Description

Field of the invention

The present invention relates to a dental implant, a method of manufacturing a dental implant and a method of placing a dental implant. Background of the invention

Dental implants of various forms, realized for example in titanium, are used and are inserted in the bone to replace natural dental elements, e.g. lost due to illness or trauma, or as an anchor for an orthodontic brace. The commercially available dental implant systems have a success rate of 90%, and after healing time, they generally have the desired strength.

However, there are still drawbacks to the known dental implants. For example, the healing time is too long (typically about 3 to 6 months). This means that, after placing a dental fixture, depending on which system a dentist uses, it takes up to 3-6 months un till the first mechanical loads can be applied (i.e. in eating). Additionally, the dental implants tend to be not suitable for patients with weak bone properties such as elderly, heavy smokers, and people who suffer from a bone tumour in the jaw. These patient are usually advised to use the traditional solutions such as partial dentures.

To improve the integration, solutions have been proposed. For example from United States Patent application publication US 2009 a cylindrical implant is known. The dental implant comprises an external thread-shaped titanium spiral which is fastened to three longitudinal reinforcing ribs arranged inside the spiral. Inside the spiral a porous insert is provided. The porous insert is made from titanium powder produced by crushing a titanium sponge by a method of hydrostatic compacting.

However, a disadvantage of this implant is that the construction is complex and requires inserting the insert into the base and providing the reinforcing ribs onto the thread-shaped spiral.

From United States Patent application publication US 2007/ 065779 (hereinafter "Mangano") a method for making an intraosseous dental implantation is known. This prior art document discloses that the method includes the steps of supplying a layer of powder of a material designed to form the dental implantation and applying a laser sintering beam to said powder to form a layer of the dental implantation and repeating the two above operations several times by depositing each time a following layer of powder over the preceding one treated with the laser beam to form the dental implantation with the laser beam being applied to the powder layers so as to form cavities on a surface of the dental implantation designed to be colonized by the patient's bone.

However, a disadvantage of the resulting implant is that although the cavities on the surface could have an osteogenic effect which reduces undesired implant induced reactions of the monolithic body, the integration of the dental implant to the jaw bone will be limited.

Summary of the invention

The present invention provides a dental implant, a method of manufacturing a dental implant and use of a dental implant as described in the accompanying claims.

Specific embodiments of the invention are set forth in the dependent claims.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

FIG. 1 shows a perspective view of a first example of a dental implant.

FIG. 2 shows the example of FIG. 1 implanted in a jaw bone shortly after implantation.

FIG. 3 shows the example of FIG. 1 implanted in a jaw bone after healing of the jaw bone. FIG. 4 shows a perspective cross-sectional view of the example of FIG. 1.

FIG. 5 shows a cross-sectional view of a second example of a dental implant.

FIG. 6 shows a cross-sectional view of a third example of a dental implant.

FIG. 7 shows a perspective, close-up view of a part of the shank of the first example.

FIG. 8 shows a perspective, close-up view of a part of the shank of the second example.

FIG. 9 shows a perspective, close-up view of a part of the shank of the third example.

FIG. 10 shows a cross-sectional view of a fourth example of a dental implant.

FIG. 11 shows perspective views of examples of unit cells suitable for a dental implant.

FIG. 12 schematically illustrates a method of manufacturing a dental implant.

FIG. 13 shows a flow-chart of a first method of manufacturing a dental implant.

Detailed description of the preferred embodiments

In the following, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.

Referring to FIG. 1, the example of a dental implant 1 shown therein can be implanted in a jaw bone of a patient, as illustrated in FIGs. 2 and 3. The dental implant comprises a monolithic body 4 of a biocompatible material. The monolithic body 4 has a longitudinal direction from an apical end 2 towards a coronal end 4. The monolithic body 4 comprises a shank 5 which extends in the longitudinal direction. A thread 6 extends circumferentially around at least a part of the shank 5. As more clearly seen in e.g. FIG. 4, the thread 6 thus extends over the surface of the porous shank 5, or said differently the porous shank 5 extends in radial direction of the implant between the longitudinal axis of the implant and the thread. When implanted in the jaw bone 100 the thread 6 holds the shank 5 in position relative to the jaw bone 100 in at least the longitudinal direction. The monolithic body further has a support platform 7 for supporting and fixating, permanently or temporarily, relative to the monolithic body a dental prosthesis or orthodontic brace.

