WO2008077443A1

WO2008077443A1 - Device for securing a dental attachment to one or more implants

Info

Publication number: WO2008077443A1
Application number: PCT/EP2007/009170
Authority: WO
Inventors: Carl Van Lierde
Original assignee: Materialise Dental N.V.
Priority date: 2006-12-22
Filing date: 2007-10-16
Publication date: 2008-07-03
Also published as: GB0625733D0

Abstract

An object of the present invention is to provide' a device (20,30 and 60) for securing a dental attachment, such as a dental bridge or other dental prosthesis, to one or more dental implants which can be, or have been, implanted in a patient's jaw. The present invention allows securing the dental attachment regardless of deviations (to a certain extent) between position and angulation of implants as in the patient's jaw and position and angulation of holes in the dental attachment that is designed for instance based on the implant planning.

Description

DEVICE FOR SECURING A DENTAL ATTACHMENT TO ONE OR MORE

IMPLANTS

FIELD OF THE INVENTION

The present invention relates to securing a dental attachment, such as a dental bridge or other dental prosthesis, to a dental implant which has been implanted in a patient's jaw. The invention is particularly useful when an attachment must be placed on more than one implant simultaneously.

BACKGROUND TO THE INVENTION

It is known to secure a dental attachment, such as a dental bridge or other dental prosthesis, to implants that have been implanted into a patient's jawbone. An attachment can be manufactured after the implant is placed in the jawbone or before the implant is placed in the jawbone.

Where the attachment (e.g. bridge) is manufactured after the implants have been installed in the patient, an impression is typically taken of the mouth to determine the locations of the implants relative to the jaw and each other, hi such cases, it is possible to plan, with some certainty, the size and shape of the attachment and the attachment is designed to have very limited play with respect to the implants. Some limited adjustment can be provided by recesses in between the attachment and the anchorage elements (also known as abutments) on the upper part of the implants. When the attachment is fitted to the implant, cement is applied to the internal surface of the recess of the attachment and the external surface of the abutment to overcome any play between these parts. Cement, or cement-like agents, may pose problems related to hardening. Most cement types harden very rapidly, making it difficult during the hardening process to achieve exact and permanent positions for the bridge. Moreover, cement may be difficult to handle in the mouth of a patient (for example, determining the correct amount of cement to use) and may cause soiling of the restoration site.

hi many cases, when the attachment is not cemented onto abutments but screwed onto abutments or directly onto the implants a two-stage procedure is used. The implants are installed in the jawbone and an impression is taken of the post-operative situation several weeks after the surgical intervention. Using impression copings, the exact positions of the implants in the mouth are transferred to a gypsum model. Implant replicas embedded in this model allow a dental technician to manufacture a prosthesis that fits exactly on the implants in the jaw of the patient. A disadvantage of this approach is that the prosthesis cannot be produced prior to instalment of the implants.

Where the attachment is designed and manufactured prior to the instalment of the implants - for so-called 'immediate loading' - the amount of play between the attachment and the implant can be considerably larger. The information about the expected implant positions must come from an implant planning system (such as SimPlant™ from Materialise Dental NV, Belgium). The implant planning system allows a clinician to determine the optimal position of the implants in a computer environment showing digital information of the patient (for example CT images). The implant plan can be used to design and manufacture the attachment and means (e.g. surgical templates such as SurgiGuide™, Materialise Dental NV, Belgium) are used to transfer the planning to the patient. The play between the implants after installation and the attachment depends on the manufacturing tolerances of the attachment and the inaccuracies inherent to the medical imaging for implant planning and the surgical process of transferring the planning to the patient. Typically the play will range from 0 to 0.5 mm in the lateral direction (known as the mesio-distal or bucco-lingual direction), 0 to 0.5 mm in the vertical direction ^"(known as the coronal-apical direction) and 0 to 5° in an angular direction.

There have been various proposals to provide a degree of adjustment between an implant and an attachment. International Patent Application WO 03/061512 describes a dental attachment with a longitudinally extending recessed wall. An implant has a longitudinally-extending portion which can fit within the recessed wall of the attachment and which can expand to anchor the attachment in a relative longitudinal displacement relative to the portion of the implant. The use of expandable components has the disadvantage that the loads are transferred to the implants by friction. This may cause problems of loosening of the attachment in case of clenching by the patient.

