GB2494099A - Dental component with an angled screw channel - Google Patents

Abstract

The present invention relates to a dental component 250 for fixation to a dental implant 210 in a patient's jaw. The apparatus comprises a component 250 with a screw channel 230, 290, a matching screw 260 and a screw seat 240. The screw channel 230, 290 is angulated relative to the longitudinal axis of the implant 210 to which the component is attached, so that the longitudinal axis of one end of the channel 230 is different to the longitudinal axis of the other end 290. The screw channel 230, 290 may be curved or comprise straight and curved portions. Preferably the screw head 270 and/or tip is beveled or chamfered. The component 250 preferably engages with the dental implant 210 using complimentary screw threads. The component 250 may also comprise an undercut portion. The dental component 250 could include an abutment, bridge or crown.

Description

Angulated Screw Channel 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 dental components with screw channels, through which a screw can be inserted in order to secure the dental component to the dental implant.

A typical arrangement for a prosthetic single tooth replacement is shown in figure 1 and comprises the following: -A dental implant 110 surgically installed in the jawbone of a patient, -A prosthesis 150 fixed to the dental implant, passing through the gum tissue (in alternative arrangements, an abutment provides a solid foundation for attachment of a separate dental prosthesis crown 150). The prosthesis has a screw channel 130 with screw channel entrance 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.

A current problem with the design of prosthesis is that the screw channel of the prosthesis has the same axis as the axis of the screw when screwed into the implant.

This means that the screw channel entrance is on the incisal edge or cusp of the prosthesis, i.e. on the visible top surface of the prosthetic tooth. This entrance is typically filled with a filler material to mask the screw channel entrance, but the resulting aesthetic effect is often imperfect due to colour mismatching.

Furthermore, the screw channel entrance is naturally a structurally weak part of the prosthesis. Therefore, it is disadvantageous to position the screw channel entrance on the incisal edge or cusp of the prosthesis, in a position subject to particular stress.

i.e. The pressure of the opposing tooth during grinding of the teeth will be applied directly to the screw channel entrance and the filler.

An equivalent problem exists for the production of bridge based prosthesis, in which an implant bridge for multiple teeth is mounted on the patient's jawbone by means of a plurality of dental implants. The implant bridge is attached to the implants by means

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of screws in the same way as the prosthetic single tooth replacement detailed above.

As a consequence, the implant bridge also suffers from the aesthetic and structural weakness problems when the screw channel entrance is on the incisal edge of prosthesis.

One solution is the use of an abutment with a separate prosthesis crown which is cemented to the abutment and which covers the screw entrance hole. However, the major disadvantage of this process is that the cement and prosthesis must be applied intra-orally. This makes the process complex and messy, as excess cement is known to cause a number of problems including poor aesthetics and gum disease problems for the patient.

When using implant bridges, a known method of providing a screw entrance which is not on the incisal edge of the bridge is to install the implant at an angle in the jaw bone so that the resultant screw entrance emerges at a point set back from the incisal edge of the tooth. However, this technique potentially results in weaker support for the implant and reduces stability over the long-term. Furthermore, it is difficult to reproduce this technique for use with single implant prostheses due to limited stability.

European patent specification EP 0695147 Bi describes an abutment comprised of two components. The first abutment component is attached to a dental implant in the usual way using a screw. The second abutment component is then attached over the top of the first component, and a second screw is screwed into the first and second abutment components at an angle to the first screw. The second screw holds the first and second abutment components together. The resultant abutment has a screw entrance at an angle from the implant longitudinal axis. The disadvantages of this system include the following. The multiple components are more expensive to manufacture than a single component abutment and can add significant expense for the patient. The fixation of the abutment to the implant is a two stage process involving application of two abutment components and two separate screws, all performed intra-orally. This is a fiddly procedure and introduces extra risks to the patient, such as the swallowing of components if the surgeon loses his grip on the components. Finally, the complex multi component structure of this abutment introduces various additional structural weaknesses which would preferably be avoided. Finally, the multi-unit abutment has a limited number of angle choices as they are expensive to customize and are normally made as a standardised product.

Furthermore, the minimum height of the abutment is limited, as the two part structure necessarily adds height to the abutment.

What is needed is a way of addressing the poor aesthetics and structural weakness resulting from a screw channel entrance located on the incisal edge of a dental prosthesis.