In the monolithic body 4, the tread 6 has a closed outer surface 60, i.e. the surface 60 closes off the inside of the thread whereas, as shown in more detail in FIG. 4, the shank 5 has an inside provided with pores 50. Due to the pores 50 the overall stiffness of the dental implant is reduced compared to an implant with a solid shank. Accordingly, the chance of stress shielding the jaw bone may also be decreased. Therefore, not only does the dental implant allow a dramatic reduction of the healing time but the dental implant can also be made suitable for patients with weak bone properties.

Because the thread 6 extends around the shank 5, different parts of the porous shank 5 are not shielded from each other by the thread 6. In the example, more specifically the porous shank 5 is not interrupted at all by the thread 6. This absence of separation allows bone-ingrowth to propagate through the entire shank regardless of the location of the shank 5 the ingrowth has started. Accordingly an improved osseo-integration of the implant 1 can be obtained. In the example, the shank-side part of the thread 6 is flush with the surface of the porous shank 5, but it will be apparent that the shank-side part of the thread 6 can be slightly recessed in the shank 5 without interrupting, at least seen in the longitudinal direction, the shank 5.

In addition, due to the porous shank 5 and the tread 6 being part of the same monolithic body, the need for special connecting parts is obviated. Since these connecting parts are relatively stiff, they restrict the lower limit of the range of possible stiffness of the implant. Accordingly, the monolithic body allows a larger range of stiffness of the implant is obtained and in particular to obtain less stiff implants.

In addition, it has been found that because to the monolithic body the dental implant has a high wear resistance and is capable of resisting loads which are significantly higher than typical bite forces for a number of cycles which is significantly higher than the number to which an implant would be exposed to in-vivo. For example, the dental implant may be implemented such that when fatigue tested in accordance ISO standard 14801:2016, the dental implant resists at least lx 10 ⁶ cycles, for example at least 3.1 χ 10 ⁶ cycles, such as 5 χ 10 ⁶ cycles or more with a load of x Newton, in which x is at least 100, for example at least 150 or more, such as 187 N or more. This may apply to a single dental implant or to a batch of dental implants. In the latter case, due to the stochastic nature of manufacturing, e.g. the batch may have at least 95% of the dental implants resting such fatigue testing, and preferably at least 99% or more.

In an experimental set-up, fatigue testing in accordance with ISO standard 14801:2016 has been performed with a load ratio R = 0.1 at a test frequency of 5 Hz, until the implant survived 5 χ 10 ⁶ cycles. This testing yielded that the implant could survive 5 x 10 ⁶ cycles with a load of 190 N.

This load of 190 N is an order of magnitude higher than typical, normal, voluntary non- dysfunctional bite forces during mastication, which are reported to be distributed around a peak of about 10-20 N and only exceptionally exceed 100 IM, see Hattori Y, Satoh C, Kunieda T, Endoh R, Hisamatsu H, Watanabe M, "Bite forces and their resultants during forceful intercuspal clenching in humans", Journal of Biomechanics 2009;42:1533-8.

As explained below in more detail, the pores provide an interface for bone in-growth in the shank. This allows, in addition or alternatively to the reduced stiffness, an increased integration in the jaw bone because the pores provide an attractive place for bone ingrowth, while the threads guarantee the strength of the design. Thus, the dental implant can osseo-incorporate into the jaw bone, i.e. ingrowth of bone matter inside the dental implant can be obtained in addition to bone on- growth on the interfaces between the dental implant and the bone. More specific, the solid parts of the pores provide a seed surface for bone material, and, after implantation, form a substrate on which osteoblasts and stem cells can grow. Without wishing to be bound to theory, it is currently believed that the solid parts of the pores initially form a seed layer for a cell growth substrate. The cell growth substrate can for example be formed by substances adsorbed to the pores, like proteins, water molecules and/or lipids. Also, the substrate may comprise substances attached to the pores, like blood platelets. After formation of the growth substrate, osteoblasts or their progenitors, such as osteochondroprogenitor cells or mesenchymal stem cells, will grow thereon and subsequently form the bone matrix in the pores, thus creating an intimate bond between the bone and the implant.

The dental implant can be placed in a jaw bone of a patient, such as the mandible or the maxilla. FIG. 2 illustrates an implant shortly after placement in the jaw bone. As shown, a cavity 101 has been provided in the jaw bone 100 and the dental implant is placed therein. The dental implant can for example be a self-tapping implant and create the cavity 101 itself or be placed in a pre- tapped cavity, and e.g. be of a non-self-tapping type. As shown in FIG. 3, after placement of the dental implant, a dental prosthesis 9 (in this example a crown) is attached to the support platform 7, in this example via an abutment 8 detachably mounted to the dental implant at the coronal end 3. It will be apparent that the platform 7 may be suitable for mounting other types of prosthesis, such as a bridge or a (partial) denture. Also, the dental implant may be used as an anchor for an orthodontic brace and the support platform may be shaped in a manner suitable to attach the orthodontic brace.

