The creation of an implant via injection moulding is preferred because it is cost effective for large volumes, as well as quicker to manufacture and easier to ensure conformity of the produced components. In addition, as mentioned above, injection moulding allows the creation of an internal thread with curved crests, in addition to curved roots, which is beneficial in preventing crack formation and implant failure.

The manufacturing of a ceramic implant according to the present invention may be accomplished according to a ceramic injection moulding (CIM) method by injecting powdered ceramic material into a shaped mould. The ceramic material is thereby generally provided as powdered material and it contains binder for better moulding or forming; the binder is preferably removed after forming by burning it out prior to sintering. Sintering provides the final shape and hardness. The skilled person is aware that during sintering the implant shrinks by a factor dependent on the material and manufacturing process, but typically by around 25%.

Particularly when manufactured by injection moulding, but also when using other manufacturing methods, the implant is preferably formed using a HIP (Hot Isostatic Pressing) process. This improves the strength of the implant by increasing the density of the material.

When the implant is formed via injection moulding, it is particularly preferred that the radially outer part of the thread profile is gradually removed within the tapered portion in order to create the required reduction in thread depth. This is because such a design is easier to implement in a moulded blind bore than, e.g. removing the radially inner part of the thread profile. In particular, it is preferred that within the tapered portion the thread profile remains constant relative to the base surface of the main portion, such that within the tapered portion the thread is gradually submerged by the tapering base surface.

According to the present invention the threaded section is located in a blind bore within the implant. Preferably the apical end of the bore is rounded, in order to prevent sharp edges and stress points in the bore. The threaded section may extend over the full length of the blind bore. In preferred embodiments however, it only extends over a part of the blind bore, as a result of which the production expenditure and complexity is reduced. In certain embodiments, the threaded section lies exclusively in the lower, i.e. apical, half of the blind bore. As a result, the length of the connecting screw can be increased, which increases the possible preload force of the screw.

According to the present invention, the blind bore extends along a central longitudinal axis. While the central longitudinal axis of the blind bore can be offset from the central longitudinal axis of the implant, it is preferable that the blind bore is coaxial with at least a part of the implant. For example, some implants are angled such that they comprise a coronal part extending along a first central longitudinal axis and an apical part extending along a second central longitudinal axis, the first and second axes being angled relative to one another. In such cases the blind bore is preferably co-axial with either the coronal or apical part of the implant. When coaxial with the apical part of an angled implant the blind bore opening will not be located at the coronal end surface of the implant but is open towards the coronal end of the implant such that the bore is accessible from the coronal end of the implant.

Most implants however extend from their apical to coronal end along a single central longitudinal axis. In such cases the blind bore is not only open towards the coronal end of the implant, but its opening is located at the coronal end surface of the implant. Preferably the blind bore is coaxial with the central longitudinal axis of the implant. In other words, preferably the implant extends from an apical end to a coronal end along a central longitudinal axis, the blind bore being open at the coronal end surface of the implant and extending towards the apical end along said central longitudinal axis. In such cases the central longitudinal axis of the bore is identical to the central longitudinal axis of the implant.

In such preferred embodiments the length of the blind bore, as measured in the longitudinal direction, is preferably more than 70% of the axial length of the implant, more preferably more than 75% and most preferably at least 80%. This is longer than the bores found in standard titanium implants. The longer the length of the blind bore relative to the length of the implant, the more balanced the mass distribution of the implant. In standard implants the apical end of the implant below the blind bore is typically solid, resulting in a greater mass. When a screw is tensioned within the bore this apical mass creates more strain within the implant. A longer bore reduces the mass at the apical end of the implant and consequently reduces the strain during use. This is particularly beneficial in ceramic implants, given the brittle nature of this material. In addition, reducing the ceramic volume of the implant reduces the possibility for defects within the ceramic material, particularly in relation to 3D printing and injection moulding methods.

These advantages are also present in angled implants in which the bore is located in the apical part of the implant. In such embodiments therefore it is preferred that the length of the blind bore, as measured in the longitudinal direction, is preferably more than 70% of the axial length of the apical part of the implant, more preferably more than 75% and most preferably at least 80%.

As discussed above, it is preferable that the threaded section does not extend over the full length of the blind bore. Further, it is preferable that the threaded section does not extend to the apical end of the bore. Therefore, it is preferred that the blind bore further comprises, apical of the threaded section, a non-threaded end section extending from the apical end of the threaded section to the apical end of the bore. This is particularly advantageous in embodiments in which a longer bore length is used, i.e. the blind bore has a length of at least 70% of the length of the implant (or apical part of an angled implant). Such a non-threaded end section lengthens the bore while maintaining the simplicity of the design and allowing the same screw length to be used with all implant lengths.