According to a first aspect of the invention, there is provided a dental component for fixation to a dental implant, the dental component comprising, a component body, a screw channel passing through the component body and forming a first opening at a first end and a second opening at a second end, a screw seat proximal to the second end of the screw channel for seating the head of a screw for the fixation of the dental component to a dental implant, wherein the longitudinal axis of the screw channel at the first end does not match the longitudinal axis of the screw channel at the second end. The screw channel may be curved between the first opening and the second opening. A portion of a screw channel wall extending between the screw seat and the edge of the first opening closest to the screw seat may have a substantially straight cross-section in the plane described by the longitudinal axis of the first end and second end. Furthermore, the entire screw channel wall extending between the screw seat and the edge of the first opening closest to the screw seat may have a substantially straight cross-section in the plane described by the longitudinal axis of the first end and second end. A portion of a screw channel wall extending between the screw seat and the edge of the first opening furthest from the screw seat may have a substantially straight cross-section in the plane described by the longitudinal axis of the first end and second end and is parallel with the longitudinal axis of the second end. A portion of a screw channel wall extending between the screw seat and the edge of the first opening furthest from the screw seat may be curved away from longitudinal axis of the screw channel at the first end in the cross-section in the plane described by the longitudinal axis of the first end and second end. The screw seat may comprise a seating surface configured to receive the screw head, wherein the circumferential edge of the seating surface adjacent the second opening is bevelled to form a chamfer.

The dental component may be an abutment. Alternatively, the dental component may be an implant mounted bridge or a screw-retained full contour crown. A portion of the screw channel between the screw seat and the second opening may comprises a recess arranged on the opposite side of the screw channel to the first opening.

In another embodiment of the invention, there is provided an arrangement for fixing a dental component to a dental implant, the arrangement comprising, the dental component of any preceding claim, the dental implant having a threaded bore configured to receive a screw, a screw for fixing the dental component to the dental implant, the head of the screw configured to rest on the screw seat when the dental component is fixed to the dental component. The head of the screw may have a chamfered top edge and/or the head of the screw may have a chamfered screw tip.

The outer diameter of the screw thread of the screw may be equal or less than 120% of the inner diameter of the screw thread.

Where the component has a straight portion of the straight screw channel, the furthest distance between an edge of the straight portion of the straight screw channel and the top of the threaded bore of the implant, when the prosthesis is fixed to the implant, may be equal to or greater than the length of the screw.

Aspects of the present invention will now be described by way of example with reference to the accompanying drawing. In the drawings: Figure 1 shows prosthetic dental solution with a dental prosthesis having a straight screw channel with a longitudinal axis matching that of the dental implant.

Figure 2 shows a dental prosthesis having an angulated screw channel.

Figures 3A to 3C show an embodiment of the screw with a cross sectional view, side view, top view and perspective view respectively.

Figure 4 shows a cylinder with chamfered edges passing through a curving passage.

Figures 5A to 5D show an embodiment of the prosthesis with a side view, cross sectional view, perspective view and top view respectively.

Figures 6A to 6C show different embodiment of the angular screw channel depending on the angle chosen for the screw channel from the vertical.

Figures 7A to 7B show a preferred embodiment of the invention having a recess to allow easier access for the screw passing through the screw channel.

Figures 8A to 8B show an alternative embodiment to that of figures 7A and 7B.

Figures 9A to 9B show another alternative embodiment to that of figures 7A and 7B.

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.

Angulated screw channel Figure 2 shows a dental prosthesis according to the present invention. Dental implant 210 comprises screw channel 230 having an inner thread configured to match the thread of screw 260 such that screw 260 can be fastened to the implant. Abutment 250 is fixed to the dental implant by means of screw 260. The prosthesis passes through the gum tissue to dental implant 210. The prosthesis has a screw channel 290 through which screw 260 is inserted. Screw channel 290 has a screw channel entrance 280 and screw seat 240 at the base of the prosthesis, upon which the head 270 of the screw 260 is seated when the prosthesis is fastened to the implant with the screw. According to the present invention, the axis of screw channel 290 (i.e. the line described by the radial centre point of the channel at any point) does not follow the axis of channel 230. In fact, screw channel 290 may be mostly straight but orientated at a different angle to channel 230. Alternatively, the axis of screw channel 290 may be curving or S-shaped. As a result, the axis of screw channel 290 at the channel entrance 280 does not match the axis of channel 230 or the axis of screw seat 240.

