Secondary part for a dental implant system and kit

Abstract

A dental implant system comprising a dental implant and a secondary part, the dental implant comprising a bore that extends from a coronal end towards an apical end along a longitudinal axis. The secondary part comprises an apical post portion arranged for insertion into the implant bore and a coronal post portion arranged to extend coronally from the implant when the apical post portion is inserted into the bore. The implant bore and the apical post portion comprise anti-rotation sections having complementary non-circular-symmetric cross-sections in a plane perpendicular to the longitudinal axis. When the apical post portion is inserted into the implant bore, the anti-rotation section of the apical post portion is accommodated within the anti-rotation section of the bore. The anti-rotation section of the apical post portion comprises a tapered segment within which at least the radially outermost portions of the anti-rotation section taper radially inwards in the apical direction such that an apically increasing gap of no more than 10° is formed between the tapered segment and the implant bore.

Description

TitleSECONDARY PART FOR A DENTAL IMPLANT SYSTEM AND KITTechnical Field

[0001] The present invention relates to a secondary part for a dental implant system, the secondary part being configured for coupling to a dental implant. The invention particularly relates to such secondary part being an abutment. The invention also relates to a combination of such a secondary part with a dental implant.Background Art

[0002] Dental implants are used to replace one or more teeth in the jawbone of a patient. Implants typically consist of two parts, an anchoring part and a support part, which can be formed integrally or as separate components. The anchoring part is inserted into the jawbone, where it osseointegrates with the bone. The support part protrudes above the gumline and provides a core support for the dental prosthesis, e.g., bridge or crown. The prosthesis can be connected to the support part via e.g., bonding (gluing or cementing) or screw thread.

[0003] When the anchoring and support parts are formed separately, the anchoring part in isolation is referred to as the implant while the support part is commonly known as an abutment. Such dental implants are commonly referred to as “two-part” or “two-piece” dental implants. During placement and osseointegration of the implant, and prior to connection of the abutment, other components may be temporarily placed on the implant. For example, a healing cap, impression post or scan body. The term “secondary part” is used herein to refer to components which are in direct contact with the implant during their use in the implant system. An abutment is an example of a secondary part.

[0004] The implant and abutment are connected in use via, e.g., gluing or threaded fastening. One component, typically the implant, comprises a bore, or cavity, into which the proximal end of the other component is inserted. Often, the bore and cooperating end of the other component have anti-rotation geometry to prevent relative rotation of the components when connected. US 2005 / 00287497 A1 , WO 2018 / 203247 A1 , and DE 10 2009027044 A1 disclose implant systems with anti-rotation geometry for ensuring properangular positioning of the abutment relative to the implant. The anti-rotation geometry of the implant can also be used to transmit torque to the implant during insertion into the bone.

[0005] Once implanted in the mouth the dental implant is provided with a prosthesis. The prosthesis can replicate a single tooth or multiple teeth. In two-part dental implants the prosthesis is usually indirectly attached to the implant by way of the abutment, and can be screwed, cemented, or otherwise fastened to the abutment. Recent advances in material and manufacturing technology have also allowed the creation of prostheses that can be directly connected to the implant. In such systems an abutment is not necessary, and the prosthesis itself forms a secondary part of the system.

[0006] During use, the dental implant system comprising the implant, abutment (where present) and prosthesis is subjected to high chewing forces over the course of its lifetime, which ideally should match that of the patient. Chewing creates a lateral force on the prosthesis, which causes the secondary part (prosthesis or abutment) to tilt and shift fractionally in relation to the implant. Repeated cyclic application of such forces causes wear and fretting on the areas of the implant system contacting one another and can led to fracturing and breakage of the system components. Broken parts must be replaced at cost and inconvenience to the patient. In particular, broken implants are not easy to replace as this involves removal of the bone surrounding the implant followed by the placement and osseointegration of a new part.

[0007] Traditionally, implants are made from biocompatible metals, such as titanium, or ceramics. Implant manufacturers continue to strive to improve the strength of implants so that these can withstand the forces transmitted to the implant during its lifetime while also enabling a reduction in the size of the implant. Implants must often fit into narrow interdental spaces, particularly when anterior teeth are replaced. Thus, it is beneficial to be able to offer small diameter, high strength implants.

[0008] For this reason, higher strength titanium-based materials can be beneficial for implant manufacture. These can be obtained by alloying (e.g., titanium zirconium), cold working or microstructure engineering (e.g., ultra-fine-grain alloys). For example, US 6 399 215 B1 discloses an implant made of ultra-fine grain (UFG) titanium. Ceramic materials, such as zirconium dioxide and aluminum dioxide, are also considered beneficial for implant manufacture due to their high strength and white appearance.

[0009] Fatigue testing of two-part implants shows that a common failure site for the implant system is the contact point between the implant and abutment, in particular at the anti-rotation geometry. Such anti-rotation geometry comprises complementary sections of the implant and abutment having a non-circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the component. Commonly used cross-sections are polygons, e.g., hexagonal or octagonal, or lobed configurations, e.g., hexalobular. The corners of a polygonal shape and the radially outer end of lobes can introduce load peaks into the system when subjected to loading such as bending or torque. In addition, in two-part implants in which the implant comprises a bore having anti-rotation geometry, the radially outer parts of the implant anti-rotation geometry form comparatively thin areas of implant wall. Thus, in existing implant systems it can occur that stress peaks are applied to the implant at its weakest, i.e. thinnest, point. This limits the forces to which the implant system can be subjected as well as the minimum diameter of implant that can be achieved.

[0010] It is an object of at least a preferred embodiment of the present invention to provide an improved secondary part for a dental implant system. It is an object to provide a secondary part which, when used in a dental implant system, provides increased strength or stability to the system.Disclosure of the Invention

[0011] According to the invention this need is met by a secondary part as it is defined by the features of independent claim 15, and by an implant system as it is defined by the features of independent claim 1 . Preferred embodiments are the subject of the dependent claims.

[0012] According to one aspect the present invention provides a dental implant system comprising a dental implant and a secondary part, the dental implant having an apical end and a coronal end and comprising a bore that extends from the coronal end towards the apical end along a longitudinal axis. The secondary part comprises an apical post portion having a longitudinal axis and being arranged for insertion into the implant bore and a coronal post portion having a longitudinal axis and arranged to extend coronally from the implant when the apical post portion is inserted into the bore, the implant and secondary part each comprising a cooperating limiting surface which, when in contact with one another, define the full insertion depth of the apical post portion. The implantbore comprises an anti-rotation section which extends over an axial length of the bore and which has a non-circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the bore along its entire axial length. The apical post portion of the secondary part comprises an anti-rotation section which extends over an axial length of the apical post portion and which has a non-circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the apical post portion along its entire axial length. When the apical post portion is inserted to its full insertion depth into the implant bore, the anti-rotation section of the apical post portion is at least partially accommodated within the anti-rotation section of the bore, thus creating an overlapping length of the bore and apical post portion anti-rotation sections. The anti-rotation section of the apical post portion is complementary to the anti-rotation section of the implant bore such that, when the apical post portion is inserted to its full insertion depth, relative rotation of the components is inhibited by contact of the anti-rotation section of the apical post portion against the anti-rotation section of the bore. The anti-rotation section of the apical post portion comprises a tapered segment within which at least the radially outermost portions of the anti-rotation section taper radially inwards in the apical direction, wherein when the apical post portion is inserted to its full insertion depth, the tapered segment is at least partially located within the overlapping length such that an apically increasing gap of no more than 10° is formed in the overlapping length between at least the radially outermost portions of the tapered segment of the anti-rotation section of the apical post portion and the radially outermost portions of the anti-rotation section of the implant bore.

[0013] By tapering at least the radially outermost portions of the apical post portion antirotation section within the tapered segment, contact between the implant and secondary part during lateral force application is increased in comparison to standard parallel walled anti-rotation sections. This enables the load to be distributed over a larger surface area of the implant and secondary part.

