WHITE, BACTERIA-RESISTANT, BIOCOMPATIBLE, ADHESIVE COATING FOR IMPLANTS, SCREWS AND PLATES INTEGRATED INTO HARD AND SOFT TISSUE AND MANUFACTURING PROCESSES

Description

[0001] The present invention relates to a dental implant with a white, bacteria-resistant, biocompatible, adhesive coating that can be integrated into hard and soft tissue, and to an associated manufacturing process. Coatings that meet requirements, particularly regarding bacterial resistance, biocompatibility, and chemical resistance, have been described in many publications. The following publications can be cited as examples: R. Thull, Electrochemical testing of (Ti,Nb)ON coated alloys, Biomedical Engineering Vol. 36(9), 214ff, 1991; W.W. Plitz, Friction and wear tests of (Ti,Nb)ON layers, Laboratory Biomechanics, Munich, 1994; R. Thull, K. Taubner, E.J. Kahle, Biological and animal experimental investigations of (Ti,Zr)O2 and (Ti,Nb)ON, Biomedical Engineering, Vol. 37, 7-8, 1992. R. Thull, K. Taubner, EJKahle, Model for the immunological testing of biomaterials, Biomedical Engineering, Vol. 37, 162-169, 1992; D. Repenning, Material sensitivity in titanium implants - Part 1, Dental Management ZMK, 2010; M. Stelzel et al., Behavior of different titanium surfaces under oral exposure - an in vivo study, Philips University Marburg, Department of Periodontology 2003; D. Repenning, Surface coating on implants, osseous integration, 53-61, Springer Verlag; Betz, Reuther, 5-year clinical study of endosseous implants with special consideration of the peri-implant tissue, German Journal of Oral and Maxillofacial Surgery, 1995.

[0002] All these layers suffer from the disadvantage that they do not meet the aesthetic criterion of a white surface. In this context, "white" is understood to mean a color range from slightly gray to slightly pinkish to pure white, which is perceived as white in the respective organic environment.

[0003] For titanium-coated dental implants in particular, there is a strong desire for aesthetically pleasing white surfaces. This applies equally to the endosseous part of the implant and the abutment. At the same time, the surfaces must meet the aforementioned biocompatibility requirements (ELISA, Thull), as well as the requirements for effective corrosion protection against the leaching of ions from the substrate material and bacterial resistance, especially against pathogenic anaerobic bacteria. Finally, a topographically optimized surface must ensure reliable osseointegration.

[0004] The coatings currently available range in color from gold (nitrides) to dark blue (ceramic titanium-zirconium oxide layers) to black (DLC = diamond-like carbon). Well-known white-gray coatings are hydroxyapatite coatings (HA coatings), which promote better bone integration. However, these HA coatings are resorbed by the tissue over time. Furthermore, they are only applied to the endosseous portion of an implant and not to the transgingival portion.

[0005] White or near-white titanium dioxide coatings produced by electrolytic processes have also become known. However, titanium dioxides do not meet the aforementioned requirements for bacterial resistance (see M. Stelzel et al., Behavior of various titanium surfaces under oral exposure – an in vivo study, Philips University of Marburg, Department of Periodontology, 2003) and only to a limited extent the requirements for biocompatibility (see R. Thull, K. Taubner, E.J. Kahle, Biological and animal experimental investigations of (Ti,Zr)O2 and (Ti,Nb)ON, Biomedical Engineering, Vol. 37, 7–8, 1992). Other well-known approaches for coating implant bodies are based on sol-gel processes and spraying methods. The latter include plasma spraying (APS), cold spraying (CGS), high-velocity oxygen fuel spraying (HVOF), arc spraying (AS), powder flame spraying (PFS), and, last but not least, wire flame spraying.All these layers suffer from the disadvantage that they cannot be applied with sufficient adhesion for medical applications and / or with sufficient precision to the delicate implant bodies.

[0006] White dental implants are currently made of zirconia all-ceramic materials. To stabilize them against fracture, the ceramics are doped with yttrium oxide. A particular disadvantage of ceramic implants is that their surfaces are not topographically optimally adjustable for reliable osseointegration, and that the risk of fracture presents a special and increased challenge to the surgical procedure and long-term stability (or early failures in the first year). Furthermore, the composition of the ceramics cannot be freely varied for material-related reasons, thus preventing adequate adaptation of the material to the biological environment.