The advantage of this arrangement is that, by using a screw channel angulated away from the axis of channel 230 as described above, the screw channel entrance location can be planned by a lab technician. This allows the screw channel entrance location to be positioned on a surface, such as the lingual or palatal surfaces (the surfaces nearest the tongue/palate and not visible to a third party) or palatal surface, which avoid structural weaknesses and which improves the aesthetic appearance of the prosthesis.

Screw adaptations A preferred embodiment of screw 260 is shown in figures 3A-3C. In this embodiment the screw has been advantageously modified to reduce the effective length of the screw. The effective length of the screw is the length of the screw as measured from the points where the surface of the screw contacts the inside surface of the angulated screw channel as the screw passes through it. An example of the effective length of a screw is shown in figure 4. Cylinder 430 is passing through curving channel 440. As is described as part of the preferred embodiment of the invention, the chamfering of the corners 410 of cylinder 430 mean that the effective length of the cylinder (i.e. the distance measured between the points on the cylinder that contact the inner surface of the channel) is reduced from L to L. Reducing the effective length of the screw ensures that the angulated screw channel can be kept as narrow as possible, advantageously improving the strength of the prosthesis, as well as minimizing the aesthetic impact at the screw channel entrance. Alternatively, by reducing the effective diameter of the screw, steeper angles of curvature may be chosen for the path of the screw channel.

In the preferred embodiment, the top end 305 of screw 260 is chamfered to provide chamfered screw head surface 310. The chamfering of this surface reduces the effective length of screw 260. This concept is illustrated in figure 4, in which a cylinder 400 having chamfered edges 410 is able to pass through a narrow screw channel 430. An equivalent cylinder without the chamfered edges is shown by the dotted line 420 and would need a significantly wider screw channel in order to pass through. Therefore, the effective length of the chamfered screw is smaller than the effective length of the non-chamfered screw. In another embodiment, top end 305 has rounded edges instead of chamfered edges.

Another modification to reduce the effective length is a chamfering (or rounding) of the screw tip as shown in figures 3A, 3B and 3C. The tip of screw 260 is chamfered to produce chamfered screw tip surface 330. This modification also provides the advantage of reducing the likelihood of the screw tip from catching on any of the screw seat surfaces during insertion. A chamfered or rounded surface is more likely to slide off an edge within the angulated screw channel rather than catching and preventing the screw from advancing.

In the preferred embodiment, thread 320 has been modified to reduce the depth of the thread relative to the shaft 315 of the screw. i.e. The difference between shaft width A and the thread outer diameter B is minimized. A typical thread 325 having an outer diameter of C is shown by the dotted line in figure 3A. A screw having this typical thread has a diameter defined by the outer edge of the thread. The thread depth is the difference between the outer edge of the thread and the inner edge of the thread, i.e. the surface of the shaft on which the thread is based. By reducing the diameter of the thread to B, the effective thread depth is of the screw is reduced. A narrower thread diameter allows a narrower screw channel. This also provides the advantage of reducing the risk of the screw thread from catching on any of the screw seat surfaces during insertion. In the preferred embodiment, shaft width A is 1.5 ± 0.1mm, and thread outer diameter B is 1.7 ± 0.15mm, within normal tolerances.

In one embodiment, the length of the screw has been reduced. A shorter screw naturally reduces the effective length of the screw allowing it to pass through a narrower or more steeply angled screw channel. However, the screw length (and consequently thread length) should not be shortened so much that the thread deformation occurs under load and the screw grip is weakened too much to ensure a strong fixation of the prosthesis to the implant over the lifetime of the prosthesis.

In one embodiment, the diameter of the screw head has been reduced. As with a reduction of the screw length, a narrowing of the screw head allows the screw to pass through a narrower or more steeply angled screw channel. However, the screw head should not be narrowed so far as to weaken the fixture of the prosthesis to the implant over the lifetime of the prosthesis. In a preferred embodiment, the diameter of the screw head is equal to or smaller than 2.6 ± 0.1mm.

Screw seat Figures 5A to 5D show the preferred embodiment of a dental implant prosthesis 500 having an angulated screw channel. Figure 5A shows an external front view of the prosthesis and screw channel entrance hole, with the internal architecture denoted by dotted lines. Figure 5B shows a side cross section of the prosthesis and angulated screw channel. The angulated screw channel connects screw channel entrance 510 to screw fixture channel 520. Once the prosthesis 500 is positioned onto the dental implant, screw 260 is inserted through screw channel entrance 510 using a driver.