[0014] This occurs due to the fact that, during the application of a lateral force to the secondary part, the apical post portion both tilts within the implant bore and slides in the axial direction. When the anti-rotation section of the apical post portion is parallel walled, i.e. cylindrical, tilting of the secondary part will cause this anti-rotation section to abut against the implant bore at a small point of contact. This contact point will then move axially within the bore, first in a coronal direction and then apically as the lateral force is first applied and then removed. Over time, this repeated rubbing action over a small areaof the implant bore can lead to failure. In contrast, when the secondary part of the present invention is subjected to a lateral force, as the apical post portion abuts the bore and begins to move coronally, the tapered segment is brought into contact with the implant bore, thus increasing the surface area over which the force is applied. In order to achieve this effect, the apically increasing gap between the components must be relatively shallow, i.e. no more than 10°, such that contact will occur between the bore and the tapered segment. If the apically increasing gap is too large, the tapered segment will not be brought into contact with the implant bore and hence there is no increased force distribution.

[0015] A secondary part having the claimed configuration therefore mitigates the risk of implant failure by distributing the loads that occur during use over a larger surface area of the implant. The risk of failure is therefore reduced, and the strength of the implant system is enhanced.

[0016] This secondary part therefore has a beneficial effect on the amount of force the system is able to withstand before implant failure.

[0017] The secondary part is thus seen as inventive in its own right and therefore, according to a further aspect, the present invention provides a secondary part for use in the inventive dental implant system.

[0018] Preferred features of both aspects are described below.

[0019] In accordance with conventional dental terminology, “apical” refers to the direction towards the bone and “coronal” to the direction towards the occlusal surface of the teeth. Therefore, the apical end of a component is the end which, in use, is directed towards or into the jawbone and the coronal end is that which is directed towards or into the oral cavity.

[0020] Unless otherwise stated a “cross-section” of any component or part of a component refers to the cross-section in a plane perpendicular to the longitudinal axis of that component or part of that component.

[0021] In the following passages, different features of the invention are defined in more detail. Each feature so defined may be combined with any other feature or features unless clearly indicated to the contrary. In particular, any feature indicated as being preferred oradvantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0022] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments.

[0023] According to the present invention both the dental implant and the secondary part comprise anti-rotation sections, both anti-rotation sections having non-circular- symmetric cross sections over their entire axial lengths. The anti-rotation section of the apical post portion is complementary to the anti-rotation section of the implant bore such that, when the apical post portion is inserted to its full insertion depth in the bore, relative rotation of the components, namely the implant and the secondary part, is inhibited by contact of the anti-rotation section of the apical post portion against the anti-rotation section of the bore. This contact between the anti-rotation sections is caused by their non- circular-symmetric cross-sectional shapes. Because the cross sections are not circular- symmetric the lateral surface of the anti-rotation sections will comprise one or more surface area which has a radial dimension. In other words, the radial distance between the lateral surface of the anti-rotation section and the longitudinal axis of the component does not remain constant. As a consequence, rotation of the secondary part within the implant bore will result in one or more of the radially dimensioned surfaces of the apical post portion anti-rotation section coming into contact with a radially dimensioned surface of the anti-rotation section of the bore and thus further relative rotation is prevented. In most commercially available dental implant systems, a relative rotational play of less than 8° is provided by complementary anti rotation sections.

[0024] Many suitable non-circular-symmetric cross sections are known within the art and any such cross-sectional shape can be used in the present invention. The crosssection of the anti-rotation sections does not need to remain constant over the full length of the anti-rotation section. Indeed, in the case of the apical post portion anti-rotation section it is necessary for the cross-section to change in order to form the taperedsegment. However, for design simplicity it is preferred that any and all changes in the cross-section of the anti-rotation sections along their length are solely the result of tapering of one or more area of the anti-rotation section.

[0025] The anti-rotation section of the implant bore may comprise a polygonal cross section along its full axial length, such as a square, hexagonal, or octagonal cross section. The corners of the polygon may be rounded or chamfered. Alternatively, the anti-rotation section of the implant bore may comprise a plurality of circumferentially spaced radially extending protrusions and / or grooves that extend over the full axial length of the antirotation section. These protrusions and / or grooves may have a cross-sectional shape that is curved, straight edged or a combination of curved and straight edged. These protrusions and / or grooves may be continuous with one another about the circumference of the anti-rotation section, in other words the edges of one groove or protrusion contact the edges of the adjacent groove or protrusion, or they may be separated from one another by straight or curved sections of the cross section.

[0026] In one preferred embodiment, the anti-rotation section of the implant bore comprises a plurality of circumferentially spaced grooves which protrude radially outwards and extend over the full length of the anti-rotation section. These grooves preferably have a fully curved cross-section in a plane perpendicular to the longitudinal axis, as this provides a better force distribution over each groove. The fully curved crosssection may have a single radius, thus forming arc shaped grooves, or it may comprise sections having differing radii, for example a central concavely curved section bordered on either side by a convexly curved section. This provides a smooth transition into and out of the groove. While it is possible for the grooves to have different shapes to one another, preferably the plurality of circumferentially spaced grooves all have an identical cross-section to one another at each axial location of the anti-rotation section. Preferably the grooves protrude from and are interposed by a base surface, although in other embodiments they may be continuous with one another. The base surface from which the grooves extend may have a circular cross-section such that the grooves extend from a curved surface. However, it is also possible for the base surface to have a polygonal cross-section such that the grooves are interposed by planar surfaces.

[0027] In a similar manner to the anti-rotation section of the implant bore, the antirotation section of the apical post portion may comprise a polygonal cross section along its full length, such as a square, hexagonal, or octagonal cross section. The corners ofthe polygon may be rounded or chamfered. Alternatively, the anti-rotation section of the apical post portion may comprise a plurality of circumferentially spaced radially extending protrusions and / or grooves that extend over the full axial length of the anti-rotation section. These protrusions and / or grooves may have a cross-sectional shape that is curved, straight edged or a combination of curved and straight edged. These protrusions and / or grooves may be continuous with one another about the circumference of the antirotation section, in other words the edges of one groove or protrusion contact the edges of the adjacent groove or protrusion, or they may be separated from one another by straight or curved sections of the cross section.

[0028] In one preferred embodiment, the anti-rotation section of the apical post portion comprises a plurality of circumferentially spaced protrusions which protrude radially outwards and extend over the full length of the anti-rotation section. These protrusions preferably have a fully curved cross-section in a plane perpendicular to the longitudinal axis, as this provides a better force distribution over each protrusion. The fully curved cross-section may have a single radius, thus forming arc shaped protrusions, or it may comprise sections having differing radii, for example a central convexly curved section bordered on either side by a concavely curved section. While it is possible for the protrusions to have different shapes to one another, preferably the plurality of circumferentially spaced protrusions all have an identical cross-section to one another at each axial location of the anti-rotation section. Preferably the protrusions extend from and are interposed by a base surface. The base surface from which the protrusions extend may be circular in cross-section such that the protrusions extend from a curved surface. However, it is also possible for the base surface to have a polygonal cross-section such that the protrusions are interposed by planar surfaces.

[0029] The anti-rotation section of the apical post portion is complementary to the antirotation section of the bore. Thus, the anti-rotation section of the apical post portion must be sized and shaped such that this can be at least partially accommodated in the antirotation section of the implant bore in such a way that relative rotation will be inhibited.

[0030] It is possible for the anti-rotation section of the apical post portion to have a different cross-sectional shape to the anti-rotation section of the bore while still being complementary to this. For example, the anti-rotation section of the bore could have a triangular cross section, and the anti-rotation section of the apical post portion could have a hexagonal cross section, wherein three surfaces of the hexagonal cross section alignin use with the three sides of the triangular cross section. Alternatively, the anti-rotation section of the bore may comprise, e.g., six circumferentially spaced grooves and the antirotation section of the apical post portion may comprise a smaller number, e.g. three, of circumferentially spaced protrusions which are spaced in such a manner that each protrusion can be simultaneously housed within a groove of the bore.

[0031] However, for design simplicity and efficiency, it is preferable that at least a portion of the anti-rotation section of the apical post portion has the same cross-sectional shape as at least a portion of the anti-rotation section of the implant bore, these portions being in axial alignment when the apical post portion is at its full insertion depth.

[0032] For example, when the anti-rotation section of the implant bore comprises a plurality of circumferentially spaced grooves which protrude radially outwards, it is preferred that the anti-rotation section of the apical post portion comprises an equal number of circumferentially spaced protrusions extending radially outwards, each protrusion sized and spaced for simultaneous accommodation in a groove of the bore. Alternatively, when the anti-rotation section of the implant bore comprises a polygonal cross-section having n sides it is preferred that the anti-rotation section of the apical post portion comprises a polygonal cross-section having an equal number of sides.