International Patent Application WO 2005/053564 describes a system to overcome lateral misalignments. An anchorage part of an attachment comprises a hole for a retaining screw and the neck of the retaining screw is smaller than the hole in the anchorage part. International Patent Application WO 92/03984 describes a device for anchoring a dental attachment to overcome angular deviations in the play between the bridge and the implants. WO 2004/105632 describes an implant having an integral bendable abutment portion. In use, the bendable portion is bent to the desired angle and then a channel in the portion is filled with a composition that can fix the portion at the desired angle. Each of the devices of WO 2005/053564 or WO 92/03984 allows a limited amount of adjustment in a single direction (longitudinal, lateral or angular). With the devices of WO 2004/105632 the abutment and the prosthesis cannot be easily removed afterwards due to the fixation with a position fixing composition.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a device and a method of securing a dental attachment, such as a dental bridge or other dental prosthesis, to one or more dental implants which can be, or have been, implanted in a patient's jaw. hi at least some embodiments, the present invention seeks to reduce or overcome at least one of the problems of the prior art methods and devices.

A first aspect of the invention provides a device for fitting a dental attachment to a dental implant comprising: a lower interface part for engaging with or in engagement with the implant; an upper interface part for engaging with or in engagement with the dental attachment; a flexible middle part connected to, or connectable to, the upper and lower interface parts which allows the interface parts to move relative to each other laterally or angularly, the flexible middle part also being capable of elongating or compressing to allow the relative distance between the interface parts to respectively increase or decrease. The flexible middle part may be rigidly connected to or connectable to the upper and lower interface parts.

The dental device according to the present invention is particularly useful when a dental attachment must be placed on more than one implant simultaneously. The term "dental attachment" means any structure (with a regular or irregular cross section, regardless of the material used) intended to connect to at least one implant. Typically dental attachments are used to transfer loads (for instance as a result of mastication) to the implants, but dental attachments may also be designed to avoid the transfer of mastication loads when secured immediately after implants are placed in the bone. In such cases the attachment serves mainly an aesthetical purpose.

It is noted that the play between the attachment and the implant may be "planned" (for example, where a dental attachment is designed prior to implant placement in a patient) or may be "unplanned" (for example, play which arises from manufacturing tolerances of the attachment). The attachments can be manufactured after the implants are placed in the jawbone or before the implants are placed in the jawbone.

The relative position and angulation of implants placed in the jawbone of the patient differs in most cases from the planned positions. The use of a device according to the present invention has the advantage that a dental attachment, which has been designed based on planned implant positions, can still be fitted on the implants (e.g. by means of screw fixation), even where the actual position (and/or angular orientation) of the implants deviates from the planned positions of the implants. Preferably, the device can cope with deviations that are within the orders of magnitude described earlier (e.g. up to approx. 0.5 mm in the lateral direction, up to approx. 0.5 mm in the vertical direction and up to approx. 5° angularly). This will normally be the case when using a means (e.g. surgical template such as SurgiGuide, Materialise Dental NV, Belgium) for transfer of the planning to the patient. Devices according to embodiments of the present invention can accommodate larger differences than those specified above by adapting the design and/or the material of the flexible part. The differences disclosed above should be viewed as convenient limits.

The device according to the present invention has another advantage in that it allows considerable freedom of the overall position of the dental attachment to be adjusted to enhance the occlusion, i.e. the position of the teeth of the dental attachment relative to the antagonists. When using a cemented prosthesis one can also change the position of the teeth of the dental attachment relative to the opposing teeth but only to a limited extent. The flexibility of the middle part can be realised by at least one of: the properties of the material used to manufacture the middle part; geometrical features of the structure of the middle part. For example, a material with a Young's modulus in the range of 1 to 5 GPa could be used, or a material such as PEEK (polyetheretherketones). The geometrical features can comprise a plurality of openings or other weakening structures which allow the middle part to flex and to compress and/or elongate. A middle part with geometrical features in the structure which allow flexibility can be formed from a material with flexible properties to give an even greater degree of flexibility.

Preferably, the device further comprises a sealing part for forming a seal between the lower part of the device and the dental attachment. This provides a physical barrier between the lower part of the device and the dental attachment that will prevent food, bacteria or other undesired substances gaining access to the inside of the dental attachment. It can also avoid the need to fill the interior of the dental attachment (and device) with cement. The sealing part is only for preventing debris or dirt from going into the dental attachment and maybe also accessing the implant. The sealing part is not used to fix the position/direction of the device.