As the position of the threaded section within the bore will determine the length of screw which can be used with the implant, the position of this threaded section will typically remain constant, relative to the coronal end of the blind bore, in different lengths of implant. This enables a standard screw length to be used with all implant lengths. Between implants of different lengths therefore, the length of the non-threaded end section will typically vary in order to extend the bore over the desired length of the implant.

Preferably the non-threaded end section has an axial length of at least one third the length of the tapered portion, more preferably a length of between one third and three times the length of the tapered portion.

The non-threaded end section may be cylindrical, curved or conical, or a combination of these shapes. In some embodiments the shape of the non-threaded end section matches that of the outer surface of the implant at the axial location of the non-threaded end section, such that the implant has an essentially constant wall thickness over the length of the non-threaded end section. Therefore, when the outer surface of the implant tapers at its apical end, it is preferable that the non-threaded end section of the bore is similarly tapered. Alternatively, when the implant is a parallel walled (cylindrical) implant, it is preferable that the non-threaded end section is cylindrical.

When the implant is manufactured by injection moulding, a more or less constant wall thickness improves the flow of feedstock during injection moulding. Thus, in such embodiments it can be particularly preferred that any non-threaded end section of the blind bore matches the shape of the outer surface of the implant at the axial location of the non-threaded end section, as discussed above. However, often a compromise is needed in order to ensure that the apical end of the blind bore does not become too narrow. If the mould pin used to form the bore is too thin, this can vibrate during the injection moulding process. Therefore, in certain preferred embodiments the non-threaded end section has a taper angle (with respect to the central longitudinal axis of the bore) that is equal to or smaller than the taper angle, where present, of the tapered portion of the threaded section. This assists in providing an optimum length and diameter of bore. Additionally or alternatively, and regardless of whether the tapered portion comprises a taper angle, in preferred embodiments the non-threaded end section has a taper angle of less than 1°, more preferably around 0.5°. This small taper angle prevents the apical end of the bore from becoming too thin, even in long bore lengths, while also assisting with demoulding. The provision of a small taper angle to assist with demoulding is beneficial in parallel walled as well as apically tapered implants.

In preferred embodiments the dental implant further comprises an anti-rotation element coronal of the threaded section. The anti-rotation element has a non-circular symmetric cross-section in a plane perpendicular to the central longitudinal axis of the blind bore. This anti-rotation element can be formed within the blind bore, or on an external surface of the implant. The anti-rotation element of the implant can be any known shape, e.g. oval, polygonal, torx, a series of alternating protrusions and recesses etc. Preferably the blind bore comprises an anti-rotation element coronal of the threaded section.

When a cooperating secondary component, such as an abutment, crown, etc., having a complementary shaped anti-rotation element is connected to the implant, axial alignment of the two anti-rotation elements prevents relative rotation of the secondary component and the implant about the central longitudinal axis of the bore. When present, the anti-rotation element of the implant can also serve as a torque transmission means for a suitable insertion tool in order to anchor the implant in the jaw bone. To this end, in a known manner, a correspondingly formed free end of an insertion tool can be brought into releasable engagement with the implant anti-rotation element in order to transmit a torsional moment to the dental implant.

The blind bore of the implant is intended to allow connection of a secondary component (e.g. abutment, healing cap etc.) to the implant via a screw connection with the threaded section. For fixedly connecting the secondary component to the implant, the secondary component may comprise an outer screw thread that is intended to engage with the main portion of the threaded section of the blind bore of the implant. Alternatively, the secondary component may comprise a through hole, through which a fixation screw can be inserted, such that the apical end of the screw protrudes out of the apical end of the secondary component and can engage with the threaded section of the implant bore.

For instance, an abutment having a screw channel can have an apical end designed for insertion into the blind bore of the implant. A fixation screw can be inserted through the screw channel of the abutment and driven into the internal thread of the implant by means of a tool introduced from above into the screw channel of the abutment, thereby fixedly connecting the abutment and the implant. The apical end of the abutment may include an anti-rotation element on its outer surface, e.g. a portion having a polygonal cross-section, that can be brought into axial alignment with a complementary anti-rotation element, e.g. a polygonal portion, provided in the blind bore, to prevent relative rotation of the implant and the abutment.

