The present invention relates to a medical device for use in the dental field. Such medical devices, in particular dental implants, are preferably made of metals such as titanium and titanium alloy. In the hydroxylated and hydrophilic state such materials can provide an excellent osseointegration.

In the area of the soft tissue, by contrast, such materials are associated with disadvantages. First, the darkish metal implant shows through the soft tissue, which may negatively influence the visual impression. Second, in the case of gingival recession, bare metal may become visible, the so called black triangle, which is highly unwanted . In order to overcome said disadvantages a large number of documents disclose metal implants with a ceramic sleeve arranged in the area of the soft tissue contact surface (for example DE 298 20 971, US 5,152,687, GB 2 139 095). Ceramic sleeves of this kind are, for example, adhesively bonded onto the implant. As a result, however, a number of problems arise which have not as yet been resolved. Using a ceramic sleeve as a separate structural part almost unavoidably results in a micro-gap, which can cause bacterial contamination. Alternatively, such a sleeve can be fitted by sintering. However, high temperatures have to be used for the sintering process, which can cause a partial oxidation of the metallic body of the implant. This has a disadvantageous effect on osseointegration. Moreover, different coefficients of thermal expansion of the materials involved can, particularly during cooling, result in the development of microstress, which can lead to hairline fractures and cracks. Coatings with silicate glass and with silicate-glass- modified ceramics are also known, for example from document WO 01/74730. A disadvantage of these is, once again, the possibility of microstress occurring as a result of the firing process at high temperatures and the at least partial oxidation of the titanium surface.

US 2003 0125416 discloses a coating composition comprising a resinous binder and a color effect colorant in particulate form. The colorant comprises an oriented periodic array of particles held in a matrix. CA 2 454 204 discloses an implant body having a coloured coronal band portion provided at the peripheral surface of the implant body. The colored portion is complementary to a natural gum tissue color.

Finally, the color of all said coatings and sleeves cannot be influenced to the desired extent, resulting in a negative visual impression.

The problem of the invention is therefore to provide a medical device which combines the excellent mechanical properties of the metals, especially of titanium, with the good esthetic properties of highly reflecting coatings.

In particular, the problem of the present invention is to provide a medical device for the restoration, replacement or correction of teeth which combines the excellent mechanical properties of the metals, especially of titanium, with the good esthetic properties of highly reflecting coatings.

The problem is solved by a medical device according to claim 1 and a method for preparing such a medical device according to claim 16. Further preferred embodiments are defined by the dependent claims.

In particular, the problem is solved by a medical device for use in the dental area made of titanium, zirconium, niobium, hafnium, tantalum, vanadium, aluminum, steel or alloys thereof, characterized in that the surface of said medical device is at least partially coated with a reflector coating, said reflector coating comprises a plurality of repeat units, and each repeat unit consisting of two layers of a Bragg reflector pair selected from the group of Ti0 ₂ /Si0 ₂ , Zr0 ₂ /Si0 ₂ , A1N/A1 ₂ 0 ₃ , Si _x N _y /Si0 ₂ , wherein x is from 1 to 4 and y is from 1 to 8, and Si/SiC>2 .

The medical device according to the present invention is for use in the dental field, and in particular, for use in the visible front part of the mouth. It is selected from the group of dental implants, orthodontic appliances, crowns, bridges and abutments. Most preferably, the medical device is a dental implant which may be a one-part or a two-part dental implant. The medical device is made of titanium, zirconium, niobium, hafnium, tantalum, vanadium, aluminum, steel or alloys thereof. Titanium or a titanium alloy is a preferred material. In case of titanium alloys, in particular alloys are preferred in which zirconium, niobium, tantalum, vanadium and/or hafnium have been added. A most preferred alloy is a titanium zirconium alloy; an example of which is Roxolid ^® . Titanium and titanium alloys are biocompatible and have excellent corrosion resistance in body fluids.