Accordingly, adjustments can be made later with the devices according to the present invention. It can be advantageous to adjust the device at a later date, for instance for a partially edentulous case. In such a case it can be useful to change from an unloaded to loaded prosthesis by decreasing the compression of the devices. It is also useful that the "abutment" can be removed at a later stage. That is in case a final prosthesis is made.

The present invention also allows the use of an economical temporary prosthesis and then to replace this by a more expensive and aesthetically optimized final one at a later date.

Preferably, the outer surface of the upper part is reduces in dimensions, e.g. is tapered or spherical in shape. This helps to guide the positioning of the device within a dental attachment and also increases the amount of play between the device and a dental attachment which can be especially useful if the implant is offset from its planned position.

Preferably, the device comprises means for securing the parts of the device in a particular configuration, once a suitable fitting has been obtained. This prevents the middle part of the device from flexing any further. The securing means can comprise a rigid element which fits within a channel inside the flexible middle part. The rigid element cooperates with the upper part and the lower part. This cooperation can comprise a screw threaded interface between the rigid element and a collar on the upper part of the device.

Advantageously, the flexible middle part is rigidly connected to the upper and lower interface parts. "Rigidly connected" means either integral formation, or joining of two parts in such a way that mechanical forces from one part are transmitted to the other part.

The lower interface part, the upper interface part and the flexible middle part can be formed from the same material, or one or more of the parts can be manufactured from different materials.

A further aspect of the invention provides a dental attachment comprising a channel for receiving a device according to any one of the preceding claims.

Preferably, the channel has a funnel-shaped portion for guiding the device into position within the channel.

Preferably, the dental attachment comprises a flange extending radially into the channel which serves as a clamping surface for clamping the device to the dental attachment.

A further aspect of the present invention provides a kit of parts comprising a device as described above and a selection of differently dimensioned variants of at least one of the upper, middle and lower parts. This allows a practitioner to assemble a modular version of the device which is suitable for each implant site in a patient. For example, the lower parts may have different heights which are compatible with different soft tissue thicknesses in individual patients, or the middle parts may have different lengths to cope with different ranges of distance between an implant and a dental attachment.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows the types of deformation (i.e. compression, elongation, lateral deformation, bending) that are possible with a device according to the present invention;

Figure 2 shows a device according to a first embodiment of the invention connecting an implant to a dental attachment;

Figure 3 shows a second embodiment of the invention including a seal between the device and the dental attachment; Figure 4 schematically shows an example of a treatment planning comprising four implants and the design of the dental attachment based on this planning;

Figure 5 shows the same planning as shown in Figure 4 with the final position of the implants as placed in the jawbone of the patient superimposed upon the planned positions; Figure 6 shows the use of four devices according to the present invention to secure the dental attachment to the set of implants shown in Figure 5;

Figure 7 shows an assembly of parts of a device according to another embodiment of the invention;

Figure 8 shows a dental implant with on top one of the possible designs of the invention;

Figure 9 shows another embodiment of the invention, where an additional fixation means is used;

Figures 10- 13 show a sequence of steps of fitting the device to an implant and to a dental attachment; Figure 14 shows an assembly of the type shown in Figure 13 compensating for an angular deviation;

Figure 15 shows a preferred embodiment of a sealing part to be fitted between the lower part of the device and a dental attachment. DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps.

According to the invention a device and method are provided for securing a dental attachment to one or more dental implants that can be, or have been, implanted in a patient's jaw. As shown in Figures 1 to 3, the device 15 has three parts: a lower part 20, an upper part 30 and a middle part 60.

The lower part 20 of the securing device 15 interfaces with an implant 10 onto which the device will be secured. Typically the lower part 20 is configured relative to the implant 10 with a male-female or female-male fitting. The base of the lower part 20 is complementary to the proximal end (the head) 11 of the implant 10 and the configuration provides tactile feedback when indexing the securing device 15 to the implant 10. hi an embodiment a hexagon protrudes from the proximal end 11 of the implant and is received in a hexagonal or conical recess in the base of the lower part 20 of the device. Alternative fittings are possible: for instance conical, octagonal, etc. The lower part 20 may be further provided with means for connecting the lower part 20 to the implant 10, such as an implant screw 25.

