than at a point below the coronal end of the bore,

the driver comprising:
a driver head having an apical and coronal end, and an axial plane parallel to the longitudinal axis of the driver,
the driver head comprising at least a first, a second, and a third portion having a polygonal cross-section in a radial plane, the radial plane being perpendicular to the longitudinal axis of the driver, wherein edges of the first portion, the second portion, and the third portion are continuous;
the first portion having a convex, rounded cross-section in the axial plane, the first portion curving radially inward towards the longitudinal axis of the driver head at apical and coronal ends of the first portion;
the second portion connected apically relative to the first portion, the second portion having a truncated triangular shape tapered towards the apical end of the driver head in the axial plane; and
the third portion connected apically relative to the second portion, the third portion forming a continuously curved apical tip of the driver head;
wherein the driver is configured to drive the screw at an angle from the longitudinal axis of the screw.

2. The combination of claim 1, wherein at least a portion of the inside surface of the bore of the screw comprises a layer of titanium nitride.

3. The combination of claim 2, wherein the screw is a dental component directly attachable to a dental implant.

4. The combination of claim 1, wherein the apical end of the bore of the screw is conical, having a widest point at the apical end of the recesses.

5. The combination of claim 4, wherein the screw is a dental component directly attachable to a dental implant.

6. The combination of claim 4, wherein a gradient angle of the conical apical end of the bore is configured to control the depth of entry of the screw head into the bore.

7. The combination of claim 6, wherein the gradient angle is configured such that the first portion having a convex, rounded cross-section contacts recesses between 25% to 75% of the length of the recess when the driver is inserted into the bore.

8. The combination of claim 1, wherein the screw is adapted to fasten a dental component to a dental implant.

9. The combination of claim 1, wherein the screw is a dental component directly attachable to a dental implant.

10. The combination of claim 9, wherein the dental component is selected from the group comprising: a cover screw, a healing abutment, and an impression coping.

11. The combination of claim 1, wherein the driver head comprises a tip portion at the apical end of the driver head having a polygonal cross-section in a radial plane of the longitudinal axis of the driver and a continuously curved apical end.

12. The combination of claim 11, wherein at least a portion of the surface of the driver head comprises a layer of titanium nitride.

13. The combination of claim 1, wherein at least a portion of the surface of the driver head comprises a layer of titanium nitride.

14. The combination of claim 1, wherein at least a portion of the contact surface is flat.

15. The combination of claim 1, wherein each contact surface runs a length from the coronal end of the bore towards the apical end of the screw at least along a portion proximate an intersection with one of the first number of equally spaced recesses.

16. The combination of claim 1, wherein the polygonal cross-section of at least a first and second portion is convex.

17. The combination of claim 1, wherein the contact surfaces and recesses form a continuous opening at the coronal end of the bore.

18. The combination of claim 1, wherein, along a radial plane passing through the first portion, distances between edges of the driver head are substantially equal.

19. A combination of a screw for a dental application, and a driver for driving the screw for fastening a dental component to a dental implant:
the screw having a coronal end and an apical end, the screw comprising:
a bore running from the coronal end of the screw along a portion of the screw towards the apical end of the screw,
a first number of equally spaced recesses arranged circumferentially around an inside surface of the bore, each recess running a length from the coronal end of the bore towards the apical end of the bore,
wherein the length of each recess is angled relative to the longitudinal axis of the screw such that the recess is further from the longitudinal axis of the screw at a point parallel with the coronal end of the bore than at a point below the coronal end of the bore, wherein each pair of adjacent recesses are connected by a contact surface on the inside surface of the bore, each contact surface running a length from the coronal end of the bore towards the apical end of the screw,
wherein each contact surface is angled away from the longitudinal axis of the screw such that the surface is further from the longitudinal axis of the screw at a point parallel with the coronal end of the bore than at a point below the coronal end of the bore, and
wherein the recesses have an arcuate shape with an apex that is radially outward of an intersection of two planes aligned with adjacent contact surfaces,

the driver comprising:
a driver head having an apical and coronal end, and an axial plane parallel to the longitudinal axis of the driver,
the driver head comprising at least a first and second portion having a polygonal cross-section in a radial plane, the radial plane being perpendicular to the longitudinal axis of the driver, wherein edges of the driver head are continuous from the first portion to the apical end of the drive head;
the first portion having a convex, substantially rounded cross-section in the axial plane, the first portion curving radially inward towards the longitudinal axis of the driver head at apical and coronal ends of the first portion; and
the second portion connected apically relative to the first portion, the second portion having a truncated triangular shape tapered towards the apical end of the driver head in the axial plane:
wherein the driver is configured to drive the screw at an angle from the longitudinal axis of the screw.

20. The combination of claim 19, wherein the driver head comprises a third portion connected apically relative to the second portion, the third portion forming a continuously curved apical tip of the driver head.

21. The combination of claim 19, wherein the first portion has a convex, rounded cross-section in the axial plane.