The surface of said medical device is at least partially coated with a reflector coating. The reflector coating comprises a plurality of repeat units and each repeat unit consists of two layers of a Bragg reflector pair selected from the group of Ti0 ₂ /Si0 ₂ , Zr0 ₂ /Si0 ₂ , A1N/A1 ₂ 0 ₃ , Si _x N _y /Si0 ₂ , wherein x is from 1 to 4 and y is from 1 to 8 (preferably Si3N ₄ /Si0 ₂ ) and Si/Si0 ₂ . Depending on the patient's needs the colour of the reflector coating may be chosen to reddish or pinkish resembling mucosa or white, creamy-white, brownish, orange or yellowish, preferably white, creamy-white, orange or yellowish, resembling bone or tooth substance.

Thus, the material of the medical device exhibits optimal stability, whereas the reflector coating esthetically adapts the color to the individual surrounding area.

The medical device according to the present invention has excellent esthetic characteristics, since it provides a color that resembles teeth or soft tissue due to the presence of the reflector coating. The mechanical integrity is very good because, for example, the strain at cracking is higher than 0.5% which corresponds to the elastic limit of titanium, i.e. the reflector coating does not crack upon elastic deformations of the medical device. In addition, the reflector coating shows a strong adhesion to the surface of the medical device, i.e., there is no spalling upon elastic deformations of the medical device.

In a preferred embodiment of the present invention the Bragg reflector pair is Zr0 ₂ /Si0 ₂ or Ti0 ₂ /Si0 ₂ . These two Bragg reflector pairs have large differences in refractive index. The difference in refractive index determines the number of layers required for a given reflectivity and the width of the stop band. A larger difference stands for a broader stop band. Therefore, large differences in refractive index permit a smaller number of .layers and have therefore a positive impact on the fabrication process. Most preferably, the Bragg reflector pair is Ti0 ₂ /Si0 ₂ because of the higher difference in refractive index. Less and thinner layers can be used to give the same result. Moreover, the corrosion properties of the device can be enhanced due to the protective nature of these ceramic layers .

In another embodiment of the present invention the reflector coating of the medical device comprises more than 1 stack, preferably 2 to 4 stacks, most preferably 2 or 3 stacks. Said stacks are arranged on top of one another and extend in essentially the same vertical plane. Each stack comprises repeat units having the same retardation R, whereby different stacks may have the same or a different retardation.

The retardation corresponds to the path difference between two light rays reflected at the interfaces of a Bragg reflector pair, i.e. one is reflected at the upper repeat unit interface (directed away from the medical device, e.g. air/Ti0 ₂ or Si0 ₂ /Ti02 with Si0 ₂ being from the upper repeat unit) and the other one at the interface inside the repeat unit (directed to the medical device, e.g. Ti0 ₂ /Si0 ₂ ) . If for example the desired wavelength λ for constructive interference, i.e. the design wavelength, is 650 nm, the optical thickness nd=A/4 is 162.5 nm (wherein n is the refractive index) . This means that the incoming light gets reflected at the interface after it has passed a virtual distance of one quarter of its wavelength. The optical thickness corresponds to the distance light would pass if it travelled in vacuum/air rather than in the thin film. The retardation (R=A/2=2nd) is 325 nm and thanks to a phase shift of λ/2 which occurs upon reflection at a medium with higher refractive index (e.g. air/Ti0 ₂ or Si0 ₂ /Ti0 ₂ ) , the two reflected light rays are now completely in phase leading to constructive interference.

Preferably, each stack is responsible for the reflection of a specific wavelength. For example, a first stack being arranged directly on the medical device reflects the smaller wavelength (blue) . A second stack, arranged directly on top of the first stack, reflects green light and a third stack, arranged directly on top of the second stack, reflects red light. Due to this arrangement the ratio of the reflected red light is higher than the ratio of the blue light. Accordingly, this results in a medical device exhibiting the reddish color of the mucosa.

In a further embodiment of the present invention each stack comprises more than 1 repeat unit, preferably from 2 to 10 repeat units, most preferably from 3 to 8 repeat units. The number of repeat units strongly influences the reflectivity achieved. Therefore, depending on the desired reflectivity of a specific design wavelength more or less repeat units are chosen for one stack. For example, a stack reflecting blue light preferably comprises 2 to 4 repeat units, a stack reflecting green light preferably comprises 2 to 6 repeat units, whereas a stack reflecting red light preferably comprises 4 to 8 repeat units.

