Ceramic Dental Implants

Abstract

The present invention relates to a ceramic dental implant (100) for implantation in a jawbone, the implant (100) extending from an apical end (103) to a coronal end (102). The implant (100) has a blind hole (104) that is open toward the coronal end (102) of the implant and extends along a central longitudinal axis LA toward the apical end (103). The blind hole (104) includes a threaded portion (107) having a base surface (108) from which threads (109) project radially inward, the base surface (108 being oriented such that the maximum radius R of the threads (109) measured from the central longitudinal axis LA is 10. MAX The thread (109) has a coronal flank (112) and an apical flank (114) connected at their radially inner ends by an apex (116), the apex (116) defining a minimum radius R of the thread (109) measured from a longitudinal central axis LA. MIN The threads (109) extend helically along the axial length of the threaded portion (107) and have a depth determined by the difference in radius between the base surface (108) and the apex (116). The threaded portion (107) has a main portion (115) within which the maximum radius R of the threads (109) is MAX remains constant along the length of the main portion (115) and a tapered portion (117) apically adjacent to the main portion (115), within which the base surface (108) is spaced apart from the maximum radius R of the threads (109) at the main portion (115). MAX Therefore, the minimum radius R of the thread (109) at the apical end of the tapered portion (117) MIN and a tapered portion (117) that tapers radially inward in an apical direction to a tapered thread (119) having a gradually decreasing thread depth, the tapered portion (117) extending over an axial length greater than the thread pitch to form a tapered thread (119) having a gradually decreasing thread depth, the tapered thread (119) extending over multiple thread turns.

Description

[Technical field]

[0001] The present invention relates to a dental implant made of a ceramic material and having an internally threaded bore. [Background technology]

[0002] Dental implants are used to replace one or more teeth in a patient's mouth. They typically include an anchor portion that is inserted into the patient's jawbone and an abutment portion that extends through the gums into the patient's mouth, where the abutment portion provides the core support for a final prosthesis (e.g., crown, bridge, complete denture).

[0003] The anchor portion and abutment portion may be provided as a single integral piece, but are more commonly provided as separate components that are connected together via screwing, adhesive bonding, a compression fit, etc. Such implant systems are commonly referred to as "two-part" or "two-piece" implants, and in isolation the anchor portion is commonly referred to as the "implant" or "fixture" and the abutment portion is commonly referred to as the "abutment" or "post."

[0004] The anchor part of a two-piece implant is usually either completely embedded in the bone, i.e. up to the level of the alveolar crest, or protrudes a few millimeters from the alveolar crest into the soft tissue. Anchor parts intended to be completely inserted into the bone are usually called "bone level" implants, while those intended to extend into the soft tissue are usually called "tissue level" implants. The abutment can be attached directly or indirectly to the anchor part through one of various known means. Most commonly, the abutment is adhesively bonded or screwed to the anchor part. In the latter case, the anchor part usually comprises a blind hole extending longitudinally with an internal thread. The abutment or another component can then be fixed to the anchor part by a screw that is fixed into the internal thread of the anchor part.

[0005] One-piece dental implants with integrally formed anchor and abutment portions may also include a female threaded blind hole to allow threaded attachment of other components of a dental system (e.g., prostheses, healing caps, etc.) to the implant.

[0006] The present invention may be applied to both one-piece and two-piece implant systems. Thus, for the remainder of this specification, references to "implant" refer to the component of the system intended for at least partial insertion into and osseointegration with bone, whether or not this includes an integral abutment.

[0007] The majority of dental implants currently in use are made from titanium or its alloys, a material that is not only sufficiently biocompatible for osseointegration, but also has the necessary strength to withstand the chewing forces that the implant will be subjected to during its lifespan.

[0008] However, from an aesthetic point of view, titanium implants have the disadvantage that they are dark in colour and therefore do not match the colour of natural teeth.

[0009] During the life of the implant, the gums, and often the jawbone, also weaken. As a result of this, the dental implant can become visible and, because it is dark in color, visually noticeable.

[0010] In contrast, the color of ceramic materials more closely matches the color of natural teeth. In addition, there is an increasing consumer desire to reduce or eliminate the use of metal in implants placed in the body. Thus, efforts are being made to provide dental implants formed from ceramic materials such as zirconia and alumina.

[0011] However, compared to metals, ceramics are brittle materials and are susceptible to breakage. Thus, there is a risk that parts of the implant system become damaged, for example when anti-rotation elements and threads are formed in the ceramic material during production. In addition, during use, material breakage can occur in areas where load peaks occur, for example in the contact areas between abutments or other components and the implant.

[0012] In particular, the fixation of an abutment or other component to an implant with a screw can lead to stress concentrations in the female threads of the implant, which can result in crack formation.

[0013] To account for the different material properties of ceramics compared to metals, the preferred designs of ceramic implant systems may differ from those of metallic systems.

[0014] US Patent No. 5,399,633 describes a ceramic dental implant formed by injection molding and equipped with an internal thread, the internal thread having rounded tops and recesses to ensure greater stability of the threaded portion.

[0015] US Patent No. 5,399,633 shows a ceramic dental implant with a long blind hole with the screw located in the lower half of the hole. The increased length of the blind hole is said to better distribute the stress in the implant body. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] U.S. Patent No. 6,280,193 [Patent Document 2] European Patent Application Publication No. 2735279 Summary of the Invention [Problem to be solved by the invention]

[0017] In view of the above-mentioned problems inherent to implants formed from ceramics, it is an object accomplished by at least preferred embodiments of the present invention to provide a ceramic implant having internal threads that are less susceptible to fracture. [Means for solving the problem]

[0018] This object is achieved by at least a preferred embodiment of the invention as defined in claim 1. Preferred embodiments are the subject matter of the dependent claims.

[0019] According to a first aspect, the present invention provides a ceramic dental implant for implantation in a jawbone, the implant extending from an apical end to a coronal end, the implant having a blind hole that is open towards the coronal end of the implant and extends along a central longitudinal axis towards the apical end, the blind hole comprising a threaded portion having a base surface, the threads projecting radially inwardly from the base surface, the base surface defining a maximum radius of the threads measured from the central longitudinal axis, the threads having a coronal flank and an apical flank connected at a radially inner end by an apex, the apex defining a minimum radius of the threads measured from the central longitudinal axis, the threads extending helically along an axial length of the threaded portion and having a depth defined by the difference in radius between the base surface and the apex. The threaded portion comprises a main section within which a maximum radius of threads remains constant along the length of said main section, and a tapered section apically adjacent to the main section, within which a base surface tapers radially inwardly in the apical direction from a maximum radius of threads at the main section to a minimum radius of threads at the apical end of the tapered section, the tapered section extending over an axial length greater than the thread pitch to form a tapered thread with a gradually decreasing thread depth, the tapered thread extending over multiple thread revolutions.