[0033] According to the present invention, the anti-rotation section of the apical post portion comprises a tapered segment within which at least the radially outermost portions of the anti-rotation section taper radially inwards in the apical direction. When the apical post portion is inserted to its full insertion depth in the implant bore, the tapered segment is at least partially located within the overlapping length, such that an apically increasing gap of no more than 10° is formed in the overlapping length between at least the radially outermost portions of the tapered segment of the anti-rotation section of the apical post portion and the radially outermost portions of the anti-rotation section of the implant bore. In order to create this apically increasing gap, within the tapered segment the radially outermost portions of the anti-rotation section of the apical post portion must taper radially inwards by a greater amount than any inward taper present in the radially outermost portions of the overlapping length of the anti-rotation section of the bore.

[0034] Preferably the apically increasing gap formed between at least the radially outermost portions of the tapered segment of the anti-rotation section of the apical postportion and the radially outermost portions of the anti-rotation section of the implant bore increases at an angle of between 1 ° and 7°, more preferably between 2° and 5°.

[0035] The anti-rotation section of the implant bore extends over an axial length of the bore and has a non-circular-symmetric cross section along its entire axial length. In some embodiments the width of the cross-section may decrease in the apical direction, thus forming a tapered anti-rotation section. Preferably however the anti-rotation section of the bore extends in a parallel manner relative to the longitudinal axis or tapers in the apical direction by no more than 1 .5°. This small taper accounts for any draft angle that may be present in the bore due to the manufacturing method of the implant, e.g., injection moulding. By providing an implant anti-rotation section with little, i.e. no more than 1.5°, or no taper a better efficiency of torque transmission can be achieved during implant insertion. In addition, any inward taper of the anti-rotation section reduces the diameter of the bore apical of the anti-rotation section. This therefore reduces the volume available for further sections of the implant bore, for example a threaded section which may be present to allow a threaded connection between the implant and various secondary parts. Providing an implant anti-rotation section with little or no taper thus maximises the available bore volume apical of the anti-rotation section.

[0036] In embodiments in which the anti-rotation section of the bore has little or no taper, it is preferred that, within the tapered segment, at least the radially outermost portions of the anti-rotation section of the apical post portion taper radially inwards at an angle of between 1 .5° and 7°, most preferably between 2° and 5°.

[0037] The taper angle of the tapered segment may remain constant over the length of the tapered segment, or it may vary within the above angle ranges. For example, the tapered segment may comprise a first part having a first taper angle, and a second part, apical and adjacent to the first part, the second part having a second taper angle greater than the first taper angle. Preferably however, for ease of manufacturing and even force distribution, the taper angle is constant over the length of the tapered segment.

[0038] In order to provide a significant increase in the contact area provided by the tapered segment, it is preferable for the tapered segment to extend over a length of at least 0.5 mm, more preferably over a length of between 0.6mm and 1.5 mm, most preferably over a length between 0.7mm and 1 .3 mm. When the length is less than 0.5mm a high force is still experienced only over a small area of the implant. When the length isgreater than 1 ,5mm this can result in too thin a wall at the apical end of the tapered segment.

[0039] In a particularly preferred embodiment, the anti-rotation section of the apical post portion comprises a tapered segment within which at least the radially outermost portions of the anti-rotation section taper radially inwards in the apical direction at a constant taper angle of between 1 .5° and 7°, more preferably between 2° and 5°, over a length of at least 0.5 mm, more preferably over a length of between 0.6mm and 1.5 mm, most preferably over a length of between 0.7mm and 1 ,3mm.

[0040] As discussed above, the apically increasing gap between the implant bore and apical post portion anti-rotation sections allows for a better force distribution during use of the implant system. According to the present invention this apically increasing gap may be present only between the radially outermost portions of the anti-rotation sections. In certain embodiments however, within the tapered segment the entire lateral surface of the anti-rotation section of the apical post portion tapers radially inwards in the apical direction such that an apically increasing gap of no more than 10° is formed in the overlapping length between the entire lateral surface of the tapered segment of the antirotation section of the apical post portion and the anti-rotation section of the implant bore.

[0041] In some embodiments, for simplicity of design, the taper of the lateral surface is uniform about the circumference of the tapered segment. Thus, in such embodiments, the tapered segment forms a frustoconical surface having a non-circular-symmetric base.

[0042] In embodiments in which the entire lateral surface of the tapered segment is uniformly tapered, it is preferred that the taper angle is less than 3°. Such a shallow taper angle ensures that a force transmitting contact with the implant bore is achieved.

[0043] In other embodiments the radially outermost portions of the tapered segment may taper at a different angle to the radially inner portions. For example, when the antirotation section of the apical post portion comprises a plurality of circumferentially spaced protrusions extending radially outwards from a base surface, within the tapered segment the protrusions may taper at a first taper angle while the base surface tapers at a second taper angle. In such embodiments it is preferable that the taper angle of the radially outermost portions of the tapered segment, e.g. the protrusions, is greater than the taper angle of the inner portions, e.g. the base surface, as this will create an increased contactbetween the tapered segment and the radially inner areas of the implant bore, where the implant wall is thicker.

[0044] In particularly preferred embodiments, within the tapered segment the radially outermost portions of the anti-rotation section taper radially inwards while the radially inner portions of the anti-rotation section extend in a parallel manner relative to the longitudinal axis or taper in the apical direction by no more than 1.5°, the taper angle of the radially outermost portions being greater than any taper of the radially inner portions. For example, when the cross section of the anti-rotation section of the apical post portion comprises a polygon, the corners of the polygon may be progressively removed in the apical direction, thus changing the shape of the polygonal cross-section over the length of the tapered segment. Alternatively, when the anti-rotation section of the apical post portion comprises a plurality of protrusions extending from a base surface, the protrusions may taper radially inwards while the base surface has little, i.e. no more than 1 .5°, or no taper.

[0045] Tapered segments having such “partially tapered” designs are preferable, as contact between the radially inner portions of the anti-rotation sections of the bore and apical post portion can be increased, thus providing a surface for force transmission which is located away from the thinnest parts of the implant wall. As this additional contact occurs at a thicker area of the implant, wear in this area is less likely to result in fatigue failure.

[0046] In such “partially tapered” embodiments the preferred taper angles of the radially outermost portions of the anti-rotation section can be larger than the preferred angles for a fully tapered tapered segment. This is because the radially inner portions of the tapered segment of the anti-rotation section provide an increased contact to the implant bore. For example, within the tapered segment the radially outermost portions of the anti-rotation section of the apical post portion may taper at an angle of between 3 and 5°. However, shallower taper angles, e.g. 2°, of the radially outermost portions can also be used in such embodiments.

[0047] According to a particularly preferred embodiment, the tapered segment of the apical post portion comprises a cylindrical base surface or conical base surface with a taper angle of no more than 1 .5°, and a plurality of protrusions extending radially outwards from said base surface, the plurality of protrusions tapering radially inwards in the apicaldirection at a taper angle greater than any taper of the base surface. The cylindrical or conical base surface can have a circular or polygonal base but is preferably circular. The protrusions preferably taper inwards at an angle of between 1.5° and 7°. In particularly preferred embodiments the protrusions taper at an angle of between 2 and 5°.

[0048] The tapered segment can extend over the entire axial length of the anti-rotation section of the apical post portion . It is however possible for the anti-rotation section of the apical post portion to comprise further segments coronally and / or apically of the tapered segment. Preferably the anti-rotation section of the apical post portion comprises, at its apical end, a runout segment in which at least the radially outermost portions of the antirotation section are rounded or chamfered by an angle greater than 30° in the apical direction. This runout segment usually has a small length and acts to prevent sharp edges at the apical end of the anti-rotation section. It may also assist in guiding the anti-rotation section of the apical post portion into the implant bore. When present this runout segment preferably has a length of less than 0.5mm. Preferably the runout segment is located directly apical of the tapered segment. In such embodiments therefore, the tapered segment extends from an axial location of the anti-rotation section to within 0.5mm of the apical end of the anti-rotation section. This is beneficial both in terms of manufacturing and to provide the greatest benefit from the inventive configuration. As lateral forces felt by the secondary part during use will result in the tilting or attempted tilting of the secondary part within the implant bore, it is at the apical end of the secondary part that the greatest force will be introduced into the system. Placing the tapered segment towards the apical end of the anti-rotation section therefore positions this segment at the location of the anti-rotation section which will in use impart the greatest lateral forces to the implant bore. More generally it is preferred that the tapered segment extends from an axial location of the anti-rotation section of the apical post portion to at least within 0.5mm of the apical end of the anti-rotation section.