In another embodiment of the present invention the retardation R of each repeat unit increases from the bottom to the top repeat unit in arithmetic, geometric or Gaussian progression. The bottom repeat unit stands within the context of the present application for the repeat unit which is directed towards the medical device, whereas the top repeat unit is the repeat unit which is directed away from the medical device.

For an arithmetic progression the retardation R of each subsequent repeat unit in direction towards the top repeat unit (that is in coronal direction) constantly increases by a specific value, preferably between 5 and 25 nm, most preferably between 10 and 20 nm, ideally 15 nm. For example, the first repeat unit (that is the bottom repeat unit) has a retardation of 215 nm, and the subsequent following repeat units arranged directly on top of the previous one have a retardation of 230 nm, 245 nm, 260 nm, 275 nm, 290 nm, 305 nm, 320 nm, 335 nm and 350 nm. In another example, the first repeat unit has a retardation of 225 nm, and the subsequent following repeat units arranged directly on top of the previous one have a retardation of 240 nm, 255 nm, 270 nm, 285 nm, 300 nm, 315 nm, 330 nm, 345 nm and 360 nm. In such arrangements only ten repeat units are necessary, which results in a slightly smaller overall thickness of the reflector coating .

For a geometric progression the retardation R of each repeat unit in direction towards the top repeat unit (that is in coronal direction) increases in comparison to the previous repeat unit by a specific percentage, preferably by 1 to 5%, including 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, and 4.5%, most preferably by 3%. As an example, the first repeat unit (that is the bottom repeat unit) has a retardation of 215 nm, and ^" the subsequent following repeat units arranged directly on top of the previous one have a retardation of 221 nm, 228 nm, 235 nm, 242 nm, 249 nm, 257 nm, 264 nm, 272 nm, 281 nm, 289 nm, 298 nm, 307 nm, 316 nm, 325 nm, 335 nm and 345 nm, whereby each value can differ within a range of +/- 1 to 3 nm. In another example the first repeat unit (that is the bottom unit) has a retardation of 225 nm, and the subsequent following repeat units arranged directly on top of the previous one have a retardation of 232 nm, 239 nm, 246 nm, 253 nm, 261 nm, 269 nm, 277 nm, 285 nm, 294 nm, 302 nm, 311 nm, 321 nm, 330 nm, 340 nm, 351 nm and 361 nm, whereby each value can differ within a range of +/- 1 to 3 nm.

For a Gaussian progression there is a Gaussian distribution centered around the retardation R of a repeat unit being in the middle of all repeat units. To determine the retardation of the repeat units, one proceeds as follows: First, one linearly distributes as many values as Bragg reflector pairs shall be present on an intervall from 0 to 1. The linear distribution for 9 Bragg reflector pairs is for example: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7,

0.8 and 0.9 with a constant difference of (number of Bragg reflector pairs + l) ^"1 . Said linear distribution is converted into a Gaussian distribution according to a method known to the skilled person. In the example, this gives the x-values -1.28, -0.84, -0.52, -0.25, 0.0, 0.25, 0.52, 0.84, 1.28. Finally, one has to choose the retardation of the central repeat unit R and the standard deviation R ₀ of the Gaussian distribution. The retardations of each repeat unit can be calculated according to .the formula R=R _p +x*R _a . In the example, the following retardations follow for R _u =300 nm and R _o =50 nm: 236 nm, 258 nm, 274 nm, 287.5 nm, 300 nm, 312.5 nm, 326 nm, 342 nm, 364 nm. This can also be done for even numbers of Bragg reflector pairs. However, there will be no central repeat unit. The linear distribution for 10 Bragg reflector pairs will be 0.05, 0.15, 0.25, 0.35, 0.45, 0.55, 0.65, 0.75, 0.85 and 0.95 with a constant difference of (number of Bragg reflector pairs) ^"1 . In a further embodiment of the present invention an intermediate layer is arranged between the surface of the medical device and the first repeat unit in order to improve the adhesion of the reflector coating and the surface of the medical device. The presence of an intermediate layer improves the long-term stability of the medical device. Preferably, the material of the intermediate layer is Zr0 ₂ , Ti0 ₂ , Zr or Ti or a mixture thereof. An intermediate layer made of Zr0 ₂ or Ti0 ₂ has typically a retardation of 200 nm to 300 nm, preferably 200 nm to 250 nm, most preferably 225 nm to 250 nm. Preferably, the intermediate layer has essentially the same retardation as the first repeat unit on the medical device (that is the bottom repeat unit) . An intermediate layer made of Zr or Ti has typically a thickness of less than 15 nm, preferably between 5 and 10 ran, including 5, 6, 7, 8, 9 and 10 nm, most preferably 10 nm.