Suitable fixation screws can be produced in a known manner from metal, preferably titanium or a titanium alloy as said materials ensure good stability, biocompatibility and sterilization. The additional advantage of metal materials is that they comprise a certain elasticity and the holding force of the fixation screw is increased as a result of the screw expanding minimally elastically along its longitudinal axis when screwed-in. The tensile force resulting from the expansion then results in a particularly sturdy connection between dental implant and secondary component. In other embodiments a ceramic or polymer screw can be used, produced by, e.g. milling. This is beneficial in meeting consumer desire for metal free dental implants.

In certain preferred embodiments the blind bore of the implant further comprises, coronal of the threaded section and, where present, the anti-rotation element, a circular symmetric non-threaded section. This non-threaded section can be tapered or non-tapered in the longitudinal direction and serves to provide a deeper and hence more stable connection between the implant and the secondary component.

Preferably the coronal circular symmetric non-threaded section is cylindrical. In other embodiments however the coronal circular symmetric non-threaded section may be conical and assist in producing a good seal, e.g. a Morse taper, between the implant and secondary component. In an alternative preferred embodiment the coronal circular symmetric non-threaded section comprises a plurality of conical and/or cylindrical segments. These can be arranged in any order. For example, the coronal circular symmetric non-threaded section may comprise a cylindrical segment followed coronally by one or more conical segments. Where a plurality of conical segments is present these may be placed sequentially or alternate with one or more cylindrical segments. The cylindrical and conical segments may have different axial lengths and the conical segments may also have different taper angles.

The outer surface of the dental implant is preferably tapered in the apical direction at least over a portion of its length, the tapering occurring within at least the apical half of the implant.

The implant preferably comprises an external screw thread for anchoring the implant within a jaw bone, which protrudes from the outer surface of the implant and extends over at least part of its length. The external thread serves for primary or immediate anchoring of the dental implant in a jaw bone. The external thread may thereby extend over the entire length of the dental implant. As an alternative to this, the external thread may extend over at least 50% of the overall length of the dental implant and preferably over at least 75% of the dental implant length, with the thread beginning at or near (e.g. within 1 mm of) the apical end. The external thread can have any known shape and may comprise one or more self-tapping groove. The thread depth of the external thread may remain constant or may vary over the length of the implant. At its coronal end the outer surface of the dental implant can comprise a thread-free portion coronal of the external thread.

To improve osseointegration, the portion of the dental implant intended for placement in the bone can have a roughened external surface according to any known technique or be surface-treated in another known manner, e.g. with a coating. By “external surface” it is meant the outer surface and, where present, the external screw thread.

According to a preferred embodiment, a plurality of implants according to the present invention are provided, the plurality of implants having different axial lengths. The position of the threaded section within the blind bore of each implant, relative to the coronal end of the blind bore, is constant. The blind bore of each implant preferably further comprises a non-threaded end section extending from the apical end of the threaded section to the apical end of the blind bore, the axial length of the non-threaded end section differing between implants, such that implants having a longer axial length have a longer non-threaded end section.

The invention further relates to a method of manufacturing the dental implant described above by injection moulding, wherein a pin is used as a negative template for the threaded section of the blind bore. This means that the outer shape of the pin comprises a thread which corresponds to the internal shape of the threaded section of the blind bore but taking into account the shrinkage factor of the ceramic after sintering. Therefore, the pin dimensions will be approximately 25% larger than the final implant dimensions.

According to another aspect therefore the present invention provides a method of manufacturing a dental implant comprising the steps of providing a mould for ceramic injection moulding, the mould comprising a pin extending along a central longitudinal axis and having a threaded section, the threaded section comprising a base surface from which a thread protrudes radially outwards, the base surface defining the minimum radius of the thread as measured from the central longitudinal axis, the thread having a coronal flank and an apical flank connected by a crest at their radially outer ends, the crest defining the maximum radius of the thread as measured from the central longitudinal axis, the thread extending in a helical manner along the axial length of the threaded section and having a depth defined by the difference in radius between the base surface and the crest, the threaded section comprising a main portion, within which the maximum radius of the thread remains constant along the length of the portion and, apically adjacent to the main portion, a tapered portion within which the maximum radius of the thread decreases in the apical direction from the maximum radius of the thread in the main portion to the minimum radius of the thread at the apical end of the tapered portion, the tapered portion extending over an axial length greater than the thread pitch so as to form a tapered thread having a gradual reduction in thread depth, said tapered thread extending over more than one thread turn, and using said mould to create a dental implant using ceramic injection moulding.