[0049] For the same reason, the benefit provided by the secondary part is most prominent in components in which the anti-rotation section is located at or close to the apical end of the apical post portion. In such systems the lateral forces experienced by the secondary part are particularly felt in the apical area of the anti-rotation section. Therefore, in preferred embodiments, the apical end of the anti-rotation section forms the apical end of the apical post portion and thus also the apical end of the secondary part.

[0050] Alternatively however, the apical post portion may further comprise a guide section apically adjacent to the anti-rotation section. Such a section typically has a maximum radius less than or equal to the minimum radius of the anti-rotation section of the apical post portion and is circular cylindrical, frustoconical or rounded in shape.

[0051] Regardless of whether a guide section is present apical of the anti-rotation section, it is preferable that the apical end of the anti-rotation section of the apical post portion is within 1 mm of the apical end of the apical post portion and thus also the apical end of the secondary part.

[0052] The tapered segment of the anti-rotation section of the apical post portion may begin at the coronal end of the anti-rotation section. However, preferably the anti-rotation section comprises, coronal of the tapered segment, a parallel walled segment. Within the parallel walled segment at least the radially outermost portions of the anti-rotation section extend in a parallel manner with respect to the longitudinal axis. Such a parallel walled segment ensures a good anti-rotation connection between the implant and the secondary part.

[0053] Preferably the tapered segment and the parallel walled segment are directly adjacent to one another. In other words, there are no intervening segments between the parallel walled and tapered segments. The cross-section of the coronal end of the tapered segment is preferably identical to the cross-section of the apical end of the parallel walled segment to provide a smooth transition between the segments.

[0054] Preferably, the parallel walled segment has a length that is in a range from 5% to 100% of the tapered segment length as measured along the longitudinal axis of the apical post portion.

[0055] In some embodiments within the parallel walled segment only the radially outermost portions of the anti-rotation section extend in a parallel manner. For example, when the anti-rotation section of the apical post portion comprises a plurality of protrusions extending from a base surface, within the parallel walled segment the protrusions may extend in a parallel manner with respect to the longitudinal axis while the base surface may taper or curve radially inwards in the apical direction.

[0056] In other preferred embodiments however, within the parallel walled segment the cross-section of the anti-rotation section remains constant such that the entire lateralsurface of the anti-rotation section extends in a parallel manner with respect to the longitudinal axis, thus forming a cylinder with a non-circular base.

[0057] According to the present invention, the apical post portion of the secondary part is arranged for insertion into the bore of the dental implant. The apical post portion may comprise additional sections in addition to the anti-rotation section, for example the guide section mentioned above. Additionally or alternatively, the apical post portion may comprise, coronal of the anti-rotation section, a conical section that tapers radially inwards in the apical direction. In such embodiments the implant bore preferably comprises, coronal of its anti-rotation section, a conical section complementary to the conical section of the apical post portion. Such complementary conical sections can be used to provide a good seal between the secondary part and implant bore and further can form the cooperating limiting surfaces of the implant and secondary part. In preferred embodiments the conical sections of the apical post portion and implant bore are located coronally adjacent to the anti-rotation sections of these components. This prevents unnecessary lengthening of the bore and apical post portion.

[0058] Alternatively to the above-described conical portion, or additionally to this, the apical post portion may comprise, coronal of the anti-rotation section, a circular cylindrical section. In such embodiments the implant bore preferably comprises a circular cylindrical section for accommodating the circular cylindrical section of the apical post portion.

[0059] In addition to the apical post portion, the secondary part further comprises a coronal post portion located coronally of the apical post portion and arranged to extend coronally from the implant when the apical post portion is inserted in the implant bore. The longitudinal axis of the coronal post portion may be coaxial with the longitudinal axis of the apical post portion, or it may extend at an angle to this. The coronal post portion may comprise a shoulder forming an apically facing limiting surface for abutment against a coronally facing limiting surface of the implant. Such mutually cooperating limiting surfaces maybe perpendicular to the longitudinal axis of the apical post portion and implant bore respectively or they may extend at complementary angles to these axes.

[0060] The secondary part may be any component intended for direct contact with the implant, for example a healing cap or impression post. The intended use of the component will dictate the shape of the coronal post portion. In an advantageous embodiment, the secondary part is an abutment. Since abutments typically transmit themost force to the implant it is this component which usually benefits most from the geometry of the invention. Both temporary and permanent abutments can benefit from the inventive geometry since both transmit load to the implant. However, most preferably the secondary part is a permanent abutment, as such components transmit greater force and have a longer lifetime than temporary abutments, which are typically only designed for use in the mouth for a limited period, e.g., up to 180 days.

[0061] The secondary part may further comprise a screw channel extending from the apical to coronal end of the secondary part. In such embodiments the implant bore preferably comprises a threaded section apical of the anti-rotation section. In this way, the implant and secondary part can be fastened together using a separate screw. The secondary part may alternatively be fastened to the implant by bonding or force fit, in which case no screw channel is necessary.

[0062] While the secondary part of the present invention improves fatigue strength in conventional Ti alloy implants, the shape of the anti-rotation section of the apical post portion has been found to be particularly beneficial when the secondary part is used with an implant formed of ultra-fine-grain (“UFG”) titanium alloy. By preventing wear at the radially outermost portions of the anti-rotation section of the implant bore, the weak point of the implant system is moved to other areas of the implant, e.g., the threaded connection between the implant and screw. The higher fatigue strength of UFG titanium results in a higher fatigue load and thus in a stronger implant system. Such a combination of secondary part and UFG implant is particularly beneficial at narrow implant diameters, e.g., less than 3.5mm. Therefore, in one preferred embodiment the implant is formed of an ultra-fine-grain titanium alloy and preferably has an outer diameter, inclusive of any thread, of less than 3.5mm.

[0063] The shape of the anti-rotation section of the apical post portion is also beneficial when used in ceramic implant systems. While ceramic materials have many benefits in relation to dental implant systems, ceramic is more brittle than metal and hence more prone to fractures. Removing peak loads and fretting wear from narrow areas of the implant wall therefore improves the strength of such implant systems. In a further preferred embodiment therefore the implant is formed of a ceramic material, for example zirconia or alumina. In such embodiments it is further preferred that the secondary part is also formed of a ceramic material.

[0064] Various effects and advantages are attained by the secondary part and dental implant system according to the invention. For illustration, the risk of fatigue-induced failure of the implant is reduced, as evidenced by tests performed for various dental implant materials, including UFG titanium.

[0065] According to one particularly preferred embodiment of the present invention, there is provided a secondary part for use in the above described dental implant system, comprising an apical post portion having a longitudinal axis and being arranged for insertion into an implant bore and a coronal post portion having a longitudinal axis and arranged to extend coronally from the implant when the apical post portion is inserted into the bore, the apical post portion comprising an anti-rotation section extending over an axial length of the apical post portion and comprising a plurality of circumferentially spaced protrusions which protrude radially outwards and extend over the full length of the anti-rotation section. The anti-rotation section of the apical post portion further comprises a tapered segment within which the plurality of circumferentially spaced protrusions taper radially inwards in the apical direction at an angle of between 2° and 5°.

[0066] Preferably the plurality of circumferentially spaced protrusions have identical fully curved cross-sections.

[0067] Preferably the plurality of protrusions extend from and are interposed by a base surface.

[0068] Preferably the base surface is cylindrical or tapers radially inwards at an angle less than the plurality of protrusions and preferably by no greater than 1 .5°.

[0069] Preferably the base surface has a circular cylindrical cross-section.

[0070] Preferably the secondary part is an abutment, preferably made from a ceramic material.

[0071] The secondary part may further have any of the non-conflicting preferred features listed above in relation to the dental implant system.

[0072] According to one preferred embodiment discussed above, the tapered segment of the apical post portion comprises a cylindrical base surface or conical base surface with a taper angle of no more than 1.5°. This base surface provides additional contactbetween the implant and apical post portion at the radially inner section of the bore, where the implant wall is thickest, and hence strongest.

