Dental implant

Abstract

A dental implant comprising a basic dental implant body (10) extending along a longitudinal axis A from an apical end (12) to a coronal end (14) disposed opposite the apical end, said basic dental implant body comprising an anchoring portion (16) oriented towards the apical end and intended to be anchored in the bone of a patient, and a head portion (18) oriented towards the coronal end and intended to form the base on which a superstructure is mounted, said anchoring part a stem (20) has a basic shape that is substantially cylindrical or that tapers in the direction towards the apical end in a cone shape, at least a part of the stem forms a region of contact with bone tissue (22), the outer surface of which forms a contact surface with bone tissue (30), and coronal to said region of contact with bone tissue there is a region of contact with soft tissue (24), the outer surface of which forms a contact surface with soft tissue (32), wherein the dental implant further comprises nanostructures formed on the soft tissue contact surface, said soft tissue contact surface on which the nanostructures are formed being smooth when considered at macroscopic and microscopic scale, characterized in that said nanostructures extend in at least two dimensions up to a maximum of 200 nm.

Description

Dental implant The present invention relates to a dental implant comprising a dental implant body as well as a process for providing enhanced protein adhesion sites on a dental implant body. Dental implants are a well-known technique. They generally comprise an anchorage portion designed to be anchored in a patient's jawbone and a head portion designed to form the base onto which a superstructure, such as a bridge or crown, is mounted. Therefore, the superstructure is often mounted using an intermediate component, that is, a so-called "secondary component" (also called an "addition"). In addition to being biocompatible and having sufficient mechanical strength, the implant is required to provide good osseointegration. The term "osseointegration" refers to the direct structural and functional connection between living bone and the implant surface. Successful osseointegration means that the implant, after achieving primary stability by screwing it into the bone, ossifies securely within a short healing time, resulting in a permanent bond between the implant and the bone. In the past, great effort has been made to improve the osteointegrative properties of implants. In addition to the importance of the implant's osseointegrative properties, there is growing evidence that good interaction between the implant and the surrounding supracrestal connective tissue (hereafter referred to as "soft tissue") is also crucial for successful implantation. This is supported by the view that soft tissue plays a fundamental role in establishing an effective seal between the oral environment and the endosseous portion of a dental implant, and thus also acts as a barrier to bacterial adhesion between the soft tissue contact surface and the soft tissue-bone contact surface of the implant. In fact, the presence of bacteria on the implant surface can cause inflammation of the peri-implant mucosa and, if left untreated, the inflammation spreads apically and results in bone resorption. As a consequence of the theory that rough surfaces accumulate and retain more plaque than smooth surfaces (see Oral Implantology, Thieme Verlag, 1996, page 438), nowadays, the soft tissue contact surface of implants is usually machined. As mentioned previously, the soft tissue contact surface ideally would not only provide a surface that shows a low tendency for bacteria to adhere, but would also allow for a relatively strong and rapid interaction between the soft tissue and the implant (also called "soft tissue integration"), in order to quickly provide an effective seal between the oral environment and the endosseous part. Document FR 2931056 teaches how to roughen the cervical region of a dental implant to improve soft tissue bonding. Furuhashi et al. ("Influence of titanium surface topography on peri-implant soft tissue integration", KEY ENGINEERING MATERIALS, vols. 52.- 530, 2012, pages 559-564) observed that the soft tissue around implant surfaces made rough by acid etching showed a stronger barrier property compared to machined implant surfaces. With the aim of improving soft tissue integration of the implant, European patent EP-A-1825830 suggests a soft tissue contact surface that is at least partially hydroxylated or silanized. In this context, the improved soft tissue integration is explained by the loose connective tissue being organized and replaced by newly formed collagen fibers. Regardless of the beneficial effects achieved by the technology described in European patent EP-A-1825830, there is a continuing need for additional simple solutions to improve the soft tissue integration of the dental implant. Therefore, the object of the present invention is to provide a dental implant having a soft tissue contact surface that establishes good soft tissue integration, i.e., a relatively strong interaction between the implant and the soft tissue in a relatively timely manner and at the same time shows a low tendency for bacteria to adhere. This problem is solved by the subject matter of claim 1. The preferred embodiments of the invention are the subject of the dependent claims. According to claim 1, the present invention relates to a dental implant comprising a basic dental implant body extending along a longitudinal axis A from an apical end to a coronal end disposed opposite the apical end. The basic body of a dental implant comprises an anchorage portion oriented towards the apical end and intended to anchor in the patient's bone, and a head portion oriented towards the coronal end and intended to form the base upon which a superstructure is mounted. Thus, the head portion can be designed to allow the superstructure to be mounted directly or indirectly, i.e., using at least one intermediate component, as is the case with multi-part dental implant systems. The anchoring portion comprises a stem having a basic shape that is substantially cylindrical or tapering towards the