In another embodiment of the present invention a highly reflecting interlayer is arranged between the surface of the medical device and the first repeat unit in order to improve the esthetic properties further. The highly reflecting interlayer is a metal film selected from the group of silver, aluminum, rhodium, gold, palladium, platinum, titanium, zirconium as well as alloys and mixtures thereof. The highly reflecting interlayer has preferably a thickness from 30 to 520 nm, preferably from 30 to 100 nm, most preferably 50 nm. Such a highly reflecting interlayer may be arranged directly on the surface of the medical device or on an intermediate layer, which improves the adhesion of the highly reflecting interlayer. The intermediate layer has typically a thickness of less than 15 nm, preferably between 5 and 10 nm, including 5, 6, 7, 8, 9 and 10 nm, most preferably 10 nm.

In a further embodiment of the present invention the reflector coating of the medical device has a thickness from 0.5 to 5 μιη, preferably from 0.8 to 2.2 μπι. The quality and adherence of such a coating is advantageous, since the medical device provides an excellent esthetic result .

In a preferred embodiment of the present invention the Bragg reflector pair is Ti0 ₂ /Si0 ₂ . Most preferably, a first stack is arranged on the surface of the medical device. Said first stack comprises a plurality of repeat units each having a retardation of 225 to 275 nm. On said first stack a second stack is arranged comprising a plurality of repeat units each having a retardation of 275 to 325 nm, or alternatively 287.5 to 337.5 nm. The first stack reflects the blue/green wavelength ( s ) , whereas the second stack reflects green and/or red wavelength. In a most preferred embodiment the first stack consists of 4 repeat units and the second stack consists of 6 units. Preferably the. outermost layer is Ti0 ₂ , since Ti0 ₂ is known to be biocompatible and has a good bone ingrowth. The first repeat unit may be arranged directly on the surface of the medical device or an intermediate layer, preferably made of Ti0 ₂ and/or of Ti, which is arranged between the surface of the medical device and the first repeat unit. Such an intermediate layer can increase the adhesion of the reflector coating on the medical device.

In another preferred embodiment of the present invention the Bragg reflector pair is Zr0 ₂ /Si0 ₂ . Most preferably, a first stack is arranged on the surface of the medical device. Said first stack comprises a plurality of repeat units each having a retardation of 200 to 262.5 nm, preferably 212.5 to 262.5 nm. On said first stack a second stack is directly arranged comprising a plurality of repeat units, each having a retardation of 250 to 300 nm. On said second stack a third stack is directly arranged comprising a plurality of repeat units, each having a retardation of 287.5 to 350 nm, preferably 287.5 to 337.5 nm. The first stack reflects the blue wavelengths, whereas the second stack reflects the green wavelengths and the third stack reflects the red wavelengths. In a most preferred embodiment the first stack consists of 4 repeat units and the second stack consists of 6 units and the third stack consists of 6 units. Preferably the outermost layer is Zr0 ₂ , since artificial teeth are made from the same material. Further it is less prone to corrosive damages than Si0 ₂ and has good soft tissue integration. The first repeat unit may be arranged directly on the surface of the medical device or an intermediate layer, preferably made of Zr0 ₂ and/or of Zr, which is arranged between the surface of the medical device and the first repeat unit. Such an intermediate layer can increase the adhesion of the reflector coating on the medical device.