[0073] This cylindrical or slightly conical base surface thus provides a beneficial effect independently of the tapered portions of the tapered segment.

[0074] Viewed from a further aspect therefore, the present invention provides a dental implant system comprising a dental implant and a secondary part, the dental implant having an apical end and a coronal end and comprising a bore that extends from the coronal end towards the apical end along a longitudinal axis. The secondary part comprises an apical post portion having a longitudinal axis and being arranged for insertion into the implant bore and a coronal post portion having a longitudinal axis and arranged to extend coronally from the implant when the apical post portion is inserted into the bore, the implant and secondary part each comprising a cooperating limiting surface which, when in contact with one another, define the full insertion depth of the apical post portion. The implant bore comprises an anti-rotation section which extends over an axial length of the bore and which has a non-circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the bore along its entire axial length. The apical post portion of the secondary part comprises an anti-rotation section which extends over an axial length of the apical post portion and has a non-circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the apical post portion along its entire axial length. The anti-rotation sections are arranged such that, when the apical post portion is inserted to its full insertion depth into the implant bore, the anti-rotation section of the apical post portion is at least partially accommodated within the anti-rotation section of the bore, thus creating an overlapping length of the bore and apical post portion antirotation sections, and further such that the anti-rotation section of the bore extends apically of the anti-rotation section of the apical post portion. The anti-rotation section of the apical post portion is complementary to the anti-rotation section of the implant bore such that, when the apical post portion is inserted to its full insertion depth, relative rotation of the components is inhibited by contact of the anti-rotation section of the apical post portion against the anti-rotation section of the bore. The apical post portion further comprises, apically adjacent to its anti-rotation section, a cylindrical extension or a conical extension with a taper angle of no more than 1 .5°. The radius of the cylindrical extension or radius of the coronal end of the conical extension is equal to the minimum radius of the apical end of the anti-rotation section of the apical post portion, said cylindrical or conicalextension being at least partially accommodated within the anti-rotation section of the bore when the apical post portion is inserted into the implant bore to its full insertion depth.

[0075] Preferably the length of the cylindrical or conical extension is at least 0.5 mm, more preferably between 0.6mm and 1.5 mm, and most preferably between 0.7mm and 1.3 mm. This length is necessary in order to provide a large enough contact area to effectively distribute the bending and fretting forces felt by the implant system and to reduce load peaks within the anti-rotation section of the implant bore.

[0076] The bore and apical post portion anti-rotation sections can have any of the crosssections described above. In particular, the anti-rotation section of the implant bore preferably comprises a plurality of circumferentially spaced grooves which protrude radially outwards and extend over the length of the anti-rotation section. These grooves preferably have a fully curved cross-section in a plane perpendicular to the longitudinal axis of the bore, as this provides a better force distribution over each groove. The fully curved cross-section may have a single radius, thus forming arc shaped grooves, or it may comprise sections having differing radii, for example a central concavely curved section bordered on either side by a convexly curved section. This provides a smooth transition into and out of the groove. While it is possible for the grooves to have different shapes to one other, preferably the plurality of circumferentially spaced grooves all have an identical cross-section to one another at each axial location of the anti-rotation section. Preferably the grooves protrude from and are interposed by a base surface, although in other embodiments they may be continuous with one another. The base surface from which the grooves extend may have a circular cross-section such that the grooves extend from a curved surface. However, it is also possible for the base surface to have a polygonal cross-section such that the grooves are interposed by planar surfaces.

[0077] The anti-rotation section of the apical post portion preferably comprises a plurality of circumferentially spaced protrusions which protrude radially outwards and extend over the length of the anti-rotation section. These protrusions preferably have a fully curved cross-section in a plane perpendicular to the longitudinal axis of the apical post portion, as this provides a better force distribution over each protrusion. The fully curved cross-section may have a single radius, thus forming arc shaped protrusions, or it may comprise sections having differing radii, for example a central convexly curved section bordered on either side by a concavely curved section. While it is possible for the protrusions to have different shapes to one another, preferably the plurality ofcircumferentially spaced protrusions all have an identical cross-section to one another at each axial location of the anti-rotation section. Preferably the protrusions extend from and are interposed by a base surface. The base surface from which the protrusions extend may be circular in cross-section such that the protrusions extend from a curved surface. However, it is also possible for the base surface to have a polygonal cross-section such that the protrusions are interposed by planar surfaces.

[0078] It is preferable that at least a portion of the anti-rotation section of the apical post portion has the same cross-sectional shape as at least a portion of the anti-rotation section of the implant bore, these portions being in axial alignment when the apical post portion is at its full insertion depth.

[0079] For example, when the anti-rotation section of the implant bore comprises a plurality of circumferentially spaced grooves which protrude radially outwards it is preferred that the anti-rotation section of the apical post portion comprises an equal number of circumferentially spaced protrusions extending radially outwards, each protrusion sized and spaced for simultaneous accommodation in a groove of the bore.

[0080] In preferred embodiments the anti-rotation section of the apical post portion comprises a parallel walled segment. Within the parallel walled segment at least the radially outermost portions of the anti-rotation section extend in a parallel manner with respect to the longitudinal axis. Such a parallel walled segment ensures a good antirotation connection between the implant and the secondary part. The anti-rotation section of the apical post portion may further comprise a tapered segment having any feature or combination of features described above. However, in the present aspect of the invention the cylindrical or conical extension provides a suitable distribution of force without the need for a tapered segment. As no tapered segment is necessary in this aspect of the present invention, it is preferred that the parallel walled segment extends from the coronal end of the anti-rotation section to at least within 0.5mm of the apical end of the antirotation section, more preferably to within 0.2mm of the apical end of the anti-rotation section.

[0081] In some embodiments, within the parallel walled segment only the radially outermost portions of the anti-rotation section extend in a parallel manner. For example, when the anti-rotation section of the apical post portion comprises a plurality of protrusions extending from a base surface, within the parallel walled segment theprotrusions may extend in a parallel manner with respect to the longitudinal axis while the base surface may taper or curve radially inwards in the apical direction.

[0082] In other preferred embodiments however, within the parallel walled segment the cross-section of the anti-rotation section remains constant such that the entire lateral surface of the parallel walled segment extends in a parallel manner with respect to the longitudinal axis, thus forming a cylinder with a non-circular base.

[0083] Preferably the anti-rotation section of the apical post portion comprises, at its apical end, a runout segment in which at least the radially outermost portions of the antirotation section are rounded or chamfered by an angle greater than 30° in the apical direction. This runout segment usually has a small length and acts to prevent sharp edges at the apical end of the anti-rotation section. It may also assist in guiding the anti-rotation section of the apical post portion into the implant bore. When present this runout segment preferably has a length of less than 0.5mm. Preferably the runout segment is located directly apical of the parallel walled segment.

[0084] The cylindrical or conical extension is located apically adjacent to the antirotation section of the apical post portion. Thus, in certain embodiments, the cylindrical or conical extension may be located apically adjacent to the parallel walled segment or, where present, the run out segment.

[0085] The cylindrical extension is preferably a circular cylindrical extension and the conical extension preferably has a circular base.

[0086] According to this aspect of the invention the cylindrical or conical extension is at least partially accommodated within the anti-rotation section of the bore when the apical post portion is inserted into the implant bore to its full insertion depth. Preferably the cylindrical or conical extension is fully accommodated within the anti-rotation section of the bore when the apical post portion is inserted into the implant bore to its full insertion depth. This prevents the need to lengthen the implant bore in order to accommodate the apical end of the cylindrical or conical extension. Preferably, when the apical post portion is inserted to its full insertion depth the cylindrical or conical extension extends to within 0.5mm, more preferably to within 0.2mm, of the apical end of the anti-rotation section of the bore. This ensures a maximum increased contact area between the bore and apical post portion.

[0087] The secondary part and implant may have any additional preferred feature or combination of preferred features described above in relation to the previous aspects of the invention. For example, the apical post portion and implant bore may comprise cooperating conical and / or cylindrical sections coronal of their anti-rotation sections. Additionally or alternatively the secondary part and implant may comprise the preferred cooperating limiting surfaces described above. The coronal post portion of the secondary part can have any of the preferred features listed above and can be any of the components listed above. Most preferably the secondary part is an abutment.