In FIG. 3, the dental implant is shown osseointegrated and/or incorporated into the jaw bone. Depending on the specific method chosen by the medical practitioner placing the dental implant, the abutment, prosthesis and/or brace may be placed immediately after placing the dental implant or some period thereafter, and more or less time for bone on-growth and ingrowth be allowed prior to mounting the dental prosthesis or orthodontic brace.

The thread 6 may be implemented in any manner suitable for the specific implementation. In the FIGs., the thread 6 is a screw thread which allows to screw the dental implant into the bone. However, the dental implant may also be a press-fit implant with an external thread.

As more clearly shown in FIG. 4, the thread may be solid to have a higher lateral stiffness than the shank and thereby provide lateral support thereto. However, depending on the specific implementation the thread 6 may be provided with one or more sealed voids under the closed surface to e.g. modulate the characteristics of the thread locally.

In the examples, the thread 6 has a helical shape and extends circumferentially around the shank with several revolutions. The flange of the thread 6 forms a ridge 61 which projects outwards from the shank 5, in a radial direction R perpendicular to the longitudinal direction L, as more clearly shown in FIG. 4.

In the example, the longitudinal axis of the helix is parallel to the longitudinal direction L of the monolithic body 4, and in this example coincides with a longitudinal axis of the shank 5, which has a cylindrical shape. The successive turns or windings of the thread 6 do not abut and are spaced apart, which leaves the outer surface of the shank 5 exposed at the root of the thread and thus provides access for bone ingrowth inside the shank 5 via the exposed areas. More specifically, the pitch of the thread 6 is larger than twice the width of the ridge 61 at the base thereof.

The thread can be a continuous thread, or as in the examples be an interrupted thread. As shown in FIG. 1, the thread can be interrupted by at least one flute 62 extending in the longitudinal direction L and which crosses the thread 6 at several turns of the thread 6. The shown flute 62 extends from the apical side 63 where the thread starts up to the coronal side 64 where the thread ends. The flute 62 is oblique relative to the longitudinal axis of the thread 5. As shown, the thread is interrupted by several flutes, in the example equidistant in the circumferential direction. The flute(s) 62 may alternatively be parallel to that axis and/or cross a limited number of the turns, i.e. less that all the turns of the thread.

The closed surface of the thread can be an interface for bone on-growth, e.g. implemented as a rough surface. The closed surface 60 of the thread can be chemically and/or mechanically treated for accelerating bone on-growth. For instance, the surface 60 can be provided with a growth enhancing coating or have been sandblasted to enhance the roughness thereof.

In a similar manner as described above with reference to the bone-ingrowth in the pores, the closed surface 60 may e.g. form a seed surface for bone matter. Thus, for example, the thread 6 may form a seed layer for the cell growth substrate, which after implantation will form on the closed surface 60. After formation of the growth substrate, osteoblasts or their progenitors, such as osteochondroprogenitor cells or mesenchymal stem cells, may grow thereon and form a bone matrix which creates an intimate bond between the bone and the thread 6.

The ridge 61 may be provided with bone grafting cavities which transport bone grafts to the shank 5 during and/or after implantation of the dental implant 1 in the jaw bone 100. For example, the closed surface 60 may be provided with small cavities to transport bone grafts to porous parts of the shank 5 to increase the osseoincorporation.

The shank 5 may be implemented in any manner suitable for the specific implementation. In FIGs. 1, 5 and 6 the shank has an elongated cylindrical shape with a longitudinal axis, indicated in FIG. 4 with line L. The shank 5 is tapered in the direction parallel to the longitudinal axis L towards the apical end 2.

The porosity of the shank will of course be non-zero and can be at least 10%, such as at least 20%, such as at least 30%, such as at least 40%, for example at least 50%, such as at least 55% or a porosity of 70% or more. This allows an acceptable osseoincorporation of the shank 5. The shank 5 may have a porosity of not more than 90%,such as not more than 80%, such as not more than 75%, for instance not more than 70%. This provides for sufficient mechanical strength of the shank 5. Preferably, the shank has a Young's modulus which is about (e.g. ± 10%) the same as of bone.