[0020] According to conventional dental terminology, "apical" refers to the direction toward the bone and "coronal" refers to the direction toward the tooth. Thus, the apical end of a component is the end that points toward or into the jawbone in use, and the coronal end is the one that points toward or into the oral cavity.

[0021] The terms "crown flank" and "apical flank" as used throughout this specification refer to the surface of the thread extending from the base surface towards the central longitudinal axis of the blind hole. The apical flank is defined as the flank facing the apical end of the implant. In other words, the crown end of the apical flank is found at the crest and the apical end of the apical flank is located at the base surface. In contrast, the crown flank is defined as the flank facing the crown end of the implant. In other words, the crown end of the crown flank is found at the base surface and the apical end of the crown flank is found at the apex.

[0022] The term "pitch" as used throughout this specification refers to the axial distance between two adjacent thread crests, in other words, the axial distance of one complete thread revolution.

[0023] According to the invention, the threaded portion comprises a tapered section, in which the base surface tapers radially inward in the apical direction. The maximum radius of the thread in the tapered section therefore decreases in the apical direction from the maximum radius of the thread in the main section, i.e. the radius of the base surface in the main section, to the minimum radius of the thread at the apical end of the tapered section. As a result, the maximum and minimum thread radii are equal to each other, resulting in a loss of thread at the apical end of the tapered section. All thread radii are measured from the longitudinal central axis of the hole. According to the invention, the axial length of the tapered section is greater than the pitch of the thread. In this way, the thread depth (i.e. the distance between the base surface and the apex) is gradually reduced over several turns of the thread, resulting in a gradual tapering out of the thread.

[0024] This differs from prior art implants where any threaded portion of a blind hole typically ends abruptly in a smooth cone with a wide cone angle. The face of this cone typically meets the bevel of the thread in a manner that results in an acute angle and causes the threads to run out in less than one turn, typically about half a turn of the thread. This acute angle, when formed in a ceramic implant, can lead to cracking and failure of the implant.

[0025] It has been found that such sharp angles can be avoided by providing a taper on the threaded portion of the blind hole at its apical end, thereby removing stress points from the system and reducing the risk of crack formation within the implant.

[0026] According to the invention, the maximum radius of the thread is defined by the base surface of the threaded portion, the minimum radius of the thread is defined by the radially innermost point of the apex, and the depth of the thread at any axial location is given by the difference between the radii of the base surface and the apex at that location.

[0027] In preferred embodiments, the minimum radius of the threads is constant at least along the entire longitudinal length of the main portion of the threaded section. Thus, in such embodiments, the thread depth and maximum radius of the threads remain constant within the main portion. This facilitates production of the hole and provides uniform force distribution during use.

[0028] In some embodiments, within the taper, the minimum radius of the thread may gradually increase in the apical direction, such that the reduction in the thread depth within the taper is caused by the taper of both the maximum and minimum radius of the thread. However, it is preferred that the minimum radius of the thread is constant along the entire length of the taper. This makes the taper easier to produce. Thus, according to this preferred embodiment, the gradual reduction in the thread depth within the taper is caused only by the taper of the base surface. In a particularly preferred embodiment, the minimum radius of the thread remains constant over the entire length of the threaded section.

[0029] In embodiments where the maximum and minimum radii of the thread, and therefore the thread depth, also remain constant along the length of the main section, it is further preferred that the thread profile remain constant along the length of the main section. "Thread profile" means a longitudinal cross section of the thread, i.e., a cross section of a two-dimensional plane that contains a number of points on the longitudinal central axis of the hole. A uniform profile is easier to manufacture and provides a consistent force interaction with the screw.

[0030] However, as a result of the required reduction in thread depth, the thread profile must be altered within the taper. Using at least some manufacturing methods, such as 3D printing, it is possible to maintain the cross-sectional shape of the thread profile while reducing its dimensions along the length of the taper. For example, the thread profile within the taper may have a triangular shape, but the dimensions of the triangle decrease in the apical direction.

[0031] However, to simplify the design, it is preferred to modify the thread profile within the taper by gradually removing areas of the initial thread profile, e.g., the main thread profile, so as to change the cross-sectional shape of the thread profile along the length of the taper. For example, within the taper, the thread profile may be modified by gradually removing a radially inner portion of the profile along the length of the taper, i.e., by modifying the apex shape. Returning to the triangle example above, in this embodiment, the tip of the triangle (the tip located at the apex) is gradually removed along the length of the taper. This design gives the visual impression that the thread apex is gradually "shaved" until the thread is completely ground away and removed.

[0032] However, within the taper, the thread profile is preferably modified by gradually removing a radially outer portion of the profile, i.e., modifying the transition from the base surface to the bevel surface of the thread; this area of ​​the thread is known as the thread root. Using the triangle example above, in this embodiment, the base of the triangle (which contacts the base surface) is gradually removed along the length of the taper. This design gives the visual impression that the thread is "sunk" below the base surface of the taper.

[0033] It is also possible to combine these approaches such that within the taper, area of ​​the thread profile is gradually removed at both the radially outer and inner portions, so that the thread appears to be shaved from the crest and simultaneously sunk from the root. However, since the object of the present invention is to progressively reduce the thread depth, it is typically preferred to gradually remove only either the inner or outer portion of the thread profile within the taper, for simplicity of design. In this way, the thread root remains constant while the crest shape changes, or the thread crest remains constant while the shape of the thread root changes.

[0034] All of the above design possibilities for modifying the thread profile may be used in embodiments where the minimum radius of the thread at the taper remains constant or increases in the apical direction.

[0035] As previously mentioned, in a preferred embodiment, the minimum radius of the thread remains constant within the taper. In one particularly preferred embodiment, within the taper, the thread profile remains constant relative to the base surface of the main section, and within the taper, the threads gradually sink into the base surface of the taper. This embodiment is an example of gradually removing the radially outer portion of the thread profile to achieve a tapered thread.

[0036] In a particularly preferred embodiment, the thread profile remains constant along the length of the main section and this profile is gradually removed in the taper section according to one of the design concepts described above.

[0037] According to the invention, the tapered thread formed in the tapered section extends over at least one revolution of the thread. In other words, the gradual reduction in thread depth occurs over a portion of the thread that extends more than 360° around the longitudinal central axis. This is achieved by providing a tapered section that has an axial length that is greater than the pitch of the thread. Preferably, the tapered thread extends over at least 2 revolutions, more preferably 2 to 8 revolutions, and most preferably 4 to 6 revolutions.

[0038] Preferably, the screw has a pitch of 0.2 mm to 0.5 mm.

[0039] Preferably, the taper extends over at least one quarter of the axial length of the threaded portion, more preferably over at least one third of the axial length of the threaded portion.