[0007] In patent literature, the closest prior art is RO 127 411 A2. Further relevant prior art is represented by the patent documents WO 2008 / 056323 A1, DE 10 2014 011972 A1, WO 2008 / 009474 A1, WO 2007 / 128285 A1 and CN 206 630 703 U.

[0008] In light of the above, the object of the invention is to overcome the aforementioned disadvantages of the prior art and to provide a coating for implants that meets both aesthetic criteria with regard to surface color and exhibits good biocompatibility, long-term stability and bacterial resistance.

[0009] This problem is solved by an implant having the features of claim 1. The problem is further solved by a method for manufacturing an implant having the features of claim 1.

[0010] Advantageous further training opportunities arise from the sub-requirements.

[0011] A key aspect of the invention is to construct the coating in multiple layers consisting of gradient layers, the oxygen content of which varies within the gradient layers. Preferably, the lowest gradient layer applied to the element is designed as a metallic adhesion promoter layer. Within the scope of the present invention, a metallic adhesion promoter layer is understood to be a gradient layer consisting of a metal and being essentially oxygen-free. This ensures optimal adhesion to the element. The gradient layers formed on the metallic adhesion promoter layer preferably have an oxygen content that increases from the lowest gradient layer applied to the element to full stoichiometry, such that the outermost gradient layer is a metal oxide layer with full stoichiometry.

[0012] According to the invention, the gradient layers contain tantalum and / or niobium. These metals are characterized by high biochemical stability. The outermost gradient layer is titanium-free and comprises a mixed phase of 20 mol% Nb₂O₃ and 80 mol% Ta₂O₅.

[0013] The gradual increase in oxygen content across the gradient layers improves adhesion between them. Both the metallic adhesion-promoting layer and the gradient layers with oxygen content below the full stoichiometry of the outermost metal oxide gradient layer exhibit coloration. In the gradient layers with oxygen content, this coloration is caused by defects in the crystal structure where electronic intermediate states form, leading to characteristic absorption and thus coloration of the material. The outermost gradient layer with full stoichiometry is crystalline and essentially lacks defects in its structure that cause coloration.This results in a coating that, due to the gradually changing oxygen content from the metallic adhesion promoter layer to the outermost metal oxide gradient layer, exhibits excellent adhesion properties and, at the same time, has a white color due to the presence of the outermost metal oxide gradient layer.

[0014] The band gap of the outermost metal oxide gradient layer is greater than 3.1 eV, so that the outermost layer does not absorb any electromagnetic waves in the visible range and therefore appears white.

[0015] Furthermore, materials, especially ceramic systems, with band gaps of more than 3.1 eV represent materials with high electrical resistance (R >> 1000 Ωcm -2< ) and help to avoid the reaction between biological tissue and an implant formed from the material by electron exchange.

[0016] The bacterial resistance, biocompatibility, and adhesive strength achieved with the coating according to the invention are advantageous for all elements used in connection with implantation. Therefore, the coating according to the invention is applicable to all implant components. It should be clarified once again that the coating according to the invention is suitable for all elements and their surfaces that can be integrated into or connected to hard and soft tissue, for example, all surfaces of implants, abutments, and connecting elements such as screws, including their entire outer surfaces as well as inner surfaces including threaded sections.

[0017] Preferably, at least one of the gradient layers containing oxygen, and in particular at least the outermost metal oxide gradient layer, has grain sizes of 5 nm or larger. The nanocrystalline structure with submicrometer grain sizes contributes to the increased fracture toughness of the layers. The grain sizes are determined by X-ray diffractometry.

[0018] According to the inventive method, the coating is preferably applied using a PVD (physical vapor deposition) process. PVD processes are typically used for coating medical implants and instruments. Their advantage lies in the high variability in setting chemical compounds, be they purely metallic, oxide, nitride, carbide, or more complex compositions.