In this respect, for example the stiffness of the host bone may be graded prior to manufacturing the implant, a porosity that corresponds to the graded stiffness suitable for the implant be determined from a predetermined relationship between stiffness grades and porosity, and the implant be manufactured subsequently with this porosity, e.g. with the process as described with reference to FIG. 10 or 11.

It will be apparent that the term "pore" and "porous" refer to a pore-size which is significantly smaller than the dimensions of the shank, e.g. an order of magnitude, and do not refer to a shank with just a single or a few chambers, or to a shank with a single or a few straight and/or crossing channels. The shank can for example have several tens, hundreds or thousands of pores. The pores can, on average have a size which is significantly larger than bone cells, and for example at least one or two orders of magnitude larger.

The average pore size of the pores can be between 0.1 and 0.8 mm, such as e.g. between 0.05 mm and 1 mm, such as in the range of 0.25 mm to 0.75 mm. Depending on the specific implementation, the pores may have the same or varying sizes (e.g. when the size is normally distributed). For example, at least 90% of the number pores can have a pore size between 0.1 and 0.8 mm.

Typical dimensions of the dental implant (although other sizes being possible as well depending on the jaw in which the dental implant has to be placed) can be a length between 5mm and 20mm and a diameter of between 3mm and 8mm.

The porosity of a shank can vary, e.g. increase or decrease, from the outside inwards, e.g. towards the longitudinal axis. The shank can for example have an, exposed, outer layer which is more porous (and/or a bigger (average) pore size and one or more inner layers which are less porous and/or with a smaller pore size than the outer layer. This allows e.g. to have a relatively stiff but still porous core of the shank, while due to the high porosity at the outside, osseointegration of the shank will be improved. For example, the outer layer may have a porosity of at least, or equal to, one of the group consisting of: 70%,80%,90% and less than 100%, such as less than one of the group consisting of: 95%, 85%,75%. The inner layer may have a porosity which (of course) is more than 0%, such as at least at least 10%, such as at least 20%, such as at least 30%, such as at least 40%, for example at least 50%, such as at least 55%. The inner layer may have a porosity which is a certain percentage less than the outer layer, which can for example be at least, or equal to, one of the group consisting of: 10%,20%,30%. The increase or decrease may be step-wise or gradual. The porosity may increase or decrease monotonically from the outside towards the longitudinal axis, but alternatively the porosity may fluctuate and (repeatedly) increase and decrease from the outside towards the longitudinal axis.

The examples of implants shown FIGs. 5 and 6 differ from the example of FIGs. 1 and 4 in the shape of the pores inside the shank.

In the shown examples, the shank 5 has an outer surface 52 extending in the longitudinal direction L which comprises a system 53 of intercommunicating pores, which allow osseo-integration of the inside of the shank beneath the outer surface into the jaw bone 100. This system may for instance comprise a system of open intercommunicating pores, such as shown in FIGs. 7-9.

The outer surface 52 is provided with outer pores 50 open to an environment of the shank 5. The shank comprises a porous inside extending from the outer surface 52 towards a longitudinal axis of the shank up to a depth D. In the shown examples, the depth D is equal to the diameter of the shank, which thus has a completely porous inside. The porous inside is in fluid communication with the outer pores, which allows bone ingrowth into the porous inside. For instance, the inner and outer pores may form an integral network of porous cells.

The porous outer surface 52 may for example have an openness, defined as the ratio of the non-closed area the outer pores occupy and the area of the outer surface, of at least 5%, for example at least 10%, and preferably at least 50%, such as at least 80%. The openness will of course be less than 100%, and may e.g. be 90% or less, for example less than 70%.

The porous inside can be of any suitable type, and the shank can for example be made of a, biocompatible, metal foam, such as an open cell metal foam. Such a foam can for example be a self- forming structure and forms a three-dimensional network of cells. The open cell metal foam may for example be a reticulated foam, as shown in the examples for instance. Also, the foam may be a regular foam or a stochastic foam. In the figures for instance the foam is a regular, reticulated foam.

The shank may consist of a single type of metal foam but may likewise comprise a mixture of foams and for example comprise a mixture of reticulated foam and partially or completely closed cells, like a closed cell foam. For instance, the mixture may consist of 50% or more of reticulated foam and 50% or less of closed cells, and for example have 90% or more of reticulated foam. As an example, the mixture may have 99% or more reticulated foam and 1% or less (but, of course, not 0%) of closed cells.