[0040] As mentioned above, according to the invention, the base surface of a threaded portion defines the maximum radius of the thread. In other words, the base surface is a surface that includes all the points of the thread that have the maximum radius at each point along the axial length of the threaded portion. Extrapolating these points gives an imaginary surface that defines the shape of the base surface. In the main part of the threaded portion, the maximum radius of the thread, and therefore the radius of the base surface, remains constant. The shape of the base surface over the length of the main part is therefore cylindrical.

[0041] According to the invention, in the taper, the tapered thread is at least partially formed by a taper of the radially inner base surface in the apical direction. The base surface in the taper can be curvedly tapered, i.e. the base surface can be radially tapered such that the shape formed by the base surface is, for example, spherical or ovoid. However, preferably, in the taper, the base surface tapers radially inward with a taper angle. The shape formed by the base surface in such an embodiment is therefore conical. This simplifies the design of the taper. The term "taper angle" as used in the context of the present invention refers to the angle formed by the surface in question with respect to the longitudinal central axis of the hole. The smaller the taper angle of the base surface, the higher the number of turns of the thread for a given pitch in the taper. A smaller taper angle results in a more gradual inward taper of the base surface and therefore a more gradual reduction in the thread depth.

[0042] The taper angle of the base surface may not be constant along the length of the tapered section. For example, the tapered section may comprise a first portion in which the base surface has a first taper angle and a second apical portion in which the base surface has a second taper angle that is greater than the first taper angle. However, preferably, the taper angle of the base surface within the tapered section is constant over the entire length of the tapered section. This is advantageous from both a manufacturing and force distribution standpoint.

[0043] In particularly preferred embodiments, the taper angle of the base surface within the tapered section is less than 20°, preferably less than 10°, and most preferably about 8°. These angles make the taper sufficiently gradual to provide the desired gradual loss of thread.

[0044] Additionally or alternatively, the taper angle of the base surface in the tapered section is preferably less than the taper angle of the crown flank of the thread. The taper angles of the apical flank and the crown flank can be the same or different. Having a taper angle of the base surface less than the taper angle of the crown flank is highly advantageous to ensure that no acute angles are formed at the intersection of the flank and the base surface.

[0045] Additionally or alternatively, it is preferred that the angles formed within the taper between the base surface and both the apical and coronal flanks are obtuse, i.e., greater than 90°, thus preventing these corners from becoming sharp and creating stress points.

[0046] All of the above-mentioned preferred configurations of the taper, individually and / or in combination, assist in creating a gradual tapered loss of the threads that prevents or reduces stress concentrations.

[0047] As previously mentioned, according to the invention, the threaded portion comprises threads projecting radially inwardly from a base surface, the threads comprising a crown flank and an apical flank connected at their radially inner ends by an apex.

[0048] Preferably, the thread has a helix angle of 50° to 70°. As used herein, the term "helix angle" refers to the angle enclosed by two flanks at an apex.

[0049] Preferably, there is a curved transition between the flank and the base surface of the thread along the length of the main part of the threaded portion. Such a curved transition helps to prevent sharp angles in the hole and reduces the possibility of stress concentration and crack formation. In a particularly preferred embodiment, when viewed in a longitudinal cross section, there is a fully curved transition between adjacent apical and coronal flanks at the radially outer ends of the apical and coronal flanks. As mentioned above, "longitudinal cross section" means a cross section taken on the central longitudinal axis of the blind hole, i.e., a two-dimensional plane that includes a plurality of points on this axis. Such a fully curved transition at the root of the thread relieves tension between the inner thread of the implant and the outer thread of the second part or fixation screw. In such an embodiment, the base surface is tangent to the curved transition. The curved transition can be elliptical or oval, but preferably, when viewed in a longitudinal cross section, the transition has the shape of a circular arc.

[0050] The transitions between the base surface and the apical and coronal flanks in the taper may also be curved as described above for the main section. This is particularly the case when the thread profile remains constant at the root while the radially inner portion of the thread is gradually removed, or when the cross-sectional shape of the thread profile remains constant while the dimensions are reduced. However, as described above, in preferred embodiments, the thread profile in the taper is modified by gradually removing the radially outer portion of the thread profile. In such embodiments, any curved transitions between the base surface and the thread flanks in the taper are preferably kept to a minimum, i.e., as required by manufacturing tolerances.

[0051] The profile, i.e., longitudinal cross section, of the thread apex, at least along the length of the main portion, may be any known shape, for example, flat, sharp, rounded. To aid in crack prevention, it is preferred that the apex profile is curved, meaning that there is a fully curved transition at the radially inner ends of the apical and coronal flanks between the adjacent apical and coronal flanks. The curved profile may be elliptical or oval. However, in a particularly preferred embodiment of the invention, the apex profile has the shape of a circular arc. As mentioned above, in a preferred embodiment, the thread apex remains constant in the taper, while the radially outer portion of the thread profile is gradually removed. In addition, in some embodiments, the cross-sectional shape of the thread in the taper remains constant, while the dimensions are gradually reduced. In particular, in such embodiments, it is preferred that the longitudinal cross section of the apex is curved, preferably having the shape of a circular arc along the entire length of the threaded portion.

[0052] Such curved apex profiles are generally not possible with screws formed by machining, but are possible if the implant is manufactured using, for example, injection molding or 3D printing.

[0053] Therefore, in a particularly preferred embodiment, the implant is manufactured by injection molding. The ceramic implant can be manufactured, for example, by milling, molding or 3D printing. Milled or 3D printed implants can be constructed with undercuts at blind holes, whereas molded implants are not possible because they cannot be released from the mold. Those skilled in the art can accurately distinguish between molded implants and milled or 3D printed implants by their contours, mold parting lines and injection ports.

[0054] Fabrication of implants by injection molding is preferred because it is quicker to manufacture and easier to ensure fit of the fabricated components, as well as cost-effective for large quantities. Additionally, as mentioned above, injection molding allows for the formation of female threads with curved crests in addition to curved roots, which is advantageous in preventing crack formation and implant failure.

[0055] The manufacture of the ceramic implant according to the present invention can be accomplished according to the ceramic injection molding (CIM) method by injecting the powdered ceramic material into a mold. Thereby, the ceramic material is generally provided as a powdered material and includes a binder for better shaping or forming, which is preferably removed before sintering by baking it after forming. Sintering provides the final shape and hardness. Those skilled in the art recognize that during sintering, the implant will typically shrink by about 25%, depending on factors that depend on the material and manufacturing process.

[0056] Especially when manufactured by injection molding, but also when other manufacturing methods are used, the implant is preferably formed using a HIP (hot isostatic pressing) process, which improves the strength of the implant by increasing the density of the material.

[0057] If the implant is formed via injection molding, it is particularly preferred that the radially outer part of the thread profile is gradually removed in the taper to form the required reduction in thread depth, since this is easier to implement such a design in a molded blind hole than, for example, by removing the radially inner part of the thread profile. In particular, it is preferred that in the taper, the thread profile remains constant relative to the base surface of the main part, and in the taper, the thread gradually sinks into the base surface of the taper.