In another embodiment of the present invention the reflector coating of the final medical device has an L*- value higher than 80, preferably from 85 to 95, most preferably 90. The L*-value is one dimension of the L*a*b*-system (L*a*b* color space) . Said system has three dimensions, that is L* for lightness and a* and b* for the color-opponent dimensions. For the purpose of this invention L* is the most important value, since L* determines the lightness of the substrate, while a* and b* only determine the hue of the color. For standard metals such as titanium, the values for a* and for b* are around 0 as they do not have any color. The best optical appearance of the medical device could be obtained in cases in which the coated surface of the final medical device has an L*-value from 85 to 90. The expression one-part implant stands for a single component implant, in which anchoring part and abutment part are configured in one piece.

The expression two-part implant stands for an anchoring part of a two-part implant system (two component implant system) . In addition to the anchoring part a two-part implant system comprises a separate abutment.

The extent of the surface of the medical device which is coated with the reflector coating is dependent on the nature of the medical device. For example for orthodontic appliances and bridges at least 50%, preferably more than 75% and most preferably more than 90% of the surface is covered by the reflector coating. In a most preferred embodiment the surface is completely covered by the reflector coating.

In contrast thereto, for, dental implants, abutments and crowns, the surface is preferably only partly covered by the reflector coating.

Generally, an abutment comprises an apical portion configured to engage the dental implant, a transition portion bordering coronally on the portion and on which coronally borders a coronal portion for attachment of the crown. The term "coronal" is here and throughout this application used to indicate a direction towards a head end or trailing end of the component discussed. Likewise, the term "apical" indicates a direction towards an insertion end of the component. Thus, apical and coronal are opposite directions. Furthermore, the term "axial direction" is used throughout this application to indicate a direction taken from the coronal end to the apical end, or vice versa. In a preferred embodiment of the present invention the transition portion of the abutment is covered with the reflector coating. In another embodiment of the present invention both, the transition portion and the coronal portion of the abutment, are covered by the reflector coating, whereas the apical portion configured to engage the dental implant is free from the reflector coating allowing a very precise connection to the implant. In another embodiment of the present invention the medical device is a two-part dental implant for attachment of artificial teeth. Said implant is generally in a cylindrical or conical shape, having an apical end with a body portion and a coronal end with a neck portion intended to receive an abutment, and a transition portion being arranged in axial direction between the body portion and the neck portion. The neck portion generally includes an unthreaded part which is in coronal direction outwardly tapering and ends in a shoulder portion with an inwardly- tapering surface.

Preferably, the total length of the implant is 6 - 19 mm in the axial direction. The body portion with the apical end is preferably 50 to 90% of the total length of the implant in axial direction. The neck portion with the coronal end, which is essentially intended to be in contact with the soft tissue, covers preferably 10 to 40% of the total length of the implant in axial direction. The transition portion covers preferably 0 to 40% of the total length of the implant in axial direction. The neck portion has preferably a length of 1 to 4, most preferably of 1.5 to 3 mm.

Said neck portion is at least partially covered with the reflector coating. In a preferred embodiment the shoulder portion of the neck portion is not covered by the reflector coating. Preferably in apical direction, at least 50%, most preferably at least 75% of the circumferential surface area of the transition portion is covered with said reflector coating. Most preferably with the exception of the shoulder portion the neck portion, that is unthreaded part which is in coronal direction outwardly tapering, is completely covered with the reflector coating. Thanks to the reflector coating almost no color change or a brightening can be observed in the peri-implant mucosa.

In a further embodiment of the present invention not only the neck portion of such a two-part dental implant but also the transition portion of the implant is at least partly coated with said reflector coating. Preferably in coronal direction, at least 25%, most preferably at least 50% of the circumferential surface area of the transition portion is covered with said reflector coating.