Preferably the thread of the pin comprises a curved transition between the base surface and the apical and coronal flanks at least along the length of the main portion. Preferably, when seen in longitudinal cross-section, the transition has the shape of a circular arc. Additionally or alternatively, the thread of the pin comprises, at least along the length of the main portion, crests having a curved longitudinal cross-section, preferably having the shape of a circular arc.

Further preferred features of the threaded section of the pin are complementary to the preferred features of the threaded section of the implant. For example, it is preferred that the thread profile within the tapered portion of the pin is altered by gradually removing the radially outer part of the profile. Additionally or alternatively it is preferred that the minimum radius of the thread remains constant along the length of the threaded section.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1A shows a longitudinal cross-section of an implant as known in the art;

FIG. 1B shows an enlargement of the threaded section of FIG. 1A;

FIG. 1C shows detail Y from FIGS. 1A and 1B;

FIG. 2A shows a longitudinal cross-section of an implant according to a preferred embodiment of the present invention;

FIG. 2B shows an enlargement of the threaded section of FIG. 2A;

FIG. 2C shows detail Y from FIG. 2B;

FIG. 2D shows a pin for producing the implant of FIG. 2A by an injection moulding method;

FIG. 3 shows an alternative preferred embodiment of an implant in accordance with the present invention; and

FIGS. 4A-E show schematic illustrations of alternative designs of thread profiles within the tapered portion.

FIG. 1A shows an implant 1 representative of the prior art. Implant 1 is adapted for use with a secondary component, e.g. an abutment (not shown), and extends along a central longitudinal axis LA from an apical end 3 to a coronal end 2. The implant 1 includes a blind bore 4 which is open at the coronal end 2 and surrounded by the coronal end surface 5 of the implant 1, which radially encircles the bore opening 6. The blind bore 4 is coaxial with the implant 1 and thus also extends along the central longitudinal axis LA. The outer surface of implant 1 is provided with an external thread 32 for screwing the implant 1 into the jaw bone of a patient.

The blind bore 4 comprises a threaded section 7, located towards the apical end of the bore 4. The threaded section 7 comprises a base surface 8 from which a thread 9 protrudes radially inwards into the bore 4 (i.e. towards the central longitudinal axis LA). As also shown in detail in FIG. 1B, the thread 9 has a coronal flank 12 and an apical flank 14 connected by a crest 16 at the their radially inner ends and extends in a helical manner along the length of the threaded section 7. As shown in FIG. 1B, the base surface 8 defines the maximum radius R_maxof the thread 9 while the crest 16 defines the minimum radius R_min, the difference between the maximum and minimum radii at any given point giving the thread depth T_D.

At the apical end of the threaded section 7 a non-threaded conical section 10 intersects the thread 9. This is shown in detail in FIG. 1C. As can be seen in this figure, the conical surface 10 intersects apical flank 14 at a sharp angle, forming a thin, sharp edge 18 in the bore. This creates a stress concentration point. When the implant 1 is made of ceramic, such a sharp edge 18 can lead to crack formation and implant failure. As can also be seen in this figure, crest 16 has a planar shape when viewed in longitudinal cross-section. Such a crest is the simplest shape to form when milling an implant but can also lead to problematic stress concentrations in ceramic implants.

FIG. 2A shows an implant 100 in accordance with the present invention. The implant 100 is made of a ceramic material, for example an aluminium or zirconium or magnesium based ceramic material, such as aluminium oxide, zirconium oxide or magnesium oxide or combinations thereof. In addition, stabilizing agents, such as yttrium or cerium oxide may be included in the ceramic material.

Similar to the prior art implant 1 described above, the inventive implant 100 extends along a central longitudinal axis LA from an apical end 103 to a coronal end 102. The implant 100 includes a coaxial, longitudinally extending blind bore 104, which is open at the coronal end 102 and extends towards the apical end 103 along axis LA. The blind bore 104 comprises a threaded section 107, having a base surface 108 from which a thread 109 protrudes radially inwards into the bore 104. The thread 109 has a coronal flank 112 and an apical flank 114 connected by a crest 116 at their radially inner ends. The thread 109 extends in a helical manner along the length of the threaded section 107. The base surface 108 defines the maximum radius R_maxof the thread 109 while the crest 116 defines the minimum radius R_min, the difference between the maximum and minimum radii at any given point giving the thread depth T_D(see FIG. 2B).