[0058] According to the invention, a threaded portion is disposed in a blind hole in the implant. Preferably, the apical end of the hole is rounded to prevent sharp edges and stress points in the hole. The threaded portion may extend over the entire length of the blind hole. However, in a preferred embodiment, it extends over only a portion of the blind hole, as a result of which the cost and complexity of production is reduced. In a particular embodiment, the threaded portion is present only in the lower half, i.e. the apical half, of the blind hole. As a result, the length of the connection screw can be increased, which increases the possible preload force of the screw.

[0059] According to the invention, the blind hole extends along a central longitudinal axis. The central longitudinal axis of the blind hole may be offset from the central longitudinal axis of the implant, but it is preferred that the blind hole is coaxial with at least a portion of the implant. For example, some implants are angled such that they comprise a coronal portion extending along a first central longitudinal axis and an apical portion extending along a second central longitudinal axis, the first and second axes being angled with respect to each other. In such a case, the blind hole is preferably coaxial with either the coronal portion or the apical portion of the implant. In the case of coaxial with the apical portion of the angled implant, the blind hole opening is not located on the coronal end surface of the implant, but is open towards the coronal end of the implant so that the hole can be accessed from the coronal end of the implant.

[0060] However, most implants extend from their apical to coronal end along a single central longitudinal axis. In such cases, the blind hole is not only open towards the coronal end of the implant, but the opening is located at the coronal end face of the implant. Preferably, the blind hole is coaxial with the central longitudinal axis of the implant. In other words, preferably, the implant extends from the apical to the coronal end along its central longitudinal axis, and the blind hole is open at the coronal end face of the implant and extends towards the apical end along said central longitudinal axis. In such cases, the central longitudinal axis of the hole is the same as the central longitudinal axis of the implant.

[0061] In such preferred embodiment, the length of the blind hole measured longitudinally is preferably greater than 70%, more preferably greater than 75%, and most preferably at least 80% of the axial length of the implant. This is longer than the holes found in standard titanium implants. The longer the length of the blind hole relative to the length of the implant, the more balanced the mass distribution of the implant becomes. In standard implants, the apical end of the implant below the blind hole is usually solid, resulting in more mass. When the screw is tensioned in the hole, this apical mass creates more strain in the implant. The longer hole reduces the mass at the apical end of the implant, which results in reduced strain during use. This is particularly advantageous for ceramic implants, considering the brittle nature of the material. Additionally, the reduction in the amount of ceramic in the implant reduces the possibility of defects in the ceramic material, especially with regard to 3D printing and injection molding methods.

[0062] These advantages also exist for angled implants in which the hole is located in the apical portion of the implant. Thus, in such embodiments, the length of the blind hole measured in the longitudinal direction is preferably greater than 70%, more preferably greater than 75%, and most preferably at least 80% of the axial length of the apical portion of the implant.

[0063] As mentioned above, it is preferred that the threaded portion does not extend over the entire length of the blind hole. Moreover, it is preferred that the threaded portion does not extend to the apical end of the hole. It is therefore preferred that the blind hole further comprises a non-threaded end portion on the apical side of the threaded portion, which extends from the apical end of the threaded portion to the apical end of the hole. This is particularly advantageous in embodiments where longer hole lengths are used, i.e. the blind hole has a length of at least 70% of the length of the implant (or the apical portion of an angled implant). Such a non-threaded end portion allows the hole to be longer while maintaining simplicity of design and allowing the same screw length to be used for all implant lengths.

[0064] Since the location of the threaded portion within the hole determines the length of the screw that can be used with the implant, the location of this threaded portion relative to the coronal end of the blind hole typically remains constant for various lengths of implants. This allows a standard screw length to be used for all implant lengths. Thus, between implants of various lengths, the length of the non-threaded end portion is typically varied to extend the hole over the desired length of the implant.

[0065] Preferably, the non-threaded end portion has an axial length that is at least one-third the length of the tapered portion, and more preferably has a length that is one-third to three times the length of the tapered portion.

[0066] The non-threaded end portion may be cylindrical, curved, or conical, or a combination of these shapes. In some embodiments, the shape of the non-threaded end portion matches the shape of the outer surface of the implant at the axial location of the non-threaded end portion, so that the implant has a substantially constant wall thickness over the length of the non-threaded end portion. Thus, if the outer surface of the implant is tapered at its apical end, it is preferred that the non-threaded end portion of the hole is similarly tapered. Alternatively, if the implant is a parallel-walled (cylindrical) implant, it is preferred that the non-threaded end portion is cylindrical.

[0067] If the implant is manufactured by injection molding, a substantially constant wall thickness improves the flow of the feedstock during injection molding. Thus, in such an embodiment, it may be particularly preferred that any non-threaded end portion of the blind hole conforms to the shape of the outer surface of the implant at the axial location of the non-threaded end portion, as described above. However, in many cases, a compromise is necessary to ensure that the apical end of the blind hole is not too narrow. If the mold pin used to form the hole is too thin, it may vibrate during the injection molding process. Thus, in certain preferred embodiments, the non-threaded end portion has a taper angle (relative to the longitudinal central axis of the hole) that is equal to or less than the taper angle of the tapered portion of the threaded portion, if present. This helps provide an optimal length and diameter of the hole. Additionally or alternatively, regardless of whether the tapered portion has a taper angle, in preferred embodiments the non-threaded end portion has a taper angle of less than 1°, more preferably about 0.5°. This small taper angle prevents the apical end of the hole from becoming too narrow, even at long hole lengths, while also aiding in mold separation. Providing a small taper angle to aid in mold separation is advantageous in parallel walled implants and apically tapered implants.

[0068] In a preferred embodiment, the dental implant further comprises an anti-rotation element on the coronal side of the threaded portion. The anti-rotation element has a non-circular symmetric cross section in a plane perpendicular to the longitudinal central axis of the blind hole. This anti-rotation element can be formed in the blind hole or on the external surface of the implant. The anti-rotation element of the implant can be of any known shape, for example, elliptical, polygonal, Torx, a series of alternating indentations, etc. Preferably, the blind hole comprises an anti-rotation element on the coronal side of the threaded portion.

[0069] If a cooperating second component, such as an abutment, crown, etc., with a complementary shaped anti-rotation element is connected to the implant, the axial alignment of the two anti-rotation elements prevents relative rotation of the second component and the implant around the longitudinal central axis of the hole. If present, the anti-rotation element of the implant may also serve as a torque transmission means for an insertion tool suitable for fixing the implant in the jawbone. For this purpose, in a known manner, the free end of the correspondingly formed insertion tool may be brought into releasable engagement with the anti-rotation element of the implant in order to transmit torsional moments to the dental implant.