[0088] Preferred embodiments of the various aspects of the present invention shall now be described, by way of example only, with reference to the accompanying drawings, in which:

[0089] FIG 1A shows a longitudinal cross-section of an implant and abutment in accordance with the prior art;

[0090] FIG 1 B shows the implant and abutment of Fig 1 A when a lateral force is applied to the abutment;

[0091] FIG 1C shows schematically the concentration of force within the implant bore when a lateral force is applied to the system of FIG 1A;

[0092] FIG 2 shows an abutment in accordance with the present invention;

[0093] FIG 3 shows the anti-rotation section of FIG 2;

[0094] FIG 4 shows a longitudinal cross-section along line A-A of FIG 3;

[0095] FIG 5 shows a cross-section along line B-B of FIG 3;

[0096] FIG 6 shows a longitudinal cross-section of an implant for use with the abutment shown in FIGs 2-5:

[0097] FIG 7 shows a cross-section along line A-A of FIG 6

[0098] FIG 8A shows a longitudinal cross-section of a combination of the implant of FIGs 6 & 7 and the abutment of FIGS 2-5;

[0099] FIG 8B shows the same combination as FIG 8A when a lateral force is applied to the abutment;

[0100] FIG 8C shows schematically the concentration of force within the implant bore when a lateral force is applied to the system of FIG 8A;

[0101] FIG 9 shows an abutment according to a further embodiment of the present invention;

[0102] FIG 10 shows the anti-rotation section of FIG 9;

[0103] FIG HA shows a longitudinal cross-section of FIG 10;

[0104] FIG 11 B shows a different longitudinal cross-section of Fig. 10;

[0105] FIG 12 shows an abutment according to a further embodiment of the present invention;

[0106] FIG 13A shows a longitudinal cross-section of a combination of the implant of FIGs 6 & 7 and the abutment of FIG 12; and

[0107] FIG 13B shows the same combination as FIG 13A when a lateral force is applied to the abutment.

[0108] The dental implant system 100 shown in Figure 1A comprises an implant 1 and abutment 2 fastened together by a screw 3. The implant 1 comprises a bore 4 that extends from the coronal end 1a of the implant 1 towards the apical end along the longitudinal axis of the implant 1 . The abutment 2 comprises an apical post portion 5 having a longitudinal axis, the apical post portion 5 being shaped for insertion into the implant bore 4. The implant 1 and abutment 2 each comprise a cooperating limiting surface 1 b, 2b which, when in contact with one another, define the full insertion depth of the apical post portion 5. The implant bore 4 comprises an anti-rotation section 4a which extends over an axial length of the bore. The apical post portion 5 comprises a complementary anti rotation section 5a. When the apical post portion 5 is inserted to its full insertion depth into the implant bore 4, the anti-rotation section 5a of the apical post portion 5 is at least partially accommodated within the anti-rotation section 4a of the bore 4 creating an overlapping length Lo of the bore and apical post portion anti-rotation sections 4a, 5a. In the implant system 100 of the prior art both the implant bore anti-rotation section 4a andthe apical post portion anti-rotation section 5a are parallel walled, meaning that the cross section of both anti-rotation sections remains constant along the length of each antirotation section.

[0109] Figure 1 B shows a close up of the implant bore 4 and apical post portion 5 when a lateral force F is applied to the abutment 2, for example during chewing. The tilting of the abutment 2 causes the parallel walled anti-rotation section 5a to abut against the implant bore 4 at a small area of contact X. This contact point moves axially within the bore 4 as the lateral force is first applied and then removed. Figure 1C shows the small area Y within the implant bore anti-rotation section 4a where the force is applied. This area Y is located towards the radially outer part of the anti-rotation section 4a, where the implant wall is narrowest. Over time this repeated rubbing action over a small area of the implant bore 4 can lead to failure.

[0110] Figures 2 to 5 show a dental abutment 20 in accordance with an embodiment of the present invention. The abutment 20 comprises a coronal end 21 and an apical end 22. At the apical end 22 the abutment 20 comprises an apical post portion 23 having a longitudinal axis Li and being arranged for insertion into an implant bore. The abutment 20 further comprises a coronal post portion 24 arranged to extend coronally from the implant when the apical post portion 23 is inserted into the bore. In the present embodiment the longitudinal axis Li of the apical post portion 23 is different to the longitudinal axis of the coronal post portion 24. However, it is also possible for these axes to be identical to one another. The coronal post portion 24 does not form a part of the present invention and can be any known shape within the art.

[0111] The abutment 20 comprises a conical limiting surface 26 which is arranged for contacting a complementary limiting surface of the implant in order to define the full insertion depth of the abutment 20. The apical post portion 23 comprises an anti-rotation section 28 which extends over an axial length of the apical post portion 23 and has a non- circular-symmetric cross section in a plane perpendicular to the longitudinal axis Li of the apical post portion along its entire axial length.

[0112] As best seen in Figure 5, the anti-rotation section 28 has a plurality of circumferentially spaced radially protruding protrusions 25 extending over the full length of the anti-rotation section 28. These protrusions 25 have a fully curved cross section and are interposed by a base surface 27. The cross section of each protrusion 25 comprisesa central convexly curved section 25a bordered on either side by concavely curved sections 25b which provide a smooth transition into and out of the protrusion 25.

[0113] In accordance with the present invention, the anti-rotation section 28 comprises a tapered segment 29 within which, in this embodiment, the entire lateral surface of the anti-rotation section 28 tapers radially inwards in the apical direction. In this embodiment the taper of the outer surface is uniform about the circumference of the tapered segment 29. In this embodiment therefore the tapered segment 29 forms a frustroconical surface having a non-circular-symmetric base. The taper angle within the tapered segment 29 is approximately 2°. The taper of the tapered segment 29 can best be seen in Figures 3 and4. The tapered segment 29 extends over a length of approximately 0.8 mm.

[0114] Coronal of the tapered segment 29 the anti-rotation section 28 further comprises a parallel walled segment 30. Within this segment 30 the lateral surface of the anti-rotation section 28 extends in a parallel manner with respect to the longitudinal axis Li.

[0115] Apically of the tapered segment 29 the anti-rotation section 28 further comprises a run out segment 32 in which the lateral surface of the anti-rotation section 28 is rounded in the apical direction. This run-out segment 32 has a length of approximately 0.22mm and prevents sharp edges at the apical end of the anti-rotation section 28. The run-out segment 32 is directly adjacent to the tapered segment 29 which in turn is directly adjacent to the parallel walled segment 30. In the present embodiment the anti-rotation section 28 is located at the apical end of the apical post portion 23, such that the apical end of the anti-rotation section 28 forms the apical end of the post portion 23 and hence the apical end 22 of the abutment 20.

[0116] Figures 6 and 7 show an implant 40 for use with the abutment 20 of Figures 2 to5. The implant 40 comprises a bore 42 extending from its coronal end 41 towards the apical end along a longitudinal axis L2. The implant bore 42 comprises a conical limiting surface 46 arranged for cooperation with the conical limiting surface 26 of the abutment 20 such that, when these surfaces 26, 46 are in contact with one another the full insertion depth of the apical post portion 28 is defined. In the present embodiment the cooperating limiting surfaces 26, 46 are complementary conical surfaces, however, in other embodiments it is possible for these surfaces to be, for example, perpendicular to the longitudinal axes Li, L2 of the components.

[0117] The implant bore 42 further comprises an anti-rotation section 48 which extends over an axial length of the bore 42 and which has a non-circular-symmetric cross section in a plane perpendicular to the longitudinal axis L2 of the bore 42 along its entire axial length. The cross-sectional shape of the anti-rotation section 48 can best be seen in Figure 7. The anti-rotation section 48 comprises a plurality of circumferentially spaced radially extending grooves 45 which extend over the full length of the anti-rotation section 48. The grooves 45 have a fully curved cross section comprising a central concavely curved section 45a bordered on either side by convexly curved sections 45b. The grooves 45a are interposed by a base surface 47. The grooves 45 of the implant anti-rotation section 48 are complementary to the protrusions 25 of the abutment anti rotation section 28 such that, when the apical post portion 23 of the abutment 20 is inserted to its full insertion depth, the protrusions 25 are at least partially housed within the grooves 45 and relative rotation of the implant 40 and abutment 20 is inhibited by contact of the lateral surface of the anti-rotation section 28 of the abutment 20 against the anti-rotation section 48 of the bore 42. The anti-rotation section 48 of the bore 42 extends in a parallel manner relative to the longitudinal axis L2.