Figure 3 shows a further embodiment of the device 15. The lower part 20 of the device can have a ridge 22 or special shape at the external surface to hold, or abut against, a sealing part 12. A circular, shaped, ring is shown in more detail in Figure 15. A sealing material may also be directly fixed to the outside of the lower part 20 of the device. The sealing provides a physical barrier between the lower part of the device and the dental attachment that will prevent food, bacteria or other undesired substances gaining access to the inside of the dental attachment. The sealing material can be an alternative to the ring 12. According to another embodiment the lower part 20 of the device 15 may exist in different heights so as to be compatible with different soft tissue thicknesses in individual patients. In use, a practitioner either selects a lower part 20 of the correct height from a set of lower parts of different dimensions (in a modular version of the device 15), or selects a device 15 having a lower part 20 of the correct height from a set of differently dimensioned devices (in an integrated version of the device 15.)

The upper part 30 of the device 15 interfaces with a dental attachment 40, 50. Figure 3 shows a dental attachment with sleeves 40 and an attachment or prosthesis 50 which fits to the outside, or inside, of the sleeves 40. According to embodiments of the present invention, the upper part 30 of the device engages in an aperture (channel) inside a sleeve 40 of the dental attachment where it abuts against a flange 42. Also, according to embodiments of the present invention, the upper part 30 of the device is provided with a means 35 to secure it to the sleeve 40 of the dental attachment. The method of securing can, for example, be a screw 35, the head of which abuts against the other side of said flange 42 provided in the aperture of the dental attachment 40 while the shaft and/or a screw thread screws into the upper part 30 in which an internal thread is provided.

Also, the upper part 30 may be cylindrical and may, at a certain distance from the top, gradually increase in diameter (towards the middle part) thereby forming a tapered section 32. The tapered surface functions as an outer guiding surface 32 to force the upper part 30 in the desired position inside the aperture within the dental attachment 40, 50.

According to one embodiment apertures are planned directly in the design and manufacturing of the dental attachment. Conversely, said aperture(s) can be created by integrating a pre-designed and preformed component into the dental attachment at the time of its production. Preferably, each aperture is divided into two portions 44, 46 (not necessarily equal in size) by an inner flange 42, with a hole passing through the flange. The upper portion 44 is preferably cylindrical in shape. The lower portion 46 is also preferentially cylindrical and also preferably has a tapered section 45 by which the diameter is gradually increased (towards apical). The resulting tapered surface 45 on the inner side of the aperture acts as a guiding surface to force the upper part 30 of the device into its desired position inside the aperture. The resulting tapered surface 45 may also increase the play between the dental attachment 40 and the device 15. When the tapered section 45 extends more to the bottom side of the sleeve 40 then there will be a larger distance between the device 15 and the lower portion 46 of the sleeve 40. This distance will allow a larger flexion (lateral or angular deformation) of the device 15. Play is then provided between the flexible middle part and the component 40.

The middle part 60 of the device is characterized in that it is flexible and can thereby compensate deviations by bending, elongating and compressing. The bending can accommodate differences in angular position of the upper and lower parts 20, 30, a lateral offset in the position of the upper and lower parts 20, 30, or a combination of these. The device 15 can also compensate a purely lateral deviation (as shown in image 3 of figure 1). This means that the central axis of the lower part 20 and the central axis of the upper part 30 remain parallel, but are no longer coincident. This can be mainly realised by shear deformation of the device and not by pure bending of the device 15.