[0070] The blind hole of the implant is intended to allow the connection of a second component (e.g., an abutment, a healing cap, etc.) to the implant via a screw connection with the threaded portion. To fixedly connect the second component to the implant, the second component may comprise an external thread intended to mate with the main part of the threaded portion of the blind hole of the implant. Alternatively, the second component may comprise a through hole, through which the fixation screw may be inserted, so that the apical end of the screw protrudes from the apical end of the second component and mates with the threaded portion of the implant hole.

[0071] For example, an abutment with a screw groove may have an apical end designed to be inserted into a blind hole of an implant. A fixation screw may be inserted through the screw groove of the abutment and advanced into the female threads of the implant by a tool introduced into the screw groove of the abutment from above, 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 with a polygonal cross-section that may be brought into axial alignment with a complementary anti-rotation element provided in the blind hole, e.g.

[0072] Suitable fixation screws can be manufactured in known manner from metal, preferably titanium or titanium alloys, since said materials guarantee good stability, biocompatibility and sterility. An additional advantage of metallic materials is that they contain a certain elasticity, which increases the retention of the fixation screw as a result of the screw stretching elastically, minimally, along its longitudinal axis when screwed in. The tension resulting from said stretching then results in a particularly robust connection between the dental implant and the second component. In other embodiments, ceramic or polymeric screws, manufactured for example by milling, can be used. This is advantageous to meet the consumer demand for metal-free dental implants.

[0073] In certain preferred embodiments, the blind hole of the implant further comprises an anti-rotation element on the coronal side of the threaded portion, if present, of the circularly symmetric non-threaded portion, which may be longitudinally tapered or non-tapered and serves to provide a deeper and therefore more stable connection between the implant and the second component.

[0074] Preferably, the coronal circular symmetric non-threaded portion is cylindrical. However, in other embodiments, the coronal circular symmetric non-threaded portion may be conical, which may help to create a good seal, e.g., a Morse taper, between the implant and the second component. In an alternative preferred embodiment, the coronal circular symmetric non-threaded portion comprises multiple conical and / or cylindrical segments. These may be arranged in any order. For example, the coronal circular symmetric non-threaded portion may comprise a cylindrical segment followed coronally by one or more conical segments. When multiple conical segments are present, they may be arranged consecutively or alternating 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.

[0075] The outer surface of the dental implant is preferably apically tapered over at least a portion of its length, the taper occurring at least in the apical half of the implant.

[0076] The implant preferably comprises an external thread for fixing the implant in the jawbone, the external thread protruding from the outer surface of the implant and extending over at least a portion of its length. The external thread serves for the primary or direct fixation of the dental implant in the jawbone. Thereby, the external thread may 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 total length of the dental implant, preferably over at least 75% of the dental implant length, the thread starting at or close to the apical end (e.g. within 1 mm). The external thread may have any known shape and may comprise one or more self-tapping grooves. 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 may comprise an unthreaded portion on the coronal side of the external thread.

[0077] To improve osseointegration, the part of the dental implant intended to be placed in the bone may have its external surface roughened according to any known technique or may be surface treated in another known manner, e.g. with a coating. By "external surface" is meant the outer surface, if present, of the male thread.

[0078] According to a preferred embodiment, a plurality of implants according to the invention are provided, the plurality of implants having different axial lengths. The position of the threaded portion in the blind hole of each implant relative to the coronal end of the blind hole is constant. The blind hole of each implant preferably further comprises a non-threaded end portion extending from the apical end of the threaded portion to the apical end of the blind hole, the axial length of the non-threaded end portion differing between the implants such that the implants having a longer axial length have a longer non-threaded end portion.

[0079] The invention further relates to a method for manufacturing the above-mentioned dental implant by injection molding, in which a pin is used as a counter form for the threaded part of the blind hole. This means that the outer shape of the pin corresponds to the inner shape of the threaded part of the blind hole, but with threads that take into account the shrinkage rate of the ceramic after sintering. The pin dimensions are therefore approximately 25% larger than the final implant dimensions.

[0080] Thus, according to another aspect, the present invention provides a method of manufacturing a dental implant, the method comprising the steps of providing a mold for ceramic injection molding, the mold comprising a pin extending along a central longitudinal axis and having a threaded portion, the threaded portion comprising a base surface, the threads projecting radially outwardly from the base surface, the base surface defining a minimum radius of the threads measured from the central longitudinal axis, the threads having a crown flank and an apical flank connected at their radially outer ends by an apex, the apex defining a maximum radius of the threads measured from the central longitudinal axis, the threads extending helically along an axial length of the threaded portion and defined by a difference in radius between the base surface and the apex. and using the mold to manufacture a dental implant using ceramic injection molding.

[0081] Preferably, the thread of the pin comprises, at least along the length of its main portion, a curved transition between the base surface and the apical and coronal flanks. Preferably, when viewed 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 its main portion, an apex having a curved longitudinal cross section, preferably having the shape of a circular arc.

[0082] Further preferred features of the threaded portion of the pin are complementary to the preferred features of the threaded portion of the implant. For example, the thread profile in the tapered section of the pin is preferably modified by gradually removing a radially outer portion of the profile. Additionally or alternatively, it is preferred that the minimum radius of the threads remains constant along the length of the threaded portion. [Brief description of the drawings]

[0083] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1A] FIG. 1A shows a longitudinal cross section of an implant known in the art. [Figure 1B] FIG. 1B shows an enlargement of the threaded portion of FIG. 1A. [Figure 1C] FIG. 1C shows detail Y from FIGS. 1A and 1B. [Figure 2A] FIG. 2A shows a longitudinal cross section of an implant according to a preferred embodiment of the present invention. [Figure 2B] FIG. 2B shows an enlargement of the threaded portion of FIG. 2A. [Figure 2C] FIG. 2C shows detail Y from FIG. 2B. [Figure 2D] FIG. 2D shows a pin for producing the implant of FIG. 2A by injection molding. [Diagram 3] FIG. 3 shows an alternative preferred embodiment of the implant according to the present invention. [Figure 4A] FIG. 4A shows a schematic diagram of an alternative design of the thread profile within the taper. [Figure 4B]FIG. 4B shows a schematic diagram of an alternative design of the thread profile within the taper. [Figure 4C] FIG. 4C shows a schematic diagram of an alternative design of the thread profile within the taper. [Figure 4D] FIG. 4D shows a schematic diagram of an alternative design of the thread profile within the taper. [Figure 4E] FIG. 4E shows a schematic diagram of an alternative design of the thread profile within the taper. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0084] Fig. 1A shows an implant 1 representing the prior art. The implant 1 is configured for use with a second component, e.g. an abutment (not shown), and extends from an apical end 3 to a coronal end 2 along a central longitudinal axis LA. The implant 1 includes a blind hole 4, which opens at the coronal end 2 and is surrounded by a coronal end face 5 of the implant 1, which radially surrounds a hole opening 6. The blind hole 4 is coaxial with the implant 1, so that it also extends along the central longitudinal axis LA. The outer surface of the implant 1 is provided with an external thread 32 for screwing the implant 1 into the jawbone of a patient.