Far wall 530 of the screw channel is configured with a curvature which guides the inserted screw down towards screw fixture channel 520. Near wall 540 is substantially straight between the screw channel entrance 510 and screw fixture channel 520, which allows space for a straight driving tool to provide a driving force onto the screw right up until the screw is fastened in the implant.

When inserting the screw through an angulated screw channel for fixation to a dental implant, there is a particular risk that the screw will end up badly aligned with the threaded screw channel in the implant, due to the arrival of the screw tip at the threaded screw channel entrance at an angle away from the axis of the threaded screw channel. This can result in an improperly inserted screw and a damaged thread on both the screw and implant. This has potentially disastrous consequences and may require removal and replacement of the dental implant in the worst case. In order to minimize this risk, the preferred embodiment comprises a undercut portion 550 of the far wall of the angulated screw channel which comprises a straight surface substantially parallel to the axis of screw fixture channel 520. This straight surface allows the longitudinal axis of the screw to be aligned with the axis of screw fixture channel 520 as the screw is inserted into screw fixture channel 520. Undercut portion 550 of the far wall of the angulated screw channel is configured to line up the head and tip of screw 260 with the axis of screw fixture channel 520 before the thread of the screw engages with the thread of the screw channel in the dental implant, ensuring a clean engagement of the threads.

Figures 6A-6C show possible configurations for undercut portion 550. In figure 6A, where the angle of the screw channel from the vertical is between 00 and 5°, no undercut is used. In figure 6B, where the angle of the screw channel from the vertical is between 5° and 150, the screw channel has a smaller undercut. In figure 6C, where the angle of the screw channel is from 15° and 25°, the screw channel has a larger undercut.

In the preferred embodiment, the distance between the top of the straight portion 550 of the undercut to the top of the screw channel in the implant (or the bottom surface of prosthesis interface with the implant) is at least as great as the effective length of the screw. This ensures that the screw is in the correct orientation before the screw tip engages the implant thread.

Screw seat 560 is configured to seat the head of screw 260 when the screw and prosthesis are fixed to the dental implant. In the preferred embodiment as shown in figures 5A and SB, the screw seat is chamfered. i.e. the screw seat surface for receiving the screw head is at an angle from the horizontal. This provides the advantage of guiding the screw tip into the screw fixture channel 520. Furthermore, the chamfering of the screw seat reduces the risk of the tip of screw 260 from catching on the screw seat during insertion of the screw through the angulated screw channel. The chamfering maybe configured with an angle which allows the tip of the screw to simply slide off the lip of the screw seat with the force of gravity or the pressure from the driver. This reduces the complexity and awkwardness of the surgical procedure of securing the prosthesis to the dental implant, which in turns improves the experience for the patient. This effect is particularly pronounced when a larger insertion angle is used and the screw tip is particularly prone to catching on non-vertical surfaces within the angulated screw channel.

Figure 7A and 7B show an embodiment of the invention wherein the dental component extends into the bore of the dental implant a distance. This extension 700 may comprise anti-rotational features matched to the implant to improve both vertical and rotational stability of the component with respect to the implant. As shown in figure 7A and 7B, extension 700 comprises a recess 710. The recess is configured to receive the edge of the screw tip as the screw is inserted, to allow the screw to enter the implant and channel below the screw seat of the component at a greater angle from the longitudinal axis of the implant. In a preferred embodiment of the invention shown in figure 7B, the recess is positioned on the far side of the screw channel to that of the screw channel entrance and is recessed enough to provide the screw tip with the space needed to allow the screw to be inserted into the implant. In the preferred embodiment, the recess cross-section in the plane of the bore inner surface may be an oval shaped. In another embodiment shown in figures 8A and 8B, the recess 810 comprises a widening of the screw channel over a length of the screw channel. In another embodiment shown in figures 9A and 9B, the recess 910 comprises a cut running from the edge of the screw seat to the end of the screw channel adjacent the implant.