apical end in a conical form. At least a portion of the stem forms a region of contact with bone tissue, the outer surface of which forms a contact surface with bone tissue. Coronal to this region of contact with bone tissue lies a region of contact with soft tissue, whose outer surface forms a soft tissue contact surface. The soft tissue contact region may be located coronally adjacent to the region of contact with bone tissue. Alternatively, a transition region may exist between these regions. According to the invention, the dental implant comprises nanostructures formed on the surface in contact with soft tissue, said nanostructures extending in at least two dimensions up to a maximum of 200 nm. These nanostructures form retention sites, allowing for better initial adhesion of proteins from the surrounding soft tissue cells. While not strictly adhering to theory, transmembrane proteins, specifically integrins, can adhere directly or indirectly—that is, through the mediation of other proteins—to the nanostructures, thereby anchoring the cells to the soft tissue contact surface of the implant. Laminins, which are linked to the extracellular domain of integrins, as well as plasma proteins such as albumin, fibrinogen, and fibronectin, may also play an important role in this complex mechanism. In short, the nanostructures that form the retention sites allow for optimal soft tissue interaction with the implant and, consequently, an effective seal is achieved between its endosseous part and the oral environment. According to the invention, the soft tissue contact surface of the basic dental implant body on which the nanostructures are formed is smooth, e.g. machined or polished. In other words, the surface topography is smooth when considered at both macroscopic and microscopic scales, yet it exhibits a nanoscopic structure due to the presence of nanostructures. These nanostructures are small enough not to interfere with the low plaque-forming tendency of the soft tissue contact surface, but large enough to allow proteins from surrounding soft tissue cells to adhere. As a result, the soft tissue contact surface has a low tendency for bacterial adhesion, while at the same time, adhesion of proteins from surrounding soft tissue cells can occur. The term "dental implant", as used in the context of the present invention, refers to the main part of a dental implant system, i.e., the part that is actually implanted in the bone. Since the soft tissue contact surface of the dental implant body is smooth, it is clearly distinguishable from the bone contact surface, which typically comprises a macroscopic topography, achieved, for example, by sandblasting and / or machining, as well as a microscopic topography, achieved, for example, by acid etching. According to a further preferred embodiment, the soft tissue contact region widens in the direction toward the coronal end and, more particularly, widens in a cup-like shape. In this embodiment, the transition from the bone contact surface to the soft tissue contact surface is even more pronounced. It is also preferred that the region of contact with bone tissue extend from the apical end towards the coronal end in a length lbcr ranging from 4 to 16 mm. Given the typical intervals of the length of a dental implant, the soft tissue contact region, therefore, preferably extends from the respective end of the bone contact region towards the coronal end a length lscr ranging from 1 mm to 3 mm. The ratio of lbcr to the total linear length of the dental implant depends on the specific type of dental implant used. Preferably, lbcr corresponds to approximately 55% to 95% of the total linear length of the dental implant. The present invention is understood to encompass dental implants in which nanostructures are formed only on the surface in contact with soft tissue, as well as embodiments in which they are formed on the surface of regions in addition to the soft tissue contact region, and embodiments in which they are formed on the entire surface of the basic body of the dental implant. As mentioned above, the present invention covers both dental implants for a one-piece dental implant system and dental implants for a multi-piece dental implant system, specifically a two-piece dental implant system. In particular, in the case of a two-piece dental implant system, the head portion of the basic dental implant body preferably comprises a shoulder that serves as a support for the abutment. It is particularly preferred that the outer surface of this shoulder also be smooth in order to avoid micro-gaps between the dental implant and the abutment. According to a further preferred embodiment, the nanostructures are at least predominantly in the crystalline phase. More preferably, the nanostructures are in a phase that is at least approximately purely crystalline. Nanostructures can have different shapes, including a needle shape, a leaf shape, a flower shape, a sphere shape, or a nodule shape. In the context of the present invention, the term "needle shape" encompasses any shape having a length-to-diameter ratio of more than 1:1. Therefore, the diameter should be understood as the expansion of the nanostructure in a direction perpendicular to the longitudinal direction. Preferably, the nanostructures have an average length-to-diameter ratio of more than 1 to 1, more preferably at least 1.5 to 1, most particularly ranging from 1.5 to 1 to 4 to 1. As mentioned, the nanostructures according to the present invention preferably extend in at least two dimensions up to a maximum of 200 nm. More specifically, the nanostructures preferably have an average diameter of approximately 10 nm to 150 nm and an average length of approximately 5 nm to 500 nm. Furthermore, it has been discovered that the presence of nanostructures can achieve relatively high hydrophilicity, which can further contribute to good soft tissue interaction. According to a preferred embodiment, the soft tissue contact surface therefore has a hydrophilicity defined by a contact angle of less than 90°, more preferably less than 30°, and most preferably less than 10°, when in contact with water. It is also preferred that the basic body of the dental implant be made of