[0085] The blind hole 4 comprises a threaded portion 7 disposed towards the apical end of the blind hole 4. The threaded portion 7 comprises a base surface 8 from which the threads 9 project radially inwardly (i.e. towards the central longitudinal axis LA) into the hole 4. As also shown in detail in FIG. 1B, the threads 9 have a coronal flank 12 and an apical flank 14 connected at their radially inner ends by an apex 16 and extend helically along the length of the threaded portion 7. As shown in FIG. 1B, the base surface 8 is spaced apart from the maximum radius R of the threads 9. MAX while vertex 16 defines a minimum radius R MIN The difference between the maximum and minimum radii at any given point is the thread depth T D Gives.

[0086] At the apical end of the threaded portion 7, a non-threaded conical portion 10 meets the threads 9. This is shown in detail in FIG. 1C. As can be seen in this figure, the conical surface 10 meets the apical flank 14 at an acute angle, forming a narrow sharp edge 18 at the hole. This creates a stress concentration point. If 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, the apex 16 has a planar shape when viewed in longitudinal section. Such an apex is the simplest shape that can be formed when milling an implant, but it can also lead to problematic stress concentrations in ceramic implants.

[0087] 2A shows an implant 100 according to the present invention. The implant 100 is made of a ceramic material, for example an aluminum, zirconium, or magnesium based ceramic material, such as aluminum oxide, zirconium oxide, or magnesium oxide, or a combination thereof. Additionally, a stabilizer, such as yttrium oxide or cerium oxide, may be included in the ceramic material.

[0088] Similar to the prior art implant 1 described above, the implant 100 of the present invention extends from an apical end 103 to a coronal end 102 along a central longitudinal axis LA. The implant 100 includes a coaxial, longitudinally extending blind bore 104 that is open at the coronal end 102 and extends along the axis LA towards the apical end 103. The blind bore 104 includes a threaded portion 107 having a base surface 108 from which threads 109 project radially inwardly into the bore 104. The threads 109 include a coronal flank 112 and an apical flank 114 that are connected at their radially inner ends by an apex 116. The threads 109 extend helically along the length of the threaded portion 107. The base surface 108 is spaced apart from the maximum radius R of the threads 109. MAX while the vertex 116 defines a minimum radius R MIN The difference between the maximum and minimum radii at any given point is the thread depth T D (See Figure 2B).

[0089] In contrast to prior art implants, the threaded portion 107 of the implant 100 comprises a main portion 115 and a tapered portion 117 apically adjacent to the main portion 115. The maximum radius R of the threads 109 within the main portion 115 MAX remains constant, while within the tapered section 117, the base surface 108 approaches the maximum radius R of the thread 109 at the main section 115. MAX Therefore, the minimum radius R of the thread 109 at the apical end of the tapered portion 117 MIN 2. The taper 117 extends radially inwardly in the apical direction to a thread depth T D The tapered base surface 108 extends over an axial length greater than the thread pitch to form a tapered thread 119 that gradually decreases in thread depth T over multiple thread revolutions. The radially inward taper of the base surface 108 is more clearly seen in Figures 4B-4E. The tapered base surface 108 has a thread depth T that gradually decreases over multiple thread revolutions. D 1C) and the threads 109 gradually disappear. Thus, the threads 109 do not break off abruptly, preventing the formation of sharp edges 18 found in the prior art (see FIG. 1C). Thus, stress points within the hole that can lead to crack formation are eliminated.

[0090] FIG. 2B shows a close-up of the threaded portion 107. The close-up shows how the taper base surface 108 tapers radially inward at a taper angle γ measured from the longitudinal central axis LA, thus forming a conical shape. The taper angle γ remains constant over the length of the tapered section 117. In this embodiment, the taper angle γ is 8°. This angle is less than the taper angle α of the crown flank 112 measured from the longitudinal central axis LA. As best seen in FIG. 2C, an obtuse angle is formed between the taper base surface 108 and both the apical flank 114 and the crown flank 112. The taper angle γ is selected such that thread loss occurs over more than three thread revolutions.

[0091] Within the main part 115, the maximum radius R MAXremains constant, forming a base surface 108 having a cylindrical shape. In addition, the minimum radius R of the thread 109 and the thread profile MIN also remains constant, providing an even force distribution during use.

[0092] Within the tapered portion 117, the minimum radius R MIN remains constant, so that the reduction in groove depth is provided only by the taper of base surface 108. The thread profile remains constant relative to the base surface of main section 115. Thus, threads 109 are gradually sunk into the tapered base surface 108 from thread root 121 to apex 116.

[0093] Alternative designs of tapered thread 119 are shown generally with reference to Figures 4A-4E. Figure 4A shows a longitudinal cross-section of a thread 400 having a uniform thread profile as may be formed in the majority of the threaded portion. Thread 400 extends from a base surface 408 and has an apical flank 414 and a coronal flank 412 connected by an apex 416. Figures 4B-4E show various ways in which this basic thread profile may be modified to form tapered threads.

[0094] 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 modified by gradually removing a radially inner portion of the profile. In this way, the thread apex 416 changes along the length of the thread while the transition from the base face 408 to the flanks 414, 412 remains constant. In FIG. 4D, the thread profile of FIG. 4A is modified by gradually removing a radially outer portion of the profile. In this way, the thread apex 416 remains constant while the transition from the base face 408 to the thread flanks 414, 412 is modified. In both FIG. 4C and FIG. 4D, an area of ​​the triangular thread profile is gradually removed, and this removal appears either at the thread apex or the thread root. If material is removed from the thread apex (the radially inner portion of the profile), this gives the visual impression that the thread tip is "shaved" until the thread is completely ground and removed (see FIG. 4C). If material is removed from the thread root (the radially outer portion of the profile), this gives the visual impression that the thread is "sunk" below the base surface (see FIG. 4D). Thus, the design of tapered section 117 is an example of this form of profile modification.

[0095] In Figures 4B-4D, the minimum radius of the thread 400 remains constant, but it is also possible for the minimum radius to increase in the apical direction. This is shown in Figure 4E, where both the inner and outer portions of the thread profile have been gradually removed, so that the thread appears to be both shaved from the apex and sunken from the root at the same time.

[0096] Each of the thread designs shown in Figures 4B-4E allows the thread depth to be gradually reduced to provide the tapered threads of the present invention.