In contrast to prior art implants, the threaded section 107 of implant 100 comprises a main portion 115 and, apically adjacent to the main portion 115, a tapered portion 117. The maximum radius R_maxof the thread 109 within the main portion 115 remains constant, while within the tapered portion 117 the base surface 108 tapers radially inwards in the apical direction from the maximum radius R_maxof the thread 109 in the main portion 115 to the minimum radius R_minof the thread 109 at the apical end of the tapered portion 117, the tapered portion 117 extending over an axial length greater than the thread pitch, so as to form a tapered thread 119 having a gradual reduction in thread depth T_Dextending over more than one thread turn. The radially inwards tapering of the base surface 108 is further clearly visible in FIGS. 4B-4E. The tapering base surface 108 results in the thread depth T_Dgradually decreasing over a number of thread turns, resulting in a gentle run-out of the thread 109. The thread 109 is therefore not cut off abruptly, and the formation of the sharp edge 18 found in the prior art (see FIG. 1C) is prevented. Hence a stress point within the bore which could lead to crack formation is eliminated.

FIG. 2B shows an enlargement of the threaded section 107. The enlarged view shows how the tapering base surface 108 tapers radially inwards at taper angle γ, as measured from the central longitudinal axis LA, thus forming a conical shape. The taper angle γ remains constant over the length of the tapered portion 117. In the present embodiment the taper angle γ is 8°. This angle is smaller than taper angle α of the coronal flank 112, as measured from the central longitudinal axis LA. An obtuse angle is formed between the tapered base surface 108 and both the apical 114 and coronal 112 flank, as can best be seen in FIG. 2C. The taper angle γ is chosen such that the thread run out occurs over more than 3 thread turns.

Within the main portion 115 the maximum radius R_maxremains constant, resulting in a base surface 108 having a cylindrical shape. In addition the minimum radius R_minof the thread 109 and the thread profile also remain constant, providing a uniform force distribution in use.

Within the tapered portion 117 the minimum radius R_minremains constant, such that the reduction in thread depth is caused solely by the taper of the base surface 108. The thread profile remains constant relative to the base surface of the main portion 115. In this way the thread 109 is gradually submerged by the tapering base surface 108 from the thread root 121 towards the crest 116.

Alternative designs of tapered thread 119 are illustrated schematically with reference to FIGS. 4A-E. FIG. 4A shows a longitudinal cross-section of a thread 400 having a uniform thread profile such as could be formed in the main portion of the threaded section. The thread 400 extends from base surface 408 and has apical 414 and coronal 412 flanks connected by a crest 416. FIGS. 4B-4E show different ways in which this basic thread profile can be altered to form a tapered thread.

FIG. 4B shows how the thread depth can be reduced by maintaining the cross-sectional shape of the thread 400 while gradually reducing its dimensions. FIG. 4C shows how the thread profile of FIG. 4A can be altered by gradually removing the radially inner part of the profile. In this way the thread crest 416 changes along the length of the thread while the transition from base surface 408 to flanks 414, 412 remains constant. In FIG. 4D, the thread profile of FIG. 4A is altered by gradually removing the radially outer part of the profile. In this way the thread crest 416 remains constant while the transition from base surface 408 to thread flanks 414, 412 is altered. In both FIGS. 4C and 4D areas of the triangular thread profile are progressively removed, with this removal either occurring at the thread crest or thread root. When material is removed from the thread crest (the radially inner part of the profile) this gives the visual impression that the thread tip is being “shaved off” until the thread is ground away entirely (see FIG. 4C). When material is removed from the thread root (the radially outer part of the profile) this gives the visual impression of the thread being “submerged” beneath the base surface (see FIG. 4D). The design of tapered portion 117 is therefore an example of this form of profile alteration.

In FIGS. 4B-4D the minimum radius of the thread 400 remains constant, however it is also possible for the minimum radius to increase in the apical direction. This is shown in FIG. 4E. In FIG. 4E both the inner and outer parts of the thread profile are gradually removed such that the thread appears to be both shaved off from the crest and submerged from the root simultaneously.

Each of the thread designs shown in FIGS. 4B-4E enables the thread depth to be gradually reduced in order to provide the tapered thread of the present invention.

Returning to the implant shown in FIGS. 2A-C, the crest 116 is curved, forming a circular arc in longitudinal cross-section over the full length of the threaded section 107. In addition, within the main portion 115, the transition between the apical 114 and coronal 112 flank at the base surface 108, known as the thread root 121 (see FIG. 2B), also forms a circular arc in longitudinal cross-section. These rounded roots