titanium or a titanium alloy. Such a basic body allows nanostructures to be formed on its surface in a relatively simple and reproducible manner, as will be shown below. In view of its use in the field of implantology, and particularly in oral implantology, any suitable grade of titanium or titanium alloy known to the expert may be used, including grade 2 to grade 4 titanium. When a titanium alloy is used, it is preferably a titanium-zirconium alloy (TiZr), which typically comprises Zr in an amount of 13 to 17%. Alternatively, a titanium-aluminum-vanadium alloy, specifically Ti-6Al-4V (TAV), or a titanium-aluminum-niobium alloy, specifically Ti-6Al-7Nb (TAN), may be used as a suitable titanium alloy for the purpose of the present invention. With regard to the use of titanium or a titanium alloy for the basic body of a dental implant, it is further preferred that the nanostructures comprise titanium hydride and / or titanium oxide. In the case of nanostructures comprising titanium hydride, they typically comprise TiH2, while in the case of nanostructures comprising titanium oxide, they typically comprise TiO2. According to a further aspect, the present invention also relates to a process for providing enhanced protein attachment sites on a basic dental implant body, as defined in claim 11. According to this process, nanostructures are grown on the soft tissue contact surface by treating the soft tissue contact surface with an aqueous solution. The characteristic that nanostructures grow means that they are not formed through a process of mechanical removal or by subjecting the body surface to other mechanical structuring processes. Rather, the formation of nanostructures occurs gradually because they "accumulate" over time when the soft tissue contact surface is treated with the aqueous solution. The term "aqueous solution", as used in the context of the present invention, encompasses both pure water and a solution in which the solvent is water. Particularly good formation / growth of nanostructures has been observed for embodiments in which the aqueous solution is an acidic solution comprising at least one component selected from the group consisting of hydrogen fluoride, nitric acid, hydrochloric acid, sulfuric acid, tartaric acid, oxalic acid, citric acid and acetic acid and / or mixtures thereof. As mentioned previously, the basic body of a dental implant is typically made of titanium or a titanium alloy. According to a well-controllable and therefore preferred process, the growth of nanostructures is carried out by cathodic polarization (also called "cathodic hydriding"), in which the basic body of the dental implant forms the cathode. A detailed description of this process will be given using the following examples. In this regard, it is particularly preferred that, prior to cathodic polarization, the soft tissue contact surface be pickled with a pickling solution to at least partially remove a layer of titanium oxide present on the soft tissue contact surface. Preferably, a pickling solution is used comprising at least one component selected from the group consisting of nitric acid, hydrofluoric acid, ammonium fluoride, hydrochloric acid, and sulfuric acid, and / or mixtures thereof, particularly a mixture of nitric acid and hydrofluoric acid. With regard to cathodic polarization, this is preferably carried out in a buffer that has a pH in the range of 0 to 6. The temperature is preferably adjusted in a range of 5 to 95 °C, preferably from 10 to 75 °C, more preferably from 15 to 50 °C, most preferably to approximately room temperature. In addition to or as an alternative to the process described above that uses cathodic polarization, nanostructures can be grown by storing the soft tissue contact surface in aqueous solution. Storage is typically carried out using a 0.9% NaCl solution, more specifically with a pH of 2 to 7, preferably 3 to 6. Alternatively, any other suitable aqueous solution including pure water can be used. According to a particularly preferred embodiment, storage is carried out for at least one month, more preferably at least two months, and most preferably at least four months. The storage time depends on the surface topography of the soft tissue contact surface of the dental implant body. For a machined surface, the storage times required for nanostructure growth have been found to be longer than for a rough surface. However, even for a machined soft tissue contact surface, nanostructures are detected after two months of storage. Regarding storage, it is also preferred that it be carried out at a high temperature, that is, a temperature above ambient temperature, since it has been shown that the formation of nanostructures is particularly pronounced at these temperatures. It has been shown that a temperature range of approximately 50 °C to 250 °C is particularly preferred, more specifically from approximately 100 °C to 180 °C, and most preferably from approximately 120 °C to 150 °C, as the storage time required for nanostructure growth can be substantially shortened. Therefore, storage for months is not required when (hydro)thermal treatment is performed at the temperatures specified above. It is understood that the process of the present invention encompasses embodiments in which only the region in contact with soft tissue is subjected to treatment with the aqueous solution, as well as embodiments in which additional regions and embodiments in which the entire surface is subjected to this treatment. As also mentioned above, the contact surface with bone tissue is preferably made rough and comprises a macroscopic topography, achieved e.g. by sandblasting and / or machining, as well as a microscopic topography, achieved e.g. by acid etching. Therefore, the process of the present invention preferably comprises the additional step of roughening the surface of at least a portion of the basic body of the dental implant, in particular by sandblasting, machining, and / or acid etching, and more particularly by sandblasting and / or machining followed by acid etching. Instead of sandblasting or machining, injection molding techniques are also conceivable for providing macroscopic roughness. For the acid etching step, a mixture