Referring to FIGs. 7-9, the porous inside can be an engineered structure with a predetermined matrix of pores. In the shown examples, the system of intercommunicating pores comprises a three dimensional matrix 54 of unit cells 55. In these examples, the matrix 54 consists of a single type of unit cells 55 and in a regular arrangement. However, the matrix 54 may comprise several types of unit cells in a more complex or irregular arrangement, e.g. with different types of unit cells or organic shaped cells in an irregular arrangement. The types of unit cells may e.g. differ in geometrical shape, openness or dimensions.

The unit cells can have one or more geometrical shapes. FIG.10 shows some examples of suitable shapes for unit cells, such as a cubic unit cell 551, diamond unit cell 552, rhombic dodecahedron unit cell 553, truncated cubic unit cell 554, truncated octahedron 555 and rhombic octahedron unit cell 556. The unit cells may likewise be Triply Periodic Minimal Surfaces (TPMS) or Voronoi structures.

In the examples of FIGs. 7-9, edges of each of multiple pores are formed by a respective open frame 530 of struts 56 formed from the biocompatible material. For those pores at least one face 57 enclosed by the struts is open and in fluid communication with other pores. The two or more faces may be open and in the examples of FIGs. 7-9, all faces are open. The system of intercommunicating pores comprises a monolithic framework 531 of struts formed by the frames 530. As explained below in more detail, this allows to manufacture the porous shank 5 together with the non-porous thread 6 together at the same time. The struts may have any suitable size for the specific implementation and type of pore cell. It has been found that a suitable average strut size of the struts is between 0.15 mm and 1 mm, such as between 0,2 mm and 0,75 mm.

The support platform may be any suitable platform. In the example of FIGs. 1 and 4, as most clearly seen in the latter, the platform 7 is a platform for attaching an abutment 8. Alternatively the platform may comprise an abutment 8 formed as an integral part of the monolithic body, as shown in FIG. 10.

The platform 7 is located at the coronal end 4 and is in the example of FIGs. 1,5 and 6 formed by a solid cap 70 at the coronal end which abuts to the shank 5 which is provided with a sleeve 72 which encloses the coronal side end of the shank 5. The cap is part of the monolithic body and has a axial bore 71 in which a projection of the abutment can be placed and e.g. be friction fitted and which terminates within the shank 5. The bore 71 includes a hexagonally shaped inner surface section at the uppermost section of the bore and a reduced diameter section 73 deeper in the bore towards the apical end of the monolithic body, where the bore extends into to the shank 5. As shown, the wall of the reduced diameter section has a closed surface.

Referring to FIG. 11, as illustrated with the blocks in the flow-chart, the examples of dental implants shown may be manufactured as illustrated therein, by providing (block 90) a biocompatible material and shaping (blocks 91-93) the biocompatible material to obtain the dental implant.

The biocompatible material can be shaped in a variety of manners, such as metal casting into a mould and locally injecting a gas to obtain a self-organising porous structure.

In this example, shaping the biocompatible material comprises producing (blocks 91-92) as an intermediate product a porous structure covered at least partially with a cover, the cover having a closed surface and (block 93) removing the cover and exposing the covered porous structure where desired to form a thread.

The complex intermediate product can be manufactured by using an additive manufacturing technique or a hybrid technique of an additive manufacturing technique plus subtractive manufacturing. Such an intermediate product can be shaped by forming successive layers of material under computer control, for example by selective laser melting or SLM. FIG. 12 schematically shows a selective laser melting machine 200 suitable to be used to shape the intermediate product.

As shown, the SLM machine 200 comprises a laser 201 which produces a laser beam 203 which scans a powder bed 204 of a selectively meltable material, in this example via scanning optics 203 that direct the laser beam over the exposed top layer of the bed 204 under control of a computer, i.e. a programmable apparatus controlling the optics 203 in accordance with a computer program which uses data representing a model of the dental implant as input. As more clearly seen in the right hand side of FIG. 12, the laser selectively melts the powder of the top layer in melting areas 300. After sintering the top layer in those areas, a new top layer is applied. In this example, the powder bed 204 is lowered, by moving the plate 208 on which the building plate the object, i.e. in this example the intermediate product, rests downwards by means of piston 207. The new top layer is applied by moving a pile of powder upwards by means of a delivery piston 205 and displacing powder projecting above an edge of the delivery system with a roller 206 to cover the top surface. As shown in FIG. 12, this successive applying of a layer of powder and locally sintering the powder results in a stack of patterned layers of sintered material which shape the object.