Bridge having an angulated screw channel In an embodiment of the invention, the dental component is an implant mounted bridge rather than a single prosthesis. Unlike a single prosthesis that is only mounted to one implant, the implant mounted bridge is a one-piece component which is mounted to multiple implants installed in the jaw bone of a patient. The bridge may comprise multiple prosthetic teeth. Once a veneering is applied to the prosthetic teeth of the bridge to ensure the aesthetics match the surrounding real teeth, the prosthesis is complete. The implant mounted bridge comprises a plurality of screw channels and screw seats similar to the above described prosthesis. The plurality of screw channels allow screws to be used to fasten the implant mounted bridge to the implants.

As with the single tooth prosthesis, it is desirable for the entrance of each screw channel to be positioned away from the incisal edge of the prosthesis in order to avoid poor aesthetics and particular stress to the otherwise structurally weak screw channel entrance. Therefore, the above principles may be applied to the planning and production of angulated screw channels in an implant mounted bridge, so that a lab technician can plan the location of the screw channel entrance. Furthermore, the same components and tools may also be used for fixing the implant mounted bridge having angulated screw channels to the plurality of implants.

Claims (1)

1. <claim-text>CLAIMS1. A dental component for fixation to a dental implant, the dental component comprising, a component body, a screw channel passing through the component body and forming a first opening at a first end and a second opening at a second end, a screw seat proximal to the second end of the screw channel for seating the head of a screw for the fixation of the dental component to a dental implant, wherein the longitudinal axis of the screw channel at the first end does not match the longitudinal axis of the screw channel at the second end.</claim-text> <claim-text>2. The dental component of claim 1, wherein the screw channel is curved between the first opening and the second opening.</claim-text> <claim-text>3. The dental component of any preceding claim, wherein a portion of a screw channel wall extending between the screw seat and the edge of the first opening closest to the screw seat has a substantially straight cross-section in the plane described by the longitudinal axis of the first end and second end.</claim-text> <claim-text>4. The dental component of any preceding claim, wherein the entire screw channel wall extending between the screw seat and the edge of the first opening closest to the screw seat has a substantially straight cross-section in the plane described by the longitudinal axis of the first end and second end.</claim-text> <claim-text>5. The dental component of any preceding claim, wherein a portion of a screw channel wall extending between the screw seat and the edge of the first opening furthest from the screw seat has a substantially straight cross-section in the plane described by the longitudinal axis of the first end and second end and is parallel with the longitudinal axis of the second end.</claim-text> <claim-text>6. The dental component of any preceding claim, wherein a portion of a screw channel wall extending between the screw seat and the edge of the first opening furthest from the screw seat is curved away from longitudinal axis of the screw channel at the first end in the crass-section in the plane described by the longitudinal axis of the first end and second end.</claim-text> <claim-text>7. The dental component of any preceding claim, wherein the screw seat comprises a seating surface configured to receive the screw head, wherein the circumferential edge of the seating surface adjacent the second opening is bevelled to form a chamfer.</claim-text> <claim-text>8. The dental component of claims 1 to 7, wherein the dental component is an abutment.</claim-text> <claim-text>9. The dental component of claims 1 to 7, wherein the dental component is an implant mounted bridge.</claim-text> <claim-text>10. The dental component of claims 1 to 7, wherein the dental component is a screw-retained full contour crown.</claim-text> <claim-text>11. The dental component of any preceding claim, wherein a portion of the screw channel between the screw seat and the second opening comprises a recess arranged on the opposite side of the screw channel to the first opening.</claim-text> <claim-text>12. An arrangement for fixing a dental component to a dental implant, the arrangement comprising, the dental component of any preceding claim, the dental implant having a threaded bore configured to receive a screw, a screw for fixing the dental component to the dental implant, the head of the screw configured to rest on the screw seat when the dental component is fixed to the dental component.</claim-text> <claim-text>13. The arrangement of claim 11, wherein the head of the screw has a chamfered top edge.</claim-text> <claim-text>14. The arrangement of claims 11-12, wherein the head of the screw has a chamfered screw tip.</claim-text> <claim-text>15. The arrangement of claims 10-12, wherein the outer diameter of the screw thread of the screw is equal or less than 120% of the inner diameter of the screw thread.</claim-text> <claim-text>16. The dental component of claim 11 as dependent on claim 5, wherein the furthest distance between an edge of the straight portion of the straight screw channel and the top of the threaded bore of the implant, when the prosthesis is fixed to the implant, is equal to or greater than the length of the screw.</claim-text>