of HCl and H₂SO₄ is preferably used. According to a preferred embodiment, only the bone-contacting surface is roughened. This results in a dental implant that has a highly osseointegrative bone-contacting surface and a soft-tissue contact surface with low plaque adhesion and improved soft-tissue interaction. The present invention is further illustrated by the accompanying Figures, of which Figure 1 shows a dental implant according to the present invention, comprising a basic dental implant body with nanostructures formed in the soft tissue contact region; and Figure 2 shows an image of the soft tissue contact surface of a dental implant according to the present invention, said image being obtained by field emission scanning electron microscopy. The dental implant 2 shown in Figure 1 comprises a basic dental implant body 10, which extends along a longitudinal axis A from an apical end 12 to a coronal end 14 disposed opposite said apical end. In the apical end region, the basic body of dental implant 10 comprises an anchorage part 16 that is intended to anchor itself into a patient's bone. In the coronal end region, the basic body of dental implant 10 comprises a head portion 18, which is intended to form the base on which a superstructure is mounted. The anchoring portion 16 comprises a stem 20, which has a basic shape that is substantially cylindrical, tapering to a rounded tip towards the apical end 12 and in which an external thread 21 is formed. The stem 20 forms a bone tissue contact region 22 that extends from the apical end 12 towards the coronal end 14, i.e., longitudinally, in a length lbcr and is intended to be in contact with the bone in the implanted state. Coronally adjacent to the bone contact region 22 is a soft tissue contact region 24, which extends from the respective end of the bone contact region 22 towards the coronal end 14, i.e., longitudinally, in a length lscr and thus widens in a cup shape. At the outermost coronal end 14 of the basic dental implant body 10 and directly adjacent to the soft tissue contact surface, a shoulder 26 is formed, which narrows in a truncated conical shape towards the coronal end 14. In addition, the coronal end 14 is provided with a recess 28, in which an attachment (not shown) can be placed. The outer surface of the bone tissue contact region 22 forms a bone tissue contact surface 30, which normally has an osteointegrative surface topography, e.g. obtainable by sandblasting and subsequent acid etching. The outer surface of the soft tissue contact region 24 forms a soft tissue contact surface 32. Nanostructures are formed on the soft tissue contact surface 32, which will be illustrated by Figure 2. In an alternative to the embodiment shown in Figure 1, in which the soft tissue contact surface 24 widens towards the coronal end 14, it is also possible for the soft tissue contact region to be cylindrical and / or kept very short. During implantation, the bone-contact region 22 is preferably fully embedded in the patient's bone and, after implantation, is therefore surrounded by bone. This allows for the rapid development of primary stability through engagement of the external thread 21 with the patient's bone. During the healing period, the bone tissue contact region 22 ossifies with the bone, while the soft tissue contact region 24 with the nanostructures formed in it interacts with the soft tissue surrounding the dental implant 2. In this sense, the nanostructures function as sites of enhanced protein adhesion, particularly for transmembrane proteins, more particularly integrins, of the surrounding soft tissue cells. After the healing period, a superstructure can be mounted on the head portion 18 of dental implant 2. This is typically done with the aid of an attachment, which is fixed in a manner known per se by means of retention, typically a screw, the outer thread of which cooperates with an inner thread (not shown) formed in the recess 28. To prevent "microgaps" from being present between the shoulder 26 and the attachment, the outer surface of the shoulder 26 supporting the attachment is usually smooth. As an alternative to these two-piece dental implant systems, the dental implant system can also be a one-piece dental implant system, in which a separate secondary / attachment is not used as a mounting part, but the mounting piece is formed as a single piece with the dental implant. Examples Sample treatment Titanium samples were crushed and polished, then washed with 40% (w / v) NaOH and 40% (w / v) HNO3 in an ultrasonic bath to remove contaminants, then washed with deionized water to achieve a neutral pH and stored at room temperature in 70% by volume ethanol. After the polishing and cleaning stages, some of the samples were treated ("pickled") for one minute in a solution containing 15 wt% HNO3 and 5 wt% HF (solution C1) at room temperature (samples p1). Alternatively, samples were treated in a solution C1 diluted twice with deionized water (samples p2), five times with deionized water (samples p5), and ten times with deionized water (samples pO). Immediately after pickling treatment, the samples were washed by immersing them in a beaker containing deionized water for 10 seconds, then mounted on a sample holder forming a cathode for cathodic polarization (or cathodic hydriding). For cathodic hydriding, current densities of 5, 10, and 15 mA / cm² were used. Hydration was performed at room temperature, and the duration was set at 0, 5, 2, and 5 hours. Tartaric acid at a concentration of 1 M and pH 1.9 was used as the electrolyte. Nanoscale analysis of the samples After the hydriding stage, a nanoscale analysis of each modified surface was performed using a field emission scanning electron microscope (FE-SEM; Quanta 200F, FEI, The Netherlands). As an example of the images obtained, Figure 2 shows the surface of sample p1, with cathodic polarization performed at a current density of 5 mA / cm² and a hydriding time of 0.5 hours. As shown in the image, the ruler at the bottom corresponds to 2 pm. The white "spots" represent nanostructures, specifically nanonodules, with a diameter well below 200 nm. These form retention sites to enhance adhesion to proteins in the surrounding soft tissue.