Upon sintering of the final layer, the object can be taken from the plate 208 and the un- sintered material removed. The intermediate product may then be subjected to post-processing, such as a heat treatment for stress relieving and tempering.

It has been found that a SLM process allows to manufacture the complex monolithic structure in a manner that requires little post processing. In fact, it is believed that the surface roughness of the product is ideal for bone on-growth and hence the intermediate product is allready suitable for use a final product, without further surface treatment.

Since the surfaces of the intermediate product have appropriate roughness, there is no need for any chemical or physical surface treatments. However, in the end some chemical or physical surface treatment may be applied to increase osseo-integration.

To improve the definition of the threads, the intermediate product may be subject to milling or other subtractive process to remove undesired material of the cover. In the examples, the cover of the intermediate product has already been shaped to have rudimentary thread shapes and the milling removes material to refine the shape thereof - e.g. to sharpen them. However, the cover of the intermediate product may be unshaped and e.g. be a solid sleeve around the porous inside that is shaped completely by milling or other partial removal thereof to obtain the thread(s) and expose the porous structure.

The manufacturing process may use data representing a model of the dental implant. In such a case the data is loaded into a data processing device, e.g. an embedded control system or other type computer performing the computer control, and the data processing device operated to control the forming to obtain a shape in accordance with the data.

The model can be obtained in any manner suitable for the specific implementation. The design may be stored on a, tan data carrier as data loadable in a computer representing a model of a dental implant is stored. Such a data carrier can be a tangible, non-transitory computer readable storage medium or a computer readable transmission medium. These computer readable media can be permanently, removably or remotely coupled to the computer. The computer readable storage medium may include, for example and without limitation, any number of the following: magnetic storage media including disk and tape storage media; optical storage media such as compact disk media (e.g., CD ROM, CD R, etc.) and digital video disk storage media; nonvolatile memory storage media including semiconductor-based memory units such as FLASH memory, EEPROM, EPROM, ROM; ferromagnetic digital memories; MRAM; volatile storage media including registers, buffers or caches, main memory, RAM, etc..

The computer readable transmission medium may be a data transmission media such as wired or wireless transmission media, just to name a few.

The model may for example be designed by using a suitable computer aided design computer program, such as as SolidWorks or CATIA etc., to make an initial model of a solid implant with the shape of the desired implant. To design a porous part which will be the dental implant shank (minus outer threads and solid inner threads), another, solid, part can be designed with CAD software which is subtracted from the first model. This results in two models: the initial model minus the porous part and a model of the porous part itself (which is still solid).

The model of the porous part can be provided with pores by adding three-dimensional structures thereto, e.g. using software such as Autodesk Within medical, Materialise Magics or Autodesk Netfabb studio etc. a. This 3D structure can be made by using open unit cells as explained earlier, such as the diamond, rhombic dodecahedron, Truncated octahedron, etc cells. The two models can then be merged together to form a monolithic model. The monolithic model is subsequently converted into a format which is appropriate for 3D printing like the STL format.

In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader scope of the invention as set forth in the appended claims.

For instance, although in the shown examples the flutes 62 are oblique relative to the longitudinal direction, the flutes 62 may e.g. be parallel thereto or at a different angle than shown.

Furthermore, although in the examples a single start thread is shown, it will be apparent that e.g. a mulitple start thread may be used. Also, in the examples the thread has a constant pitch. However, the pitch may vary over the length of the thread.

Likewise, the monolithic body may be made of any suitable biocompatible material. The material may for example contain a material out of the group consisting of: metals, metal compounds, metal alloys, metal composites, polymers, ceramics. The bio compatible material can contain a metal out of the group consisting of: titanium, tantalum, niobium, stainless steel, cobalt chrome alloys, zirconia, or a compound, alloy or composite thereof. Other suitable biocompatible materials can contain a polymer out of the group consisting of polyaryletherketone, polyether ether ketone, polyetherketoneketone.

Also, although in the examples the shank 5 is shaped as a tapered circular cylinder and the thread is a tapered thread, the shank may e.g. have a conical shape, or be not tapered and the thread be a straight thread. Furthermore, although in the shown examples the treadform is a tapered triangle, other threadforms may be suitable as well.

However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms "a" or "an," as used herein, are defined as one or more than one.

Moreover, the terms "front," "back," "top," "bottom," "over," "under" and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

Also, the use of introductory phrases such as "at least one" and "one or more" in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.