[0097] Returning to the implant shown in Figures 2A-2C, the apex 116 is curved to form a circular arc in longitudinal cross section over the entire length of the threaded portion 107. In addition, within the main portion 115, the transition between the flanks of the apex 114 and the crown 112 at the base surface 108, known as the thread root 121 (see Figure 2B), also forms a circular arc in longitudinal cross section. These rounded roots 121 between the flanks and the apex 116 prevent stress concentration in these narrow areas of the thread 109. Although the rounded roots 121 are possible with the base surface 108 of the implant formed by milling, it is not possible to form the rounded apex 116 by conventional milling techniques. This can be seen in the implant 1 in Figure 1, where the apex 116 is a flat surface in longitudinal cross section. To form the rounded apex 116, the implant 100 needs to be 3D printed or injection molded. A pin 200 that is suitable for use in injection molding and that can be used to form the threaded portion 107 of the implant 100 is shown in FIG. 2D.

[0098] The pin 200 of FIG. 2D is placed in a mold, where the mold has a hollow internal space corresponding to the external shape of the implant to be produced. The pin 200 comprises a mold opposite the shape of the threaded portion 107 of the implant 100, meaning that the mold opposite has an external shape corresponding to the internal shape of the threaded portion 107 in the future implant 100. The dimensions of the pin 200 are approximately 25% larger than the desired dimensions of the finished threaded portion 107 to take into account the shrinkage that occurs during the sintering step of the ceramic implant production. If the hole 104 of the implant includes additional features, for example an anti-rotation element, a collar corresponding to the desired additional feature is placed around the pin 200 to suitably modify the internal shape of the hole 104 to be produced. A ceramic material is injected into the mold around the pin 200. This produces a solid stable green body that can be removed from the mold, and upon removal of the pin (and optionally the collar) from the body, an implant as shown in FIG. 2A according to the present invention can be obtained through sintering.

[0099] The pin 200 includes an axis 222 that extends from the apical end 203 to the coronal end 202 along a central longitudinal axis LA, and includes an outer threaded portion 207. The threaded portion 207 includes a base surface 208 from which threads 209 project radially outward. Thus, in contrast to the final threads 109 of the implant, the base surface 208 defines a minimum radius R of the threads 209. MIN The thread 209 has a crown flank 212 and an apical flank 214 connected to a radially outermost point by an apex 216, the outermost point of which is defined by a maximum radius R MAX Because the pin 200 is an inverse template, the apical flank 214 of the pin 200 provides shape for the crown flank 112 of the implant 100, while the crown flank 212 of the pin 200 provides shape for the apical flank 114 of the implant 100. Similarly, the apex 216 of the pin 200 defines the base surface 108 and the root 121 of the implant 100, while the base surface 208 of the pin 200 defines the apex 116 of the implant 100.

[0100] The threaded portion 207 of the pin 200 includes a main portion 215 and a tapered portion 217 apically adjacent to the main portion 215. Within the main portion 215, a maximum radius R of the threads 209 MAX remains constant. Within the tapered section 217, the maximum radius R MAX is the maximum radius R of the main part 215 MAX Therefore, the minimum radius R of the thread 209 at the apical end of the tapered portion 217 MIN The tapered section 217 extends over an axial length that is greater than the thread pitch such that a tapered thread 219 is formed in the tapered section 217 that extends over multiple thread revolutions.

[0101] The shape of the apex 216 in the tapered section 217 of the pin 200 reflects the desired shape of the base surface 108 of the tapered section 117 of the implant 100 to be manufactured. Thus, in this embodiment, the apex 216 tapers radially inward with a taper angle of approximately 8° to form a conical surface.

[0102] The implant 100 shown in Fig. 2A is configured for use with a second component, such as an abutment (not shown) or a direct connection prosthesis. Additionally, a temporary second component may be fitted to the implant 100 prior to connection of the abutment, such as a healing cap or impression post. All of these components may be connected to the implant 100 by a threaded portion 107.

[0103] The outer surface of the implant 100 is provided with external threads 132 and self-cutting grooves 135 for screwing the implant 100 into a hole (not shown) in the patient's jawbone. The threads 132 may begin near the apical end 103 of the implant and extend to the coronal end 102. However, in this embodiment, the implant includes an unthreaded coronal neck portion 120. The coronal end surface 105 of the implant 100 is planar and transverse to the central longitudinal axis LA. The coronal end surface 105 radially surrounds the coronal opening 106 of the blind hole 104.

[0104] In addition to the threaded portion 107, the blind hole 104 comprises a circular symmetrical non-threaded portion 134 located at the coronal end of the hole 104. This coronal circular symmetrical non-threaded portion 134 may be cylindrical or conical, or in this case comprises a plurality of conical and cylindrical segments 134a, 134b, 134c. By providing such a coronal circular symmetrical non-threaded portion 134, the second component can be located deeper within the implant 100, thus providing a more stable connection. Any conical surface of the coronal circular symmetrical non-threaded portion 134, for example the conical surface 134c, can also be used to form a seal between the implant and the second component. Alternatively, the seal with the second component can be formed using the coronal end surface 105.

[0105] The blind hole 104 further comprises an anti-rotation element 130, which is disposed coronally of the threaded portion 107 and apically of the coronal circularly symmetric non-threaded portion 134. In this embodiment, the anti-rotation element 130 comprises a plurality of circumferentially spaced ribs 133 projecting radially inwardly into the hole 104. The anti-rotation element 130 thus has a non-circular symmetric cross-section in a plane perpendicular to the central longitudinal axis LA. When an abutment or other second component having a complementary anti-rotation element is inserted into the hole 104, the ribs 133 engage complementary grooves in the second component to prevent relative rotation about the central longitudinal axis LA. Such complementary anti-rotation elements are well known in the art of dental implants and may have alternative cross-sectional shapes, e.g., polygonal, elliptical, etc.

[0106] Inside the blind hole 104 and apically adjacent to the anti-rotation element 130, the implant 100 includes a cylindrical portion 138 having a non-threaded surface that extends to the threaded portion 107 described above. Varying the length of this cylindrical portion 138 changes the depth at which the threaded portion 107 begins and thus a depth that can be used to determine the length of a screw required for use with the implant 100. Such a cylindrical portion can be used, for example, to ensure that the threaded portion 107 is only present in the bottom half of the implant 100.

[0107] Apically adjacent to the threaded portion 107, the implant 100 includes a non-threaded end portion 140 that is curved and tapered in the apical direction. The non-threaded end portion 140 extends from the apical end of the threaded portion 107 to the apical end 144 of the blind hole 104. The non-threaded end portion 140 increases the length of the hole 104 without requiring the threaded portion 107 to be lengthened. The increased length of the hole 104 reduces the amount of apical end of the implant 100, thus reducing distortion during use.

[0108] Because the location of the threaded portion 107 determines the length of the screw that can be used with the implant 100, the location of the threaded portion 107 relative to the coronal end 102 of the implant 100 generally remains constant, regardless of changes in the overall length of the implant 100. This allows abutments and other secondary components to be sold with standard screw lengths that can be used with a range of implants, independent of the length of those implants. Because the location and length of the threaded portion 107 typically remains constant, the length of the non-threaded end portion 140 may be increased in implants of larger lengths to reduce the amount of apical portion of the implant.