Claims

1. A dental implant comprising a basic dental implant body (10) extending along a longitudinal axis A from an apical end (12) to a coronal end (14) disposed opposite the apical end, said basic dental implant body comprising an anchoring portion (16) oriented towards the apical end and intended to be anchored in the bone of a patient, and a head portion (18) oriented towards the coronal end and intended to form the base on which a superstructure is mounted, said anchoring portion, a stem (20) having a basic shape that is substantially cylindrical or tapering in the direction towards the apical end into a cone shape, at least a portion of the stem forming a bone contact region (22), the outer surface of which forms a bone contact surface (30), and coronal to said bone contact region is disposed a soft tissue contact region (24),whose outer surface forms a soft tissue contact surface (32), wherein the dental implant further comprises nanostructures formed on the soft tissue contact surface, said soft tissue contact surface on which the nanostructures are formed being smooth when considered at the macroscopic and microscopic scale, characterized in that said nanostructures extend in at least two dimensions up to a maximum of 200 nm.

2. Dental implant according to claim 1, wherein the soft tissue contact surface (32) of the dental implant body on which the nanostructures are formed is machined or polished.

3. Dental implant according to any of claims 1 to 2, wherein the dental implant body (10) is made of titanium or a titanium alloy.

4. Dental implant according to any of the preceding claims, wherein said nanostructures comprise titanium hydride, particularly TiH2,and / or titanium oxide, particularly TiO2.