The middle part 60 is connected to the upper part 30 and the lower part 20 of the device. The flexibility of the middle part 60 can be provided by the properties of material used for this part or due to geometrical features (such as openings or other weakening structures) provided in it, or due to a combination of both of these. Preferably, the flexibility is sufficient to allow a range of movement at least from 0 to 0.5 mm in the lateral direction (known as the mesio-distal or bucco-lingual direction), and/or 0 to 0.5 mm in the vertical direction (known as the coronal-apical direction) and/or 0 to 5° in an angular direction, as shown in Figures 1 and 6. According to one embodiment, the middle part 60 is designed with a perforated wall in which the perforations, for example, have the shape of a honeycomb structure. According to another embodiment the middle part 60 is formed as a set of circular discs 65 that are connected to each other pair wise by two or more connection stubs 66 positioned radially-symmetric about the longitudinal axis of the set of discs. The connection stubs between two adjacent pairs of discs are turned at a certain angle relative to one another. According to a preferred embodiment, the middle part 60 of the device may be tapered (i.e. the diameter increases from apical to occlusal) to increase the play between the device and the aperture in the dental attachment. The middle part 60 can be connected to one, or both, of the other parts 20, 30 in a permanent manner, such as by manufacturing the parts 20, 30, 60 integrally with one another (e.g. by overmoulding the middle part around the upper part and lower part). Alternatively, the middle part 60 can be manufactured as a part which is separate from one, or both, of parts 20, 30 and a practitioner can connect parts 20, 30, 60 together before fitting the device 15 to a patient. Preferably one or more of the parts 20, 30, 60 are provided in a range of different dimensions and a practitioner can select an appropriate upper part 20, middle part 60, and lower part 30 that are appropriate to each of the implant sites. The connection between the separate parts 20, 30, 60 can be a detachable connection, which can allow a practitioner to change one or more of the parts if a better fitting is required.

Parts (upper, lower and middle) of the device can comprise assemblies of individual assembly pieces. Each of the parts can be made from a single material, or one or more parts or assembly pieces can be made from different materials. Alternatively, the entire device 15 can be made as a single, integrally formed, piece, from one or more materials. A single one of the parts 20, 30, 60 can be formed from individual pieces. For instance, the different parts can already be assemblies from different individual pieces, when these are for instance made from more than one material.

While it is advantageous that the device 15 should allow a range of movement between a dental attachment 40, 50 and an implant, it is also desirable that the parts 20, 30, 60 of each device 15 can be secured in the relative positions which achieve a good fitting of the dental attachment to the implants. Figures 10-13 show a way of achieving this securing of the parts 20, 30, 60. A securing means (e.g. threaded pin 36) extends through an internal channel along the middle part 60 of the device. The distal tip 38 of the screw presses against the head of screw 25 fitted in the lower part 20, such that further (elastic) deformation of the middle part 60 is prohibited. This prevents mobility of the dental attachment 40, 50 after it has been secured on the implants 10. This mobility may result from external loading (as a result of mastication) of the dental attachment. The securing means may be a pin (cylindrical, conical, or other shape) passing through the hole in the inner flange 42 of the aperture in the dental attachment and through the upper part 30 and middle part 60 of the device, and making contact with the lower part or the screw fixing the lower part onto the implant. The securing means is provided with features to fix it to the upper part (e.g. a screw thread on the pin 36 which cooperates with a screw threaded collar on the upper part 30). According to a preferred embodiment the securing means may be tapered at the apical part, to allow the required deformation of the middle part (i.e. the securing means does not restrict the deformation of the middle part 60). The securing means may also have another shape (e.g. spherical) at the bottom (apical) end. The use of fixing means 35-38 in this manner can avoid the need to use any fixing compositions to set the device in a desired position. The screw 35 will prevent any further compression of part 60 of the device. This does not imply that it also prevents the parts from being pulled apart from one another. Accordingly, there is no means that prevents the parts from being pulled apart from another, except for the limited elongation of the middle part 60. As explained further in the text below, one intended to use of the device is for multiple implant dental attachments in combination with at least one rigid connection between implant and dental attachment, which will limit the movement of the dental attachment due to pulling forces on the dental attachment.

According to another embodiment the device could be directly incorporated in the design of the dental attachment. For example, the device can be directly integrated into the dental attachment, which means that the upper part 30 of the device is integrated into the design of the dental attachment and the middle part is assembled directly into the dental attachment.

The device 15 secures the prosthesis (dental attachment) to the implant(s) and may, or may not, extend beyond the gingival tissue.