[0109] An example of this is shown in Figure 3. The implant 300 shown in Figure 3 corresponds substantially to the implant 100 of Figure 2A. In particular, the threaded portion 307 and all parts of the coronal hole 304 of the threaded portion 307 are identical to Figure 2A. The apical portion of the blind hole 304 differs only in that the non-threaded end portion 340 apically adjacent to the threaded portion 307 is much longer than the corresponding non-threaded end portion 140 of the implant 100 shown in Figure 2A. This is because the implant 300 has a larger axial length than the implant 100, and therefore the longer non-threaded end portion 340 prevents a larger volume at the apical end of the implant 300. The non-threaded end portion 340 is slightly conical, for example with a taper angle of 0.5°, to aid in mold separation. The taper angle of the non-threaded end portion 340 is smaller than the taper angle of the taper of the threaded end portion 307. At its apical end, non-threaded end portion 340 is curved and apically tapered towards the apical end 344 of blind bore 304. This rounding of the apical end of bore 304 helps to avoid areas of stress concentration.

[0110] As known in the art, to improve osseointegration, the external implant surface may be provided with additional or non-additive surface structures, which may be created by mechanical polishing processes, chemical etching, laser treatments, additive processes, and combinations thereof, as known to those skilled in the art of dental implantology.

[0111] The above-described embodiments are merely illustrative, and one of ordinary skill in the art will recognize that alternative arrangements are possible that fall within the scope of the claims. For example, any known anti-rotational element may be used, including an anti-rotational element disposed externally to the implant. The taper of the threaded end portion may taper about a radius rather than an angle, or may comprise multiple taper angles. The hole may be located in the coronal or apical portion of the angled implant.

Claims

1. A ceramic dental implant (100, 300) for implantation into a jawbone, said implant extending from an apical end (103) to a coronal end (102), said implant comprising: a blind hole (104, 304) that is open towards the coronal end (102) of the implant and extends along a central longitudinal axis (LA) towards the apical end (103), the blind hole (104, 304) comprising: The threaded portion (107, 307) has a base surface (108) from which threads (109) project radially inward, the base surface (108) being oriented along a maximum radius (R) of the threads (109) measured from the longitudinal central axis (LA). ＭＡＸ ), said thread (109) having a coronal flank (112) and an apical flank (114) connected at their radially inner ends by an apex (116), said apex (116) defining a minimum radius (R) of said thread (109) measured from said longitudinal central axis (LA). ＭＩＮ ) that extends helically along the axial length of the threaded portion (107, 307) and has a depth (T) that is determined by the difference in radius between the base surface (108) and the apex (116). Ｄ ) The threaded portion (107, 307) A main portion (115), within which the maximum radius (R ＭＡＸ ) remains constant along the length of said body portion; A tapered portion (117) apically adjacent to the main portion (115), within the tapered portion (117), the base surface (108) is aligned with the maximum radius (R ＭＡＸ ) to the minimum radius (R ＭＩＮ ) , the tapered portion (117) is tapered radially inwardly in the apical direction to a thread depth (T Ｄ a tapered portion (117) extending over an axial length greater than the thread pitch to form a tapered thread (119) in which the thread pitch is gradually reduced, the tapered thread (119) extending over a number of thread revolutions; A ceramic dental implant comprising:

2. The minimum radius (R ＭＩＮ 2. The ceramic dental implant of claim 1, wherein the thickness of said threaded portion (107, 307) remains constant over the entire length of said threaded portion (107, 307).

3. 3. The ceramic dental implant of claim 2, wherein a thread profile remains constant along the length of the main portion (115), and within the tapered portion (117) the thread profile remains constant relative to the base surface (108) of the main portion (115), and within the tapered portion (117) the threads (109) gradually sink into the tapered base surface (108).

4. 4. The ceramic dental implant according to claim 1, wherein the tapered thread (119) extends over at least two turns.

5. 5. The ceramic dental implant according to claim 1, wherein over the entire length of the tapered portion (117), the base surface (108) tapers radially inwardly with a constant taper angle (γ).

6. 6. The ceramic dental implant of claim 5, wherein the taper angle (γ) of the base surface (108) in the tapered portion (117) is less than the taper angle (α) of the crown flank (112) of the thread (109).

7. when viewed in the longitudinal cross-section, along the length of the main portion (115) of the threaded portion (107, 307), there is a substantially curved transition between adjacent apical and coronal flanks (112, 114) at radially outer ends of the apical and coronal flanks; 7. The ceramic dental implant of claim 1, wherein the longitudinal cross-section of the thread apex (116) is curved at least along the length of the main portion (115) such that there is a sufficiently curved transition between adjacent apical and coronal flanks (112, 114) at the radially inner ends of the apical and coronal flanks.

8. 8. The ceramic dental implant according to claim 1, wherein the implant is manufactured by injection molding.

9. the implant extends along the longitudinal central axis (LA) from an apical end (103) to a coronal end (102), the blind hole (104, 304) being open at a coronal end face (105) of the implant; 9. The ceramic dental implant according to any of the preceding claims, wherein the length of the blind hole (104, 304), measured in the longitudinal direction, is greater than 70% of the axial length of the implant.

10. 10. The ceramic dental implant of claim 1, wherein the blind hole (104, 304) further comprises a non-threaded end portion (140, 340) on the apical side of the threaded portion (107, 307) extending from the apical end of the threaded portion (107, 307) to the apical end (144, 344) of the hole (104, 304).

11. A method for manufacturing a dental implant (100, 300), comprising the steps of: Providing a ceramic injection mold, the mold comprising: A pin (200) extending along a central longitudinal axis (LA) and having a threaded portion (207), said threaded portion (207) comprising: A base surface (208) from which threads (209) project radially outward, the base surface (208) being axially spaced apart from the minimum radius (R) of the threads (209) measured from the longitudinal central axis (LA). ＭＩＮ ), the thread (209) having a coronal flank (212) and an apical flank (214) connected at their radially outer ends by an apex (216), the apex (216) defining a maximum radius (R) of the thread (209) measured from the longitudinal central axis (LA). ＭＡＸ ), the threads (209) extend helically along the axial length of the threaded portion (207) and have a depth defined by the difference in radius between the base surface (208) and the apex (216), the threaded portion (207) defining: A main portion (215), within which the maximum radius (R ＭＡＸ ) remains constant along the length of said body portion (215); A tapered portion (217) apically adjacent to the main portion (215), the maximum radius (R) of the thread (209) being within the tapered portion (217). ＭＡＸ ) is the maximum radius (R ＭＡＸ ) to the minimum radius (R ＭＩＮ ), the tapered section (217) extending over an axial length greater than the thread pitch to form a tapered thread (219) with a gradually decreasing thread depth, the tapered thread (219) extending over multiple thread turns; and using the mold to manufacture a dental implant using ceramic injection molding; A method comprising:

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