5. Dental implant according to any of the preceding claims, wherein the nanostructures are at least predominantly in the crystalline phase.

6. Dental implant according to any of the preceding claims, wherein the nanostructures have an average length-to-diameter ratio of more than 1:1, preferably at least 1.5:1, and more preferably 1.5:1 to 4:

1.

7. Dental implant according to any of the preceding claims, wherein the nanostructures have an average diameter of approximately 10 nm to 150 nm and an average length of approximately 5 nm to 500 nm.

8. Dental implant according to any of the preceding claims, wherein the soft tissue contact surface (32) has hydrophilicity defined by a contact angle of less than 90°, more preferably less than 30°, and most preferably less than 10°.when in contact with water.

9. Dental implant according to any of the preceding claims, wherein the bone contact region (22) extends from the apical end (12) towards the coronal end (14) by a length lbcr ranging from 4 to 16 mm.

10. Dental implant according to any of the preceding claims, wherein the soft tissue contact region (24) extends from the respective end of the bone contact region (22) towards the coronal end (14) by a length lscr ranging from 1 mm to 3 mm.

11. Process for providing enhanced protein adhesion sites in a dental implant base body (10) extending along a longitudinal axis A from an apical end (12) to a coronal end (14) disposed opposite the apical end, said dental implant base body comprising an anchoring portion (16) oriented towards the apical end and intended to anchor in the bone of a patient,and a head portion (18) oriented towards the coronal end and intended to form the base on which a superstructure is mounted, said anchoring portion, a stem (20), having a basic shape that is substantially cylindrical or tapering towards the apical end into a cone shape, at least a portion of the stem forming a bone tissue contact region (22), the outer surface of which forms a bone tissue contact surface (30), and coronal to said bone tissue contact region is disposed a soft tissue contact region (24), the outer surface of which forms a soft tissue contact surface (32), wherein the nanostructures are grown on the soft tissue contact surface by treating the soft tissue contact surface with an aqueous solution,The soft tissue contact surface on which the nanostructures grow is smooth when considered at both macroscopic and microscopic scales.

12. A process according to claim 11, wherein the dental implant body is made of titanium or a titanium alloy.

13. A process according to claim 11 or 12, wherein the aqueous solution is an acidic solution comprising at least one component selected from the group consisting of hydrogen fluoride, nitric acid, hydrochloric acid, sulfuric acid, tartaric acid, oxalic acid, citric acid, and acetic acid, and / or mixtures thereof.

14. A process according to any one of claims 11 to 13, wherein the growth of the nanostructures is carried out by cathodic polarization, wherein the dental implant body forms the cathode.

15. A process according to claim 14, wherein prior to carrying out the cathodic polarization,The soft tissue contact surface is pickled with a pickling solution to at least partially remove a layer of titanium oxide present on the soft tissue contact surface.

16. Process according to claim 15, wherein the pickling solution comprises at least one component selected from the group consisting of nitric acid, hydrofluoric acid, ammonium fluoride, hydrochloric acid, and sulfuric acid, and / or mixtures thereof, in particular a mixture of nitric acid and hydrofluoric acid.

17. A process according to any of claims 14 to 16, wherein the cathodic polarization is carried out in a buffer having a pH in the range of 0 to 6.

18. A process according to any of claims 14 to 17, wherein the cathodic polarization is carried out at a temperature in the range of 5 to 95 °C, preferably from 10 to 75 °C, more preferably from 15 to 50 °C.

19. A process according to any one of claims 11 to 13, wherein nanostructures are grown on the soft tissue contact surface by storing the soft tissue contact surface in the aqueous solution.

20. A process according to claim 19, wherein the storage is carried out for at least one month, more preferably at least two months, and most preferably at least four months.

21. A process according to claim 19 or 20, wherein the storage is carried out above ambient temperature, in particular at a temperature in the range of 50°C to 250°C, more particularly from 100°C to 180°C, and most preferably from approximately 120°C to 150°C.

22. A process according to any one of claims 11 to 21, wherein it further comprises the step of roughening the surface of at least a portion of the basic dental implant body, in particular by sandblasting.Machining and / or acid etching, and more particularly by sandblasting and / or machining followed by acid etching.

23. Process according to claim 22, wherein only the surface in contact with bone tissue is roughened.

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