In another embodiment of the present invention the transition portion and the neck portion of such a two-part dental implant comprise a reflector coating, but the reflector coating of the transition portion exhibits a different color than the reflector coating of the neck portion. In another embodiment of the present invention both, the transition portion and the neck portion with the exception of the shoulder portion of the two-part implant, are completely covered with the reflector coating, whereas the body portion is bare metal, which is preferably surface treated, to ensure an optimal osseointegration . According to another embodiment of the present invention, the edge of the reflector coating facing toward the body portion and extending along the circumference of such a two-part dental implant is formed in a curved shape, with at least one rise, preferably two such rises, and one dip, preferably two such dips, so that the natural shape of the bone is simulated. In this way it can be ensured that, ideally, all the soft tissue contact surfaces are provided with the reflector coating. With such a configuration of the edge of the reflector coating, it is possible to effectively avoid the color of the basic material of the implant showing through the soft tissue in the implanted state. The configuration of the edge can in this case be made universal to match most bone shapes but can also be made individual, that is to say for each individual implant. In particular, it is possible, by means of CAD/CAM, to exactly register the surface of the implant to be coated via the bone shape of the patient and to provide the implant with the reflector coating accordingly.

The present invention also provides a method for producing a medical device as described above.

In order to obtain the reflector coating the surface to be coated is treated by sputter deposition (for example magnetron sputtering, ion assisted sputtering, gas flow sputtering, radio frequency sputtering) , chemical vapor deposition (metal-organic chemical vapor deposition, metal-organic vapor phase epitaxy) , atomic layer deposition, pulsed laser deposition, preferably by reactive direct current magnetron sputtering in case of Ti0 ₂ and ZrC>2 or reactive radio-frequency magnetron sputtering in case of Si0 ₂ . Said methods are known to the persons skilled in the art.

According to a further preferred embodiment the surface of the medical device which has to be coated is mechanically (for example by milling, turning, grinding, polishing or blasting) pretreated, or laser pretreated, or chemically (for example by etching or electro polishing) pretreated, or ion pretreated (ion bombardment), or pretreated by a combination thereof. The pretreatment can be carried out together with the surface treatment of other parts of the implant, for example when roughening the surface of the body portion or directly before carrying out the coating process. The pretreated surface has preferably a surface roughness S _a from 50 to 1000 nm, most preferably from 80 to 600 nm. In addition, if the coating is carried out directly under vacuum any oxide layer which may be present is removed by such a pretreatment which allows for a better adhesion of the reflector coating.

In the present invention the surface roughness S _a (mean surface roughness) is defined according to ISO 25178. It may be measured for example by a confocal microscope ( surf explorer NanoFocus AG) (scan mode: piezo, lens: 20x, light source: LED with green light, measuring range: 798 μπι x 798 μιτα) . Preferably, the following operators are used for the determination of the roughness: Non-measured points filled (Replaces non-measured points by a smooth shape calculated from the neighbors. Dilates the non- measured points by 1.57 urn) ; Spatial Filtering (Median (denoising) filter, filter size 3x3); Levelling (Least square plane. Levelling by subtraction); Form Removal (Polynomial of order 2. Apply non-measured points to the form alone); Thresholding (Material ratio 0.1% - 99.9%. Reduce height/depth; Without the need of a mathematical filter, thresholding artificially truncates an image at 0.1% from the top and 99.9% from the bottom at the same time) ; Filtering -> Roughness (Gaussian Filter, cut-off 31 μπι, cut surface edges) . .