[0019] According to the invention, oxide layers, at least nanocrystalline, are produced as gradient layers using PVD processes, wherein the band gap Eg of at least the outermost gradient layer is greater than 3.1 eV. Adhesion of the layers is achieved by first applying a metallic adhesion promoter layer to the element and subsequently adjusting the oxygen content of the layers to full stoichiometry, preferably within less than 500 nm. It is essential that the gradient layers are defect-free to such an extent that no electronic states arise that either lead to a reduction of the band gap or serve as absorption centers for longer-wavelength light.

[0020] A particular disadvantage of PVD processes, namely that the deposition conditions occur outside of thermodynamic equilibrium, is overcome by applying the coating at elevated temperatures above T=300°C and / or by subsequently curing the layers under an oxygen atmosphere. The additional requirement of bacterial resistance is preferably met through the multiphase formulation of the layers. Multiphase layers vary the pzzp (point of zero zeta potential) at the surface, thereby inducing bacterial repulsion.

[0021] The invention will below be described with regard to further features and advantages using exemplary embodiments, which are explained in more detail with reference to the figure.

[0022] This shows Fig. 1 a schematic view of an element with a coating according to the invention.

[0023] Fig. 1Figure 20 shows an element formed by an implant, such as a screw or plate, that can be integrated into hard and soft tissue. A coating according to the invention, consisting of several gradient layers 11, 12, 13, is applied to the element 20. The lowest gradient layer 11 formed on the element 20 is a metallic adhesion-promoting layer. The outermost gradient layer 13 is a white layer containing a metal oxide with full stoichiometry. Between the gradient layers 11 and 13, one or more gradient layers 12 are formed, the oxygen content of which increases from the lowest gradient layer 11 formed on the element 20 to the outermost gradient layer 13 with full stoichiometry.

[0024] In the simplest case, the white layer is made of zirconium dioxide. Zirconium dioxide is used as an all-ceramic material in implantology. However, it has not yet been possible to apply zirconium dioxide as a firmly adhering white layer to titanium implant bodies. In the embodiment according to the invention, a metallic layer of zirconium with a thickness of 20 nm is first deposited as the lowest gradient layer 11 onto the element 20, the surface of which is preferably roughened and, in a preferred embodiment, made of titanium. Subsequently, oxygen is successively supplied by means of a PVD-typical reactive process, and the layer is finally built up via the gradient layers 12 to the full stoichiometry present in the outermost gradient layer 13. The total thickness of the coating is preferably set to 5 micrometers.The process can be carried out in such a way that the deposition takes place at an elevated temperature, so that instead of the otherwise PVD-typical (X-ray amorphous) layer, at least a nanocrystalline layer is formed.

[0025] In a second embodiment, a mixture of 20 mol% Nb₂O₅ and 80 mol% Ta₂O₅ is used for the outermost gradient layer 13, and the full stoichiometry is built up from the lowest, metallic gradient layer 11 via the intermediate gradient layers 12. These layers are characterized by particularly high biochemical stability and a negative surface potential. The negative surface potential ensures stable adsorption of calcium ions and thus reliable osseointegration.

[0026] In the further example, a layer with the stoichiometry ZrTi₂O₆ is used as the outermost gradient layer 13. (Ti,Zr)O₂-x layers are highly biocompatible and bluish-black due to their high defect structure, their X-ray amorphous morphology, and their imprecise composition. The coating according to the invention has an outer gradient layer 13 with a band gap Eg of 3.1 eV or larger and is stoichiometrically precise. This gradient layer 13 is nanocrystalline. Due to its high negative free energy of formation, the outermost gradient layer 13 also exhibits significantly improved biochemical stability. Its point of zero potential is at pH 6–7.

Claims

1. An implant which is formed by a dental implant having an enossal part and an abutment, characterised in that a white, bacteria-resistant, biocompatible, adherent coating is applied both onto an enossal part and onto the abutment of the dental implant, wherein the coating has a structure made from metalliferous gradient layers (11, 12, 13) having a varying oxygen content, wherein the band gap (Eg) of the outermost gradient layer (13) is greater than 3.1 eV, wherein the outermost gradient layer is crystalline, and wherein the gradient layers (11, 12, 13) have tantalum and / or niobium, wherein the outermost gradient layer has a titanium-free mixed phase made of 20 mol % of Nb2O3 and 80 mol % of Ta2O5.