[0118] Figure 8A shows a longitudinal cross section through the dental implant system 500 comprising the abutment 20 of Figures 2 to 5 and the implant 40 of Figures 6 to 7. The apical post portion 23 has been inserted to its full insertion depth into the implant bore 42 such that the cooperating limiting surfaces 26, 46 are in contact with one another. In this position, the anti-rotation section 28 of the abutment 20 is partially accommodated within the anti-rotation section 48 of the bore 42, thus creating an overlapping length Loof the two anti-rotation sections 28, 48. The tapered segment 29 of the anti-rotation section 28 of the abutment 20 is located within the overlapping length Lo and thus creates an apically increasing gap G of 2° in the overlapping length Lobetween the lateral surface of the tapered segment 29 of the anti-rotation section 28 of the abutment 20 and the antirotation section 48 of the implant 40.

[0119] When a lateral force F is applied to the abutment 20, the tapered segment 29 is brought into contact with the implant bore 42, thus increasing the surface area over which force is applied. This can be seen schematically in Figures 8B and 8C. These figures show that the force is applied to the implant over a greater area Z, and at locations having a thicker wall, compared to prior art systems. In comparison to the prior art therefore, the implant system 500 and abutment 20 of the present invention enable a better forcedistribution during use of the system, which in turn prevents localized wear and fretting of the implant 40 during the life of the system. This reduces the risk of breakage and fracturing of the implant 40 and can therefore enable implants of smaller diameters to be produced. The design of the present invention is particularly beneficial in ceramic implant systems, as the brittle nature of ceramic makes such systems particularly liable to breakage.

[0120] Figures 9, 10 and 11A- B show a further embodiment of an abutment 60 according to the present invention. The abutment 60 of the second embodiment is similar to that of the previous embodiment and like features will be referred to by like reference numbers. In the interests of brevity these features will not be discussed in detail, but the description above applies equally to these features of the second embodiment. The abutment 60 comprises an apical post portion 63 and a coronal post portion 64, the apical post portion 63 having at its apical end an anti-rotation section 68. The anti-rotation section 68 comprises a plurality of circumferentially spaced radially extending protrusions 65 interposed by a base surface 67. The cross section of the anti-rotation section 68 of the abutment 60, taken along line B-B of Fig. 10, is identical to the cross section of the first abutment 20 shown in Figure 5.

[0121] The anti-rotation section 68 of the abutment 60 comprises at its coronal end a parallel walled segment 70 and at its apical end a curved run out segment 72, both sections being identical to the equivalent sections of abutment 20. In between and adjacent to the parallel walled segment 70 and runout segment 72, the anti-rotation section 68 comprises a tapered segment 69. In contrast to abutment 20, the tapered segment 69 of abutment 60 is only partially tapered. The radially outer portions taper inwards in the apical direction while the radially inner portions extend in a parallel manner relative to the longitudinal axis Li. In other words, in the present embodiment, the radially extending protrusions 65 taper radially inwards over the length of the tapered segment 69 while the base surface 67 extends in a cylindrical, i.e. parallel, manner over the length of the segment 69. In the present embodiment the protrusions 65 taper radially inward within the tapered segment 69 at an angle of 4°. The taper angle of this second embodiment is greater than the taper angle of the first embodiment, due to the increased contact which is provided by the parallel walled base surface 67.

[0122] The partially tapered nature of the tapered segment 69 can be seen in the longitudinal cross sections of Figures 11A and B. Figure 11A shows a longitudinal crosssection taken through the protrusions 65 of the anti-rotation section 68. Here it can be seen that the protrusions 65 taper inwards over the length of the tapered segment 69. Figure 11 B shows a longitudinal cross section taken through the base surface 67. Here it can be seen that, within the tapered segment 69, as within the parallel walled segment 70, the base surface 67 extends parallel to the longitudinal axis Li of the apical post portion 63.

[0123] The abutment 60 shown in Figures 9, 10 and 11A-B can be used in combination with the implant 40 of Figures 6 and 7, in which case the conical limiting surface 66 of abutment 60 cooperates with conical limiting surface 46 of the implant bore 42 to define the full insertion depth of the apical post portion 63. The parallel walled base surface 67 within the tapered segment 69 increases the contact between the radially inner portions of the anti-rotation sections 48, 68 of the bore 42 and apical post portion 63, thus providing a surface for force transmission which is located away from the thinnest parts of the implant wall, namely the implant wall in the area of grooves 45. As the additional contact occurs at a thicker area of the implant, wear in this area is less likely to result in fatigue failure.

[0124] Figures 12 and 13A-B show an abutment 200 of the second aspect of the present invention which can be used in combination with the implant 40 shown and described in relation to Figures 6 and 7. The abutment 200 comprises a conical limiting surface 226 at the coronal end of its apical post portion 223, this surface being coronally adjacent to the anti-rotation section 228. The anti-rotation section 228 has the cross section shown in Figure 5 and comprises a plurality of circumferentially spaced axially extending protrusions 225 interposed by a base surface 227. In contrast to the first aspect of the present invention, the anti-rotation section 228 does not comprise a tapered segment. Instead, the anti-rotation section 228 comprises a parallel walled segment 230, within which the entire lateral surface extends in a parallel manner relative to the longitudinal axis Li of the apical post portion 223, and a run out segment 232. The apical post portion 223 further comprises, apically adjacent to the anti-rotation section 228, a circular cylindrical extension 235 having a radius equal to the minimum radius of the apical end of the anti-rotation section 228, which in the present embodiment is the radius of the base surface 227. In other embodiments the extension can be a conical extension with a taper angle of no more than 1 .5°.

[0125] The circular cylindrical extension 235 provides additional contact between the implant 40 and abutment 200 at the radially inner section of the anti-rotation section 48, where the implant wall is thickest and hence strongest.

[0126] Figure 13A shows the abutment 200 of Figure 12 in combination with the implant 40 of Figures 6 and 7. Limiting surface 226 of the abutment 200 is in contact with the cooperating limiting surface 46 of the implant 40, such that the apical post portion 223 is inserted to its full insertion depth within the implant bore 42. In this position, the antirotation section 228 of the apical post portion 223 is partially accommodated within the anti-rotation section 48 of the bore 42, thus creating an overlapping length Loof the implant bore and abutment anti-rotation sections 48, 228. This overlapping length Loprevents relative rotation between the components. The circular cylindrical extension 235 is also accommodated within the anti-rotation section 48 of the implant 40. In this way, the lateral surface of the circular cylindrical extension 235 is located in close proximity to the base surface 47 of the implant anti-rotation section 48.

[0127] When the system with abutment 200 is placed under a lateral load F, as shown schematically in Figure 13B, the circular cylindrical extension 235 of abutment 200 is brought into contact with the base surface 47 of anti-rotation section 48 of the implant 40. Thus, increased surface contact is created at the radially inner portion of the implant antirotation section 48, where the implant wall is thicker and thus less liable to damage. The increased surface contact also serves to effectively distribute the bending and fretting forces felt by the implant system and to reduce load peaks within the anti-rotation section of the implant bore, whereby, the cylindrical extension provides a suitable distribution of force without the need for a tapered segment.

[0128] The above embodiments are described by way of example only and other variations are possible which fall within the scope of the claims. For example, the antirotation sections can have a polygonal cross-section, or the apical post portion antirotation section can comprise a plurality of circumferentially spaced radially extending grooves while the implant bore anti rotation section comprises a plurality of circumferentially spaced radially extending protrusions. The number of protrusions of one component may be different to the number of grooves of the complementary component. Sections described as being parallel walled above may also have a slight taper of no more than 1 .5° while the taper angles within the tapered segment can be any angle up to10°. The apical post portions of the abutments described above may also form part of alternative secondary components, such as prostheses, healing caps, etc.