Figures

Fig 1 shows a detail view of the medical device ;

Fig. 2a to Fig. 2c show three specific embodiments of the present invention;

Fig. 3 shows a further embodiment of the present invention;

Fig. 4 shows a Bragg reflector scheme;

Fig. 5 shows spectral reflectance curves the Si0 ₂ /Ti0 ₂ Bragg reflector;

Fig. 6a to 6c show the color change in covering mucosa (pig experiment) . Fig. 1 shows a detail view of the medical device according to the present invention. The base body 5 of the medical device is made of titanium, zirconium, niobium, hafnium, tantalum, vanadium, aluminum, steel or alloys thereof. The surface 6 of said medical device is at least partially coated with a reflector coating 10. Said reflector coating 10 comprises a plurality of repeat units 15. Each unit consists of two layers 16, 17 of a Bragg reflector pair selected from the group of Ti0 ₂ /Si0 ₂ , Zr0 ₂ /Si0 ₂ , A1N/A1 ₂ 0 ₃ , Si _x Ny/Si0 ₂ , wherein x is from 1 to 4 and y is from 1 to 8 (preferably Si ₃ N ₄ /Si0 ₂ ) , and Si/Si0 ₂ .

Fig. 2a shows a two-part implant 1', i.e. the anchoring part of a two-part implant system, which is an example for a medical device according to the present invention. Such a two-part implant 1' is made of titanium, zirconium, niobium, hafnium, tantalum, vanadium, aluminum, steel or alloys thereof, preferably of titanium or of a titanium alloy. Said implant 1' is in a cylindrical or conical shape, having an apical end 25 with a body portion 20 and a coronal end 35 with a neck portion 30 intended to receive an abutment, and a transition portion 40 being arranged in axial direction A between the body portion 20 and the neck portion 30. The neck portion 30 includes an unthreaded part 31 which is in coronal direction outwardly tapering and ends in a shoulder portion 32 with an inwardly-tapering surface. The body portion 20 is intended to be directed against the bone tissue in the implanted state, whereas the neck portion 30 is intended to be directed against the soft tissue in the implanted state. The transition portion 40 may be directed towards the soft tissue and the bone tissue depending on the depth to which the implant is screwed or on the tissue reaction. The neck portion 30 is at least partially covered with the reflector coating 10, which comprises a plurality of repeat units (not shown) . Fig. 2b shows another embodiment of the present invention. In contrast to the embodiment of Fig. 2A not only the neck portion 30 but also the transition portion 40 of the implant is at least partly coated with said reflector coating 10. Preferably, in coronal direction, at least 25%, most preferably at least 50% of the circumferential surface area of the transition portion is covered with the reflector coating 10, which comprises a plurality of repeat units (not shown) .

Fig. 2c shows another embodiment of the present invention. In contrast to the embodiment of Fig. 2A with the exception of the shoulder portion 32 the neck portion 30 and transition portion 40 of the implant are completely coated with the reflector coating 10, which comprises a plurality of repeat units (not shown) . The body portion 20 is bare metal, which is preferably surface treated, to ensure optimal osseointegration .

Fig. 3 shows another embodiment of an implant 1' . In this case, the edges 45 of the reflector coating are formed along the circumference of the implant 1' in a curved shape, with at least one rise 50 and one dip 55, so that, in the implanted state, the natural shape of the bone is simulated by these edges 45. Examples

Bragg reflectors are deposited on 0.5 mm thick Ti grade 4 sheet (ThyssenKrupp Materials Schweiz AG, Wil, Switzerland) . The Ti samples are punched to a diameter of 15 mm and are differently pretreated. Pickled, but else untreated samples will be referred to as rolled. Other surface treatments include polishing (0.02 pm Si0 ₂ + H ₂ 0 ₂ ) , fine-blasting with glass beads (40 to 70 ym Si0 ₂ , 4 bar), sandblasting (Biloxit No. 360, 4 bar) and machining. Deposition (PVD Products sputter system, Wilmington, Massachusetts, USA) :

- Ti0 ₂ : 300 Watt, 50 seem (cmVmin) Ar flow, 4.25 seem 0 ₂ flow, 5 mTorr chamber pressure, 12 rpm substrate rotation, deposition at room temperature (without substrate heating), approx. 10 nm/min

- Si0 ₂ : 300 Watt RF power, 50 seem Ar flow, 3.25 seem 0 ₂ flow, 5 mTorr chamber pressure, 12 rpm substrate rotation, deposition at room temperature, approx. 24 nm/min The optical evaluation of the samples was performed by spectrophotometric measurements using a spectrophotometer CM 2600-d (Konica Minolta, Tokyo, Japan) . The resulting reflectance curves and L*a*b*-values were examined with the manufacturer's software SpectraMagic (Konica Minolta). The observer angle was set to 2° and the D65 standard light source with 100% UV with specular reflection included was used. For the measurement of diffused illumination the device uses an integrating sphere with apertures of 3 mm in diameter (SAV - small area view) . Before each measurement the spectrophotometer was zero- calibrated with a black box (CM-A 32) and then calibrated with a white plate (CM-A 142). The mean reflectance and L*a*b*-values were automatically averaged from three measurements of each specimen.