Figures 4 to 6 show an example of how the device according to the present invention can be used. A set of four implants 10 are to be fitted to a patient and a dental attachment or prosthesis 50 is to be fitted to these implants 10, such that it spans the implants. Figure 4 shows the planned positions of the implants, at implant sites A, B, C, D. Figure 5 shows the actual positions of the implants in the patient's jaw, overlaid upon the planned positions. It can be seen that: the actual position of an implant may be offset laterally in any direction from the planned position; the actual position may be inclined at an angle from the planned position; or the actual depth of the implant may differ from the planned depth. These differences can all exist in the jaw of a patient at the same time, and although not shown in Figure 5, these differences could all exist at a single one of the sites A, B, C, D. Figure 6 shows a dental attachment 40, 50 fitted to the set of implants 10, using a device 15 at each implant site. It can be seen that the upper, middle and lower parts, 20, 30, 60 of each device 15 co-operate with the implants 10 and the dental attachment 40, 50 to accommodate any differences in the actual position of the implant, compared to the planned position of the implant, while maintaining a secure fitting of the dental attachment 40, 50. Looking at the implant sites in detail: at site A the actual position of the implant is deeper than was planned. Accordingly, flexible part 60 elongates. At implant site B the actual position of the implant is offset laterally from the planned position. Part 60 flexes to adopt an 'S' shape. At implant site C the actual position of the implant is higher than the planned position. Part 60 compresses. At implant site D the actual position of the implant is angularly offset from the planned position. Part 60 flexes to adopt an arc shape.

The example shown in Figures 4 to 6 shows a device 15 according to the present invention being used at each of the implant sites A-D. However, it is also possible to use device 15 at fewer sites, with conventional, rigid, abutments being used at the other implant sites. For a dental attachment supported by two or more implants, it is usually possible to position the dental attachment correctly on at least one implant and to secure the dental attachment on that implant by means of a screw; either directly or by use of a standard abutment. To compensate for the deviations between the remaining placed implants and the corresponding apertures in the dental attachment, the device according to the present invention is used to allow screw fixation of the dental attachment.

An exploded view of a first kit of parts in accordance with an embodiment of the present invention is shown in Figure 7. This kit includes a securing device 15 comprising upper, lower and middle parts, 20, 30 and 60. The kit may include an implant 10 and optionally securing devices 25 and/or 35 as described above. The kit may also include the dental attachment 40. Another kit provided by the present invention includes the dental attachment 40 and the device 15.

A side view of another kit in accordance with an embodiment of the present invention is shown in Figure 8. This kit includes a securing device 15 and an implant 10. Also shown in this drawing are the optional geometrical features such as openings or other weakening structures 65, e.g. holes or slits in the middle part 60, that provide flexibility to this part as discussed above.

Fig.9 shows the feature of a 'finger' on the upper part for locating in a channel on the middle part. The upper part is located in a particular orientation. The upper part can be oriented parallel to the corresponding hole in the dental attachment.

Figures 10 to 13 illustrate, in detail, how a device 15 is fitted. Each of Figures 10 to 13 shows three views of the same set of components: a side view, a cross-sectional view and an isometric view. Before fitting the device 15, implants 10 are fitted in the patient's mouth. In a known manner, CT-based planning can be used to plan the implant sites and a surgical template can be used to transfer the planning to the patient's mouth, and guide the installation of the implants (e.g. using a SurgiGuide, Materialise Dental NV, Belgium). The pre-operatively manufactured dental attachment must then be fixed onto the implants. Referring firstly to Figure 10, the lower part 20 of the device 15 is placed on top of the implant 10, and then the base of the middle part 60 of the device is placed into a cup-shaped recess in the lower part 20. Both parts are fixed to the implant by means of a screw 25. The lower part 20 is made of metal to ensure a perfect fit with the implant 10. In this embodiment, screw 25 secures both the middle and lower parts to the implant because middle part 60 fits within lower part 20. In Fig. 2 the screw 25 only secures the lower part because in Fig.2 the middle part is formed integrally with the lower part.

Referring to Figure 11, the upper part 30 of the device 15 is fitted within the top of the middle part 60. The upper part 30 is made of metal and is surrounded by the flexible middle part 60 of the device. A finger-like shape at the top of the middle part 60 locks the upper part 30 in place. The 'finger-like shape' can be a ridge which extends vertically, to fit with a corresponding groove/channel in the outer surface of the upper part as shown in Fig. 9. The finger-like shape refers to the vertical cylindrical walls at the top of part 60, that have a horizontal ridge extending to the middle. In Figure 11 there are four finger-like shapes, created by adding vertical grooves. Without vertical grooves there would be no finger like shapes and a full cylindrical wall would not allow pushing in part 30. Figure 9 also shows one of these vertical grooves. Fixation pin 36 is then screwed within the upper part 30. The fixation pin 36 can be fitted before the attachment. Fixation pin 36 can be screwed in partly before placing the dental attachment, and is only screwed to the bottom after placing the dental attachment. Included within the scope of the present invention is to first place the dental attachment and then screw in fixation pin 36.