Claims

Claims1 . A dental implant system (500) comprising a dental implant (40) and a secondary part (20, 60), the dental implant (40) having an apical end and a coronal end (41) and comprising a bore (42) that extends from the coronal end towards the apical end along a longitudinal axis (L2), the secondary part comprising an apical post portion (23, 63) having a longitudinal axis (Li) and being arranged for insertion into the implant bore and a coronal post portion (24, 64) having a longitudinal axis and arranged to extend coronally from the implant when the apical post portion is inserted into the bore, the implant and secondary part each comprising a cooperating limiting surface (26, 66, 46) which, when in contact with one another, define the full insertion depth of the apical post portion, the implant bore comprises an anti-rotation section (48) which extends over an axial length of the bore and which has a non-circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the bore along its entire axial length, the apical post portion of the secondary part comprises an anti-rotation section (28, 68) which extends over an axial length of the apical post portion and which has a non-circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the apical post portion along its entire axial length, the anti-rotation sections being arranged such that, when the apical post portion is inserted to its full insertion depth into the implant bore, the anti-rotation section of the apical post portion is at least partially accommodated within the anti-rotation section of the bore, thus creating an overlapping length (Lo) of the bore and apical post portion anti-rotation sections, the anti-rotation section of the apical post portion being complementary to the anti-rotation section of the implant bore such that, when the apical post portion is inserted to its full insertion depth, relative rotation of the components is inhibited by contact of the anti-rotation section of the apical post portion against the anti-rotation section of the bore characterised in that the anti-rotation section of the apical post portion comprises a tapered segment (29, 69) within which at least the radially outermostportions of the anti-rotation section taper radially inwards in the apical direction, wherein when the apical post portion is inserted to its full insertion depth, the tapered segment is at least partially located within the overlapping length such that an apically increasing gap (G) of no more than 10° is formed in the overlapping length between at least the radially outermost portions of the tapered segment of the antirotation section of the apical post portion and the radially outermost portions of the anti-rotation section of the implant bore.

2. A dental implant system (500) as claimed in claim 1 , wherein the anti-rotation section (48) of the implant bore (42) comprises a plurality of circumferentially spaced grooves (45) which protrude radially outwards and extend over the full length of the anti-rotation section, and wherein the anti-rotation section (28, 68) of the apical post portion (23, 63) comprises a plurality of circumferentially spaced protrusions (25, 65) which protrude radially outwards and extend over the full length of the anti-rotation section.

3. A dental implant system (500) as claimed in claim 1 , 2 or 3, wherein at least a portion of the anti-rotation section (28, 68) of the apical post portion (23, 63) has the same cross-sectional shape as at least a portion of the anti-rotation section (48) of the implant bore (42), these portions being in axial alignment when the apical post portion is at its full insertion depth.

4. A dental implant system (500) as claimed in any preceding claim, wherein the apically increasing gap (G) formed between at least the radially outermost portions of the tapered segment of the anti-rotation section (28, 68) of the apical post portion (23, 63) and the radially outermost portions of the anti-rotation section (48) of the implant bore (42) increases at an angle of between 1° and 7°, more preferably between 2° and 5°.

5. A dental implant system (500) as claimed in any preceding claim, wherein the antirotation section (48) of the bore (42) extends in a parallel manner relative to the longitudinal axis or tapers in the apical direction by no more than 1 .5°.

6. A dental implant system (500) as claimed in claim 5, wherein, within the tapered segment (29, 69) at least the radially outermost portions of the anti-rotation section (28, 68) of the apical post portion (23, 63) taper radially inwards at an angle of between 1 .5° and 7°, most preferably between 2° and 5°.

7. A dental implant (500) system as claimed in any preceding claim, wherein the antirotation section (28, 68) of the apical post portion comprises a parallel walled segment (30, 70) coronal to the tapered segment (29, 69), within which at least the radially outermost portions of the anti-rotation section extend in a parallel manner with respect to the longitudinal axis (Li).

8. A dental implant system (500) as claimed in any preceding claim, wherein the taper angle is constant over the length of the tapered segment (29, 69).

9. A dental implant system (500) as claimed in any preceding claim, wherein the tapered segment (29, 69) extends over a length of at least 0.5 mm, more preferably over a length of between 0.6mm and 1 .5 mm, most preferably over a length between 0.7mm and 1 .3 mm.

10. A dental implant system (500) as claimed in any preceding claim, wherein within the tapered segment (29, 69) the entire lateral surface of the anti-rotation section (28, 68) of the apical post portion (23, 63) tapers radially inwards in the apical direction such that an apically increasing gap (G) of no more than 10° is formed in the overlapping length (Lo) between the entire lateral surface of the tapered segment of the anti-rotation section of the apical post portion and the anti-rotation section of the implant bore.11 .A dental implant system (500) as claimed in claim 10, wherein the taper of the lateral surface is uniform about the circumference of the tapered segment (29, 69).

12. A dental implant system (500) as claimed in any of claims 1 to 9, wherein within the tapered segment (29, 69) the radially outermost portions of the anti-rotation section (28, 68) taper radially inwards while the radially inner portions of the anti-rotation section extend in a parallel manner relative to the longitudinal axis (Li) or taper inthe apical direction by no more than 1 .5°, the taper angle of the radially outermost portions being greater than any taper of the radially inner portions.

13. A dental implant system (500) as claimed in any of claims 1 to 9 or 12, wherein the tapered segment (69) of the apical post portion (63) comprises a cylindrical base surface (67) or conical base surface with a taper angle of no more than 1.5°, and a plurality of protrusions (65) extending radially outwards from said base surface, the plurality of protrusions tapering radially inwards in the apical direction at a taper angle greater than any taper of the base surface.

14. A dental implant (500) system as claimed in any preceding claim, wherein the tapered segment (29, 69) extends from an axial location of the anti-rotation section (28, 68) of the apical post portion (23, 63) to at least within 0.5mm of the apical end of the anti-rotation section.

15. A secondary part (20, 60) for use in the dental implant system (500) as claimed in any preceding claim, comprising an apical post portion (23, 63) having a longitudinal axis (Li) and being arranged for insertion into an implant bore and a coronal post portion (24, 64) having a longitudinal axis and arranged to extend coronally from the implant when the apical post portion is inserted into the bore, the apical post portion comprising an anti-rotation section (28, 68) extending over an axial length of the apical post portion and comprising a plurality of circumferentially spaced protrusions (25, 65) which protrude radially outwards and extend over the full length of the anti-rotation section, the anti-rotation section of the apical post portion further comprising a tapered segment (29, 69) within which the plurality of circumferentially spaced protrusions taper radially inwards in the apical direction at an angle of between 2° and 5°.

16. A dental implant system comprising a dental implant (40) and a secondary part (200),the dental implant having an apical end and a coronal end (41) and comprising a bore (42) that extends from the coronal end towards the apical end along a longitudinal axis (L2), the secondary part comprising an apical post portion (223) having a longitudinal axis (Li) and being arranged for insertion into the implant bore and a coronal post portion having a longitudinal axis and arranged to extend coronally from the implant when the apical post portion is inserted into the bore, the implant and secondary part each comprising a cooperating limiting surface (46, 226) which, when in contact with one another, define the full insertion depth of the apical post portion, the implant bore comprises an anti-rotation section (48) which extends over an axial length of the bore and which has a non-circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the bore along its entire axial length, the apical post portion of the secondary part comprises an anti-rotation section (228) which extends over an axial length of the apical post portion and has a non- circular-symmetric cross-section in a plane perpendicular to the longitudinal axis of the apical post portion along its entire axial length, the anti-rotation sections being arranged such that, when the apical post portion (223) is inserted to its full insertion depth into the implant bore (42), the anti-rotation section (228) of the apical post portion is at least partially accommodated within the anti-rotation section (48) of the bore, thus creating an overlapping length (Lo) of the bore and apical post portion anti-rotation sections, and further such that the antirotation section (48) of the bore extends apically of the anti-rotation section (228) of the apical post portion, the anti-rotation section (228) of the apical post portion (223) being complementary to the anti-rotation section (48) of the implant bore (42) such that, when the apical post portion is inserted to its full insertion depth, relative rotation of the components is inhibited by contact of the anti-rotation section of the apical post portion against the anti-rotation section of the bore, the apical post portion (223) further comprising, apically adjacent to its antirotation section (228), a cylindrical extension (235) or a conical extension with a taper angle of no more than 1 .5°, the radius of the cylindrical extension or radius ofthe coronal end of the conical extension being equal to the minimum radius of the apical end of the anti-rotation section of the apical post portion, said cylindrical or conical extension (235) being at least partially accommodated within the anti-rotation section (48) of the bore (42) when the apical post portion is inserted into the implant bore to its full insertion depth.

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