Bragg reflectors made from Si0 ₂ /Ti0 ₂ with 6 Bragg reflector pairs (i.e. 12 layers) of design wavelength A _d 650 nm (retardation: 325 nm) on top of 4 Bragg reflector pairs (i.e. 8 layers) with design wavelength λ _α 480 nm (retardation: 240 nm) were tested on different Ti substrates (Figure 4). The outermost layer directed to the air (directing away from the surface of the medical device) is Ti0 ₂ . The layer being directly on the surface of the medical device is Si0 ₂ . The total thickness of the reflector coating is 1.55 μπι.

Figure 5 shows spectral reflectance curves of the Si0 ₂ /Ti0 ₂ Bragg reflector on differently pretreated Ti substrates (sample 1: white standard; sample 2: Ti rolled; sample 3: Ti polished; sample 4: Ti glass-blasted; sample 5; Ti sandblasted; sample 6: Ti machined)

The highest reflectance is achieved for the polished substrate. However, not much reflectance is lost with the rougher substrates (rolled, glass-blasted, machined) . Apart from the sandblasted substrate, all the samples are promising for esthetical coatings. Pig maxillae test

The influence of several parameters, such as color, surface treatment of the substrate, coating system and mucosa thickness, on the esthetic appearance was investigated. For statistical reasons, six pig maxillae were used. A palatal mucosa flap, which exhibits similarities to human mucosa with respect to color and texture, was prepared for each maxilla according to the procedure described in Jung et al, in vitro color changes of soft tissue caused by restorative materials, in International Journal of Periodontics & Restorative Dentistry, 2007, 27(3): p. 251-257). Tissue grafts with a thickness of 1 mm and 2 mm were prepared, which were placed beneath the mucosal flap. This flap exhibited a thickness of 1 mm, cor±esponding to the critical case in human patients with grayish appearance of prosthetic appliances through soft tissue. Spectrophotometric measurements were taken from the region where samples were placed underneath the flap. The differences AL* , Aa* and Ab* were then calculated by subtracting the baseline measurement (tissue flap on bone) from the measurement of the sample below soft tissue. The overall color change ΔΕ was calculated by the following equation:

ΔΕ = [ (AL* ) ² + (Aa*) ² + (Ab*) ² ] ⁰ " ⁵ In literature, a threshold value of ΔΕ > 3.7 is considered to be a clinically distinguishable color difference in the intraoral environment. Figures 6a to 6c show the color change of the covering mucosa. The thickness of the mucosal flap is in figure 6a 1 mm, in figure 6b 2 mm and in figure 6c 3 mm.

- Sample 1: Ti rolled;

- sample 2: Ti polished;

- sample 3: Ti glass-blasted;

- sample 4: Ti sandblasted;

- sample 5: Ti machined.

All tested samples revealed an overall color change in covering mucosa. The color change decreases with increasing tissue thickness, as it can be observed in the bar chart for 1 mm (Figure 6a) , 2 mm (Figure 6b) and 3 mm (Figure 6c) thick tissue. The only critical case (mucosa thickness of 1 mm) is regarded for further discussion. Dark or gray appearance of the covering mucosa was pronounced for the coating on the sand-blasted substrate (L*-value lower than for tissue on bone) . Slight deviations around ΔΕ of 3.7 can be observed for rolled, polished, glass-blasted and machined samples. The L*- values for these samples were slightly higher than for tissue on bone. However, a brightening of the soft tissue could not be observed by eye.