Referring to Figure 12, the dental attachment 40 is positioned over the device 15. The funnel shaped lower portion of the attachment serves to guide the middle and upper parts 30, 60 into position and also forces the middle part 60 of the device 15 to deform (if required). The securing means used to secure the upper part of the device to the attachment consists of a fixation pin 36 and a nut 37. The fixation pin 36 is screwed down until it contacts the lower screw 25. The nut 37 is then screwed onto the head of the fixation pin 36, and locates against flange 42 of the dental attachment 40, to secure the dental attachment 40 onto the upper part 30. Before screwing the nut 37 onto the fixation pin 36, the position of the dental attachment can still be slightly changed by screwing the fixation pin 36 in or out. This can be useful for changing the position of the attachment relative to the opposing dental arch, hence enhancing the occlusion.

Claims

1. A device for fitting a dental attachment to a dental implant comprising: a lower interface part for engaging with or in engagement with the implant; an upper interface part for engaging with or in engagement with the dental attachment; a flexible middle part connected to, or connectable to, the upper and lower interface parts which allows the interface parts to move relative to each other laterally or angularly, the flexible middle part also being capable of elongating or compressing to allow the relative distance between the interface parts to respectively increase or decrease.

2. A device according to claim 1 wherein the flexibility of the middle part is realised by at least one of: the properties of the material used to manufacture the middle part; geometrical features of the middle part.

3. A device according to claim 1 or 2 wherein the middle part of the device is manufactured using a material with a Young's modulus in the range of 1 to 5 GPa.

4. A device according to claim 3 wherein the material is PEEK (polyetheretherketones).

5. A device according to claim 2 wherein the geometrical features comprise a plurality of openings in the structure of the middle part.

6. A device according to claim 5 wherein the openings form a honeycomb pattern.

7. A device according to claim 2 wherein the structure of the middle part comprises a set of circular discs, with adjacent pairs of discs being connected to each other by at least two connection stubs.

8. A device according to claim 7 wherein the connection stubs are positioned radially-symmetric about a central axis of the discs, with the connection stubs connecting adjacent pairs of discs being offset by a predetermined angle relative to each other.

9. A device according to any one of the preceding claims further comprising a sealing part for forming a seal between the lower part of the device and the dental attachment.

10. A device according to any one of the preceding claims wherein the outer surface of the upper part is tapered.

11. A device according to any one of the preceding claims further comprising means for securing the parts of the device in a particular configuration.

12. A device according to claim 11 wherein the securing means comprises a rigid element which is arranged to fit within a channel within the flexible middle part and which is arranged to cooperate with the upper part and the lower part.

13. A device according to claim 11 or 12 wherein the securing means is also arranged to secure the dental attachment to the upper part of the device.

14. A device according to any one of claims 11 to 13 wherein the securing means comprises a pin which has a threaded outer surface for cooperating with a threaded collar on the upper part.

15. A device according to claim 14 wherein the securing means further comprises a threaded nut for fitting to the top of the pin.

16. A device according to any one of claims 11 to 15 wherein the securing means is inwardly tapered towards its distal end.

17. A device according to any one of the preceding claims wherein the lower interface part, the upper interface part and the flexible middle part are formed from the same material.

18. A device according to any one of claims 1 to 16 wherein one or more of the parts are manufactured from different materials.

19. A device according to any one of the preceding claims wherein the flexible middle part is rigidly connected to the upper and lower interface parts.

20. A device according to any one of the preceding claims wherein the flexible middle part is detachably connectable to at least one of the lower interface part and the upper interface part.

21. A device according to any one of claims 1 to 19 wherein the lower interface part, the upper interface part and the flexible middle part are formed integrally.

22. A dental attachment comprising a channel for receiving a device according to any one of the preceding claims.

23. A dental attachment according to claim 22 wherein the channel has a funnel- shaped portion for guiding the device into position within the channel.

24. A dental attachment according to claim 22 or 23 further comprising a flange extending radially into the channel which serves as a clamping surface for clamping the device to the dental attachment.

25. A dental attachment according to any one of claims 22 to 24 in the form of a dental bridge or a dental prosthesis.

26. A kit of parts comprising: a device according to any one of claims 1 to 21; and, a selection of differently dimensioned variants of at least one of the upper, middle and lower parts.