2. The implant according to Claim 1, wherein the lowermost gradient layer (11) applied onto the implant (20) is a metallic adhesive bonding layer, the outermost gradient layer (13) is a metal oxide layer having full stoichiometry, and wherein the intermediate gradient layers (12) have an oxygen content which increases from the lowermost gradient layer (11) applied onto the implant to the outermost gradient layer (13) to the full stoichiometry.

3. The implant according to Claim 1 or 2, wherein at least one of the gradient layers (12, 13) having an oxygen content, preferably at least the outermost gradient layer (13), has grain sizes of 5 nm or greater.

4. The implant according to any one of the preceding claims, wherein the gradient layers (11, 12, 13) further have aluminium and / or tin.

5. The implant according to any one of the preceding claims, wherein the concentration of the metals in the gradient layers (12, 13) is adjusted with at least binary oxides so that the gradient layers (12, 13) having at least binary oxides have a band gap (Eg) of greater than 3.1 eV.

6. The implant according to any one of the preceding claims, wherein one or more gradient layers (11, 12, 13) contain(s) carbon and / or oxygen and / or boron and / or fluorine.

7. The implant according to any one of the preceding claims, wherein the lowermost gradient layer (11) applied onto the implant has a thickness of 50 nm or less.

8. The implant according to any one of the preceding claims, wherein the total thickness of the gradient layers (12) having a reduced oxygen stoichiometry is 500 nm or less, preferably 200 nm or less, further preferably 100 nm or less, further preferably 60 nm or less.

9. The implant according to any one of the preceding claims, wherein the thickness of the outermost gradient layer (13) is 10 µm or less.

10. The implant according to any one of the preceding claims, wherein the total thickness of the coating is between 3 µm and 7 µm, preferably between 4 µm and 6 µm, further preferably between 4.5 µm and 5.5 µm.

11. A method for producing a white, bacteria-resistant, biocompatible, adherent coating on an implant according to any one of the preceding claims, having the following steps: - applying a metallic adhesive bonding layer as a first gradient layer (11) onto the surface of the implant (20) by means of PVD (physical vapour deposition), - applying gradient layers (12, 13) having tantalum and / or niobium, as well as oxygen, onto the metallic adhesive bonding layer (11) having an increasing oxygen content by increasing the oxygen content during the application of the gradient layers (12, 13) until the full stoichiometry in the outermost gradient layer (13) is reached, wherein the band gap (Eg) of the outermost gradient layer (13) is greater than 3.1 eV, wherein the outermost gradient layer has a titanium-free mixed phase made of 20 mol % of Nb2O3 and 80 mol % of Ta2O5.

12. The method according to Claim 11, wherein the application of the gradient layers (11, 12, 13) is carried out at a temperature of 300°C or higher.

13. The method according to Claim 11 or 12, wherein the gradient layers (11, 12, 13) are cured under an oxygen atmosphere.

14. The method according to any one of Claims 11 to 13, wherein the gradient layers (11, 12, 13) are configured so that they have grain sizes of 5 nm or greater.

15. The method according to any one of Claims 11 to 14, wherein the gradient layers (11, 12, 13) further have aluminium and / or tin.

16. The method according to any one of Claims 11 to 15, wherein the application of the gradient layers (11, 12, 13) is carried out such that the lowermost gradient layer (11) applied onto the implant (20) is a metallic adhesive bonding layer, the outermost gradient layer (13) is a metal oxide layer having full stoichiometry, and wherein the intermediate gradient layers (12) have an oxygen content which increases from the lowermost gradient layer (11) applied onto the implant to the outermost gradient layer (13) to the full stoichiometry.

17. The method according to any one of Claims 11 to 16, wherein the concentration of the metals in the gradient layers (12, 13) is adjusted with at least binary oxides so that the gradient layers (12, 13) having at least binary oxides have a band gap (Eg) of greater than 3.1 eV.

18. The method according to any one of Claims 11 to 17, wherein one or more gradient layers (11, 12, 13) contain(s) carbon and / or oxygen and / or boron and / or fluorine.